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Several phosphate-bonded castables were prepared using corundum as a raw material and 48 wt.% phosphoric acid as a binder. The phase composition, microstructural evolution, and properties of the castables samples were analyzed, and a relationship between the microstructures and properties of the castables was established. The results revealed that the cold modulus of rupture of the specimens increased by 19 % to 33.02 MPa after firing at 1 100 °C when the alumina micropowder content increased from 10 % to 15 %. X-ray diffraction analysis revealed that corundum and AlPO4 were present in the castables fired at both 1 100 °C and 1 500 °C. The intensities of the AlPO4 diffraction peaks increased as the alumina micropowder content and sintering temperature increased. Scanning electron microscopy revealed that AlPO4 was tightly arranged and packed with particles.

A graphite/SiC composite was synthesized at different calcination temperatures using microsilica and carboxymethylated cellulose. The oxidation resistance and wettability (with water) of graphite/SiC were investigated. The results showed that carboxymethylated cellulose could react with microsilica to form a coating of SiC on the surface of graphite at elevated temperatures. Consequently, SiO₂ phase was converted into SiC phase above 1 600 °C. The microstructure of the SiC coating on graphite became denser with the increase in temperature. Thermogravimetric curves revealed that the weight loss of graphite was approximately 97.3 wt.% whereas the value decreased to 29.78 wt.% when SiC was formed. Differential scanning calorimetry analysis showed that the SiC coating decreased the enthalpy of the carbon oxidation reaction from 12.02 kJ g⁻¹ to 1.14 kJ g⁻¹, confirming excellent oxidation resistance. Furthermore, the water contact angle of graphite was approximately 78.5° whereas that of the graphite/SiC composite was reduced to 43°. The study of the formation of graphite/SiC composite showed that SiO₂ could be reduced using carboxymethylated cellulose to SiO (g), which was deposited on the graphite to form SiC coating.

In this paper, using industrial alumina, calcined magnesite, ground calcium carbonate as raw materials, spinel-containing calcium aluminate cements (CMA) were prepared at 1500 °C with different calcine holding times (3 h and 6 h). The mineral composition and microstructural characteristics of prepared cement samples were studied using X-ray diffraction and scanning electron microscopy, and their hydration and rheological behavior were also investigated. The results indicated that increasing holding time can promote growth of CaAl2O4 grains and reduce setting time. The hydration mechanism of CMA follows the nucleation and crystal growth–diffusion (NG–D) process, and the hydration rate of CMA–3 h in the acceleratory period is higher than that of CMA–6 h, but there is no significant distinction in deceleration and stabilization periods. The slowdown of hydration rate directly affects the rheological behavior of CMA slurry, leading to decrease in yield stress, and thixotropic character. Also, the storage modulus (G') growth rate of CMA–3 h slurry is significantly higher than for CMA–6 h slurry, indicating the CMA synthesized at 1500 °C for 6 h possesses lower hydration activity.

The influence of the addition of Ni(NO3)2 · 6H2O on the microstructure and mechanical properties of low-carbon MgO–C refractory composites was investigated. The results indicated that MgO whiskers and carbon nanotubes could be generated in low-carbon MgO–C refractory composites with Ni(NO3)2 · 6H2O in a reducing atmosphere at 1 200 °C. The magnitudes of the cold crushing strength, the cold modulus of rupture, the fracture displacement, and the residual cold crushing strength are increased by 47 %, 66 %, 8 % and 26 %, respectively. The MgO–C refractory composites with the addition of 0.6 wt.% Ni(NO3)2 · 6H2O result in better overall properties. The MgO whiskers were generated via a dissolution–diffusion–precipitation mechanism, and their growth is in accordance with the vapour–liquid–solid model.

A series of high alumina refractory castables were prepared via casting with tabular alumina aggregates (0.088 – 5 mm), fine powders, and calcium aluminate cement as starting materials. The effect of the median diameter of alumina (D50 = 7.26 μm, 5.33 μm, 2.37 μm) on the thermo-mechanical properties of the refractory castables was investigated. The results indicate that the decrease in the alumina particle size from 7.26 μm to 2.37 μm has little influence on both the apparent porosity and bulk density of castables. However, the median pore size of castables fired after 1 600 °C decreased drastically from 4.7 μm to 2.4 μm correspondingly, which led to significant growth in the strength and thermal shock resistance of castables. The cold modulus of rupture and crushing strength were increased by 201 % and 120 %, respectively. At the same time, the hot modulus of rupture and elastic modulus were also increased by 143 % and 127 %, respectively. The residual elastic modulus was enhanced twice after three thermal cycles.

In this study, La–Zn-substituted SrFe12O19 ferrites were synthesized using the traditional ceramic process. The by-products of iron oxide scales from a steel plant were used as the main raw materials. The influence of the La–Zn substituent and the calcination temperature on the microstructure and magnetic properties of Sr1 − x La x Fe12 − x Zn x O19 ferrites was investigated. The results showed that with the increase in the x value, the crystalline lattice constant of the a- and c-axes and the cell volume decreased. There was no α-Fe2O3 phase in the ferrites when the value of x was 0.3. The corresponding saturation magnetization (M s) and remnant magnetization (M r) values were, respectively, about 65 emu g− 1 and 39.5 emu g− 1. Both values of M s and M r rise to the maximum value. When the calcination temperature was reduced from 1200°C to 1150°C, the average particle size decreased from 0.9 μm to 0.7 μm and M s remained at 65 emu g− 1. However, the coercivity increased from 2690 Oe to 3100 Oe.

Upon application of nano-sized metallic Ni particles as catalyst, the in-situ synthesis mechanism of spinel whiskers in MgO–C refractories was studied. Their phase composition and morphology were determined by means of X-ray diffraction and scanning electron microscopy supported by energy dispersive spectroscopy. The results show that when the catalyst of nano-sized Ni was added in MgO–C refractories, the granular MgAl2O4 (MA) spinels transformed into the shape of whiskers at 1 200 °C. The presence of Ni catalyst can accelerate the generation of Mg vapor, which can react with Al vapor to form MA spinel whiskers. Through dissolution and precipitation, MA spinel crystals nucleate directly and grow into whiskers from the catalytic droplets of nano-sized metallic Ni particles. The growth of spinel whiskers follows a typical vapor–liquid–solid (V–L–S) growth mechanism.