SHS Reaction Research Articles

Propagation rate and product modulation in SHS reactions via focused microwave heating

This study investigated how locally focused microwave (MW) energy can be used to manipulate the local burn rate and product composition in an SHS reaction. Ball milled Al/Zr/C composites were prepared by ink-printing and locally heated by a monopole MW antenna remotely. Color pyrometry and infrared thermometry were used to analyze the local burn rate and temperature profile of the combustion. The local induced heating by the microwave resulted in an acceleration of the local burn rate (> 2.5×) from which an effective-activation energy of ∼ 30 kJ/mol was extracted. The burn rate under these various conditions were found to be independent of the measured heat flux to the pre-heating zone. This coupled wit the low value of the activation energy implies mass transfer control. Product analysis showed that the mole fraction of ZrC in the product increases with local burn rate. This study demonstrated localized MW energy offers the potential to dynamically modulate burn rate and modify spatial distribution of product formation in SHS reaction.

CHROME PLATING OF PRESS TOOLING USED IN THE PRODUCTION OF NEW ELASTOMERIC MATERIALS

This research has produced multicomponent titanium-doped chromium coatings to strengthen the working surfaces of press tooling dies operated under aggressive conditions during the vulcanization of products from new elastomeric materials. The pressing was carried out on a hydraulic vulcanization press 100-400 2E. with plate sizes 400x400 of new elastomeric materials based on 10 wt.% carbonized fiber from PAN (RC Helper) or (USA), which significantly increases the heat capacity of rubber based on a copolymer of vinyl develfluoride and hexopropylene by 15-30% in the operating temperature range from 323 to 348 K. In the work, samples from mass-produced steels such as steel 20, steel 45, U8, 40H, and 40H16M were used for coating. Mixtures of powders with a dispersion of 60-250 microns of the following materials were used as reaction agents. In determining the required dispersion of reagents, we were guided by studies that found that the maximum completeness of the transformation is observed when using a reaction mixture with a fraction of 100-120 microns. The protective coatings on samples under the conditions of the SHS were obtained at the developed pilot plant DSTU12, consisting of the following main functional systems: reaction equipment; system for monitoring and controlling technological parameters; and gas utilization system. The organization of the SIS consists in creating a powder mixture and an environment that provides exothermic interaction at the local initiation of the process (ignition). Then, the reaction wave propagates spontaneously (combustion) and the synthesized product is cooled. According to the type of chemical reaction, three SWS processes can be distinguished: direct synthesis from elements; direct synthesis from compounds and exchange reactions; and metallothermal SHS (reactions with a reducing step). The surface microhardness of multicomponent chrome layers alloyed with titanium and boron is 20000 - 22000 MPa, which is due to the presence of the phase FeB. The microhardness of the alloyed Fe2В phase is 15000 – 16000 MPa. When chromium coatings are alloyed with titanium on the considered structural materials, the following phases are formed: (Fe,Cr)23C6, (Fe,Cr)7C3, Cr3C2, as well as phases: Fe2Ti, Cr2Ti. The surface microhardness of titanium-alloyed chromium coatings is: on steel 20 – H100= 16000 MPa, (phases: (Cr,Fe)23C6, (Cr,Fe)7C3, Fe2Ti, Cr2Ti, α- solid solution of Ti and Cr in α- iron), on steel 45 – H100 = 18000 MPa (phases: (Cr,Fe)23C6, alloyed with titanium, α-solid solution of chromium in iron with Cr2Ti inclusions), on U8 – H100= 19500 MPa (phases: directly on the outer side of the coating there is a zone of carbides (Fe,Cr)23C6, (Fe,Cr)7C3, Cr3C2, (Ti,Cr)C).

