Self-propagating High-temperature Combustion Synthesis Research Articles

Computer molecular-dynamic simulation of shs microkinetics in the atomic structure with a checkerboard-like arrangement of nanoscale blocks of Ni and Al atoms

The article presents the results of computer simulation of the propagation of the combustion wave of "self-propagating high-temperature synthesis (SHS)" process in an atomic layered structure. In each layer of the structure, nanosized blocks of two types alternate: a block of the first type is composed as a packet of unit cells of Ni atoms, and a block of the second type is composed of a packet of elementary cells of Al atoms. In each pair of layers adjacent to each other, sequences of alternating blocks of two types are shifted relative to each other by one block, so the full layered structure of the layers with alternating blocks in them is associated with a chessboard pattern. Computer simulation of SHS in such a structure was carried out using the LAMMPS software package taking into account parallel computations, which uses the molecular dynamics method and the interatomic interaction potential in the embedded atom" model (EAM). In addition to the LAMMPS package, the authors implemented program procedures for calculating the temperature and density profiles of the substance along the motion direction of the SHS combustion wave front, which made it possible to carry out temperature analysis of the SHS microkinetics (to estimate the velocity of the combustion wave front) and recognition of intermetallic phases in the reaction volume of the Ni-Al system when using the OVITO package.

The synthesis of the MoSi<sub>2</sub> material under the influence of the shift pressure

The self-propagating high-temperature synthesis (SHS) was used to prepare the molybdenum disilicide powder material by means of the aluminum and silicon reduction. It was shown that the mechanical action applied to the material after the SHS combustion wave has passed it through, can destroy the synthesized pellets which the conventional self-propagating high-temperature synthesis has created. The mechanical action's increasing in the course of the SHS-crushing breaks the agglomerated particles up to the fner fractions, as well; as it changes the morphology of the synthesized powder.Ill.3. Ref. 8.

Catalytic combustion of soot over Cu, Mn substitution CeZrO2-δ nanocomposites catalysts prepared by self-propagating high-temperature synthesis method

This study concentrates on improving the low temperature performance of CDPF catalysts. The self-propagating high temperature combustion synthesis method was applied to synthesize a series of CeZrO2-δ, CuCeZrO2-δ, and MnCuCeZrO2-δ catalysts, which were coated on DPF substrate. The performance of the catalysts was fully investigated by the soot temperature programmed combustion, which showed that these catalysts with nanometer size have a high catalytic activity of soot combustion at low temperatures. Compared with Ce0.05Zr0.05O2-δ, Cu0.9Ce0.05Zr0.05O2-δ and Mn0.09Cu0.81Ce0.05Zr0.05O2-δ showed excellent low temperature soot oxidation activities and much higher CO2 selectivity. BET, XRD, TEM, and XPS were employed to characterize the structural and physical-chemical properties of catalysts. The XRD results indicated that catalysts with 90% Cu possess evenly distributed crystalline grains and small particle size, which is responsible for its excellent oxidation activity by providing more active sites as well as forming good connection between the catalyst and soot. The XPS results demonstrated that the Cux+ has a significant association with the formation of NO2, thus promoting the soot oxidation, and that the synergetic effect between Cux+ and Mnx+ contributes most to the improvement of the catalytic activity. The partial substitution with Mn could enhance the chemisorbed oxygen, which further improved NO oxidation and CO2 selectivity. Furthermore, the soot combustion reaction mechanism was examined with in situ DRIFTS. The results exhibited that the active sites of Cu0.9Ce0.05Zr0.05O2-δ and Mn0.09Cu0.81Ce0.05Zr0.05O2-δ could generate more reactive oxygen for NO oxidation and that the uniformly dispersed Cux+ and Mnx+ in Ce lattice could adsorb NO2 to form nitrite and nitrates, which behaved as a carrier of NO2 and transported it around the surface of soot, thus facilitating the soot combustion, especially at low temperatures.

