Solid Solution Powders Research Articles

Ternary phase diagram and the formation mechanism of two distinct solid solutions of amino acid systems: l -Valine/ l -norvaline and l -valine/ l -alanine

Abstract The ternary phase diagram of l -valine ( l -Val)/ l -norvaline ( l -Nva)/water system was determined at 293.15 K, in which the tie lines clearly indicate the formation of complete solid solution and X-ray powder diffraction (XRPD) analysis of the solid phases further confirms complete miscibility of l -Val and l -Nva molecules in the solid state. Further, homogeneous solid solution can be obtained via mechano-chemical method of non-solution system and via anti-solvent method. Similar composition analysis of solid and liquid phase suggests that l -Val and l -alanine ( l -Ala) is partially miscible with only a narrow scope of component substitution. The similarity degree of the three amino acids in cell dimensions and supramolecular organization determines the miscibility of l -Val and l -Nva or l -Val and l -Ala, and the investigation in molecular incorporation of l -Val/ l -Nva system was developed. Applying the experimental solid-liquid equilibrium data, fractional crystallization is verified as an effective purification method.

Gd\u2013Bi\u2013Ce\u2013O materials as catalysts in CO oxidation

Ceria-based solid solutions doped by Gd and/or Bi were synthesized by co-precipitation method from acid aqueous solution of cerium, gadolinium, and bismuth salts, followed by calcination at the temperature of 500 °C. Characterization of the synthesized samples by many methods was carried out. It is shown that all obtained powders of solid solutions crystallized into a cubic structure of the fluorite type, with an average particle size of 10–17 nm, and for the sample obtained through intermediate acetylacetonate complexes was 5–8 nm. The samples had a mesoporous structure with a pore diameter of 2–5 nm. These systems were tested as the catalysts in CO oxidation in the model gas mixture by the flow method. Gd0.05Bi0.15Ce0.8O2 system obtained through intermediate acetylacetonates has the highest activity, so this sample can be used as a catalyst.

Synthesis of nanocrystalline Ce0.95Mn0.05O2 solid solution powders as support for nickel catalyst in dry reforming reaction

For the preparation of the Ce0.95Mn0.05O2 solid solution as a catalyst support, the co-precipitation, sol-gel and hydrothermal methods were applied and the 10wt.%Ni/Ce0.95Mn0.05O2 catalysts were synthesized by the wet impregnation method on the prepared supports. The physicochemical characteristics of the samples were determined by the X-ray diffraction (XRD), BET surface area, scanning electron microscopy (SEM), temperature programmed reduction and oxidation (TPR and TPO) analyses. The results revealed that the carrier prepared by the co-precipitation method showed higher potential as a catalyst carrier. The investigation of the influence of the nickel content over the carrier prepared by the co-precipitation method showed that the 10wt.% Ni was the optimum content to prepare a catalyst with acceptable catalytic performance in dry reforming reaction. The catalysts with higher percentage of nickel exhibited a higher degree of deactivation due to severe carbon deposition.

Effects of La2O3 on the microstructure and tribological properties of plasma-sprayed Cr2O3–TiO2 coatings

Cr2O3–TiO2 coatings with different proportions of La2O3 were deposited by atmospheric plasma spraying. The coatings were evaluated by hardness tester, surface roughness tester, SEM and wear tester. The experiment results showed that the addition of La2O3 could improve the microhardness and decrease porosity, wear rate and surface roughness of the coating. The coating containing 2 wt.% La2O3 had the best tribological properties. The dominant wear mechanism is a mixture of abrasive wear and adhesive wear. The microscopic analysis suggests that the addition of La2O3 could refine the microstructure and promote the formation of solid solution powder, and then affect the properties of coatings.

Yolk–shell-structured (Fe0.5Ni0.5)9S8 solid-solution powders: Synthesis and application as anode materials for Na-ion batteries

