Cordierite Phase Research Articles

Preparation of cordierite powder by chemical coprecipitation–rotation evaporation and solid reaction sintering

At present, the formation conditions of cordierite were relatively harsh, the formation temperature was close to the decomposition temperature, and it was difficult to control the sintering temperature. In order to solve the problem of cordierite synthesis, cordierite powders were synthesized by chemical coprecipitation–rotation evaporation and solid reaction sintering. The thermodynamics, thermal analysis, phase composition, specific surface area, morphology, and grain size distribution of the samples sintered at different temperatures were systematically studied. SEM micrographs showed that the crystal structural evolution of cordierite was divided into three processes; the temperatures of 1000 °C (the formation of hexagonal flake–like grain) and 1200 °C (the formation of flaky texture grain) were two important sintering transition points. The specific surface area of the sample sintered at 1400 °C was 1.76 m2/g, and the grain size was well developed with the range of 196.5–222.7 nm. Phase analysis revealed that the main crystal phase of samples sintered at 1200 °C was cordierite phase and a little spinel phase and mullite phase, and the peak intensity of the characteristic peaks at 1400 °C was more intense.

Processing of electric ceramic insulators from slate rocks and MgO

ABSTRACT Ceramic bodies enriched with cordierite were successfully fabricated via solid state process using natural raw materials such as slate and kaolin, and their dielectric properties were investigated. Four batch compositions were designed, and partial substitution of MgO for slate was performed to increase the Mg content in the fabricated bodies and enhance the cordierite formation. The petrographic description, phase evolution, porosity, microstructure, mechanical properties and thermal expansion properties were systematically investigated. Different crystalline phases were present in the samples fired in the temperature range 1175–1250°C; the cordierite phase appeared in batch CS and was well crystallized in batch DS. As a result of the low porosity and existence of the mullite phase, sintered AS samples displayed the highest mechanical properties. The dielectric results indicated that the dielectric loss for the sintered bodies was within the range 10−2–10−3. A better loss tangent value was observed for batch DS. The tested samples were insulators, suggesting their potential use in microelectronic packaging and electro-ceramic protective coatings.

An example of uraniferous leucogranites in the Rössing South-West deposit, Namibia

The southern Central Zone (sCZ) of the Neoproterozoic to early Palaeozoic Damara orogenic belt hosts significant uranium deposits in Namibia. Rössing South-West, a leucogranite-hosted uranium deposit in the sCZ is partitioned into two sections; north-easterly and south-westerly sections with the latter (termed mining licence 120, i.e. ML121) forming the locus of this investigation. The deposit lies within the vicinity and to the west of the Welwitschia lineament which served as a conduit for mineralized fluids along with the Rössing and Husab deposits. Mineralogy and major and trace element geochemistry of the uraniferous leucogranites in ML121 suggest they are S-type granites derived from a sedimentary source as evidenced by the presence of igneous phases of garnet and cordierite together. Microscope and electron microprobe results from 133 powdered, drill core and hand samples prove that the deposits host similar primary uranium mineralization (chiefly uraninite which mainly exist as independent uranium minerals) and similar secondary U mineralization. At Rössing-SW U minerals include uraninite, coffinite, pitchblende, betafite, uranophane, betauranophane, carnotite, gummite and might partially exist as Th isomorphs. Mineralization at all locales is associated with post-tectonic D and E-type sheeted leucogranites containing quartz, alkali-feldspar and variable amounts of plagioclase producing rocks of variable compositions from tonalite to alkali-feldspar granite. Total reserves calculated at a cut-off grade of 100 ppm were reported as 171 Mt of ore at 376 ppm for Rössing and 205 Mt of ore at 497 ppm for Husab (probable). The Rössing-SW orebody is open-ended however total inferred resources stand at 304.4 Mt of ore at 235 ppm while measured resources stand at 8830t ore at circa 231 ppm. A comparison of the geological parameters (uranium mineralogy, leucogranite petrology and geochemistry) suggests similar ore composition. Consequently, ore from Rössing-SW's ML121 area could be processed at existing metallurgical plants (such as at Rössing or Husab) with a probable increase in U3O8 yield.

Total recycling of all the components from spent auto-catalyst by NaOH roasting-assisted hydrometallurgical route.

