Formation, Structure and Properties of Bulk Metallic Glasses

1.IntroductionTheformationofmetallicglassesbydirectquench-ingfromthemeltwasfirstdiscoveredin196obyDuwezandhisco-workersinaAu-25at.pctSialloy[']bya'guntechnique'[2].Thistechniqueen-abledcoolingrateoflo6K/s,thuscreatinganewseriesofmaterials.Thediscoveryofmetal1icglassesandmetastab1ephasehasledto-explosiveresearchanddevelopmefltofmetallicglassesandothercrys-tallinematerialsquenchedfrommelt[3'4].Metallicglasses,whichareobtainedbytherapidquenchingofmetallicmelts,arenoncrystallineoramorphous,likeo…     

Photochromic glasses: Properties and applications

Photochromic materials are those which react reversibly to light. Photochromism is therefore distinguished from the familiar photographic processes, which, because of the chemical development of the image, are essentially irreversible. Many organic materials, and a few inorganic ones, show this phenomenon. Their general properties are described, with particular emphasis on those of a system of photochromic glasses. The behaviour of these glasses results from reaction of light with silver halide crystals deliberately formed in the glass during its manufacture. The mechanism of the photolytic reactions is postulated, and compared with the theory of the photographic process for silver halides. Reversibility of photochromism in these glasses is explained by prevention of diffusion of the products of photolysis from the original crystal site within the glass structure, and their subsequent recombination when the activating light is removed. These glasses show large ranges in all their photochromic properties resulting from ranges in composition, and in size and number of the included crystals. The behaviour of typical glasses, in both sunlight and under artificial sources, is reported in this paper, and some applications for these glasses are suggested.     

Metallic glasses from “alchemy” to pure science: Present and future of design,processing and applications of glassy metals

Metallic glasses, first discovered a half century ago, are currently among the most studied metallic materials. Available in sizes up to several centimeters, with many novel, applicable properties, metallic glasses have also been the focus of research advancing the understanding of liquids and of glasses in general.Metallic glasses (MGs), called also bulk metallic glasses (BMGs) (or glassy metals, amorphous metals, liquid metals) are considered to be the materials of the future. Due to their high strength, metallic glasses have a number of interesting applications, for example as coatings. Metallic glasses can also be corrosion resistant. Metallic glasses, and the crystalline materials derived from them, can have very good resistance to sliding and abrasive wear. Combined with their strength – and now, toughness – this makes them ideal candidates for bio-implants or military applications. Prestigious Journals such as “Nature Materials”, “Nature” frequently publish new findings on these unusual glass materials. Moreover Chinese and Asian scientists have also been showing an interest in the study of metallic glasses.This review paper is far from exhaustive, but tries to cover the areas of interest as it follows: a short history, the local structure of BMGs and the glass forming ability (GFA), BMGs’ properties, the manufacturing and some applications of BMGs and finally, about the future of BMGs as valuable materials.     

Charge‐Transporting Molecular Glasses

Among organic materials vitrification for many years was regarded mainly as a privilege of polymers. However, recently a lot of attention is paid to organic low molar mass compounds that readily form glasses above room temperature. Such compounds are called molecular glasses or amorphous molecular materials. Among these materials the most widely studied are charge‐transporting molecular glasses used in copiers and laser printers, organic light‐emitting diodes, photovoltaic devices, and as photorefractive materials. Two types of molecular glasses, i.e., p‐type (hole‐transporting), and n‐type (electron‐transporting) are discussed. Work of the laboratories of the authors is emphasized. In addition, an overview of current and potential applications for these materials is presented.     

Fracture resistance of technical and optical glasses: edge flaking of specimens

We present the results of fracture resistance tests for technical and optical glasses performed by indentation flaking of the rectangular specimen edge. The features of crack propagation in these glasses are analyzed during chipping fracture caused by indentation with blunt and sharp diamond indenters. By comparative analysis of the values for resistance to edge flaking and those for fracture resistance, new data on the mechanical behavior of the above glasses in fracture are obtained. In particular, it is shown that these glasses, along with ceramic materials used to produce armor, have an enhanced resistance to the onset of fracture.     

Fluoride glasses

A new family of vitreous materials based on the glass forming ability of some specific fluorides is presented. Conditions of formation, stability against devitrification, chemical durability, and structural models are examined in comparison with the traditional oxide glasses. The ZrF₄-based glasses and some other multicomponent materials are examined in depth in view of their promising optical properties, which arise from their broad transmission range from ultraviolet to mid infrared and their potential as ultratransparent materials for long distance repeaterless optical fibre. Other active optical applications of doped glasses, such as lasers and their electrical and magnetic properties, are also discussed.     

