| LaMgAl11O19(LMA) is a kind of hexaaluminate material which has been developed in recent years.Besides the low thermal conductivity,other important properties that LaMgAl11O19 gets are low modulus of elasticity,high melting point and phase stability at high temperatures,and these are all of great value in the field of thermal insulation.Appropriate raw materials and synthesis temperatures for the preparation of LaMgAl11O19 fine powders and aggregates by solid-state reaction were investigated in this paper,as well as the processing conditions of LaMgAl11O19 refractories using self-made LaMgAl11O19 fine powders and aggregates.The phase, microstructure,micro component and properties(mainly including sintering character, intrinsic thermal properties,mechanical properties,refractoriness,thermal shock resistance and anti-corrosion properties of steel slag) were studied systematically.The results showed that LaMgAl11O19 powders synthesized with Al(OH)3,La2O3, 4MgCO3·Mg(OH)2·5H2O as the raw materials calcined at 1300℃for 4h were of high sintering activity,and moreover,and the LaMgAl11O19 grains take the form of plate-like morphology.The LMA aggregates were prepared using La2O3, 4MgCO3·Mg(OH)2·5H2O andα-Al2O3 as the raw materials sinterd at 1650℃for 8h by one-step solid-state reaction,the bulk density was 3.74g/cm3,and the compressive strength at ordinary temperature was 100.8MPa.The thermal diffusivity and thermal conductivity of LaMgAl11O19 dense ceramic was 0.553mm2/s and 2.55W/m·K, respectively.Also the average thermal expansion coefficient from 200℃to 1200℃was 9.17×10-6/K,and the Young's modulus and Poisson's ratio was 295GPa and 0.23, respectively.Experiments showed the flexural strength dropped with fine powders decreasing, while the content of the aggregate had a certain influence on the compressive strength. When the content of the fine powders was 35wt%,LaMgAl11O19 refractories had a highest compressive strength of 95.7MPa.LaMgAl11O19 samples'dimensional stability was good with the linear shrinkage rate after secondary sintering was 0.21%～0.10%.The refractoriness was above 1740℃,and it was still behaved as magnetoplumbite structure with good phase stability at high temperatures after the refractoriness test.Thermal shock resistant test was conducted withΔT=1200℃,the results indicated that the LaMgAl11O19 refractories had the best thermal shock resistance with the content of fine powders was 40wt%,and it still remained 66.1%of residual flexural strength after thermal shock resistant testing,which was better than MA and MS samples.Under the same conditions,the LMA samples'anti-corrosion property of steel slag was almost even to that of MA,and better than that of MS.It's believed that the matrix in LaMgAl11O19 refractories reacted with steel slag to produce the MgAl2O4 and Fe+2Al2O4 at high temperatures,and the dense transitional layer of LaFeAl11O19 prevented the steel slag from further corrosion and penetration to inside the samples.
|
PDF Full Text Request