Synthesis of Ti3AlC2 by SHS and thermodynamic calculation based on first principles

In this paper, a self-propagating high-temperature combustion synthesis with the pseudo-hot isostatic pressing process (SHS/PHIP) was employed to fabricate high-pure Ti3AlC2 (Φ 240 mm). In addition, the first principle with quasi-harmonic approximation was applied for the thermodynamic properties’ investigation of Ti2AlC and Ti3AlC2, including Gibbs free energy, enthalpy, and entropy. With temperature increasing, Gibbs free energy increases, but enthalpy and entropy decrease. The present work provides the theoretical proof for the synthesis mechanism of Ti3AlC2 by SHS/PHIP.

Sintering behavior and properties of SiC/Si3N4 composite

SiC/Si3N4 composite was pressureless sintered using self-propagating high-temperature combustion synthesis α-Si3N4 powder and appropriate amount of β-SiC powder. Both of the sintering additive systems were used, which were YAN (Y2O3–Al2O3–AlN) and YN (Y2O3–AlN). The influences of β-SiC content on sintering behavior of SiC/Si3N4 composite were investigated. The results show that the density, shrinkage, bending strength, hardness, and fracture toughness of the samples with two sintering additive systems increase first with the increase of the contents of β-SiC and then decrease even when β-SiC contents continually increase. The tendency of weight loss of the samples is opposite. The β-SiC content of the samples with the best mechanical properties is different in two systems. For YAN system, the best mechanical properties of the samples are gained when β-SiC content reaches 10 %, while as for YN system it is 5 %. The properties of YN samples are superior to YAN samples. J phase (2Y2O3·Si2N2O) forms in YN system easily. A small amount of M phase (Y2O3·Si3N4) is observed in YAN system.

Lead Evaporation from CRT Glass and Nanocrystallization Mechanism in the High-temperature Self-propagating Process

Lead evaporation and recovery of nanoparticle materials from waste cathode-ray tube (CRT) glass using the self-propagating high-temperature synthesis (SHS) method was investigated. The reaction temperature and combustion velocity of the mixture of Fe2O3-Mg-CRT in the SHS process were studied in detail. Then the lead extraction ratio, phase compositions as well as the micromorphology of extracted PbO nanoparticles were examined. The thermodynamics of lead evaporation and nanocrystallization mechanism were also analyzed. It can be found that the SHS reaction temperature and combustion velocity decrease with increasing CRT glass content, and the addition of CRT glass as a diluent can be used to control the SHS lead extraction behavior to obtain PbO nanoparticles with good desperation and morphology. With 40wt% CRT glass addition, about 93% of lead can be recovered from CRT glass as nano-sized PbO with high purity. The collected PbO nanoparticles are almost spherical in shape with particle sizes ranging from 40 nm to 50 nm, which are mainly from the volatilization and rapid condensation during the SHS process. The study indicates a novel method to recycle and reuse waste CRT glass.

Effect of discrete period lengths of mechanic activation on layerwise SHS combustion in low-energy Nb-Si system

We studied how the lengths of discrete periods of mechanical activation of a Nb-Si powder mixture influence the parameters of the layerwise mode of self-propagating high-temperature synthesis (SHS). It is shown that the way of configuring the discrete periods influences the maximum temperature and the rate of the subsequent layerwise SHS combustion.

Microstructure and Properties of TiC/Ni3Al Composites Prepared by Pressureless Melt Infiltration with Porous TiC/Ni3Al Preforms

