Papers by Keyword: SHS

Abstract: The objective of thiswork was to investigate the microstructure and adhesion of NiAl coating whichformed by self propagation high temperature synthesis (SHS) process. Ni/Almixture and an underlayer material which used Ni and Al were compacted to forma bilayer pellet and subsequently put on a steel substrate. The Ni/Al reactionwas ignited using induction heating in a combustion chamber of argon gas. Themorphology and microstructure of the products were observed using SEM and XRD.The results showed that further reactions between NiAl coating and underlayermaterials formed several intermetallic phases. The role of Al and Ni underlayeron the microstructure, porosity and the adhesion between coating and thesubstrate was observed.

Abstract: We show here that Ni₃Al compound which is widely used as the base metal for advanced multipurpose hot-resistant alloys may be efficiently bulk nanostructured for improving its physical and strength characteristics. Developing the nanostructured component in the bulk of the intermetallic compound is achieved by plastic deformation of an SHS product during its synthesis and crystallization under conditions of thermal explosion of nickel/aluminum powder mixture of stoichiometric composition. It was shown that the nanosize component is formed on the basis of intermetallic Ni₃Al synthesized by SHS under hot forging conditions from nickel/aluminum powder mixed with an inert binder component. Developing the nanosize structural components improves strength of the intermetallic alloy.

Abstract: C_f/ZrC-xCu composite ceramics with different Cu content were prepared by self-propagating high-temperature synthesis/pseudo–hot isostatic pressing (SHS/PHIP). The effect of Cu content on the microstructure and properties of C_f/ZrC composite ceramics were investigated. Our results indicated that carbon fiber was serious chemical damaged in the absent of Cu, accompanied by attenuating of the reinforced effect.Whereas, the density of the complex was increased in the present of Cu content in a dose-dependent-way due to the better fluidity of Cu. Adding to Cu into the complex material leads to the increased diffusion resistance of the elements, decreased damage of the carbon fiber. Meanwhile, the ability of flexural strength manifested as incureasing-decreasing manners according to the elevation of Cu content, while, the fracture toughness was increased gradually. We finally concluded that we could get the best composite ceramic in the present of 25V% of Cu.

Abstract: In this paper mathematical model of self-propagating high-temperature synthesis combined with extrusion was proposed and investigated. The problem was solved in one-dimensional formulation with consideration of viscous, thermal and concentration stresses. Evolution of temperature, density was investigated.

Abstract: In this work, a series of samples of Mo (Si_1-xAl_x)₂ (X =0, 0.10,0.20,0.30,0.40) were prepared by self-propagating high-temperature synthesis (SHS). The influence of the addition of Al on the structures and the micrographs of the final compounds were investigated. X-ray diffraction pattern characterization (XRD) and scanning electron microscopy (SEM) were used to characterize the obtained products. It was found that, the reactions between Mo and Si could be promoted with introducing Al during the SHS process. The high temperature β-MoSi₂ phase with hexagonal structure (C40) was obtained and the peaks of the C40 phase shifted towards a higher d value with increasing aluminum substitution. The substitution of Al could reach to 40%. The morphology of the final products was similar with that of the raw Mo powders, which was independent of Al contents.

Abstract: In order to study the treatment of simulated radioactive graphite contains ⁹⁰Sr by SHS and its β-irradiation stability, waste forms were prepared in accordance with the reaction 3C + 4Al + 3TiO₂ = 2Al₂O₃ + 3TiC+Q, by self-designed SHS equipment. Then the β-ray irradiation experiments were done at dose of 10⁶Gy to evaluate its radiation resistance. The phase composition and morphology of the prepared waste forms before and after irradiation were characterized by X-ray diffractometer (XRD) and scanning electron microscope (SEM). The XRD results indicated that the major composition of the waste forms were Al₂O₃, TiC, C, TiO₂ and AlN after reaction in atmosphere, and the SrO solid solubility could be up to 8wt%. It was found that the surface morphology of waste forms were mostly plate-shaped and mainly in about 10μm. The structure and microscopic morphology of waste forms didn't change significantly before and after irradiation according to the XRD spectra, SEM photos. Moreover, the calculated cell parameters results suggested that the lattice parameters of the main phase (TiC, Al₂O₃) changed about 10^-3~10^-2nm after irradiation, and the degree of changes in cell volume was about 10^-4~10^-3nm³ magnitude. The simulated ⁹⁰SrO–containing radioactive graphite waste forms showed a certain β-ray radiation resistance.

