裂纹玻璃晶化法制备建筑装饰用微晶玻璃

制备建筑装饰用微晶玻璃的现役工艺主要有烧结法和压延法两种,前者容易出现气孔缺陷,后者不能生成纹理.为克服现役工艺的不足,本文提出裂纹玻璃晶化法工艺,即以裂纹玻璃作为母玻璃,通过烧结、晶化二步热处理而制备出微晶玻璃.XRD测得裂纹玻璃晶化法微晶玻璃样品的主晶相为β-硅灰石;ESEM观察到样品的微观结构由不均匀分布的粒径在0.2~0.5μm的晶体组成;利用比重仪测得样品的气孔率低于现役烧结法样品.实验表明,裂纹玻璃晶化法能克服现役工艺的不足,制备出气孔率低、具有类似古生物残骸纹理的微晶玻璃,装饰效果更佳.     

红外玻璃陶瓷的力学性能

在一定的温度和时间下对GeS2-Sb2S3-CsCl系红外玻璃进行微晶化处理,制备了新型的红外透明玻璃陶瓷.测定了微晶玻璃的力学性能和光学性能,研究了微晶化处理条件对微晶玻璃的力学性能和光学性能的影响.研究结果表明,玻璃基体中析出微晶晶体,使材料的断裂韧性和裂纹初始应力显著增大,但这种增大效应取决于析晶相的种类和晶体尺寸.为了保持微晶玻璃的红外透明性,析出的晶体尺寸应小于100nm.     

溶胶-凝胶涂层增强锂云母微晶玻璃

对溶胶－凝胶涂层增强锂云母微晶玻璃进行了研究．结果表明：浸涂溶胶－凝胶涂层的锂云母微晶玻璃较未浸涂前,其抗弯强度增加８％～４８％借助扫描电子显微镜（ＳＥＭ）对涂膜前后锂云母微晶玻璃的表面显微结构进行了研究,发现锂云母微晶玻璃强度增加是由于溶胶粒子进入锂云母微晶玻璃内部,填充晶相与玻璃相之间的微孔,弥合内部微裂纹．     

锂铝硅微晶玻璃自增强机制分析及表面强化技术进展

锂铝硅(LAS)微晶玻璃凭借优异的零膨胀特性和较高的可见光透过率获得了广泛的应用和研究。LAS微晶玻璃中大量的石英固溶体颗粒对裂纹扩展有明显的阻碍作用,裂纹尖端的应力释放和裂纹弯曲等独特的断裂机制可有效实现结构自增强。鉴于LAS微晶玻璃和基础玻璃的相似性,在保持零膨胀和高透过的前提下,其表面强韧化技术成为其另一个重要的研究方向。本文全面论述了国内外锂铝硅微晶玻璃表面强韧化处理技术的研究进展,对我国今后该领域的技术创新和应用具有指导作用。     

球晶材料的TEM—EDAX剖析

观察了R₂O－RO－Al₂O₃-SiO₂系某一整体析出球晶的微晶玻璃中球晶的生长过程．获得随着晶化时间的增加或晶化温度升高,球晶直径增大;但球晶数目保持不变．发现了核化温度与球晶直径关系呈抛物线型．以TEM－EDAX剖析了球晶的雏型内部和近邻玻璃基体的显微结构及其演变．清楚地揭示了球晶生长过程中所发生的组成变化．     

锗酸盐微晶玻璃的表面析晶过程研究

分析了锗酸盐微品玻璃表面析晶过程中离子的运动与迁移方式,对长时间晶化后微晶玻璃中形成的孔洞和气孔的成因进行了分析.认为锗酸盐微晶玻璃中孔洞的形成是由于在表面析晶过程中,随晶化时间的延长,内部离子不断向表面迁移,以致在内部出现离子耗空层,最终形成孔洞.而析晶过程中玻璃中气孔的不断长大是由于气孔等缺陷部位本身能量较高,在晶化过程中离子将优先从气孔位置不断迁移至表面析晶层,所以在析晶过程中气孔将不断扩大.     

掺杂ZnO-Al2O3-SiO2微晶玻璃的研制及吸收光谱特性

在ZnO-Al2O3-SiO2系统玻璃中掺入少量晶核剂TiO2,再掺入过渡金属离子和稀土离子,在高温下熔制得到透明母体玻璃.对上述玻璃进行晶化热处理,最后得到透明微晶玻璃.测定了晶化前后玻璃的密度与硬度变化.用差热分析(DTA)确定晶化温度,用X射线粉末衍射确定微晶相,并用透射电镜观察了晶相的形貌.测定并讨论了所得微晶玻璃在紫外波段至近红外波段的吸收光谱特性.研究结果表明微晶化后的密度与硬度都增大.掺杂于微晶玻璃中的Cr离子和Co离子的吸收光谱在微晶前后发生较大差异,而其余均未明显变化,这一现象归属于掺杂离子所处的不同位置所致.     

