Showing papers in "Transactions of The Indian Ceramic Society in 2015"

Preparation and Characterization of Glass Ceramic Foams Produced from Copper Slag

Abstract: Using wastes as starting raw material is a common method to reduce the production costs. In the present work, preparation of glass ceramic foams using iron-rich copper slag, supplied from Sarcheshmeh Copper Complex in the Kerman Province of Iran, has been investigated. Two glass compositions were selected for preparation of glasses from slag with different amounts of Fe2O3 based on conventional soda lime glass containing Fe2O3 as additive. Glasses with 47 wt% slag (24 wt% Fe2O3) and 32 wt% slag (16 wt% Fe2O3) were prepared. Powder glasses were mixed with 3 wt% SiC and heated with the heating rate of 10oC/min up to the reaction temperature (800o, 850o, 900o, 950o and 1000oC) and soaked for 25 min. Then, the samples were subjected to DTA, XRD and SEM. The results showed that achieving glass ceramic foam from glass containing 47 wt% slag was impossible due to intense crystallization of pyroxene phases while glass ceramic foam with relative density of 0.18 was obtained using glass containing 32 wt% slag at fi...

Luminescence Properties of Eu2+/Eu3+ Activated Barium Aluminate Phosphors with Gd3+ Concentration Variation

Abstract: BaAl2O4:Eu2+/Eu3+ (1 mol %) co-doped with varying concentrations of Gd3+ (1, 2, 5 and 10 mol%) were prepared by combustion synthesis method at 600°C. All the compositions were investigated for their structural and photoluminescence properties. Samples prepared in open atmosphere showed the presence of both Eu3+ and Eu2+ states which indicates the reduction of Eu3+ to Eu2+ during the preparation of these compounds. The prepared materials at 600°C showed high intense broad peaks around 498 nm corresponding to Eu2+ and small peaks in the red region which are attributed to the presence of Eu3+. In the 1000°C annealed compounds, the intensity of the peak at 498 nm got increased. The intensity of this broad band for BaAl2O4:Eu2+/Eu3+(1 mol%):Gd3+(1 mol%) was three times than that of BaAl2O4:Eu2+/Eu3+(1 mol%). Thus second rare earth ion (Gd3+) acted as a good sensitizer and enhanced the photoluminescence intensity. The XRD spectra revealed the presence of hexagonal phase of BaAl2O4 as main phase and a small amou...

Structure Formation of a Double Sintered Nanocrystalline Silica Xerogel Converted From Sago Waste Ash

Abstract: In the present study, double sintered nanocrystalline silica xerogel (NSX) bulk material has been produced from amorphous silica xerogel (ASX) powders extracted from sago waste ash. The ASX powders have been sintered at 1200°C, milled, pressed and then re-sintered at temperatures ranging from 1200° to 1600°C. The crystallization process of the NSX has been examined by thermal analysis (DSC/TGA) and X-ray diffraction (XRD), while the functional groups and the structure have been identified by infrared and Raman spectroscopy, respectively. From the DSC analysis it has been found that the tetragonal phase of α-cristobalite transforms to the stable phase of SiO2, namely cubic β-cristobalite in the samples re-sintered at 1600°C. This observation has been corroborated by an analysis of the XRD patterns, infrared and Raman spectra. The obtained data suggest that such novel material could be considered as an appropriate alternative for deposition of ceramic coatings on various machine and tool parts, e.g. compone...

Recycling of Boron Waste to Develop Ceramic Wall Tile in Turkey

Abstract: In the present study, dissolution unit's waste of Kirka borax mine, Turkey (BW) was employed in different amounts as a partial substitution for the marble in order to develop an experimental wall tile body composition. A series of ceramic tile formulations were prepared with 2, 4, 6 and 9 wt% of BW incorporation into the batch compositions and shaping by dry pressing under laboratory conditions. The obtained samples were single fast-fired at a peak temperature of 1150°C for a total firing time of 38 min (from cold-to-cold) under industrial conditions. Some technological properties of the resultant products, namely linear firing shrinkage, water absorption and bending strength were determined as a function of increasing BW content in place of marble at these temperatures. The phase contents of the starting raw materials and fired compositions of BW were determined by XRD. The relevant polished surfaces of selected fired samples were examined using SEM and EDX. According to the results, increased presence o...

