Cordierite-mullite Ceramics Research Articles

Castable refractory materials from magnesium oxychloride cement-bonded cordierite-mullite

Cordierite-mullite ceramics are well-suited for use as kiln furniture due to their superior mechanical strength and thermal shock resistance. This study explores the development of cordierite-mullite refractory castables bonded with magnesium oxychloride (MOC) cement. These castables were created using calcined kaolin aggregates and a matrix comprised light-burned magnesia, calcined alumina, milled sand, and magnesium chloride hexahydrate. Interaction between light-burned magnesia and magnesium chloride hexahydrate produced a needle-like MOC cement phase, significantly enhancing the green strength of the castables. After firing at 1350 °C for 4 h, the MOC crystals decomposed, forming robust cordierite and mullite phases. The resulting sintered castables demonstrated a modulus of rupture of 14.55 MPa, a bulk density of 1.95 g/cm3, a porosity of 24.84 %, and a thermal expansion coefficient of 2.89x10−6°C−1. These findings indicate the effectiveness of MOC cement bonding for manufacturing high-strength cordierite-mullite refractory castables, making them ideal for kiln furniture applications.

Co‐utilization of secondary aluminum dross and ferronickel slag for preparation of cordierite–mullite insulating ceramic

AbstractBecause of the low utilization rate, a large amount of metallurgical slag was piled up or buried each year, resulting in serious environmental pollution and resource waste. This study focused on the value‐add utilization of secondary aluminum dross (SAD) and ferronickel slag (FNS) by preparing porous cordierite–mullite ceramics (CMC) for thermal insulation. The detailed thermodynamic calculation of the preparing process was carried out by using the phase diagram and equilibrium component function module in FactSage 8.1 software, which provided precise theoretical guidance for the practical synthesis experiment. The phase component, microstructure, and mechanical and thermal insulation properties of the prepared CMC at an FNS addition from 5 to 30 wt% were investigated by an X‐ray diffractometer, scanning electron microscopy assembled with an energy‐dispersive spectrometer, and a laser thermal conductivity testing instrument, respectively. It was shown that the original mineral phase of the raw materials applied can be converted to cordierite, mullite, and spinel after sintering at 1350°C, which results in higher strength and lower thermal conductivity of the prepared ceramics. Moreover, the increase of FNS addition promoted the content of cordierite and the microstructure densification of CMC. With the increase of FNS addition, the apparent porosity of CMC decreased from 41.7% to 34.4%, and the average pore size varied from 46.7 to 29.0 μm. The CMC with the lowest thermal conductivity of 0.86 W/(m K) was achieved at 20 wt% of FNS addition, which also had a good compressive strength of 52.8 MPa. The results proved the feasibility of preparing high‐strength thermal insulation ceramics by recycling hazardous metallurgical slag of SAD and FNS, proposing a novel route for high value‐added utilization of industrial solid waste.

Tailoring dielectric properties of cordierite-mullite ceramics through Ceramic Injection Moulding

Cordierite-mullite ceramics have been processed by Ceramic Injection Moulding (CIM) for the first time. The comparison with cordierite-mullite ceramics obtained by conventional ceramic process (CP) proves the effect of processing on the structure, microstructure, thermal and dielectric properties. CIM processing favours formation of larger content of mullite phase, a more homogeneous microstructure and reduced porosity than by conventional processed ceramics. These factors strongly condition the dielectric behaviour, which is analyzed by complex impedance formalism up to 850 °C and 1 MHz. The conduction mechanism is thermally activated and the activation energy is ~2.5 times larger in CP than in CIM ceramics. Thermal expansion coefficient is tuned by processing method, ranging from 3.9·10−6 °C−1 to 4.6·10−6 °C−1. All these findings show the strong influence of processing in cordierite-mullite ceramic composites. This work shows that tailoring composition and CIM parameters allow cordierite-mullite composites to precisely fulfill the requirements for future electronic applications.

Effects of SiC content on thermal shock behavior and elastic modulus of cordierite–mullite composites

Cordierite (Mg2Al4Si5O18) is a commercially available ceramic with low fracture toughness that hampers its broad industrial applications. Although several studies have reported the mechanical improvement of cordierite using various reinforcements, modulating its mechanical and thermal shock characteristics is not explored precisely. In the present research, we investigated the manufacturing of cordierite–mullite ceramics and the role of SiC on their thermomechanical properties. The in-situ formed mullite particles were obtained by mixing andalusite-talc-alumina and addition of SiC. It was found that thermal shock behavior and elastic moduli are dependent on SiC content and retained porosity. Furthermore, the addition of SiC to cordierite-based ceramics could enhance the thermal shock resistance via proper activation of the crack bridging mechanism in the matrix of the prepared composite.

