Influence of Amorphous Grain Boundary Phases on the Superplastic Behavior of 3-mol%-Yttria-Stabilized Tetragonal Zirconia Polycrystals (3Y-TZP)

Amorphous silicate grain boundary phases of varying chemistry and amounts were added to 3Y-TZP in order to determine their influence on the superplastic behavior between 1200° and 1300°C and on the room-temperature mechanical properties. Strain rate enhancement at high temperatures was observed in 3Y-TZP containing a glassy grain boundary phase, even with as little as 0.1 wt% glass. Strain rate enhancement was greatest in 3Y-TZP with 5 wt% glass, but the room-temperature hardness, elastic modulus, and fracture toughness were degraded. The addition of glassy grain boundary phases did not significantly affect the stress exponent of 3Y-TZP, but did lower the activation energy for superplastic flow. Strain rate enhancement was highest in samples containing the grain boundary phase with the highest solubility for Y₂O₃ and ZrO₂, but the strain rate did not scale inversely with the viscosity of the silicate phases. Grain boundary sliding accommodated by diffusional creep controlled by an interface reaction is proposed as the mechanism for superplastic deformation in 3Y-TZP with and without glassy grain boundary phases.     

刚性光纤元件芯皮玻璃的酸溶性

五个系统玻璃试样置于不同酸溶液中浸泡不同时间,然后测量其浸泡前后厚度、重量及分光光谱透过率。结果表明:玻璃的酸溶性与时间、温度和酸浓度以及玻璃的组成有关;碱硼硅酸盐和铅硅酸盐玻璃在酸或碱溶液中浸泡后几乎无变化,适于作微通道板和凹陷面板皮玻璃;镧硼硅酸盐、镧钡硼硅酸盐和镧钡硼酸盐玻璃在酸溶液中有不同程度的重量损失。只要选用合适的酸溶液配方,就能设计出相应的微通道板和凹陷面板芯玻璃。     

Low-Temperature Aging of t'-Zirconia: The Role of Microstructure on Phase Stability

Polycrystalline, tetragonal ( t ') zirconia samples containing 3 and 4 mol% yttria were fabricated by annealing pressureless-sintered samples in air at ∼ 2100°C for 15 min. The grain size of these fully tetragonal samples was on the order of 100 to 200 μm. Domain structure of the samples and of a 3-mol%-yttria-doped tetragonal zirconia single crystal was examined by transmission optical microscopy under polarized light and by transmission electron microscopy. The orientations of the domain/colony boundaries were in accord with the predictions of group theory. As-polished surfaces of polycrystalline t ' materials showed no monoclinic phase even after 1000 h at 275°C in air. By contrast, conventionally yttria-doped tetragonal zirconia polycrystalline (Y-TZP) ceramics of grain size >0.5 μm showed substantial transformation. Surface grinding enhanced the resistance to degradation of Y-TZP but decreased that of t ' materials. Even then, the t ' materials exhibited better resistance to degradation than the Y-TZP ceramics. Excellent resistance of the t ' materials to low-temperature aging despite a very large grain size and the opposite effect of grinding on phase stability are all explained on the basis of ferroelastic domain structure of these materials.     

Corrosion of Alumina in Aqueous Hydrofluoric Acid

A variety of alumina-based ceramics were evaluated for dissolution in an azeotropic aqueous hydrofluoric acid test protocol at temperatures up to 200°C. Weight change measurements and microstructure analysis showed that HF corrosion in polycrystalline aluminas generally occurred at grain boundaries by the dissolution of silicate-based, glass grain boundary films that segregate to grain boundaries. These materials often have useful service lifetimes even though thermodynamic calculations indicate high solubilities. It is proposed that corrosion rates are controlled by chemical reactions at the solid/liquid interface, the physical structure of the solid, and microstructure. The addition of MgO to alumina greatly increased corrosion resistance by removing silicate-based glassy grain boundary films.     

Microstructural and Chemical Influences of Silicate Grain-Boundary Phases in Yttria-Stabilized Zirconia

The microstructure and chemistry of grain-boundary phases in silicate-doped Y₂O₃─ZrO₂ ceramics were evaluated by analytical electron microscopy. Two different silicate compositions were used: one an aluminosilicate and the other a borosilicate glass. These grain-boundary phases had a significant impact on the grain morphology, the chemical composition of the grains, and the crystallization of second phases. These results indicate that controlled additions of specific glass phases may provide a means for tailoring the microstructure and physical properties of zirconia ceramics.     

