Metals

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12 pages, 6050 KiB

Open AccessArticle

Influence of Magnetic Fields Assisted for Preparation of Ferromagnetic Mono- and Bi-Metallic Co and Co–V SHS Catalysts on Their Activity in Deep Oxidation and Hydrogenation of CO₂

by Elena Pugacheva, Vyacheslav Borshch, Svetlana Zhuk, Dmitrii Andreev, Denis Ikornikov, Olga Boyarchenko and Olga Golosova

Metals 2022, 12(1), 166; https://doi.org/10.3390/met12010166 - 17 Jan 2022

Viewed by 1410

Abstract

Co–Al and Co–V–Al intermetallics produced by centrifugal self-propagating high-temperature synthesis (SHS) were used as precursors for preparation of catalysts for deep oxidation and hydrogenation of CO₂. Leaching in NaOH solution and stabilization with H₂O₂ solution of precursors were [...] Read more.

Co–Al and Co–V–Al intermetallics produced by centrifugal self-propagating high-temperature synthesis (SHS) were used as precursors for preparation of catalysts for deep oxidation and hydrogenation of CO₂. Leaching in NaOH solution and stabilization with H₂O₂ solution of precursors were carried out in permanent magnetic field (MF) (0.24 Т) and alternating magnetic field (0.13 Т, 50 Hz). Prepared Co и Co–V (95Co–5V, 90Co–10V) granular catalysts with size of 100–300 µm were characterized by XRD, SEM, EDS, and BET method and revealed to have a scaly surface structure. It was shown that the type of MF affects phase composition and surface morphology, as well as specific surface and activity in deep oxidation of CO and hydrocarbons as an important part of the neutralization of gas emissions, and hydrogenation of CO₂, the processing of which would reduce atmospheric pollution with this greenhouse gas. Catalysts obtained in alternating MF was found to possess higher activity in the process of deep oxidation. Full article

(This article belongs to the Special Issue Metallothermic Reactions)

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16 pages, 4301 KiB

Open AccessArticle

Ta/Ti/Ni/Ceramic Multilayered Composites by Combustion Synthesis: Microstructure and Mechanical Properties

by Olga Kamynina, Sergey Vadchenko, Natalia Shkodich and Ivan Kovalev

Metals 2022, 12(1), 38; https://doi.org/10.3390/met12010038 - 24 Dec 2021

Cited by 6 | Viewed by 2000

Abstract

Ta/Ti/Ni/ceramic multilayered composites were successfully prepared by combustion synthesis. Laminated composites Ti–Ta–(Ti + 0.65C)–Ni–(Ti + 1.7B)–(Ti + 1.7B)–Ta–Ni-Ti and 3(Ti + 1.7B)–Ta–(5Ti + 3Si)–Ta–(Ti + 1.7B)–Ta–(5Ti + 3Si)–Ta–3(Ti + 1.7B) were combustion synthesized in an Ar atmosphere using (1) metallic foils (Ti, Ta, [...] Read more.

Ta/Ti/Ni/ceramic multilayered composites were successfully prepared by combustion synthesis. Laminated composites Ti–Ta–(Ti + 0.65C)–Ni–(Ti + 1.7B)–(Ti + 1.7B)–Ta–Ni-Ti and 3(Ti + 1.7B)–Ta–(5Ti + 3Si)–Ta–(Ti + 1.7B)–Ta–(5Ti + 3Si)–Ta–3(Ti + 1.7B) were combustion synthesized in an Ar atmosphere using (1) metallic foils (Ti, Ta, Ni) and (2) reactive tapes (Ti + 0.65C), (Ti + 1.7B), and (5Ti + 3Si), which, upon combustion, yielded ceramic layers as starting materials. The microstructure, crystal structure, and chemical composition of multilayered composites were characterized by SEM, EDX, and XRD. Their flexural strength was measured at 1100 °C. Upon combustion, Ta foils turned strongly joined with Ti ones due to the development of high temperature in the reactive layers yielding TiC_x and TiB_y. The formation of a liquid phase between metallic foils and reactive tapes and mutual interdiffusion between melted components during combustion favored strong joining between refractory metallic foils. Good joining between metals and ceramics is reached due to the formation of thin interfacial layers in the form of cermets and eutectic solutions. Full article

(This article belongs to the Special Issue Metallothermic Reactions)

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15 pages, 3672 KiB

Open AccessArticle

Discrete One-Stage Mechanochemical Synthesis of Titanium-Nitride in a High-Energy Mill

by Oleg Lapshin, Olga Shkoda, Oksana Ivanova and Sergey Zelepugin

Metals 2021, 11(11), 1743; https://doi.org/10.3390/met11111743 - 30 Oct 2021

Cited by 8 | Viewed by 1426

Abstract

Discrete (discontinuous) mechanochemical synthesis of titanium nitride was experimentally investigated. The experimental results show that mechanical activation intensifies the chemical conversion in the Ti-N system, and the discrete synthesis of the final product is conducted under “soft” controlled conditions without high heat release. [...] Read more.

