M. SAHNOUNE Foudil

The synthesis of forsterite can be challenging because the initial oxides react slowly and undesirable compounds like enstatite (MgSiO3) can form instead of forsterite (Mg2SiO4). Although several methods have been developed to overcome these challenges, the synthesis of forsterite using the solid-state reaction of nanopowders has not been investigated. This study aims to explore the possibility of producing forsterite by reacting MgO and SiO2 nano-powder. The initial oxides were wet ball milled, dried, and reaction sintered. Spectroscopy and microscopy methods were used to analyze the formed phases and study the formation kinetics. The density, coefficient of thermal expansion (CTE), and hardness of sintered samples were measured using a densimeter, a dilatometer, and a hardness tester, respectively. The results demonstrated that it is possible to synthesize forsterite by solid state reaction of pure MgO and SiO2 nano-powders. The reaction between the two compounds begins at a temperature as low as 860 °C and leads to the formation of forsterite by a two-step formation mechanism. The first reaction involves the reaction of MgO and SiO2 to form enstatite, and the second one produces forsterite as a result of enstatite reacting further with MgO. The activation energy values ranged from 1028.89 to 1105.655 kJ/mol for the formation of forsterite, and from 456.316 to 488.08 kJ/mol for the formation of enstatite. Monolithic forsterite was completely formed at a low temperature of 1200 °C for a relatively short duration of 2 h. The sample sintered at 1400 °C for 2 h, had a density of 2.96 g/cm3, a Vickers hardness of 7.64 GPa, and a coefficient of thermal expansion of 10.24 × 10−6/K measured in the temperature range of 200–1300 °C.

This study investigates the structural, electrical, and dielectric properties of GdCrO3 (GCO) compounds. X-ray diffraction analysis confirmed the formation of the perovskite phase of GCO, crystallizing with the Pbnm space group. Scanning electron microscopy (SEM) was employed to examine the morphology and chemical composition of the powder, ensuring compound homogeneity, while transmission electron microscopy (TEM) provided insights into the internal structure and finer morphology of the GCO sample. Electrical measurements revealed that GCO exhibits semiconductor behavior, with a notable increase in conductivity as temperature rises, attributed to enhanced charge carrier mobility and hopping conduction mechanisms. Dielectric analysis demonstrated significant frequency-dependent behavior, characterized by various polarization effects and relaxation phenomena. GCO is a promising material for energy storage due to its giant permittivity and low energy loss. The activation energies derived from the electrical and dielectric measurements indicate higher resistance within the grains compared to the grain boundaries, suggesting complex conduction processes. Additionally, the dielectric loss spectra revealed substantial losses, likely due to defect states such as oxygen vacancies and mixed valence states, indicating a highly disordered material. These comprehensive insights into the structural and functional properties of GCO highlight its potential applications in electronic and electrical devices where controlled conductivity and dielectric properties are crucial.

The current research study investigated the impact of lacunar manganite on the magnetocaloric effect and explored the correlation between the electrical and magnetic properties of the La0·8Na0.1□0.1MnO3 compound. Structural analysis confirmed the presence of a predominant phase and a minor Mn3O4 phase. The observed hysteresis loop indicates the exchange bias effect, suggesting the material's suitability for spintronic and magnetic read-write head devices. The magnetocaloric properties of the polycrystalline manganites La0·8Na0.1□0.1MnO3 were examined through resistivity and magnetic measurements. The sample exhibits a negative maximum magnetic entropy change ΔS of 5.56 J/kg.K around its Curie temperature (TC = 295K) at a magnetic field of 5T. The magnetocaloric effect value was estimated using a phenomenological model based on magnetization calculations as a function of temperature under different magnetic fields M (T, H). The magnetic entropy ΔSM was determined using Landau's phase transition theory. The relationship between magnetic order and transport behavior, expressed through the resistivity and magnetization relationship near TC, was consistent with Maxwell–Weiss relation results. The findings indicate that the studied sample is an excellent candidate for multifunctional spintronic devices, magnetic read-write head devices, and magnetic refrigeration.

In this study, structural features of Na2MxZn1-xP2O7 (M = Cu, Ni and Co; x = 0 and 5 mol %) glass compounds
were investigated. X-ray diffraction (XRD) and X-ray Absorption Fine Structure (XAFS) analysis techniques were
used to investigate the phase identification and the local atomic environment around Zn element. Non-doped and
Cu co-doped compounds show an amorphous glassy character while a tetragonal Na2ZnP2O7 phase was observed
in Ni or Co co-doped samples. Fourier-transformed magnitudes of the Extend X-ray Absorption Fine Structure
(EXAFS) show a disorder state for pure sample and copper doping compound. On the other hand, nickel or cobalt
co-doped compounds show a structural order by the formation of ZnP2O7 sheet. Therefore, transition metals
(TMs) co-doped phosphate glass play a key role in the structural order /disorder of the glass compounds, by
maintaining and reinforcing or even weakening the network structure

The present study investigates the thermal behavior and structural properties of Na2CuxZn1-xP2O7 (x = 0, 1 and 5
mol%) glasses. Differential thermal analysis (DTA) under non-isothermal conditions and X-ray diffraction (XRD)
techniques were used to explore the effect of CuO amount on the crystallization kinetics of the glasses. The
characteristic temperatures were used to calculate the activation energy, enthalpy, Gibbs free energy and entropy
as well as morphological parameters. A correlation between the obtained results from these two techniques
provides valuable information about the crystallization behavior of these glasses as well as the structural role
played by the transition metal oxide. In the present glass system, CuO increased the characteristic temperatures
and energies of activation and it acted as a structure modifier. Moreover, a bulk crystallization mechanism with
different dimensional growth of crystals for non-doped and doped samples was obtained. The kinetic evolution
was compared and confirmed using different methods

Effect of transition metal ion (Co2+) on the local atomic structure in sodium-zinc-phosphate glass: XAFS and XRD studies

Kinetics, Phase Transformations and Sintering of Mg-doped LaMnO3
Foudil SAHNOUNE1, Amar DJEMLI1, Abdelmadjid BOUSSENDEL1, Essebti Dhahri2, and Nouari Saheb3
1physics and materials chemistry laboratory, Department of Physics, University of M’sila, 28000 M’sila, Algeria
23Laboratoire de Physique Appliquée, Faculté des Sciences, Université de Sfax, B.P.1171, 3000 Sfax, Tunisia
3Dep. of Mechanical Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
Abstract
Lanthanum manganite (LaMnO3) is a complex oxide compound with various applications in wide fields, including solid oxide fuel cells, magnetic and electronic devices, catalysts, and multiferroics. Several available methods were used by researchers to prepare LaMnO3 such as solid-state synthesis, sol-gel method, hydrothermal synthesis, co-precipitation method, and assisted microwave synthesis, choosing a method depends on several factors, like desired particle size, morphology, purity, crystal structure of the LaMnO3, and the availability of resources and equipment.
This study investigated the kinetics of LaMnO3 doped with magnesium ceramics synthesized using sol-gel method and starting materials as lanthanum nitrate (La (NO3)3*6H2O), manganese nitrate (Mn(NO3)2*6H2O), Magnesium nitrate (Mg(NO3)2*6H2O), and citric acid monohydrate (C6H8O7*H2O). In order to characterize the results, various techniques were used, including thermogravimetry (TG), differential thermal analysis (DTA), and X-ray powder diffraction (XRD). The activation energy (Ea) of La0.7Mg0.3MnO3 phase formation was measured by heat treating the sample up to 600 °C in various rates (0.3, 0.5, 0.7, and 1 °C/min) using differential thermal analysis (DTA). Using Kissinger, Boswell, and Ozawa methods Ea values were calculated and found to be 184, 189, and 185 kJ/mol, respectively.
Both the growth morphology parameter n and the dimension of crystal growth m were determined to be approximately 1.5, suggesting that bulk nucleation with a constant number of nuclei was the dominant mechanism in La0.7Mg0.3MnO3 crystallization, which was followed by one-dimensional growth controlled by interface reaction. The tracking of the phase Transformations done by DTA at different temperatures (260, 400, 700, and 1100 °C) were analyzed using X-ray diffraction. Additionally, we analyzed the material's structural properties at different sintering temperatures (700, 800, 900, 1000, and 1100 °C) for 4 hours. Finally, we examined the changes in the crystal dimension of the material in consideration of both temperature and time.
Keywords: Phase Transformations, activation energy, Sintering, crystallization kinetics
 Corresponding Author Email: foudil.sahnoune@univ-msila.dz

Lanthanum Manganite LaMnO3 Crystallization Kinetics Prepared Through Sol-Gel Auto-Combustion Method