Total recycling of all valuable metals such as PGMs, Ce, Al and Mg from the spent automobile catalysts has been explored. The alkali roasting was performed under NaOH, 0.5-3.0 g; temperature, 300-800 °C; and time, 10-60 min. The phase transformation from cordierite to the soluble products (NaAlO2, Na2MgSiO4) was influenced by the temperature, following the diffusion-controlled model (Ea(roasting), 6.4 kJ/mol). XRD analysis of the roasted mass revealed that the refractory phases of cordierite and γ-alumina could be eliminated at ≥600 °C at sample-to-NaOH mass ratio, 1:1. The leaching of the roasted mass followed an intermediate-controlled mechanism for aluminum leaching with (Ea(Al-leaching) value of 20.3 kJ/mol), while it was diffusion-controlled for magnesium leaching (Ea(Mg-leaching), 8.9 kJ/mol). At the optimum leaching condition (1.0 M H2SO4, 90 °C, 60 min, yielding >95% aluminum and magnesium), a significant amount of PGMs was also leached. Thereafter, the cementation process was investigated with Al0-powder that could precipitate >99% PGMs within 15 min at 90 °C. The yielded concentrate of PGMs and CeO2 was subsequently leached in 6.0 M HCl with 2.0 M NaClO3 that dissolved >97% PGMs, leaving the residue as the CeO2 concentrate. Individual metals can be recovered by following established separation and purification techniques.

Influence of Mechanical Activation on the Phase Formation in the Synthesis of Cordierite from Talc and Andalusite

Cordierite is known as a leading candidate material for many applications. In this study, mechanical activation assisted synthesis of cordierite using andalusite as a starting material was attempted and phase formation of powder obtained from the heat treatment of talc-andalusite-silica system was investigated. The stoichiometric composition of cordierite (2MgO·2Al2O3·5SiO2) was prepared and ground in planetary ball mill at the rotational speed of 300 and 500 rpm for 0, 30, 60 and 90 min. The powder mixtures were heat treated in air at the temperature ranging from 1150 to 1350°C for 2 hours. Thermal reaction, phase present and microstructure of the starting materials and synthesized products were analyzed by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. It was found that cordierite phase increased with the grinding time and speed and synthesis temperature. The kinetics of phase formation in this system were also discussed.

Effect of NiO and MoO3 addition on the crystallinity and mechanical properties of α-cordierite and β-cordierite in the MgO-Al2O3-SiO2 system

Abstract The cordierite is one of the most important phases within the MgO-Al2O3-SiO2 (MAS) system. In this study, the crystallization and microstructure of cordierite was analyzed. Four samples were prepared, which were subjected to a thermal treatment at a temperature of 1200 °C with a permanence time of 2 h. The temperature of the thermal treatment was selected depending on the critical working temperature, specific applications such as coatings of glass ceramic materials, according to the literature review. Characterization was performed by thermal analysis, X-ray diffraction, scanning electron microscopy, microhardness tests and nano-indentation to observe the effect of NiO (0–3 %wt) addition, on the formation and crystallization of α and β cordierite phases. The X-ray diffraction results showed that the formation of α-cordierite was promoted by crystallization of several metastable phases with the addition of NiO. Meanwhile a decrease of the β-cordierite phase was observed, to give rise to formation of α-cordierite as %wt. NiO increases. The average crystal size of the crystalline phases was larger in the sample without NiO addition, and the sizes of the crystals, especially α-cordierite decrease with higher concentrations of NiO, and the crystals within the domains become smaller, which results in a microstructure and better mechanical properties (hardness = 8–11 GPa and Effective elastic modulus = 11–14 GPa), than those reported in the lit erature (hardness = 7–8 GPa and Effective elastic modulus = 10–13 GPa).

Structural origin of negative thermal expansion of cordierite honeycomb ceramics and crystal phase evolution with sintering temperature

The structural origin of the negative coefficient of thermal expansion (CTE) along the c-axis in cordierite is investigated using high temperature X-ray diffraction. The evolution of the lattice parameters, bond length, covalent character, and electron density distributions are analyzed with increasing temperature. The increase of covalent character of the tetrahedral bonds in the six-membered hexagonal ring is considered as the possible origin for the negative expansion. In addition, the bridging oxygen can act as a buffer absorbing thermal energy and prevents the increase in M1-O-M2 bond. The electron density distribution indicates that the linking oxygen strongly vibrates transversely across two coordinate M1-O-M2 linkages. The CTE and pore size and distribution change drastically at near 1300 °C due to the substantial increase in cordierite phase proportion and the formation of a liquid phase. Raw materials are consumed completely at 1450 °C and the CTE decreases to 1.3 ppm K−1.

