What Is High Temperature Refractory?
High-temperature refractory makes bricks, linings, and other parts of furnaces, kilns, fireboxes, and fireplaces. It is a refractory ceramic material that can withstand extremely high temperatures, some exceeding 2000 degrees Celsius.
The properties of refractories depend on their chemical mineral composition and the distribution of impurities. These factors can seriously affect the RUL (refractoriness) of refractory products.
When high temperature precast refractory products are used, some physical and chemical changes occur during the firing process. These sintering changes do not reach equilibrium at the fired temperature, resulting in some expansion or shrinkage of the refractory brick.
This can cause the bricks to break down quickly and damage or even burn out during refractory firing. These bricks can be referred to as those with poor thermal shock stability or temperature sudden change resistance.
Thermal processors often face increased production demands that require furnaces to operate at higher temperatures for extended periods. These rapid increases in operating temperature can lead to phase changes in the refractory matrix, which cause lower-temperature glassy phases that soften the stubborn and shorten its life.
Expansion or Shrinkage
Refractories can be used for various high-temperature applications, such as furnace linings and kilns. They are characterized by the chemical, physical, and mineralogical properties that allow them to withstand high temperatures and corrosive environments.
Refractory materials can undergo expansion or shrinkage when heated to a high temperature. This is known as reheat change and can affect the shape of refractory bricks.
Expansion (creep) – This property determines how a refractory deforms in a given time and at a specific temperature. This critical property helps refractories maintain dimensional stability under constant thermal cycling and corrosion from hot liquids and gases.
Shrinkage: This property determines the degree of deformation a refractory undergoes when heated to a high temperature. This critical property allows refractories to resist slag penetration and physical wear.
These properties can be tested by using a variety of methods. These include pyrometric cone equivalent, refractoriness, thermal expansion under load (creep), hot modulus of rupture, and thermal shock resistance.
Thermal Shock Stability
When high-temperature refractory is used in furnaces, linings and other applications, thermal shock stability is essential. This is because the sudden temperature changes can produce a transient mechanical load on the material that will cause cracks to form.
The stress that occurs in thermal shock is primarily determined by the differential expansion of the material under different temperature change rates. This is a characteristic of many materials, such as ceramics and glass.
However, other materials, such as metals, are very resistant to thermal shock because their heat conductivity is so strong. The physical change in the size of these materials is usually even, as it is a result of their high heat conduction properties.
Thermal Shock Resistance
Thermal shock resistance is the ability of a material to resist rapid and sudden temperature changes. This is important for refractory ceramics, often used in applications that experience abrupt temperature gradients.
For example, pouring hot coffee into a mug is a mild thermal shock that most ceramic products can withstand. Putting a frozen casserole into the oven or subjecting an open flame to a ceramic pan are much more drastic temperature changes and require unique materials to resist this.
The ceramic refractories that resist sudden temperature changes typically have several micro-cracks and pores in their structure, which help prevent the formation of permanent thermal stresses and damage. This helps to ensure their high thermal shock resistance.