牙科长石瓷的可加工性研究

对放电等离子烧结技术（SPS）制备的样品和德国产品Vita Mark Ⅱ样品进行同条件的CAD／CAM加工，并对成型性、表面光洁度、咬合情况等进行对比。通过可加工指数指标对长石瓷的可切削性进行了评价，探讨了长石瓷可切削性的机理．结果表明，SPS制备的长石瓷具有良好的加工性，能够满足临床应用的要求。     

放电等离子烧结纳米晶ZrO2陶瓷研究

采用放电等离子烧结技术对纳米级ZrO2粉体进行致密化研究.运用XRD、SEM、TEM以及显微硬度仪对粉末及块体进行分析.实验结果表明运用放电等离子烧结技术对ZrO2(3Y)粉体进行致密化无法同时实现晶粒度与相对密度的最佳结合.目前,最佳晶粒尺寸100nm左右时相对密度95.8%,最大Kic=11.85MPa·m1/2.     

放电等离子烧结法制备牙科陶瓷的研究

采用放电等离子烧结(SPS)法制备长石类牙科陶瓷,研究了烧结工艺对其性能的影响。结果表明,在压力30MPa,烧结升温速度100℃/min,烧结温度1120-1300℃下,SPS能够实现长石瓷的高密度烧结,断裂韧性达到1.4MPa·m1/2以上。     

放电等离子烧结中颈部形成机理探讨

放电等离子烧结(Spark Plasma Sintering,简称SPS)是一种新的固体压缩烧结技术,它具有升温速度快、烧结时间短、冷却速度快、外加压力和烧结气氛可控、节能环保等鲜明特点,成为材料发展和组织优化的有力工具.SPS在材料制备中的应用越来越广泛,但现阶段对SPS烧结过程的认识远未形成统一观点.SPS过程中颈部的形成是一个关键的阶段,影响到整个烧结过程.本文针对火花等离子烧结颈部的形成机理进行分析认为(1)在SPS烧结非金属材料过程中颈部的形成机理可能是塑性变形和蠕变;(2)导电材料烧结颈部形成过程中可能有火花放电现象发生,其主要机理可能是熔化和凝固、塑性变形、蠕变.同时,本文以纯铜为例,对其SPS烧结过程和结果进行了分析,对烧结过程中颈部的形成情况进行观察,并给出了解释.     

新型牙用碳纳米管种植体材料的制备

采用放电等离子烧结(SPS)法,在烧结温度为1 200℃,压力从20 MPa到60 MPa的条件下,以聚碳硅烷(PCS)为结合剂,制备出一种新型的大块多壁碳纳米管(MWCNTs).用SEM和TEM进行观察.结果表明,烧结后材料的纳米级结构仍被保留;XRD分析显示,纳米管通过聚碳硅烷热解的SiC纳米晶相互粘结;随着PCS含量的增加及烧结压力的升高,材料的密度和维氏硬度增加,比表面积减少.动物试验表明,CNTs/PCS材料的炎性反应随着PCS含量增加有轻度增加;通过此种方法制备的碳纳米管,物理性能接近于骨组织,且具有较好的生物相容性,是适宜的候选牙用种植体材料.     

放电等离子烧结(SPS)YAG陶瓷的初步研究

研究了采用放电等离子烧结(Spark Plasma Sintering SPS),利用高纯的氧化钇和氧化铝,在1500～1700℃,真空度优于10Pa,反应快速合成YAG陶瓷,但试样的致密度不高,而低气孔率是制备透明陶瓷的关键,实验表明,TEOS的掺加和粉料粒度的减小对烧结试样致密度的提高有一定的作用.     

放电等离子烧结与传统烧结法制备（Ba，Sr）TiO3陶瓷的性能比较

研究分别采用了放电等离子烧结方法(Spark Plasma Sintering,SPS)和普通烧结方法,对(Ba,Sr)TiO3陶瓷进行不同温度下的烧结(1200～1300℃),进而研究了放电等离子烧结对(Ba,Sr)TiO3陶瓷性质的改良能力.实验表明,同温度下SPS法烧结的(Ba,Sr)TiO3陶瓷具有更大的相对介电常数,更低的电流损耗.同时,从SEM照片中观测到SPS烧结法可以较好的改进陶瓷的表面致密度.另外,1240℃下用SPS方法烧结的(Ba,Sr)TiO3陶瓷有着最优良的性质.     

可加工陶瓷研究的新进展

从微观结构设计出发,进行可加车性能的研究已成为陶瓷材料研究领域的热点之一。从改善陶瓷材料可加工性的方法着手,简要介绍可加工陶瓷研究的新进展,并对各种方法的优点与不足之处进行评述。     

非传统粉末冶金制备生物医用多孔钛及其性能

以生物医用球形雾化钛粉为原料,碳酸氢铵做造孔剂,采用放电等离子烧结(SPS)技术制备了生物医用多孔钛块体材料。采用XRD、SEM分别对所制备的多孔钛的物相组成、微观形貌进行分析,并研究了多孔钛的力学性能及成骨细胞在其表面的粘附生长情况。结果表明:通过调节造孔剂添加量、控制烧结工艺可制备孔隙率为50.3%～70.5%、孔径为100～300μm的多孔钛,其力学性能(抗压强度为24.40～68.96MPa、弹性模量为1.010～1.287GPa)与人体松质骨相匹配。与SD大鼠成骨细胞的联合培养结果表明,该材料的粗糙表面和多孔结构可粘附生长成骨细胞,具有良好的生物相容性。     