Discrete (discontinuous) mechanochemical synthesis of titanium nitride was experimentally investigated. The experimental results show that mechanical activation intensifies the chemical conversion in the Ti-N system, and the discrete synthesis of the final product is conducted under “soft” controlled conditions without high heat release. The new theory of mechanochemical synthesis and the mathematical model based on it were used for theoretical evaluation of the dynamics of titanium activation in the nitrogen medium. It was found that the discrete mode of synthesis includes two factors accelerating mechanochemical reactions in the Ti-N synthesis: structural (grinding of metallic reagent and formation of interfacial areas) and kinetic (accumulation of excess energy stored in the formed structural defects in metallic reagent). The kinetic constants of the process were found using experimental data and the inverse problem method. The diagrams defining the controlled modes of obtaining titanium nitride particles with the given characteristics were constructed. A mathematical model for theoretical estimation of the dynamics of activation of titanium powder in the nitrogen medium was developed using a new macrokinetic theory of mechanochemical synthesis. Full article

(This article belongs to the Special Issue Metallothermic Reactions)

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10 pages, 4000 KiB

Open AccessArticle

Effects of Fe/Si Stoichiometry on Formation of Fe₃Si/FeSi-Al₂O₃ Composites by Aluminothermic Combustion Synthesis

by Chun-Liang Yeh, Kuan-Ting Chen and Tzong-Hann Shieh

Metals 2021, 11(11), 1709; https://doi.org/10.3390/met11111709 - 26 Oct 2021

Cited by 5 | Viewed by 1653

Abstract

Aluminothermic combustion synthesis was conducted with Fe₂O₃–Al–Fe–Si reaction systems under Fe/Si stoichiometry from Fe-20 to Fe-50 at. % Si to investigate the formation Fe₃Si/FeSi–Al₂O₃ composites. The solid-state combustion was sufficiently exothermic to sustain the [...] Read more.

Aluminothermic combustion synthesis was conducted with Fe₂O₃–Al–Fe–Si reaction systems under Fe/Si stoichiometry from Fe-20 to Fe-50 at. % Si to investigate the formation Fe₃Si/FeSi–Al₂O₃ composites. The solid-state combustion was sufficiently exothermic to sustain the overall reaction in the mode of self-propagating high-temperature synthesis (SHS). Dependence of iron silicide phases formed from SHS on Fe/Si stoichiometry was examined. Experimental evidence indicated that combustion exothermicity and flame-front velocity were affected by the Si percentage. According to the X-ray diffraction (XRD) analysis, Fe₃Si–Al₂O₃ composites were synthesized from the reaction systems with Fe-20 and Fe-25 at.% Si. The increase of Si content led to the formation of both Fe₃Si and FeSi in the final products of Fe-33.3 and Fe-40 at.% Si reaction systems, and the content of FeSi increased with Si percentage. Further increase of Si to Fe-50 at.% Si produced the FeSi–Al₂O₃ composite. Scanning electron microscopy (SEM) images revealed that the fracture surface morphology of the products featured micron-sized and nearly spherical Fe₃Si and FeSi particles distributing over the dense and connecting substrate formed by Al₂O₃. Full article

(This article belongs to the Special Issue Metallothermic Reactions)

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12 pages, 6219 KiB

Open AccessArticle

Energetic Materials Based on W/PTFE/Al: Thermal and Shock-Wave Initiation of Exothermic Reactions

by Ivan Saikov, Stepan Seropyan, Andrey Malakhov, Gulnaz Saikova, Igor Denisov and Evgenii Petrov

Metals 2021, 11(9), 1355; https://doi.org/10.3390/met11091355 - 29 Aug 2021

Cited by 8 | Viewed by 1792

Abstract

The parameters of combustion synthesis and shock-wave initiation of reactive W/PTFE/Al compacts are investigated. Preliminary thermodynamic calculations showed the possibility of combustion of the W/PTFE/Al system at high adiabatic temperatures (up to 2776 °C) and a large proportion of condensed combustion products. The [...] Read more.

The parameters of combustion synthesis and shock-wave initiation of reactive W/PTFE/Al compacts are investigated. Preliminary thermodynamic calculations showed the possibility of combustion of the W/PTFE/Al system at high adiabatic temperatures (up to 2776 °C) and a large proportion of condensed combustion products. The effect of the Al content (5, 10, 20, and 30 wt%) in the W/PTFE/Al system on the ignition and development of exothermic reactions was determined. Ignition temperatures and combustion rates were measured in argon, air, and rarefied air. A correlation between the gas medium, rate, and temperature of combustion was found. The shock initiation in W/PTFE/Al compacts with different Al content was examined. The extent of reaction in all compacts was studied by X-ray diffraction. The compositions with 10 and 20 wt% Al showed the highest completeness of synthesis after combustion and shock-wave initiation. Full article

(This article belongs to the Special Issue Metallothermic Reactions)

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14 pages, 6073 KiB

Open AccessArticle

Reactive Ni–Al-Based Materials: Strength and Combustion Behavior

by Stepan Seropyan, Ivan Saikov, Dmitrii Andreev, Gulnaz Saikova and Mikhail Alymov

Metals 2021, 11(6), 949; https://doi.org/10.3390/met11060949 - 11 Jun 2021

Cited by 16 | Viewed by 2411

Abstract

The effect of PTFE, continuous boron, and tungsten fibers on the combustion behavior and strength of reactive Ni–Al compacts was examined in this study. The introduction of continuous fibers into Ni–Al compacts according to the developed scheme was found to increase the flexural [...] Read more.