Development and mechanical properties of metal–particulate glass matrix composites from recycled glasses

The great number of glasses available from recycling activity and vitrification treatment of industrial wastes leads to the need for new applications, with the development of new materials, such as low-cost composite materials from a powder technology route. In the present work a variety of recycled glasses is investigated, in order to obtain aluminium reinforced glass matrix composites via cold-pressing and viscous flow sintering. A good compatibility between lead silicate glasses from cathode ray tubes dismantling and aluminium reinforcement is found to be effective. Composites exhibiting good mechanical properties were developed from these materials. A particular attention was due to fracture toughness (K_IC) determination. The absolute K_IC of glass matrix composites value remains low, but a notable increment in relation to unreinforced matrix is observed.     

Optical properties of oxide glasses containing transition metals: Case of titanium- and chromium-containing glasses

One of the major driving forces for the development of new glasses is the demand for high optical non-linearity with reduced cost and a higher damage resistance. Oxide glasses with large non-linear refractive index and non-linear absorption coefficient are promising materials for fiber telecommunication and for non-linear optical devices such as ultrafast optical switches, power limiters, real time holography, self-focusing, white-light continuum generation and photonic applications. To get insight into the optical absorption in amorphous materials, studies are still needed for revealing the nature of photoelectronic excitations in these materials by comparison with that in crystals which have been understood firmly based on band theory. Although the IR absorption loss in oxide glasses is larger than of fluorides, low light scattering loss is expected in these oxide glasses because they have lower glass transition temperature. In addition, small concentration of dopant such as alkaline metal and alkaline earth metal elements gives rise to the structural relaxation of the frozen-in density fluctuations even below glass transition temperature T_g, adding to the reduction of T_g as well. A review of the fundamentals and recent research advances in optical properties of oxide glasses containing chromium or titanium is presented.     

生物玻璃的研究与发展

生物玻璃的研究已达二十多年，现已成为材料学、生物化学以及分子生物学的交叉学科。由于生物玻璃具有人体硬或软生命组织有机联结的特点，在骨科、牙科、中耳等方面，对人体的伤害部位可进行修护治疗以至康健，其前景可观。生物玻璃主要由Ｓｉ、Ｎａ、Ｃａ以及Ｐ的氧化物组成。被发现具有生物活性的玻璃已有一系列组成，并且对这些系列玻璃已积累了大量的模拟人体溶液实验数据。常用的模拟人体溶液有两种：其一是Ｔｒｉｓ缓冲液；其     

Thermisches Bonden von Bauteilen aus mikrostrukturiertem Glas

Thermal bonding of microstructured glass elements At the Technische Universität Ilmenau microstructurable glasses and microstructurable glasses with special p_H‐sensitive properties were developed. The glasses are microstructurable by an UV‐lithographic process. For the realization of sensors, based on these glasses, joining processes are necessary. The paper presents the thermal bonding as a possible joining technology. The results of thermal bonding experiments were discussed. Advantages are the good stability of the joint and the joining without supporting materials.     

A critical study of the emergence of glass and glassy metals as “green” materials

In 2008, The National Academy of Engineering (NAE – Washington, DC) identified the glass family (glasses, glass ceramics and glass composites) as central to many of the great engineering achievements of the twentieth century: the development of solid state lasers and optical glass fibers, biomaterials, glasses for imaging technologies, and glass films in microelectronic devices.The work reported in this paper discusses the importance of glass and metallic glasses as environmental friendly materials and also provide some points of view about the future influence of these materials for the related fields of industrial engineering and industrial ecology. The environmental capabilities of metallic glasses (MGs), which are considered to be among the important materials of the future, have not been sufficiently investigated. However, some aspects have yet to be done: the biocompatibility of most MGs, obtaining valuable MGs from waste materials, using MGs in green energy applications (solar cells and hydrogen production), using MGs in catalyst systems, as well as the possibility for using MGs in systems for retention and purification of dangerous pollutants and in the nuclear industry.     

Sol-gel processing of materials for electronic and related applications

Various techniques of sol-gel processing for the preparation of electronic and related materials are described and reviewed. Typical examples are chosen from thin films and coatings of gels, crystalline materials and glasses as also bulk glasses to illustrate the variations in processing parameters and material properties.     

Electrical properties of glasses in the Na2O–MoO3–P2O5 system

A range of coloured electronic or mixed ionic–electronic glasses has been evidenced in the Na₂O–MoO₃–P₂O₅ system. The properties of these glasses have been studied along different composition lines corresponding either to a fixed Na₂O content or a constant Mo/P ratio. An EPR spectroscopy investigation of these glasses has allowed to determine the Mo⁵⁺ ion percentages in these materials. The electrical properties of these glasses have been studied by impedance spectroscopy, and the electronic and ionic contributions have been evaluated. The properties of these sodium glasses have been compared with those of lithium glasses with the same compositions.     

