Solid-state Combustion Reactions Research Articles

Crystal Structure, Ionic Conductivity, Dielectric Properties and Electrical Conduction Mechanism of the Wyllieites Na1.5Mn3.5(AsO4)3 and Na1.5Mn3Fe0.5(AsO4)3

Na1.5MnII3MnIII0.5(AsO4)3 and Na1.5MnII3FeIII0.5(AsO4)3 compounds were synthesized via a high-temperature solid-state combustion reaction. The obtained samples were submitted to structural, morphological, and electrical characterizations. X-ray diffraction measurements revealed that both compounds crystallize in the monoclinic system with the space group P21/c. The lattice parameters were determined to be a = 6.78344 Å, b = 12.93830 Å, c = 11.22825 Å, and β = 98.5374° for Na1.5MnII3MnIII0.5(AsO4)3, and a = 6.76723 Å, b = 12.9864 Å, c = 11.256 Å, and β = 98.8636° for Na1.5Mn2+3Fe3+0.5(AsO4)3. The structures consist of octahedral MnII and MnIII or FeIII ions connected by sharing edges, forming infinite chains. These chains are further connected by AsO4 tetrahedra, resulting in a three-dimensional anionic framework with tunnels parallel to the a-direction and cavities according to the c-direction. The structural models were validated using bond valence and charge distribution analyses. In addition to the structural characterization, the electric results depended on the crystal structures, indicating the potential of the studied materials for being used in several applications.

The solid-state combustion synthesis of in-situ hybrid (Al3Ni+Al2O3)/Al composites and evaluation of its mechanical properties

In-situ hybrid (Al3Ni+Al2O3)/Al composites with bimodal size particles distributions were fabricated via an Al-NiO solid-state combustion reaction and subsequent hot extrusion process. The reaction system between Al and NiO was investigated by differential thermal analysis (DTA). The presence of Al2O3 and Al3Ni in the matrix was verified by XRD/EDS analysis. The in-situ formed Al3Ni phase with varying morphologies and sizes such as particle, plate, strip and flake at different sintering temperatures were observed. And the exothermic reaction of Al-NiO can be reduced to below the melting point of Al, and the desirable sintering temperature was. 600 ℃. In hot-extruded samples, both nano Al2O3 and Al3Ni particles distributed homogeneously, and most of Al3Ni particles is smaller than 2 µm in size. When NiO content increases from 8% to 12%, Al matrix grains in composites can be refined from 1.7510 µm to 1.2050 µm. The mechanical properties of composites are enhanced significantly due to the introduction of Al3Ni and Al2O3 particles, and can be up a YS of 322 MPa and a UTS of 407 MPa in the 15% NiO-Al composite. In addition, when the content of NiO increases from 10% to 12%, the strength of composites enhances without obvious sacrifice of EI. The strengthening and toughening mechanisms also was discussed in detail.

Thermochemical reactions of Al-based intermetallic composites to AlN

Rapid, self-sustaining thermochemical reactions of reactive materials are not well understood at molecular/atomic levels, regarding how they evolve chemically and release energy at high temperatures. This situation emphasizes the need of real-time structural and temperature data obtained during thermochemical reactions in reactive materials. In this paper, we describe time- and angle-resolved x-ray diffraction (TARXD) capable of probing the structural and temperature evolution of reactive materials upon thermal ignitions using pulse laser- and electric-heating. Several types of reactive materials were investigated to elucidate chemical mechanisms for: (i) intermetallic exchange reactions in Al/Ni(50:50) to Al3Ni2 and Al3Ni, upon rapid quenching of molten phases of Al/Ni alloys; (ii) diffusion-controlled, solid-state combustion reactions in intermetallic composites of (Al/Ni(50:50) + h-BN) and metallic composites (Al + h-BN) to produce h-AlN; and (iii) combustion reactions of metallic mixtures (Al + B) with N2 in air to produce metastable cubic AlN.

