4 Indicators That Determine The High-temperature Performance Of Refractories

 Refractory materials in the process of use, by the high temperature (generally 1000 ~ 1800 ℃) under the physical, chemical, mechanical and other effects, easy to melt and soften, or by the fusion of abrasion, or produced by the collapse of the damage and other phenomena, so that the operation is interrupted, and staining of materials. Therefore, the refractory material must have the ability to adapt to the nature of various operating conditions. The following are the four indicators that determine the high temperature performance of refractory materials:

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 Refractoriness refers to the temperature at which a material reaches a specific degree of softening at high temperatures, characterizing the performance of the material to resist high temperatures. Refractoriness is the basis for determining whether a material can be used as a refractory material. The International Organization for Standardization stipulates that inorganic non-metallic materials with a refractoriness of more than 1500℃ are refractory materials. It is different from the melting point of the material, which is the comprehensive performance of the mixture of various minerals composed of multi-phase solids.

 The most fundamental factor in determining the refractoriness is the chemical mineral composition of the material and its distribution, various impurity components, especially those with strong flux effect will seriously reduce the refractoriness of the material. Therefore, in the production process should consider taking appropriate measures to ensure and improve the purity of raw materials.

 Refractoriness is not an absolute physical quantity specific to a material, it is a relative technical index of the material when it reaches a specific degree of softening measured under specific test conditions. The test material in accordance with the prescribed method into a truncated triangle cone (referred to as test cone), and in a specific heating rate with a fixed bending down the temperature of the standard truncated triangle cone (referred to as the standard cone), in the established heating rate and a certain atmosphere under the conditions of heating to test the degree of bending down the degree of bending down the degree of the standard cone bending down the degree of comparative method of determining the degree of refractoriness. Truncated triangular cone bottom of each side of the length of 8mm, the upper bottom of each side of 2mm, 30mm high. measurement, in the high temperature of the cone may appear inside the liquid phase. With the increase in temperature, the amount of liquid phase increases, the viscosity of the liquid phase decreases, the cone softens, when the softening to a certain extent, the cone due to its own weight and gradually bent down. When the test cone and the standard cone at the same time bent down until its apex and the chassis contact, the standard cone has been determined by the bending down the temperature shall prevail, as the refractoriness of the test cone. Common refractory raw materials and refractoriness of the material is shown in Table 1.

 It is also called load softening point of refractory material or load deformation temperature of refractory material, which indicates the resistance performance of refractory material to the joint action of high temperature and load under constant load or the temperature range of refractory material showing obvious plastic deformation. Through the refractory material load softening temperature can be deduced from its maximum operating temperature, load softening temperature to a certain extent that the refractory material in its use of similar cases of structural strength, can be used as a basis for determining the maximum operating temperature of refractory materials. The high-temperature load-softening deformation temperature of commonly used materials is shown in Table 2.

 The main factor determining the load softening temperature is the chemical mineral composition of the material, but also directly related to the production process of the material. The firing temperature of the material has a greater influence on the load softening deformation temperature, if the firing temperature is increased appropriately, the starting deformation temperature will be increased due to the reduction of porosity, crystal growth, and good bonding. Improve the purity of raw materials, reduce the content of low melt or flux, will improve the load softening deformation temperature. For example, sodium oxide in clay bricks and alumina in silica bricks are harmful oxides.

 Refractory materials for a long time at high temperatures, resulting in volume expansion, called residual expansion. Refractory material residual expansion (deformation) size, reflecting the high temperature volume stability of good and bad, the smaller the residual deformation, the better the volume stability; on the contrary, the worse the volume stability, the more likely to cause deformation or damage to the masonry. Commonly used re-firing line change to determine the high temperature volumetric stability of the material, it is an important indicator for assessing the quality of the material. National standards for commonly used refractory materials, the re-burning line change index is shown in Table 3.

 Most refractories shrink at high temperatures. In the re-firing, most refractories are contracted, mainly because the material at high temperatures in the liquid phase will fill the pores, so that the particles further tighten, close, recrystallization occurs, which leads to the further densification of the material. There are also a few materials in the re-firing expansion, such as silicon bricks due to the use of polycrystalline transformation accompanied by expansion, this is because of silicon bricks in the firing of the quartz has not been transformed at high temperatures will continue to be transformed into scaly quartz or square quartz, the volume of expansion of silicon bricks in the quartz has not been transformed by about 10%. In order to reduce the material re-firing contraction and expansion, appropriate to increase the firing temperature and extend the holding time is effective, but should not be too high, otherwise it will cause the material organization vitrification. Reduce the thermal shock stability. Because of the firing and use, the quartz particles in the material to produce expansion, the town offset the contraction of the clay, so the volume of semi-silica bricks change is small, and in some cases a slight expansion.

 The ability of a refractory material to resist rapid changes in temperature without damage is called thermal shock stability. This property is also known as thermal shock resistance or resistance to rapid changes in temperature.

 The main factors affecting the thermal shock stability index of a material are the physical properties of the material, such as thermal expansion and thermal conductivity. Generally speaking, the greater the linear expansion of the material. The worse the thermal shock stability; the higher the thermal conductivity of the material, the better the thermal shock stability. In addition, the organizational structure of the refractory material, the composition of the particles and the shape of the material all have an effect on the thermal shock stability. 

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