Year 2013, Volume 33

Abstract

The rapidly growing market demand for nanoparticles calls for cost-effective and environmentally friendly technologies for their large-scale production. We developed a new, simple, economical and energy efficient synthesis of nanostructured complex oxides from inexpensive reactant mixtures, referred to as Carbon Combustion Synthesis of Oxides (CCSO). In CCSO the exothermic oxidation of carbon nanoparticles generates a steep thermal reaction wave that propagates through the solid reactant mixture converting it to the desired complex oxide product. CCSO is a modified form of SHS that maintains the advantages of SHS and circumvents some of its disadvantages. Specifically, it enables a more economical synthesis of complex oxides. The carbon used in CCSO is not incorporated in the product and is emitted from the sample as a CO₂. A large gas emission provides a convective cooling mechanism trough the sample that significant reduces local temperature and prevents product partial melting and particles growth. CCSO does not require use of expensive fuel reactants and complex equipment and can be scaled up for continuous mass production. This paper reviewed the recent progress in the synthesis of advanced complex oxides nanoparticles by using carbon combustion process.

Abstract

A synthesis study of W₂B₅ powder was carried out by double self-propagating hightemperature synthesis (D-SHS) from CaWO₄, Mg and B₂O₃ mixture and followed by HCl leaching methods. In the first stage of SHS reaction, molar composition ratio of CaWO₄:B₂O₃:Mg mixture was selected as 1:1:8 (SHS-1) and 1:2.5:8 (SHS-2). The both SHS products were then acid leached (HCl) at optimum conditions for 1 hour and 80 °C to eliminate MgO, Mg₃B₂O₆ and Ca₃(BO₃)₂ phases. The first leached products were consisted of W, WB, W₂B₅, and W₂B phases. In the second stage of SHS process, the both leached products were reacted with the same amount of Mg and B₂O₃ mixture keeping previous initial ratio values (1:8 and 2.5:8). A successful SHS reaction was achieved only by using the mixture with leached SHS-2 product. After following acid leaching, the chemical composition of the leached D-SHS product was found to be 98.2 wt. % W₂B₅, 1.2 wt. % WB₄, and 0.6 wt. % WB.

Abstract

In this study, the self-propagating high-temperature synthesis (SHS) and following acid leaching techniques were carried out to produce zirconium diboride (ZrB₂) powder. In the SHS experiments, technical grade ZrO₂ powder, and different amounts of B₂O₃ and Mg powders were used. The SHS products were obtained in the form of black, spongy solid. In the leaching step, the effect of different acid concentrations on selective leaching was investigated by using optimum SHS product to eliminate the impurities such as MgO, Mg₃B₂O₆ and Mg₂B₂O₅. The products obtained were characterized by using XRD, ICP and SEM techniques.

Abstract

The increased interest in nanostructured materials is due to improvements in the mechanical properties presented for these materials. Significant increases in properties such as hardness, wear resistance and in some cases, strength and toughness of nanostructured ceramics have been reported, compared to conventional ceramics. High-energy milling can lead to selfsustaining reactions in a variety of systems. In this study, reactive high-energy milling was used to synthesis niobium carbide (NbC) nanoparticles. The reaction products were de-agglomerated and mixed with commercial ultra-fine alumina powder to produce alumina matrix nanocomposites with 5vol% of nanometric NbC. Alumina/NbC nanocomposite produced using powder obtained by reactive present good microstructural characteristic, high densities, good hardness and higher toughness. What makes this material an interesting alternative for production of ceramic cutting tools.

Abstract

Basic stages of progress in composite materials, prepared by SHS method, from a scientific approach to a promising and rapidly developing applications are discussed in this paper. The systematic review of different forms of composites prepared directly by SHS or by SHS-origin precursors is presented. Powders are usually the starting material for manufacturing of ceramic and a lot of attention has been paid to find new routes for synthesis powders in form of nano or micro particles. The present work is aimed at efficient and convenient powder processing by SHS as an important target for future composites technology. The use of SHS may bring a considerable development in ceramic technology, by enabling a manufacturing of sinterable, high-purity nano or micro powders. It can be demonstrated in different ceramic systems explored by the authors and coworkers using SHS e.g. (a) Si-C-N, (b) Al-O-N as well as (c) Ti-Si-C-N. Rapid combustion conditions were successfully used to manufacturing composite powders and nanopowders suitable for preparing multiphase composite materials having controlled properties.

