Partially crystallized elastomer as a nanocomposite model

Data on the influence of crystallization on the mechanical properties of elastomers — the elastic modulus, the relaxation properties, in particular, restorability in compression, and the tensile strength — have been generalized. These data have been compared to those on the influence of active fillers and a much higher crystallization efficiency has been shown. The size of single crystals has been evaluated for most crystallizable rubbers. It has been inferred that the nanosize of single crystals of elastomers and their direct bond with the elastomer matrix influence the mechanical properties of elastomer materials. In considering a partially crystallized elastomer as a nanocomposite model, one can formulate requirements imposed on efficient nanofillers for elastomer materials. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 19–23, September–October, 2005.     

Hydrolytic stability and acid resistance of porous silicate ceramics

Different inorganic binders (sodium aluminate, silicate, and aluminosilicate) have been used to engineer porous silicate ceramics, and the effect of the binder on the hydrolytic stability and acid resistance of the ceramics has been assessed. Only the ceramics based on the aluminosilicate binder are found to be hydrolytically stable, with an insignificant strength loss (≃6%) in 20% sulfuric acid, and can therefore be used as filtering materials for removing mechanical impurities from sulfuric acid solutions. A key role in the structural degradation of the porous silicate ceramics is played by the solution acidity rather than by the nature of the acid or its concentration.     

Phase transitions in zirconium dioxide and related materials for high performance engineering ceramics

Because of its outstanding mechanical properties, zirconia-based ceramics are considered as some of the best potential materials within the engineering ceramics field that might be widely used to substitute various metallic parts and specific alloys. Taking into account the transformation toughening mechanisms that operates in their microstructure, important properties can be obtained. Phase transitions as well as transformation toughening in ZrO₂ are reviewed briefly with the purpose to understand its effects in some composites and glass systems. Zirconia ceramics as high toughness materials for cutting tool, metal forming applications, mechanically superior ceramics called partially stabilised zirconia (PSZ), solid electrolytes, have been fabricated using the martensitic nature of the tetragonal to monoclinic phase transition.     

Nanostructured materials by mechanical alloying: new results on property enhancement

Mechanical attrition—the mechanical alloying or milling of powders—is a very versatile and potent method of obtaining nanocrystalline or ultrafine grain structures with enhanced properties. This article presents three examples of enhanced properties obtained by materials in which the grain size has been reduced to the nanoscale or ultrafine scale by ball milling and consolidation of powders. Very high strength/hardness—the highest hardness yet reported for crystalline Mg alloys—for a ball milled Mg₉₇Y₂Zn₁ alloy is due in part to the nanocrystalline grain structure, along with nanoscale precipitates. A ternary Cu-base alloy with a low stacking fault energy was found to have both high strength and good ductility in a nanocrystalline material synthesized by the in situ ball milling consolidation method. This is another example that shows nanocrystalline materials need not be brittle. It is shown that bulk thermoelectric materials with superior properties can be produced by the ball milling and consolidation of powders to provide an ultrafine grain structure.     

A basis for the évolution of strategy for a futuristic development of building materials

Conclusions A basis for evolving strategy for development of building materials maintaining the mass—energy— environment balance is outlined. The technical, ecological and economic dictates of the future compell us to develop building materials aligning with nature — using natural resources and converting society’s wastes into wealth. Energy requirements in the manufacture and use of materials will be a prime consideration. Greater thrusts to the engineering and industrial aspects of manufacture and utilization of building materials is futuristically important.     

Theoretical and experimental studies of the porous structure and adsorption properties of carbofibrous materials

We have made theoretical and experimental studies of the porous structure and adsorption properties of activated carbon fibrous materials and granular activated carbon with respect to vapors of benzene, toluene, ethylacetate, and acetone. The parameters of the porous structure of adsorbents have been determined by the adsorption by them of the standard substance — benzene — and used to calculate their adsorption characteristics with respect to the investigated organic solvents. A good agreement between the calculated and experimental characteristics for all investigated adsorbents has been obtained. The dependence of adsorption properties of activated carbon fibrous adsorbents and granular activated carbon on the volume and size of adsorbing pores, as well as on the molecular polarizability of the adsorptive, has been established.     

Integrated structures and materials design

This paper introduces the concept of␣Integrated Structures and Materials Design (ISMD). ISMD combines materials engineering and structural engineering for the purpose of more effectively achieving targeted structural performance, by adopting material composite properties as the shared link. An application example, design of a bridge deck link-slab, is used to illustrate the essential elements of ISMD. It is shown that the composite hardened properties—tensile strain capacity, microcrack width, and Young’s Modulus, as well as composite self-consolidating fresh properties, are amongst the most important composite parameters that govern the targeted structural performance of safety, durability and ease of design and implementation. These are also properties that can be controlled in an Engineered Cementitious Composite—an ultra ductile concrete, by tailoring the ingredients for desired fiber, matrix and interface micromechanical parameters. Broad implications of ISMD on educational approach, research collaboration, and next generation infrastructure development, are briefly discussed.     

