Does the crucible used for calcination of copper nitrate in a high-temperature muffle furnace need a lid?

The crucible does not need to be covered during the calcination of the high temperature muffle furnace. According to the actual situation of the sintered sample, for the sample that will be volatilized during calcination, it is necessary to cover the lid during the calcination, but the sample that does not volatilize during the calcination , You can choose not to cover the lid.