Express-diagnostics of the properties of ЫРЫ materials using chrono-topographic analysis of thermal vision data

Subject of research: the article is devoted to the development of a methodology for express diagnostics of material properties based on the measurement of macrokinetic parameters of the SHS process.
 Purpose of research: plotting the dependence of the microhardness of SHS products on the propagation velocity of the SHS wave and its temperature.
 Methods and objects of research: the research objects were the SHS process in the Ni-Al system and the reaction products; To measure the propagation velocity of a high-temperature synthesis wave, an original method of chrono-topographic analysis of thermal imaging data was used; temperature control was carried out by an original method of spectral-brightness pyrometry. The study of the microhardness of experimental samples was carried out using an FM-800 microhardness tester.
 Main results of research: in the course of experimental studies, it was shown that the error in determining the propagation velocity of the SHS wave by the method of chrono-topographic analysis of thermal imaging data is 0.1 %, and the error in temperature measurement by the method of spectral-brightness pyrometry is estimated at 0.5 %. It is concluded that the main factor influencing the total error in the SHS wave propagation velocity in the experiment is the inaccuracy of setting the charge parameters for a set of samples. The absolute value of the total error was 3.2 %. A diagnostic trajectory has been constructed that makes it possible, based on the SHS propagation rate and reaction temperature, to evaluate the microhardness of the product and draw a conclusion about the quality of charge preparation for the production of a material with desired properties.

Recognition of Synthesized Intermetallic Interlayers at the Interface in Ti@Al "Core — Shell" Nanoparticles Based on Computer Molecular-Dynamic Simulation

The paper presents the results of applying a new method, previously developed by the authors, based on precalculated sets of 3D distributions of a matter density. The method is designed to recognize the spatial 3D distributions of the synthesized intermetallic compounds in the volume of a nanoparticle. A set of 3D distributions of a matter density in the volume of a cubic Ti@Al core — shell nanoparticle corresponds to a set of successive time points. It is calculated based on the results of the computer molecular dynamics simulation of self-propagating high temperature synthesis in the nanoparticle. Computational experiments are performed using the LAMMPS software package. Based on the obtained results, thermal and microstructural analyses are performed, confirming the multistage mechanism for the formation of intermetallic phases during the SHS reaction in the Ti-Al reaction medium. The sets of 3D distributions of the matter density and 3D distributions of synthesized intermetallic compounds in the volume of a nanoparticle corresponding to the sequence of time points are calculated. The paper shows the advantage of the method for recognizing 3D distributions of synthesized intermetallic compounds, proposed by the authors, over the methods of similar analysis built into the OVITO software package.

3D Visualization of Heterophase Intermetallic Structures Based on Computer Simulation of SHS in a Nanosized Ti-Al Layered-Block Structure

he paper presents the results of thermal and microstructural analysis of the SHS of intermetallic compounds in a nanosized atomic layer-block structure of Ti-Al, obtained using the freely available software packages LAMMPS and OVITO, as well as using the software of the authors of the paper. Using the LAMMPS package in the version of parallel computing, the software implementation of which is based on the "molecular dynamics" method, the SHS process is simulated. For 3D visualization of simulation results, the OVITO package is used. Among the results of microstructural analysis, noteworthy is the appearance of stable heterophase intermetallic structures during the SHS reaction, which were confirmed using the OVITO package and the software module developed by the authors for calculating a set of matter density profiles of the SHS-product. In heterophase intermetallic structures, it was possible to detect local features in the form of layered quasi-coherent intermetallic interlayers with the presence of two-dimensional defects in crystal lattices — twinning planes delimiting pairs of grains (twins) with symmetrical lattices reorientation.

Study on tensile, bending, fatigue, and in vivo behavior of porous SHS–TiNi alloy used as a bone substitute

