Hojjatie B, Anusavice K J
Department of Dental Biomaterials, College of Dentistry, University of Florida, Gainesville 32610-0446.
J Dent Res. 1993 Mar;72(3):566-71. doi: 10.1177/00220345930720030201.
The objective of this study was to test the hypothesis that quenching of porcelain in silicone oil rather than in compressed air will significantly increase the flexure strength by reducing the potential for crack formation during transient cooling. A secondary hypothesis to be tested is that the initial tempering temperature can be reduced significantly below the porcelain maturing temperature of 982 degrees C but well above Tg without a decrease in strength. Opaque-body porcelain disks, 16 mm in diameter and 2 mm in thickness, with a thermal contraction mismatch (delta alpha) of -1.5, 0, and +3.2 ppm/degrees C were tempered from initial temperatures of 650, 750, 850, and 982 degrees C in silicone oil with kinematic viscosities of 50, 1000, and 5000 centistokes. Porcelain disks were also subjected to three cooling procedures in air: slow cooling in a furnace (SC), free convective cooling in a laboratory bench (FC), and tempering (T) by blasting the surface of body porcelain with air. The crack size induced by a Vickers microhardness indenter was measured within one minute after crack development. For determination of the influence of initial cooling temperature on biaxial flexure strength, six body porcelain disks (delta alpha = 0) were tempered in air from initial temperatures of 650, 750, 850, and 982 degrees C. The mean crack size of specimens tempered in oil was significantly smaller (p < or = 0.001) than that of specimens that were slowly-cooled or fast-cooled in air for all thermal contraction mismatch cases.(ABSTRACT TRUNCATED AT 250 WORDS)
与在压缩空气中骤冷相比，在硅油中骤冷能通过降低瞬态冷却过程中裂纹形成的可能性，显著提高弯曲强度。另一个待验证的次要假设是，初始回火温度可大幅降至低于982℃的瓷成熟温度，但远高于玻璃化转变温度（Tg），且强度不会降低。对直径16毫米、厚度2毫米、热收缩失配（δα）为-1.5、0和+3.2 ppm/℃的不透明体瓷盘，在运动粘度为50、1000和5000厘沲的硅油中，从650、750、850和982℃的初始温度进行回火处理。瓷盘还在空气中经历了三种冷却程序：在炉中缓慢冷却（SC）、在实验室工作台上自由对流冷却（FC）以及通过向体瓷表面喷气进行回火处理（T）。在裂纹产生后一分钟内，测量维氏显微硬度压头引起的裂纹尺寸。为确定初始冷却温度对双轴弯曲强度的影响，对六个体瓷盘（δα = 0）在空气中从650、750、850和982℃的初始温度进行回火处理。在所有热收缩失配情况下，油中回火处理的试样的平均裂纹尺寸明显小于在空气中缓慢冷却或快速冷却的试样（p≤0.001）。（摘要截选至250字）