Preparation of Cordierite-mullite Ceramics for Solar Thermal Storage

We developed cordierite-mullite composite ceramic materials to package and encapsulate PCM, and presented a preparation process from raw materials of kaolin, talc and alumina. The properties and microstructre of cordierite-mullite composite ceramic were studied. Due to the strengthening effects of mullite, the sample C2 (80 wt% of cordierite and 20 wt % of mullite) sintered at 1 420 °C possessed excellent physical properties. Determined by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analysis, cuboid-shaped cordierite crystals and needle-like or long quadrilateral-prism mullite crystals with staggered patterns were found, which endowed the composites preferable mechanical strength. After 30 cycles of thermal shock (room temperature to about 1 100 °C, air-cooled), the sample presented superior thermal shock resistance, which is suitable to be applied as solar thermal storage materials.

Effects of Y2O3 Additive on Mechanical and Thermal Properties of Cordierite-Mullite Ceramics

Cordierite is an alumina-magnesia-silica compound widely used as a thermal shock resistant material due to its high thermal shock resistance, low coefficient of thermal expansion (CTE), low dielectric constant, and good electrical insulation. However, its narrow sintering temperature range and low mechanical strength hinder its application in ceramic heaters. Although mullite shows excellent thermal and chemical stability, heat resistance, and mechanical strength, it has the disadvantages of high sintering temperatures (1600-1700 °C) and poor thermal shock resistance. In this study, a composite phase was prepared by mixing cordierite and mullite to expand the narrow sintering temperature range of cordierite and adjust its CTE to be similar to that of Si. Furthermore, Y₂O₃ was added to reduce the sintering temperature and to increase the mechanical strength. Therefore, the composite showed the highest density of 2.5 g/cm³ at 1380 °C when the ratio of mullite to cordierite was 20 wt%. When 11 wt% Y₂O₃ was added to this composition, the highest density was 2.8 g/cm³ for a sintering temperature of 1320 °C, and the mechanical strength was relatively good as 180 MPa of 3-points bending strength was comparatively good. The CTE was 2.6×10-6.K-1, which was similar to that of Si.

Thermal Shock Resistance of Mullite-Cordierite Ceramics from Kaolin, Talc and Alumina Raw Materials

Abstract Thermal shock resistance of mullite-cordierite ceramics using combinations of kaolin, talc and alumina was studies. Ceramic specimens rectangular in shape and of size 1.0 cm x 1.0 cm x 8.0 cm were hydraulic pressed under pressure of 150 kg/cm2 and then sintered at 1350 °C for 20 minin air atmosphere. After firing, the physical and mechanical properties of the ceramic materials were investigated regarding to their phase compositions. It was found that the shrinkage, water absorption, apparent porosity and flexural strength varied from 7.3 % to 10.6 %, 5.1 % to11.6 %, 10.6 % to24.5 % and 38.5 to 46.5 MPa, respectively. The best ratio of the synthesis cordierite-mullite ceramics was KA2, which composed of 78.33% kaolin, 12.58% talc and 9.09% alumina, and had efficient thermal shock resistance, thermal expansion coefficient of 4.61 x 10-6 oC-1, microstructure of mullite-cordierite, and the highest thermal shock resistance at 300 oC.

Effects of ZrO2 Addition on Mechanical Strength and Thermal Shock Resistance of Cordierite-Mullite Ceramics

Cordierite composed of an alumina-silica-magnesia compound has a low coefficient of thermal expansion(CTE) and excellent thermal shock resistance. It also has a low dielectric constant and high electrical insulation. However, due to low mechanical strength, it is limited for use in a ceramic heater. In this study, ZrO2 is added to an 80 wt% cordierite-20 wt% mullite composition, and the effect of ZrO2 addition on the mechanical strength and thermal shock resistance is investigated. With an increasing addition of ZrO2, cordierite-mullite formed ZrO2, ZrSiO4 and spinel phases. With sintering conducted at 1400 °C with the addition of 5 wt% ZrO2 to 80 wt% cordierite-20 wt% mullite, the most dense microstructure forms along with an excellent mechanical strength with a 3-point flexural strength of 238MPa. When this composition is quenched in water at ΔT = 400 °C, the 3-point flexural strength is maintained. Moreover, when this composition is cooled from 800 °C to air, the 3-point flexural strength is maintained even after 100 cycles. In addition, the CTE is measured as 3.00 × 10−6·K−1 at 1000 °C. Therefore, 80 wt% cordierite-20 wt% mullite with 5 wt% ZrO2 is considered to be appropriate as material for a ceramic heater.