Multicomponent metal sulfide materials with a yolk–shell structure and a single phase were studied for the first time as anode materials for sodium-ion batteries. Yolk–shell-structured Fe–Ni–O powders with a molar ratio of iron and nickel components of 1/1 were prepared via one-pot spray pyrolysis. The prepared Fe–Ni–O powders were transformed into yolk–shell-structured (Fe0.5Ni0.5)9S8 solid-solution powders via a sulfidation process. The initial discharge and charge capacities of the (Fe0.5Ni0.5)9S8 powders at a current density of 1 A·g−1 were 601 and 504 mA·h·g−1, respectively. The discharge capacities of the (Fe0.5Ni0.5)9S8 powders for the 2nd and 100th cycle were 530 and 527 mA·h·g−1, respectively, and their corresponding capacity retention measured from the 2nd cycle was 99%. The (Fe0.5Ni0.5)9S8 powders had high initial discharge and charge capacities at a low current density of 0.1 A·g−1, and the reversible discharge capacity decreased slightly from 568 to 465 mA·h·g−1 as the current density increased from 0.1 to 5.0 A·g−1. The synergetic effect of the novel yolk–shell structure and the multicomponent sulfide composition of the (Fe0.5Ni0.5)9S8 powders resulted in excellent sodium-ion storage performance.

Synthesis of (Ti, W, Mo, Ta, Cr)(C, N) solid solution powders by carbothermal reduction-nitridation in an open system

The single-phase (Ti, W, Mo, Ta, Cr)(C, N) solid solution powders were successfully synthesized from oxides by carbothermal reduction-nitridation (CRN) in an open system. It was investigated in this paper that the effects of synthesizing temperature and isothermal time on the C/N ratio, free carbon content, oxygen content, as well as the morphology of the synthesized powders. Powder X-ray diffraction results show the single-phase solid solution could be prepared with the minimum temperature at 1600 °C for 4 h. The phase transformations of titanium compound from raw material to final products during the whole process were as follows: Anatase-TiO2 → Rutile-TiO2 → Ti4O7 → Ti3O5 → Ti(C, N). The morphological and microstructural investigations indicate that Ti, W, Mo, Ta and Cr were homogeneously distributed in the solid solution powders. Ultimately, the homogeneously distributed single-phase (Ti, W, Mo, Ta, Cr)(C, N) powders with an average size of ∼2 μm were obtained by heating the reaction system at 1800 °C for 4 h. The chemical composition of the solid solution with the optimal process could be drawn as (Ti0.882, W0.068, Mo0.030, Ta0.015, Cr0.005)(C0.72, N0.28), in which the C/N ratio is close to 7/3, and the oxygen and free carbon contents are both less than 0.3 wt.%. In addition, the obtained multi-solid solution powders were also used in the preparation of (Ti, M)(C, N)-based cermets to show its high potential in future applications.

Mechanically Assisted Solid-State Mixing and Spark Plasma Sintering for Fabrication of Bulk Nanocomposite (WC/7(10Co/4Cr))-Based ZrO2 Systems

Mechanically induced solid-state mixing, using high-energy ball milling technique, was employed for preparing WC/7 wt.% (10Cr/4Cr) solid-solution powders. The solid-solution powders obtained after 50 h of milling were mechanically mixed for 50 h together with small weight fractions (0-7 wt.%) of (ZrO2 + 1.5 wt.% Y2O3) powders. The powders were then consolidated in vacuum under a uniaxial pressure of 30 MPa at 1250 °C, using spark plasma sintering. The consolidated bulk samples were nearly full dense and maintained their nanocrystalline structure after this consolidation step. The results showed that the consolidated samples over the entire range of ZrO2 concentrations (0–7 wt.%) had low values for Young’s modulus (297–318 GPa) due to their nanocrystalline structures. Moreover, the WC/7 wt.% (10Cr/4Cr)/7(ZrO2-1.5 mol.% Y2O3) showed excellent wear resistance, indexed by its low-value friction coefficient (~0.29).

Synthesis of (Cr,V)2(C,N) solid solution powders by thermal processing precursors

The single-phase (Cr,V)2(C,N) solid solution powders were fabricated via carbothermal reduction-nitridation (CRN) processing technique. The effects of heat treatment temperature, nitrogen pressure and carbon proportion were experimentally studied in detail by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and thermal analysis. The chemical transformations of vanadium and chromium compounds were as follows: precursors → V2O3, Cr2O3 → Cr3C2, Cr2O3, (Cr,V)2(C,N) → (Cr,V)2(C,N). When the heat-treated temperature was below 1200 °C, chromium oxides didn’t completely react. However, higher temperature ∼1300 °C could not only lead to the segregation of some nitrides and carbon black, but also to the occurrence of fiber-bridged particles. The system nitrogen pressure over 0.03 MPa would cause a subtle transformation of (Cr,V)2(C,N) to VCrN2. When the carbon proportion was below 15 wt%, the oxides could not be completely reduced, while when the carbon proportion was above 15.5 wt%, some undesired carbides, like Cr23C6 and Cr3C2, would form. Ultimately, the homogeneously distributed pure-phase (Cr,V)2(C,N) spherical particles with the average size of ∼1.5 μm were obtained at the optimal conditions of the treatment of precursors at 1200 °C for 1 h with the nitrogen pressure of 0.03 MPa and carbon content of 15.5 wt%. The chemical composition of the solid solution with the optimal process could be drawn as (Cr0.85V0.15)2(C0.57N0.43). Thermal processing precursors method shows the advantages of lower synthesis temperature, shorter period and finer particles when comparing with the conventional preparations.

