Application of the SHS technique in the synthesis of the perovskite-type MgxCyNi3 compound

The almost complete conversion of a powder mixture of the elements into the perovskite-type Mg_xC_yNi₃ compound has been obtained in two steps, applying the SHS technique followed by an isothermal treatment at 1123 K. No evidence was found for Mg loss due to volatilisation, as well as of unreacted C, at the end of the preparation. Two new ternary phases, that may be referred to as Mg_2+xNiC_y and Mg_1+xNi₂C_y, grew during the combustion process; though different, their crystal structures appear to be strongly related to those of Mg₂Ni and MgNi₂, respectively. Isothermal treatments at 973 K failed in the formation of the perovskite-type compound as a single product, since it was found coexisting with Ni and Mg_1+xNi₂C_y, probably on account of the relatively short reaction times.The samples were characterised by means of XRPD and SEM-EDS analyses after each step of preparation.     

Silicide formation during heat treatment of thin Ni-Pt and Ni-Pd solid-solution films and Pt/Ni bilayers on (111)Si

It is shown that isothermal heat treatment of (Ni-Pt)/Si and Pt/Ni/Si heterostructures leads to the formation of oriented Ni-and Pt-based silicide solid solutions. Owing to the three equivalent azimuth orientations in the basic lattice orientation relationship for the Si-Ni_1?x Pt_xSi system, the resulting silicides have a nanocrystalline substructure. The stability of the substructure is due to the optimal interfacial lattice match and near-special grain-boundary misorientations. The silicide phases Ni_1?x Pt_xSi and Pt_1?y Ni_ySi (or Ni_1?x Pd_xSi and Pd_1?y Ni_ySi) may undergo segregation, having the same lattice orientation. In both systems, the segregation is associated with the predominant Ni diffusion. The second component (Pt) is shown to stabilize the orthorhombic Ni-based silicide and to prevent NiSi₂ formation. Photon processing accelerates diffusion and leads to the formation of phase-pure Ni_1?x Pt_xSi solid solutions.     

Preparation of low-temperature graphite fluorides through decomposition of fluorinated-graphite intercalation compounds

The decomposition of C _x FCl _y · zR (R = N₂O₄, N₂O, SO₂) fluorinated graphite intercalation compounds at 370–420 K leads to the formation of C _x FCl _y graphite fluorides with x close to 2 and y close to 0.1. The C _x FCl _y fluorides are first-stage compounds with an interlayer spacing of 0.60–0.61 nm. According to the synthesis conditions and their structure, these compounds can be classed with low-temperature C₂F graphite fluorides. They are stable in air and inert atmospheres up to 720–750 and 750–780 K, respectively, which is comparable to the thermal stability of high-temperature CF and C₂F graphite fluorides.     

Phase transformation and hardness of the Ni–P–Al ternary coatings under thermal annealing

Ternary Ni–P–Al coatings were fabricated by the dual-gun rf magnetron sputtering technique. The as-deposited Ni–P–Al coatings exhibited a major Ni nanocrystalline phase (with a (111) texture) with Al and P co-deposited. After 400 °C heat treatment, various Ni_xP_y compounds, including Ni₁₂P₅, Ni₅P₂, and Ni₃P, formed within the recrystallized Ni matrix. Accordingly, the hardness of the coating increased to 10 GPa due to the Ni_xP_y precipitation. For heat treatment temperatures higher than 450 °C, Ni_pAl_q hard phases were observed in the ternary Ni–P–Al coating. A further increase in coating hardness from 10 to 12 GPa was revealed. The hardening of the annealed Ni–P–Al coatings was attributed to precipitation of Ni–P and Ni–Al compounds formed around 400 and 500 °C, respectively. A two-stage hardening in Ni–P–Al coating by Ni_xP_y and Ni_pAl_q precipitation through heat treatment was then demonstrated. Through surface analysis, the increase in surface roughness for the Ni–P–Al coating due to the formation of Ni_xP_y and Ni_pAl_q compounds was revealed.     

