Preheating a crucible prior to strong heating prevents?
Preheating a crucible before strong heating can be done for a number of reasons depending on the application for which the crucible will be used. Firstly, preheating of a crucible before use is important for reducing thermal stress on the crucible. This is extremely important when using a crucible for the first time, as it will keep it from cracking thanks to a slow controlled heating, ensuring it will last longer. It is also important in applications where very high levels of heat are necessary, such as in smelting, where high levels of heat are used to isolate various metals based on their melting points.
A second reason to preheat a crucible is to ensure accurate measurements. If a crucible is weighed cold, or below room temperature, it is possible that moisture may become trapped in the material of the crucible. This moisture leads to variable amounts of excess weight. By using a series of preheating and cooling steps each time a measurement is taken, one can extract this moisture reliability, and repeatably, and get a more accurate measurement of the crucibles weight before the substance is placed inside. This is critical when exact measurements down to ten-thousandths of a gram must be made. Without proper preheating before measurements, not only is accuracy decreased, but replicability in measurement as well. Hope this helps!