Abstract: Hypoeutectic and hypereutectic Al₂O₃+ZrO2 multiphase ceramic-lined composite pipes were produced by using the gravitational separation self-propagate high-temperature (SHS) process. The microstructure of the ceramics was observed by means of SEM and EPMA. The multi-phase ceramics base consists of lamellar or rod-like eutecticum of ZrO₂ with Al₂O₃, and Al₂O₃ dendrite is distributed between (Al₂O₃+ZrO₂) eutecticum and the ZrO₂ is distributed on boundary area between (Al₂O₃+ZrO₂) eutecticum in appearance of band and particle alone in the hypoeutectic multi-phase ceramics, and ZrO₂ is distributed between (Al₂O₃+ZrO₂) eutecticum in appearance of snowflake-like or fishbone-like in hypereutectic multi-phase ceramics. On the basis of combustion synthesis, material thermodynamics, metallurgy dynamics and ceramics materials theory, the formation of microstructure mechanism have been systematically investigated.

Abstract: A combustion synthesis method has been developed for synthesis of Eu²⁺ doped CaAlSiN₃:Eu²⁺ phosphor and its photoluminescence properties were investigated. Ca, Al, Si, and Eu₂O₃ powders were used as the Ca,Al,Si,and Eu sources. NaN₃ and NH₄Cl were found necessary to be added for the formation of the product phase and addition of Si₃N₄ was found to enhance the product yield. These powders were mixed and pressed into a compact which was then wrapped up with an igniting agent (Mg+Fe₃O₄). The reactant compact was ignited by electrical heating under a N₂ pressure of 0.8 MPa. The synthesized CaAlSiN₃:Eu²⁺ phosphor absorbs light in the region of 240-520 nm and shows a broad band emission in the region of 500-800 nm due to the 4f⁶5d¹4f⁷ transition of Eu²⁺.The synthesized phosphor thus has a potential application as a red phosphor for white LED lighting.

Abstract: One of the materials with high potential for application as a refractory material is aluminum oxynitride with spinel-type structure, γ-alon. Alon materials, single-phase or composites, are characterized by good mechanical properties, high thermal shock resistance and a high corrosion and erosion resistance. Another advantage is possibility of usage of SHS method for producing of relatively good sinterable powders of γ-alon, however, are characterized by poor compressibility. This paper describes a method of compaction of SHS-derived γ-alon powder using the hydrolysis reaction of aluminum nitride, which is one of the products of SHS synthesis. The green bodies made from the powder with addition of 10 mas.% of water after two weeks of storage reach a strength level up to 30 MPa and an open porosity of less than 30%. Pressureless sintering of the such compacts allows to achieve 95% of theoretical density at 1700°C in less than one minute.

Abstract: In order to evaluate the performance of the self-propagating high-temperature synthesis (SHS) to treat ⁹⁰SrO-contained radioactive graphite in N₂ atmosphere, waste forms were prepared with the self-developed SHS reactor according to the waste forms formulation designed with a solid-soluted content of 010 wt% (calibrated in mass, hereinafter the same). The waste forms were made with the exothermic reaction (3C + 4Al + 3TiO₂ = 2Al₂O₃ + 3TiC + Q), where, ⁸⁸SrO (a stable Sr isotope)-containing ⁸⁸SrO was used to simulate ⁹⁰SrO. And the raw materials for the waste forms were the powdery materials of graphite (C), aluminum (Al) and titanium dioxide (TiO₂). Then, X-ray diffractometer (XRD) and scanning electron microscope (SEM) were used to test and analyze the phase composition and morphology of the prepared waste forms. According to the results in dealing with the treatment with the given exothermic reaction of the ⁹⁰SrOcontaining radioactive graphite in N₂ atmosphere, the SrO solid solubility could be up to 8 wt%. Besides, with a SrO content of 0~2 wt%, the major composition of the waste forms was including: alumina (Al₂O₃) in diamond scheme, titanium carbide (TiC) in cubic phase, graphite (C), anatase titanium dioxide (TiO₂) and aluminum nitride (AlN) in cubic phase. Comparatively, with a SrO content of 3~8 wt%%, the major composition of the waste forms was including: alumina (Al₂O₃) in diamond scheme, titanium carbide (TiC) in cubic phase, graphite (C), anatase titanium dioxide (TiO₂), aluminum nitride (AlN) in cubic phase and rhomboid aluminum titanate (Al₂TiO₅). Furthermore, diffractive peaks of unidentified phase occurred at 2θ = 7.7°, 15.6°, 19.8° and 24.1° position, whose intensities were increased with the increasing additional SrO content. The grain sizes of the prepared waste forms are mainly within 515μm, majorly exist in pieces.