Effect of Microstructure on the Properties of Synthetic Refractory Aggregates
TL;DR: In this paper, four types of refractory aggregates (three sintered mullites using different starting materials and one tabular alumina) were synthesized by reaction sintering process and their properties evaluated.
Abstract: Four types of refractory aggregates (three sintered mullites using different starting materials and one tabular alumina) were synthesized by reaction sintering process and their properties evaluated. The microstructures of the aggregates have been studied by Scanning Electron Microscopy and correlated with the properties of the corresponding aggregates. The performance of these aggregates was also studied at high temperatures by using it in castables.
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TL;DR: In this article, the effect of reactive alumina and its different proportions on physico-mechanical properties of conventional high alumina castables were studied by using calcium aluminate cement as a binder and various refractory properties of the prepared castables, i.e. apparent porosity, bulk density, cold crushing strength, hot modulus of rupture, etc.
Abstract: The effect of reactive alumina and its different proportions on physico-mechanical properties of conventional high alumina castables were studied. The castables with different percentages of reactive alumina were prepared by using calcium aluminate cement as a binder and various refractory properties of the prepared castables, i.e. apparent porosity, bulk density, cold crushing strength, hot modulus of rupture were studied. The mineralogical analysis was done by X-ray diffractometry, whereas morphological analysis was carried out by scanning electron microscopy. The results showed that the castable with high percentage of reactive alumina hydrated early as well as developed early sintered strength due to its faster rate of hydration and higher reactivity at lower temperature. The hot modulus of rupture was also found to be higher in the castable with more reactive alumina. Mineralogical analysis showed well developed mullite and corundum phases in the refractory concrete which was supported by morphologic...
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TL;DR: In this article, a linear relationship was obtained between the percent of theoretical density and the logarithm of time for compositions in the range 73-75 wt% Al{sub 2}O{sub 3}/SiO{ sub 2} ratio.
Abstract: Sintering behavior of mullite-containing powders was studied over a range of chemical compositions (Al{sub 2}O{sub 3}/SiO{sub 2} ratio). Densification measurements were made for both liquid phase-containing and solid state systems. Small amounts of liquid phase were observed to have a significant effect on densification rate. A linear relationship was obtained between the percent of theoretical density and the logarithm of time for compositions in the range 73-75 wt% Al{sub 2}O{sub 3}. Currently available models for intermediate stage sintering kinetics were considered to be inadequate for these systems. Grain boundary transport 0r diffusion appeared to be the primary mechanism of densification.
86 citations
TL;DR: In this article, the authors used the reaction sintering of calcined alumina and calcined sillimanite to develop high alumina aggregates for refractories applications using titania additive.
Abstract: Reaction sintering of beach sand sillimanite and calcined alumina is an innovative as well as cost effective method of mullite formation. In the present investigation, beach sand sillimanite and calcined alumina in microfine state were used as starting materials to develop high alumina aggregates for refractories applications using titania additive (0–6 wt%). The raw materials and additive (TiO 2 ) were mixed in definite proportion and sintered in compacted form at 1400–1550°C with 2 h soaking. It was determined that, alumina/silica ratio of the batch controls densification, flexural strength and microstructural development of the aggregates. Aggregates with almost zero porosity were developed at a sintering temperature of 1500°C with the help of titania additive. Gradual addition of TiO 2 up to 4 wt% promotes the densification process, however, TiO 2 affects the high temperature flexural strength of the aggregates. Aggregates developed from sillimanite sand at 1500°C indicates that the mullites formed are not ideal 3:2 type, but are 1:1 type. Mullite formed in the silica rich composition is long and elongated in nature. At the densification temperature of 1500°C up to 3·06 wt% TiO 2 enters into the mullite structure as solid solution.
37 citations
TL;DR: In this article, les proprietes mecaniques de ceramiques de mullite en fonction de leur composition chimique a temperature ambiante and dans l'air a 1300°C.
Abstract: On etudie les proprietes mecaniques de ceramiques de mullite en fonction de leur composition chimique a temperature ambiante et dans l'air a 1300°C. On note des differences significatives dans la resistance a la flexion et la tenacite quand la composition change
19 citations
TL;DR: In this article, reaction-bonded alumina was fabricated using standard powder preparation methods and the low-pressure injection molding (LPIM) forming technique, followed by reaction sintering.
Abstract: Reaction-bonded alumina was fabricated using standard powder preparation methods and the low-pressure injection moulding (LPIM) forming technique, followed by reaction sintering. The feasibility of LPIM was investigated in terms of the compounding ability of a highly agglomerated mechanically alloyed powder in a non-polar organic vehicle, and the microstructural homogeneity and resulting reliability of sintered LPIM parts. The green density of LPIM parts after debinding, roughly corresponding to the solids loading in the LPIM feedstock, was in the range of fractional density achieved by dry pressing, although the powder packing and aluminium particle deformation during forming were not the same. LPIM forming and debinding induced microstructural inhomogeneities (i.e. larger voids due to trapped air and density fluctuations) which were reflected in a slightly lower Weibull modulus, while the average strength did not differ significantly from the values obtained with dry pressed samples. The microstructure and mechanical properties of sintered parts were also related to the purity of the starting powders. The presence of impurities in the starting aluminium powder resulted in a somewhat coarser microstructure, characterized by a broader Al2O3 grain-size distribution, as well as in the presence of a thin glassy phase on the grain boundaries and in partial destabilization of dispersed tetragonal (Y2O3-stabilized) ZrO2 particles. In spite of a less favourable microstructure, the room-temperature strength and Weibull modulus were still comparable to those obtained from high-purity starting powder.
14 citations