Al-coated iron particles: Synthesis, characterization and improvement of oxidation resistance

A Fluidized Bed Metal Organic Chemical Vapour Deposition (FB-MOCVD) process has been successfully applied to coat Fe particles with Al. N₂ inert gas was used to transport the organometallic Al precursor (liquid triethylaluminium) inside the fluidized bed reactor whose temperature is 350 °C. XPS analyses and TEM observations have revealed the presence of a thin alumina layer surrounding the Al coating. Oxidation treatments, performed in the temperature range 350-500 °C, demonstrate that this multi-scale coating constitutes an efficient barrier to protect iron particles against oxidation. Such a treatment may be used to perform environmental barrier coatings around magnetic powders.     

The limiting molar partial enthalpies of mixing of iron, cobalt, nickel, palladium and platinum in liquid gallium and indium

Gallium and indium have been used as solvents for the determination of the molar partial enthalpy of mixing Δ_mixh_m^o(TM, Ga or In) (denoting liquid transition metal (TM) in infinite liquid gallium or indium) of the pure liquid transition metals Fe, Co, Ni, Pd and Pt by direct reaction calorimetry between 1000 K and 1500 K with the exception of Δ_mixh_m^o(Fe, In) (because of the shape of its equilibrium phase diagram). All the limiting enthalpies listed below refer to the liquid state. With pure gallium as solvent, they correspond to the reaction

TM(liq) − nGa(liq) → TM₁Ga_n(liq)

at the experimental temperature T_e, with n 1.

1. (i) Δ_mixh_m^o in gallium is found for Fe, Co, Ni, Pd and Pt to be −2, −44, −82, −144 and −155 kJ mol⁻¹.

2. (ii) Δ_mixh_m^o in indium is found for Co, Ni, Pd and Pt to be +28, −25, −127 and −114 kJ mol⁻¹.

In both solvents, these limiting enthalpies vary with a similar trend. This observation makes it possible to predict the limiting molar partial enthalpy Δ_mixh_m^o(Fe, In) of mixing of iron in indium as +70 kJ mol⁻¹. The results have been compared with the data proposed by Miedema and co-workers.     

A review of saturated vapour pressures and allied data for the principal corrosion products of iron, chromium, nickel and cobalt in flue gases

Available data describing the saturated vapour pressures and allied equilibria of chromium, nickel, cobalt and iron, and their oxides, hydroxides, chlorides and sulphides, are reviewed and a full list of references to the original sources is given. The data seems generally to be adequate for an understanding of the chemical processes which occur when steels containing these elements are corroded in flue gas environments, except for those describing the Cr---S, Ni---S and Co---S systems.     

Sulfidation-oxidation of nickel and cobalt—reactions between the metals and their sulfates

A differential thermal, thermogravimetric analysis (DTA-TGA) study shows that both nickel and cobalt react with their respective sulfates to form oxide (NiO or CoO) and sulfide (Ni₃S₂ or Co₉S₈ and Co₄S₃). In the case of the Ni+NiSO₄ reaction, it is clear that the reaction occurs at T < 530°C and may be a solid-state process. A similar process is found for the cobalt+CoSO₄ reaction. These reactions are briefly discussed with respect to studies of the oxidation-sulfidation of Co or Ni under conditions which produce the sulfate as a stable phase. It is proposed that the rate-determining step in these studies is the formation of the sulfate.     

Investigation on synthesis, pressureless sintering and hot pressing of chromium diboride

Experimental investigations were carried out on synthesis of chromium diboride through boron carbide reduction of Cr₂O₃. The products obtained were characterized by X-ray diffraction and the process optimized to prepare single-phase CrB₂ powder. Densification of CrB₂ was investigated by pressureless sintering and hot pressing. A maximum of 93% ρ_th was obtained by pressureless sintering at 1850 °C after a prolonged duration of 360 min. However, near theoretical density was achieved by hot pressing at 1600 °C and 35 MPa pressure for 2 h. The hardness and fracture toughness of fully dense CrB₂ was measured as 22 GPa and 3.5 MPa m^1/2, respectively. The mode of fracture in pressureless sintered samples is intergranular whereas that in hot pressed is transgranular.     