Electronic Property of the C-Site Doped MgCNi

C-site doped MgCNi₃ compounds, MgC_1?x B _x Ni₃ (x=0.15, 0.20) and MgC _y Ni₃ (y=1.00, 0.80, 0.65), have been investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The binding energies of Ni 2p3/2 and C 1s for undoped MgCNi₃ are 853.173 eV and 283.640 eV, respectively. Interestingly, the binding energy of Ni 2p3/2 is found to shift to a lower value with decreasing C-site occupation in MgC _y Ni₃ samples. The C-site doped by boron could also lead to a slight decrease of the binding energy of Ni 2p3/2. However, the C-site doping has few effects on the binding energy of C 1s. It is suggested that there is charge transfer from Ni- to C-site atom. The hybridism between Ni and C has an important effect on the superconductivity of MgCNi₃.     

Improved microwave dielectric properties of Nd(Mg0.5Sn0.5)O3 ceramics with Ni2+ substituting

This study elucidates the microwave dielectric properties and microstructures of Nd(Mg_0.5?xNi_xSn_0.5)O₃ ceramics with a view to their potential for microwave devices. The Nd(Mg_0.5?xNi_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd(Mg_0.43Ni_0.07Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A dielectric constant ( $ \varepsilon_{r} $ ) of 19.3 and a quality factor (Q × f) of 93,400 GHz and a temperature coefficient of resonant frequency ( $ \tau_{f} $ ) of ?66 ppm/ °C were obtained for Nd(Mg_0.43Ni_0.07Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h.     

Revealing the Kinetic Balance between Proton-Feeding and Hydrogenation in CO2 Electroreduction

Electrocatalytic reduction of CO₂ to high-value-added chemicals provides a feasible path for global carbon balance. Herein, the fabrication of Ni_NPx@Ni_SAy-NG (x,y = 1, 2, 3; NG = nitrogen-doped graphite) is reported, in which Ni single atom sites (Ni_SA) and Ni nanoparticles (Ni_NP) coexist. These Ni_NPx@Ni_SAy-NG presented a volcano-like trend for maximum CO Faradaic efficiency (FE_CO) with the highest point at Ni_NP2@Ni_SA2-NG in CO₂RR. Ni_NP2@Ni_SA2-NG exhibited ≈98% of maximum FE_CO and a large current density of −264 mA cm⁻² at −0.98 V (vs. RHE) in the flow cell. In situ experiment and density functional theory (DFT) calculations confirmed that the proper content of Ni_SA and Ni_NP balanced kinetic between proton-feeding and CO₂ hydrogenation. The Ni_NP in Ni_NP2@Ni_SA2-NG promoted the formation of H* and reduced the energy barrier of *CO₂ hydrogenation to *COOH, and CO desorption can be efficiently facilitated by Ni_SA sites, thereby resulting in enhanced CO₂RR performance.     

Using ionic liquid as the solvent to prepare Pd–Ni bimetallic nanoparticles by a pyrolysis method for ethanol oxidation reaction

Room temperature ionic liquids (RTILs) of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) is used as the solvent for the first time to prepare multi-walled carbon nanotubes (MWCNTs) supported nanocomposite catalysts of Pd_xNi_y (atomic ratios of Pd to Ni are 1:1, 1:1.5, 1:2, and 1:2.5) nanoparticles (denoted as Pd_xNi_y/MWCNTs) by using a simple pyrolysis process. The Pd_xNi_y/MWCNTs catalysts are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results show that the Pd_xNi_y nanoparticles (NPs) are quite uniformly dispersed on the surface of MWCNTs with an average crystallite size of ∼7.0 nm. The electro-catalytic activity of the Pd_xNi_y/MWCNTs catalysts for ethanol oxidation reaction (EOR) is examined by cyclic voltammetry (CV). It is revealed that the onset potential is ∼80 mV lower and the peak current is about three times higher for ethanol oxidation for MWCNT catalysts with Pd₁Ni_1.5 compared to those of Pd/MWCNTs. The catalytic mechanisms of the Pd₁Ni_1.5/MWCNTs towards EOR are also proposed and discussed.     