Abdelmadjid BOUSSENDEL1, Amar DJEMLI1, Foudil SAHNOUNE1, 2

1physics and materials chemistry laboratory, Department of Physics, University of M’sila, 28000 M’sila, Algeria
2Research Unit on Emerging Materials (RUEM), Ferhat Abbas of Setif 01, Setif 19000, Algeria


Abstract

This study focused on the synthesizing, phase transformation, and sintering behavior of Lanthanum manganite (LaMnO3), and the importance of such material due to its imbedded potential applications in various fields, including catalysis, energy storage, and solid oxide fuel cells. The sol-gel auto-combustion method was used in the preparation of the LaMnO3 sample, Sol-Gel method is known to it superior qualities such as high purity, homogeneous materials, and the ability to control particle size and morphology. The investigation of LaMnO3 sample phase transformation and sintering behavior was done in this study using several analytical techniques, thermogravimetry (TG), differential thermal analysis (DTA), and X-ray diffraction (DRX) analysis. In order to describe the energy barrier required for a particular process to occur such as a phase transformation or a chemical reaction, the activation energy (EA) for the phase transformation was calculated using three different methods: The Kissinger, Boswell, and Ozawa method. EA value was determined to be 173.8, 184, and 170 kJ/mol, respectively. which provides important information about the energy requirements for the phase transformation to occur for LaMnO3 materials, this information is extremely useful in the conditions of the process throughout designing and optimizing. The parameters that describe the reaction mechanism and the rate of the process are called kinetic parameters of Avrami n and m, which were calculated and found to be approximately 1.5. Overall, this study is essential because it provides insightful scope into the phase transformation and sintering behavior of LaMnO3.

Keywords: differential thermal analysis, Phase Transformations, activation energy, crystallization kinetics


 Corresponding Author Email: abdelmadjid.boussendel@univ-msila.dz

In this study, the sol-gel method of low-temperature synthesis was utilized to create mullite/cordierite precursor
powder. The materials (TEOS) Si(C2H5O)4, Al(NO3)3.9H2O and Mg(NO3)2 were utilized as source of SiO2, Al2O3,
and MgO oxides respectively in order to create mullite/cordierite precursor gel with various concentrations and
designations (MC00, MC10, MC20, MC30, MC40, and MC50). Crystalline phases were seen and described using
scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). After the powder was formed at
1600 ◦C for an hour, its sintering was looked at. For all mixes, as the cordierite concentration rises, the bulk
density rises and the open porosity decreases. The existence of a vitreous phase may be the cause of the rise in
bulk density and reduction in open porosity seen with rising temperatures.
The dielectric characteristics of the samples have been examined at room temperature; the relative dielectric
constant (εr), loss tangent (tan δ), and dielectric characteristics were assessed at frequencies of 0.1 Hz, 1, 10, 100,
and 1000 kHz. At 1 kHz, the relative dielectric constant values are closest to those of mullite (εr = ~5 to ~ 6),
and c at 1 kHz. On the other hand, the lowest dielectric losses were observed (tan δ from ~0.06 to ~ 0.04). The
Electrical properties, electrical resistivity, AC conductivity, impedance spectroscopy, electrical modulus, and the
relative quality factor (QF) of pure mullite and mullite/cordierite composite sintered at 1600 ◦C for 1 h (MCyy)
samples were investigated as a function of cordierite content at varied frequencies (0.01 Hz, 1 kHz, 100 kHz, and
1000 kHz). The hardness (HV) and coefficient of thermal expansion (CTE) of the composite material that underwent
sintering at a temperature of 1600 ◦C were determined by the use of a hardness tester and a dilatometer,
respectively. The rise in temperature, coupled with an equal quantity of cordierite, resulted in an elevation of the
apparent density and a reduction in the open porosity. In the case of the specimen subjected to sintering at a
temperature of 1600 ◦C, the introduction of cordierite content in the range of 0–40% resulted in an observed rise
in HV value from 9.15 to 12.99 GPa. However, a further increase in cordierite content to 50% led to a decrease in
HV value to 10.99 GPa. Nevertheless, the CTE value throughout the temperature range of 50–1200 ◦C exhibited a
consistent decline, ranging from 5.37 × 10􀀀 6 to 2.32 × 10􀀀 6 K􀀀 1. Notably, the composite material consisting of
50 wt% cordierite had elevated HV and the most minimal CTE value.

Crystallization Kinetics of LaMnO3 from Sol-Gel Synthesized Precursors

Foudil Sahnoune1,2, Amar Djemli1,2, Nadjib Baadji1, Essebti Dhahri3, and Nouari Saheb4

1Physics Department, Faculty of Science, University Mohamed Boudiaf of M’sila, 28000 M’sila, Algeria
2physics and materials chemistry laboratory, Department of Physics, University of M’sila, 28000 M’sila, Algeria
3Laboratoire de Physique Appliquée, Faculté des Sciences de Sfax, Université de Sfax, B.P.1171, 3000 Sfax, Tunisia
4Dep. of Mechanical Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
*Corresponding author: foudil.sahnoune@univ-msila.dz


This study focused on the synthesizing, phase transformation, and sintering behavior of Lanthanum manganite (LaMnO3), the importance of such material due to its imbedded potential applications in various fields, including catalysis, energy storage, and solid oxide fuel cells. The sol-gel method was used in the preparation of the LaMnO3 sample, Sol-Gel method is known to it superior qualities such as high purity, homogeneous materials, and the ability to control particle size and morphology. The investigation of LaMnO3 sample phase transformation and sintering behavior was done in this study using several analytical techniques, thermogravimetry (TG), differential thermal analysis (DTA), and X-ray diffraction (DRX) analysis. In order to describe the energy barrier required for a particular process to occur such as a phase transformation or a chemical reaction, the activation energy (EA) for the phase transformation was calculated using three different methods: The Kissinger, Boswell, and Ozawa method. EA value was determined to be 173.8, 184, and 170 kJ/mol, respectively. which provides important information about the energy requirements for the phase transformation to occur for LaMnO3 materials, this information is extremely useful in the conditions of the process throughout designing and optimizing. The parameters that describe the reaction mechanism and the rate of the process are called kinetic parameters of Avrami n and m, which were calculated and found to be approximately 1.5. Overall, this study is essential because it provides insightful scope into the phase transformation and sintering behavior of LaMnO3.
Keywords: Lanthanum manganite, In Situ XRD, kinetic parameters, Avrami parameter, Activation energy
REFERENCES
[1] Moure, Carlos, and Octavio Peña. "Recent advances in perovskites: Processing and properties." Progress in Solid State Chemistry 43.4 (2015): 123-148.
[2] Tomaszewski, P. E., et al. "X-ray study of structural phase transitions in nanocrystalline LaMnO3+ δ perovskite." Phase Transitions 92.6 (2019): 525-536.
[3] Assirey, E. Abdul Rahman. "Perovskite synthesis, properties and their related biochemical and industrial application, Saudi Pharm." J 27.6 (2019): 817-829.
[4] Wenwei, Wu, et al. "Nanocrystalline LaMnO3 preparation and kinetics of crystallization process." Advanced Powder Technology 24.1 (2013): 154-159.
[5] Mrázek, Jan, et al. "Crystallization kinetics and structural properties of nanocrystalline europium-yttrium-titanate (Eu0. 5Y0. 5) 2Ti2O7." Advanced Powder Technology 33.3 (2022): 103501.

One of the key problems to overcome, in the development of electronic substrates, is that of thermal distortion because of thermal mismatch between silicon and the substrate. The aim of this work is to design a mullite-cordierite composite material, with coefcient of thermal expansion tailored to silicon substrate applications. Dense, hard, and thermally stable Al6Si2O13–Mg2Al4Si5O18 composite was produced by sintering amorphous precursor powder synthesized through the sol–gel method. Si(C2H5O)4, Al(NO3)3.9H2O, and Mg(NO3)2.6H2O were used, as source of SiO2, Al2O3, and MgO oxides, respectively, to
prepare mullite-cordierite precursor powders. Fourier-Transform Infrared spectroscopy (FTIR), Thermogravimetry (TG), Dilatometry, Diferential Thermal Analysis (DTA), and X-ray powder Difraction (XRD) methods were used to characterize the synthesized amorphous powder and its crystallization. The microstructure of specimens sintered at 1600 °C for 1 h was analyzed using a scanning electron microscope (SEM). The hardness (HV) and coefcient of thermal expansion (CTE) of the composite sintered at 1600 °C were measured by using a hardness tester and a dilatometer, respectively. The results show
the increase in density and decrease in open porosity with the increase in temperature and equivalent amount of cordierite. For specimens sintered at 1600 °C, the increase in cordierite content from 0 to 40 wt.% increased the HV from 9.18 to 13.08 GPa; a further increase to 50 wt.% decreased it to 11.15 GPa. Sample containing 40 wt.% cordierite had the highest value of hardness (HV=13.08 GPa), representing an increase of 42.48% with respect to monolithic mullite. The CTE of the composites (in the range 50–1000 °C) showed continuous decrease from 5.23× 10–6 to 2.26× 10–6 K−1 with the increase in cordierite content from 0 to 50%. Sample containing 50 wt.% cordierite displayed the lowest thermal expansion (CTE of 2.26× 10−6 K−1), representing a decrease of 56.78% with respect to monolithic mullite.