Effect of Al(OH)3 content on the microstructure and strength of porous cordierite-mullite ceramics prepared by an in-situ pore forming technique

Five porous cordierite-mullite ceramics with similar porosity and different neck characteristics were prepared from Al(OH)3, magnesite, silica and clay using an in-situ pore-forming technique. The phase composition, pore and neck characteristics and strength of the porous ceramics were investigated by an X-ray diffractometer (XRD), a scanning electron microscopy (SEM) and a microscopy measured method, etc. The experimental results showed that Al(OH)3 content had a significant effect on the pore size distribution and neck characteristics (neck size distribution, total value of neck size and phase composition) and then affecting the strength. With an increase in Al(OH)3 content, the median pore size decreased, the total length of necks and the uniformity of neck size increased, also the mullite content of necks increased, resulting in the increase of strength of the porous cordierite-mullite ceramics. When the Al(OH)3 content was 64.9 wt%, the porous cordierite-mullite ceramics had the best performance of high apparent porosity of 45.1 % and high compressive strength of 55.9 MPa.

Reuse of spent FCC catalyst, waste serpentine and kiln rollers waste for synthesis of cordierite and cordierite-mullite ceramics

Spent fluid catalytic cracking (FCC) was gathered from several petrochemical plants and calcined in a rotary furnace between 1000 and 1100°C in order to remove sulphur and hydrocarbon based impurities. Calcining process on FCC led to formation of AlVO4 ceramic phase, so converted the hazardous waste to non-hazardous applicable raw material. In this study, two ceramic bodies as cordierite and cordierite-mullite were synthesized with calcined spent FCC, waste serpentine, kiln rollers waste and high grade kaolin as raw materials. The XRD results showed that the cordierite and cordierite-mullite were synthesized successfully so that 96.4% of F1 (cordierite) sample fired at 1400°C was cordierite phase and F2 (cordierite-mullite) sample fired at 1450°C was completely cordierite and mullite phases. The synthesized cordierite and cordierite-mullite samples had lower porosity values and coefficient of thermal expansion (CTE) than similar industrial products. The negative CTE value that obtained from the cordierite sample up to 800°C is favorable for some applications. The considerable results of the synthesized cordierite and cordierite-mullite from this work present cost reduction of the two ceramic bodies production and may help to solve the environmental problems with the use of three waste sources in large scales.

Thermal and Microstructure Stability of Cordierite–Mullite Ceramics Prepared from Natural Raw Materials-Part II

Thermal and Microstructure Stability of Cordierite–Mullite Ceramics Prepared from Natural Raw Materials-Part II

Thermal and Microstructure Stability of Cordierite–Mullite Ceramics Prepared from Natural Raw Materials

In this study, attempts were undertaken to explore the possibilities to prepare cordierite–mullite composites with potentiality to be used as refractory materials from natural raw materials. Solid state reaction sintering different sample powders at different temperatures from 1,250 to 1,400°C has been applied to prepare cordierite–mullite ceramics. XRD has proved the presence of cordierite and mullite in different ratios as major phases. Thermal shock test method based on heating–quenching procedure, supplemented by scanning electron microscopy and mercury intrusion porosimeter, has been used to demonstrate the thermal stability of different samples.

Characterization of cordierite-mullite ceramics prepared from natural raw materials

Abstract Series of six cordierite-mullite ceramics were synthesized via solid state reaction at various temperatures from 1250 °C for pure cordierite to 1500 °C for pure mullite. Then the samples were submitted to the test of thermal shock resistance based on cycling heating-quenching procedure. X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Mercury intrusion porosimeter (MIP) have been used to characterize the samples before and after cycling heating-quenching method. Sample 6 was broken after 35 heating-quenching cycles, while the five other reminded stable. The refractoriness of samples is found to be higher than that of commercial ones. XRD shows that heating-quenching procedure has led to crystallization of cordierite and mullite phases. Apart from sample 6, the pore structure is stable with slight consolidation. The microstructure images confirm the results of XRD and MIP showing crack in sample 6 only, but compact and larger particles resulting from crystal growth in other samples due to the repeated action of heating.