The effect of PTFE, continuous boron, and tungsten fibers on the combustion behavior and strength of reactive Ni–Al compacts was examined in this study. The introduction of continuous fibers into Ni–Al compacts according to the developed scheme was found to increase the flexural strength from 12 to 120 MPa. Heat treatment (HT), leading to chemical interaction of the starting components, increases the strength of compacts at temperatures not exceeding 550 °C. The combination of reinforcement and HT significantly increases the strength without reducing reactivity. Experimental results showed that strength and combustion rate increase with the reduction in PTFE to 1 wt % in Ni–Al compacts. A favorable effect of the addition of PTFE from 5 to 10 wt % on the reduction of the threshold for the shock-wave initiation of reactions in Ni–Al was established. The obtained results can be used to produce reactive materials with high mechanical and energy characteristics. Full article

(This article belongs to the Special Issue Metallothermic Reactions)

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7 pages, 1946 KiB

Open AccessArticle

Mo–Nb–Si–B Alloy: Synthesis, Composition, and Structure

by Dmitrii Andreev, Yurii Vdovin, Vladimir Yukhvid and Olga Golosova

Metals 2021, 11(5), 803; https://doi.org/10.3390/met11050803 - 14 May 2021

Cited by 2 | Viewed by 1637

Abstract

Cast refractory alloys Mo–Nb–Si–B were prepared by centrifugal self-propagating high-temperature synthesis (SHS) from metallothermic mixtures containing MoO₃, Nb₂O₅, Al, Si, and B powders, and additive of Al₂O₃ as a temperature-moderating and chemically inert agent. [...] Read more.

Cast refractory alloys Mo–Nb–Si–B were prepared by centrifugal self-propagating high-temperature synthesis (SHS) from metallothermic mixtures containing MoO₃, Nb₂O₅, Al, Si, and B powders, and additive of Al₂O₃ as a temperature-moderating and chemically inert agent. Variation in the centrifugal acceleration and amount of the additive affected the composition and structure of cast Mo–Nb–Si–B alloys. In a wide range of values, the combustion temperature was found to exceed 3000 K, and the combustion products were obtained as two-layer ingots of target Mo–Nb–Si–B alloy (lower) and Al₂O₃ slag (upper). Full article

(This article belongs to the Special Issue Metallothermic Reactions)

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11 pages, 3776 KiB

Open AccessFeature PaperArticle

Synthesis of FeSi-Al₂O₃ Composites by Autowave Combustion with Metallothermic Reduction

by Chun-Liang Yeh and Kuan-Ting Chen

Metals 2021, 11(2), 258; https://doi.org/10.3390/met11020258 - 3 Feb 2021

Cited by 7 | Viewed by 1708

Abstract

Fabrication of FeSi-Al₂O₃ composites with a molar ratio of FeSi/Al₂O₃ ranging from 1.2 to 4.5 was conducted by the self-propagating high-temperature synthesis (SHS) method. The synthesis reaction involved metallothermic reduction of Fe₂O₃ and SiO [...] Read more.

Fabrication of FeSi-Al₂O₃ composites with a molar ratio of FeSi/Al₂O₃ ranging from 1.2 to 4.5 was conducted by the self-propagating high-temperature synthesis (SHS) method. The synthesis reaction involved metallothermic reduction of Fe₂O₃ and SiO₂ by Al and the chemical interaction of Fe and Si. Two combustion systems were examined: one contained thermite reagents of 0.6Fe₂O₃ + 0.6SiO₂ + 2Al, and the other had Fe₂O₃ + 2Al to mix with different amounts of Fe and Si powders. A thermodynamic analysis indicated that metallothermic reduction of oxide precursors was sufficiently exothermic to sustain the combustion reaction in a self-propagating mode. The SHS reaction carrying out co-reduction of Fe₂O₃ and SiO₂ was less exothermic, and was applied to synthesize products with FeSi/Al₂O₃ = 1.2–2.5, while the reaction reducing only Fe₂O₃ was more energetic and was adopted for the composites with FeSi/Al₂O₃ = 2.5–4.5. Moreover, the former had a larger activation energy, i.e., E_a = 215.3 kJ/mol, than the latter, i.e., E_a = 180.4 kJ/mol. For both reaction systems, the combustion wave velocity and temperature decreased with increasing FeSi content. Formation of FeSi-Al₂O₃ in situ composites with different amounts of FeSi was achieved. Additionally, a trivial amount of aluminum silicate was detected in the products of high FeSi contents due to dissolution of Si into Al₂O₃ during the SHS process. Full article

(This article belongs to the Special Issue Metallothermic Reactions)

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