Nanostructured bioceramics for maxillofacial applications

Biomaterials science and technology have been expanding tremendously the recent years. The results of this evolution are obvious in maxillofacial applications especially with the contemporary development of Nanotechnology. Among biomaterials, bioceramics possess a specific field due to various interactions with the biological tissues. The combination of bioceramics and nanotechnology has resulted in enhanced skeletal interactions in maxillofacial applications. Nanotechnology secures better mechanical properties and more effective biological interactions with jaws. The main production methods for the synthesis of nanostructured materials include plasma arcing, chemical vapour deposition, sol–gel and precipitation. The bioceramics in Dentistry comprise inert, bioactive, resorbable and composite systems. The purpose of the present article is to describe the available nanotechnology methods and how these could be addressed to synthesise maxillofacial bioceramics with advanced properties for better biological applications. Additionally, it describes specific clinical applications in maxillofacial surgery of these biomaterials—either by themselves or in combination with others—that can be promising candidates for bone tissue engineering. Such applications include replacement of lost teeth, filling of jaws defects or reconstruction of mandible and temporomandibular joint.     

Advances in sulfide phosphors for displays and lighting

For traditional applications such as cathode ray tubes and fluorescent lamps, many inorganic phosphors have been optimised during decades. For new applications in display and lighting technology, novel materials are being developed. After giving a short history of sulfide phosphors, the present paper will focus on Ca_1−x Sr _x S:Eu single crystal particle phosphors. The material is grown by solvothermal synthesis, process not needing toxic gases or high temperature processing steps. This phosphor combines a broad excitation spectrum and a broad—saturated red—emission spectrum, which makes it an ideal material for wavelength conversion in LEDs for general lighting.     

Single-wall carbon nanotubes as attractive toughening agents in alumina-based nanocomposites

The extraordinary mechanical, thermal and electrical properties of carbon nanotubes have prompted intense research into a wide range of applications in structural materials, electronics, chemical processing and energy management. Attempts have been made to develop advanced engineering materials with improved or novel properties through the incorporation of carbon nanotubes in selected matrices (polymers, metals and ceramics). But the use of carbon nanotubes to reinforce ceramic composites has not been very successful; for example, in alumina-based systems only a 24% increase in toughness has been obtained so far. Here we demonstrate their potential use in reinforcing nanocrystalline ceramics. We have fabricated fully dense nanocomposites of single-wall carbon nanotubes with nanocrystalline alumina (Al2O3) matrix at sintering temperatures as low as 1,150 degrees C by spark-plasma sintering. A fracture toughness of 9.7 MPa m 1/2, nearly three times that of pure nanocrystalline alumina, can be achieved.     

Thermal Conductivity Measurements of Thin Insulating Layers Deposited on High-Conducting Sheets

The thermal conductivity of thin insulating layers and coatings deposited on high-conducting sheets has been measured using the hot disk technique. The need for this type of measurements stems mainly from the electronics industry. In many situations, the materials supporting the thin layers or films are in the shape of thin sheets—often highly conducting ceramics, metals or anisotropic composites with a high-conducting component in the plane of the sheet. The present measurement setup has some interesting advantages with possibilities to design and optimize a system for performing convenient measurements on textiles. Although apparent properties are studied in the present investigation, the need to address thermal contact problems in general engineering constructions, including interfacial layers and thermal contact resistances, is discussed here. Experiences in this field indicate that, in order to perform correct thermal analysis and design, it is necessary to treat bulk material, thermal contact resistances, and interfaces separately. This is demonstrated by the fact that there is often a difference in interface conditions when performing a measurement as compared with the situation in which a manufactured component is being used.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

The effects of crystallography on grain-boundary migration in alumina

The sintering process of ceramics involves mass transport across grain boundaries resulting in the migration of these boundaries. When there is a liquid at the interface—as in liquid-phase sintering—the mass transport can be enhanced. In this study, electron backscatter diffraction has been used to examine grain-boundary migration of controlled interfaces in alumina. The interfaces were prepared by hot pressing single-crystal and polycrystalline alumina to single-crystal alumina substrates of known orientation. EBSD patterns, taken near the sintered interfaces, have been used to study the effects of crystallography on migration direction and rate.     

Werkstoffkundliche Basis für die Konstruktion mit Ingenieurkeramik

Fundamental Properties for the Design with Engineering Ceramics Within the class of technical ceramics a new group of high quality materials has been developed, called “engineering ceramics”. A definition is given, some of their properties and future applications for mechanical design are pointed out. Comparing to the fundamental properties and definitions known for metallic materials the distinctions and different approach for the design with engineering ceramics are discussed.     