Effect of particle size on the pore characterization and strength of porous cordierite-mullite ceramics prepared by a pore-forming in-situ technique

The porous cordierite-mullite ceramics were prepared by the pore-forming in-situ technique. The characterizations of porous cordierite-mullite ceramics were determined by an X-ray diffractometer (XRD), a scanning electron microscopy (SEM), and a microscopy measured method, etc., and the effect of particle size on phase composition, pore characterization and strength were investigated. It?s found that particle size affects strongly the formations of cordierite and mullite, and then changes the pore characterization and strength. With the decrease of the particle size, the sintering temperature at which the formations of cordierite and mullite take place extremely fast decreases, the pore size distribution becomes from bi-peak mode to mono-peak mode, the porosity and the median pore size decrease but strength increases. The most opposite mode is the specimen sintered at 1400 ?C from the grinded powder with an average particle size of 10.2 ?m, which consists of cordierite, mullite and minor spinel, and has a high apparent porosity (40 %), a high compressive strength (58.4 MPa), a small median pore size (6.3 ?m) and well-developed necks between particles.

Low-Temperature Preparation of Porous Cordierite-Mullite Ceramics Using Rice Husk as Silica Source and Pore-Forming Agent

Si and C of rice rusk were used as silica source and pore-forming agent to prepare cordierite-mullite ceramics at 1380°C for 5 h soaking. The Nd2O3 additive was added to improve the sintering properties. The bending strength, porosity, and thermal expansion coefficient were measured. The composition was characterized by X-ray diffraction (XRD). The microstructures of the sintered samples were observed by scanning electron microscopy (SEM). The cordierite-mullite ceramic doped with 2% Nd2O3 have high prorosity and low thermal expansion coefficient, its bending strength reaches 20.55 MPa. The addition of Nd2O3 decreases the mullite formation temperature to 1200 °C

Effects of sintering temperature on pore characterization and strength of porous cordierite–mullite ceramics by a pore-forming in-situ technique

AbstractPorous cordierite–mullite ceramics with high strength were prepared by a pore-forming in-situ technique. The phase compositions, pore characteristics, and strength were investigated through X-ray diffractometry, scanning electron microscopy, and a microscopy measurement method. It is found that the sintering temperature strongly affects the formation of cordierite and mullite and the sintering, and thus changes the pore characteristics and strength. The formation of cordierite and mullite takes place on a large scale at 1430°C. The pore size distributions are bimodal in specimens sintered at 1370°C, 1400°C, and 1430°C, and mono-modal in a specimen sintered at 1450°C. The strength increases slightly when the sintering temperature increases from 1370°C to 1400°C, and increases significantly when the sintering temperature is increased to 1430°C. The most appropriate mode is a specimen sintered at 1430°C which has high cordierite (42 wt.%) and mullite content (53 wt.%), high apparent porosity (44%), high compressive strength (30.6 MPa) and a relatively homogeneous pore-size distribution.

Effect of SiC on Microstructures and Properties of Cordierite-Mullite Multiphase Ceramics Material

In this paper, cordierite-mullite multiphase ceramics material was prepared using cordierite powder, mullite particles, fused silica, magnesia and alumina as main starting material. Effects of addition of 2%~10% SiC on the thermal expansion, flexural strength and thermal shock resistance were studied, and the fracture surface morphology was observed with Scanning Electron Microscope (SEM). The results showed that the multiphase ceramics material’s thermal expansion coefficient and flexural strength had little change. The thermal shock resistance of cordierite-mullite multiphase ceramics material varied as increasing-decreasing with the increase of SiC content, when the content of SiC was as high as 4%, the highest conservation rate of the flexural strength after 1100°C~water(3 times) was 72.08%, and the thermal shock resistance of cordierite-mullite multiphase ceramics material was superior.

Intensification of sintering of mullite-cordierite ceramics using mineralizers

The effect of various mineralizers on the process of sintering of ceramic materials in the MgO – Al2O3 – SiO2 system is investigated. The possibility of decreasing the firing temperature and expanding the firing interval of cordierite-mullite ceramics by using these mineralizers is demonstrated.

Slip casting of cordierite and cordierite– mullite materials

The obtention of cordierite and cordierite–mullite ceramics by slip casting is studied. Aqueous slips with solids contents up to 65 wt% were used. The effect of the deflocculant content and the mixing time on the rheological behavior was studied, showing always a shear thickening behavior, which can be deletereous for demolding and handling. The rheological behavior became Newtonian by reducing the solid content up to 60 wt% and adding a plasticizer. This led to higher green densities (near 63% th). Different firing cycles were tested to improve the sintered density, reaching values between 96·5 and 97·5% th. In all cases, both the green and the sintered densities were significantly higher than those obtained by axial pressing.