白榴石微晶化增强牙科玻璃陶瓷机制的实验研究

目的 探讨K2O(氧化钾）在白榴石微晶化增强牙科玻璃陶瓷的原材料组分与比例方面的规律以及白榴石微晶含量对该玻璃陶瓷抗压强度的影响。方法 利用特定的热处理温度程序对不同K2O含量的玻璃陶瓷原材料进行热处理，比较热处理后样品的显微结构及其中白榴石微晶的含量，测试各组玻璃陶瓷的抗压强度。结果 高钾配比组原材料热处理后的样品中白榴石微晶化情况良好，分布均匀，晶粒约0.8μm，其玻璃陶瓷的抗压强度可达206.6MPa。白榴石微晶化增强的牙科玻璃陶瓷的抗压强度与白榴石微晶含量之间呈相关关系。结论 K2O在原材料中的配比对白榴石微晶化及其增强的牙科玻璃陶瓷的显微结构和相关性能有较大影响。白榴石微晶含量对该玻璃陶瓷的抗压强度有明显影响。     

牙科可切削云母微晶玻璃呈色的研究

目的 研制用于牙科计算机辅助设计与辅助制作磨牙冠、可提供多种颜色选择的可切削四硅酸氟云母微晶玻璃。方法 采用正交设计技术，对影响微晶玻璃颜色的基础配方、色料组成及热处理制度进行筛选。结果 从基础配方中选择出影响呈色的2个主要因素：晶核剂F含量、Mg^2 ／K^ 比例；从多种色料中选择出主要色料CeO2；从热处理制度中选择出成核制度：650℃保持1h和晶化制度：1000℃或1050℃保持3h～4h,，结论 所研制的云母微晶玻璃，可提供4～5种牙科颜色，其切削性能良好，完全可以满足计算机辅助设计．辅助制作(CAD／CAM)系统的要求。     

K2O-Na2O-Al2O3-SiO2系统牙科微晶玻璃匹配氧化铝陶瓷的初步研究

目的:研究 K₂O-Na₂O-Al₂O₃-SiO₂系统牙科微晶玻璃匹配氧化铝陶瓷的热处理温度制度。方法:根据氧化铝陶瓷的热膨胀系数调整K₂O-Na₂O-Al₂O₃-SiO₂系统牙科微晶玻璃的原材料配比,利用K₂O-Na₂O-Al₂O₃-SiO₂系统牙科微晶玻璃的热处理温度制度形成微晶玻璃-氧化铝陶瓷复合材料;利用偏振光显微镜和X射线衍射分析仪观察样品的形态及显微结构特性,利用材料试验机测试材料的抗压强度。结果:经过原材料组份的调整,白榴石晶粒约1.0 μm、在玻璃基质中分布均匀;微晶玻璃-氧化铝陶瓷复合材料的抗压强度为500 MPa。结论:K₂O-Na₂O-Al₂O₃-SiO₂系统牙科微晶玻璃的热处理温度制度适合匹配氧化铝陶瓷。     

白榴石含量对K2O-Al2O3-SiO2系统牙科玻璃陶瓷的断裂韧性影响的实验研究

目的：确定白榴石含量与K2O-Al2O3-SiO2系统牙科玻璃陶瓷材料断裂韧性的关系,探讨白榴石含量影响K2O-Al2O3-SiO2系统牙科玻璃陶瓷断裂韧性的机理。方法：选择5组相同组分、不同比例的玻璃陶瓷原材料,经＂白榴石微晶化＂热处理工艺加工,制成含有不同白榴石含量的K2O-Al2O3-SiO2系统牙科玻璃陶瓷试件;用单边切口弯曲梁法测试样品的断裂韧性,计算断裂韧性值;分析样品的显微结构和测定白榴石含量;对5组样品的白榴石含量和断裂韧性值数据进行相关回归统计学分析。结果：白榴石晶粒约1.0μm、在玻璃基质中分布均匀;K2O-Al2O3-SiO2系统牙科玻璃陶瓷的断裂韧性与白榴石含量有相关关系。结论：白榴石含量对K2O-Al2O3-SiO2系统牙科玻璃陶瓷的断裂韧性有明显影响,在一定范围内,该陶瓷的断裂韧性随白榴石含量增高而增大。     

氧化铝含量对牙用四硅氟云母微晶玻璃性能的影响

目的：研究氧化铝含量改变对CAD／CAM加工用四硅氟云母微晶玻璃的微观结构及力学性能的影响。方法：采用K2O-MgO-MgF2-SiO2系统研制四硅氟云母微晶玻璃，通过扫描电镜观测及力学性能测试，比较在两个不同晶化温度(1060℃和1160℃)下，三种不同氧化铝含量(0％、1％和2％)，对四硅氟云母徽晶玻璃的微观结构及力学性能的影响。结果：增加氧化铝的含量可以减小微晶玻璃的晶粒尺寸和径厚比；当晶粒直径介于2～5μm之间时，材料的三点弯曲强度及断裂韧性最好，过大和过小的晶粒尺寸和径厚比都不利于材料力学性能的提高。结论：云母微晶玻璃的微观结构随氧化铝含量的改变而改变，增加氧化铝含量可以降低云母微量玻璃的析晶能力。     