In this work, mullite/cordierite precursor powder was prepared through a technology of low-temperature synthesis
by using the sol-gel process, tetraethyl orthosilicate (TEOS) as a source of silicon oxide SiO2, and aluminum
nitrate nonahydrate Al (NO3)3.9H2O as a source of aluminum oxide (Al2O3) and magnesium nitrate hexahydrate
Mg (NO3)2.6H2O as a source of magnesium oxide MgO was used as raw materials to synthesize mullite/cordierite
precursor gel with a concentration (sample containing 50 wt% of cordierite and 50 wt% of mullite) and named as
(MC50). The objective of this study is to find a suitable kinetic model to study the phases and the mechanisms of
their formation in mixtures, with the prediction of the system’s behavior under selected thermal conditions,
including finding the kinetic and thermodynamic media that describe these interactions. To follow and characterize
the crystalline phases and their transformation as a function of temperature utilizing differential thermal
analysis (DTA), Dilatometry (DIL), and powder X-ray diffraction (XRD). The results show that the crystallization
process occurred in the temperature interval between (900–1350) ◦C. In the temperature range of (900–1000) ◦C,
spinels between Al–Si and Al–Mg with the chemical formulas (Al4Si3O12 and MgAl2O4) were formed. When the
thermal treatment temperature increases from (1000–1100) ◦C, mullite is produced. As the temperature increases,
the amount of Mg–Al spinel decreases to form amorphous silica, and μ-cordierite has appeared at
1250 ◦C. With an increase in temperature up to 1350 ◦C, α-cordierite appeared as a stable phase. The reason for
this is the presence of the spinel (Al–Mg) phase that helped it form.
To determine the reaction kinetics of these transformations at high temperatures, the mixture 50/50 mullite/
cordierite was selected to study its kinetics. The activation energy values (Ea/Tm) (Tm is the maximum temperature
of the transformation, i.e., the maximum peak temperature is not related to the crystallization fraction
α) calculated by Ozawa, Boswell, and Kissinger methods are in good agreement with the evident activation
energy (Eα/Tα) (Tα is the degree of the heat of transformation in terms of crystallization fraction α changes from
0<α < 1) calculated using the KAS and FWO methods.
For the purpose of calculating the interaction model and finding the media that determine the interaction
model based on the experimental data, Mal´ek’s methodology method was used. The best kinetic model is the
ˇSest´ak - Berggren model to describe the reaction process to form spinel, mullite, and α-cordierite. From the SB
model, the equations Kinetics and all kinetic parameters (n, m, ln(k0)) that describe the kinetics of the reactions
and mechanisms of formation of spinel, mullite, and α-cordierite in the mixture are, respectively, (2.14, 0.023,
65.21), (1.62, 0.1232, 81.76), and (1.41, 0.2859, 91.13). While the values of Gibbs free energy ΔG#, enthalpy
ΔH#, and entropy ΔS# were as follows: 407.254 kJ mol􀀀 1, 976.756 kJ mol􀀀 1 and 415.561 J mol􀀀 1K􀀀 1 for
Mullite formation, and 471.64 kJ mol􀀀 1, 1255.16 kJ.mol-1 and 491.75 J mol􀀀 1K􀀀 1 for the formation of
α-cordierite.
Comparison of simulation curves with experimental data obtained at different temperatures gives good
agreement with the thermal analysis data (Experimental), which indicates that the Model of ˇSestak 􀀀 Berggren, is
the best suitable kinetic model for studying and describing the reaction technique for MC50 prepared by the solgel
method.

In the present investigation, the crystallization kinetics of a glass with a molar composition 25Na2O-25ZnO-50P2O5 (NZPO) is studied by means of a non-isothermal differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. XRD pattern of the as-synthesized glass indicates an amorphous glassy structure without additional crystalline phase. Moreover, the heat-treated glass sample shows the crystallization of the Na2ZnP2O7 crystalline phase. The glass transition peak temperature increases with increasing heating rates and is ranged from 505.3 to 601.6 K. The crystallization shows the same behavior and the obtained values are ranged from 685.2 to 731.2 K. The activation energies for glass transition and crystallization are determined using different approaches and are in the range of 25.9–30.5 and 82.8–112.0 kJ mol−1, respectively. The n and m kinetic parameters are each close to 3.0, which indicates bulk nucleation process with 3D growth of crystals.

In this work, we have developed a series of materials AFe1􀀀 xMnxO3 (A= La0.67Ca0.13Ba0.2) with x = 0, 0.03 and
0.06 by the self-combustion method using glycine and annealed at 1173 K. Analysis of X-ray diffractograms
shows that these compounds crystallize in the same cubic structure with the same space group Pm3m.
Morphology and EDS analysis confirm the presence of all the elements and attests to the purity of these compounds.
Electrical measurements show that at low temperatures, these compounds obey Jonscher’s modified law,
whereas above 420 K they obey Jonscher’s classical law. The adjustment of the Nyquist diagrams leads to
modeling these samples at low temperatures by two electric circuits connected in series (Rg//CPEg) + (Rgb//
CPEgb) reflecting the contributions of the grains and the grain boundaries. Dielectric analysis indicates high
permittivity and low loss suggesting that these compounds are good candidates for use in the electronic systems
industry and supercapacitor applications.

The aim of this study is to shed more light on the formation of mullite and the kinetics of mullitization from sol-gel synthesized precursors. Tetraethylorthosilicate (TEOS) and aluminum nitrate nonahydrate (ANN) were used, as a source of silica and alumina, respectively, for the synthesis of homogenous mullite precursor powder. The mullitization process was characterized by thermogravimetry (TG), differential thermal analysis (DTA), thermodilatometric analysis (TDA), and x-ray powder diffraction (XRD) techniques. It was found that mullite started to crystalize at temperatures of 1050, 1200, and 1241 °C as determined by XRD, DTA, and TDA, respectively‏. Mullite crystallization kinetics was thoroughly investigated under isothermal and non-isothermal conditions using DTA. The activation energy for mullite formation was calculated, for different crystallization fractions, following the Freidman, Kissinger, Boswell, and Ozawa methods. The average values were found to be 1282.92, 1324.30, 1336.93, and 1283.09 kJ/mol, respectively. The kinetic parameters and the crystallization mechanism were determined and the results were compared with those available in the literature. The Sestak Berggren SB(m,n) model was found to be the most suitable for the determination of mullite crystallization mechanism. The calculated average values of the Gibbs free energy (ΔG#), enthalpy (ΔH#), and entropy (ΔS#) for mullite formation, at different heating rates, were 433.98 kJ/mol, 1294.20 kJ/mol, and 566.23 J/mol.K, respectivel

....

The focus of this work is on the synthesis of forsterite (Mg2SiO4) bioceramics from SiO2 and MgO nanopowders. The used raw materials powders (initial powders) were mixed, ball milled and sintered within the temperature range of 1100–1500 °C for 2 h. Differential thermal analysis, dilatometry, Thermogravimetry, thermodilatometric analysis and x-ray diffraction, complementary techniques were used to study the sintering behavior and The crystalized phase during the thermal treatment. X-ray diffraction method was used to characterize the specimens heat-treated in both the dilatometer and furnace. The results shows that the forsterite bioceramic synthesized from pure nano-oxide powders begin to crystallize at 900 °C and completed at 1400 °C for the heat-treated specimens by furnace.

