Preliminary Research On Synthesis Of A Kind Of Dental Gypsum Of Molding Materials

[Objective] To base on domestic and oversea productive technology and principle of gypsum, to combine with development of modern resin, and to improve traditional productive technology exploratively, the aim is to analyze influential factors in the course of synthesis of hemihydrated gypsum, enhance purity of hemihydrated gypsum on productive technology, synthesize a kind of dental gypsum and research preliminary on these existing questions about insufficient mechanical strength and worse surface hardness of present gypsum of molding materials to certain extent. [Methods] To classify these three influential factors as distilled water group, Calcium Chloride gypsum and sodium Succinate group. To adopt high purity of dehydrated gypsum, Calcium Chloride and sodium Succinate as raw materials, and add supplementary additives into test group's study gypsum, additives are Postassium Sulfate, Calcium Oxide and Gum Arabic. After improving traditional productive technology of gypsum exploratively, to synthesize hemihydrated gypsum through controlling strictly pressure and temperature in the course of productive technology, and compare study gypsum's physical and mechanical properties with Shanghai Heraeus superhard gypsum's of control group. To analyze results through statistical methods, and possess significant difference when P<0.05(a=0.05). [Results] To observe that effect of volume of distilled water on synthesis of hemihydrated gypsum is bigger, and the effect better when distilled water: raw materials as 150ml:100g; whereas effect of Calcium Chloride and sodium Succinate smaller, and the effect better when Calcium Chloride: dehydrated gypsum as 1:2, sodium Succinate as 0.75%. after lots of explorative researches and refer to domestic and oversea main productive technology ,the productive technology's parameters of study gypsum are as follows: distilled water: raw materials as 165ml : 100g, Calcium Chloride : dehydrated gypsum as 1:2, sodium Succinate as 0.75%; vapouringtemperature as 142℃, pressure as 0.3Mpa, time as 6h, drying temperature as 120℃, time as 4h. Comparison study gypsum's properties of test group with Shanghai Heraeus superhard's of control group is as follows: percentage of hemihydrated gypsum, crystal shape, Brinell hardness, compressive strength, bending strength, expanding ratio and water/powder(W/P) are, respectively, 91.61%, 88.51%, short prism; 13.3@0.2927HB, 8.98 @ 0.5193HB; 56.30176 @2.45594Mpa, 53.03302 @ 3.41610Mpa; 9.634 @ 0.73645Mpa, 14.683 @ 1.01473Mpa; 9.250E-02@2.5000E-02, 9.000E-02@5.1335E-02; 20%, 22%. Statistical analysis indicates: significant difference is observed between Brinell hardness and bending strength of the test group and the control group's (P<0.05); significant difference is not observed between two groups' compressive strength (P>0.05); in addition, significant difference is not observed between two groups' expanding ratio, either.[Conclusion] Effect of volume of distilled water bigger; but effect of Calcium Chloride and sodium Succinate smaller. Study gypsum' s physical and mechanical properties of test group is basically similar to Shanghai Heraeus superhard gypsum's of control group.