High Alumina Castables: Effect of Alumina Sols and Distribution Coefficients

Abstract: Two different alumina sols were prepared using different precursor sources and the sols were solely used as binder in no cement high alumina castable. The sols were characterized for their solid content, pH, particle size, zeta potential, thermal behaviour through DSC-TG, phase formation on calcination, etc. The sols were used as sole binder in high alumina castables with different particle size distribution, as per Dinger and Funk model, to attain different flow consistency. The castables were processed conventionally and heat treated at three different temperatures. Different physical and mechanical properties were evaluated and compared. Sol prepared from nitrate precursor resulted in better properties when used as binder in castables as compared to that prepared from commercially available boehmite powder. No deformation in the castables was observed on firing at 1650oC, much above the application temperature of any cement/ sol bonded castables. Absence of any component other than alumina nullifies an...

Precipitated CaCO3 with Unique Crystalline Morphology Prepared from Limestone

Abstract: A carbonation method has been applied to induce the precipitation reaction of calcium carbonate powders with unique morphology. The reaction was strongly influenced by temperature, pH, CO2 gas flow rate and flow duration. Characterization of the as-prepared CaCO3 by XRD and SEM demonstrated that the vaterite phase was mostly formed at low temperature and CO2 gas flow rate. Phase transformation from vaterite to calcite phases at room temperature was initiated by the formation of calcite structure in ¼ spherical shapes and was followed by transformation to the rhombic structure. The highest growth of calcite structure, resulting in purity up to 98.6%, occurred at the CO2 gas flow rate of 5 SCFH in 36 s. Aragonite particles were produced at CO2 gas flow rate of 0.5 and 5 SCFH to yield 99.2% and 72.3% phase purities, respectively, with needle-like morphology at a higher temperature of 85oC. Furthermore, the reaction with lower CO2 gas flow rate (2 SCFH) led to the formation of aragonite with a flower-like mor...

Synthesis, Characterization and Effect of Precipitating Agent on the Antibacterial Properties of Cobalt Ferrite Nanoparticles

Abstract: Cobalt ferrite nanoparticles have been synthesized by co-precipitation method using three different precipitating agents, viz. ammonium hydroxide, sodium hydroxide and monoethanolamine. The average particle size of the nanoparticles varied in the range 17-70 nm by varying the precipitating agents. The phase formation of the synthesized nanoparticles was performed via X-ray diffraction. Fourier infrared spectroscopy also confirmed the product formation. The microstructure and elemental composition were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy respectively. The precipitating agents were varied to vary the size and to study the effect of size on the morphology and antibacterial properties. The effect of precipitating agents and particle size on the antibacterial activity was carried out against the microorganism Staphylococcus aureus (gram positive bacteria) quantitatively by spread plate method.

Fabrication of Mullite Bonded Porous SiC Ceramics via Sol-Gel Coated Precursor

Abstract: In the present work oxide bonded porous SiC ceramics were fabricated using surface modified sol-gel mullite coated SiC particles. The coated powder was characterized by measuring zeta potential at different pH, XRD analysis, thermal analysis and FTIR spectroscopy. To observe the role of mullite source on the properties of final ceramics two other sources of mullite (commercial mullite and synthesized mullite through sol-gel route) were also used. Porous SiC ceramics were prepared by sintering powder compact of mullite coated SiC/SiC+mullite particles in air at 1300°C for 3 h keeping the mullite content same. The morphologies, phase composition, porosity, pore size distribution and mechanical strength of porous ceramics were examined as a function of mullite source. It was observed that the coating of SiC particles by sol-gel mullite precursor effectively reduced the % SiC oxidation degree from 51 to 33%. The ceramics obtained from sol-gel coated precursor had a flexural strength of ∼23 MPa at porosity of ...

