Mori T
J Dent Res. 1986 Jun;65(6):877-84. doi: 10.1177/00220345860650060201.
This study examined the thermal behavior of cast gypsum specimens, with and without additives, by means of simultaneous differential thermal analysis-thermogravimetry (DTA-TG) and dilatometry. Specimens were prepared from wet-calcined hemihydrates (Hydrocal and Densite). The additives studied were boric acid (H3BO3) and sodium chloride (NaCl), and these were added to the hemihydrate powders in concentrations of 2 wt% (in the case of H3BO3) and 0.5 wt% (in the case of NaCl). A large shrinkage was observed in the range of 300 to 500 degrees C, and this was greatly reduced when either H3BO3 or NaCl was present. The dehydration of gypsum (calcium sulfate dihydrate) was not completed until the initial stage of this large shrinkage was reached, but the phase transition of calcium sulfate anhydrite (III-CaSO4 to II-CaSO4) was the major cause for the large shrinkage. This phase transition occurred over a much wider temperature range than that suggested by the DTA-TG results. Dehydration conditions similar to those employed in wet calcination of gypsum appeared to be produced under atmospheric pressure when NaCl was present.
本研究通过同步差示热分析-热重分析法（DTA-TG）和膨胀测定法，研究了添加和未添加添加剂的铸型石膏试样的热行为。试样由湿煅半水合物（Hydrocal和Densite）制备而成。所研究的添加剂为硼酸（H3BO3）和氯化钠（NaCl），它们以2 wt%（对于H3BO3）和0.5 wt%（对于NaCl）的浓度添加到半水合物粉末中。在300至500摄氏度范围内观察到较大的收缩，当存在H3BO3或NaCl时，这种收缩会大大减小。石膏（二水硫酸钙）的脱水直到达到这种大收缩的初始阶段才完成，但无水硫酸钙（III-CaSO4向II-CaSO4）的相变是导致大收缩的主要原因。该相变发生的温度范围比DTA-TG结果所显示的要宽得多。当存在NaCl时，在大气压下似乎会产生与石膏湿煅所用条件相似的脱水条件。
