Mixture Of Chromium Oxides Research Articles

Single-step formation of Cr2N nanoparticles by pulsed laser irradiation

Chromium nitride nanoparticles with mean diameter distribution between 0.8 nm and 30 nm were produced by laser irradiation of a chromium target immersed in liquid nitrogen. Cr was directly converted to chromium nitride nanoparticles according to selected-area electron diffraction analyses using the transmission electron microscopy technique. Crystalline nanoparticles mostly consist of Cr2N, which is commonly reported together with the conversion of Cr2N to CrN and the mixture of chromium oxides. In addition, there is no evidence of oxidation by storage or photodegradation of the nanoparticles in isopropyl alcohol suspensions. The intensity profile of small-angle X-ray scattering indicates that the geometrical shape of the nanoparticles is not spherical but cylindrical with aspect ratio (height-to-radius) of 0.35–0.05. UV-Vis absorption spectroscopy reveals the presence of surface plasmon absorption at the ultraviolet region at wavelengths of 350, 372, and 397 nm. First-principles calculations of density of states, dielectric function, and optical conductivity performed within the theoretical framework of density functional theory for Cr2N with a hexagonal structure corroborate the formation of surface plasmons.

Microstructural evolution and oxidation resistance of T92 boiler tube steel upon long-term supercritical steam test

High-chromium heat-resistant steels are widely used as key materials to improve the condition of steam pressure and temperature in the boiler tube system of the supercritical power plants. Material-related failures in boiler system have occurred mainly due to internal oxidation and corrosion. For the stable maintenance of boilers, determination of the corrosion mechanism, microstructural evolution and data collection pertaining to the oxidation is essential. In this study, the supercritical steam test was carried out on T92 steel at the temperatures of 600/650/700°C for 10,000/15,000/20,000h. The matrix of steels and the oxide scale layers were investigated after steam treatment using scanning electron microscopy, back-scattered electron microscopy and electron backscattered diffraction. The oxide scale layers from the outer surface to the matrix consisted of: i) an outer layer of nanoscale iron oxide (Fe2O3); ii) inner layer of microscale crystals of Fe3O4, and iii) a mixture of chromium oxide and chromite (Cr2O3 and FeCr2O4) adjacent to the matrix.

Comparative Study of Mechanical Activation Improved by High Energy Ball Mills in Chromium Oxide Reduction

The processes of high-energy milling and gained importance among the unconventional methods. In this work, we seek to compare the power supply two types of high energy mills (vibratory mill (SPEX) and planetary mill) with the variation of the milling power. The millings were carried out with a mixture of chromium oxide and aluminum metalic. The reduction of chromium oxide does not occur instantaneously, but gradually as the progress of milling with mechanical activation of powders, this mechanical activation occurs leading to the solid state reaction occurs. The results were obtained for thermal analysis of the samples. The energy released varies, exhibiting a maximum mechanical activation for the range of powers milling studied. The correlation between the energy mills can be made by identifying the milling power is reached at which the maximum in each mechanical activation mill and quantifying this activation.

Characterisation of the surface topography, tomography and chemistry of fretting corrosion product found on retrieved polished femoral stems

This study presents the characterisation of the surface topography, tomography and chemistry of fretting corrosion product found on retrieved polished femoral stems. Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) and Fourier Transform Infrared Spectroscopy (FI-IR) were utilised in order to assess the surface morphology of retrieved Metal-on-Metal Total Hip Replacements and surface chemistry of the films found on the surface. Gross slip, plastic deformation and directionality of the surface were extensively seen on the proximal surfaces of the retrievals. A more corrosive phenomenon was observed in the distal regions of the stem, demonstrating a seemingly intergranular attack. Tribochemical reactions were seen to occur within the stem–cement interfaces with tribofilms being observed on the femoral stem and counterpart PMMA bone cement. XPS, TEM–EDX and FT-IR analyses demonstrated that the films present in the stem surfaces were a complex mixture of chromium oxide and amorphous organic material. A comparison between current experimental and clinical literature has been conducted and findings from this study demonstrate that the formation and chemistry of films are drastically influenced by the type of wear or degradation mechanism. Films formed in the stem–cement interface are thought to further influence the biological environment outside the stem–cement interface due to the formation of Cr and O rich films within the interface whilst Co is free to migrate away.