Intermetallic porous SHS–TiNi alloys exhibit tangled and specific stress–strain characteristics. This article aims to evaluate the findings emanating from experiments using standard and proprietary instruments. Fatigue testing under repeated complex loading was used to measure the total number of load cycles before failure of the SHS–TiNi samples occurred. Of the tested samples, seventy percent passed through 106 cycles without failure due to the reversible martensite transformation in the TiNi phase, one of the prevailing constituents of a multiphase matrix. The fractured surfaces were analyzed using scanning electron microscopy and confocal laser scanning instruments. Microscopy studies showed that the entire surface of the sample is concealed by miscellaneous strata that result from the SHS processand effectively protect the porous alloy in a corrosive environment. Numerous non-metallic inclusions, which are also attributed to the SHS reaction, do not have a significant impact on the deformation behavior and fatigue performance. In this context, the successful in vivo functioning of porous grafts assessed in a canine rib-plasty model allows the bone substitute to be congruentially deformed in the body without rejection or degradation; it thus has a long operational life, often greater than 17 ×106 (22 × 60 × 24 × 540) cycles. It acknowledges the potential benefits of SHS–TiNi as a superior osteoplastic material and its high resistance to corrosion fatigue.

Combined Use of SHS and SPS: Important Mechanistic Details

The processes of current flow and reaction initiation in a mixture of Ti–Cu spherical particles were studied in model experiments and in real conditions of SPS processing. Our results allow us to conclude that the local overheating during SPS-consolidation of powder materials is caused by the formation of some preferable current pathways within which current density is markedly greater than within the adjacent areas. This leads to the breakdown of thin dielectric layers (oxide films, vacuum nanogaps) at particle-to-particle contacts, the conductivity of this route sharply grows, and the constituent particles become overheated selectively. In turn, local overheating gives start to SHS reaction and formation of reacted areas in the sample bulk. Our results may turn useful to those engaged in the optimization of process charts and process conditions for SPS-consolidation of materials.

New criteria for the applicability of combustion synthesis: The investigation of thermodynamic and kinetic processes for binary Chemical Reactions

Combustion synthesis is a novel technique that utilizes the exothermic heat of a chemical reaction to maintain the reaction and to rapidly prepare materials. But, hitherto, none of unified criterion for the validation of combustion synthesis has been proposed. Herein, we proposed the conditions need to be met. In terms of kinetics, at the adiabatic temperature (Tad), the diffusion distance of atoms (lTad) within 0.1 s should be larger than the particle size of the reactants(d), that is, lTad≥d. For systems that satisfy Tad/Tm,L≥1(where Tm,L is the melting point of the low-melting point component of the reactants), the presence of a liquid phase significantly increases the atomic diffusion distance from nanometers to tens of microns, making the criterion lTad≥d simplified to Tad/Tm,L≥1 in most situations. In terms of thermodynamics, the system needs to ensure that the reaction components are in an activated state, that is, Tad/Tm,H≥0.7, where Tm,H is the melting point of the high-melting point component. The criteria for the SHS reactions proposed in this study further improve the theoretical understanding of SHS reactions, and provide guidance for exploring the ultra-fast synthesis of binary and multicomponent compounds.

Mechanoactivated SHS in the Ti–Ni System: Influence of Preheating Temperature

Product composition and combustion parameters for non-activated and mechanically activated Ti–Ni mixtures were explored as a function of preheating temperature T0. Upon an increase in T0, frontal combustion of activated blends was found to change to a mode of thermal explosion at T0 around 190°С. Frontal combustion of non-activated blends was accompanied by local melting over the entire range of T0. Our results may turn helpful in theoretical modeling of SHS reactions.

Microstructure and Mechanical Properties of <i>In Situ</i> Cast Aluminum Based Composites Reinforced with TiC Nano-Particles

This work concerns microstructure and mechanical properties investigations of aluminum based composite strengthened with the TiC particles being in nanometer size. The composites were fabricated by the casting method combined with in-situ formation of TiC particles. Applying a suitable composition of components and moderators of SHS reaction which occur during casting, it was possible to cast the samples with TiC particles of size of 150 nm and faceted shape. Microstructure investigations using scanning and transmission electron microscopy (SEM and TEM) allowed to identified the distribution of TiC particles and their preferred location in the microstructure of composites. Also the additional precipitates with different size and shape were identified in investigated samples. Significant increase of strength was observed in in-situ cast composites in comparison to Al-1000 alloy mainly due mainly due to coefficient of thermal expansion and elastic modulus mismatch between the reinforcements and the metal matrix, Hall-Pecht relation and also in minority the Orowan effect.