Reaction sintering and joining nickel aluminide to AISI 316 stainless steel by self-propagating high temperature synthesis

Abstract

Self-propagating high temperature synthesis (SHS) is a process whereby reactants are ignited to spontaneously transform to products in an exothermic reaction. The aim of this study is to propose a method to join nickel aluminide with AISI 316 stainless steel by SHS and to study the combustion synthesis of nickel aluminide. From the heat of combustion synthesis junctions were formed between annular AISI 316 stainless steel and a powder metallurgy compact of Ni and Al blends. The Al mole ratio for testing the joining grade in the initial powder mixture varied from 25 at.-% to 40 at.-%. In order to check the sufficiency of the SHS reaction, the test temperature was compared with the thermodynamic calculation values. The metallographic analysis indicated that NiAl and Ni₃Al were formed in the joint layer.     

Formation of metastable solid solutions of boron in nickel under mechanochemical synthesis from Ni-B and Ni-Nb-B mixtures

Using high-energy ball milling of Ni₈₇B₁₃ and Ni_{87 ? x} Nb _x B₁₃ component mixtures (x = 7, 10, 12, 14) for 2 h, nanocrystalline alloys containing fcc solid solutions of Ni〈B〉 and Ni〈Nb,B〉 were obtained. According to the results of X-ray analysis, oversaturated solid solutions of Ni〈B〉 are interstitial solutions; those of Ni〈Nb,B〉 are substitutional solutions or mixed substitutional-interstitial solutions. Upon heating of the alloys, exothermal effects appear on differential scanning calorimetry (DSC) curves; they are attributed to decomposition of metastable solid solutions and to crystallization of the amorphous phase appearing in mechanical alloying. After heating to 720°C, the Ni₈₇B₁₃ alloy contained stable phases of Ni and Ni₃B; the Ni₇₅Nb₁₂B₁₃ alloy contained a τ phase (Ni₂₁Nb₂B₆) and a metastable solid solution of Ni〈Nb〉.     

Synthesis of Cu3(PO4)2 · H2O based solid solutions through Co or Ni substitution for Cu

New substitutional solid solutions have been synthesized: (Cu_{1 ? x} Co_x)₃(PO₄)₂ · H₂O (0 < x ≤ 0.20), (Cu_{1 ? x} Ni_x)₃(PO₄)₂ · H₂O (0 < x ≤ 0.12), and (Cu_{1 ? y} Co_y)₃(PO₄)₂ · H₂O (0.55 ≤ y ≤ 0.65). The first two solid solutions are isostructural with Cu₃(PO₄)₂ · H₂O (monoclinic symmetry, sp. gr. C2/c); the third solid solution also has a monoclinic structure, which is a Cu₃(PO₄)₂ · H₂O related superstructure. The lattice parameter b of (Cu_{1 ? y} Co_y)₃(PO₄)₂ · H₂O (0.55 ≤ y ≤ 0.65) is almost twice that of (Cu_{1 ? x} Co_x)₃(PO₄)₂ · H₂O (0 < x ≤ 0.20), while their a and c parameters differ little. The solid solutions have been characterized by chemical analysis, x-ray diffraction, IR spectroscopy, and thermal analysis.     

Ferromagnetic element microalloying and clustering effects in high Bs Fe-based amorphous alloys

Fe_(83)(Co_x,Ni_y)(B_(11)Si_2P_3C_1)_(1-x,y/17)(x,y=1–3)amorphous alloys with high saturation magnetic flux density(B_s)and excellent soft-magnetic properties were developed and then the microalloying and clustering effects were explored.The microalloying of Co and Ni improves the B_sfrom 1.65 T to 1.67–1.72 T and 1.66–1.68 T,respectively.The Ni-doped alloys exhibit better soft-magnetic properties,containing a low coercivity(H_c) of about 5.0 A/m and a high Effective permeability(μ_e)of(8–10)×10~3,whereas the microalloying of Co leads to a deteriorative H_c of 5.0–13.0 A/m and a μ_eof(5–8)×10~3.Moreover,microalloying of Ni can increase the ductile-brittle transition(DBT)temperature of the ribbons,while a totally opposite effect is found in the Co-doped alloys.The formation of dense α-Fe(Co,Ni)clusters during annealing process is used to explain the distinct effects of Co and Ni microalloying on the magnetic properties and bending toughness.     