金属材料裂纹愈合的研究进展与展望

金属材料表面及内部的裂纹扩展是引起金属构件断裂失效的主要原因之一,裂纹研究一直是金属材料领域的一个重要方向。综述了近年来国内外对金属材料裂纹(表面裂纹、内部裂纹)愈合研究的进展,介绍了物质补给与能量补给的各类方法,物质补给方法主要包括钎焊法和表面筑膜法,能量补给方法主要包括加热法与施加脉冲电流法。总结了影响金属材料愈合的因素及愈合机制,并对未来金属材料的裂纹愈合研究作出了展望。     

硅碱钙石微晶玻璃的析晶特性及其增韧机理研究

通过调整热处理工艺制备了不同结构的R₂O-CaO-SiO₂-F系硅碱钙石微晶玻璃, 分析了析晶特性和力学性能, 重点研究以硅碱钙石为主晶微晶玻璃的裂纹扩展机制及增韧机理。结果表明, 基础玻璃在低温处理时首先析出CaF₂微晶作为异质晶核, 一步法处理后得到岛屿状硬硅钙石/硅碱钙石复相微晶玻璃, 两步法处理后得到了力学性能优异、具有板条交错结构的硅碱钙石微晶玻璃。研究发现, 硅碱钙石微晶玻璃的裂纹扩展受到周围板条晶体取向及晶界影响, 存在穿晶断裂和沿晶断裂两种模式扩展, 呈现出随机取向的折线或台阶状裂纹路径。其中具有一定长径比的板条状硅碱钙石具有较好的桥联作用, 承载补强效果显著, 此外硅碱钙石晶体与玻璃相之间存在的残余应力, 有利于缓解裂纹应力集中以及增加裂纹扩展能。即, 硅碱钙石微晶玻璃优异的力学性能是各种增强和增韧机制综合作用的结果。     

上转换发光氧氟微晶玻璃的研究进展

综述了近年来用于上转换发光的氧氟微晶玻璃的研究概况,阐述了氧氟微晶玻璃的组分与结构、微晶的形成与检测、上转换发光机理及影响因素.最后指出了上转换发光氧氟微晶玻璃目前存在的问题和今后发展的方向.认为氧氟微晶玻璃今后的发展重点将是实现材料的器件化,并实现高效率的短波长激光输出,尤其是蓝绿激光输出.     

Effect of humidity on crack healing in glass from in-situ investigations using an ESEM

In-situ healing of Vickers indentation cracks in soda-lime-silicate glass was observed using an environmental scanning electron microscope (ESEM). The change in crack length as a function of time and temperature was studied. The effect of the initial humidity level on the crack healing behavior was also investigated in-situ by varying the initial temperature of the specimen and the ESEM specimen chamber pressure. The crack healing results were fit to an equation previously used to describe thermal and mechanical fatigue crack behavior in ceramics.     

Some recent results on crack healing of poly(methyl methacrylate)

The solvent healing and void growth of poly(methyl methacrylate) (PMMA) at elevated temperatures were studied. In addition to entanglement between two or more broken polymeric chains, the chemical bonds between two polymeric broken chains were produced during healing in methanol or d₁-methanol. Cracks in PMMA were induced either by Nd-YAG laser irradiation or by acetone immersion. The solvents occupied the voids enclosed by polymeric chains. The chemical bonds and structure were analyzed with FTIR and NMR spectroscopy. The results show that in addition to mechanical lock of broken chains, hydrogen bond increases with uptake of solvent which enhances the crack healing. The cylindrical crack in PMMA was healed at temperatures 110-160 °C and spherical void was grown at temperatures 170-190 °C. This suggests that annealing above the glass transition temperature of polymer is a necessary condition for thermal healing, but not for the sufficient condition.     

FATIGUE CRACK PROPAGATION AND CRACK CLOSURE BEHAVIOR IN POLYCARBONATE AND FIBRE REINFORCED POLYCARBONATE

Abstract— Fatigue crack propagation was investigated in polycarbonate and glass fibre reinforced polycarbonate and the effect of stress ratio and glass fibre content determined. The addition of glass fibre increases the tensile strength, but does not always contribute to an increase in fatigue crack propagation resistance. For polycarbonate the effect of stress ratio can be partly explained by using crack closure concepts as other researchers have suggested, but for glass fibre reinforced polycarbonate this was not possible. Fractography revealed a void growth process, which occurred by decohesion at the interface of the glass fibres and the base material, which was dependent on the maximum stress intensity factor. The process of linking the voids and the main crack growth behavior depended on the stress intensity factor range, Δ K. A proposed crack propagation model can explain the effect of stress ratio on crack propagation in fibre reinforced polycarbonate.     

