Advantages of Thermal Analysis Crucible Cover:

Improving the temperature distribution in the crucible is conducive to uniform temperature inside the reaction system.

Effectively reduce the influence of radiation effect and sample color.

Prevent the flying of extremely light fine sample powder and prevent it from drifting away with the dynamic atmosphere or being taken away in the process of vacuum extraction.

The sensor can be effectively prevented from being polluted during the reaction process ( e.g. splashing of the sample or overflowing of foam ).

The purpose of the crucible cover hole:

Keep the sample in contact with the atmosphere, allow a certain degree of gas-solid reaction, and allow the gas products to be carried away with the dynamic atmosphere.

so as to keep pressure balance inside and outside the crucible.

Disadvantages of crucible capping:

The contact between the reaction atmosphere and the sample is reduced, which greatly hinders the gas-solid reaction ( oxidation, reduction and adsorption ).

For chemical reactions with gas phase products, the partial pressure around the reactants is higher due to the slow removal of product gas, which may affect the reaction rate and chemical equilibrium ( DTG )

Peak drift to high temperature ), or for some competitive reaction mechanism may affect the composition of the product.

( Change the weightlessness rate of TG weightlessness step )

For the test of physical effects ( melting, crystallization, phase change, etc. ) or the test focusing on DSC, capping is usually selected.

For unknown samples, capping is usually chosen for safety reasons.

For gas-solid reactions ( such as oxidation induction period test or adsorption reaction ), open crucible is used ( not stamped ).

For reactions with gas product generation ( including most decomposition reactions ) or TG - biased tests, the choice of capping or not can be made according to the reaction conditions and actual reactor simulation on the premise of not polluting and damaging the sample holder.

For liquid phase reaction or reaction in volatile solvent, if the reactant or solvent is easy to volatilize at the reaction temperature, a pressed aluminum pans and lids should be used ( temperature and pressure are relatively high

Low ) or medium pressure, high pressure crucible ( higher temperature and pressure ).The same is true for reactions in closed reaction systems that need to maintain product partial pressure.