Effect of cooling rate on the location and chemistry of glassy phases in silica-doped 3Y-TZP ceramics

The morphology and the composition of glassy phases in silica-doped 3Y-TZP ceramics are studied for two extreme conditions of cooling. On the one hand, materials quenched after sintering exhibit silica-rich glassy phases both at grain boundaries and multiple junctions, with an enrichment of yttrium and zirconium. These observations are related to equilibrium at high temperature. On the other hand, materials slowly cooled exhibit glassy phases only at multiple junctions. During specific conditions of cooling, it is thus shown that dewetting can occur, giving rise to a low temperature equilibrium without glassy phase.     

Cubic-Formation and Grain-Growth Mechanisms in Tetragonal Zirconia Polycrystal

The microstructure in Y₂O₃-stabilized tetragonal zirconia polycrystal (Y-TZP) sintered at 1300°–1500°C was examined to clarify the role of Y³⁺ ions on grain growth and the formation of cubic phase. The grain size and the fraction of the cubic phase in Y-TZP increased as the sintering temperature increased. Both the fraction of the tetragonal phase and the Y₂O₃ concentration within the tetragonal phase decreased with increasing fraction of the cubic phase. Scanning transmission electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) measurements revealed that cubic phase regions in grain interiors in Y-TZP generated as the sintering temperature increased. High-resolution electron microscopy and nanoprobe EDS measurements revealed that no amorphous layer or second phase existed along the grain-boundary faces in Y-TZP and Y³⁺ ions segregated at their grain boundaries over a width of ∼10 nm. Taking into account these results, it was clarified that cubic phase regions in grain interiors started to form from grain boundaries and the triple junctions in which Y³⁺ ions segregated. The cubic-formation and grain-growth mechanisms in Y-TZP can be explained using the grain boundary segregation-induced phase transformation model and the solute drag effect of Y³⁺ ions segregating along the grain boundary, respectively.     

Microstructural Characterization and Role of Glassy Layer Developed on Inconel 690 During a Nuclear High-Level Waste Vitrification Process

The interaction of Inconel 690 metallic components with borosilicate melt leads to development of a partially amorphous and a partially crystalline layer within borosilicate melt adjacent to the interface. Such a heterogeneous layer is referred to here as a glassy layer. In the present investigation, the glassy layer is constituted of several phases, e.g. a Cr₂O₃ layer, a Ni₂CrO₄ needle, and NiCr₂O₄ cubic phases. Incorporation of such a glassy layer within the melt pool can lead to significant microstructural changes in the melt. Formation of barium chromate and nickel silicate has been observed in a sodium barium borosilicate melt with excess amount of Cr₂O₃ and NiO, respectively.     

Accelerated Aging in 3-mol%-Yttria-Stabilized Tetragonal Zirconia Ceramics Sintered in Reducing Conditions

The aging behavior of 3-mol%-yttria-stabilized tetragonal zirconia (3Y-TZP) ceramics sintered in air and in reducing conditions was investigated at 140°C in water vapor. It was observed by X-ray diffraction (XRD) that 3Y-TZP samples sintered in reducing conditions exhibited significantly higher tetragonal-to-monoclinic transformation than samples with similar density and average grain size values but obtained by sintering in air. This fact is explained by the increase of the oxygen vacancy concentration and by the presence at the grain boundary region of a new aggregate phase formed because of the exolution of Fe²⁺ ions observed by X-ray photoelectron spectroscopy.     

CaO含量对镧硼硅酸盐玻璃陶瓷晶相和化学稳定性的影响

采用熔融冷却法制备了Na₂O-CaO-La₂O₃-B₂O₃-SiO₂玻璃,经热处理获得了硅酸盐氧基磷灰石硼硅酸盐玻璃陶瓷,并采用X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、差示扫描量热法(DSC)、产品一致性试验(PCT)法等方法探究了CaO取代SiO₂对该硼硅酸盐玻璃陶瓷物相、微观结构和化学稳定性的影响规律。结果显示:随着CaO含量增加,硅酸盐氧基磷灰石晶相衍射峰增强,其他晶相的衍射峰减弱直至消失,当CaO摩尔分数为15%时获得只含CaLa₄(SiO₄)₃O晶相的玻璃陶瓷样品;CaO含量会对玻璃陶瓷的晶相种类和晶体形状、大小、分布产生影响,CaO含量变化会造成陶瓷相晶体发生团簇和长大;采用PCT法浸泡28 d后,所有样品关于Si、Ca、La三种元素的归一化浸出率(g·m^-2·d^-1)均保持在10^-3数量级以下,表明其具有优异的化学稳定性,且CaO摩尔分数为15%的玻璃陶瓷样品化学稳定性最优异。研究结果表明,硅酸盐氧基磷灰石硼硅酸盐玻璃陶瓷是固化富La和某些锕系元素高放废物的潜在基材。     

Transmission Electron Microscopy of Thin Glass Samples

Mechanical thinning and fracturing techniques for preparing thin glass samples for direct-transmission electron microscopy are discussed. A modification of the Doherty and Leombruno procedure for mechanically thinning ceramic materials is described. These techniques make possible more reliable electron microscope studies of fine-scale submicrostructure in glass systems. Electron microscope observations on fused silica, an alkali borosilicate glass, and some binary silicate glasses are reported and discussed in terms of present understanding of glass structure.     

