Xiangcheng Li

The relationship between the pore size distribution and the thermo-mechanical properties of high alumina refractory castables

Abstract 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-situ formation of MgO whiskers and CNTs and their influence on the mechanical properties of low-carbon MgO–C refractory composites

Abstract 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.

In-situ catalytic growth of MgAl2O4 spinel whiskers in MgO–C refractories

Abstract 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.

Effects of La–Zn substituent and calcination temperature on the microstructure and magnetic properties of Sr-ferrites

Abstract 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−xLaxFe12−xZnxO19 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 (Ms) and remnant magnetization (Mr) values were, respectively, about 65 emu g−1 and 39.5 emu g−1. Both values of Ms and Mr 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 Ms remained at 65 emu g−1. However, the coercivity increased from 2690 Oe to 3100 Oe.

Effect of Nano Metallic Fe on Al 5 O 6 N Synthesis in Al 2 O 3 -C Refractories

Al2O3-C refractory samples were prepared using corundum, flake graphite, Al and Si powders and phenolic resin as raw materials. The in-situ synthesis mechanism of Al5O6N in Al2O3-C refractories was studied and the effect of adding nano metallic Fe on the formation and microstructure of Al5O6N phase was also investigated. Thermodynamic calculations show that Al5O6N can potentially be synthesized in a reducing atmosphere at 1600°C over a narrow range of N2 and CO pressures. Experimental results proved that Al5O6N phase was synthesized after 1600°C heat treatment when nano Fe was added to Al2O3-C refractories. As the content of nano Fe increases, Al5O6N particles show disappearance of oriented growth, with octahedron shapes turning into spherical agglomerations.

Influence of pore structure parameters on thermal properties of corundum based castables

A series of corundum based castables bonded by ρ–Al2O3 were prepared and fired at different temperature. Influences of apparent porosity and pore size distribution on thermal properties of the samples at different temperature were studied. The relationship between different pore size intervals and thermal conductivity of the samples was also discussed based on grey relational theory. The results show that thermal properties including thermal conductivity, thermal diffusivity and specific heat decline as apparent porosity of the samples increases. When apparent porosity of the samples keeps stable with little fluctuation, thermal conductivity increases as median pore size of the samples increases. It is found that thermal conductivity of the samples at a certain temperature presents the largest grey relational degree with the pore size interval that takes up the dominant volume ratio.