Fabrication and Properties of Closed-pore Al_2O_3-based Refractory Aggregates

A novel Al2O3 based refractory aggregate with closed-pore structure was fabricated utilizing superplastic- ity with submicro-sized Al2O3 and MgO as raw materi- als, and SiC as a high temperature pore-forming agent. The effect of MgO on porosity, phase composition and microstructure of the refractory aggregate has been inves- tigated. For comparison, the common Al2O3-based refractory aggregates and porous ones with open-pore structure were also prepared. The results indicate that the closed porosity of Al2O3-based refractory aggregate in- creases as the content of MgO increases. When the con- tent of MgO is 15 mass%, the closed and apparent poros- ities are 14.5% and 1.1%, respectively. The main phase compositions are Al2O3 and MgAl204. The formation mechanism of closed pores is that the fine-crystalline- grain Al2O3 ceramic possesses superplastic deformation ability after adding MgO at high temperatures. When SiC powder is added to the Al2O3 ceramic, the generated gases by the reaction of SiC at the sintering temperature can provide a pressure to make grain boundaries slide. Then, the gases are enclosed by crystalline grains to form the closed pores. The slag corrosion resistance of the fabrica- ted closed-pore Al2O3-based refractory aggregate is better than the common refractory aggregate and porous ones.

Effect of TiO_(2) addition on microstructures and properties of Mgo-Cao refractory aggregates

MgO-CaO(40 wt.%CaO)refractory aggregates were prepared using the calcined dolomite and light-burned magnesia fine powder as raw materials and TiO_(2) as additive.The effect of TiO_(2) on their phase composition,microstructures and properties was investigated by X-ray diffraction and scanning electron microscopy.The properties such as bulk density,apparent porosity,relative aggregate tube strength and hydration resistance were also investigated.The results showed that the CaTiO_(3) generated by the reaction between CaO and TiO_(2) was distributed around the CaO grain boundaries and intermittently distributed with MgO,which formed an isolation layer around CaO and greatly improved the hydration resistance.Meanwhile,the introduction of TiO_(2) promoted sintering and increased the grain size,further improving the strengths and hydration resistance of the materials.In addition,the most significant enhancement in the hydration resistance and strengths of the samples was achieved when 1.0-2.0 wt.%TiO_(2) was added.In this case,the relative strength of aggregate increased from 33.3% to 37.3%-43.1%,and the mass gain after the hydration test decreased from 3.13% to 1.26%-1.45%.

Influence of Pore Forming Agent on Properties of Micro-pored CA_6-MA Material

Micro-pored CA6 -MA lightweight material with CAM： MA mass ratio of 7：3 was prepared using Al（OH） 3, MgCO3 and CaCO3 as starting materials, and anthracite. sweet potato starch and anthracite ＋ sweet potato starch as pore forming agent （PFA） with an addition of 10 mass%, 20 mass% and 30 mass%, respectively. The starting materials were dry mixed, wet co-milled in a ball mill for 1 h. slip cast into cylindrical specimens with a diameter of 60 ram. and then calcined at 1 450 ℃ for 3 h. With the increase of PFA addition,, apparent porosity increases, and bulk density decreases. The influence of different PFAs on properties of the micro-pored LW CAM -MA aggregate was investigated. The achieved CAM - MA, by adding 30% sweet potato starch, has a porosity of 76. 8%, bulk density of 0. 78 g · cm^ - 3 and median pore size of 1.90 μm.