DENTAL INVESTMENT BASED ON NEW EXPANSION MECHANISM

利用一种新型磷酸铝化合物亚磷酸铝Al_2(PHO_3)_3的热分解和分解相的结晶生长，研制了牙用投资、石膏结合投资和磷酸盐结合投资。用x射线衍射和气相色谱法研究了作为耐火材料加入的亚磷酸铝的热分解过程。室温下为无定形的亚磷酸铝随着温度的升高而膨胀，而进一步加热时转变为正磷酸铝和甲基磷酸铝的晶体生长，这有助于投资的大幅膨胀。由于热膨胀的量可以毫无困难地调节，因此有可能开发仅使用膨胀的牙科投资。采用添加亚磷酸铝作为耐火材料制备石膏粘结投资料，并对其物理性能进行了研究。用MOD金属模具对银钯金合金铸件的适应性进行了检验。可以在不改变处理性能（如水粉比、流量和凝固时间）的情况下调节加热膨胀量。尽管如此，用这种试验投资获得的铸件表现出良好的适应性和外表面光滑。通过控制Al_2(PHO_3)_3的加入量，可使固化膨胀率降至0.2%以下，具有较高的抗压强度。在牙科材料中添加SiO_2作为附加耐火材料，当控制Al_2(PHO_3)_3和SiO_2的用量时，热膨胀率几乎呈线性增加。

Dental investments, gypsum-bonded and phosphate-bonded investments were developed using the expansion originating form thermal decomposition and crystal growth of decomposed phases of a new aluminum phosphate compound, aluminum phosphite Al_2(PHO_3)_3. The thermal decomposition of aluminum phosphite that was added as a refractory was investigated thermal analytically together with x-ray diffraction and gas-chromatography. The aluminum phosphite, which was amorphous at room temperature, expanded as the temperature increased, while transforming to crystal growth of aluminum orthophosphate and aluminum methaphosphate, which took place when heated further, contributed to a large expansion of the investments. Since the amount of thermal expansion could be regulated without any difficulty, it would be possible to develop dental investments that employ expansion alone.Gypsum-bonded investment was prepared by addition of aluminum phosphite as a refractory and some physical properties were investigated. Also adaptability of castings made of Ag-Pd-Au alloys was examined with MOD metal mold. It was possible to regulate amounts of heating expansion without changing handling properties such as water-to-powder ratio, flow and setting time.Nevertheless, the castings obtained with this trial investments showed good adaptability and their outer surfaces were smooth. Also the compressive strength was shown to be high enough for use as dental investments and the setting expansion could be lowered to less than 0.2% by controlling the amount of Al_2(PHO_3)_3 added. With a dental investment, in which SiO_2 was added as an additional refractory, the thermal expansion increased almost linearly during the heating when the amounts of Al_2(PHO_3)_3 and SiO_2 were controlled.