Magnetic and Microstructure Properties of Ni-Doped ZnO Films and Powder by Sol–Gel Process

Zn_1?x Ni _x O precursor solutions with a different ratio (x=0.01?C0.03) were prepared by sol?Cgel synthesis using Zn and Ni based alkoxide. Reel-to-reel sol-dip coating method was used to grow Zn_1?x Ni _x O films. Zn_1?x Ni _x O powders and films, annealed at various temperatures, were tried to observe the doping ratio and temperature effects on magnetic and microstructure properties. The surface morphologies of all samples were characterized by ESEM and EDS. The crystal structures of the ZnNiO powders were characterized using 2???C?? x-ray diffraction (XRD). The alterations of the lattice parameters have been obtained by the TREOR program. ESR spectra of Zn_1?x Ni _x O powder samples were collected at room temperature. The magnetization and microstructure of the powders and films with different dopant ratios, temperature, and the time of annealing process are presented.     

Synthesis of Bimetallic Conductive 2D Metal–Organic Framework (CoxNiy‐CAT) and Its Mass Production: Enhanced Electrochemical Oxygen Reduction Activity

The development of new electrocatalysts for electrochemical oxygen reduction to replace expensive and rare platinum‐based catalysts is an important issue in energy storage and conversion research. In this context, conductive and porous metal–organic frameworks (MOFs) are considered promising materials for the oxygen reduction reaction (ORR) due to not only their high surface area and well‐developed pores but also versatile structural features and chemical compositions. Herein, the preparation of bimetallic conductive 2D MOFs (Co_xNi_y‐CATs) are reported for use as catalysts in the ORR. The ratio of the two metal ions (Co²⁺ and Ni²⁺) in the bimetallic Co_xNi_y‐CATs is rationally controlled to determine the optimal composition of Co_xNi_y‐CAT for efficient performance in the ORR. Indeed, bimetallic MOFs display enhanced ORR activity compared to their monometallic counterparts (Co‐CAT or Ni‐CAT). During the ORR, bimetallic Co_xNi_y‐CATs retain an advantageous characteristic of Co‐CAT in relation to its high diffusion‐limiting current density, as well as a key advantage of Ni‐CAT in relation to its high onset potential. Moreover, the ORR‐active bimetallic Co_xNi_y‐CAT with excellent ORR activity is prepared at a large scale via a convenient method using a ball‐mill reactor.     

Structural and electronic properties of Zn1−xMgxSySe1−y alloys

The structural and electronic properties of Zn_1−xMg_xS_ySe_1−y quaternary alloys have been investigated using the full potential-linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). We used the generalized gradient approximation (GGA) that is based on exchange-correlation energy optimization for calculating the total energy. Moreover, the Engel–Vosko GGA formalism is applied so as to optimize the corresponding potential for band-gap structure calculations. We investigated the effect of composition on lattice constant, bulk modulus and band gap. A non-linear dependence on the compositions x and y is observed for all the three properties. The energy gap E_g(x, y) has been determined over the entire compositions x and y. In addition, the energy gap of zinc-blende Zn_1−xMg_xS_ySe_1−y quaternary alloys in conditions of lattice matched to GaAs substrate has been investigated.     

Dislocation reduction in nitride-based Schottky diodes by using multiple MgxNy/GaN nucleation layers

We present the characteristics of nitride-based Schottky diodes with a single low-temperature (LT) GaN nucleation layer and multiple Mg_xN_y/GaN nucleation layers. With multiple Mg_xN_y/GaN nucleation layers, it was found that reverse leakage current became smaller by six orders of magnitude than that with a conventional LT GaN nucleation layer. This result might be attributed to the significant reduction of threading dislocations (TDs) and TD-related surface states. From the double crystal X-ray diffraction and photoluminescence analyses, it was found that the introduction of multiple Mg_xN_y/GaN nucleation layers could be able to effectively reduce the edge-type TDs. Furthermore, it was also found that effective Schottky barrier height (Φ_B) increased from 1.07 to 1.15 eV with the insertion of the multiple Mg_xN_y/GaN nucleation layers.     