Designing Novel Sulphate-based Ceramic Materials as Insertion Host Compounds for Secondary Batteries

Abstract: Rechargeable batteries have propelled the wireless revolution and automobiles market over the past 25 years. Developing better batteries with improved energy density demands unveiling of new cathode ceramic materials with suitable diffusion channels and open framework structure. In this pursuit of achieving higher energy density, one approach is to realize enhanced redox voltage of insertion of ceramic compounds. This can be accomplished by incorporating highly electronegative anions in the cathode ceramics. Building on this idea, recently various sulphate- based compounds have been reported as high voltage cathode materials. The current article highlights the use of sulphate (SO4) based cathodes to realize the highest ever Fe3+/Fe2+ redox potentials in Li-ion batteries (LiFeSO4F fluorosulphate: 3.9V vs Li/Li+) and Na-ion batteries (Na2Fe2(SO4)(3) polysulphate: 3.8V vs Na/Na+). These sulphate-based cathode ceramic compounds pave way for newer avenues to design better batteries for future applications.

Solid Particle Erosion Behaviour of Plasma-Sprayed Conventional and Nanostructured Al2O3-13 wt% TiO2 Ceramic Coatings

Abstract: In this study, conventional and nanostructured Al2O3-13 wt% TiO2 coatings were fabricated by plasma spraying. The microstructural characteristics, bonding strength and solid particle erosion behaviours of the two types of coatings were compared. Results indicated that the traditional coating has a typical laminated structure. The nanostructured coating exhibited a bimodal microstructure consisting of fully melted regions and partially melted regions. The bonding strength and erosion wear resistance of the nanostructured coating were considerably better than those of the conventional one due to compact microstructure and nanoparticles of partially melted regions. Erosion failure analysis showed that the conventional coating was dominated by brittle erosion, whereas the nanostructured coating was dominated by brittle erosion as well as some ductile erosion.

SnO2 Based Ceramics for Hydrogen Sensors: Current Status and Perspectives

Abstract: Significant developments have been made in the area of metal oxide semiconducting ceramic gas sensors since its invention. Currently, these sensors are extensively used for domestic, industrial and environmental applications. These are the simple type of gas sensors possessing superiority due to compact size, simple fabrication technique, durability, low cost, minimal power consumption and simple electronic circuits. Tin dioxide (SnO2) has been widely investigated as the most challenging semiconducting material for its strong gas sensing properties for more than five decades. In this review, we have focussed mainly on the response of SnO2 and SnO2 based modified materials towards hydrogen gas in the parts per million (ppm) to percentage (%) level. It is a highly challenging task to fabricate SnO2 based sensor devices exhibiting high sensitivity, stability and above all selectivity towards hydrogen. Though we have been partially successful in fabricating SnO2 based sensor units exhibiting high sensitivity ...

Fabrication and Characterization of Diopside-based Glass-Ceramics from Granite Wastes

Abstract: Diopside-based glass-ceramics were obtained by mixing 58.2∼61.5 wt% granite wastes with other components. Based on the CaO-MgO-Al2O3-SiO2 (CMAS) system, the effects of CaO/MgO ratio and heat treatment on crystallization, microstructure and properties of the glass-ceramics were investigated. Results showed that the crystallization peak temperature decreased with the replacement of CaO by MgO. Bulk crystallization of CMAS glass-ceramics by one stage heat treatment was achieved by optimizing the CaO/MgO ratio. The most suitable mass ratio of CaO to MgO in this work was 1.25, because of higher crystallinity of diopside and its desirable fine grained microstructure. The mechanical properties of glass-ceramics obtained by one stage heat treatment were a little worse than that of two stage heat treatment. Considering the simpler manufacturing process and lower energy consumption, one stage heat treatment was a more promising and economical method for rolling process.