Properties of CuCr contact materials with low chromium content and fine particles

1　INTRODUCTIONCuCralloyhastakentheplaceofCuBialloyforitsexcellentelectricpropertiesandhasbeenwidelyusedinmediumvoltage ,highcurrentvacuuminter rupter[1,2 ] .CuandCrhaveverylittlesolubilityineachother .Atroomtemperature ,thesolubilityisapproximatelyzero .Infact,Cu Cralloyisapseudo alloywiththemixtureofCuandCrcomponent .Cu CrcontactmaterialsreservetheexcellentpropertiesofCuandCrcomponent,sothecontactmaterialshaveexcellentelectricproperties.TheoptimalcontentofCrinCuCrcontactmate rialh…     

Transformation/dissolution studies on the release of iron and chromium from particles of alloys compared with their pure metals and selected metal oxides

Transformation/dissolution (T/D) data for different Cr‐ and Fe‐based alloys (a FeCr alloy, stainless steel AISI 316L, an alloy side product (SP) from stainless steel production) compared with their pure metals (Cr, Fe) and selected metal oxides (Cr₂O₃, Fe₃O₄) was generated and is used throughout the entire REACH assessment documentation of chromium metal and ferrochromium alloys to derive conclusions regarding their acute and chronic ecotoxicity hazard classification. Short and long term tests were conducted to assess data for acute and chronic aquatic toxicity following the recognized standardized T/D protocol. Tests were performed in media of different pH (pH 6.0 and pH 8.0), time periods, and solution composition, also investigating the effect of different experimental parameters. Generated data elucidates the complexity of the metal release process and its dependence on many interacting material‐, surface‐, and experimental factors as well as on the chemistry of the metal–water system being metal species specific. It is evident that the extent of metal release cannot be predicted by either the bulk or the surface composition, and that metal speciation measurements of released metals are essential to assess aquatic toxicity induced by metal/alloy particles. Observed released Fe and Cr concentrations were significantly lower than reported acute and chronic ecotoxicological endpoints.     

CO_2焊/喷射高碳铬铁合金粉复合堆焊层耐磨性

采用CO2焊/喷射送粉复合堆焊新方法,通过喷射高碳铬铁粉体,研究送粉量及送粉气流量对堆焊层硬度及耐磨性的影响,并通过XRD,TEM等分析方法研究了堆焊层组织结构与耐磨性的影响规律.结果表明,当送粉速度800 g/h,送粉气体流量5L/min时,堆焊层硬度为55 HRC,耐磨性与单纯H08Mn2Si焊丝堆焊相比提高了4倍...     

Evaluation of the degree of transformation for exchange reactions with simultaneous diffusion of steel with chromium,vanadium, and aluminum

Conclusions The method considered for evaluating the degree of equilibrium transformation for exchange reactions during multicomponent impregnation makes it possible to estimate qualitatively the effect of mixture composition and process temperature on the yield of reaction products and to provide satisfactory agreement of calculated results with experimental data.Moscow Aviation Institute (MAI). Moscow Institute of Chemical Machine Building (MIKhM). Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 14–18, June, 1986.     

A review of the role of short-circuit diffusion in the oxidation of nickel,chromium, and nickel-chromium alloys

The evidence for short-circuit diffusion during the oxidation of nickel, chromium, and nickel-chromium alloys is reviewed. On the basis of experimental evidence for the Ni/NiO and Cr/Cr₂O₃ systems, inferences are made about the role of short-circuit diffusion through the oxide scales forming on the binary nickel-chromium alloys. The review highlights the importance of scale microstructure in governing oxidation rates.     

The growth of carbon coating layers on iron particles and the effect of alloying the iron with silicon

Magnetic fine particles of metallic Fe coated with graphitic carbon layers were synthesized by annealing Fe₂O₃ particles with carbon powders at 1673 K in nitrogen atmosphere. For comparison, SiC was added to Fe₂O₃. X-ray diffraction measurement showed that the lattice constants of Fe changed depending on the Si contents. Mössbauer spectroscopy confirmed that Fe-Si alloys were formed by the Si addition and that the iron carbide disappeared. Electron microscope images revealed that the thickness of carbon coating layers increased from 24 nm to 36 nm as a result of the Si addition. Soaking tests showed that the corrosion resistance of the carbon-coated Fe particles was improved by the addition of Si. The results suggest that Si caused C to leave the Fe cores and move to the surface to form a carbon coating.     

