Chromium Metal Powders Research Articles

Sliding Wear Behavior of Cu + Sn + Cr Composites by Taguchi Technique

In tribological industries, metal matrix composites are now being more commonly used because of their inherent properties such as high stiffness, high strength, high toughness. The effect on tribological properties of chromium-reinforced bronze-based metal matrix composites was investigated. In a bronze matrix, chromium metal powders of 40 μm particle size were reinforced to yield composite samples of ratios 5, 10 and 15 percent by means of powder metallurgy. As per ASTM G99, the manufactured composite specimens were subjected to sliding wear tests using pin-on—disc system. The sliding wear experiments were carried out by following the Taguchi methodology and the variance approach analysis was used to assess the effect of wear factors such as applied load, sliding speed, material composition and sliding distance on wear resistance of manufactured composites. In addition, multiple linear regression analysis and signal-to-noise ratio were used to analyze bronze-based metal matrix composite wear behavior. The injection of chromium metal powders into bronze matrix material as reinforcement material increases the tribological characteristics.

Microstructural characterization and mechanical properties development with Ti, Cr, or Ni addition for low carbon steel butt joints

Welding is one of the most important industrial process, therefore many practical techniques are developed to obtain an efficient and cost effective welding for different kind of metals. In this research, the microstructural characterization and mechanical properties of welded joints using TIG welding were studied for 1020 AISI low carbon steel. Titanium, Chromium, or Nickel powder were added to the welded joint one at a time by paste it with paraffin wax in the form of a thin layer. The welds were conducted and tested, then results were compared with and without adding Ti, Cr, or Ni metal powder. The welding process was done at a constant DC current (200 Amps. and 20 Volts) using weld filler metal type ER70S-3. Tests results showed that the tensile strength of the welded joint without adding metal powders was approximately 2% higher than the tensile strength of the base metal. Additionally, the tensile strength enhanced by approximately 27%, 21%, and 2% for Titanium, Nickel, and Chromium metal powder addition to the welded joints respectively. The bending strength values for all welded joints were also higher than the base metal. Furthermore, the hardness values were increased in the welded zone for all specimens. This can be attributed to the difference in the behavior of each metal powder at high temperature. The obtained results provide an experimental reference for the development of a new welding technique. It can be used in practical welding applications to obtain the desired properties using a suitable metal powder or a combination of them.

Structural Changes in С36 Laves Phase Intermetallic Compound TiCr2 During Hydrogenation–Dehydrogenation Process

The paper deals with melting of titanium and chromium metal powders in plasma of abnormal glow discharge which results in the formation of the hexagonal С36 Laves phase compound TiCr2 with a = 4.928 A and c = 15.983 A lattice parameters. The hydrogenation–dehydrogenation process is used to prepare the powder of C36 Laves phase intermetallic compound TiCr. The hydrogenation–dehydrogenation process is performed at 100°C, 2 atm hydrogen pressure and 30 min ageing followed by vacuum cooling. The prepared metal powder is characterized by rounded lamellar and coarse particles 6 ± 2 μm and 21 ± 7 μm in size, respectively.

Surface passivity largely governs the bioaccessibility of nickel-based powder particles at human exposure conditions

The European chemical framework REACH requires that hazards and risks posed by chemicals, including alloys and metals, are identified and proven safe for humans and the environment. Therefore, differences in bioaccessibility in terms of released metals in synthetic biological fluids (different pH (1.5–7.4) and composition) that are relevant for different human exposure routes (inhalation, ingestion, and dermal contact) have been assessed for powder particles of an alloy containing high levels of nickel (Inconel 718, 57 wt% nickel). This powder is compared with the bioaccessibility of two nickel-containing stainless steel powders (AISI 316L, 10–12% nickel) and with powders representing their main pure alloy constituents: two nickel metal powders (100% nickel), two iron metal powders and two chromium metal powders. X-ray photoelectron spectroscopy, microscopy, light scattering, and nitrogen absorption were employed for the particle and surface oxide characterization. Atomic absorption spectroscopy was used to quantify released amounts of metals in solution. Cytotoxicity (Alamar blue assay) and DNA damage (comet assay) of the Inconel powder were assessed following exposure of the human lung cell line A549, as well as its ability to generate reactive oxygen species (DCFH-DA assay). Despite its high nickel content, the Inconel alloy powder did not release any significant amounts of metals and did not induce any toxic response. It is concluded, that this is related to the high surface passivity of the Inconel powder governed by its chromium-rich surface oxide. Read-across from the pure metal constituents is hence not recommended either for this or any other passive alloy.

