Preparation and properties of enstatite ceramic foam from talc

The effective method of preparation, stabilization and high temperature treatment of enstatite ceramic foam is described in this work. The technique is based on foaming of suspension of talc, on the stabilization of foam structure and on final high temperature treatment after drying. The spontaneous delamination of aggregates and the redistribution of talc particles in foam are driven by decreasing surface energy. The changes of phase composition as well as the mechanism and the kinetics of processes which take place during the thermal treatment were described. The treatment within the temperature range from 1150 to 1250 °C provides the ceramic foam via sintering without melted phase, whereas a liquid phase sintering occurs at higher temperatures. The final temperature of sintering is 1300 °C. Increasing amount of melted phase supports the formation of enclosed porosity and formed glass stabilizes the high temperature protoenstatite polymorph in the foam.     

Effect of addition of talc on the sintering characteristics of fly ash based ceramic tiles

The sintering characteristics of fly ash–talc mixtures having 0–100% talc (w/w) in the presence of 10% (w/w) sodium hexa meta phosphate (SHMP) have been studied. In the fly ash rich mixtures, the presence of needle shaped mullite and rhombohedral aluminum phosphate phases is responsible for providing impact strength to sintered tile bodies. On gradual addition of talc, the decrease in the concentration of sillimanite and increase in the concentration of sodium magnesium phosphate crystals is responsible for the observed improvement in the impact strength of tiles. With increase in talc content, initially the % water absorption decreases to reach a minimum for a fly ash–talc mix containing 60% (w/w talc) where after it again starts increasing. The apparent density of the tile samples increases with increasing talc content in the raw mix due to densification as well as higher density of talc as compared to fly ash.     

Mechanical properties of ceramic bodies based on calcite waste

Physico-mechanical properties (flexural strength, Young modulus, bulk density, change of dimensions, porosity) as well as the mineralogical composition were studied on samples with difference content of calcite after firing at 900, 1000, 1100 and 1200 °C. It was found that anorthite and mullite are the main crystalline phases of the fired samples containing the calcite. The anorthite/mullite ratio depends on the firing temperature and the initial amount of calcite waste. The higher the temperature of the firing and the higher the amount of calcite waste, the more anorthite is created in the samples. Presence of calcite decreases sample contraction during sintering. Porosity decreases with the increase of the firing temperature, but the sample with the content of calcite 20 wt% shows approximately constant porosity. Flexural strength and Young modulus of the reference sample and the sample with 10 wt% of calcite waste increase in their value. These mechanical parameters increases very slightly for the sample with 20 wt% of calcite waste.     

Determining anisotropy and the artificial structural properties in plastic ceramic bodies

Glass and Ceramics -     

Effect of alumina addition on properties of glass/ceramic composite

Abstract

A series of glass/ceramic composites were prepared from pyrex borosilicate glass with silica. The effects of 15 vol.-% alumina addition on cristobalite formation in this system have been studied. Cristobalite formation in the composites has been found to decrease with addition of alumina, which may be attributed to a strong coupling reaction between Al³⁺ from alumina and K⁺ from pyrex borosilicate glass. The resulting glass/ceramic composites containing alumina have low thermal expansion coefficient owing to the presence of a lower amount of cristobalite in the glass matrix. The formation of cristobalite limits the efficiency of the ceramic substrate when used in circuit boards.     

Investigation the effect of FeNiCoCrMo HEA addition on properties of B4C ceramic prepared by spark plasma sintering

In this study, monolithic B₄C and B₄C-based ceramics incorporating FeNiCoCrMo dual-phase (FCC and BCC) high entropy alloys (HEAs) were produced by spark plasma sintering (SPS). The effect of additives on the densification behavior, mechanical properties, microstructures, and phase evaluation of the samples were investigated. X-ray analysis confirmed the existence of FCC structured HEA and depletion of BCC structured HEA, after high-temperature reaction between B₄C-HEAs. The addition of HEAs enhanced the densification behavior by liquid phase sintering. Furthermore, hardness and fracture toughness values of the samples increased with increasing HEAs content. Fracture toughness and hardness values for all composites were higher than the monolithic B₄C. A combination of the highest density (∼99.22 %) and the best mechanical properties (32.3 GPa hardness and 4.53 MPa m^1/2 fracture toughness) was achieved with 2.00 vol.% HEA addition.     