In this article, porous TiC/Ni3Al preforms were fabricated by self-propagating high-temperature combustion synthesis (SHCS). Then, the porous TiC/Ni3Al preforms were densified with infiltrated Ni3Al melt via the conventional pressureless infiltration, and TiC/Ni3Al composites were prepared. The composites were characterized by microstructure observation and mechanical property measurements. The results demonstrate that the wetting ability of liquid Ni3Al to porous TiC/Ni3Al preforms is better than that of liquid Ni3Al to TiC preforms. The porous TiC/Ni3Al preforms can be completely infiltrated by Ni3Al melt via pressureless infiltration technique, and then densified TiC/Ni3Al composites without defects can be obtained. During the infiltration process, both Ni3Al and TiC/Ni3Al preforms were thermally and chemically stable, and the infiltration resulted in no new phases. Comparing the similar composites prepared with TiC preforms infiltrated by melt Ni3Al via pressureless infiltration, bending strength of the TiC/Ni3Al composites of this work was much improved with higher reliability. The interfaces between TiC particles and the intermetallic compound Ni3Al were the main points of failure in the composites. Strengthening mechanism of the TiC/Ni3Al composites consisted of mainly pullout of TiC particles from the matrix and crack deflection surrounding Ni3Al particles.

Effect of self-propagating high-temperature combustion synthesis on the deposition of NiTi coating by cold spraying using mechanical alloying Ni/Ti powder

Nickel titanium alloy powder was fabricated by mechanical alloying process. The powder was employed to form Ni50-Ti50 alloy deposit by cold spraying. The thermal stability of the as-milled powders was characterized by differential scanning calorimetry. The surface morphology and cross-sectional microstructure of the coatings were examined by scanning electron microscopy (SEM). The coating microstructure was also characterized by X-ray diffraction analysis. It was observed that the Self-propagating High-temperature combustion Synthesis (SHS) phenomenon occurs during cold spraying using Ni/Ti mechanical alloying powders. The deposition efficiency of Ni50-Ti50 coating was significantly influenced by the SHS reaction level of MA powder. The gas temperature igniting the SHS reaction during cold spraying decreased with the increase of ball milling time. The ignition of SHS reaction led to partial melting of Ni/Ti powder. It was found that the melted particle fraction which resulted from SHS reaction led to splashing of spray particles off substrate on impact, which significantly decreased the deposition efficiency. A model was proposed to explain the coating deposition behavior during cold spraying using the mechanically alloyed metastable Ni/Ti powder with the stoichiometry of a NiTi intermetallic compound.

Microstructure and Wear Resistance of TiC/Ni3Al Composites Made by Pressureless Melt Infiltration Processing

Porous TiC-Ni3Al performs were fabricated by using Ni, Al, Ti and graphite powder with self-propagating high-temperature combustion synthesis (SHS) method. Then, the porous perform were infiltrated with melt Ni3Al via the conventional pressureless infiltration process to prepare TiC/Ni3Al composites. Effects of the infiltration temperature and time on the microstructure, hardness and wear resistance of the composites were studied. XRD, SEM and EDS were used to analyze the phase identification and the solubility of Ni3Al and TiC in each other. The results show that pressureless melt infiltration is an effective method to fabricate dense TiC/Ni3Al composites. The infiltration time can greatly decrease when the infiltration temperature suitably increases. No obvious effect of the infiltration temperature and time on the hardness and the wear resistance of the composites were found. Ni3Al and TiC were well bonded, and they are the only two phases in the composites after infiltration. The wear resistance of TiC/Ni3Al composites including 70% and 80% TiC were promoted 3.25 and 4.33 times compared with pure Ni3Al, respectively.

Emission phenomena in a SHS combustion wave

There are numerous experimental data indicating that the action of electromagnetic and magnetic fields on the combustion wave of self-propagating high-temperature synthesis (SHS) changes the process kinetics and the structure and properties of the reaction products. Emission phenomena in the combustion wave have received less attention. High rates of chemical energy dissipation in SHS (1012 W/m3) are accompanied by physical phenomena such as the occurrence of a potential difference between the combustion front and reaction products, free electron emission from the combustion wave, and acoustic emission. Detailed studies of these nonequilibrium phenomena provide a deeper understanding of the reaction mechanism in solid flames to use nonthermal methods of combustion control.