This work reports on the formation kinetics of magnesium aluminate spinel (MAS), from α-Al2O3 and
MgO nanopowders. A non-isothermal kinetic analysis was performed by the thermodilatometric analysis
(TDA) for the first time. The measure- ments were carried out using a dilatometer on compact
samples with heating rates from 3 to 11 °C min–1. Phases formed during the spinelisation process,
in specimens heat-treated in both the dilatometer and furnace, were characterized by X-ray
diffraction (XRD). The use of pure nano-oxide powders to produce spinel reduced the formation
temperature and activation energy. MAS started to form, in the furnace heat-treated specimens, at
1000 °C and its formation was complete at 1400 °C. For specimens heated in the dilatometer, MAS
formation temperature increased from 1002 to 1061 °C with the increase in heating rate from 3 to 11
°C min−1. The activation energy for spinelisation, under non-isothermal conditions, was calculated
by linear reaction models (Integral isoconversional methods) using Flynn–Wall–Ozawa (FWO) method.
Boswell, and Kiss- inger equations. The average activation energy (Ea), correlation coefficient
(R2), Avrami parameter (n), and dimensionality of crystal growth (m) were equal to 293.31 kJ mol−1,
0.99, 1.22, and 0.98, respectively. The Johnson–Mehl–Avrami (JMA) reaction model, following Ligero
method (Differential isoconversional methods), was used to analyze spinelisation kinetics under
non-isothermal conditions. The average activation energy (Ea), correlation coefficient (R2), Avrami
parameter (n), and the frequency factor (k0) were found to be 283.90 kJ mol−1, 0.99, 1.2, and 4.17
× 108 s−1, respectively.
Keywords Spinel · MgAl2O4 · Nanopowders · Thermodilatometric analysis · Spinelisation kinetics

This work reports, for the first time, the kinetics of α-cordierite (Mg2Al4Si5O18) formation from Al2O3, SiO2, and MgO nano-oxide powders. Isothermal and non-isothermal kinetic analysis was performed by Differential Thermal Analysis (DTA) and thermodilatometric analysis (TDA). The thermal measurements were performed at high heating rates (20–70 ◦C/min) for DTA and low rates (3–9 ◦C/min) for TDA. Phase transformations leading to the formation of α-cordierite were characterized by x-ray diffraction (XRD). The Kissinger, Boswell, and Ozawa methods were used to calculate the activation energy. The Avrami parameter (n) and dimensionality of crystal growth (m) were calculated using the Augis–Bennett and Matusita equations, respectively. Analysis of samples heated in the DTA equipment or the dilatometer confirmed that the reaction of MgO, Al2O3, and SiO2 led to the formation of enstatite, cristobalite, and metastable μ-cordierite. The later transformed to stable α-cordierite. The activation energy calculated by both isothermal and non-isothermal treatments is 633 and 667 kJ/mol, respectively, for DTA; and is 544 and 646 kJ/mol, respectively, for TDA. The growth morphology parameters n and m, obtained from isothermal and non-isothermal DTA treatments, are both close to 2 indicating that bulk nucleation with constant number of nuclei is dominant in α-cordierite crystallization followed by two- dimensional growth of α-cordierite crystals with plate-like morphology controlled by interface reaction. While those obtained from isothermal and non-isothermal TDA treatments, are both about 1.5 indicating that bulk nucleation is dominant in α-cordierite crystallization followed by three-dimensional growth of α-cordierite crystals with polyhedron-like morphology controlled by diffusion from a constant number of nuclei. A low co-efficient of thermal expansion (CTE) of 0.9 × 10􀀁 6/◦C was measured, in the range 200–1350 ◦C, for a sample sintered at 1400 ◦C for 2 h.

Low-cost, dimensionally stable, and hard cordierite ceramic materials were prepared by reaction sintering two Algerian natural clay minerals and synthetic magnesia. The microstructure and hardness of the developed materials were characterized by a scanning electron microscope and a hardness tester, respectively. Differential thermal analysis, dilatometry, and Raman spectroscopy were used to analyze the transformation of phases and sintering behavior. The coefficient of thermal expansion (α) was determined from dilatometry experiments. The microstructure of DT00M sample synthesized from stoichiometric powder mixture (clay minerals and synthetic magnesia) consisted of cordierite only. Whereas cordierite, magnesium silicate, and sapphirine phases were present in DT04M and DT08M samples prepared from non-stoichiometric powder mixtures containing excess magnesia of 16 and 20 wt.%, respectively. The values of the activation energy (Ea) and frequency factor (A), for cordierite crystals, varied from 577 to 951 kJ/mol, and 1.54 × 1018 to 1.98 × 1030 S−1, respectively. The kinetic parameter n for the formation of cordierite had values between 2 and 3. While the Gibbs free energy (ΔG#), enthalpy (ΔH#), and entropy (ΔS#) values were found to be in the range 431–483 kJ/mol, 564–938 kJ/mol, and 70–313 J/mol, respectively. Samples sintered at 1300 °C for 2 h showed higher values of hardness compared with those sintered at 1250 °C. The DT04M sample had the highest hardness value of 9.45 GPa, demonstrating an increase of 12.5% with respect to monolithic cordierite (DT00M). In the temperature range 100–1300 °C, DT04M and DT08M samples showed better dimensional stability compared to monolithic cordierite. The DT08M sample showed the lowest thermal expansion (α = 2.32 × 10−6/°C), demonstrating a decrease of 31.3% with respect to monolithic cordierite.

Electronicand thermoelectric properties of three principal representatives of the LiCdP, LiCdAs and LiCdSb filled-tetrahedral compounds have been studied ab initio. We use the full-potential Linearized augmented plane-wave plus local orbitals method (FP-LAPW+lo) as implemented in the Wien2K code with the original TB-mBJ functional to model the exchange-correlation potential. Qualitatively, the investigated compounds show similar energy band dispersion; indirect band gap Г-X was found for the three considered compounds. A combination between The FP-LAPW+lo band stucture and the semi-classical Boltzmann transport theory were used to investigate the thermoelectric properties, the potential of the studied compounds as thermoelectric materials at three applied temperature (i.e., T=300, 600 and 900 K) was assessed. The calculated values of the Seebeck coefficient (i.e., 265, 259 and 248 µV/K) decreases going from LiCdP to LiCdAs to LiCdSb, this can be attributed to the trend of semiconducting materials where Seebeck coefficient decreases with decreasing band gap. The thermoelectric efficiency was evaluated through calculating figure of merit ZT. Intrinsically, figure of merit is about 0.8, this value might be greater by tuning the electronic structure via hole-doping.

The effect of CaO on cordierite formation from kaolin-MgO-CaO powder mixtures, milled for 5 h and reaction sintered for 2 h in the temperature range 900-1400 °C, was investigated. Phases formed in the developed materials were characterized by x-ray powder diffraction method (XRD) and Raman spectroscopy. Non-isothermal differential thermal analysis (DTA) and thermogravimetric (TG) experiments were performed from room temperature to 1400 °C, at heating rates from 20 to 40 °C/min. Activation energies were determined using Kissinger method. It was found that sintering the stoichiometric kaolinmagnesia mixture led to the nucleation and growth of monolithic cordierite; while cordierite along with anorthite were present in the other two samples where 4 or 8 wt% of CaO was added. The increase in CaO decreased cordierite formation temperature and increased the activation energy, which ranged from 445 to 619 kJ/mol for μ-cordierite and from 604 to 1335 kJ/mol for α-cordierite. Keywords: Clays; MgO; Cordierite; Sintering; Kinetics

The influence of temperature and magnesia content on the formation of phases and their transformation kinetics in stoichiometric and non-stoichiometric cordierite ceramics prepared from Algerian kaolinite precursors was investigated. High-temperature X-ray diffraction was used to study the formation of phases and their transformations. Non-isothermal
differential thermal analysis was used to determine kinetic parameters for the formation of l and a cordierite. Activation energies were calculated by Kissinger, Boswell, and Ozawa equations. The Augis–Bennett and Matusita equations were used to calculate the mode of crystallization (n) and dimension of growth (m) parameters, respectively. The synthesized
materials showed similar phase transformations, which finally led to the formation of cordierite in stoichiometric kaolinite– magnesia mixture, and cordierite along with other phases in kaolinite–magnesia mixture containing excess magnesia. The activation energy for the formation of a cordierite was higher than that of l cordierite. Energies of formation of l and a
cordierite phases in the non-stoichiometric samples were higher than those in the stoichiometric sample. The activation energy was less sensitive to the calculation method; however, it changed significantly with MgO content. Activation energies between 573 and 964 kJ mol-1 were obtained. Magnesia changed the crystallization mode and crystal growth dimension. The kinetic parameters n and m, for the formation of l or a cordierite, had values between 2 and 3.
Keywords Kaolinite  Magnesia  Cordierite  Solid-state reaction  Phase transformation kinetics

Morphological and electrical properties of AlMg thin films and the impact of the elaboration conditions on their quality are investigated. For this purpose, thin layers of AlMg of different Mg content were deposited by vacuum evaporation on a monocrystalline silicon substrate in the MECA2000 evaporator. The properties were studied by the X-ray diffraction technique (XRD), XRF, the optical and mechanical profilometer and the four-probe method. The interpretation of the X-ray diffraction spectra allowed us, among other things, to affirm that the films are poly-crystalline with β and δ phases. Generally, the lattice parameter of the Al-Mg samples was slightly higher compared to the bulk one amassif. As a result, our samples show a general increase in grain size as the thickness increases. Observations with optical profilometry, we have established that the surface is of dense appearance with presence of many grains. The results of the measurement of the roughness show increased values with the increase of x at.% Mg whose maximum is at 190 nm corresponding to a x at.% Mg of 97. As for the electrical measurements, they report a maximum resistivity of 3.6 × 10−3 Ω.cm

