New processes in material production under high pressure

Low-pressure cold spraying (LPCS) is a coating technique, in which a portable cold spray system, e.g., DYMET 304K system is used to prepare technical coatings. Usually, compressed air is used as the process gas. The LPCS process is an appropriate method for spraying of metallic-ceramic composite powder materials, e.g., Cu, Ni, Zn, Al with additions of Al2O3 particles in the powder blends. The main functions of the hard ceramic particles are cleaning the nozzle, activating the sprayed surface and peening the coating structure. This method has advantages for example in the field of repairing and restoration applications. For that, repairing casting defects and voids is one interesting application of the process. For these purposes, zinc-based composite materials are recommended for restoration and repairing of corrosion and mechanical damages. In this study, Zn+Al+Al2O3, Zn+Cu+Al2O3 and Zn+Ni+Al2O3 composite materials were investigated. Zinc and aluminum give corrosion resistance by cathodic protection whereas copper and nickel will provide also more mechanical resistance. Coating properties, such as microstructures, open-cell potential behavior and mechanical properties (hardness and adhesion strength) were investigated. The coatings have relatively dense coating structures and for corrosion resistance, zinc gives a cathodic protection for other materials in these composite coatings. Furthermore, mechanical properties are sufficient due to the relatively high hardness and adhesion to the Fe52 steel base material. These coatings have high potential in their use as repair materials for macroscopic casting defects.

Composite materials are engineered materials made from two or more constituent materials. They have significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure. The advantage of composite material is that they exhibit the best qualities of their components or constituents and often some qualities that neither constituent possesses. The properties that can be improved by forming a composite material are strength, stiffness, corrosion resistance, wear resistance, weight, thermal insulation, thermal conductivity, etc. Composite materials can be classified and characterized into four commonly accepted types; (1) fibrous composite materials that consist of fibers in a matrix, (2) laminated composite materials that consist of layers of various materials, (3) particulate composite materials that are composed of particles in a matrix and (4) the combination of some or all the first three types (Jones, 1999). According to the matrix phase the composites are divided into three groups; (1) metal matrix composites (MMCs), (2) polymer matrix composites (PMCs) and (3) ceramic matrix composites (CMCs). Ceramic materials in general have very attractive properties e.g.: high strength and high stiffness at very high temperatures, chemical inertness and low density. In the presence of flaws (surface or internal) they are prone to catastrophic failures. Ceramic materials can be toughened by incorporating fibers and thus exploit the attractive high-temperature strength and environmental resistance of ceramic materials without risking a catastrophic failure (Chawla, 1987). According to the basics written above, a monolithic silicone carbide (SiC) was used as a matrix phase, which has been recognized as one of the most promising structural materials for many thermo-mechanical applications because of its excellent hightemperature strength and modulus, good oxidation resistance, high hardness, low specific weight and low density (Xin-Bo & Hui, 2005; Xin-Bo et al., 2000; She et al., 1999). The problem with monolithic SiC is its low thermal shock resistance, which leads to cracking and catastrophic failure of the material. Thermal shock resistance and crack propagation can 6

Matrices are essentially binders for the reinforcements of composite material. Appropriate selection of fine chemicals is vital for the creation of desired matrices for generating composite materials. In fact, matrix is a subclass of a composite material. Matrices are generally of four kinds such as (i) polymer (hard as well as flexible), (ii) metal, (iii) ceramic, and (iv) cement. Each type of these subclasses of the matrix is discussed with a brief of their pros and cons. Polymer matrices are generally organic based whereas metal or ceramic matrices are inorganic in nature. Hard plastic matrix as well as flexible rubbery matrix are also discussed in the light of their applications. Carbon as matrix material for hi-tech C/C (carbon/carbon) composite materials is also stated. Cement is a special kind of inorganic matrix material because of its very special solidification mechanism during the formation of concrete composite; and it carries bulk values in the engineering area. For higher temperatures, carbon, ceramic or metal matrix materials are useful. Ceramics possess various conductivities, but they have poor tensile strength despite their ability to afford high-temperature products. Generally lightweight metals such as titanium, aluminum, magnesium, and intermetallics such as Ni-aluminide and Ti-aluminide are used; and the operating temperature can be extended to 2000 °C. The advantages of metal matrices are higher strength and ductility than those of polymers. Carbon matrix based carbon/carbon (C/C) composites can be used even at the temperature of ~3000 °C, but are preferred only in critical engineering areas of applications. Different types of matrix material may also prove to be efficacious constituent item for innovative design of integrated structure in the ever challenging area of Blast and penetration resistant materials (BPRM).

