M. HERAIZ Menad

One of the key challenges in developing mullite–cordierite electronic substrates is achieving phase homogeneity and controlling porosity to optimize thermal conductivity while maintaining a controlled microstructure. We produced precursor powder for mullite/cordierite composites (Mu/C Com.) for use in multifunctional substrates and electronic components using the sol–gel technique at low temperatures. The precursor powders for the (Mu/C Com.) were made utilizing SiO2 and Al2O3 oxides, respectively, from Si(C2H5O)4 and Al (NO3)3.9H2O, respectively. Structural phases were identified using XRD and refined using the Rietveld method. Microstructure, grain size, and elemental composition were examined by SEM/EDX. Density and porosity were measured via Archimedes’ method. XRD showed pure crystalline mullite for all compositions, while cordierite remained amorphous. Increasing cordierite content reduced grain size by 55%, lowered porosity, and increased bulk density (up to 2.643 g/cm3 for Mu-C30).
The dielectric constant decreased with both frequency and cordierite content. A temperature-activated rise in ε′ and ε′′ above 280 °C was observed. AC conductivity followed Jonscher’s power law, and activation energies decreased from 0.14 to 0.10 eV with increasing cordierite, indicating facilitated ionic transport. The variation in the maximum imaginary component of the modulus and impedance with frequency implies the presence of a non-Debye relaxation phenomenon. These results demonstrate that dense, sol–gel-derived Mu/C composites exhibit low dielectric loss and stable dielectric behavior at high frequency, making them promising candidates for electronic substrates, high-frequency circuit packaging, and ceramic capacitor applications.

Due to the rapid development of telecommunications systems toward 5G and 6G, there is a high demand for dielectric materials with low dielectric permittivity and low tangent. In this study presents a comprehensive investigation of sol–gel derived forsterite (Mg2SiO4) ceramics, focusing on their structural, microstructural, and dielectric properties. XRD and Rietveld-refinement analysis confirmed phase-pure orthorhombic forsterite (space group Pbnm) with no secondary phases. FESEM/EDS analysis revealed a well-defined microstructure and stoichiometric Mg2SiO4 composition (Mg:Si:O ≈ 2:1:4 atomic ratio). The bulk density was measured as 2.56 g/cm3, corresponding to ~78% of theoretical density. Dielectric and impedance spectroscopy studies demonstrated excellent functional properties: low relative permittivity (εr ~ 9.12 at 1 MHz) and minimal loss tangent (tan δ < 0.015). Complex impedance analysis showed a decrease in the real part of impedance (Z′) with increasing frequency and temperature, while Nyquist plots exhibited single semicircular arcs, indicative of non-Debye relaxation dominated by grains. Electrical modulus spectra revealed relaxation peaks shifting to higher frequencies with temperature. The exponent s decreased from 1.85 (100 °C) to 1.76 (400 °C), indicating correlated barrier hopping (CBH) conduction. The DC conductivity followed Arrhenius behavior with an activation energy (Ea) of 0.19 eV, consistent with polaron-assisted transport. This work established structure-property relationships linking sol–gel processing, microstructure, and optimized dielectric performance.

The study focused on analysing the kinetics of halloysite decomposition using the differential thermal analysis (DTA) technique. Tests were carried out across a temperature span from ambient temperature to 1673 K, employing heating rates spanning from 5 to 20 °C.min−1. X-ray diffraction and Fourier transform infrared spectroscopy (FT-IR) were utilized to identify the phases formed at different temperatures. Activation energies for halloysite decomposition were determined through isothermal and non-isothermal treatments, yielding values of approximately 151.68 kJ mol−1 and 173.14 kJ mol−1, respectively. The Ligero method's Avrami constant parameter (m) and the Matusita method's numerical factor parameter ( n), linked to crystal growth dimensions, were both around 1.5. These findings indicate that the degradation of halloysite is primarily governed by bulk nucleation, succeeded by the 3-dimensional growth of meta-halloysite characterized by polyhedron-like structure, regulated by diffusion from a consistent number of nuclei. The frequency factor for halloysite dehydroxylation was established at 8.48 × 10⁸ s⁻1.