Mullite (3Al2O3•2SiO2) as the main phase in SiO2-Al2O3 system is one of the most commun studied ceramic materials has low toughness and hardness, better thermal shock resistance, excellent high temperature mechanical properties, high thermal and chemical stability, low thermal expansion coefficient and high creep resistance. In this present study, Mullite of stoichiometric composition has been synthesized by sol-gel process followed by calcination. Tetraethyl orthosilicate (TEOS) as silica source and Aluminum nitrate nonahydrate (Al(NO3)3.9H2O) as alumina source. Thermogravimetry (TG), differential thermal analysis (DTA), dilatometry, high temperature x-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) complementary techniques were used to analyses the transformation of phases and sintering behaviour, The coefficient of thermal expansion (α) and investigate crystallization kinetics. Different crystalline phases were present in the samples sintered in the temperature range 900–1400 °C, the Mullite phase started to crystallize at 1100 °C, and the formation of highly dense Mullite (96%) was complete at 1350 °C. The activation energy values for Mullite formation calculated using Kissinger, Boswell, and Ozawa methods. The kinetic parameters n and m had values close to 2. Bulk nucleation with a constant number of nuclei was the dominant mechanism in cordierite crystallization, followed by two-dimensional growth controlled by interface reaction.

Keywords: Mullite, Sintering, Differential Thermal Analysis, Dilatometry

Mullite (3Al2O3·2SiO2) as the main phase in SiO2- Al2O3 system is one of the most commun studied ceramic materials has low toughness and hardness, better thermal shock resistance, excellent high temperature mechanical properties, high thermal and chemical stability, low thermal expansion coefficient and high creep resistance. In this present study, Mullite of stoichiometric composition has been synthesized by sol-gel process followed by calcination. Tetraethyl orthosilicate TEOS as silica source and Aluminum nitrate nonahydrate Al(NO3)3.9H2O as alumina source. Thermogravimetry (TG), differential thermal analysis (DTA), dilatometry, high temperature x-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) complementary techniques were used to analyses the transformation of phases and sintering behaviour, The coefficient of thermal expansion (α) and investigate crystallization kinetics. Different crystalline phases were present in the samples sintered in the temperature range 900–1400 °C, the Mullite phase started to crystallize at 1100 °C, and the formation of highly dense Mullite (996%) was complete at 1350 °C. The activation energy values for Mullite formation calculated using Kissinger, Boswell, and Ozawa methods. The kinetic parameters n and m had values close to 2. Bulk nucleation with a constant number of nuclei was the dominant mechanism in cordierite crystallization, followed by two-dimensional growth controlled by interface reaction.

Electronic and thermoelectric properties of three principal representatives of the LiZnP, LiZnAs and LiZnSb filled-tetrahedral compounds have been studied ab initio. We use the full-potential Linearized augmented plane-wave plus local orbitals method (FP-LAPW+lo) as implemented in the Wien2K code with the original TB-mBJ functional to model the exchange-correlation potential. Qualitatively, the investigated compounds show similar energy band dispersion; indirect band gap Г-X was found for the three considered compounds. A combination between The FP-LAPW+lo band stucture and the semi-classical Boltzmann transport theory were used to investigate the thermoelectric properties, the potential of the studied compounds as thermoelectric materials at three applied temperature (i.e., T=300, 600 and 900 K) was assessed. The calculated values of the Seebeck coefficient (i.e., 265, 259 and 248 µV/K) decreases going from LiZnP to LiZnAs to LiZnSb, this can be attributed to the trend of semiconducting materials where Seebeck coefficient decreases with decreasing band gap. The thermoelectric efficiency was evaluated through calculating figure of merit ZT. Intrinsically, figure of merit is about 0.8, this value might be greater by tuning the electronic structure via hole-doping.

We report ab-initio density functional theory calculations of the electronic and optical properties of the spinel oxides GeMg2O4, GeZng2O4 and GeCd2O4 using the full potential linearized augmented plane-wave method. To calculate the electronic properties, the exchange-correlation interaction was treated with various functionals. We find that the newly developed Tran–Blaha modified Becke–Johnson functional significantly improves the band gap value. All considered GeB2O4 compounds are direct band gap materials. The band gap value decreases with increasing atomic size of the B element. The decrease of the fundamental direct band gap (Γ–Γ) when one moves from GeMg2O4 to GeZn2O4 to GeCd2O4 can be attributed to the p–d mixing in the upper valence bands of GeZn2O4 and GeCd2O4. The lowest conduction band, which is mainly originated from the s and p states of the Ge and B (B = Mg, Zn, Cd) atoms, is well dispersive, similar to that of transparent conducting oxides such as ZnO. The topmost valence band, which is originated from the O-2p and B-d states, is considerably less dispersive. Optical spectra in a wide energy range from 0 to 30eV are provided and the origin of the observed peaks and structures are assigned. We find that the zero-frequency limit of the dielectric function increases with decreasing band gap value.

Mullite porous ceramics were prepared by an in situ reaction join technique using a Kaolinite,
aluminum oxide, and silicon carbide as raw materials. The raw materials were mixed in different ratios. From homogeneous mixture, standard samples were prepared via uniaxial compaction. The Kaolinite was a reaction sintered with Alumina and SiC, a in the temperature range 1200–1600 °C for
2 h. Dilatometry, X-ray diffraction (XRD), and scanning electron microscopy (SEM) complementary techniques were used to characterize the prepared materials. The effect of SiC content on the microstructure, densification, and hardness of the samples was investigated. All prepared samples showed the same phase transitions that ended at 1500 ° C with the formation of mullite in kaolinitealumina mixture and kaolinite-alumina -SiC mixture. The kaolinite experiences transformation into mullite and excess silica, the mullite and the silica phases contents increased with increased sintering temperature. It is also commonly observed that the SiC content reduces the density gradually while increasing the sintering temperature . The sintering percentage of samples sintered decreased with an increase in SiC content. The pores in the mullite ceramics were formed by accumulating particles of SiC. The surface of SiC was oxidized to SiO2 at high temperature. With further increasing the temperature, SiO2 reacted with Al2O3 to form mullite. SiC particles were bonded by the oxidationderived SiO2 and mullite. The results show that when 2 wt % SiC and 14% SiC were added, the open porosity of the porous mullite were 3.1 % and 16.8 %, respectively. The Vicker’s microhardness of mullite was measured under an applied indentation load of 500 g, showed values of hardness decreased with an increase in SiC content.

Cordierite (Mg2Al4Si5O18) formation via sol-gel route using Tetraethyl orthosilicate TEOS, Aluminum nitrate nonahydrate Al(NO3)3.9H2O, and Magnesium nitrate hexahydrate Mg(NO3)2.6H2O as starting materials was studied by means of high-temperature by heating from room temperature up to 1350 °C. Differential thermal analysis (DTA) technique, under non-isothermal conditions is the appropriate for studying high-temperature reaction kinetics. The activation energies and kinetics parameters of cordierite formation measured by both isothermal (Johnson–Mehl–Avrami (JMA) theory using Ligero method) and non-isothermal (Ozawa, Boswell and Kissinger methods) treatments. The growth morphology parameters n (Avrami parameter which indicates the crystallization mode) and m (a numerical factor which depends on the dimensionality of crystal growth) were also determined. Powders obtained were characterized using high temperature x-ray powder diffraction (XRD), and Scanning electron microscopy (SEM). Finally, the thermodynamic parameters (ΔG#, ΔH# and ΔS#) for cordierite crystals were determined.

The kinetics of discontinuous precipitation of Ag2 Al intermetallic in alloy Al – 10% Ag is studied after 10-h
holding in vacuum at 530°C and subsequent water quenching. The DSC and dilatometric curves are plotted for heating rates ranging from 5 to 20 Kmin. The activation energy of formation of the Ag2 Al -phase is computed from the DSC data with the help of the Boswell equation and by the Kissinger method.