SCSTempCal Software for Solution-Combustion-Synthesis Applications

Windows-based SCSTempCal computer program for calculating maximum combustion temperatures (Tmax) attained in SCS reactions was suggested in both English and Russian versions. The program affords for estimating Tmax at four approaches, as well as for modeling SCS reactions by method of successive corrections. Program performance was illustrated on the example of SCS reactions yielding simple and complex oxides. Using the synthesis of α-SiC as an example, we demonstrated the applicability of our program to conventional SHS reactions. The program may turn interesting for researchers, students, graduate students, and production specialists engaged in the problem. SCSTempCal program is available for free as a supplementary file.

Self-combustion of Ti-C and Ti-Al Powder Mixture in a Nitrogen Atmosphere: Product Application as Reinforcement in Metal Matrix Composites

In this work, two copper metal matrix composites (MMCs) reinforced with 20 wt.% of Ti(C,N) or Ti2AlN particles were studied. The reinforcement particles were synthesized by flash sintering under 2 bar nitrogen atmosphere causing an SHS reaction ignited by electrical current. This reaction led to produce TiC0.7N0.3 solid solution for the MMC1 reinforcement and Ti2AlN, TiN, and Ti3Al titanium aluminide for the MMC2 reinforcement. Both MMCs were densified by liquid phase sintering. The structural characterization was performed by XRD analysis while the morphology and chemical element distribution of both MMCs were analyzed by SEM and EDS. The structure of the two MMCs was relatively dense and showed good wettability. The mechanical and tribological behavior of MMCs evaluated by nanoindentation and wear testing reveals that the addition of 20 wt.% of reinforcement considerably improves the properties of copper matrix. Indeed, the MMC1 proved to be 3 times harder and 10 times more wear-resistant than the MMC2 composite.

Effect of mechanical pre-activation on the nitriding of aluminum ferrosilicon in the combustion mode

A ceramic β-SiAlON-based composite is obtained by the SHS method using aluminum ferrosilicon as a raw material. The effect of mechanical pre-activation of a reaction mixture on the nitriding of aluminum ferrosilicon is studied. Mechanical activation of initial powders initiates SHS reaction at lower pressures and diameters, i.e. expands the parameters of combustion of aluminum ferrosilicon in nitrogen. It is shown that the nitriding of mechanically activated powders in the combustion mode can be used to obtain products with a higher nitrogen content. The products were investigated thoroughly. XRD analysis showed the presence of major phase β-Si3Al3O3N. As being one of the most widely used structural ceramics for various applications, exhibits excellent mechanical strength and superior high temperature properties.

Thermostimulation of titanium aluminide synthesis by high-calorie mixtures

A comparative microstructural and phase analysis of titanium aluminide samples obtained by SHS method in shells from a highly exothermic thermite mixture and an equimolar mixture of Nickel and aluminum is carried out. The energy of exothermic reactions of the shells allows heating the charge on the basis of titanium and aluminum and starting the SHS reaction in it. In the sinter sample in the Ni-Al shell, the reaction of titanium aluminide synthesis was not complete; the samples have a high-porous structure with small frame inclusions of intermetallides. In the synthesis of samples in the shell of the thermite mixture obtained alloy, optimal porosity and structure. The main phase in the samples obtained in different modes is titanium aluminide, also in both samples there are inclusions enriched in titanium (Ti3Al, Ti2Al phases), while the phase analysis did not reveal the presence of the initial components of the charge.

Preparation of Green Mixtures for SHS Reactions: Characterization by Impedance Spectroscopy

The processes occurring during mixing two-component fuel–oxidizer powder mixtures in a ball-mill were explored by the methods of impedance spectroscopy. A transition from the ‘globular’ to ‘framed’ type of conductivity was found to happen after 15 hours of ball milling. Impedance spectroscopy can be used to determine (1) the moment of homogenization and (b) the onset of mechanochemical reaction in the course of intermixing.