氧化钾的含量对牙科微晶玻璃析晶性能的影响

目的 研究氧化钾（K2O）的含量对牙科微晶玻璃析晶性能的影响。方法 在Li2O-SiO2-Al2O3-P2O5-ZnO体系的基质玻璃中添加不同含量的K2O,根据差热分析（DTA）曲线确定微晶玻璃的热处理制度,采用X射线衍射分析和扫描电子显微镜（SEM）观测来比较不同的K2O含量对牙科Li2O-SiO2-Al2O3-P2O5-ZnO体系微晶玻璃析晶成分和显微结构的影响。结果 K2O的引入有助于降低玻璃基体的粘度,促进基质玻璃的析晶。在基质玻璃中添加5.3 wt%的K2O可以使玻璃在热处理后析出较多的二硅酸锂晶体,晶体呈板条状,长度约为4 μm,在玻璃基质中分布均匀。 结论 添加一定量的K2O有助于提高牙科Li2O-SiO2-Al2O3-P2O5-ZnO体系微晶玻璃的析晶性能。     

牙科用云母微晶玻璃的微观结构对其力学性能的影响

目的：研究牙科CAD／CAM加工用四硅氟云母微晶玻璃的微观结构对其力学性能的影响，方法：采用K2O－MgO-MgF2-SiO2系统来研制云母微晶玻璃，通过差热分析（DTA），X射线衍射分析（XRD），扫描电子显微镜观测（SEM）及力学性能测试，比较了三种不同晶化温度下，四硅氟云母微晶玻璃的微观结构对其力学性能影响，结果：随着晶化温度的逐步升高，四硅氟云母的晶粒大小和径厚比逐步增大，抗弯强度和断裂韧性亦逐渐增高，维氏硬度和脆性指数随温度升高而降低。结论：云母微晶玻璃的微观结构对其力学性能起决定作用，而微观结构与晶化温度密度相关。     

氧化锂含量对牙科云母微晶玻璃析晶性能的影响

目的:研究Li2O对SiO2-Al2O3-MgO-Na2O-K3O-F云母玻璃陶瓷析晶性能、显微结构和抗弯强度的影响.方法:在玻璃基础成分中添加不同含量的Li2O,由差热分析(DTA)曲线确定热处理制度,采用X射线衍射分析(XRD)、扫描电子显微镜(SEM)和三点弯曲强度测试来观测和比较晶体成分、形貌和材料的力学性能.结果:3组玻璃的核化温度为530℃,最适晶化温度随Li2O含量的增加而降低.680℃热处理1 h后,含4%Li2O的母体玻璃析出的云母晶体发育完全,抗弯强度最高(183.82±12.47)MPa.结论:添加一定量的Li2O有助于改善SiO2-Al2O3-MgO-Na2O-K2O-F系云母玻璃陶瓷的析晶性能和力学强度.     

牙科用云母微晶玻璃的微观结构对其力学性能的影响

目的 :研究牙科CAD/CAM加工用四硅氟云母微晶玻璃的微观结构对其力学性能的影响。方法 :采用K2 O -MgO -MgF2 -SiO2 系统来研制云母微晶玻璃 ,通过差热分析 (DTA)、X射线衍射分析 (XRD)、扫描电子显微镜观测 (SEM )及力学性能测试 ,比较了三种不同晶化温度下 ,四硅氟云母微晶玻璃的微观结构对其力学性能影响。结果 :随着晶化温度的逐步升高 ,四硅氟云母的晶粒大小和径厚比逐步增大 ,抗弯强度和断裂韧性亦逐渐增高 ,维氏硬度和脆性指数随温度升高而降低。结论 :云母微晶玻璃的微观结构对其力学性能起决定作用 ,而微观结构与晶化温度密切相关     

晶化热处理对牙用玻璃陶瓷断裂韧性的影响

目的：探讨热处理过程对玻璃陶瓷断裂性能的影响。方法：按不同晶化温度条件分组，利用X射线衍射技术鉴定晶相，计算结晶率，同时采用显微压痕法测量相应条件下材料的显微硬度（Hv)及断裂韧性（KIC)。结果：该材料的主晶相为四硅酸氟云母晶体，在830℃-950℃的晶化温度范围内，随晶化温度升高，结晶率呈上升趋势，HV和KIC也不断增大，且与结晶率之间存在相关关系。结论：玻璃陶瓷的结晶过程是影响其断裂韧性的重要因素。     

