A method is proposed for quantitative evaluation of the change in specific volume of refractory substance during a liquid -solid phase transition according to the surface shape of a flat ingot crystallized under conditions of central symmetrical heating. The accuracy of the estimate is up to 5 -8%. With certain limitations the method is applied to a quantitative estimate of the volumetric effect of crystallization and in a number of cases melt density of the refractory materials themselves, for which obtaining information about melt density by any other method is impossible. Using the proposed method an estimate is provided for the density of molten yttrium and erbium oxides close to the melting temperature (for Y 2 O 3 T m = 2440°C, for Er 2 O 3 T m = 2430°C respectively).
A device is described for comparative evaluation of the thermal shock resistance of ceramic specimens of identical shape and dimensions by recording acoustic emission (AE) pulses during air cooling from 1000C. The number of AE pulses in a unit of time, whose intensity exceeds the 10% level of maximum signal intensity, is used as a comparative characteristic for thermal shock resistance of ceramic materials. Comparison of the AE pulse distribution with respect to amplitude contains additional information about the thermal shock resistance of comparable specimens. With use of high-temperature furnaces with a considerable working volume and treatment of repeated cooling conditions the measurement part of the device may be used for evaluating the comparative thermal shock resistance of ceramic specimens and objects of any shape and size during cooling from above 1000°C.
Mathematical modelling of the distribution of strain in layered quartz ceramics with protective coating of niobium (tantalum) pentoxide from two sides is reported. It is found that fragmentation of the basic layer (decreasing the area of the continuous boarder between layers) and smoothing of sharp edges of the base fragments should reduce the strains on the boundary between the substrate and coating and, correspondingly, enhance the thermal resistance of the samples. Treatment of the niobium pentoxide coating by concentrated light induces a network of fractal micro-and nano-size fractures that compensates the difference of thermal expansion between the layers.
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