Zirconia nano-powder – a useful precursor to dense polycrystals

The main problem of utilization of ceramic nanopowders consists in their tendency to form hard agglomerates. The inter-agglomerate space forms pores surrounded by numerous elementary particles (crystallites). Such pores cannot be easily removed from the system during pressureless sintering. So, the obvious strategy for a technologist is to eliminate such pores at the level of shaping operations. Dry pressing is a frequently applied shaping technique of ceramic materials. That is why mechanical strength of agglomerates should be as low as possible. It enables the elimination of inter-agglomerate pores to occur under moderate pressures, applied during the shaping process. This problem will be illustrated using the really nanometric (below 10nm) zirconia-yttria solid solution powder. The methods of effecting agglomerate strength will be shown. One of the elaborated powder preparation rout results in extremely soft agglomerates.

Physicochemical, structural and induced ferromagnetic properties of Co–In-codoped CdO synthesised via Cd chloride: significant effect of post-treatment hydrogen

Nanoparticle solid solution powders of cadmium oxide doped with different concentrations of cobalt and indium ions were synthesised by solvothermal method through CdCl 2 ⋅ H 2 O precursor route. The objective of the present work is to study and develop conditions necessary to create stable room-temperature ferromagnets (RT-FMs) in transparent conducting oxide (TCO) CdO for applications in the field of dilute magnetic semiconductors (DMSs). To achieve this aim, cobalt (Co2+) dopant ions were used as a source of stable FM, while In3+ dopant ions supply free electrons that enhance the electronic medium of interaction. The electronic medium in the host CdO lattice, which carries the long-range spin–spin (S.S) exchange interaction between localised Co2+ (3d) spins of dopant ions, was further developed by annealing in hydrogen gas (hydrogenation). The crystalline structure of the powder samples was investigated by the X-ray diffraction (XRD) method. The optical absorption properties were studied by diffuse reflection spectroscopy (DRS). Magnetic measurements reveal that the Co–In-codoped CdO powder has FM properties superimposed on paramagnetic (PM) behaviour. However, annealing in hydrogen atmosphere strongly boosts the created FM so that the saturation magnetisation increases ∼90 times. Physical explanations and discussion are given in the article. Thus, it is proved that the magnetic properties could be tailored to TCO CdO by Co-doping and post-treatment under H 2 atmosphere.

Thermal Decomposition of Supersaturated Ti<sub>1-x</sub>Al<sub>x</sub>N Solid Solution Synthesized by High-Energy Milling

Supersaturated titanium-aluminum nitride (Ti1-xAlxN) is a very attractive material for a wide range of applications due to its high oxidation and wear resistance accompanied by high strength, hardness, thermal conductivity and thermal shock resistance. Currently, its applications are limited to coatings obtained by physical or chemical deposition. Bulk materials based on Ti1-xAlxN may be fabricated by powder metallurgy approach using powders synthesized by high-energy ball milling (HEBM), which composition corresponds to supersaturated Ti1-xAlxN solid solution. In the present study, thermal stability of the supersaturated Ti1-xAlxN solid solution was investigated. According to the quasi-binary TiN-AlN phase diagram, constructed using density functional theory (DFT) analysis, the concentration ranges, where decomposition takes place through spinodal decomposition or through nucleation and growth, were determined. Experimental study on thermal stability of solid Ti1-xAlxN solution powder was conducted by means of differential scanning calorimetry (DSC), Brunauer-Emmited-Teller (BET) and XRD. The results indicated that spinodal decomposition of Ti1-xAlxN starts at 800°C, while at temperature higher than 1300°C regular decomposition (nucleation and growth) is occur.