Crystal Structure and Thermal Expansion Coefficient of Cordierite Honeycomb Ceramics

Cordierite honeycomb ceramics are sintered under a range of sintering atmosphere and temperature conditions. The linear thermal expansion coefficient (CTE) is measured along the extrusion direction. The samples sintered in an enclosed crucible have a much lower CTE than those sintered in open air. The CTE decreases with increasing sintering temperature up to 1450 °C. The polymorphic phases, texture, amorphous phase, impurity crystals, and porosity are analyzed using scanning electron microscopy, HR‐TEM, porosimeter, and Rietveld refinement method. The sintered samples consist of two polymorphic phases: indialite (hexagonal symmetry) and cordierite (orthorhombic symmetry). Both the volume % of the cordierite phase and the crystal texture increase with increasing sintering temperature. The orthorhombic distortion of cordierite from the hexagonal lattice (indialite) increases with increasing sintering temperature. The characteristic six‐membered ring of the (Si,Al)‐O4 tetrahedra in the cordierite structure shows substantial changes in the bond length due to Al‐Si ordering. Amorphous phase and impurity crystal phases such as silimanite and spinel remain at temperatures as high as 1450 °C. The effect of the polymorphic phases, the degree of texture, amorphous phase, impurity crystal phases, and the orthorhombic distortion is discussed in relation to the CTE characteristics of honeycomb.

Effect of reduced Al2O3 mole ratio on fabrication of cordierite ceramic by solid-state sintering method

Cordierite ceramic was fabricated by reducing Al2O3 mole ratio from 2.0 to 1.4 with kaolin, silicon dioxide and magnesium oxide as the raw materials. The effect of reduced Al2O3 mole ratio on the sintering behaviors, phase transition, main properties, and microstructure were characterized in detail. The results show that cordierite phase becomes the main crystallization phase at 1300?C, and mullite phase can be consumed to produce cordierite phase by reducing Al2O3 mole ratio. But additional quartz phase still exists until 1400?C. Moreover, the open porosity, pore connectivity and pore size increase as Al2O3 mole ratio reduces from 2.0 to 1.4 while the linear shrinkage percent and bulk density decrease with the reduced Al2O3. It is considered that the sintering activity of the raw materials at low temperature decreases due to the increase of chemically pure magnesium oxide and silica with the decrease of Al2O3 mole ratio, while the crystallization process, pore growth and cordierite phase rather than the liquid phase control the densification process at high temperature.

Zeolite usage as source of silica to produce cordierite in MgO\u2013Al2O3\u2013SiO2 system

In this study, natural zeolite was used as source of silica to produce cordierite. MgO and Al2O3 were added to zeolite to obtain the cordierite stoichiometry. Mixture of these raw materials was mechanically activated for different durations. The mechanically activated powder mixture was characterized using XRD, DSC, SEM, specific surface area, and particle size analyzer. The pycnometer method was used to measure the densities of mechanically activated powder mixtures. Mechanically activated for 60 min powder mixture was sintered at 1150–1350 °C for 1 h. The sintering behavior of the samples was determined by measuring the linear shrinkage, density, and apparent porosity. The phases in the sintered samples were identified by XRD. Cordierite and spinel phases were detected for sintered at a temperature higher than 1150 °C but corundum accompanied to cordierite and spinel at 1150 °C. The microstructure of the samples was examined using both SEM and AFM. The sintering behavior and microstructural properties of the samples changed with an increase in the sintering temperature. As the apparent porosity increased with increasing sintering temperature, linear shrinkage and density values decreased. Density values were determined as 2.31–2.69 g/cm3 depending on the temperature. The grains coarsened at higher temperature and the average grain size depending on the temperature was 1.34–1.96 μm. From the results optimum sintering temperature was determined as 1250 °C. Dense material was produced at a temperature as low as 1250 °C using zeolite as raw material.