Microstructure and mechanical properties of additive manufactured steel-Al structure materials with nickel gradient layers

The microstructure and mechanical properties of steel/Al structure material produced by additive manufacturing(AM) was investigated in this work based on the cold metal transfer welding.The results show that the microstructure gradually changed from the steel side to the aluminum side.The microstructure in the steel layer consisted of vermiform like 8ferrite and austenite structure,while in the aluminum layer the microstructure was constituted by α-Al grains and typical reticulate distributive Al-Si eutectic structure.Besides,a 7 μm thickness Ni-Al intermetallic compound layer was emerged at the interface of nickel and aluminum layer.The maximum room-temperature tensile strength of the Steel-Al structure materials was found to be 54 MPa,the rupture morphology showed a brittle fracture characteristic.     

Cu、Cr、Ni元素对高强耐候钢腐蚀稳定性的影响

高强耐候钢化学成分中的Cu、Cr和Ni可有效促进含α-FeOOH稳定化锈层的形成,使钢的耐大气腐蚀性能得以提高。通过试验,Cu质量分数由0.35%降至0.22%,Cr质量分数由0.60%降至0.40%,Ni质量分数由0.25%降至0.13%时,钢的相对腐蚀速率由48.23%降至48.94%,腐蚀速率基本不变,均满足55%相对腐蚀率的要求,表明Cu、Cr和Ni含量在一定范围内波动不会对高强耐候钢的耐腐蚀性能产生明显影响,耐腐蚀性能稳定。     

综合利用钛铁矿制备二氧化钛、钛酸锂和磷酸铁锂

以钛铁矿为原料,经机械活化-盐酸浸出得到水解钛渣和富铁浸出液;用H2O2将水解钛渣中的Ti配位溶出,得到配位浸出液,并以其为反应物制备纳米级片状的过氧钛化合物;该过氧钛化合物经洗涤、煅烧制备得到纳米级片状的TiO2,其纯度高达99.31%(质量分数)。将过氧钛化合物与Li2CO3混合,球磨后煅烧合成性能优良的锂离子电池负极材料Li4Ti5O12。以富铁浸出液为原料,经选择性沉淀制备含少量Al和Ti的FePO4.xH2O,并以其为前驱体制备了Al-Ti掺杂的LiFePO4。该LiFePO4在1C和2C倍率下的首次放电比容量分别达151.3和140.1(mA.h)/g,循环100次之后容量无衰减。该方法也可用于钛白粉副产品硫酸亚铁的回收利用,制备性能优异的LiFePO4。     

钨对铸态过共晶高铬铸铁组织、力学性能和磨料磨损性能的影响

通过合金成分设计,制备了不同钨含量的过共晶高铬铸铁。研究了钨含量对材料微观组织、力学性能和磨料磨损性能的影响。结果表明,钨元素添加使得过共晶高铬铸铁中初生碳化物粗化,钨含量从0增加到2.84%时,高铬铸铁的硬度由51 HRC提高到56 HRC,冲击吸收能量先升高后下降,最高达5.8 J/cm2。同时,过共晶高铬铸铁三体磨料磨损性能得到提高。     

热处理对含钨过共晶高铬铸铁组织与性能影响

试验利用金相、EDS面扫描、力学性能测试等方法,对不同淬火及回火温度对含钨高铬铸铁组织与性能进行了研究。试验结果表明,淬火温度升高使试样基体中共晶碳化物减少,二次碳化物增多,淬火温度在1000 ℃时,试样综合性能较好;回火温度升高,试样基体马氏体细化,二次碳化物增多粗化,当回火温度为360 ℃时,试样综合性能较好。     

The determination of the cold forgeability for specimens with axial notches of heat resisting and corrosion resisting chromium nickel steels

In the present paper cold forging of cylindrical specimens is studied. Tree types of Cr-Ni steels were used for failure limit diagrams determination. The different specimen geometries were tested with different friction conditions between tools and specimen involving concentrically grooved tool platens and smooth platens to generate different deformation conditions at the equatorial surface of specimens. Specimens with v-shaped axial notches with different depths were used.