Synthesis and heat treatment of sprayed high-temperature NiAl–Ni3Al coatings by in-flight combustion synthesis (CAFSY)

Combustion-Assisted Flame SpraYing (CAFSY) of intermetallic coatings is a new, cost-efficient and on-site-applicable thermal spraying process for applying Ni–Al intermetallic overlays or bond-coats on metallic substrates for protection at high temperature. This is the synthesis of desired intermetallic phases inflight and in-situ on the substrates during oxy-acetylene thermal spraying, using only low cost base-metal powders. By adjusting the spraying conditions (initial composition, spraying distance, substrate temperature, and flame temperature), excellent Ni–Al-based coatings have been produced on various substrates, including mild steel, stainless steel, and aluminum alloys. In some cases, however, the intermetallic phases formed on the substrates during CAFSY have been found to be metastable or the nickel and aluminum powders have not reacted sufficiently. In such cases, post-spraying heat treatments of the coatings allow the solid-state combustion reactions to proceed to completion in the coating. In many cases, it was found that increasing the temperature and the duration of the heat treatment increased the amount of intermetallic compounds (NiAl, Ni3Al, NiAl3, and Ni2Al3) in the coating up to as much as 90 vol %. In particular, all remaining aluminum reacts completely by forming Ni–Al intermetallics in the coatings. In all cases, porosity of the coatings remains below 3% while adhesion strength increases and reaches 57 MPa. The CAFSY method is a special manifestation of combustion synthesis, along the lines of the well-known SHS method. Without the need for expensive pre-alloyed intermetallic powders, optimization of spraying conditions allows very fast, in-flight reactions between component base metal powders to produce the required coating alloys when they reach the surface of the substrate. The actual mixture of the intermetallic phases of the coatings and their properties can be optimized for any industrial use by controlling spraying conditions and composition of powder mixtures.

Efficient Synthesis of Stoichiometric Lithium Tantalate Powder by a Solid-State Combustion Route

Stoichiometric lithium tantalate (SLT) powder was prepared by a solid-state combustion method from the raw powder of Li2CO3, Ta2O5, and urea, which is characterized by a short reaction time and relatively low temperatures. The urea, added into the mixture (Li2CO3 and Ta2O5), serves as a fuel and an inducer to produce intermediate compounds and cause a solid-state combustion reaction as well. Various temperatures and urea contents were employed to optimize the synthesis of SLT. The chemical process and the quality of LiTaO3 powder were investigated by X-ray diffraction, electron microscope, thermogravimetry, and Raman spectroscopy. The optimized synthesis shows great capability to reduce the volatilization of lithium-ion and presents an efficient way to manufacture high-quality SLT.

Facile synthesis of LiMn2O4 octahedral nanoparticles as cathode materials for high capacity lithium ion batteries with long cycle life

Spinel lithium manganate octahedral nanoparticles have been prepared by high temperature solid-state combustion reaction using cellulose as fuel. The crystal structure, morphology, and electrochemical performance of the as-prepared materials are analyzed by X-ray diffraction (XRD), electron microscopy, and electrochemical testing. The XRD results show that the materials are single-phase and perfectly crystalline with a spinel structure. Microscopic observations reveal that the nanoparticles possess octahedral morphology, with an average particle size of about 165.4 nm and a uniform particle size distribution. The lithium manganate octahedral nanoparticles exhibit excellent initial discharge capacity of 118.5 and 78.3 mAh g−1, and about 72.49% and 94.6% of its initial discharge capacity can be retained even after 1600 cycles at 10 C and 3000 cycles at 20 C, respectively. The excellent electrochemical performance of the lithium manganate can be mainly attributed to the strong MnO6 framework mitigates the occurrence of Mn dissolution, maintains structural stability, and allows higher Li+ diffusion during electrochemical cycling. Furthermore, the nano-sized octahedral structure not only facilitates fast ion diffusion, but also mitigates the manganese dissolution due to the exposed (111) crystal planes, where the solid electrolyte interphase (SEI) forms.

Long cycle life, high rate capability of truncated octahedral LiMn2O4 cathode materials synthesized by a solid-state combustion reaction for lithium ion batteries

Truncated octahedral LiMn2O4 nanoparticles were prepared by a high temperature solid-state combustion reaction using starch as fuel. The structure and morphology of the as-prepared material were analyzed by X-ray diffraction and electron microscopy. The results obtained show that the materials possess a perfect spinel structure, truncated octahedral morphology with an average grain size about 101.8nm and uniform particle size distribution. The truncated octahedral LiMn2O4 exhibits high capacity and long-term cyclability with an initial discharge capacity of 107.9mAhg-1 at 5C. The capacity retention is 91.39% after 1000 cycles at 20C. The excellent electrochemical performance can be mainly attributed to the nano-sized truncated octahedral structure, narrow particle size distribution and relatively lower crystallinity.