Critical tuning of magnetron sputtering process parameters for optimized solar selective absorption of NiCrOx cermet coatings on aluminium substrate

NiCrOx ceramic–metal composites (i.e. cermets) exhibit not only oxidation and moisture resistances, which are very important for industrial applications, but also remarkable solar selective absorption properties. In order to reach the best optical performances with only one coating layer, tuning of the magnetron sputtering process parameters (O2 flow rate, pressure and deposition time) was performed systematically. The process window turned out to be very narrow implying a critical tuning of the parameters. The optimal operating point was determined for a single layer coating of NiCrOx on an aluminium substrate, leading to a spectrally integrated solar absorption as high as 78%. Among various material properties, the focus was put on the optical reflectance of the coating/substrate system, which was measured by UV–vis–NIR spectrophotometry. Using complex refractive index data from the literature, the theoretical reflectance spectra were calculated and found to be in good agreement with the measurements. Chemical analysis combined with scanning electronic and atomic force microscopies suggested a cermet structure consisting of metallic Ni particles and a compound matrix made of a mixture of chromium oxide, nickel oxide and nickel hydroxide.

Failure analysis of cemented metal-on-metal total hip replacements from a single centre cohort

This paper presents the failure analysis of cemented metal on metal (MoM) total hip replacements (THR) from a single centre cohort. In this paper all retrieved femoral stems were implanted and revised at the Norfolk and Norwich University hospital by three specialist hip surgeons. All patients were subjected to the same combination of metallic implants, operative and follow up procedure. Between 1997 and 2008, 652 Ultima TPS™ femoral stems with the Ultima MoM articulation (DePuy International, Leeds) were implanted. At 2–9 years follow up, 90 revisions had been performed. Upon removal extensive fretting-corrosion of the cemented portions of the femoral stems was seen, resulting in high metal ion levels. In order to fully understand the factors resulting in failure of these cemented MoM THR optical light microscopy, Scanning Electron Microscopy with integrated Energy Dispersive X-ray spectroscopy (SEM/EDX) and X-ray Photo-electron spectroscopy (XPS) were utilised in order to assess the surface morphology and chemistry of retrieved MoM THR and surface chemistry of the films found on the surface. Gross slip, plastic deformation and directionality of the surface were extensively seen on the proximal surfaces of the retrievals. A more corrosive phenomenon was in the distal regions of the stem, demonstrating a seemingly inter-granular attack. SEM/EDX analysis demonstrated that black films present commonly seen on the highly worn regions of the cemented portions of the femoral stem were a complex mixture of chromium oxide, protein and amorphous carbon. XPS demonstrated films were Cr, O rich, mixed with organic material.

In-Situ Synthesis of Alumina Reinforced (Fe,Cr)3Al Intermetallic Matrix Nanocomposite

In this study, a mixture of chromium oxide, elemental iron, and aluminum powders was subjected to high energy ball milling to produce Al2O3 reinforced (Fe,Cr)3Al matrix nanocomposite. The structural changes of powder particles during milling were investigated by X-ray diffractometry. Cross-sectional microstructure of powder particles after different milling times was observed by scanning electron microscopy using back scatter mode. The change in morphology of powder particles was followed by scanning electron microscopy observations. The transmission electron microscopy was used to confirm the development of nano-sized structure in the final product. The changes in phase composition, structure and morphology of powder particles suggested that during milling, Al gradually reacts with Cr2O3 leading to the formation of metallic Cr and Al2O3 phases and concurrently, the reduced Cr and remaining Al diffuse into the Fe lattice and as a result, a Fe(Al,Cr) solid solution forms. This structure was transformed to (Fe,Cr)3Al intermetallic compound at longer milling times.

Preparation of ortho-para ratio controlled D2 gas for muon-catalyzed fusion

A negative muon in hydrogen targets, e.g., D2 or D-T mixture, can catalyze nuclear fusions following a series of atomic processes involving muonic hydrogen molecular formation (muon-catalyzed fusion, muCF). The ortho-para state of D2 is a crucial parameter not only for enhancing the fusion rate but also to precisely investigate various muonic atom processes. We have developed a system for controlling and measuring the ortho-para ratio of D2 gas for muCF experiments. We successfully collected para-enriched D2 without using liquid-hydrogen coolant. Ortho-enriched D2 was also obtained by using a catalytic conversion method with a mixture of chromium oxide and alumina. The ortho-para ratio of D2 gas was measured with a compact Raman spectroscopy system. We produced large volume (5-30 l at STP), high-purity (less than ppm high-Z contaminant) D2 targets with a wide range of ortho-para ratios (ortho 20%-99%). By using the ortho-para controlled D2 in muCF experiments, we observed the dependence of muCF phenomena on the ortho-para ratio.

