Refractory material in the absence of load resistance to high temperature action without melting performance called refractoriness. The meaning of refractoriness is different from that of melting point, which is the temperature at which the crystalline phase of pure material is in equilibrium with its liquid phase, such as the melting point of alumina is 2050℃, and the melting point of silicon oxide is 1713℃. But the general refractory material is composed of a variety of minerals multiphase solid mixture, not single-phase pure material, so there is no certain melting point, its melting is in a certain temperature range, that is, only a fixed melting start temperature and a fixed melting end temperature. When heated, there will be reactions between various mineral components of refractory materials, and the formation of fusible low melting point combination and soften it, so refractoriness only shows the temperature when refractory materials soften to a certain degree, is the basis for judging whether materials can be used as refractory materials.
When determining refractoriness, the refractory material sample is made into a triangular cone with an equilateral triangle and an upper bottom edge of 2mm, a lower bottom edge of 8mm and a height of 30mm. The triangular cone specimens are heated together with the standard cone for comparison (WZ and 1/10 of its refractoriness). The triangular cone is deformed and bent under the action of high temperature. When the apex of the triangular cone is bent and touches the bottom plate (used to place the sample cone), the temperature at this time (compared with the standard cone) is called the refractoriness of the material.
The basic factors determining refractoriness are the chemical mineral composition and distribution of materials. All kinds of impurities, especially those with strong flux effect, will seriously reduce the refractoriness of products. Therefore, the main way to improve the refractoriness of refractory materials is to take appropriate measures to ensure and improve the purity of raw materials.
Refractoriness and melting point are two completely different concepts. For single-phase polycrystalline refractory, its refractoriness is generally lower than the melting point of crystal. However, for refractory materials with high viscosity liquid phase formed at high temperature, the refractoriness can also be higher than the melting point.
It should be noted that refractoriness does not represent the actual service temperature of refractories. Because at this temperature refractories no longer have mechanical strength or resistance to erosion, it is not correct to say that "the higher the refractoriness, the better the brick". Refractory material in use through high temperature function at the same time, often accompanied by load and other material flux, and products cannot be used as products refractoriness temperature limit, only can be used as a reasonable choice of refractory reference, only after considering other properties, to determine the value of the refractory material.