Abstract

The presentation will report on the adoption of two different approaches based on selfpropagating high-temperature synthesis (SHS) to produce cermets. The first of these concerns the formation of the solid solution carbide, (Ti,V)C, of various compositions in an iron matrix by starting with elemental powders. It was observed that two types of carbide particles were generated within the matrix; a (Ti,V)C carbide of submicron size and a TiC-rich carbide of slightly higher size. Comparison of SHS Fe-TiC products showed that the addition of vanadium led to refinement of the carbide dispersions. The mechanism of formation of Fe-(Ti,V)C cermets will be discussed using chemical thermodynamic analysis. The second SHS approach involves the reaction between titanium and graphite by dropping compacted powders into a copper melts at 1250˚C. The process yielded dispersions of TiC within the matrix as well as graphite flakes. The reaction mechanism will be discussed and the potential of SHS to yield dispersions within metal matrices will be assessed.

Abstract

Some of ternary materials in the Ti-Al-C system are called MAX-phases and are characterised by heterodesmic layer structure. Their specific structure consisting of covalent and metallic chemical bonds influence its semi-ductile features locating them on the boundary between metals and ceramics, which may lead to many potential applications, for example as a part of a ceramic armour. Ti₂AlC is one of this nanolaminate materials. Self-propagating High-temperature Synthesis (SHS) was applied to obtain sinterable powders of Ti₂AlC Utilization of heat produced in exothermal reaction in adiabatic conditions to sustain process until all substrates are transformed into product is one of the advantages of the method that result in low energy consumption and low cost combined with high efficiency. Different substrates were used to produce fine powders of ternary material. Phase compositions of obtained powder were examined by XRD method. Than selected powders were used for sintering in various temperature both in a presureless sintering and hot-pressing in argon atmosphere. Properties and phase composition of obtained products were examined.

Abstract

The Self-Propagating High-Temperature Synthesis (SHS) method has been used to produce a new class of active catalyst materials based on metals, metal oxides and spinels for various applications. The method is characterized by very fast processing times (of the order of minutes), relatively low preheating temperatures and very high reaction temperatures produced as a result of carefully designed exothermic reactions. A large range of materials have been produced and characterized by a variety of physico-chemical and mechanical tests. This review devoted to Catalytic properties of SHS products. A number of catalytically active materials all over the world have been identified which offer promise for applications ranging from oxidation of CO and hydrocarbons to reduction of NO_x, methane dehydrogenation and other.

Abstract

In the work, interrelations between morphology of porous metalloceramics and thermal modes of SHS wave have been revealed on the basis of complex investigations including highspeed microvideo filming and dynamic pyrometry of processes, the physical and chemical analysis of products by the example of various intermetallic and hybrid (Ni, Co, Сr-Al, Ti-B-Cu, Ti-Si), metallothermic (FeTiO₃-Al, Si, C; FeO-Al₂O₃-MgO-Al, etc.) systems.

Abstract

Self-propagating High-temperature Synthesis (SHS) technology is characterized with high-temperature generation, spontaneous reaction propagation and rapid synthesis. Our research and development on simultaneous synthesis and sintering has progressed by applying mass force effects to SHS technologies; metal-ceramic composite pipe formation with centrifugal force on thermite reactions (“Centrifugal-thermite Process”) and fine ceramic composite synthesis under micro-gravity environments (MGE) formed with a free-fall, parabolic flight and sounding rocket. The process has successfully attained to produce more than 3 m long composite-layered pipes with significant feature for the production in its reaction propagation under centrifugal effect as well as the centrifugal force and reaction heat. In the latter, the TiB₂-Al composite synthesis under a free fall MGE, for example, has made clear that the lack of mass migration and the improvement of wetting between TiB₂ and Alunder the MGE affect the formation of a fine and dense cermet-like structure in the products. Anapproach on the mass-forced SHS technologies performed is introduced by designingproduct densities and SHS reaction system.

Abstract

The work deals with the review, analysis, systematization and classification SHS- refractories of a «Furnon» class are. The chronology of researches, introduction into industry are given, economic feasibility of their application in industries are shown. Comparative characteristics and distinctions of SHS- refractories with classical refractory are given. Current status, prospects and possible fields of using refractories produced by SHS method are considered.

Abstract

Functionally Grated Materials (FGMs) have usually been expected as candidates for a wide variety of industrial applications due to their desirable properties such as high heat resistance capability, good wear resistance, bio-compatibility, chemical stability and so on. Scaling-up and three dimensional (3-D) near-net shape forming technique for FGMs are one of the most important key-factor to produce the industrial engineering components and products in practical use. On the other hand, it is generally well known that the Spark Plasma Sintering (SPS) method is a novel process to produce homogeneous FGMs, nano-structural sintered compact, thermoelectric semiconductors and bio-medical materials in shorter sintering time with finer microstructure. This paper will present development of FGMs fabricated by SPS and future prospects of SPS on research and industrialization activities in Japan. A brief historical review progress of SPS technology is also given and the applicable field is exemplified. Then, the paper is focused on manufacturing processes on FGM by SPS technology.