Chemical Stability of Chromium Carbide and Chromium Nitride Powders Compared with Chromium Metal in Synthetic Biological Solutions

Chromium carbide (Cr-C) and chromium nitride (Cr-N) powders were compared with a chromium metal powder (Cr-metal) to evaluate their chemical stability in solution. All three powders were exposed in five different synthetic biological solutions of varying pH and chemical composition simulating selected human exposure conditions. Characterisation of the powders, using GI-XRD, revealed that the predominant bulk crystalline phases were Cr7C3 and Cr2N for Cr-C and Cr-N respectively. The outermost surface of Cr-C, determined by XPS, contained Cr7C3 and Cr2O3 and the corresponding measurement on Cr-N revealed Cr2N and CrN apart from Cr2O3. The presence of Cr2O3 was verified by XPS investigations of the Cr-metal powder. The mean particle size was similar for Cr-metal and Cr-N but slightly smaller for Cr-C. All three powders were poorly soluble and released very low amounts of chromium (<0.00015 μg Cr/μg loaded particles) independent on test solution. Slightly higher chromium concentrations were determined in the more acidic media (pH 1.7 and 4.5) compared with the near-neutral solutions (pH 7.2 and 7.4). Cr-C released the lowest amount of Cr despite having the largest surface area a feature attributed to the strong covalent bonds within the matrix.

In vitro percutaneous absorption of metal compounds

It is well known that contact with metals can be responsible for allergic contact dermatitis; also, there is experimental evidence that nickel ions are readily available on the surface of used coins containing nickel and copper. The aim of this study was to prove that metal powders of nickel (Ni), cobalt (Co) and chromium (Cr) dispersed in synthetic sweat are oxidised into respective ions that can permeate the skin. Suspensions of 5 g of metal powder (Ni, Co and Cr) in 100 mL of synthetic sweat at pH 6.5 were prepared and shaken with a stirring plate at room temperature for 30 min. Human skin membranes were set up in Franz-diffusion cells and 2 mL of the freshly made suspension were applied to the outer surface of the skin for 24 h. The appearance of metal ions in the aqueous receptor phase (NaCl 0.9%) was quantified by Electro Thermal Atomic Absorption Spectroscopy (ETAAS). Also, metals ions were analysed using Differential Pulse Polarography (DDP), Differential Pulse Voltammetry (DPV) and Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) techniques both in the receiving phase and in the donor solution to evaluate the presence of different ionic metallic species. DPP and DPV measurements of cobalt and nickel suspensions confirmed the presence of Co 2+ and Ni 2+ ions in concentration, respectively of 33.3 ± 3.2 and 27.1 ± 3.2 mg L −1. Chromium ions concentration below 0.1 mg L −1 were found in chromium suspensions bearing evidence of synthetic sweat inefficacy of oxidising chromium metal powder. Cobalt and nickel skin permeation was demonstrated in in vitro experiments using the Franz cell system giving a permeation flux of 0.0123 ± 0.0054 μg cm −2 h −1 for cobalt and of 0.0165 ± 0.00036 μg cm −2 h −1 for nickel and a lag time of 1.55 ± 0.71 h for cobalt and of 14.56 ± 0.56 for nickel. Chromium below 0.1 μg L −1 was found in the receiving solutions. Our experiments demonstrated that metallic nickel and cobalt can be oxidised when suspended in synthetic sweat, while chromium would probably need stronger oxidising conditions. Metallic ions can permeate the skin and the Franz cell system showed that it is possible to measure a flux of ions through the skin for cobalt and nickel but not for chromium.