电解铜粉和雾化铜粉对SPS过程中显微组织演变的影响

以电解铜粉和雾化铜粉为SPS烧结原材料,对它们在SPS烧结过程中的烧结曲线、烧结体显微组织的演变过程,以及烧结温度对烧结体相对密度的影响进行了分析、比较,并分析了其中的原因。得到电解铜粉和雾化铜粉在SPS烧结过程中显微组织演变特征和规律不同的结论。     

Study on machinable glass-ceramic containing fluorophlogopite for dental CAD/CAM system

The glass-ceramic mainly containing fluorophlogopite is one of widely used dental ceramics. In the K₂O-CaO-MgO-Al₂O₃-SiO₂-F system, a new-type glass-ceramic containing fluorophlogopite Ca-mica has been synthesized. Its crystalline was studied by XRD and EDS. The fluorophlogopite whose formula postulated K_{1 − X} Ca _X/2Mg₃AlSi₃O₁₀F₂ was its main crystalline. The microstructure of the glass-ceramic displayed typical machinable microstructure with lath like crystals isolated and interlocking with different aspect ratio. The material also showed better bending strength (228.11 ± 7.55 MPa). It took less than 12 minutes to fabricate a whole crown by dental CAD/CAM system with the glass-ceramic.     

Kinetics of isothermal phase transformations in a dental porcelain

The dissolution of leucite (KAlSi₂O₈) and the precipitation of sanidine (Na _x K_1–x AlSi₃O₈; 0.1<x<0.3), occurring during isothermal heat treatments of a dental porcelain for porcelain-fused-to-metal restorations, was studied. The identification of phases was performed by X-ray diffraction, optical and scanning electron microscopy. An isothermal time-temperature-transformation (TTT) diagram, from 800 to 1000°C, and for periods up to 1440 min, is proposed. No metastable cubic leucite was retained by air-quenching in any sample. No increase of leucite volume fraction was observed.     

Effect of surface topography on the color of dental porcelain

The objectives of this study were to evaluate the color difference depending on the surface topography of roughness and glazing, and to determine the effects of color measuring geometry and the standard illuminant on the color of a dental porcelain. Disk specimens of A3 shade were fired with commercial dental porcelain for PFM. Specimens were divided into non-polished (ST 1), polished with 200, 400, 1000, 1500-grit SiC papers (ST 2, 3, 4, 5) and glazed (ST 6) groups. After measuring the average surface roughness (Ra), color was determined under the illuminant A and D65 on a spectrophotometer with the specular component excluded (SCE) and included (SCI) geometry. Ra values were significantly influenced by the surface topography. With the SCE, the CIE L* value after glazing was significantly lower than that after polishing. Color differences (E*) measured with the SCE were higher than those with the SCI (2.61–4.66 vs. 0.93–1.57). Therefore the SCE geometry seemed to more accurate protocol for the color measurement of dental porcelain.     

Microstructure effect on the properties of a commercial low-fusing dental porcelain

The aim of this study was to investigate the effect of firing cycle on a dental porcelain microstructure in order to correlate microstructure changes with mechanical and thermal properties. A commercial low-fusing dental porcelain powder (Omega 900, Vita) was investigated for this purpose. The powder was treated at different temperatures in the range 750–1000 °C. The fired samples were characterized in terms of their morphology and microstructure, and their mechanical and thermal properties were evaluated. The results showed that firing temperature affects porcelain microstructure influencing significantly in this way both the mechanical properties and the thermal expansion coefficient of the fired objects. Firing at 800 °C led to a homogeneous structure. After treatment at this temperature, the leucite crystals exhibit their maximum concentration and they are well dispersed into the glassy phase. As a consequence the optimum mechanical strength and the maximum thermal expansion coefficient are observed in these samples.     

Effect of transient stress on acoustic emission behaviour during firing of dental porcelain

Acoustic emission activity was measured in the glass transition range of dental porcelain during firing. Transient and residual stresses in porcelain during cooling from a temperature higher than porcelain sag point and during re-heating of the tempered porcelain were calculated by computer simulation using a viscoelastic stress analysis. The detected acoustic emission event was discussed with the relative rules of the simulated transient stresses. High acoustic emission activity was detected at the temperature where the internal stress faded away for heating and build up for cooling. The low-level acoustic emission pulses were only detected in the following conditions: (1) in the temperature range where porcelain behaved like an elastic solid; (2) at temperatures higher than the deformation point of porcelain; (3) with a re-heating process of the porcelain without tempered stress. From these results, it was concluded that elastic energy is released related to transient stress in porcelain during viscoelastic deformation and can be detected by the acoustic emission method. The acoustic emission method is considered to be helpful in non-destructive testing in order to understand transient stress due to viscoelastic deformation of glassy materials in heat treatment.     

Ageing reactions in a high carat gold alloy for dental porcelain bonding

The phase transformation during continuous heating of a high carat gold alloy used for porcelain bonding was investigated by electrical resistivity measurements, hardness tests, X-ray diffraction and scanning and transmission electron microscopy. Four reaction stages (I, II, III and IV) were found. Stage I corresponded to the formation of a short-range order. A discontinuous precipitation took place in stage II, which contributed to remarkable hardening. Stages III and IV were reactions to the stable phases at each temperature region, and resulted in softening. The activation energies for stages I, II and III are 27.1, 33.8 and 58.2 kcal/mol, respectively.