摘要
Mold powder is generally made of SiO2 and CaO with little amount of calcium fluoride(CaF_(2))and carbon.Basically,F^(-)has a crucial effect on viscosity and crystallization of the powder.However,emission of toxic materials containing F^(-)constituent such as HF and SiF4 leads to serious environmental pollution.Overall,six powder samples were made during this research to study the effects of such compounds as calcium fluoride(CaF_(2))and manganese oxide(MnO)on the crystallization of mold powder and compare with that of the original mold powder.Having considered the chemical compounds of these six samples,two were finally chosen:powder sample A and powder sample E.The former was a simulated sample of the original mold powder using CaF_(2),and the latter was a less-F^(-)sample in which MnO was used as a substitution for F^(-)in the compounds of the mold powder.In other words,the amount of F^(-)was cut in half comparing to that of the original mold powder.The thermal gravimetric analysis(TGA)was performed on the original mold powder,the simulated sample of the original mold powder and the less-F^(-)sample.The results of the TGA demonstrated the reduction of thermal loss in samples A and E comparing to the original mold powder.On the other hand,the results of differential thermal analysis(DTA)of these three samples,i.e.,original mold powder and samples A and E,demonstrated that melting and crystallization temperatures of the original mold powder were similar to those of samples A and E.Therefore,it can be concluded that samples A and E are potential laboratory-scale substitutions for the original mold powder.
