Advanced silicon nitride ceramic compact was prepared by colloidal process. The rheological
behaviors of the Si3N4 powders were emphatically investigated. At the same time, the effects of the
dispersant, pH value and ball milling time on the silicon nitride slurry were discussed. The results showed
that the addition of the dispersant could shift the value of Zeta potential and improve the fluidity of silicon
nitride slurries. The well fluidity can be achieved when the amount of the dispersant was 1.2wt%. Besides,
a ball milling time of 8h was appropriate. Statistic pattern recognition was used to predict the processing
parameters. Then the high density of green compact could be attained while the volume fraction of solid
powders was up to 40%, and the fracture toughness of the sintered body reached 7.2MPa·m1/2. The
microstructure of final sintered ceramic was observed by scanning electron microscope (SEM).
In order to enhance the density and decrease the sintering temperature,Al2O3/Si3N4 compound ceramics were sintered by pressureless using β- Si3N4 as raw materials and Al2O3 as sintering additives. The effects of Al2O3 as additive on the Vickers hardness and the sintering characteristic of Al2O3/Si3N4 compound ceramics were studied. The results shows that adding 9-15% nano- Al2O3 can get Al2O3/Si3N4 compound ceramics only in 1650°C by pressureless sintering because of nano- Al2O3’sintered. As a consequence, the relative density increases from 89% with micro alumina to above 97% with nano- Al2O3, the Vickers hardness increases from 1043.5MPa to 1356.0 MPa.
Lightweight materials applied in construction field were prepared using waste iron mine tailings (WIMT) as raw materials, the commercial silicate cement (CSC) as cementing agent, NaOH as the alkali activator, and triethanolamine lauryl sulfate (TLS) as foaming agent via foam-gelcasting method. The effects of water/cement (W/C) mass ratio (0.6-1.0), addition of NaOH (0-0.15wt%) and foaming agent (0-0.3vol%) on the porosity, bulk density, and mechanical properties of the iron mine tailing-based lightweight materials were studied. The results showed that the mechanical properties of iron mine tailing-based lightweight materials were improved by adding NaOH, the as-prepared materials had a 7-day compressive strength of 5.18 MPa, porosity of 51.40%, bulk density of 1.73 g/cm3and thermal conductivity of 0.193 W・(m-1K-1) when the W/C ratio was 0.8, the mass ratio of WIMT/CSC/NaOH 1.85:1:0.15, and foaming agent content 0.3vol%.
Mullite can be prepared as lightweight refractories for its low thermal conductivity, advanced volume stability at high temperature environment. Using industrial alumina and nature silica powders as starting materials, the mullite aggregates with microporous structure were synthesized by adding some burning-out materials as pore forming agents. The effects of burning-out materials on the pore size distribution, mullite contents and microstructure of microporous mullite have been investigated. The results show that the effects on the mullite contents and microstructure of microporous mullite are significant. All the burning-out materials have a similar effect for the pore size distribution.
Mullite has low thermal conductivity, advanced volume stability at high temperature, and is suit to prepare lightweight refractories. The micropored mullite aggregates has been produced by using industrial alumina and natural silica as starting materials, adding some burning-out materials, then fired at 1350°C for 6h. The influences on the bulk density, pore size distribution and microstructure of microporous mullite of adding these burning-out materials, such as carbon black, coke, and anthracite have been investigated. The conclusions are that the influences on the bulk density and microstructure of micropored mullite aggregates are significant. These three burning-out materials have a similar effect for the pore size distribution. The microporous mullite aggregates has the smallest bulk density and more uniform microstructure by using anthracite as the burning-out material.
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