What Does Refractory Brick Mean?
Refractory brick is a ceramic material that is normally used in high-temperature environments because of its lack of flammability and because it is a decent insulator, which reduces the amount of energy loss. Refractory brick is typically comprised of aluminum oxides and silica. It is also known as "firebrick."
At elevated temperatures, substances with liquid phases usually react chemically with the refractory brick, resulting in refractory consumption. Although it may not be immediately obvious, the oxidation and reduction state of the environment as redox conditions or oxygen activity can participate in and influence the chemical reactions that are to take place.
Besides the chemical reactions that occur during corrosion, physical changes occur as well; and the corrosion process may accelerate these physical changes. Corrosion of refractories can be also defined as the refractory wear caused by loss of thickness and mass from the exposed face of a proposed refractory. The exposed face of a proposed refractory is caused by a chemical attack which, in turn, is caused by a corroding fluid in a process where the refractory and the corroding fluid react when approaching chemical equilibrium in the zone of contact between the refractory and the fluid.
Corrosionpedia Explains Refractory Brick
Refractory brick is frequently used to construct kilns, furnaces and other high-temperature enclosures. That's because refractory brick reduces heat loss and the chance of an unintended fire.
The composition of the refractory brick will determine what temperatures it can withstand. Some types of refractory brick can withstand temperatures of over 2,100 degrees Celsius (3,600 degrees Fahrenheit). However, bricks heated above these temperatures will typically begin to melt.
Refractory brick is formed by a variety of brick-making processes—for example, soft-mud casting, hot pressing and dry pressing. Depending on the material of the refractory brick, some processes will work better than others. Refractory brick is typically formed into rectangular shapes measuring nine inches long by four inches wide (22.8 centimetres by 10.1 centimetres) and a between one and three inches thick (2.5 centimetres to 7.6 centimetres).
Corrosion reactions proceed in the direction of localized chemical equilibrium. Essentially, corrosion reactions are what happens when the system trying to achieve compatibility and attempts to do this by progressing toward equilibrium. Refractories, generally, are rarely at chemical equilibrium because they are typically made from a mixture of different minerals. Although at an immediate corrosion interface that may exist between the refractory and the slag, the localized volume elements tends to be at or close to chemical equilibrium. The reactive component in the phenomenon that occurs during refractory corrosion is called the “slag”.
The matrix is the area of sintered fines that holds bonded bricks and monolithic refractories together. Corrosion usually affects the weakest component of the refractory at a higher rate than denser or higher purity particles that may be in the area and acts faster in such areas. In extreme cases of a matrix attack, there is rapid erosion of refractory aggregate that at times occurs.
Slag attack is particularly important in refractories. The refractory's structural strength may be affected significantly by liquid slags' solvent action. Slag attack on refractories can happen in two ways:
- Corrosion. This type of slag attack refers to the wear and tear on refractories which happens in slag's static chemical attack.
- Erosion. This is caused by mechanical action—i.e., the process of breaking down and subsequently washing away refractory materials by contacting molten slag.
This method to test slag attack is called "pill test" and is used when the quantity of slag is less compared to the quantity of refractories. During a pill test, the slag—which is normally in the form of a pill, hence the name—is placed on the refractory body or in a cavity which has been made inside and heated. The test observes:
- The slag's depth of penetration inside the refractory.
- The spreading of the molten mass.
- Corrosion is observed during the test .
Together, these factors determine the measures of the attack.