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ZrP 2 O 7 -based fiber composites were prepared by in situ synthesis and their microstructure, thermal conductivity, mechanical and dielectric properties were determined. The chemical reaction with BPO 4 as the phosphorus source and nano-ZrO 2 as the zirconium source was initiated at 900°C, which promotes liquid-phase sintering and reduces the sintering densification temperature of the ZrP 2 O 7 -based fiber composites by generating small ZrP 2 O 7 grains and low-melting B 2 O 3. The lower sintering densification temperature and the appropriate amount of network formers effectively suppressed the high-temperature crystallization phenomenon of the high-silica-oxygen fibers, strengthened the interfacial bonding between the fibers and the matrix, and improved the interfacial debonding problem of the ZrP 2 O 7 -based fiber composites. It is found that the ZrP 2 O 7 -based fiber composites possess low dielectric constant, low dielectric loss, good thermal conductivity, and acceptable mechanical properties, which can meet the relevant application requirements of centimeter-wave technology. • After heat treatment at 1250°C, BZ4 possessed the best overall properties. • The interfacial bonding between fiber and matrix was improved by in-situ synthesis. • A small amount of B oxide was introduced in situ to improve the high temperature crystallization of the fibers. [ABSTRACT FROM AUTHOR]

Injecting lance is a key equipment for hot metal pretreatment. In this work, the lance castables with high mechanical properties and thermal shock resistance were obtained by adding alumina bubbles, due to its spherical shape and hollow structure. It is found that the addition of alumina bubble improves the flow values of castables. The bulk density values of samples with the addition of 4 wt% alumina bubbles (AB4) were the best of all the experimental castables. Alumina bubble addition is effective in heightening the thermal expansion, thermal conductivity of mullite castables and can resist the sharp decrease in thermal expansion above 1300 °C. The addition of alumina bubble can improve the mechanical strength of mullite castables. After heating at 1400 °C, a strong chemical bond forms between the bubbles and the binding phases. Due to the appropriate bonding at the alumina bubble/matrix interface, AB4 castable exhibits a relatively better thermal shock resistance. [ABSTRACT FROM AUTHOR]

The widespread use of ternary lithium-ion battery cathode Li(Ni x Co y Mn 1−x−y)O 2 (LNCM) materials in energy storage equipment has resulted in an increase in the demand for insulating refractory of roller kiln. However, the severe corrosion during LNCM calcination will result in desquamate and damage of the insulating refractory. In this study, the corrosion resistance of bubble alumina brick (bubble alumina), mullite and CA 6 (calcium hexaaluminate) insulating refractories was thoroughly investigated. This study combined the laboratory scale experiments on the interfacial reaction and after life cycle analysis on industrial insulating refractory to investigate the interactions between the insulating refractories and LNCM precursor mixture powders after the calcination temperature of 950 °C for 10 h and the corrosion behaviour of the LNCM precursor to different insulating fire bricks after the heat treatment temperature of 950 °C for 10 h every time and repeated 10 times according to the actual LNCM preparation system. The phase composition and microstructure of the three insulating refractories before and after corrosion were characterised to obtain a comprehensive understanding of the corrosion mechanism and behaviour. Results showed that the CA 6 has excellent corrosion resistance and has the potential to be used in the lithium battery industry. • CA6 insulating refractories were successfully prepared by industrial production process. • CA6 insulating refractories and commercially available insulating refractories were compared and evaluated. • The feasibility of applying CA6 insulating refractories to kiln lining materials for LNCM production was evaluated. • The prepared CA6 insulation refractory has a good prospect of industrial application. [ABSTRACT FROM AUTHOR]

This paper focused on the effect of hydrochloric acid and nitric acid on phase transformation of gamma to alpha alumina. The microstructure, phase composition of specimens and crystallite sizes of α-Al 2 O 3 are investigated by X-ray diffraction, SEM, Scherrer formula and external standard method. The results showed that the phase transitions of alumina was affected by the kinds and concentrations of inorganic acid. Hydrochloric acid was more advantageous to promote the transformation of γ-alumina to α-alumina than nitric acid above 900 °C. In addition, the α-fraction of specimens obtained by Al 2 O 3 -HCl gels increased from 71.0% to 87.1% after calcination at 1000 °C when acid concentration increased from 0.1*10-4 mol/L to 0.1mol/L. On the contrary, the α-fraction of specimens obtained by Al 2 O 3 -HNO 3 gels decreased from 79.4% to 73.9%. And at 1100 °C up to nearly 100% of α-alumina in the specimens was obtained. Moreover, both hydrochloric acid and nitric acid were beneficial to the growth of the crystallite sizes of prepared α-Al 2 O 3 . Meanwhile the effect of hydrochloric acid on the phase transitions of alumina was further promoted by employing a two-step heat-treatment method. XRD and SEM confirmed that the first-step heat-treatment played an important role in the course of the calcination processes for low-temperature of α-alumina formation. [ABSTRACT FROM AUTHOR]