The Investigation of Neutron Interactions with HfB2 – A Simulation Study

Abstract: HfB2 with excellent thermal and mechanical properties have attracted attention to discover its radiation properties for use fusion facilities. Geant4 has been used to simulate HfB2 neutron interaction study. For this purpose a virtual experiment has been performed to examine suitability of HfB2 as a neutron bombardment target. The low energy thermal neutrons produce a large number of alpha particles. The α particles ratio varies tremendously up to 1.8 MeV of α energy. For 10 MeV neutrons the α particles spectrum follows a flat trend over 5 MeV α particles energies. The low energy thermal neutrons also produce high energy prompt gamma rays up to 20 MeV. The backscattered neutron and forward scattered neutron spectrum has been studied.

Influence of β-Sialon/Ti(C, N) Powders on the Corrosion and Oxidation Resistance of Zero-Cement Al2O3-SiC-C Refractory Castables

Abstract: Al2O3-SiC-C refractory castables added with β-sialon/Ti(C, N) powders were prepared with silica sol and phenolic resin as binding agents at room temperature. The effects of β-sialon/Ti(C, N) powders, silica sol and phenolic resin on slag penetration and corrosion resistance as well as oxidation resistance of the refractory castables were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscope. Corrosion resistance and oxidation resistance mechanisms of the Al2O3-SiC-C refractory castables were also discussed. The results showed that the castables obtained with silica sol as the binding agent at a temperature of 1450oC presented better oxidation resistance. The oxidation resistance and slag erosion resistance of the refractory castables could be improved by adding Ti(C, N)/β-sialon powders. Static crucible method and fractal dimension calculation result showed that the prepared castables possessed excellent slag erosion resistance.

Electrical Transport of Mixed Phased Glassy Nanocomposites

Abstract: Ionic conductivity and conductivity relaxation of ZnO doped silver molybdate glass-nanocomposite systems have been studied. X-ray diffraction studies have been carried out to obtain the particle size and the distribution of ZnO, Ag2MoO4, Ag2Mo2O7 and Ag6Mo10O33 nanoparticles dispersed in glass-nanocomposites. A symmetric stretching of the Mo–O octahedral units has been found in the FTIR study. It has also been noted that as ZnO content increases, the bond strength of Mo–O becomes weaker. Ionic relaxation data of glass-nanocomposites have been analyzed in the framework of the electric modulus formalism. It has been observed that the electrical conductivity depends upon the ZnO content added to the system.

Bioactive Glass and Biopolymer Based Composite Scaffold for Bone Regeneration

Abstract: The composite scaffold of chitosan-gelatin reinforced with bioactive glass particles was prepared using freeze drying method after blending chitosan and gelatin solution with bioactive glass where glutaraldehyde acted as a cross-linking agent for biopolymers. Bioactive glass particles were synthesized using sol-gel route and characterized using XRD and FTIR. The composite scaffold was prepared at a fixed solid loading of 30 wt% with a composition of gelatin, chitosan and bioactive glass at 20:50:30 in weight. Characteristic IR band for (–C=N–) bond in the prepared composite scaffold confirmed inter gelatin and chitosan-gelatin cross-linking in the scaffold with the help of glutaraldehyde. Total porosity in the scaffold varied between 75% and 80% as determined by Archimedes principle. Microstructural investigation using scanning electron microscopy revealed well interconnected porosity in the scaffold with pore size in the range of 100–150 μm. Bioactive glass particles were found to be well dispersed in th...

A Novel Synthesis Process of ZnO Nano Powders in Granule Form

Abstract: ZnO nano powders, which have different morphologies and agglomerate structures, were continuously produced from Zn(NO3)2.6H2O, NH3 and NaOH by a novel synthesis process: modification and combination of precipitation method with spray dryer. The synthesized powders were characterized by different methods such as SEM, TEM, DTA-TG, XRD, BET and Nanosizer. They represent a spherical granule form with a considerably high specific surface area of 39-41 m2.g–1 and nano particle size 50-550 nm, 5-300 nm and 26-39 nm according to Nanosizer, TEM and BET, respectively.