Combustion synthesis/quasi-isostatic pressing of TiC–NiTi cermets: processing and mechanical response

TiC–NiTi composites were produced by a technique combining self-propagating high-temperature synthesis (SHS) of elemental powders of Ni, Ti, and C with densification by quasi-isostatic pressing (QIP). In order to create a one-step synthesis/densification process, the Ti + Ni + C reactant material was surrounded in a bed of graphite and alumina particulate before initiation of the combustion reaction. The sample was ignited within the particulate and subjected to a uniaxial load immediately after passage of the combustion wave. The constitutive response, composition and resulting structures of the composites with varying volume fractions of NiTi are characterized. Powder mixtures prepared anticipating the formation of stoichiometric TiC result in the formation of composites with a eutectic matrix of Ni₃Ti and NiTi. This titanium impoverishment of the matrix is consistent with the formation of nonstoichiometric TiC _x during the combustion reaction. The Ni₃Ti phase can be suppressed by anticipating the formation of TiC_0.7 and adjusting the chemical content of the reactant mixture to include additional titanium. These cermets combine the high hardness of the ceramic phase with the possible shape memory and superelastic effects of NiTi.     

Effect of barium on the structure and dielectric properties of multicomponent ceramics based on ferroelectric relaxors

High-density ceramic samples of mPb(Mg_1/3Nb_2/3) · yPb(Zn_1/3Nb_2/3) · nPb(Ni_1/3Nb_2/3) · xPbTiO₃ (m = 0.4541, y = 0.0982, n = 0.1477, x = 0.3) solid solutions, unmodified and barium-modified, with the composition lying in a morphotropic phase region, have been prepared by a conventional ceramic processing technique. We demonstrate that barium substitution for 5% of the lead on the A site allows one to obtain ceramics containing no pyrochlore phase. Modification with barium shifts the solid solution from the morphotropic to a tetragonal phase region. In addition, barium doping increases the average grain size of the ceramic from 2–3 to 3–4 μm and changes the type of fracture from intergranular to mixed (intergranular and transgranular). Modification with barium increases the relative dielectric permittivity ?/?₀ (at E = 0) of the material by more than a factor of 2 (from 4300 to 9100). We conclude that materials based on the ceramics studied can find practical application and examine ways of further improving their piezoelectric performance.     

A study of combustion synthesis reaction in the Ti + C/Ti + Al system

Combustion synthesis (SHS) of the Ti + C/Ti + Al system was investigated by using titanium, graphite and aluminum powders as reactants. These powders were thoroughly mixed and pressed into cylindrical compacts, and heated in an argon atmosphere. The effects of the reactant composition and the heating rate were studied. The phase identification and morphology observation of the products were carried out by X-ray diffraction (XRD) and scanning electronic microscopy (SEM), respectively. XRD analysis showed that the products, in addition to the expected TiC/TiAl phases, also contained an appreciable amount of the ternary carbide (i.e., Ti _x AlC). The heating rate was found to strongly affect the extent of the combustion reaction. A possible reaction mechanism based on the experimental results was proposed to describe the whole process of the SHS reaction and the characteristic product morphology. It was considered that the ternary carbides may be formed by the peritectic reaction between TiC and the Ti–Al melt during the cooling stage after combustion.     

Nanostructured electrode materials for Ni-MH x batteries prepared by mechanical alloying

Nanocrystalline TiFe- and Mg₂Ni-type alloys were prepared by mechanical alloying followed by annealing. The structure and electrochemical properties of these materials were studied. The properties of hydrogen host materials can be modified substantially by alloying to obtain the desired storage characteristics. It was found that the respective replacement of Fe in TiFe by Ni and Mn improved not only the discharge capacity but also the cycle life of these electrodes. On the other hand, a partial substitution of Mg by Mn in Mg_2?x M _x Ni alloy leads to an increase in discharge capacity, at room temperature. Furthermore, the effect of the nickel and graphite coating on the structure of the nanocrystalline alloys and the electrodes characteristics were investigated. In Mg₂Ni-type alloy mechanical coating with graphite effectively reduced the degradation rate of the studied electrode materials.