Water-enhanced crystallization of leucite in dental porcelain

OBJECTIVE: The purpose of this study was to determine whether long-term exposure of dental porcelain to saliva during temporary cementation of a porcelain-fused-to-metal (PFM) restoration could enhance leucite crystallization if the restoration is refired. Such water-enhanced leucite crystallization in dental porcelains could lead to porcelain-metal thermal incompatibility problems. METHODS: Six commercial dental body porcelains and the Component No. 1 (leucite-containing) frit of the Weinstein et al. [13] patent were studied. For each porcelain, 30 coupon specimens were randomly assigned to a treatment group. Ten specimens were placed in artificial saliva, 10 in distilled water, and 10 in a desiccator and were stored for six months. At the end of the six months, an additional 10 coupons of each porcelain were prepared to serve as a control. All 40 specimens of each porcelain were randomized and subjected to one additional firing. Leucite weight fraction was determined by quantitative X-ray powder diffraction analysis via an internal standard technique. RESULTS: Comparisons among the treatments via the least-squares-means test-adjusting for porcelain showed that the saliva group mean leucite weight fraction was significantly higher than that of the other groups. The change in porcelain thermal expansion that would be associated with a leucite change in this range would be between 0.2 x 10(-6) K-1 and 0.3 x 10(-6) K-1. SIGNIFICANCE: The results of this work constitute the first demonstration that moisture absorbed by a porcelain can act as a glass modifier and enhance the crystallization of the glass during subsequent firing. The effect was sufficiently large to generate thermal expansion changes that would exceed the maximum safe mismatch between porcelain and metal.     

High-temperature X-ray diffraction measurement of sanidine thermal expansion

Dental porcelains that are designed to be fused to PFM (porcelain-fused-to-metal) alloys are formulated by their manufacturers to be closely matched in thermal expansion to these alloys. The high thermal expansion of the mineral leucite has been exploited to regulate porcelain expansion. Leucite, however, has been observed to convert to the sanidine polymorph of feldspar during certain heat treatments within the normal firing range of dental porcelain. The effects of this conversion on porcelain thermal expansion and porcelain-metal thermal compatibility have been uncertain, due to the paucity of published data on the thermal expansion of sanidine. The purpose of this study was to measure the thermal expansion of sanidine by high-temperature X-ray diffraction over the temperature range in which thermal mismatch stresses can develop in porcelain-fused-to-metal restorations, i.e., from room temperature to 700 degrees C. The lattice parameters a, b, c, and beta were determined from the d-spacings and hkl values of multiple reflections by means of a least-squares iteration. The dependence of each lattice parameter on temperature was determined via analysis of variance, and the coefficient of thermal expansion, alpha, was obtained from this analysis. The lattice parameters of sanidine at room temperature were determined to be: a = 0.8524 +/- 0.0015 nm, b = 1.3020 +/- 0.0004 nm, c = 0.7165 +/- 0.0002 nm, and beta = 116.02 degrees +/- 0.01 degree (mean +/- 95% confidence interval). The linear thermal expansion coefficient, a, over the range from room temperature to 700 degrees C was determined to be 4.1 x 10(-6) K(-1) +/- 0.6 x 10(6) K(-1) (mean +/- 95% confidence interval). Because the coefficient of thermal expansion for sanidine is substantially lower than that of leucite (the effective linear thermal coefficient of thermal expansion of leucite over the range of 25 degrees to 700 degrees C is 28 x 10(-6) K(-1)), the conversion of leucite to sanidine during porcelain heat treatments would produce a detrimental lowering of the porcelain thermal expansion.     

Isothermal phase transformations of a dental porcelain.

OBJECTIVES: The purpose of this investigation was to determine if the change in the leucite weight fraction during an isothermal heat treatment could be estimated by observing the deformation of PFM strips in a high-heating-rate, computer-controlled bending beam viscometer (BBV). METHODS: Specimens of a commercial body porcelain were fired according to the manufacturer's instructions-50 disk specimens for quantitative X-ray diffraction (XRD) and 100 bimaterial strip specimens for BBV. The XRD specimens were annealed at temperatures between 650 and 1000 degrees C, and leucite weight fraction was measured using an alumina internal standard. The BBV specimens were annealed in the BBV using time-temperature schedules designed to elucidate the leucite crystallization behavior between 700 and 1000 degrees C. Timoshenko's equation for a bimaterial thermostat was used to estimate the change in the thermal expansion of the porcelain near room temperature. Changes in leucite weight fraction were determined from these thermal expansion changes. RESULTS: The means and SDs were compared to values obtained by quantitative XRD. Good agreement was obtained between values of leucite weight fraction derived from beam deformation and those determined by quantitative XRD (p> or =0.45). The anneal sequence showed that the increase in leucite weight fraction at 800 or 900 degrees C is reversible by an anneal at 1000 degrees C. SIGNIFICANCE: The BBV technique yields comparable results to quantitative XRD and provides the opportunity to efficiently monitor porcelain leucite changes nondestructively over multiple heat treatments. This technique could prove useful for testing firing schedules designed to stabilize the leucite content in dental porcelain.     

