What happens to clay when it is fired in a kiln?

by yuvaporn t October 12, 2020

The important step in making ceramic workpiece that has been discussed previously is raw firing. However, many people still wonder about various reaction steps in the raw firing. What the reaction will be like while firing? We have a simple explanation about the process of change to let you know

First step: water attached to the outside of the molecule is evaporated > Even if the workpiece is dried but there was still moisture left. Raw firing will allow the moisture to evaporate completely in the temperature range of 110-120 degrees Celsius until the clay becomes completely dried and the color of the clay will begin to fade.
Step 2: Water in the molecule breaks down > In the temperature range of 120-350°C, the water crystals in the clay molecules begin to decay. Only oxides and organic compounds are left in the clay. When firing at this temperature range if the workpiece has a lot of moisture or the molding thickness is not the same, it will crack or explode.
Step 3: Chemical and Physical Changes > In the temperature range of 350-450°C, the water crystals in the clay structure will completely decompose. In this period, the firing temperature must be increased slowly because if it is fast, it will accelerate the rapid decomposition of water molecules, especially the surface. When the surface shrinks a lot but the interior shrinks less, it will then crack.
Step 4: The firing range > In the temperature range of 700°C, organic matter such as carbon and sulfur gas will burn and produce carbon monoxide, carbon dioxide, sulfur monoxide, sulfur dioxide at 900°C but some sulfur compounds burn completely until 1100 - 1150 °C.