A novel synthesis of B–Al–Ca–O–(N) glasses by self-propagating high-temperature combustion method

Glasses in the B–Al–Ca–O–(N) system have been prepared by self-propagating high-temperature combustion synthesis (SHS) directly from mixed powders of B, Al and CaO under pressurized dry-air of 3 MPa. The nitrogen content of the SHS product is 0.63 mass%, the value of which is about 30 times higher than that of conventional molten glass fabricated in air. Their initial reactants, B and Al when ignited, transform instantaneously into oxides, nitrides and oxynitride with a high exothermic heat of reaction. Sequentially the reacted products in a liquid state solidify into a glass material by rapid cooling. The glass forming region is similar to that of the same oxide glass system prepared by the conventional melting method.

Osteoblast-like cell mineralization induced by multiphasic calcium phosphate ceramic

The work presented here examines the effect of multiphasic CaP materials on the activity of SaOS-2 osteoblast like cells. Heterogeneous calcium phosphate (HCaP) was synthesized using self-propagating high temperature combustion synthesis (SHS). All samples were characterized using XRD, SEM, and FTIR. Cell culture procedures of HCaP with SaOS-2 cells followed ASTM 813-01. Samples were examined by Environmental SEM (ESEM) and EDS to characterize the mineral content of the cultures. Gold-coated samples were used for high-resolution imaging. Biomineralization was noted in unconditioned cultures exposed to HCaP while the controls (cells only in media and HCaP only in media) showed no mineralization. Calcium phosphate plate-like structures were identified adjacent to cells expressing calcium phosphate containing vesicles. These structures are similar to the organophosphate crystals seen in other published works. Plate-like crystals were noted in the larger membrane vesicles of SaOS-2 cells indicating the occurrence of cellularly mediated biomineralization.

Characterization and microstructural studies of LiFe5O8 synthesized by the self propagating high temperature combustion method

LiFe5O8 was synthesized by the self-propagating high temperature combustion synthesis using lithium acetate and iron acetate as starting materials and glycine as reductant. The reaction was rapid when the ignition temperature was reached and the product was a light and porous mass of solid material. Analysis using X-Ray powder diffraction and SEM revealed the amorphous nature of the LiFe5O8 precursor material. From particle size analysis, the precursor material was much less than 100 nm, but increased upon annealing at 650 °C and 900 °C.

Properties of Refractory Composites Prepared from Alkaline-Earth Chromates by Self-Propagating High-Temperature Synthesis

Refractory composites MgCrO4 + Mg + MgO and MCrO4 + Al + Al2O3 (M = Mg, Ca, Ba) prepared by self-propagating high-temperature synthesis (SHS) are studied in model experiments, and their properties and conditions for SHS combustion reactions are discussed.

Combustion synthesis of alkaline-earth substituted lanthanum manganites; LaMnO3, La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3

Alkaline-earth substituted lanthanum manganites La1 − xAxMnO3 (A = Ca, Sr; x = 0, 0.4) were synthesized in air by self-propagating high-temperature synthesis (SHS): a combustion process involving the reaction of lanthanum(III) oxide, calcium oxide (or carbonate), strontium peroxide, manganese metal powder and sodium perchlorate. A very sensitive thermal imaging method was used to study the combustion characteristics of the SHS-process. This method is based on the continuous measurement of the combustion process using an IR-camera and software developed by MIKRON Instrument Co., Inc. (M9100 Pyrovision Series – Imaging Pyrometer). X-Ray powder diffraction, scanning electron microscopy (SEM)/energy dispersive analysis by X-rays (EDAX), infrared spectroscopy and vibrating sample magnetometry were carried out on all samples. X-Ray diffraction data showed that single-phase orthorhombic LaMnO3 and monoclinic La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3 were formed. Magnetic properties were found to transform from antiferromagnetic for LaMnO3 to weak ferromagnetic for La0.6Ca0.4MnO3 to strong ferromagnetic for La0.6Sr0.4MnO3. The experimental results show the SHS route is useful for the synthesis of multicomponent Mn-based oxides. The thermal imaging work enables accurate monitoring of the SHS combustion process and enabled velocity of propagation, maximum temperature, cooling rates, synthesis wave width and synthesis wave path to be determined with high precision.