New composite sorbents of water and ammonia for chemical and adsorption heat pumps

New sorbents of water and ammonia — “salt in porous matrix” composites and “salt on fiber” composites — have been reviewed. The possibility of “constructing” the sorption properties of the composites at the nanophase level by varying their composition, the size of the host-matrix pores, and synthesis conditions has been shown. The application of the new materials in adsorption refrigerating devices has been considered. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 6, pp. 160–175, November–December, 2006.     

Plaster of Paris as a model material for brittle porous solids

Plaster of Paris is a brittle, porous solid, easy to shape, which has potential as a model material for the study of brittle, porous, solids such as ceramics, rocks and cement. This paper describes the mechanical properties of plaster of Paris — modulus, strength, fracture toughness, etc. — as a function of porosity. The material is then used to study the initiation and propagation of cracks in compression, as a function of porosity, stress state and stress concentration.     

Nanocrystalline magnetic alloys and ceramics

Magnetic properties of materials in their nanocrystalline state have assumed significance in recent years because of their potential applications. A number of techniques have been used to prepare nanocrystalline magnetic phases. Melt spinning, high energy ball milling, sputtering, glassceramization and molecular beam epitaxy are some of the physical methods used so far. Among the chemical methods, sol-gel and co-precipitation routes have been found to be convenient. Ultrafine particles of both ferro- and ferrimagnetic systems show superparamagnetic behaviour at room temperature. Coercivity(H _c ) and maximum energy product(BH) _max of the magnetic particles can be changed by controlling their sizes. The present paper reviews all these aspects in the case of nanocrystalline magnetic systems — both metallic and ceramics.     

Preparation and characterization of glass composite using metal particles coated with semiconductive SnO2 fine particles obtained via sol—gel method

SnO₂—glass composites are promising materials for nitrogen-fireable thick film resistor systems. However, the SnO₂—glass composite has many undesirable properties which should be improved for industrial application, such as a high electrical resistivity and a large negative temperature coefficient of electrical resistance. This work was undertaken to make a survey of the methods for improvement in the electrical properties of the SnO₂—glass composites. The effect of the addition of Cu particles, with a large positive temperature coefficient of electrical resistance, on the electrical properties of SnO₂—glass composites has been investigated. Cu particles have been coated with semiconductive SnO₂ fine particles by hydrolysing tin and antimony ethoxides then firing. The coated particles have been applied as conductive components in the glass composite. Using SnO₂-coated Cu particles, Cu and SnO₂ particles are homogeneously dispersed in a glass matrix, and the electrical properties of the glass composites largely depend on the volume fraction of Cu in the glass composite. The volume fraction of Cu in the glass composite is determined by a Cu/SnO₂ volume ratio in the coated particles. From the experimental evidence, it is thought feasible to produce the glass composite having well-controlled electrical properties by the suitable selection of the Cu/SnO₂ ratio in the coated particles. This revised version was published online in July 2006 with corrections to the Cover Date.     

Skeletal tissues as nanomaterials

Collagen is the most abundant protein in the body and, though the fibre-forming collagens have a ‘common’ structure, it is adapted to perform a large range of functions—from the differing mechanical needs of tendon versus bone to forming a transparent support structure in the cornea. This perfidy also suggests that collagen could form a generic basis for a range of scaffold needs for tissue engineering or medical device coating applications. We at the London Centre for Nanotechnology—a joint venture between University College London and Imperial College—are taking a bottom-up approach having decided that many of the ‘accepted dogmas’ of collagen biology may not be quite as soundly based as currently held. We are using several of the tools of ‘hard’ nanotechnology—such as atomic force microscopy—to re-examine collagen structure with the longer term aim of using such information to design materials with appropriate physical attributes. Examples of our current research on mineralised and soft tissue collagens are presented.     

Microwave processing of WC-Co composities and ferroic titanates

 The innovations in microwave processing of ceramics have been dominated to date by serendipitous discovery, because the interaction between such radiation as delivered via available tools and the materials of widely varying properties, sizes, and shapes is so complex that it has defied quantitative analysis. For over 10 years a wide variety of inorganic ceramic and semiconducting materials have been synthesized, sintered, and reacted in our own labs, including microwave hydrothermal synthesis of metals, ferrites, and electroceramic phases. These local results are summarized and used as the reference point for reporting on two different new advances: sintering of WC-Co composite tool bits and other similar objects in under 15 min, while retaining extremely fine microstructures, without any grain growth inhibitors; using reduced TiO₂ or Ta₂O₅ for the synthesis of phases such as BaTiO₃, Ba3MgTa₂O9, and Pb(Zr.Ti)O₃ in a few minutes in a 2.45 GHz field at the astonishing temperatures of 300–700 oC. Received: 2 January 1997 / Accepted: 27 March 1997     

含硅有机/无机纳米杂化材料

综述了由有机硅氧烷制备有机/无机材料的sol gel方法,介绍了由此得到的杂化材料在光电材料、高性能陶瓷和聚合物以及其它功能性材料等方面的应用,并对新的sol gel原料作了展望。