Effect of temperature and magnesia on phase transformation kinetics in stoichiometric and non-stoichiometric cordierite ceramics prepared from kaolinite precursors

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 μ and α 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 α cordierite was higher than that of μ cordierite. Energies of formation of μ and α 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 μ or α cordierite, had values between 2 and 3.

Reduction of chromium ore by recycled silicon cutting sludge waste with carbon addition

A basic study on the feasibility of producing ferrochrome (silicon) alloys using Si sludge waste collected from the silicon ingot cutting process was carried out, and the effects of the addition of carbon components, reaction time, and reaction temperature on the silicothermic reduction of chromium ore by Si sludge were studied. The cordierite (Mg2Al4Si5O18) phase was generated in the slag, and the Fe–Cr(–Si)–C alloy was formed by the silicothermic reduction. Moreover, the addition of carbon powder lowered the reduction initiating temperature, and the reduction ratio based on the oxygen content was evaluated at around 68–88% at 1573 K, which increased with an increase in carbon. However, it was difficult to find a significant difference in the reduction behavior in response to increasing the holding time. The reduced ferrochrome (Fe–Cr) metal alloy droplets coalesced more intensively with an increase in reduction temperature, and for manufacturing the Fe–Cr alloy, it is estimated that a temperature of 1773 K or higher is required for good separation of the slag and the metal. Furthermore, the metallization ratio was defined, and higher values are evaluated for Fe than for Cr.

Effect of Fe2O3 addition on sintering behavior of cordierite ceramic obtained by solid-state sintering method

Cordierite ceramics were prepared by solid-state sintering method and kaolin; silicon dioxide and magnesium oxide were used as the raw materials with Fe2O3 as the sintering addition. The effects of Fe2O3 additive amount on sintering behaviors and main properties were studied in detail. As the results, Fe2O3 promotes the sintering process and the cordierite phase also increases. As the sintering temperature and Fe2O3 additive amount increase, the mechanism of sintering shrinkage process changes. And after 1200 °C, the porosity decreases with the increasing Fe2O3 additive amount while the shrinkage percent and bulk density increase. However, excess Fe2O3 will gather in the pore walls and restrain the transformation from spinel phase to cordierite phase.

Mechanistic Insight into Etching Chemistry and HF-Assisted Etching of MgO-Al₂O₃-SiO₂ Glass-Ceramic.

The present study focuses on the etching conditions and mechanism of MgO-Al2O3-SiO2 glass-ceramic (MAS) in hydrofluoric acid (HF). The results show that the amorphous phase has 218 times higher etching rate than pure cordierite crystal at room temperature. In addition, the activation energies of cordierite and amorphous phases in the HF solution are 52.5 and 30.6 kJ/mol, respectively. The time (tad) taken for complete dissolution of the amorphous phase depends on the HF concentration (CHF). Based on the etching experiments, a new model is established and refined to assess the tad evolution. In addition, a highly crystalline cordierite phase, with the high specific surface area (59.4 m2·g−1) and mesoporous structure, has been obtained by HF etching. This paper presents novel insights into the etching chemistry and opens up avenues for further research in the area of cordierite-based catalytic ceramics.

Phase transformation and microstructural evolution of black tourmaline mineral powders during heating and cooling processes

The microstructural evolution of black tourmaline was studied at various temperatures from ambient one to the melting point through novel combined characterizations of metallographic microscopy and X-ray diffractometry established for high temperature measurements. The grain size was found to decrease gradually with the increase in the temperature, and it decreased rapidly at 950 °C. Tourmaline began to melt at 1050 °C and melted completely at 1200 °C. As the system was cooled down to 950 °C, the tourmaline phase precipitated in the molten body, and its grain size increased gradually. However, as the temperature went below 950 °C till to room temperature, more tourmaline phases formed whereas the grain size decreased, which could be attributed to the competitive growth between the tourmaline and cordierite phases. Moreover, the previously remaining melt was rapidly solidified due to the retention of solid state, and a portion of the tourmaline nuclei formed by the heterogeneous nuclei grew up when the temperature decreased from 1200 to 1050 °C. The average grain size of the tourmaline phase increased to the maximum when the temperature decreased to 950 °C, and it continued to decrease with a further decrease in the temperature to 25 °C, indicating that the tourmaline grain refinement was related to the pinning effect of the second relative grain boundary.