The kinetic parameters such as activation energy E and the growth morphology parameters n and m were determined by a non-isothermal method. The microstructure variations of the precipitation and dissolution of GP zone and metastable phase 0 in Al-3wt.% Cu were analyzed by optical microscopy and X-ray diffraction. The kinetics of GP zone and metastable phase 0 in Al-3wt.% Cu was investigated using differential thermal analysis between room temperature and 430 C at heating rates of 20, 25 and 30 Cmin-1. The activation energies of GP zone precipitation, formation of 0= and dissolution of 0 were 26, 105 and 77 kJmol-1, respectively. The growth morphology parameters n (Avrami parameter which indicates the crystallization mode) and m (a numerical factor which depends on the dimensionality of crystal growth) are both about 1.5.
DOI: 10.12693/APhysPolA.134.45
PACS/topics: differential thermal analysis (DTA), precipitation, activation energies

The aim of the present work is to explore the utilization of Algerian kaolin (DD2) and calcium carbonate (CaCO3) to synthesis of anorthite. Also, the effect of B2O3 addition on the properties of prepared anorthite was investigated. Compacted samples were sintered at temperatures between 1100 and 1300 C for 2 h. All samples were characterized by X-ray diffraction, differential thermal analysis/thermogravimetric analysis, apparent density and open porosity measurements. The experimental results show the formation of anorthite in all samples. The increase in B2O3 ratio promoted the formation and the densification of anorthite at lower temperature.
DOI: 10.12693/APhysPolA.134.460
PACS/topics: anorthite, effects of B2O3, kaolin, dielectric properties

The structural, elastic and thermodynamic properties of the LiZnN, LiZnAs and LiZnSb filled-tetrahedral compounds were investigated through ab initio full-potential linearized augmented plane wave calculations. Calculated structural parameters, including the lattice constant (a), bulk modulus (B) and its pressure derivative (B'), for the considered compounds using both the local density (LDA) and generalized gradient approximations (GGA) are in good agreement with the available experimental and theoretical data. The single crystal elastic constants were numerically estimated using total energy-strain approach with two different sets of distortions. The polycrystalline aggregate elastic parameters were calculated from the single crystal elastic constants via the Voigt–Reuss–Hill approximations. Mechanical stability, sound velocities, ductility/brittleness, elastic anisotropy, Debye temperature and pressure dependence of the elastic constants of the title compounds were also assessed. Temperature dependences of the lattice parameter, bulk modulus, volume thermal expansion coefficient, isochoric and isobaric heat capacity and Debye temperature in a wide temperature interval at some different fixed pressures were predicted through the quasi-harmonic Debye model.

The structural, electronic and optical properties of the LiZnP, LiZnAs and LiZnSb filled-tetrahedral compounds were explored using the full-potential (Linearized) augmented plane-wave plus local orbitals method (FP-(L)APW+lo)). Calculated structural parameters, including the lattice constant (a), bulk modulus (B) and its pressure derivative (B'), for the considered compounds using both the local density (LDA) and generalized gradient approximations (GGA) are consistent with the available data in the scientific literature. As the density functional theory with the common LDA and GGA underestimates the band gap, we have used a newly developed functional that is able to accurately describe the electronic structure of semiconductors, namely the Tran–Blaha-modified Becke–Johnson potential. The three investigated compounds demonstrate semiconducting behavior with indirect band gap (Γ–X) ranging from about 1.41 to 1.90 eV. The charge-carrier effective masses were evaluated at the topmost valence band and at the bottommost conduction band. The evolution of the value and nature of the energy band gap under pressure effect was also investigated. Optical functions of the tile compounds, including the dielectric function , refractive index , extinction coefficient , reflectivity , absorption coefficient and electron energy-loss function ,were calculated for the energy range 0-20eV. The origins of the peaks and structures in the optical spectra were determined in terms of the calculated energy band structures.

The structural, electronic and optical properties of three principal representatives of the LiZnP, LiZnAs and LiZnSb filled-tetrahedral compounds have been explored from first-principles (full-potential (Linearized) augmented plane-wave plus local orbitals method (FP-(L)APW+lo)). The structural parameters, including the lattice constant (a), the bulk modulus (B) and its pressure derivative (B') of the considered compounds are calculated using both the local density (LDA) and generalized gradient approximations (GGA) to the exchange-correlation potential are consistent with the literature data.The single crystal elastic constants are numerically estimated using total energy-strain approach with two different sets of distortions. The polycrystalline aggregate elastic parameters are calculated from the single crystal elastic constants via the Voigt–Reuss–Hill approximations. Mechanical stability, sound velocities, ductility/brittleness, elastic anisotropy, Debye temperature and pressure dependence of the elastic constants of the title compounds are also assessed. Since DFT with the common LDA and GGA underestimates the band gap, we use a new developed functional able to accurately describe the electronic structure of semiconductors, namely the Tran–Blaha-modified Becke–Johnson potential. The three investigated compounds demonstrate semiconducting behavior with indirect band gap(Γ–X) ranging from about 1.41 to 1.90 eV. The charge-carrier effective masses are evaluated at the topmost valence band and at the bottommost conduction band. The evolution of the value and nature of the energy band gap under pressure effect is also investigated. Optical functions, including the dielectric function , the refractive index , the extinction coefficient , the reflectivity , the linear absorption spectrum and the electron energy-loss are calculated for the energy range 0-20eV. The origins of the peaks and structures in the optical spectra are determined in terms of the calculated energy band structures.

We report ab-initio density functional theory calculations of the structural, electronic and optical properties of the spinel oxides GeMg2O4,GeZng2O4 and GeCd2O4 using the full-potential linearized augmented plane-wave method. The structural parameters calculated using both the local density and generalized gradient approximations to the exchange-correlation potential are consistent with the literature data. To calculate the electronic properties, the exchange-correlation potential is treated with various functionals, and we find that the newly developed Tran–Blaha-modified Becke–Johnson functional significantly improves the band gap. We predict a direct band gap in all of the considered GeB2O4 compounds, and the band gaps continuously decrease as the atomic size of the B element increases. The decrease in the fundamental direct band gap (Γ–Γ) from GeMg2O4 to GeZn2O4 to GeCd2O4 can be attributed to p–d mixing in the upper valence bands of GeZn2O4 and GeCd2O4. The lowest conduction band is well dispersive, similar to that found for transparent conducting oxides such as ZnO. This band is mainly defined by the s and p electrons of the Si and B (B = Mg, Zn, Cd) atoms. The topmost valence band isconsiderably less dispersive and is defined by O-2 pand B–d electrons. The charge-carrier effective masses are evaluated at the topmost valence band and at the bottommost conduction band that were calculated. The frequency-dependent complex dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity and electron energy loss function were estimated. We find that the value of the zero-frequency limit of the dielectric function ε(0) increases as the band gap decreases. The origins of the peaks and structures in the optical spectra are determined in terms of the calculated energy band structures.

Algerian clay from Al-maathed was studied by dilatometric analysis technique. The activation energies measured by both isothermal (Johnson-Mehl-Avrami theory using Ligero method) and non-isothermal (Kissinger methods) treatments were 980 and 1050 kJmol-1, respectively. The growth morphology parameters n (Avrami parameter) which indicates the crystallization mode were found to be almost equal to 1.5, using non-isothermal treatments, and equal to 1.4 using isothermal (Ligero method). The numerical factor which depends on the dimensionality of crystal growth m obtained by Matusita et al. equation was 1.50. Analysis of the results shows that the bulk nucleation is the dominant mechanism in -quartz crystallization and the three-dimensional growth of -quartz crystals with polyhedron-like morphology occurs, controlled by diffusion from a constant number of nuclei.
DOI: 10.12693/APhysPolA.134.86
PACS/topics: ceramics, thermal analysis, powders

The aim of the present work is to explore the utilization of Algerian kaolinite, magnesium oxide and SiC to synthesise Cordierite (Mg2Al4Si5O18)-SiC composites ceramics through reaction sintering and investigate the phase transformation and sintering behavior of the composites. The raw powder mixtures were wet ball milled in a planetary ball mill. Powders' morphology and the microstructure of the sintered samples were characterized by means of a scanning electron microscope. The mixtures were prepared to obtain 100/00 (wt-%), 90/10 and 80/20 Cordierite/SiC composites. The samples were sintered at 1100, 1200 and 1300°C four 2 h. The bulk density of the samples was determined using Archimedes principle. Differential thermal analysis (DTA), thermogravimetry (TG), X-ray diffraction (XRD), and scanning electron microscopy (SEM) complementary techniques were used to characterize the phases transformation and densification behavior of Cordierite (Mg2Al4Si5O18)-SiC composites.

Keywords: composite, Cordierite, Phase transformation

The results of studies of crystallization kinetics of α-cordierite ceramic from MgO–Al2O3–SiO2–TiO2 glasses that are obtained via melt cooling using Differential thermal analysis (DTA), Thermogravimetric analysis (TG), X-ray diffraction (XRD) and scanning electron microscopy (SEM) are presented. DTA experiments were carried out on samples between room temperature and 1400 °C under argon gas flowing at a rate of 40 cm3/min. Heating rates of 10, 20, 30, 40, and 50 °C/min were used in this investigation. X-ray diffraction was used to characterize the phase transformations of the sintered powders. The activation energy values for α-cordierite formation, using DTA results was measured under both isothermal (Johnson–Mehl–Avrami (JMA) theory using Ligero method) and non-isothermal (using Kissinger, Boswell, and Ozawa methods) treatments were found to be equal to 845 and 720 kJ mol-1, respectively. The growth morphology parameters n (Avrami parameter) were found to be almost equal to 1.5, using non-isothermal treatments, and equal to 1.5 using isothermal ( Ligero method ) and m (the numerical factor) was 1.5 obtained by Matusita et al. equation. The growth morphology parameters n and m are both approximated as 1.5, which is an indication of a three dimensional growth from a constant number of nuclei and resulting in a polyhedron -like morphology controlled by diffusion.