Microstructure and Corrosion Behaviour of Plasma Sprayed Bilayered Ceramic Coatings

Abstract: This paper deals with the fabrication of ZrO2, Al2O3, ZrO2/Al2O3 and Al2O3/ZrO2 coatings on 304 stainless steel substrate by atmospheric plasma spraying. The microstructure and phase composition of the as-sprayed coatings were examined by scanning electron microscopy and X-ray diffraction. Hardness measurements were carried out using a Vickers hardness testing machine. Corrosion behaviour of the coatings was studied by salt spray testing in a mist of 5 wt% NaCl. Results indicate that the bilayered Al2O3/ZrO2 coating exhibits superior corrosion resistance when compared with that of the other coatings and this is ascribed to the presence of dense microstructure with very few pores in the coating.

Microwave Dielectric Properties of Sol-Gel Processed Bi4Si3O12 Ceramics and Single Crystal

Abstract: Microwave dielectric ceramics Bi4Si3O12 was made from powders prepared via sol-gel method as a potential candidate of low temperature co-fired ceramics in microwave applications. The microwave dielectric properties of sol-gel processed Bi4Si3O12 ceramics were compared with that of single crystal. The sintering temperature of the ceramics ranged from 920° to 1010°C. The best microwave dielectric properties were obtained when the ceramics was sintered at 980°C for 8 h with a permittivity of ∼8.8, a Q×f value of ∼41,898 GHz (at 11.5 GHz) and a temperature coefficient value of –72 ppm/°C. The permittivity, Q×f value, and temperature coefficient value of Bi4Si3O12 single crystal were ∼15.9, 45,326 GHz (at 7.0 GHz) and –92 ppm/°C, respectively.

Influence of Ferrum on Crystallization and Microstructure of Steel Slag Based Glass-Ceramics

Abstract: The influence of iron content and oxidation state on the crystallization and microstructure of steel slag based glass-ceramics was investigated in the CaO-Al2O3-SiO2-MgO-FeOx system. The crystallization mechanism of parent glass and microstructure of final products were studied by thermogravimetry and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM). The results indicate that part of Fe3+ appeared as six-coordinated [FeO6] octahedron and acted as network modifier with more ferrous or metallic irons being further oxidized to ferric irons. The crystalline temperatures of glass samples shifted to higher values as the iron content became lower supported by the result of crystallization activation energy. The crystal morphology of low iron content samples appeared mainly in the form of cluster or column and limited amount of granule, while sample with high iron content was principally composed...

Synthesis and Characterization of Yttria Nanopowders by Precipitation Method

Abstract: In this investigation, yttria nanopowder was synthesized by precipitation method using yttria micro powder and ammonium hydrogen carbonate as precursor materials. The most important parameters, aging time and calcination temperature, have been reviewed in detail. The effects of aging time (3, 6, 12 and 24 h) and calcination temperature (700o, 800o, 900o, 1000o and 1100oC) were studied. Disk samples were fabricated from nanopowder at 1800oC and 50 Mpa via SPS method. Synthesized phases, thermal behaviour and particle size were shown by X-ray diffraction pattern, thermogravimetry and differential thermal analysis, and field emission scanning electron microscopy, respectively. Fourier transform infrared spectroscopy was used for bonding study before and after heat treatment at different temperatures.

Ultraviolet Light Induced White Emission of Eu3+ and Dy3+ Co-Doped Oxyfluoride Glass-Ceramics Containing LaF3 Nanocrystals

Abstract: Dy3+ single doped and Dy3+-Eu3+ co-doped transparent glass-ceramics (GC) containing hexagonal LaF3 nanocrystals were fabricated by melt-quenching method and subsequent heating. XRD, TEM, absorption and emission spectra were used to investigate the structural and luminescent properties of resulting GC. Excited by 390 nm, the Dy3+-Eu3+ co-doped GC exhibited bright white emission with CIE coordinates 0.345, 0.333. Judd-Ofelt intensity parameters, radiative probability, luminescence branching ratio, cross-sections and effective bandwidth were calculated. The Judd-Ofelt parameters (Ω2, Ω4 and Ω6) have indicated that GC has a high asymmetrical and covalent feature. The resulting GC may be used in the white light emitting diode fields.