Experimentally determined strain paths at free surface and at notches were used for theoretical calculations of the stress state at the free surface and notch, void growth in the material and failure limit. These calculations were based on a crack initiation model and void growth model which takes both the influence of state of stress and effective strain into account.

A satisfactory agreement was found between experimental determined failure limits and theoretical calculations based on experimental strain paths.     

Corrosion behavior of CrN, Cr2N and π phase surfaces on nitrided Ni-50Cr for proton exchange membrane fuel cell bipolar plates

The relationships between nitridation, microstructure and corrosion were studied for a thermally nitrided model Ni-50Cr (wt.%) alloy to gain insight into the protection of metallic bipolar plates in proton exchange membrane fuel cells (PEMFCs). Surface layers containing CrN, Cr₂N or ternary Cr-Ni-N π phase nitride were formed, dependent on the nitridation conditions. Studies in aerated pH 3 sulfuric acid at 80 °C indicated that the best corrosion resistance was exhibited by CrN + Cr₂N surface layers, which were more corrosion resistant than Ni-50Cr metal, Cr metal, and nitrided Cr. X-ray photoelectron spectroscopy (XPS) analyses indicated oxygen enrichment of the polarized surfaces in the form of Cr-oxide and Cr-oxynitride species. Such oxygen enrichment does not appear to result in detrimental increases in interfacial contact resistance/electrical properties of the surface.     

Nano-wear, nano-hardness and corrosion-resistance of electroplated nickel surfaces after co-implantation of Cr and N2 ions

In this work, a successful sequential co-implantation treatment of Cr⁺ and N₂⁺ ions into electrodeposited nickel plates is presented. The goal of this treatment is the simultaneous enhancement of the wear resistance, mechanical stability and corrosion-protection properties of the Ni surfaces. The ion-implanted surfaces have been characterized by glow-discharge optical-emission spectroscopy, X-ray diffraction, nano-hardness, roughness, nano-wear and potentio-dynamic corrosion tests. It has been observed that the implantation of Cr⁺ or N₂⁺ alone is not sufficient to achieve simultaneously the enhancement of both the wear-resistance and the corrosion-protection properties. Conversely, the sequential implantation of Cr⁺ and N₂⁺ at 140 keV and fluencies of 3 × 10¹⁷ and 1.5 × 10¹⁷ ions/cm² respectively, permits the formation of a functional surface capable of reducing both the corrosion rate and the wear rates, with respect to those exhibited by the un-implanted Ni surfaces.This treatment can be used to protect the surfaces of micro-embossing/stamping dies based on electroformed Nickel, as an alternative to other coating strategies. Furthermore, the ion implantation assures the non-modification of the net-shape and surface finish of these types of dies, which is of crucial importance when they are used for high-precision micro-texturing/imprinting applications.     

Effects of Si, W and W–Mo on isothermal oxidation behaviors of Nb/Nb5Si3 in situ composites at high temperature

The effects of Si, W and W–Mo on the isothermal oxidation behaviors of Nb/Nb₅Si₃ in situ composites in static air at 1000 and 1200 °C for 20–100 h were investigated on as-cast materials. The results show that the oxidation kinetics of each alloy was not changed whether at 1000 or 1200 °C, and the oxidation mechanism were not changed. The oxidation resistance of Nb/Nb₅Si₃ in situ composites was sensitive to Si content, and the oxidation rate of Nb-10Si alloy was more than twice as many that of Nb–20Si alloy. By alloying of W, the oxidation resistance of Nb–20Si–10W alloy was improved significantly, because the WO₃ scale can provide the adherence for the creaked Nb₂O₅ scale and reduce the diffusion of oxygen through the scale. Comparing to alloying with W, the poor oxidation resistance of Nb–20Si–10W–10Mo alloy was attributed to the evaporation of MoO₃ and highly porous scale.