Combustion synthesis of chromium-substituted lithium ferrites Li0.5Fe2.5−xCrxO4 (x≤2.0): Rietveld analysis and magnetic measurements

Pure and chromium-substituted lithium ferrites Li0.5Fe2.5−xCrxO4 (x≤2.0) have been made in air by self-propagating high-temperature synthesis (SHS), a combustion process involving the reaction of lithium peroxide, iron oxide, chromium oxide and iron or chromium metal powders. Reactions were performed in zero field and in an applied magnetic field of 1.1 T. Both the zero field and the applied field SHS reactions proceeded with a synthesis wave which spread out from the point of initiation. Notably the applied field synthesis waves were faster and hotter than their zero field counterparts. The products from the SHS reaction were ground and sintered at 1150°C for 2 h. Rietveld analysis of the powder X-ray data on the sintered samples showed that in all cases a cubic spinel ferrite was produced which showed a decrease in the lattice parameter with increasing Cr content. The x=0 applied field sample showed 87% superstructured and 13% disordered LiFe2.5O4 whilst the zero field sample showed 30% superstructured LiFe2.5O4 and 70% disordered LiFe2.5O4. X-ray line broadening indicated crystallites of order 70–90 nm in all samples. Electron microprobe analysis and EDAX showed that the samples were homogeneous and had the expected Fe to Cr ratios. Mössbauer and magnetic hysteresis data showed a significant change in sublattice occupancy and net magnetisation with Cr content. Coercive forces in the Cr-doped ferrites were larger than in pure compositions. Samples prepared in an applied magnetic field exhibited smaller coercivity and saturation magnetisation compared to those prepared in zero magnetic field.

Self-propagating high-temperature synthesis of lithium-chromium ferrites Li0.5Fe2.5-xCrxO4

Pure and chromium-substituted lithium ferrites have been made in air by self-propagating high-temperature synthesis (SHS), a combustion process involving the reaction of lithium peroxide, iron oxide, chromium oxide and iron or chromium metal powders. Three series of SHS samples were produced: by SHS only; by SHS followed by sintering at C for 2 h; and by SHS in a magnetic field of 1.1 T followed by sintering at C for 2 h. X-ray data showed that a cubic spinel ferrite was produced in all cases, with single-phase products achieved after sintering. Systematic changes in lattice parameter were seen both as a function of Cr content and, for the sintered samples, as a result of the field applied during SHS. Scanning electron microscopy showed that the crystallites had sizes of order . Electron microprobe analysis and EDAX indicated that the samples were homogeneous and had the expected Fe-to-Cr ratios. Mössbauer and magnetic hysteresis data showed that there were significant changes in sublattice occupancy and nett magnetization with Cr content. Coercive forces in the Cr-doped ferrites were larger than those in pure compositions. Some differences between Mössbauer and magnetization parameters of the sintered zero-field and applied-field SHS samples were observed.

Self propagating high-temperature synthesis of chromium substituted magnesium zinc ferrites Mg0.5Zn0.5Fe2−xCrxO4 (0≤x≤1.5)

Magnesium ferrite MgFe 2 O 4 and chromium substituted magnesium-zinc ferrite Mg 0.5 Zn 0.5 Fe 2–x Cr x O 4 (0≤x≥1.5) have been made in air by self-propagating high temperature synthesis (SHS), a combustion process involving the reaction of magnesium, zinc, iron(III) and chromium(III) oxides with iron or chromium metal powders and sodium perchlorate. This produced an orange-yellow propagation wave of velocity 2-3 mm s –1 . Two series of SHS samples were produced: series 1, SHS followed by annealing at 1400°C for 2 h and series 2, SHS in a magnetic field of 1.1 T followed by annealing at 1400C for 2 h. X-Ray data showed that in all cases nearly phase pure cubic spinel ferrites were produced. Changes in the cubic lattice parameter were seen as a function of Zn and Cr content. Room temperature and 80 K Mossbauer data showed a significant change in sublattice occupancy with Cr content. Magnetic hysteresis data for series 1 and 2 showed that the coercive force of doped samples is higher than pure compositions whilst magnetisation is lower. It was also shown that the use of a magnetic field during SHS can influence the microstructure and magnetic properties of the final material.