ABSTRACTThe purpose of this study is to examine the moderating role of state work pressure (conceived as a hindrance demand) on the relationships between situational emotional demands (conceived as a challenge demand) and tension, emotional exhaustion and work engagement within nursing while considering job resources as covariates. Ninety-seven nurses from two German hospitals provided 1026 measurements. Multilevel analyses indicated a significant Work Pressure × Emotional Demands interaction for emotional exhaustion, with high situational work pressure exacerbating the positive association between state emotional demands and emotional exhaustion. Furthermore, work pressure moderated the relationship between emotional demands and vigour: state emotional demands related negatively to vigour only when work pressure was higher than usual, while the relationship was non-significant when work pressure was lower than usual. For dedication, similar results were obtained: state emotional demands were negatively associated with dedication only when combined with high situational work pressure; with low situational work pressure, state emotional demands did not relate to dedication. Contributing to the job demands-resources literature, this study shows that there are stress-exacerbating and stress-buffering interactions between different job demands from a within-subject perspective. However, we did not find positive relationships between challenge demands and work engagement, even in the case of low situational hindrances, indicating that there are conditions for the functioning of job demands as a challenge beyond hindrances.

Matrix is an essential constituent for the formation of a composite material. Matrices are a subclass of materials, and they are generally of four kinds: (i) polymer, (ii) metal, (iii) ceramic, and (iv) cement. Each type of these subclasses of matrix is presented with a brief description of their pros and cons. Polymer matrices are organic-based, whereas metal or ceramic matrices are inorganic in nature. Carbon as a matrix material for high-tech carbon–carbon composite materials is also mentioned. Cement is a special kind of matrix material because of its very special solidification mechanism during the formation of concrete composites; and it is of high value in civil engineering. For higher temperature, metal, ceramic, or carbon matrix materials are useful. Generally, lightweight metals such as titanium, aluminum, and magnesium, and intermetallics such as nickel aluminide and titanium aluminide are used; the operating temperature can be extended to 2,000°C. Metal matrices have higher strength and ductility than polymers but at the cost of higher density. Ceramics have various conductivities, but they have poor tensile strength despite their ability to afford high-temperature products. Carbon matrix-based C/C composites can be used up to 3,000°C but only in critical areas of applications.

Composite materials based on metal and ceramic matrices appear in the design of parts and structures. The mechanical properties of the constituents of these com-posite materials are comparable. The design of parts made of polymer composite materials is usually based on the assumption of elastic deformations of constituents of the composite material, including the polymer matrix. This assumption does not always work for metal and ceramic composite materials, which makes it difficult to optimize products made of such materials. In addition, the assumption of the elas-ticity of the composites makes it impossible to estimate the ultimate deformation of the parts. In this connection, nonlinear properties of inhomogeneous, transversally anisotropic composite materials based on metallic or intermetallic matrices are dis-cussed here. It is assumed that the nonlinear properties of composite materials are formed by the nonlinear behavior of the matrix. Earlier, on the basis of the modi-fied theory of plastic flow, nonlinear dependences of the deformation of an anisot-ropic matrix were obtained. The modified theory of plastic flow makes it possible to take into account the nonlinear dependence not only between deviators of stresses and deformations, but also between the first invariants of stresses and de-formations. The nonlinearity in the dependence of the first invariants can be caused by particular manufacturing technology. Five independent strain curves for unidi-rectionally reinforced composite materials were obtained using the Maxwell and Feucht models. The obtained relations are used to find the stress-strain curves of an aluminum alloy unidirectionally reinforced with boron fibers.

Production of electric power by nuclear power plants (NPP) in the world and in Russia accounts for about 17%. Much attention is currently paid to safe NPP operation and to enhancement of their reliability. Present-day nuclear power plants with high-temperature gas-cooled rectors require development and application of new composite materials capable to withstand high temperatures and mechanical stresses. Ceramic composite materials where whiskers of heat-resistant chemical compounds are used as reinforcement fibers look promising for those purposes. The paper investigates and analyses the opportunity of applying whiskers as reinforcement fibers for heat-resistant composite ceramic building materials. Studies revealed that whiskers of silicon carbide and aluminium nitride are resistant towards high temperature heating without notable change in their chemical composition. It was found out that mono crystals of silicon carbide have higher mechanical strength owing to lack of defects in its structure. Linear heat expansion factors of silicon carbide that are needed for thermo-chemical calculations of composite materials on its base were determined.