This research explores the fabrication of mullite precursor powder utilizing the sol-gel process at low temperatures.
Silicon (Si(C2H5O)4) and aluminum nitrate nonahydrate (Al(NO3)3.9H2O) were employed as the sources of SiO2 and Al2O3 oxides, respectively. Various analytical techniques, such as Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), dilatometry, differential thermal analysis (DTA), and Xray powder diffractometer (XRD), were utilized to investigate the formation and crystallization of the amorphous powder. The microstructure of specimens sintered at 1600 ◦C for 1 h was examined utilizing scanning electron microscopy (SEM). Measurements of hardness (HV) and coefficient of thermal expansion (CTE) were conducted on mullite samples heated to 1600 ◦C and then cooled, revealing an increase in HV from 888 to 1000 HV as the sintering temperature rose from 1500 to 1600 ◦C. The CTE of mullite within the temperature range of 50–1300 ◦C was determined as 5.23 × 10􀀀 6/◦C. Additionally, the dielectric and electrical characterization of mullite was analyzed utilizing complex impedance spectroscopy at a frequency of 0.1–106 Hz and conductivity measurements over a temperature range of 40–400 ◦C. The real and imaginary parts of the dielectric permittivity exhibited frequency-dependent and temperature-dependent behaviors. Significantly, the observed variations in
the imaginary component of the modulus and impedance maximum frequency point to a relaxation process that
is not Debye-type, with calculated activation energies (Ea) consistent across different methods.

The preparation and characterization of mullite-cordierite composites are the major objectives of the research work. The initial powders of the used raw materials were combined, ball milled, and sintered for two hours at a temperature between 1000 and 1400 °C. The sintering behavior and the formed phase throughout the thermal process were investigated using a number of complementary techniques including thermogravimetry (TG), differential thermal analysis (DTA), dilatometry, x-ray powder
diffraction (XRD), and scanning electron microscopy (SEM). Dilatometry (DL) analysis and differential thermal analysis (DTA) High

In this study, we utilized the sol-gel technique at low temperatures to generate precursor powder for mullite. To make the mullite precursor powders, Si(C2H5O)4 and Al (NO3)3.9H2O were used as sources of SiO2 and Al2O3 oxides, respectively. For example, X-ray powder diffractometer (XRD) were used to study the amorphous powder that was made and how it crystallized. The microstructure of specimens subjected to sintering at 1600 °C for 1 hour was scrutinized through a scanning electron
microscope (SEM). the samples' dielectric properties were studied at room temperature. The relative dielectric constant (εr), loss tangent (tanδ), and dielectric properties were checked at 0.1, 1, 10, 100, and 1000 kHz. Notably, at 1 kHz, the relative dielectric constant values closely resembled those of mullite (εr= ~5 to ~6), accompanied by the lowest observed dielectric losses (tanδ = ~0.17 to ~0.04).

– In the present work, cordierite–mullite composites were produced using a sol-gel technique. Different amounts of cordierite (0, 10, and 20 wt.%) were added to the mullite, and the calcined gels were sintered at 1550–1600°C for 1 h. The phase composition and sample morphology were evaluated via X-ray diffraction (XRD) and scanning electron microscopy analysis. The sintering parameters in terms of bulk and apparent density were determined .the thermal expansion coefficient (TEC) and mechanical properties were also evaluated. The sintering parameters in terms of apparent and bulk density were calculated.

In this work, forsterite precursor powder was prepared through a technology of low-temperature ‎synthesis by using ‎the sol-gel process, tetraethyl orthosilicate, and Mg(NO3)2.6H2O were used as raw materials to synthesize forsterite. To pursue and characterize the crystalline phases and their transformation as a function of temperature, Thermogravimetry, differential thermal analysis, X-ray diffraction and Fourier-transform infrared spectroscopy was used.
The results showed that the crystallization process occurred in the temperature range of 650 to 1100 °C. Forsterite, a mineral with the chemical formula Mg2SiO4, was formed in the 650–800 °C temperature range. When the temperature is increased from 800 °C to 1100 °C, forsterite becomes more crystallized. The obtained results agree with the X-ray diffraction analyses that approve that there is just one phase (forsterite).
The activation energy values (Ea/Tm) calculated by Ozawa, Boswell, and Kissinger methods are in good agreement with the activation energy (Eα/Tα) calculated using the KAS and FWO methods. So as to determine the interaction model and find the parameters that determine the interaction model based on the experimental data, Malék's methodology method was used. The Šesták - Berggren model is the most appropriate kinetic model to describe the reaction process to form forsterite. 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 forsterite are, respectively, 1.02 , 0.36, and 26.8. While the values of Gibbs free energy #ΔG, enthalpy #ΔH, and entropy #ΔS were as follows: 294.871 kJ/mol, 252.938 kJ/mol, and -40.5 J/mol.K for forsterite formation.

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.

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.

CHARACTERIZATION OF CORDIERITE/MULLITE COMPOSITES PREPARED BY SOL-GEL TECHNIQUE

Preparation of ceramic composite powders by By the sol-gel Method

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.

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

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.

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.

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.

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

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

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