增韧Al2O3结构陶瓷氧化反应裂纹愈合动力学研究(Ⅰ) 理论模型

氧化反应引起裂纹愈合是结构陶瓷提高强度的一个重要途径．针对目前研究中缺乏定量性这一不足之处，本文从热力学和动力学角度研究了氧化反应与裂纹愈合、强度提高之间的定量关系．建立了裂纹愈合模型，并进行了动力学研究，分析了高温加热时间、温度、裂纹尺寸对裂纹愈合及材料强度的影响．以期为裂纹愈合与强度恢复的定量或半定量的研究，实现人为精确控制裂纹愈合的程度提供一定的理论依据．     

Self‐Healing Materials

Self‐healing materials are able to partially or completely heal damage inflicted on them, e.g., crack formation; it is anticipated that the original functionality can be restored. This article covers the design and generic principles of self‐healing materials through a wide range of different material classes including metals, ceramics, concrete, and polymers. Recent key developments and future challenges in the field of self‐healing materials are summarised, and generic, fundamental material‐independent principles and mechanism are discussed and evaluated.     

On Stressed State of Transversely Isotropic Medium with an Arbitrarily Oriented Spheroidal Void or Penny-Shaped Crack under Internal Pressure

The paper addresses the problem of stress distribution in an elastic transversely isotropic material containing an arbitrarily oriented spheroidal void or a penny-shaped crack under internal pressure. A solution to the problem is set up using the equivalent-inclusion method, triple Fourier transform in space variables, and the Fourier image of Green's function for infinitely anisotropic space. Some double integrals over a finite domain for the void as well as loop integrals for the crack are computed by Gaussian quadrature formulas. The results obtained in particular cases are compared with the data reported elsewhere. The effects of the void geometry, material's elastic properties, orientation of a void or a crack on the stress distribution on the void surface or on the stress intensity factor at the crack front are studied. The most critical void orientation has been found. __________ Translated from Problemy Prochnosti, No. 5, pp. 58 – 70, September – October, 2005.     

Kinetics of self-repair in inorganic glasses: modeling and experimental verification

A novel concept of self-repairable glass useful as seals in solid oxide fuel cells (SOFCs) is proposed, developed, and used for making metal-glass–ceramic seals for enhancing reliability and life. In this concept, cracks created during SOFC operation are repaired by the crack healing process driven by the viscous flow of the glass. An approach for studying the kinetics of crack healing in glasses responsible for the self-repair is described and used to study the crack healing behavior. The cracks are created by a microindenter, and the progression of healing of cracks thus created on a silicate glass surface is experimentally determined at different annealing temperatures and times. Sequential changes in the crack morphology during thermal healing are also studied to identify the three stages of crack healing process. A crack healing model, based on the relationship among crack length, time, temperature, glass viscosity, and its flow behavior is developed in order to describe and predict the time required for self-repair on a glass surface. The predictions from the developed model is then compared with the experimental data and found to be in good agreement. These results also demonstrated the relative importance of the different stages of crack healing on the overall healing or self-repair behavior.     

几种生物陶瓷材料的裂纹扩展特性

采用破坏力学中的双扭矩实验法，研究了玻璃陶瓷、云母陶瓷、氧化铝陶瓷、氧化锆陶瓷材料分别在大气、水环境中的静负荷和循环负荷下的裂纹扩展特征，阐明了水环境和循环负荷对材料裂纹扩展特性（KI－V特征）的影响。所研究的材料在水环境下的裂纹扩展速度均加快，但玻璃陶瓷和氧化锆陶瓷材料更为明显。在静负荷下这几种材料的裂纹扩展阻力由小到大的次序为：玻璃陶瓷（N－0），玻璃陶瓷（N－11），云母陶瓷，氧化锆陶瓷和氧化铝陶瓷，对于氧化铝和氧化锆陶瓷材料在循环负荷下的裂纹扩展速度均明显加快。     

On the estimation of the toughness of surface microcracks

Hardness testing is a method frequently used for evaluating the resistance of body surfaces to the influence of contact loading. The Vickers hardness test is applied for this purpose in a case when the material is sufficiently ductile and no cracks occur in the corners of the indents. Testing of the surface hardness of such materials as glass and ceramics on the basis of the Vickers testing method must take into account the energy that is spent on crack spreading. This paper describes a more exact and accurate method for evaluating resistance to microcrack formation on the surface of a material. To evaluate the conditions for crack spreading, it is necessary to test a specimen under loading in bulk. The suggested procedure involves a bent strip. As bending stresses are known, from the differences in crack length along and across the strip, the resistance of the material surface to crack propagation is determined.     

Mechanical characterisation of glass fibres as an indirect analysis of the effect of surface treatment

Tensile strength of E-glass fibres have been analysed using a bimodal Weibull two parameter cumulative distribution function. The bimodal character were associated to surface and internal flaws, respectively. Influence of silane coating as well as industrial sizing on the flaws distribution was quantitatively characterised. A qualitative interpretation of their effect based on a combination of probabilistic and deterministic approaches were proposed in terms of crack healing. It was demonstrated there that mechanical testing of fibres can be used as an indirect observation technique of the consequences of the surface treatment. An analogy is proposed between the sizing treatment of glass fibres and the strengthening of silica glass by means of hybrid organic-inorganic coatings.