Studies on Thermal-Shock Resistance of Alumino-silicate Refractories in Relation to Strength, Thermal Expansion and Modulus of Elasticity
TL;DR: In this article, the effects of mechanical strength, linear thermal expansion and modulus of elasticity on thermal-shock resistance of alumino-silicate refractories have been studied and the results have been statistically analyzed.
Abstract: The effects of mechanical strength, linear thermal expansion and modulus of elasticity on thermal-shock resistance of alumino-silicate refractories have been studied and the results have been statistically analysed. An equation correlating thermal-shock resistance of these refractories to their strength, thermal expansion and modulus of elasticity has been suggested on the basis of the observations made.
Citations
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TL;DR: The thermal expansion of hard porcelain samples is a function of the asymmetry of size distribution of mullite crystals and internal stresses originating in the samples from the thermal expansion mismatch between the phases also influence the thermal-shock resistance as mentioned in this paper.
Abstract: Thermal-shock resistance of hard porcelain samples are dependent on the concentrations of the crystalline phases (mullite and quartz) and the glassy phase and also on the size of mullite crystals. Internal stresses originating in the samples from the thermal expansion mismatch between the phases also influence the thermal-shock resistance. The thermal expansion of the samples is a function of the asymmetry of size-distribution of mullite crystals.
11 citations
TL;DR: In this article, the glassy phase was ceramized by incorporating Cr2O3, V2O5 and TiO2 into the refractories as nucleating agents and subsequent heat-treatment.
Abstract: Low-grade fireclay refractories contain large amounts of glassy phase. The properties, e.g. mechanical strength, thermal-shock resistance, refractoriness-under-load, refractoriness and also porosity and bulk density of these refractories before and after ceramization of their glassy phase were investigated. The glassy phase was ceramized by incorporating Cr2O3, V2O5 and TiO2 into the refractories as nucleating agents and subsequent heat-treatment. Significant improvement in mechanical strength and thermal-shock resistance of the ceramized refractories was observed.
1 citations
TL;DR: In this paper, the effects of shape, size and relative proportions of the crystalline phases usually present in the aluminosilicate refractories on their thermal-shock resistance are compared.
Abstract: Thermal-shock resistance of aluminosilicate refractories is influenced by their chemical composition and mineralogical constitution. Attempts have been made in this paper to compare the effects of shape, size and relative proportions of the crystalline phases usually present in the aluminosilicate refractories on their thermal-shock resistance.
1 citations
TL;DR: In this article, samples of seven alumino-silicate refractory compositions were subjected to thermal-shocks of increasing severity and their spalling characteristics were studied in relation to their strength and porosity, as well as development of cracks in them.
Abstract: Samples of seven alumino-silicate refractory compositions prepared from china clay, quartz and calcined alumina had been subjected to thermal-shocks of increasing severity and their spalling characteristics were studied in relation to their strength and porosity, as well as development of cracks in them.
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TL;DR: In this paper, the sources and calculation of thermal stresses are considered, together with the factors involved in thermal stress resistance factors, and properties affecting thermal stress resilience of ceramics are reviewed and testing methods are considered.
Abstract: The sources and calculation of thermal stresses are considered, together with the factors involved in thermal stress resistance factors. Properties affecting thermal stress resistance of ceramics are reviewed, and testing methods are considered.
658 citations
TL;DR: In this paper, the authors measured the thermal stress resistance of sintered alumina with porosity from the radial temperature difference required to fracture hollow cylinders under steady-state conditions.
Abstract: Sintered alumina with from 4 to 50% porosity was prepared by incorporating crushed naphthalene in a casting slip. Thermal stress resistance was determined from the radial temperature difference required to fracture hollow cylinders under steady-state conditions. Thermal stress resistance decreases with increasing porosity; resistance to thermal stresses at 50% porosity is about one-third of that estimated for zero porosity.
Summary and Conclusions
Samples with controlled porosity were prepared by incorporating naphthalene flakes in an alumina casting slip. Samples were prepared and fired under identical conditions so that the continuous solid phase was identical for all samples. Steady-state thermal stress tests described lead to the following conclusions:
(1) Resistance to thermal stress, R (maximum steady-state Δt for fracture), decreases with increasing porosity. The resistance for a sample with 50% porosity is about one-third that for dense samples.
(2) Resistance to thermal stress determined by the maximum heat flow permissible, R', decreases more rapidly than R because increasing porosity lowers the thermal conductivity. This factor for a sample with 50% porosity is about one-sixth the value for dense samples. This is the factor generally applicable to thermal shock conditions.
(3) Resistance to thermal fracture with a constant rate of surface temperature rise is directly proportional to R, since thermal diffusivity is unaffected by porosity.
63 citations
TL;DR: In this article, the surface where fracture originates may be represented as a continuum over which flaws of differing "critical breaking stresses" are distributed, and the distribution function for the flaws is given by Sσ where σ is the tensile stress initiating fracture and S and b are constants which are properties of the surface for slowly increasing stresses.
Abstract: A single number called the “strength” does not serve to describe adequately the fracture properties of glass subjected to a slowly increasing tensile stress. Instead, it is found that the surface where fracture originates may be represented as a continuum over which flaws of differing “critical breaking stresses” are distributed. The distribution function for the flaws is given by Sσ where σ is the tensile stress initiating fracture and S and b are constants which are properties of the surface for slowly increasing stresses. The testing procedure and nature of the flaws are discussed.
24 citations