Keywords: Cordierite, Differential thermal analysis, Avrami parameter, numerical factor, Activation energy.

In this paper, we investigate the effect of CaO additions on phase transformation and densification behavior of cordierite obtained by mixing Algerian kaolin and magnesium oxide. The starting raw materials were mixed through the planetary ball mill using Zirconia balls for 5 h. The mixtures were sintered between 900 and 1300°C for 2 h. The bulk density was measured by water immersion method. The phases formed were studied by X-ray diffraction and Raman spectroscopy. Differential thermal analysis (DTA) and Thermogravimetric analysis (TG) under flow of argon gas using different heating rates, under non-isothermal condition was used to study the kinetics of thermal process of kaolin/magnesium oxide with the addition of various amounts of calcium hydroxide as sintering aid. DTA and TG experiments were carried out on powders between room temperature and 1300 °C, at heating rates from 10 to 40 °C.min-1. The effect of CaO additions on the activation energies have been measured by differential thermal analysis, from non-isothermal treatments, using Kissinger, Boswell and Ozawa methods were around 600 and 800 kJ mol-1. The Avrami parameter of growth morphology is about 2.1 by using non-isothermal treatments and the dimensionality of crystal growth, m, is around 1.9. Results show that the growth morphology parameters n and m are near to two. The bulk nucleation with constant number of nuclei was dominant in cordierite crystallization followed by Two-dimensional growth with plate morphology controlled by the interface reaction.

Keywords: Cordierite, Differential thermal analysis, kinetic, Phase transformation

In this study, the effect of MgO additive on the mechanism and kinetic parameters of Cordierite crystallization synthesized through reaction sintering of Algerian kaolinite with
synthetic magnesia was studied using differential thermal analysis (DTA) technique. DTA experiments were performed from room temperature to 1400 °C at different heating rate from 10, 20… until 50 °C/min. The activation energies were measured by both isothermal (Johnson–Mehl–Avrami (JMA) theory using Ligero method) and non-isothermal (Kissinger methods) treatments. Moreover, the growth morphology parameters n (Avrami parameter which indicates the crystallization mode) and m (the numerical factor which depends on the dimensionality of crystal growth) were calculated to be about 1 using non-isothermal and isothermal (Ligero method) treatments for the samples without MgO additive, and 2 to 3 for the samples contain 4 and 8 wt% MgO addition, respectively. The results showed that the bulk nucleation with constant number of nuclei was dominant for all samples, followed by two-dimensional growth of crystals with plate’s morphology for samples with 00 and 4 wt% MgO addition controlled by diffusion and Interface reaction, respectively while growth of crystals for the sample contain 8 wt% MgO controlled by Interface reaction followed by Three-dimensional (polyhedron).
Keywords: kinetic parameters, Cordierite, Phase transformation, Differential Thermal Analysis.

In this study mixtures of Algerian kaolinite (kaolin Tamazarte (KT) and kaolin of Djebel Debbagh (DD1)) with magnesium oxide with and without boron oxide B2O3 additive were investigated in order to obtain a dense cordierite also called indialite. The addition of B2O3 has promoted the formation of α-cordierite either by crystallization of the residual glass or by transformation of µ-cordierite. The differential thermal analysis and thermogravimetric analysis experiments were carried out on ceramic samples in the temperature range between room temperature and 1300°C at different heating rates. In order to determine the phases and their transformations in cordierite powders treated at different temperatures between 900 and 1300 °C with steps of 50 °C the X-ray diffraction analysis was used.
DOI: 10.12693/APhysPolA.134.75
PACS/topics: ceramics, thermal expansion, differential thermal analysis, reactions

In this work, Algerian kaolinite, a naturally occurring clay mineral, was used as low-cost precursor for the synthesis of cordierite ceramics. The kaolinite was mixed with synthetic magnesia, and the mixture was ball milled and reaction sintered in the temperature range 900–1350 °C for 2 h. Thermogravimetry (TG), differential thermal analysis (DTA), dilatometry, high temperature x-ray powder diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) complementary techniques were used to analyze sintering behavior, characterize phase transformations, and investigate crystallization kinetics. Milling the kaolinite and magnesia mixture for 10 h yielded a homogenous powder, decreased the average particle size, and improved the roundness of particles. Different crystalline phases were present in the samples sintered in the temperature range 900–1150 °C, the cordierite phase started to crystallize at 1200 °C, and the formation of highly dense cordierite (99%) was complete at 1250 °C. The activation energy values for cordierite formation calculated using Kissinger, Boswell, and Ozawa methods were found to be equal to 577, 589, and 573 kJ/mol, respectively. The kinetic parameters n and m had values close to 2. Bulk nucleation with a constant number of nuclei was the dominant mechanism in cordierite crystallization, followed by two-dimensional growth controlled by interface reaction.
Keywords
A. Solid state reactionD. ClaysD. CordieriteD. MgO

Thermal analysis techniques remain important tools amongst the large variety of methods used for analysis of the precipitation and dissolution of the Guinier–Preston zone and metastable phase 0 in Al–3wt% Cu. In the present study, the kinetics of precipitation and dissolution of the Guinier–Preston zone and metastable phase 0 in Al–3wt% Cu was investigated using differential scanning calorimetry carried out between room temperature and 430 C at heating rates of 20, 25, and 30 C min?1. The activation energies evaluated through isothermal differential scanning calorimetry treatment using the Johnson–Mehl–Avrami theory were 25, 100, and 80 kJ mol-1 for the Guinier–Preston zone precipitation, formation of 0= and dissolution of 0, respectively. The Avrami constant n obtained by the Ligero method was about 1.5 for the formation of 0= indicating that bulk nucleation
is dominant in 0= formation controlled by diffusion from a constant number of nuclei.
DOI: 10.12693/APhysPolA.131.133
PACS/topics: 81.30.Mh, 81.70.Pg, 81.30.Bx

In this study, the mechanism and kinetic parameters of Al–Si spinel crystallization from Algerian Tamazarte kaolinite was studied by Differential thermal analysis (DTA) technique, which were carried out on samples between room temperature and 1400°C at different heating rates (10–40°C/min). X-ray diffraction was used to identify the phases present in the samples. The activation energies measured by both isothermal (Johnson–Mehl–Avrami (JMA) theory using Ligero method) and non-isothermal (Kissinger methods) treatments are 870 and 810 kJ/mol, respectively. The growth morphology parameters n (Avrami parameter which indicates the crystallization mode) were found to be almost equal to 1.08, using non-isothermal treatments, and equal to 1.17 using isothermal (Ligero method) and m (the numerical factor which depends on the dimensionality of crystal growth) was 1.07 obtained by Matusita and al. equation. Analysis of the results showed that bulk nucleation was dominant in Al–Si spinel crystallization followed by two-dimensional growth of mullite crystals with plates morphology controlled by diffusion from a constant number of nuclei.

