Q1: The refractory brick which has good thermal shock resistance at high temperature but cracks on cooling below 400°C is

ANS:C - silica

Silica refractory bricks, also known as silica bricks or siliceous bricks, are made primarily of silica (silicon dioxide, SiO2) as the main constituent. These bricks are widely used in various industrial applications where resistance to high temperatures and thermal shock is required. Here are some key characteristics and properties of silica refractory bricks:

1. High Melting Point: Silica has a high melting point, making silica bricks suitable for applications where they are exposed to extremely high temperatures, such as in furnaces, kilns, and glass-making processes.
2. Excellent Thermal Insulation: Silica bricks offer good thermal insulation properties, helping to maintain high temperatures within industrial processes while minimizing heat loss to the surroundings.
3. Chemical Inertness: Silica is chemically inert and does not react with most chemicals at high temperatures, making silica bricks suitable for use in corrosive environments or in contact with acidic or alkaline materials.
4. Resistance to Thermal Shock: Silica bricks exhibit good resistance to thermal shock, allowing them to withstand rapid temperature changes without cracking or spalling. This property is particularly important in applications where the material is subjected to alternating heating and cooling cycles.
5. Low Thermal Expansion: Silica bricks have relatively low thermal expansion coefficients, which means they maintain their shape and dimensions even when exposed to significant temperature variations.
6. Brittle Nature: Silica bricks tend to be brittle, especially at lower temperatures, and may be prone to cracking under mechanical stress or impact. This brittleness should be considered when designing and handling structures made of silica refractory materials.

Overall, silica refractory bricks are valued for their high-temperature performance, thermal insulation properties, chemical resistance, and ability to withstand thermal shock, making them suitable for a wide range of industrial applications where these characteristics are required.