The fabrication of multi-core structure cermets based on (Ti,W,Ta)CN and TiCN solid-solution powders

A novel multi-core structure cermets consisted of both black-core/rim structure and grey-core/rim structure were obtained by partially replacing TiCN powder with (Ti,20W,15Ta)CN powder via low-pressure sintering process. The toughness and strength of TiCN-based cermets were optimized and its feature of high hardness was maintained simultaneously. Systematically, it was investigated that the influences of various weight ratios of both (Ti,20W,15Ta)CN/TiCN and Co/Ni on the microstructure and mechanical properties of the multi-core cermets. The results showed that the addition of (Ti,20W,15Ta)CN powder could cause the refinement of the core size and the occurrence of the secondary phase (W,Mo,Ti)3+x(Co,Ni)3−xC (0<x≤1), both of which are responsible for the significant improvement of the mechanical properties. The appearance of the secondary phase was found under two circumstances, one was when the weight ratio of (Ti,20W,15Ta)CN/TiCN was 6:4 while that of Co/Ni was 5:5(cermet M60) and the other was when that of (Ti,20W,15Ta)CN/TiCN was 5:5 with pure Co binder (cermet C50). And there is a monotonous escalation of the fracture toughness (KIC) of the cermets while increasing the (Ti,20W,15Ta)CN content. The optimal comprehensive mechanical performance was found in cermet M60 with transverse rupture strength (TRS) of 1903.32MPa, Vickers hardness (HV30) of 16.33GPa and fracture toughness of 12.19MPa·m1/2.

Durablility of Methane Steam Reforming Catalysts Prepared By Exsolution and Infiltration

Methane steam reforming reaction is the most important chemical process to produce hydrogen or synthesis gas. Hydrogen is heavily consumed for ammonia production, the cryogenics industry and methanol production. Recently, the hydrogen demand is expected to increase as fuel cells become more widely accepted and are used more in the near future. For effective production of hydrogen or synthesis gas, the role of the reforming catalyst becomes more significant. Especially, highly active and stable catalyst is necessary for an on-site reformer for fuel cell systems. In conventional technology, the methane steam reforming reaction is conducted on supported noble metals- (Pt, Pd, Rh, Ru, and Ir) or nickel-based catalysts at temperature up to 700~800°C and steam to methane rations between 2 and 4. However, these catalysts suffer from the deactivation by agglomeration and carbon deposition. Noble metal-based catalysts are less sensitive to carbon deposition than nickel-based catalyst. However, high cost and limited availability are major concern. In this study, nickel-based nanocomposite catalysts were fabricated by exolution process. The exsolution means the process to precipitate particles from solid solution by means of the heat treatment in a specially-controlled atmosphere. This process is distinguished from the infiltration in which particles are precipitated from solutions by evaporation. First, Mg1-xNixO solid solution powders were synthesized from aqueous magnesium and nickel nitrate solution by precipitation technique and then the powder was heat-treated in reducing atmosphere at 600 to 900°C. SEM and TEM images revealed that the nano-sized nickel particles were homogeneously dispersed in the Mg1-xNixO solid solution matrix and the size and morphology of nano nickel particles can be controlled by the heat-treatment condition. Catalytic activity for the methane steam reforming or methane particle oxidation reaction and durability of the Ni/Mg1-xNixO was investigated in terms of nickel contents and sizes.

Fabrication and characterisation of copper–alumina nanocomposites prepared by high-energy fast milling

Two different methods are used to prepare Cu–20 vol-% Al2O3 nanocomposite powders via high-energy planetary fast milling. In the solid solution method, CuO powder was added to the Cu–Al solid solution powder, and the composite was fabricated by milling after 100 h. In the direct mixing method, Cu and Al2O3 powders were mechanically milled via high-energy planetary fast milling for 100 h. The transition electron micrographs (dark and white fields) revealed the presence of Al2O3 nanoparticles in crystalline Cu matrices for both methods. However, the density and bending strength of the nanocomposites produced via the solid solution method were higher than those of the samples produced via the direct mixing method.

Low-temperature spin relaxation in compacted powders of CrO2 solid solutions with iron impurities

The effect iron impurities have on the low-temperature behavior of the magnetoresistance of compacted powders of CrO2 ferromagnetic half-metal with anisotropic particle shape is investigated. The strong dependence of magnetoresistance on the spin relaxation rate during specimen magnetization reversal is revealed. It is shown that the addition of Fe impurities increases the powders’ coercive force and reduces tunnel magnetoresistance. A resonance mechanism of carrier tunneling in powders of CrO2 solid solutions with iron impurities is proposed.