Structural Evolution and Property of Hot-pressed Palygorskite Clay

Abstract: Structural evolution of palygorskites, calcinated from 300° to 1200°C, was studied and ceramic materials were fabricated by hot pressing three types of palygorskite (PG1, PG2 and PG3) at 1000°C. In the calcination process, palygorskite transformed into cordierite, cristobalite and enstatite at 1200°C. After hot pressing, the bending strength and Young's modulus of PG1 ceramics reached 187 MPa and 87 GPa, respectively showing 125% and 30% increase compared to that of PG2 ceramics. The highest mechanical properties of PG1 ceramics can be attributed to its distinct fracture mode, namely intragranular fracture. Moreover, graphite carbon was detected in PG1 ceramics. Carbon-reinforced palygorskite-based ceramics was obtained by hot pressing synthesized acetamide modified pure palygorskite (PG3). Acetamide was carbonized during hot pressing. The bending strength of the carbon-reinforced PG3-based ceramics was 100 MPa, which showed a 33% increase compared with that of the PG3 ceramics.

Effect of Nano-ZrO2 Addition on Microstructure, Mechanical Property and Thermal Shock Behaviour of Dense Chromic Oxide Refractory Material

Abstract: To obtain a good performance hot-face lining material in gasifier, nano-ZrO2, up to 5 wt%, was added into chromic oxide powder with 3 wt% TiO2 followed by sintering at 1500°C for 2.5 h. The effect of nano-ZrO2 addition on microstructure, mechanical property and thermal shock behaviour was studied. ZrO2 promoted densification at contents higher than 1 wt%. Microcracks and phase transformation toughened the dense chromic oxide refractory material. The main reason for decrease of strength was the existence microcracks in specimens and weakening of intergranular fracture. Dense chromic oxide refractory material with 2∼3 wt% nano-ZrO2 possessed good densification, uniform microstructure, normal mechanical property and proper thermal shock resistance. The rupture strength retention ratio was nearly twice than that of chromic oxide material without ZrO2 after three cycles of quenching test from 950°C to cold water.

Electrodeposition Synthesis of Polyaniline-Modified TiO2 Nanotube Arrays with Enhanced Photoelectrochemical Property

Abstract: Polyaniline-modified TiO2 nanotube arrays (PANI/TNTs) were fabricated by a constant voltage electropolymerization method. The self-organized TiO2 nanotube arrays with an inner diameter of approximately 100 nm and a length of 4 μm were prepared by a two-step anodization at 20 V for 3 h, and then the polyaniline was deposited on the surface of the TiO2 nanotube arrays. The phase composition, morphology and property of PANI/TNTs were characterized by X-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy and UV-vis diffuse reflectance spectroscopy. The prepared PANI/TNTs showed enhanced visible light absorption and corresponding visible light photocatalytic activity. Furthermore, the PANI/TNTs also exhibited higher electrochemical behaviour than that of TiO2 nanotube arrays.

Synthesis of Novel Al2O3-Mullite-cBN Composites from a Mixture of Al2O3 with SiO2 Nanolayer Coated cBN by Rotary CVD and Spark Plasma Sintering

Abstract: In the present study, novel Al2O3-mullite-cBN composites were synthesized from a mixture of Al2O3 and SiO2 coated on cBN (cBN/SiO2) by spark plasma sintering. SiO2 nanolayer was coated on cBN powder (cBN/SiO2) by rotary CVD using tetraethyl orthosilicate as a precursor and O2 as a reactive gas. The thickness of SiO2 nanolayer (TSSiO2) increased from 32 to 52 nm with increasing FO2 from 0 to 0.42×10−6 m3.s−1, and then decreased to 25 nm with increasing FO2 to 0.42×10−6 m3.s−1. The cBN/SiO2 powder was mixed with Al2O3 and consolidated by spark plasma sintering at 1473–1873 K for 0.6 ks. A uniform mullite (Al6Si2O13) phase was formed at 1673 K by the reaction of SiO2 nanolayer with Al2O3. At a sintering temperature of 1573 K and TSSiO2=52 nm, the relative density and the hardness of Al2O3-mullite-cBN was 97% and 24.9 GPa, respectively. The obtained hardness was about 3.9 GPa higher than that of monolithic Al2O3, 12.4 GPa higher than that of SiO2-cBN, and 8.9 GPa higher than that of SiAlON-cBN and mullite-cBN...