Mechanical properties of bulk metallic glasses

The mechanical properties of bulk metallic glasses, including their superior strength and hardness, and excellent corrosion and wear resistance, combined with their general inability to undergo homogeneous plastic deformation have been a subject of fascination for scientists and engineers. The scientific interest stems from the unconventional deformation and failure initiation mechanisms in this class of materials in which the typical carriers of plastic flow (dislocations) are absent. Metallic glasses undergo highly localized, heterogeneous deformation by formation of shear bands, a particular mode of deformation of interest for certain applications, but which also causes them to fail catastrophically due to uninhibited shear band propagation. Varying degrees of brittle and plastic failure creating intricate fracture patterns are observed in metallic glasses, quite different from those observed in crystalline solids. The tension–compression anisotropy, strain-rate sensitivity, thermal stability, stress-induced crystallization and polyamorphism transformations, are some of the attributes that have sparked engineering studies on bulk metallic glasses. Understanding of the glass-forming ability and the deformation and failure mechanisms of bulk metallic glasses, has given insight into alloy compositions and intrinsically-forming or extrinsically-added reinforcement phases for creating composite structures, to attain the combination of high strength, tensile ductility, and fracture toughness needed for use in advanced structural applications. The relative ease of fabricating metallic glasses into bulk forms, combined with their unique mechanical properties, has made these materials attractive options for possible applications in aerospace, naval, sports equipment, luxury goods, armor and anti-armor systems, electronic packaging, and biomedical devices.     

Processing of ceramics and glasses in space

Possible experiments in space on ceramics, composites and inorganic glasses are listed. Advantages in processing these materials under microgravity conditions, anticipated effects and likely problems are discussed. Theoretical conclusions and experimental results to date are reviewed. It is suggested that experiments on metallic glasses in space could prove to be rewarding.     

Glass-metal particulate composites

Oxide glasses containing ultrafine metal particles have interesting physical properties and have been widely used in practical systems. The various preparational techniques developed so far for making these materials are discussed. Electrical conduction in these composites is controlled by electron tunnelling between the metal islands. At high electric fields certain glasses containing bismuth granules show a memory switching effect. The latter has been explained by a particle stretching model. Optical absorption characteristics of these composites can be explained on the basis of various effective medium theories developed so far for inhomogeneous materials. Glasses containing ferromagnetic metal grains show a superparamagnetic behaviour with a transition temperature below 300 K. Improvement in the mechanical properties of glasses can be achieved by incorporating metal particles of suitable characteristics within them. In this paper the present state of understanding of all these properties is reviewed.     

Accurate magneto-optic sensitivity measurements of some diamagneticglasses and ferrimagnetic bulk crystals using small applied AC magneticfields

Many materials exhibit a relatively large Faraday effect. A plane polarized optical beam passing through these materials has its plane of polarization rotated by a measurable amount proportional to the applied magnetic field strength parallel to the propagation direction of the beam. Some of the most sensitive materials of this kind are diamagnetic glasses and ferrimagnetic crystals. We have made accurate measurements of the magneto-optic sensitivity of a variety of diamagnetic glasses and ferrimagnetic bulk optic crystals using small applied ac magnetic fields in contrast to the more common technique involving very strong applied dc magnetic fields     

A study of the electrical and optical properties of the GeO2-TeO2 glass system

Results of measurements of the d.c. electrical conductivity, optical absorption edge and infrared optical absorption of GeO₂-TeO₂ glasses are reported. Conduction in these glasses is found to be electronic and the hopping of polarons seems to be the dominant process in the transport mechanism. The electrical activation energy decreases with the increase of tellurium content and this decrease corresponds to a decrease in the optical energy gap. The optical gap is of the order of 2.74 eV, somewhat lower than for many other oxide based glasses. Most of the sharp absorption bands characteristic of the basic materials GeO₂ and TeO₂ are modified with the formation of broad and strong absorption bands in the process of going from the crystalline to the amorphous state. Density measurements show the glasses to have a compact structure.     

Structure,thermal properties,dissolution behaviour and biomedical applications of phosphate glasses and fibres: a review

For the last few decades, there has been a growing interest in using glasses for biomedical applications. Bioactive glasses are a group of surface reactive glasses which can initiate a range of biological responses by releasing ions into the local environment. Silicate, borate and phosphate glasses are known to show good bioactive characteristics and could be potentially used as favourable templates for bone-tissue formation. Phosphate glasses are unique group of materials that offer great potential for hard and soft tissue engineering over other types of bioactive glasses due to their fully resorbable characteristics, with some formulations possessing chemical composition similar to the mineral phase of natural bone. Moreover, these phosphate glasses can be prepared as fibres which could be used for soft tissue engineering and as fibrous reinforcement for resorbable polymers such as poly-(lactic acid) for fracture fixation applications. This review details some of the properties of phosphate glasses, such as thermal, viscosity/temperature, dissolution and biocompatibility of and how different factors can effectively alter these properties. The effect of the addition of different modifier oxides on the structure in terms of chain length is included. This review also reports on the manufacturing process, mechanical properties and biomedical application of phosphate glass fibres. A brief comparison between three different types of bioactive glasses has also been presented in this review. The main aim of this review is to present the factors affecting the properties of phosphate glasses and glass fibres and how these may be exploited in the design of a biomaterial.