Microstructure and mechanical properties of WC–(Ti, M)(C, N)–Co cemented carbides with different nitrogen contents

Three kinds of (Ti, M)(C1−x, Nx) (M = Ta, Nb, W) quaternary solid-solution powders with various nitrogen contents were synthesized by carbothermal reduction–nitridation (CRN) process. Effect of nitrogen content on the microstructure and mechanical properties of WC–(Ti, M)(C1−x, Nx)–Co cemented carbides fabricated by sinter-hot isostatic pressing (HIP) were systematically investigated in this paper. The results show that the nitrogen content in the carbonitride raw powders strongly influences the morphology, the grain size and the compositions of the cemented carbides. All the cemented carbides with different nitrogen contents have a similar microstructural appearance: weak core–rim structure consisting of solid-solution phase embedded in WC–Co system. It is also observed that the carbonitride solid solution could somewhat reduce the WC grain growth, and the effectiveness of refining and the rim thickness are sensitively related to the nitrogen content of (Ti, M)(C1−x, Nx) solid solutions. In addition, with an increase in the nitrogen content, mechanical properties of these hard metals are enhanced, which were discussed in terms of the constituent, the microstructure and the solution behavior of the carbonitride solid solutions.

Synthesis, Characterization, and Consolidation of Cr2(C,N) Solid Solution Powders

Single‐phase Cr2(C,N) powders, which are mainly composed of large worm‐like particles with the diameter of 1–3 μm, have been successfully synthesized by carbothermal reduction nitridation (CRN) method at 1200°C for 1 h in N2 atmosphere for the first time. The phase evolution and morphology were investigated using XRD, TG‐DSC, SEM, and TEM techniques. The reactions during the synthesis process were proposed and analyzed. The surface of Cr2(C,N) determined by XPS is mainly composed of four elements, Cr, N, C, and O. Furthermore, the attempts to consolidate Cr2(C,N) powders were carried out using spark plasma sintering (SPS), and the fully densified bulk ceramics were obtained at 1200°C. The effect of sintering temperature on phase composition and mechanical properties were also discussed.

Microwave-assisted synthesis of W1−xMoxO3·0.33H2O compounds with enhanced band gap

Optoelectronic solid solution powder materials with phase W1−xMoxO3·0.33H2O (where X = 0, 25, 50, 75 and 100 %), were synthetized using hydrothermal synthesis assisted by microwave heat radiation. The crystallographic phase was identified by X-ray diffraction and RAMAN techniques. The morphology was studied by means of electron microscopy techniques (SEM and TEM). Materials with X = 0, 25, 50 and 75 % were indexed with orthorhombic phase and material with X = 100 % was indexed with hexagonal phase (a combination of MoO3 and MoO3·0.55H2O phases). The band gap for each material (X = 0, 25, 50, 75 and 100 %) was determined using Kubelka–Munk theory and Tauc plots, being W0.25Mo0.75O3·0.33H2O (WM75m) the best compound with 1.90 eV. Because of the experimental results, it can be concluded that the band gap behavior is related with particle size and Mo percent content thus originating a decrease in parameter or axis “b” of the crystal lattice.

Fabrication of Nb3Al superconductor by the optimized mechanical alloying method with low temperature

Mechanical alloying was used to synthesize Nb3Al superconductor successfully, and the process was optimization under various preparation conditions. In the current study, Nb3Al superconductor with Tc of 15.6K was directly prepared from high quality Nb (Al) solid solution by mechanical alloying method and heat treatment at a low temperature of 800 to 900°C. The results showed that Nb3Al superconducting wire with high performance could be prepared after heat treatment below the melting point of Cu (1080°C) and using Nb (Al) solid solution and conventional powder in tube (PIT) method, thus effectively avoiding ultra-high temperature heat treatment and special rapid heating and quenching(RHQ) device.

Preparation of CuCr1-xFexO2 Delafossite Solid Solution Powder Via a Self-Combustion Glycine Nitrate Process

Porous CuCr1-xFexO2 (x = 0 – 1) solid solution powders were successfully prepared by glycine nitrate process without post-annealing treatment or ambient control. The structure of the powders was confirmed by X-ray diffraction. The morphology of the powders was observed by scanning electron microscopy. The morphology varied from cotton candy-like to coral-like with increases in iron (x) content. The specific surface area of self-combusted CuCr1-xFexO2 (x = 0 – 1) powders varied from 25.723 m2/g to 4.94 m2/g with increases in iron (x) content, which is greater than the specific surface area of powders prepared by solid state reaction.