Crystallization of high-strength fine-sized leucite glass-ceramics

Manufacturing of leucite glass-ceramics often leads to materials with inhomogeneous microstructures. Crystal-glass thermal mismatches which produce microcracking around larger crystals-agglomerates are associated with reduced mechanical properties. The hypotheses were that fine (< 1 μm) crystal size and uniform microstructure in a thermally matched glass would increase the biaxial flexural strength (BFS). Glass was synthesized, attritor-milled, and heat-treated. Glasses and glass-ceramics were characterized by XRD, SEM, and Dilatometry. Experimental (A, M1A and M2A) and commercial glass-ceramics were tested by the BFS test. Experimental glass-ceramics showed an increased leucite crystal number and decreased crystal size with glass particle size reduction. Leucite glass-ceramics (< 1 μm) showed minimal matrix microcracking and BFS values of [mean (SD) MPa]: M1A = 253.8 (53.3); and M2A = 219.5 (54.1). Glass-ceramics M1A and M2A had higher mean BFS and characteristic strength than the IPS Empress Esthetic glass-ceramic (p < 0.05). Fine-grained, translucent leucite glass-ceramics were synthesized and produced high mean BFS.     

Stress induced phase transformation of a cesium stabilized leucite porcelain and associated properties.

OBJECTIVES: The addition of CS2O to dental porcelains might provide a means for controlling the thermal expansion and toughness of feldspathic porcelains. The purpose of this investigation was to determine for a leucite porcelain the effect of CS2O content upon its coefficient of thermal expansion (alpha), toughness, hardness, and content of low (tetragonal) leucite and high (cubic) leucite. METHODS: In order to determine the amount of low leucite in the specimens, an x-ray calibration curve for low leucite and an internal standard of copper was obtained using quantitative x-ray diffraction techniques. Utilizing a stress induced phase transformation between low and high leucite, an x-ray intensity conversion ratio (r) was determined for high leucite so that the calibration curve for low leucite could be used to determine the amount of high leucite present in the experimental porcelains. Specimens were prepared with various amounts of CS2O (0.0, 0.5, 1.0, 1.5, 2.0 mol%) so that, except for the as-received porcelain (A), all had the same thermal history. Specimens were tested for content of low and high leucite, hardness (Vickers), toughness (indentation-strength method), and coefficient of thermal expansion (alpha) over two temperature ranges (30-500 degrees C and 30-640 degrees C). Fractured surfaces were examined with a scanning electron microscope (SEM). For each property, specimen groups were compared for statistical differences. These comparisons were statistically analyzed using analysis of variance (ANOVA) and Fisher's protected least significant differences (PLSD). RESULTS: Quantitative x-ray examination of abraded and heat-treated specimens demonstrated that a stress induced phase transformation occurred which could be reversed by heat treatment. The conversion ratio was determined as r = 1.93 +/- 0.29. The addition of CS2O lowered the wt% of low leucite from 63 +/- 6% to 0% and increased the amount of high leucite from 0% to 62 +/- 5%. ANOVA showed that the addition of CS2O had a significant effect on alpha (p < 0.0001), hardness (p < 0.005), and toughness (p < 0.0001). CS2O significantly (PLSD) lowered the alpha (p < 0.0001), hardness (p < 0.01), and toughness (p < 0.0001) of a high-content leucite porcelain. SIGNIFICANCE: A stress induced phase transformation of high leucite to low leucite was demonstrated and, as a consequence, suggested the potential for phase transformation toughening. The alpha of a leucite porcelain could be controlled by stabilizing high (cubic) leucite to room temperature with the fraction of high leucite dependent upon the amount of CS2O added. A method was developed to determine the amount of high leucite present in a porcelain.     

Plat-Ⅱ型铸造玻璃陶瓷晶化热处理程序的研究

探讨Ｐｌａｔ－Ⅱ型铸造玻璃陶瓷化热处理程序。方法本实验以Ｐｌａｔ－Ⅱ型铸造玻璃瓷材料的差为基础,首先确定该材料的晶化温度范围,再用扫描电镜观察各种受控温度处理下试件晶化的情况,以确定Ｐｌａｔ－Ⅱ型铸造玻璃陶瓷的晶经热处理程序。