Burning velocities in catalytically assisted self-propagating high-temperature combustion synthesis systems

The current work presents an experimental study of catalytically assisted self-propagating high-temperature synthesis (SHS) of the tantalum/carbon material system. The effects of controlled amounts of two gas-phase transport agents (carbon dioxide and vaporized iodine) were examined. The gas-phase transport agents resulted in burning velocities 2 to 4 times faster than burning velocities observed in comparable catalytically assisted and unassisted Ta/C SHS systems. The gas-phase transport agents clearly augment the combustion synthesis process. The burning velocities of the catalytically assisted, non-melting SHS systems were found to be strong functions of particle size, pressure and the amount of gas-transport agent present. The results are compared with previous studies of both catalytically assisted and unassisted Ta/C SHS, and discussed in the context of proposed transport mechanisms.

Thermophysical Properties of Al<sub>2</sub>O<sub>3</sub>-TiC<sub>x</sub> (x = 0~1) Composites Prepared by Self-Propagating High-Temperature Synthesis (SHS)

Al 2 O 3 -TiC ceramic is an important industrial material which is widely used as wear-resistant parts such as cutting tools. Self-propagating high-temperature synthesis (SHS) provides an attractive practical alternative to the conventional methods of producing this kind of materials because SHS offers advantages with respect to process economics and process simplicity. On the other hand, the properties of Al 2 O 3 -TiC ceramic depends on the stoichiometry factor x of TiC x . Out previous work has shown that the properties of Al 2 O 3 -TiC ceramic can be improved by FGMs (Functionally Graded Materials) concept. In the present work, dense Al 2 O 3 -TiC x ceramics with x value in the range of 0∼1 were manufactured by SHS combustion reaction: 3TiO 2 + 3xC + 4Al → 3TiC x + 2Al 2 O 3 . Only cost effective raw materials were used. Thermophysical properties of SHS produced Al 2 O 3 -TiC x ceramics (x=0∼1), such as thermal diffusivity, thennal conductivity and specific heat were investigated as functions of the stoichiometry factor x of TiC x .

Pulsating instability in the nonadiabatic heterogeneous SHS flame: Theory and experimental comparisons

Linear pulsating instability of the nonadiabatic heterogeneous self-propagating, high-temperature synthesis (SHS) flame is analyzed based on a premixed mode of propagation for the bulk flame supported by the non-premixed reaction of dispersed nonmetals in the liquid metal. The formulation allows for volumetric heat loss in the bulk flame and temperature-sensitive Arhenius mass diffusion in the liquid with infinitely fast surface reaction in the diffusion limit, as is the case for most SHS processes. Neutral stability boundary, which separates the regime of steady combustion from that of pulsating combustion, has been obtained by determining the critical heat-loss parameter as functions of the eldovich number, melting parameter, and melting point of the metal Results show that the instability is promoted by increasing the heat generation rate at the bulk flame and/or reducing the heat-transfer rate from the flame, particularly by increasing the mixture ratio, decreasing the degree of dilution, decreasing the size of the nonmetal particles, increasing the compact diameter, and decreasing the thermometric conductivity of the compacted mixture. The theoretical results are found to agree well with available experimental data, in trend and in approximate magnitude, indicating that the heterogeneous theory for the SHS flame propagation captures the essential features of this unstable SHS combustion process.

Specific features of the behavior of synthetic diamond in a self-propagating high-temperature synthesis (SHS) combustion wave

The behavior of synthetic diamond powder in an SHS combustion wave is considered by using the model Ti-B-diamond system as an example. The results presented show that the diamond can retain its properties when exposed to the extreme thermal conditions realized in an SHS combustion wave.