Vanadium in Borosilicate Glass

Understanding the role of V₂O₅ within borosilicate glass matrices is important for the development of novel matrices toward immobilization of sulfate containing high‐level nuclear wastes. Present investigation shows, within sodium barium borosilicate glass matrix V₂O₅ can be homogeneously added up to 5 mol% and beyond which it separates out into three phases, for example, (i) silica (ii) Barium (Ba) – Vanadium (V) oxide, and (iii) glass matrix. ²⁹Si MAS NMR (Nuclear Magnetic Resonance) studies of the samples show that below 5 mol% V₂O₅ addition, silicate network is dominantly constituted of Q² and Q³ structural units, whereas above this, the network gets more polymerized through formation of Q³ and Q⁴ units. In case of borate network, ¹¹B MAS NMR investigations revealed that the concentration of BO₄ [(0B, 4Si)] unit increases gradually up to 5 mol% and then it decreases at the cost of BO₄ [(1B, 3Si)], BO₃ (symmetric) and BO₃ (asymmetric) units. Micro‐Raman analyses of the samples showed that with additions of V₂O₅ in diluted concentrations, amorphous silicate network remained unaltered, whereas some amplification in signals corresponding to ring‐type metaborate and VO₅ units exists. It is therefore apparent from both MAS‐NMR and micro‐Raman studies that with V₂O₅ additions within the solubility limit (≤5 mol%), borate network gets depolymerized leading to decrease in hardness from an average value of 5.0–4.2 GPa.     

Refined Model of Electromigration of Ag/Pd Electrodes in Multilayer PZT Ceramics Under Extreme Humidity

The phenomenon of silver electromigration has been examined in multilayer structures comprised of a low-firing PZT-based ceramic with inner Ag_{1− x} Pd _x electrodes (0< x <0.3). Under high humidity and dc bias, the time-to-failure was found to increase significantly with Pd content for x >0.1. Failed samples exhibited metallic-like transport properties including Ohmic behavior and a low temperature coefficient of resistance. Subsequently, electron microscopy of cross-sectioned samples revealed high concentrations of Ag in grain boundaries confirming Ag migration as the failure mechanism. Furthermore, it was found that the failure rate did not improve substantially by replacing a pure Ag anode with a higher Pd composition. This observation appears to conflict with previous conceptual models in which Ag migration originates mainly from the anode. It is suggested that Ag diffusion during sintering results in a background concentration of Ag within the ceramic which later contributes to the electrolytic flux of Ag⁺ ions under high humidity. This effect may be more apparent in low temperature sintered materials where residual grain boundary phases become vulnerable pathways for moisture penetration.     

两步烧结法制备纳米氧化钇稳定的四方氧化锆陶瓷

采用共沉淀法制备纳米氧化钇稳定的四方氧化锆（yttria stabilized tetragonal zirconia,3Y-TZP）粉体。利用X射线衍射、N2吸附–脱附等温线,透射电子显微镜对3Y-TZP粉体的物理性能和化学性能进行表征。研究了纳米3Y-TZP粉体的烧结曲线,分析了3Y-TZP素坯在烧结过程中的致密化行为和显微结构,探讨了两步烧结工艺对3Y-TZP纳米陶瓷微观结构的影响。结果表明：采用共沉淀法,在600℃煅烧2h后,可获得晶粒尺寸为13nm、晶型发育良好、团聚较少的纳米3Y-TZP粉体;采用两步烧结法,将素坯升温至1200℃保温1min后,再降温到1050℃保温35h,可获得相对密度大于98%,晶粒尺寸约为100nm的3Y-TZP陶瓷。两步烧结法通过控制煅烧温度和保温时间,利用晶界扩散及其迁移动力学之间的差异,使晶粒生长受到抑制,样品烧结致密化得以维持,实现在晶粒无显著生长前提下完成致密化。     

氧化锆增韧陶瓷的室温动态疲劳

用动态疲劳试验法研究了３Ｙ－ＴＺＰ和３Ｙ－ＴＺＰ／Ａｌ_２Ｏ_３（２０ｗｔ％）陶瓷在空气中的室温动态疲劳，并讨论了疲劳慢裂纹扩展特性。另外利用动态疲劳数据对两种陶瓷的平均寿命进行了预测。两种陶瓷材料在室温下均存在着慢裂纹扩展，主要是由空气中水蒸汽的应力腐蚀所造成的，且裂纹是沿晶界玻璃相扩展的。相变诱发的表面压应力和裂纹尖端的正应变可提高疲劳抗力。在８００ＭＰａ应力作用下，３Ｙ－ＴＺＰ和３Ｙ－ＴＺＰ／Ａｌ_２Ｏ_３（２０ｗｔ％）的平均寿命分别为２４ｍｉｎ和７２ｈ，平均寿命随应力的增大而缩短．     