Amorphous In-Ga-Zn-O (a-IGZO) thin film transistors, because of their relatively low mobility, have limits in attempts to fulfill high-end specifications for display backplanes. In-Zn-O (IZO) is a promising semiconductor material for high mobility device applications with excellent transparency to visible light region and low temperature process capability. In this paper, the effects of working pressure on the physical and electrical properties of IZO films and thin film transistors are investigated. The working pressure is modulated from 2 mTorr to 5 mTorr, whereas the other process conditions are fixed. As the working pressure increases, the extracted optical band gap of IZO films gradually decreases. Absorption coefficient spectra indicate that subgap states increase at high working pressure. Furthermore, IZO film fabricated at low working pressure shows smoother surface morphology. As a result, IZO thin film transistors with optimum conditions exhibit excellent switching characteristics with high mobility (≥ 30cm2/Vs) and large on/off ratio.

Embedding optical fibers into composite material is becoming a common procedure in various applications. Telecommunication optical fibers are commercially provided with acrylate or polyimide coating which are suitable when embedded into those materials. The situation is completely different when one think to embed optical fibers into metallic or ceramic materials or more in general when the application is at very high temperature. In this paper we use the electrowinning technique to deposit a sufficiently high thickness of a metallic protecting coating on optical fibers to be embedded into metallic and ceramic materials. A cylindrical cell has been used to electrodepose a uniform thickness of metal on optical fibers after making it conductive by a thin layer of graphite or aluminum. Metals having high melting temperature have been used to prepare the electrolyte. Different operative conditions such as current density, temperature, solution pH have been tested to optimize both process and protective coating properties.

New composite ceramic materials enable to improve mechanical properties and various performances more than monolithic ceramic materials. Generally, composite ceramic materials include more than two different materials, in addition, more than two crystal structures in case of α and β crystal phase composite Si3N4 material in this research. Composite ceramic materials enable to get various different characteristics that show excellent properties, not only mechanical properties but electrical properties, resistance to oxidation and wear. Properties improvement develops many new applications with superior performance more than conventional materials. In this research, we have developed various ceramic reinforced composite, based on Al2O3 and ZrO2 ceramics with carbide and nitride particles or whisker addition. Farther more we have developed α and β crystal phase composite Si3N4 material by researching the sintering additives stoichiometric ratio and sintering condition. Finally we succeeded in applying ceramic composite materials to various industrial parts, for example, Al2O3-TiC thin magnetic slider substrate, Al2O3-SiC whisker based cutting tool, Si3N4 squeezing roll and wear parts, ZrO2-WC ceramics punch and die for high speed pressing.

The article analyzes the work of the neutralization systems of nitrogen oxides used on modern trucks with diesel ICE. It is stated that the modern development of technologies for electronic fuel injection and catalytic neutralization of combustion products provides an opportunity to implement the processes of neutralization of nitrogen oxides with an efficiency up to 90%. The most effective method to reduce the exhaust emissions of diesel engines is to purify exhaust gases in the car exhaust system using the SCR-NH3 method. A significant drawback of this system is the presence of a toxic substance ammonia regulated by Regulation No. 49-06. Regulation No. 49-06 provides for the control in operation of emissions of nitrogen oxides by the on-board diagnostics system by introducing emission limit values, but monitoring of ammonia emissions in operation is not provided. It is noted that the state sanitary standards of the Russian Federation and the environmental monitoring service, prescribe in regulatory documents the control of the limit of emissions of harmful substances of ammonia and nitrogen oxides with MPCss 0.04 mg / m3. Thus, an identical approach to limiting these emissions is provided. In order for the purification system to function effectively with ammonia and to support the neutralization reaction, it is necessary to adjust the purification system and maintain the optimum temperature range of operation. It is noted that to ensure a high activity of reduction reactions, it is necessary to adjust the cleaning system and maintain the optimum temperature range of operation, the temperature is about 350-550 ° C. In this regard, the possibility of refining the neutralization system by the injection of urea into the cylinder of an internal combustion engine at the expansion stroke to neutralize nitrogen oxides and reduce ammonia emissions, as well as to increase the efficiency of a diesel engine, using the heat of exhaust gases by creating high pressure in the working cylinder work and boost pressure. When dosing urea solution having a high heat capacity through the nozzle and the subsequent process of expansion of exhaust gases, the temperature value in the cylinder of the internal combustion engine reaches the required value for the reduction reaction. High temperature, ensuring the removal of the reaction products, contributes to the high efficiency of maintaining the process of neutralization of NOx. Intra-cylinder cooling of the engine with urea-injected water solves the problem of thermal stress of the parts of the cylinder-piston group of a highly forced internal combustion engine without a significant increase in heat loss of the internal combustion engine.