The Optimal Ratio of Mixed Talc Silica and Narathiwat Clay for Cordierite-Mullite Refractories

In this paper, effects of incorporation of Narathiwat clay (NT), talc and silica on the mechanical properties of cordierite-mullite refractories were investigated. The starting raw materials were mixed in different ratios and fired at 1300 °C for 2 hours. XRD patterns of fired refectories indicated cordierite and mullite phases. The fired samples were studied the firing shrinkage, water absorption, bulk density, apparent porosity and bending strength of the cordierite-mullite refractories. The optimum condition was achieved for the composition of 20% Talc that had shrinkage: 11.78%, water absorption: 4.16%, bulk density: 2.28 g/cm3, apparent porosity: 9.2% and bending strength: 330.82 kg/cm2. The results thus showed that Narathiwat clay, talc and silica was a potential materials for use kiln furniture cordierite-mullite refractories.

Phase formation and crystallization kinetics in cordierite ceramics prepared from kaolinite and magnesia

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 2h. 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 10h 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 573kJ/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.

Cordierite obtained from compositions containing kaolin waste, talc and magnesium oxide

The purpose of this study was to obtain cordierite from compositions containing kaolin waste (with different particle-size distributions), talc and magnesium oxide, for use in the production of refractory and insulating materials. The samples were characterized by means of the following techniques: chemical analysis by X-ray fluorescence, X-ray diffraction, particle size analysis and thermogravimetric and differential thermal analysis. The microstructure of the samples was analyzed using scanning electron microscopy. Rectangular test specimens (50mm × 15mm × 5mm) were prepared by uniaxial pressing (13.0MPa), dried at 110°C/24h and sintered at temperatures of 950, 1050, 1150, 1250 and 1350°C. The mineralogical analysis revealed the beginning of the formation of characteristic peaks of cordierite phase at 1250°C, and more intense peaks were identified at 1350°C. The morphological analysis revealed rose-like and hexagonal tube-like crystals.

Synthesis of cordierite using industrial waste fly ash

Fly ash is a product arising from coal combustion in thermal power plants. It represents a major source of environmental pollution. It is well known by its chemical composition rich of SiO2 and Al2O3. With the aim of preserving the environment against this contamination, fly ash was used along with the starting materials for producing glass cordierite (2MgO, 2Al2O3, 5SiO2). Four formulations were developed by mixing the silica gel, magnesium chloride (MgCl2.6H2O) and fly ash in the percentages enclosing the stoichiometry of cordierite (2MgO, 2Al2O3, 5SiO2). Different experimental techniques (DTA/TGA, X-ray diffraction, FTIR and SEM) were used to characterise the prepared formulations. The results shown that for all formulations, a cordierite phase was obtained at 1200 °C along with several secondary phases such as mullite, cristobalite, silicon oxide, enstatite and spinel. At 1300 °C, pure indialite (α-cordierite) was obtained along with a small amount of spinel. The four formulations sintered at 1200 °C exhibit a homogenous morphology and high porosity. The acicular-shaped indialite grains were observed in both formulations with excess of alumina and excess of magnesia.

PLCL electrospun fibers improved with tourmaline particles to prevent thrombosis

The microstructural evolution of black tourmaline was studied at various temperatures from ambient one to the melting point through novel combined characterizations of metallographic microscopy and X-ray diffractometry established for high temperature measurements. The grain size was found to decrease gradually with the increase in the temperature, and it decreased rapidly at 950 °C. Tourmaline began to melt at 1050 °C and melted completely at 1200 °C. As the system was cooled down to 950 °C, the tourmaline phase precipitated in the molten body, and its grain size increased gradually. However, as the temperature went below 950 °C till to room temperature, more tourmaline phases formed whereas the grain size decreased, which could be attributed to the competitive growth between the tourmaline and cordierite phases. Moreover, the previously remaining melt was rapidly solidified due to the retention of solid state, and a portion of the tourmaline nuclei formed by the heterogeneous nuclei grew up when the temperature decreased from 1200 to 1050 °C. The average grain size of the tourmaline phase increased to the maximum when the temperature decreased to 950 °C, and it continued to decrease with a further decrease in the temperature to 25 °C, indicating that the tourmaline grain refinement was related to the pinning effect of the second relative grain boundary.