Aging behavior of Y-TZP with bioglass addition and its impact on the flexural strength and osteoblastic cell response

Y-TZP containing Ca₂P₂O₇ are promising bioceramics with potential applications in dental implants and dentistry. These ceramics were developed by the introduction of a refractory sol-gel derived CaO-P₂O₅-SiO₂ bioglass into Y-TZP; Ca₂P₂O₇, and ZrSiO₄ phases were formed in situ after sintering. The aging process of Y-TZP with different glass additions was studied. The effect of glass addition on the flexural strength and osteoblastic cell response of non-aged and aged Y-TZP was investigated. Y-TZP exhibited the most pronounced tetragonal (t) to monoclinic (m) transformation of zirconia (ZrO₂) during aging; the addition of glass contents between 5 and 20 vol% improved the aging resistant of Y-TZP. Y-TZP flexural strength markedly decreased with increasing aging time; in contrast, the ceramics with glass did not alter their flexural strength upon aging. An increase in the Ca₂P₂O₇ content with increasing glass up to 10 vol%, promoted both the cell viability and the osteogenic differentiation of UMR-106 cells on non-aged and aged samples. The high micro-roughness of Y-TZP with 20 vol% glass after aging, limited the proliferation and the osteogenic potential of the cultures. Y-TZP with 10 vol% glass had the best combination of properties in terms of flexural strength and osteoblast cell response.     

Grain Size Control of Tetragonal Zirconia Polycrystals Using the Space Charge Concept

Grain growth kinetics and grain-boundary segregation of 12Ce-TZP and 2Y-TZP, containing divalent to pentavalent cationic dopants, were studied. In all cases, normal grain growth follwing the parabolic growth relation was observed at higher temperatures. The mobility of grain boundaries was suppressed by the addition of divalent and trivalent cations, unchanged or enhanced by the addition of tetravalent and pentavalent cations. Larger cations have a stronger effect in suppressing grain growth. From ESCA, AES, and STEM analysis of the near grain-boundary regions, it is further concluded that only divalent and trivalent cations segregate. These observations can be satisfactorily rationalized using the space charge concept and the model of impurity drag.     

Structure and Chemistry of Yttria-Stabilized Cubic-Zirconia Symmetric Tilt Grain Boundaries

The atomic structures of two symmetric [001] tilt grain boundaries in yttria-stabilized cubic-zirconia, Σ5 (310) and near-Σ13 (510), are studied by Z -contrast scanning transmission electron microscopy. Both boundaries are composed of periodic arrays of highly symmetric structural units, with a distinct unit for each boundary. Oxygen K -edge electron energy-loss spectra show that the oxygen coordination is similar between the bulk and grain boundary, indicating that oxygen ions within the grain boundary reside in distorted tetrahedral sites. Atomic models of the grain boundaries are proposed that are consistent with the experimental data. The core structures are different from previously studied metal or oxide grain boundaries and are unique to the fluorite structure. Yttrium segregation to the grain boundaries is also investigated by electron energy-loss spectroscopy. Yttrium is found to segregate preferentially to the Σ5 grain boundary, and the spatial distribution of the segregation layer is confined to within 1 nm of the boundary plane.     

Polarographic Analysis for Antimony in Glass

Antimony, usually added as a fining agent in a concentration range of about 0.2 to 2.0% Sb₂O₃, can be determined readily in many types of glass with a polarograph. Interfering elements are seldom encountered in common glass compositions, so chemical separations are not necessary. The mean difference between chemical and polarographic analyses for twenty-one glasses covering soda-lime, borosilicate, lead, and barium compositions is about 0.02% Sb₂O₃.     

Influence of Calcination Temperature on the Microstructure and Mechanical Properties of a Gel-Derived and Sintered 3 mol% Y-TZP Material

A pure coprecipitated 3 mol% Y-TZP powder was subjected to two calcination temperatures, 600° and 1000°C, prior to compaction and sintering. Significant differences in the initial sintering behavior were observed. The lower temperature calcined powder exhibited abnormal grain growth. The resultant mechanical properties mirrored the microstructure with the lower temperature calcined material having lower flexural strength. Hardness measurements of the two sintered bodies revealed significant differences in the two phases of the lower temperature calcined material. Differences in reactivity of the two powders after calcination are suggested as the basis for the difference in microstructure and resultant mechanical properties.