Metallothermic SHS in Conditions of Artificial Gravity: Mathematical Modeling

Metallothermic SHS in conditions of artificial gravity was numerically modelled for the 3NiO + 2Al → Al2O3 + 3Ni reaction taken as an example. The process was assumed to include (a) high-temperature combustion reaction yielding liquid products, (b) their gravity-assisted separation, and (c) cooling down. In our ‘throughout’ mathematical model, a three-component emulsion—gas, metal, and ceramics—with individual translational velocities and temperatures was considered. Our model may expectedly extend the range of control means for SHS reactions in extreme conditions.

Thermally coupled SHS processes in layered (Fe2O3 + 2Al)/(Ti + Al)/(Fe2O3 + 2Al) structures: An experimental study

TiAl intermetallic was prepared through thermal coupling of highly exothermic Fe2O3–Al reaction (donor) and low-caloric Ti–Al reaction (acceptor). Green compacts represented three-layer ‘donor–acceptor–donor’ sandwich-type structures. The combustion process was video taped and combustion temperatures in the bulk of donor and acceptor layers and at the interfaces were monitored with a set of thermocouples. The results of video filming and thermocouple measurements allowed us to establish which mode of thermally coupled SHS reaction took place in our conditions. The combustion product was found to contain the TiAl intermetallic with small admixture of Ti3Al and unreacted Al.

Facile and rapid synthesis of Mo5SiB2-based ceramics from solid-phase combustion reaction with reducing stages

Thermite-based combustion reaction combining MoO3 and B2O3 as the oxidants, Al as the reductant, with Mo, Si, and B powders was conducted to fabricate Mo5SiB2–Al2O3 composites. Combustion synthesis involving co-reduction of MoO3 and B2O3 is less exothermic than that adopting MoO3 as the sole oxidizing agent. The resulting products with Mo5SiB2/Al2O3 ratios between 0.8 and 1.3 were synthesized from the MoO3/B2O3-based samples and those between 1.25 and 2.5 from the MoO3-based samples. These two combustion reactions were shown to have low activation energies of Ea = 60.7 and 86.5 kJ/mol, indicating that the SHS reactions involving aluminothermic reduction of either MoO3/B2O3 or MoO3 significantly reduce the kinetic barrier of forming Mo5SiB2. In particular, it was found that prolonged reaction times contributed to the improvement in evolution of Mo5SiB2 from intermediate phases (Mo3Si and MoB) for the samples with a reaction front speed slower than 4 mm/s or a pulsating combustion wave. The as-synthesized composites exhibit a dense morphology with connecting plate-like Mo5SiB2 grains.

Application of SHS in the Manufacture of (NiAl/Ni3Al)/TiB2 Composite

The aim of this study was to demonstrate the advantages and the method of application of the SHS process in the manufacture of (NiAl/Ni3Al)/TiB2 composites. A comparison was made between sinters manufactured by FAST/SPS using two different routes to process the substrates, which formed the composite matrix. The evaluation criteria were based on measurements of selected physical, mechanical, and tribological properties, and on microstructure examinations. The evaluation has indicated a preferable method for the manufacture of composites, where the SHS reaction takes place during compaction of the powder mixture. This produces a sinter characterized not only by the high degree of sintering, and high values of the Young’s modulus and HV1 hardness, but also by the satisfactory resistance to tribological wear. Additionally, the use of this process saves energy and reduces product-making cost, owing to a less expensive technique of making individual substrates.

High-temperature reactive melt spreading: Experimental modeling of SHS reactions

Initial stages of high-temperature spreading and inreaction of molten droplets with solid substrates were experimentally investigated in the systems Ti–C and Nb–B. Thin layer of solid product (carbide, boride) crystalline grains forms immediately in the spreading frontier, while the melt infiltrates through nano-scale gaps between grains. The formation of a continuous layer of oxidation- and wear-resistant solid refractory (∼ 3000°C) product can be utilized for coating protection of refractory metals and carbon materials, as well as in high-temperature joining of carbon materials via a thin layer of titanium carbide.