AES investigation of the stainless steel surface oxidized in plasma

Auger electron spectroscopy (AES) depth profiling was used to study the oxidation phenomena of AISI316L stainless steel during treatment with oxygen plasma. Samples were exposed to low-pressure RF plasma with a high dissociation degree, so that the flux of oxygen atoms onto the sample surface exceeded 10 24 m −2 s −1. A set of samples was oxidized 4 min at different temperatures up to 1300 K during plasma treatment. AES measurements showed that the oxide film thickness increased with the increasing temperature. The thickness of the oxide film on the samples oxidized in plasma at 300 K was nearly the same as for the untreated sample. The thickness of the oxide film of the samples which were oxidized at 1000 K was about 170 nm and it consisted of iron oxide. The thickest oxide film of about 350 nm was found on the samples heated in oxygen plasma to 1300 K. Depth profiling showed the uppermost layer of manganese oxide, followed by a mixture of chromium oxide and iron oxide. The scanning electron microscope analyses showed a dramatic increase of the surface roughness.

Development of large area sputtered solar absorber coatings

For effective solar collectors a simple black paint is inadequate. A solution is the use of solar selective coatings, which one of is known as black chromium, deposited electrochemically. The coatings we prepared were produced by reactive dc-magnetron sputtering. The coating consists of a graded mixture of chromium oxide and chromium nitride. Experimental design procedures (face centered cubic plans) were applied for the optimization of the production parameters. The maximum sample size was 0.6 m × 1.1 m in the lab and 2 m × 3 m in a following pilot production plant. The coating is deposited directly on copper sheets without the commonly used anti-corrosion nickel coating in between, on a metallic infrared reflecting coating on float glass or high temperature stable polymers. The durability of the absorbers was found to be sufficient for the application in ventilated flat plate collectors containing moisture according to the tests and requirements proposed by the Solar Heating and Cooling Program of the International Energy Agency.

Study of a hollow cathode arc discharge in the presence of chromium oxide

A hollow cathode arc discharge in hydrogen has been used for the purpose of chromium oxide reduction, the solid oxide being placed inside the anode. Mass transport from the oxide to the gas phase and excitation conditions in the plasma have been investigated. The results show that a substantial amount of oxide is transferred to the gas phase with subsequent reduction and deposition inside the cathode cavity, in the form of a pure metal. The residual part condenses on the discharge chamber wall as an amorphous substance, containing 50–60% of Cr metal, and on the anode surface under the form of a mixture of chromium oxide and metal crystals (10%). From spectroscopic investigations it follows that, inside the anode zone, total Cr concentration in the gas phase is of the order of 1014 cm−3, the excitation temperature of the atoms and ions being 4500 and 5500 K, respectively, and the ionization temperature being about 6000 K.

Corrosion of Fe-Ni-Cr, Fe-Cr-AI, and Fe-Ni-Cr-AI Alloys in H2/H2O/H2S Mixtures at 1200 °C

A series of Fe-Ni-Cr, Fe-Cr-AI, and Fe-Ni-Cr-Al alloys has been exposed at 1200 °C in atmospheres of controlled oxygen and sulfur potentials, after preoxidation in air or in impure argon. The corrosion behavior has been interpreted on the basis of phase-stability diagrams. The presence of iron and nickel-rich spinel particles in the outer layers of the initial oxide scales plays an essential role in the resistance to sulfur attack. When the oxygen potential is sufficiently low, these spinels are reduced to a mixture of chromium oxide and an Fe-Ni alloy. The latter can then form sulfides which are liquid at high temperatures and which accelerate the penetration of sulfur into the underlying metal.

水素雰囲気における酸化クロム，黒鉛混合物からの炭化クロム生成について

In order to make clear the formation process of Cr3C2 from a mixture of chromium oxide and solid carbon, the carburization reaction of chromium oxide to Cr3C2 was carried out at temperatures ranging from 1100 to 1500°C in hydrogen stream (500 ml/min).\ oindentThe cross-sections and surfaces of partially carburized pellets were observed by a scanning electron microscope.The results were summarized as follows:(1) The carburization products were Cr3C2, Cr7C3 and Cr23C6. Cr3C2 and Cr7C3 consisted of a single phase were obtained.(2) At the reaction temperature of 1100°C, the yield of Cr3C2 reached 93%.(3) The formed chromium carbides resembled in shape, but they were identified to be Cr3C2, Cr7C3 and Cr23C6.(4) The formed chromium carbides were polycrystalline. The crystal grain in each phase grew up with an increase of the carburization temperature.(5) The formation reaction of chromium carbides was markedly affected by the pressure of CO gas.