Thermal Conductivity of Al2O3/Glass/Cf Composite Substrates Prepared by Low Temperature Sintering

Abstract: Carbon fiber (Cf) with high thermal conductivity was introduced into the alumina based composites. To avoid oriented alignment of carbon fibers and carbothermal reactions during the sintering process, the Al2O3/glass/Cf substrate was hot pressed under a segmental pressure procedure at 1123 K. Experimental results showed that the thermal conductivity of Al2O3/glass/Cf increased with the contents of Cf when the volume of Cf was below 30%. The thermal conductivity of Al2O3/30% glass/30% Cf was as high as 28.98 W.(mK)–1, which was 4.56 times and 2.23 times higher than that of Al2O3/30% glass and AlN/30% glass, respectively. However, the thermal conductivity of Al2O3/glass/Cf decreased with the contents of Cf when the volume of Cf was over 30%. In the Al2O3/30% glass/30% Cf composite, carbon fibers lapped with each other and formed a three dimensional network in the matrix. The three dimensional network of carbon fibers brought excellent heat conducting performance to the Al2O3/30% glass/30% Cf composite.

Effects of In-Plane Geometric Shapes on Thermal Shock Resistance of Ultra-High Temperature Ceramic Components

Abstract: In thermal structural engineering, ceramic components can have various shapes and be constrained. It is traditionally known that the thermal shock resistance (TSR) of ceramic components (with conduction occurring in the thickness direction), such as disk, oval plate and rectangular plate, is independent of the in-plane geometric shapes. The present study shows that this is valid for ceramic components that are free, but when the components are constrained, the in-plane geometric shapes can have significant effects on the TSR of ceramics. Three types of components, with the edges of the lower surfaces clamped are studied. Under the second or third type thermal boundary conditions, the TSR of the disk is the best; that of the oval plate decreases as the ellipticity increases; and that of the rectangular plate is approximately equal to that of the oval plate with ellipticity of 1.2. This is because that the asymmetry of the in-plane geometric shapes, as well as the asymmetry of the mechanical boundary condit...

Dehydration-Rehydration Characteristics of Gibbsitic Bauxite under Equilibrium Condition

Abstract: Dehydration-rehydration study of bauxite rock carries a great practical significance in preparing different alumina products, predicting the structure-property relationship of the high alumina bearing ore for its effective utilization and controlling the drying-firing schedule of bauxite based various alumina ceramics. This paper presents a comprehensive thermal dehydration-rehydration behaviour of the naturally occurring bauxite rock of India in powder form in relation to variation of temperature of thermal treatment and relative humidity of the environment.

Fabrication and Properties of Boron Carbide/Graphite Ceramic Pellets

Abstract: Boron carbide (B4C)/graphite (C) ceramic pellets containing 25 wt% B4C as an ideal structural component in Chinese 10 MW high temperature gas-cooled test reactor (HTR-10) were successfully prepared by a two-stage operation method at low temperature. Initially, the samples were pressurelessly sintered at 1373 K and subsequently infiltrated with phenolic resin, pyrolysed at 1473 K, then coated with carbon by chemical vapour deposition at 1273 K. Morphology and structure of the samples were analysed by SEM and X-ray diffraction. The mechanical properties of the sintered bodies were also investigated. Superior properties were obtained due to the formation of pyrolytic carbon during the two-stage operation process. Density and compression strength of the samples were 1.94 g.cm–3 and 620 N, respectively. In addition, the rate of abrasion and moisture resistance were near zero for the samples.