The purpose of implants is to replace, restore, maintain or improve the functionality of various tissues and organs of the human body. Their use in modern medicine has significantly improved treatment methods and increased the quality and life expectancy of patients. The most preferable from the point of view of the possibility of imparting the required mechanical properties, the relatively low cost of the material and low production costs are metal implants. Metals and their alloys in the production of implants are superior to ceramic and polymer materials in a range of properties such as tensile strength, endurance limit, wear resistance, hardness, elasticity, viscosity, shape memory effect. The paper provides an overview of the designs of modern implants for various purposes and the metal materials used for their production. An analysis of literature sources has shown that modern implants made of metal materials represent a wide range and have significant differences in shape and size. Some of them are characterized by a small cross-section and rigidity, while possessing elastic properties. Other products are load-bearing, in some cases massive, structures. According to the proposed classification, according to their purpose, metal implants are divided into: dental, cranial, maxillofacial, vertebral, traumatological, cardiovascular and joint endoprostheses. An analysis of the advantages and disadvantages of the main metal materials used in the production of implants (corrosion-resistant steel, titanium and titanium alloys, cobalt-chromium alloys and nitinol) has been performed. It has been established that all currently used biocompatible metal materials are not completely inert towards the body. Each material in any case causes some reaction in the surrounding tissues. The greatest biocompatibility and corrosion resistance in the body is provided by technical titanium, which, however, has low strength characteristics.

Frost usually grows on the cooling surface of heat transfer equipment, which often operates under different working pressures. In such conditions, one of the fundamental influencing factors of frosting, the diffusion coefficient of water vapor around the cooling surface, is different from that in the normal atmosphere pressure. In order to investigate the pressure effect on frosting, a test rig for frosting visualization is designed. The role of working pressure around the cooling surface on the frost crystal morphologies and frost layer characteristics is evaluated under different air parameters and temperatures of cooling surface. The vertical growth and lateral distribution of frost crystals are strongly related to working pressure around the cooling surface. More frost crystal morphologies and faster growth rate of frost layer are presented at a lower pressure. The frost thickness, frost accumulation and density reduce with higher pressure. The dimensionless correlation of frost thickness is proposed considering working pressure around the cooling surface, humid air parameters, and temperature of cooling surface.

This article analyzes six types of composite pipes that are good replacements for corrosive steel and metal pipes for oil, gas, and water. The analysis of the six samples of composite pipes was done using the software program Hoffman Engineering, which is intended for the design and calculation of various types of products made of composite materials. For the analysis of the six composite pipes, the same diameter and the same length were taken, and variable parameters are: the type of material from which the composite pipes are made (carbon/epoxy, carbon-glass/epoxy and glass/epoxy), and the angle of winding of the fibers (10º and 90º degrees). Using the Hoffman Engineering software package, an analysis of the durability of the six differently designed composite pipes at high internal pressure was performed. The same conclusion was obtained from all analyses: the high internal pressure resistance of composite pipes is highly dependent on the fiber winding angle and the type of fibers used. Composite pipes obtained with a fiber winding angle of 90º have twice the internal pressure resistance compared to composite pipes obtained with a fiber winding angle of 10º. Composite pipes based on carbon fibers have the highest resistance to internal pressure, then composite pipes based on hybrid materials (glass and carbon fibers) and finally composite pipes based on glass fibers. Finally, a comparison was made with the obtained laboratory results for the same composite pipes. The same conclusion was obtained from all analyses: the high internal pressure resistance of composite pipes is highly dependent on the fiber winding angle and the type of fibers used. The composite pipes obtained by this process are durable and resistant to very high pressures.

The article presents the results of comparative tests on the wear resistance of composite materials (CM) sintered at high pressures and temperatures based on impact diamond (diamond-lonsdaleite abrasive — DLA) when processing silicon carbide (SiC). To assess the CM performance based on impact diamonds, a method has been developed for determining the wear resistance, based on the determination of the CM specific productivity. It is shown that for CMs based on impact diamond, it is expedient to use SiC as a binder. For CMs based on impact diamond with an additive of 40 vol.% SiC, specific productivity when machining a silicon carbide wheel is 25–30 % higher than for compositions containing dense BN phases — wBN and cBN. The decrease in the specific productivity of CM “impact diamond — cBN” relative to CM “impact diamond — SiC” is determined by the higher dispersion of crystals of dense BN phases in comparison with SiC, which generally impairs the abrasive ability of the material. In this case, the addition of a coarse fraction of impact diamond 100/63 μm to the charge composition does not lead to an increase in the specific productivity of the abrasive element as compared to CM based on DLA with a particle size of less than 40 μm. Preliminary mechanical activation of the initial charge also reduces the CM abrasive ability due to the formation of a highly dispersed structure of the material.