Refractory properties research

3. High temperature use properties of refractory materials

3.1 Refractoriness

The property that the refractoriness resists high temperature when it is not loaded and does not melt is called refractoriness. For refractory materials, the meaning of refractoriness is different from the melting point. The melting point is the temperature at which the crystalline phase of the pure substance is in equilibrium with its liquid phase. However, the general refractory material is a heterogeneous solid mixture composed of various minerals, not a pure phase of a single phase, so there is no melting point, and the melting is carried out within a certain temperature range, that is, only a fixed initial melting temperature and A fixed melting end temperature. In this temperature range, the liquid phase and the solid are present at the same time.

The refractoriness is a technical index. The measuring method is a truncated triangular cone made of test materials. The upper side is 2 mm long on each side, and the lower bottom is 8 mm long and 30 mm high. (The angle between the side and the vertical direction is 80) Equilateral triangle. When heated at a certain heating rate, it gradually deforms and bends due to its own weight. When it is bent until the apex is in contact with the chassis, it is the refractoriness of the sample.

3.2 high temperature volume stability

When the refractory material is used for a long period of time at a high temperature, the performance of the outer shape of the refractory material which remains stable without undergoing a change (shrinkage or expansion) is called high temperature volume temperature. It is an important indicator for assessing the quality of a product.

During the firing process, the physicochemical changes in the refractory material generally do not reach the equilibrium state at the firing temperature. When the product is subjected to high temperature for a long time, some physical and chemical changes will continue. On the other hand, in the actual firing process, for various reasons, there may be insufficiently baked products. When such products are used in a kiln and then subjected to high temperature, some firing changes continue, resulting in products. The volume changes—contraction or expansion—this irreversible volume change is called residual shrinkage or expansion, also known as reburning shrinkage or expansion. The size of the reburning volume change indicates the high temperature volume stability of the product.

3.3 Thermal shock stability

The property of a refractory material against a sharp change in temperature without damage is called thermal shock stability. It is well known that materials rise or contract with temperature rise and fall, and if this expansion or contraction is constrained and cannot develop freely, stress is generated inside the material. Such internal stress caused by thermal expansion or contraction of the material is called thermal stress. Thermal stress is generated not only under mechanical constraints, but also in temperature gradients in the homogeneous material, the difference in thermal expansion coefficients between the phases in the heterogeneous solid, and even the anisotropy of the thermal expansion coefficient in the single-phase polycrystal. Both are the source of thermal stress.

Thermal shock damage of refractory materials can be divided into two categories: one is instantaneous fracture, called thermal shock fracture; the other is cracking, spalling, then fragmentation and deterioration under the action of thermal shock cycle, and finally The overall damage is called thermal shock damage.