Department of Biomaterials & Bioengineering, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramotocho,Tokushima 770-8504, Japan.
Dent Mater J. 2012 Feb 3;31(1):120-4. doi: 10.4012/dmj.2011-199. Epub 2012 Jan 21.
The porosity of gypsum-bonded investments for set and heated compacts was measured and theoretically computed quantitatively, because porosity is an effective factor for determining the strength, setting/heating expansion, and permeability of compacts at casting. A helium gas pycnometer was used to measure the solid volume of fine powders, powder-water mixtures, and porous compacts. The compositions of the conventional cristobalite investment and rapid-heating type investment were estimated from the measured solid densities of the as-received powders and the set investments. The porosity and water content of the set investments were determined from the experimental data. Excess water content in the set investment was calculated in relation to the elapsed time from the start of mixing with water. The experimental porosities of the set and heated investments were about 40% for dry set >compacts and about 50% for fired compacts, which well agreed with the numerically computed estimations, respectively.
石膏结合剂的铸造包埋材料的多孔性已被测量并进行了定量理论计算，因为多孔性是决定铸模强度、凝固/加热膨胀和渗透性的有效因素。氦气比重瓶被用于测量细粉末、粉末-水混合物和多孔铸模的固体体积。传统的方石英包埋料和快速加热型包埋料的组成是根据收到的粉末和凝固的包埋料的实测固体密度来估算的。凝固包埋料的多孔性和含水量是根据实验数据确定的。凝固包埋料中的多余水分含量与开始与水混合后的时间有关。干燥凝固>铸模的凝固和加热包埋料的实验多孔性约为 40%，烧制铸模的多孔性约为 50%，分别与数值计算的估算值很好地吻合。