Spark plasma synthesis and densification of TaB 2 by pulsed electric current sintering

The synthesis and consolidation in one processing step of single phase tantalum diboride by Spark Plasma Sintering (SPS) is proposed. TaB 2 formation from Ta and B elemental powders takes place at about 800 °C through a solid-state combustion reaction while product densification requires higher temperatures. Consolidation is significantly improved (~ 96% density) when increasing the applied pressure from 20 to 60 MPa immediately after the synthesis reaction occurs. Simplicity, short duration, milder temperatures and pressure conditions, in comparison with other routes utilized so far for obtaining bulk TaB 2 are, along with the good mechanical properties of the obtained product, the main benefits of the adopted approach.

Synthesis of nano-size BaMgAl 10O 17:Eu 2+ blue phosphor by a rapid exothermic reaction

Ultrafine particles of BaMgAl 10O 17:Eu 2+ (BAM) phosphor were synthesized by a solid-state combustion reaction in a powder bed of 0.9BaCO 3+MgO+5Al 2O 3+0.05Eu 2O 3+ k(KClO 3+1.5C) composition. A large exothermic reaction of the mixture (KClO 3+1.5C) leads to a self-sustaining combustion mode. Under optimized combustion conditions, the product consisted of BAM powder and KCl was obtained. BAM ultrafine particles resulting from the combustion process were easily obtained by simply washing the salt by-product with water. Combustion-processed BAM phosphor shows a homogeneous grain size of 100–500 nm, good dispersity, regular morphology, and improved luminescence properties.

Bifurcation of a helical wave from a traveling wave

Spin mode instabilities have been observed in solid-state combustion reactions and in propagating fronts of polymerization among others, that is, when some conditions are changed, a planar traveling wave may lose its stability and there appears a planar wave or a helical wave propagating in the form of spiral encircling the cylindrical sample with several reaction spots. In the present paper, we study the existing condition of stable helical waves and the transition process of wave patterns from a static mode to pulsating and/or helical modes. By using a full system of reaction-diffusion equations, we clarify that a stable helical wave can bifurcate directly from a planar traveling wave and that helical waves with different numbers of reaction spots can coexist stably.

The effect of large magnetic fields on solid state combustion reactions: novel microstructure, lattice contraction and reduced coercivity in barium hexaferrite

Combustion reactions of BaO2, Fe2O3 and Fe performed in large applied fields have revealed unexpected modifications in the microstructure of the multiphase combustion product, and in the lattice parameters and coercivity of monophase BaFe12O19 obtained by post-production grinding and sintering.

Spin mode instabilities in propagating fronts of polymerization

Abstract We have observed two instabilities in propagating fronts of methacrylic acid polymerization, both of which give the appearance of a spin mode. One occurs with liquid monomer when the tube is subjected to an external airflow to increase the rate of heat loss. It is novel instability caused by convection related to bubble formation. Spinning modes very similar to ones observed in solid-state combustion reactions were observed when the initial methacrylic acid/initiator solution was maintained at 0°C. The helical pattern left in the polymer and temperature profile measurements confirm for the first time the presence of a true spin mode in a constant velocity polymerization front.

Traveling fronts of addition polymerization with a solid monomer

autocatalytic reaction in an unstirred vessel can support a constant velocity wavefront resulting from the coupling of diffusion to the chemical reaction. Propagating fronts of polymerization have been studied in the former Soviet Union.l-lo We have been investigating polymerization fronts with high boiling point monomers that can be studied visually11-13 and by NMR.14 Propagating fronts of solid-state combustion reactions have been studied as a means to make new materialsl>l7 and to observe nonlinear propagation phenomena such as pulsating and spinning fronts.Ic28

Combustion synthesis of advanced materials

A variety of advanced materials can be synthesized using solid-state combustion reactions, following two different modes of synthesis, the self-propagating mode and the thermal explosion mode. Combustion synthesis offers many potential advantages over conventional techniques of synthesis, including relatively simple equipment, shorter processing times, lower energy requirements, higher product purities, and the possibility to synthesize metastable phases. Various aspects of combustion synthesis are discussed in this review. They include thermodynamic considerations, theory and mechanisms, and structure-forming processes. The influence of processing variables on reaction progress and structure formation is discussed in detail. Some novel technologies and materials based on combustion synthesis are also described. The principles of chemical reaction engineering, combined with concepts and techniques of materials science, provide a suitable basis for studies of combustion synthesis.