In this study, three-B-site perovskite Ba(Zr 1–2x Ti x Ce x)O 3 (x=0–0.2) materials with the co-substitution of Ti4+ and Ce4+ at the Zr-site of barium zirconate (BaZrO 3) were successfully prepared. The analyses of XRD & Rietveld method, SEM, and TEM indicated that the substituted ions Ti4+ and Ce4+ entered the BaZrO 3 lattice to form a single-phase solid solution, showing a conventional primitive cubic perovskite structure (Pm-3 m space group), and its lattice parameters gradually increased from 0.4192 nm to 0.4206 nm with x value. The sample with x=0.1 exhibited relatively optimal structural uniformity and densification, as well as comprehensive physical properties. The sample Ba(Zr 0.8 Ti 0.1 Ce 0.1)O 3 showed a minimum mean grain size of 1.50 μm. And due to the combined effect of solid solution formation and grain refinement, it displayed an apparent porosity of 1.42 % with a cold modulus of rupture (CMOR) of 123.8 MPa, and a thermal conductivity at ambient temperature of 2.197 W/mK. Furthermore, this three-B-site perovskite Ba(Zr 1–2x Ti x Ce x)O 3 exhibits excellent high-temperature stability. This study demonstrates the promising application of the dense, high-strength, and low-thermal conductivity Ba(Zr 0.8 Ti 0.1 Ce 0.1)O 3 perovskite material in the field of advanced refractory ceramics. • A three-B-site perovskite Ba(Zr 1–2x Ti x Ce x)O 3 (x=0–0.2) were prepared via high-temperature solid-state method. • The analyses indicated the formation of a solid solution, showing a conventional primitive cubic perovskite structure. • Sample Ba(Zr 0.8 Ti 0.1 Ce 0.1)O 3 displayed an apparent porosity of 1.42 % with a cold modulus of rupture of 123.8 MPa, and a thermal conductivity at ambient temperature of 2.197 W/mK. [ABSTRACT FROM AUTHOR]

In this study, barium zirconate was synthesized by solid-state reaction using barium carbonate and zirconium dioxide. The reaction process and optimum heat treatment condition were determined by the techniques of X-ray diffraction, scanning electron microscopy & energy dispersive spectroscopy, and thermogravimetric & differential scanning calorimetry, etc. The results showed that the solid-state reaction starts at 1000 °C, and the optimum synthesis temperature was determined as 1200 °C. The reaction kinetic parameters were calculated using the Kissinger method, Ozawa's method, and Coats-Redfern method, the reaction activation energies of the first two were 251.42 kJ·mol−1 and 261.35 kJ·mol−1, respectively. The reaction mechanism was determined by the Coats-Redfern method based on different kinetic models, it follows the diffusion-controlled kinetics, and belongs to 1-D diffusion reaction. The reaction activation energy decreased from 342.56 kJ·mol−1 to 272.32 kJ·mol−1 as the heating rate increased from 5 K·min−1 to 20 K·min−1. • The reaction for the solid-state synthesis of BaZrO 3 from BaCO 3 and ZrO 2 starts at 1000 °C and completes at 1200 °C. • The Kissinger and Ozawa's method calculated the reaction activation energies of 251.42 and 261.35 kJ·mol−1 respectively. • The reaction activation energy decreases as the increase of heating rate under Parabolic law-one-way transport. [ABSTRACT FROM AUTHOR]

Abstract Mullite-corundum foamed ceramics were prepared by direct-foaming method using white clay and industrial alumina as raw materials, and micro-pore-foaming agent (MPFA, the main composition was sodium dodecyl benzene sulfonate) as foaming agent. Effect of the MPFA addition on the phase compositions, microstructures and physical properties of the foamed ceramics were investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), etc. The results showed that the specimens fired at 1500 °C mainly consisted of needle-like mullite, corundum, and a small amount of glass phase. The MPFA decreased the viscosities and then increased the volume expansion of foamed slurries. Meanwhile, the adding of the MPFA caused the increases of apparent porosities and average pore sizes, and the decrease of strengths of the fired specimens. The optimized product was a specimen with 1.0 wt% MPFA fired at 1500 °C which had a high porosity of 73.7%, a proper compressive strength of 3.05 MPa, a low thermal conductivity of 0.287 W/(mK) (1000 °C) and a positive reheating linear change. Based on the experimental dates, an emendatory GE model was presented, which could predict accurately the effective thermal conductivity at 1000 °C of the mullite-corundum foamed ceramics with different pore characteristics. Highlights • The mullite-corundum foam ceramics with low conductivity and sufficient strength were prepared. • The optimized product was a specimen with 1.0 wt% MPFA fired at 1500 °C. • A modified GE model, taking the conduction and radiation into account, was presented. [ABSTRACT FROM AUTHOR]

Foamed mullite-SiC ceramics were prepared by using white clay, industrial alumina and silicon powder as raw materials. The effects of the clay content on the phase composition, microstructure and thermal properties of foamed ceramics were investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The fired foamed mullite-SiC ceramics contained mullite, corundum and β-SiC. With an increase of clay content, the apparent porosity decreased, while the compressive strength and thermal conductivity increased. The optimized composition had a clay content of 44 wt% clay, which yield a high porosity of 72.9%, an excellent compressive strength of 5.6 MPa and a low thermal conductivity of only 0.267 W/(m·K). An adjusted GE thermal conductivity model assuming an appropriate emissivity of 0.35 was highly capable to predict the effective thermal conductivities of the foamed mullite-SiC ceramics with different pore characteristics at 800 °C. • The mullite-SiC foamed ceramics with low conductivity were prepared. • Microstructure and properties were optimized by changing clay content. • The optimized product was a specimen with 44 wt% clay content. • A revised model was presented to predict effective thermal conductivities. • Code-Aster was used to analyse heat-insulating performances of foamed ceramics. [ABSTRACT FROM AUTHOR]