Influence of yttrium oxide addition and sintering temperature on properties of alumina-based ceramic cores

Al₂O₃-based ceramic cores with a uniform microstructure were fabricated successfully by a traditional pressing forming method, in which Al₂O₃ powders were used as matrix and yttrium oxide as additive. The influences of yttrium oxide content and sintering temperature on properties of ceramic cores were studied carefully. Results indicated that a higher sintering temperature benefited the preparation of ceramic cores with excellent properties. As the temperature was above 1400°C, the reaction of Al₂O₃ and yttrium oxide occurred, leading to the formation of YAG phases. And, YAG was uniformly adhered on the surface of Al₂O₃ particles, exerting a good role in connecting Al₂O₃ particles. Based on XRD analyses, it was found that the increase in the sintering temperature could promote the formation of more YAG phases. When sintering temperature was adjusted to 1600°C, with the increase in the yttrium oxide content, their relative density developed a trend of decreasing first and then increasing, while the apparent porosity had an opposite change tendency. With the increase in the sintering temperature, the line shrinkage and bending strength of Al₂O₃-based ceramic cores both increased gradually. In our research, their bending strength reached to 53.5 MPa and apparent porosity was 33.9% when the ceramic cores were prepared with 9 wt% yttrium oxide at 1600°C.     

Novel mullite-cordierite ceramic refractory fabricated from halloysite and talc

This research work aims to fabricate industrial refractory bricks using cheap and abundant kaolin DD₃ constituted of Halloysite. The fabrication process consists on mixing the crushed raw materials (Kaolin/Clay, Fireclay, Talc) with the respective proportions and an optimized granulometry, shaped by a uniaxial hydrostatic pressure of 250 bars, followed by drying at 100°C and sintering at 1300°C. The addition of Talc - at first with water, Fireclay and AP/DD₃- as a source of MgO promotes the increase of Cordierite formation in order to obtain high heat resistance shock and reduced thermal expansion. Three assays are studied with AP Clay and DD₃ Kaolin weight ratios (100/0, 50/50 and 0/100) % corresponding to (ER₀, ER₁ and ER₂) respectively. Mineralogical analysis results of the new refractory bricks, indicate the presence of Mullite and Cordierite as major phases besides Corundum and Quartz as minor phases. All products (ER₀, ER₁ and ER₂) are found to be argillaceous refractory with Alumina concentration (40 < Al₂O₃ < 45%, FC 40 group) and a melting point higher than 1600°C. The mechanical resistance of the samples is of the same order of magnitude; reaching 51 MPa.     

Sintering mechanism and properties of corundum-mullite duplex ceramic with MnO2 addition

Corundum-mullite duplex ceramic (CMC) is excellent engineering material that can be strengthened by the addition of various compounds. In this study, the sintering mechanisms of CMC with two nAl₂O₃: mSiO₂ stoichiometric ratios (n = 1, m = 0; n = 3, m = 2) were investigated with different amounts of MnO₂ addition. The phase transition, microstructure, distribution of elements and ionic valence of the ceramics were identified via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), respectively. The results show that Al³⁺ ions in the corundum lattice are replaced by Mn²⁺ ions. The distorted crystal structure could promote the sintering reaction and leads to a lower sintering temperature. Hence, this study provides beneficial guidance for the industrial production of CMC at lower temperatures and, therefore, with lower energy consumption.     

Determining the plasticity of clays and ceramic bodies

Glass and Ceramics -     

The effect of talc-chlorite schist on properties of ceramic tiles

In order to use fine-fraction talc-chlorite to improve the properties of ceramics, they were tested as a grog additive to clay in ceramic tile mixtures. The use of talc-chlorite increases the strength and decreases the shrinkage of tiles, compared to traditional mixtures, and ensures a minimum number of components in the batch.     

The effect of heat and mass addition on the base pressure of bodies of revolution at supersonic speeds

The results of an experimental investigation of the influence of mass addition and afterburning of combustion products of pyrotechnic mixtures in the base region of axisymmetric bodies in supersonic air flow at Mach numbers of 1.2–3.0 are reported. It is shown that the base-pressure increment increases monotonically to a maximum value with an optimum injected-mass flow rate. The value of this increment reduces as the Mach number decreases. A dependence generalizing the experimental data is presented.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 3, pp. 107–112, May–June, 1996.