In this study, the mechanism and the kinetic parameters of the thermal decomposition of gibbsite Al(OH)3 were studied by differential thermogravimetry technique under non-isothermal conditions, between room temperature and 1200 K at heating rates of 5, 10, 15 and 20 °Cmin-1. The obtained differential thermogravimetry curves show clearly three In this study, the mechanism and kinetic parameters of the thermal decomposition of gibbsite Al(OH)3 was studied by differential thermogravimetry (DTG) technique under non-isothermal conditions, which were carried out on samples between room temperature and 1200K at heating rates of 5, 10, 15 and 20°C min-1. the obtained DTG curves show clearly three distinct peaks: the first peak is due to the partial de-hydroxylation of gibbsite, Among the 32 types of non-isothermal kinetics differential equations, we find that the most suitable mechanism is (A3/2: g(x) = [-ln(1-x)]2/3) or called it Avrami- Erofeev eq. Order=2/3 We find the value of the activation energy (EA) and pre-exponential factor (K0) correspond to are 157 KJ/mol and 7,58×1015 s-1 respectively. The second peak correspond to the decomposition of gibbsite to boehmite, we get that the most suitable mechanism is controlled by the rate of second-order reaction (F2: g(x) = (1-x)-1-1) under applied condition. We also find the value of the activation energy (EA) and pre-exponential factor (K0) correspond to 243 kJ mol−1 and 3,73 x 1022 s−1, respectively. The third peak is due to the transformation of boehmite to alumina. However the mechanism for such transformation is better described by the one-and-half rate order reaction (F3/2: g(x) = (1-x)-1/2-1). In addition, the values of EA and K0 were determined around 296 kJ mol−1 and 1,82x1019 s−1, respectively. The results of differential thermogravimetry (DTG) were supplemented by differential thermal analysis (DTA), X-ray powder diffraction (XRPD) analysis for samples of gibbsite treated at different temperatures between 200 and 1200°C with steps of 200°C.
Keywords: gibbsite, boehmite, decomposition kinetics, TG/DTG, Activation energy

Clay is one of the most used natural materials in the ceramic industry with various applications such as pottery, tiles, cement and bricks. The latter are used as a building material because of their excellent thermal and mechanical properties. In the present study, Algerian clay from Al-maathed area, M’sila district, was used to prepare bricks. The chemical composition of the clay was determined using X-ray fluorescence. Firing of clay was carried out in the temperature range 20–1000 °C, at different heating rates. The present phases and their transformations, the activation energy, and the sintering mechanism were evaluated using X-ray diffraction, differential thermal analysis, thermogravimetric analysis and dilatometry. The activation energy for the sintering mechanism obtained from non-isothermal treatments is 420 kJ/mol. The value of the Avrami exponent, n, is determined from the shape of the crystallization exothermic dependence. It is related to m parameter (a numerical factor which depends on the dimensionality of crystal growth) obtained by Matusita method. Both of which are about 1.2 for clay sintering. These values indicate that bulk nucleation is dominant in clay sintering by three dimensional growth, with polyhedron-like morphology controlled by interface reaction.
DOI: 10.12693/APhysPolA.131.566
PACS/topics: 81.05.Mh, 81.70.Pg, 81.30.Mh

investigated by using differential thermal analysis. The differential thermal analysis and the thermogravimetric experiments were carried out on samples between room temperature and 1400 °C, at heating rates from 10 to 40 °Cmin-1. X-ray diffraction was used to identify the phases present in the samples. The activation energies measured by differential thermal analysis from isothermal and non-isothermal treatments using Johnson-Mehl- Avrami methods with Ligero approximation and using Kissinger-Akahira-Sunose methods were around 145 and 159 kJ/mol, respectively. The Avrami parameter n which indicates the growth morphology parameters were found to be almost equal to 1.60, using non-isothermal treatments, and equal to 1.47 using isothermal treatments. The numerical factor which depends on the dimensionality of crystal growth was 1.60 obtained using Matusita et al. equation. The frequency factor calculated using the isothermal treatment is equal to 1.173 * 107 s-1. Analysis of the results have shown that bulk nucleation was dominant during kaolinite transformation, followed by three-dimensional growth of meta-kaolinite with polyhedron-like morphology, controlled by diffusion from a constant number of nuclei.
DOI: 10.12693/APhysPolA.131.382
PACS/topics: 82.30.Lp, 81.05.Je, 81.05.Mh, 81.70.Pg

The aim of this work is the substitution of the bovine bone by the natural phosphate from Djebelel-Onk (Tébessa, East of Algeria). We prepared two composites (bone/Al2O3 and natural phosphate/Al2O3) by reaction sintering. Different experimental techniques, including density, porosity, X-rays diffraction, and SEM techniques, were used to analyze the formation and transformation of phases at different temperatures. From the X-ray diffraction patterns, we put in evidence the formation of several phases. Through these results, we lighted the possibility of preparing bioceramics from natural phosphate (bone and natural phosphate). The presence of the different materials was confirmed by the micrographic observations.
DOI: 10.12693/APhysPolA.131.117
PACS/topics: 81.05.Je, 81.05.Mh, 87.85.jf

The decomposition kinetics of Algerian Tamazarte kaolinite (TK) was investigated using thermogravimetric analysis (TG). Differential thermal analysis (DTA) and TG experiments were carried out between room temperature and 1400 °C, at different heating rates from 10 to 40 °C/min. The activation energies, measured by DTG from isothermal treatments using
Johnson−Mehl−Avrami (JMA) and Ligero methods and by non-isothermal treatments using Ozawa, Boswell and Kissinger methods, were around 151 and 144 kJ/mol, respectively. The Avrami parameter of growth morphology (indicating the crystallization mode) was found to be around 1.57 using non-isothermal treatments; however, when using isothermal treatments it is found to be equal to 1.35. The numerical factor, which depends on the dimensionality of crystal growth, is found to be 1.53 using Matusita equation. The frequency factor calculated by the isothermal treatment is equal to 1.55×107 s−1. The results show that the bulk nucleation is followed by three-dimensional growth of metakaolinite with polyhedron-like morphology controlled by diffusion from a constant number of nuclei.
Key words: kaolinite; decomposition kinetics; Avrami parameter; activation energy; growth morphology

In this study, Algerian halloysite, a naturally occurring clay mineral, was used as low-cost precursor for the production of mullite-zirconia composites. The halloysite was reaction sintered with boehmite and zirconia in the temperature range 1250–1650 °C for 2 h. Differential thermal analysis (DTA), thermogravimetry (TG), dilatometry, high temperature X-ray diffraction (XRD), and scanning electron microscopy (SEM) complementary techniques were used to characterize the prepared materials. The influence of ZrO2 content on the
microstructure, densification, hardness, and coefficient of linear thermal expansion of the composites was investigated. Algerian halloysite was found suitable material for the synthesis of low-cost mullite based composites. All prepared samples exhibited same phase transformations that ended at 1550 °C with the formation of monolithic mullite in halloysite-boehmite mixture and mullite-zirconia composites in halloysiteboehmite-zirconia mixture. The composite materials showed higher values of hardness and coefficient of linear thermal expansion compared with monolithic mullite. The composite containing 10% ZrO2 possessed the highest hardness value of 13.5 GPa. The composite containing 30% ZrO2 possessed the lowest value of linear coefficient of thermal expansion of 7.5725 ×10−6 K−1 between 200 and 1500 °C.
Keywords:
Clay minerals
Halloysite
Gibbsite
Boehmite
Reaction sintering
Mullite-zirconia composites

This work presents the experimental results of the differential scanning calorimetry (DSC), hardness measurements (Hv) and X-ray diffraction (XRD) analysis, investigating the kinetics
of precipitation phenomena in Al-7 wt % Mg alloy. In the XRD and DSC curves indicates the formation of the intermediate precipitation of b-(Al3Mg2) phase respectively.
The activation energies associated with the processes have been determined according to the three models proposed by Kissinger, Ozawa and Boswell. Consequently, the nucleation
mechanism of the precipitates can be explained. These phases are confirmed by the XRD analysis.
© 2016 The Physical Society of the Republic of China (Taiwan). Published by Elsevier B.V.

In this present study, the thermal decomposition of gibbsite Al(OH)3 was studied by the Differential Thermal Analysis (DTA) technique under non-isothermal conditions, the gibbsite powder were carried out between room temperature to 900 °C using heating rates of 5, 10, 15 and 20 °C/min.The obtained DTA curves show two different peaks: the first peak is due to partial dehydroxylation of gibbsite and formation of boehmite, the value of the activation energy (EA) corresponds to 143 KJ/mol. The second peak corresponds to transformation of gibbsite to a-Al2O3 phase, the activation energy (EA) was found around to 185 KJ/mol. The values of apparent activation were determined by Ozawa–Flynn–Wall (OFW), Boswell and Kissinger–Akahira–Sunose (KAS) methods and by applying the basic solid-state kinetic equations. The phases formed and the structural changes were investigated by differential thermogravimetry (DTG) and X-ray diffraction (XRD) for gibbsite powder treated at different temperatures from room temperature to 1100 °C.
Keywords: Activation energy, Decomposition kinetics, Differential Thermal Analysis (DTA), Gibbsite.

Low-cost materials based on hydroxyapatite(HAp),anorthite and mullite were prepared from mixtures of Algerian kaolin(DD2)and natural phosphate (NP).Three different compositions(20K, 50K and 80K)with 20, 50 and 80wt% Kaolin were studied. In the20K samples(with 80% natural phosphate),HAp based ceramics were obtained by the solid-state reaction (SSR).Anorthite–HAp composites were formed at 1100 1C in the 50K samples remaining stable up to1300 1C. The primary mullitization occurred by SSR in the 80 K sample at 1000 C followed by formation of anorthite from the phosphate dissolution. These results show that the reaction sintering of kaolin/phosphate mixtures is afeasible route to obtain HAp, anorthite materials that can be used in electronics industry, industrial heat exchangers and biomedical applications.
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