Reduction of chemical oxygen demand of industrial wastes using subcritical water oxidation

Abstract If wastes have strong toxicity, high organic content, and a deep hue, they are difficult to handle in the waste disposal. It is very practical that waste of this kind is treated by Subcritical Water Oxidation (SWO). In our work, caprolactum (CPL) waste, purged from a petrochemical plant, and dyeing waste, purged from a textile plant, were individually treated by a semi‐batch SWO process. Within a one‐hour treatment, Chemical Oxygen Demand (COD) reduction reached 89% for CPL waste (6.90 MPa, 260°C) and 95% for dyeing waste (6.90 MPa, 240°C). There is also a great improvement in hue, especially for the dyeing waste. When CPL wastewater was treated by the SWO process using a chromium metal powder as a catalyst, COD reduction improved further under the same operating conditions. A kinetic model was used to illustrate the oxidation mechanism and the effectiveness of the catalyst. The oxygen concentration in the effluent showed that oxygen consumption corresponded to COD reduction. With the monitoring ...

Radiotracer technique in adsorption study, part II. Adsorption of phosphate ions on chromium metal powder

The adsorption of phosphate ions on chromium metal powder from aqueous solutions of sodium dihydrogen phosphate labelled with 32P has been studied as a function of concentrative (10-3 to 10-6 mol l-1), temperature (303-323 K), and pH (3.5-10.6) of the adsorptive solution. The time for the equilibrium establishment was found to be about 4 hours and it is dependent on the solution acidity. The smooth and continuous growth of phosphate adsorption follows the first order kinetics and the rate constants are found to be of the order of 10-3 min-1. The results show that the adsorption in the system under study obeys the Freundlich isotherm. The increase in temperature from 303 K to 323 K does not effect the process markedly. The adsorption kinetics of phosphate ions is highly dependent on pH of the adsorptive solution. On the basis of the present data the nature and mechanism of the adsorption are discussed.

溶融塩浸せき法による超硬合金へのＶ，Ｎｂ，Ｔａ炭化物被覆

In the previous paper, it was reported that Cr7C3 layer can be easily formed on cemented carbides immersed in a borax bath containing pure chromium metal powder, and the oxidation and corrosion resistances of the cemented carbides, thus treated, can be remarkably improved. The present study was undertaken to investigate the possibilities of VC, NbC and TaC coatings on cemented carbides. Both NbCl5 and electrolytically dissolved Nb in the borax bath were effective in providing NbC layer on cemented carbide. VC layer was obtained in the bath containing VCl3, and TaC layer was obtained in the borax bath containing electrolytically dissolved Ta. These layers can be thought to be formed by the reactions between atomic V, Nb or Ta in the bath and either C in Co binder phase or, to some extent, carbon in WC carbide. The parabolic law can be applied to the relation between the thickness of the NbC layer and the treating time. The corrosion resistance of cemented carbides against 10%HNO3 and 10%H2SO4 aqueous solutions was remarkably improved by NbC and TaC coating.

A Comprehensive Nitrogen Method

Abstract A single comprehensive nitrogen method applicable to all fertilizers and to all forms of fertilizer nitrogen has been developed. The method utilizes untreated chromium metal powder in an acid medium to reduce nitrates. It quantitatively reduced nitrates alone, nitrates in the presence of organic matter, and nitrates in samples with high C1"/N03_ratios. Quantitative results were obtained with both solid and liquid fertilizer samples and with highly refractory organic samples. When subjected to the ruggedness test of Youden the method was "rugged."

The production of anaerobic conditions with chromous salts.

Summary: The absorption of molecular oxygen by chromous salts provides one of the most efficient methods of producing anaerobic conditions. In previous applications to anaerobic culture, hydrogen and chromous ions were produced by the action of sulphuric acid on chromium; chromium metal powder suitable for use in this method is however difficult to obtain. An alternative method of generating hydrogen and chromous sulphate from a mixture of chromic sulphate, zinc and sulphuric acid is described. A new indicator of anaerobic conditions which can be used repeatedly is also described.