The Light Weight Calcium Hexaluminate Low-Preparation And Performance Research

lightweight refractory material is helpful for energy saving and environmental friendliness that is wildly used in high temperature industry, thanks to their high porosity, low thermal conductivity and thermal capacity. For some severe applications, it is critical whether the lightweight insulating refrctories have high refractoriness and good resistances to reducing atmosphere and alkali attack. Calcium hexaluminate ?CA₆? is featured by high melting point, good resistances to alkali and reducing atmosphere attack, it is meaningful to develop micro-porous CA₆ aggregate and lightweight castables, so as to overcome the weakness of conventional insulating castables. The traditional preparation methods of calcium hexaluminate has been limited by high calcination temperature and sophisticated equipment, which hinder the development of calcium hexaluminate in high temperature industry. So in this paper a innovative preparation process for high quality calcium hexaluminate at lower temperature was investigatd.Using Industrial aluminum hydroxide, calcium hydroxide and paper-making white mud as starting materials, calcium hexaluminate aggregate and lightweight brick can be prepared through wet co-grinding the starting materials, autoclaving at various temperatur, drying and calcining. The influences of the ratio of raw materials, temperature of hydrothermal treatment, the particle size, holding time, calcination temperature on properties and micro morphology of the precursor and CA₆ aggregates were investigated. The properties of the lightweight CA₆ aggregates, such as phase composition, pore size distribution, bulk density, apparent porosity and strength,etc.,were also characterized. The results show that the precursor obtained from 200? hydrothermal treatment can prepare the calcium hexaluminate refractory material after sintered at 1450? for 3h. The prepared CA₆ with the feature of pore size distribution of 0.4?m-1.4?m and total porosity of 79.36%, compared to 32.57% of the controlling examples ?without hydrothermal treatment sample?, is more porous than the control. The results shows that hydrothermal treatment has a important role in preparing of lightweight calcium hexaluminate. The phase structure changed from gibbsite into boehmite when the temperature of hydrothermal treatment at 175? for 8 hours, which makes the morphology of sample has transformed the tabular gibbsite into the dimensional flake boehmite.When paper-making white mud as starting materials, the diffraction peak of CA₆ appeared at 1350?, and calcium hexaluminate began a large number of generated and into main crystal phase at 1450?. Gibbsite began a little number of generated into boehmite when the temperature of hydrothermal treatment at 175? for 8 hours. When hydrothermal treatment reached 200?,the gibbsite completely generated into dimensional flake boehmite. The precursor obtained from 200? hydrothermal treatment sintered at 1500? for 3h can prepare a large number of calcium hexaluminate crystal with complete crystal structure, crystal size distribution uniform, particle size about 1?2?m, the thickness of crystal just only a few tens of nanometer.The bulk density of the obtained CA₆ aggregate increased with the holding time increasing. The bulk density of CA₆ aggregate increased with the increasing of hydrothermal treatment temperature. The aggregate strength decreased with the increasing of holding time. When the holding time is 3h, the aggregate strength decreased by 22%,and when the hydrothermal treatment temperature is 200?, the aggregate strength decreased by 29.5%.This shows that the hydrothermal treatment has a greater influence on the CA₆ aggregate strength.