Papers by Keyword: Chromium Oxide

Abstract: The chromium oxide powders are transformed into plasma sprayable particles by using synthetic polymers for agglomeration. In order to carry out the agglomeration process, spray drying technique was employed. This research work highlights the significance of the process variables that control the synthesis of plasma spray powder and consequently, the properties that were suited for plasma spray coating. Energy Dispersive Spectroscopy (EDS) was used to characterize the elemental composition, while scanning electron microscopy (SEM) was used to analyse the morphology and powder grain sizes and X-ray diffraction (XRD) was used to identify the phase structure. And for the development of coatings on the substrates, Atmospheric plasma spray (APS) technique was used. The plasma sprayable powders were created with the intention of investigating for use as corrosion-resistant coatings.

Abstract: In this paper, we present the development of new types of boron carbide-based ceramics. Boron carbide is applied in the electronics and nuclear industries as well as for production of the grinding and abrasive materials, protective plates for body armor. The interaction of boron carbide with chromium nano-oxide additives (1-5 wt.%) during sintering was studied by mass spectrometry. It is shown that the formation of chromium nano-boride takes place at the stages of formation of metallic chromium, the lowest chromium boride and chromium carbide. The maximum solubility of chromium in the boron carbide lattice was found to be 0.5 wt.%. A composite material based on boron carbide, В₄С with CrB₂ nano-inclusions, was prepared. The bending strength and modulus of normal elasticity were equal to 44.6 MPa and 449.5 GPa, respectively. Micro-hardness and residual porosity were determined to be 40 GPa and 5-7 %.

Abstract: This research presented the surface oxidation of stainless steel grade 304 (S304) welded by a gas tungsten arc welding (GTAW) process. The welded S304 was inspected by visual and penetrant testing methods. The surface of the welded specimen was oxidized by the chromic solution to an obtained oxide film on S304 welded specimen. After that, the structural phase and crystallite size of the oxide film were investigated by X-ray diffractometer (XRD). The thickness of the obtained film was analyzed by an atomic force microscope (AFM). Furthermore, the effects of the oxide film on hardness and corrosion properties of specimen were analyzed by Vickers hardness tester and potentiostat instrument to study the correlation between the property of oxide film and the surface properties of the welded pipe S304 after oxidation.

Abstract: We present the results obtained using Cr₂O₃ as selective absorbing layer on aluminium film substrate. The thin films were deposited by electron beam evaporation using a multiple crucible e-gun able to deposit 4 materials in sequence without breaking the vacuum. Optical characterization of the multilayer films is based on ellipsometry and hemispherical reflectivity. The complex refractive index has been determinate and it has been used to design a selective solar absorber with high absorptance.

Abstract: This paper aims to study the correlation between some parameters of the metalspraying by APS process and the level of chromium oxide (Cr₂O₃) adhesion to the base material. Among the properties of the layers deposited by APS are those of wear resistance. In the context of evaluating the coatings properties and understanding aspects related to the coat structure phenomena, the purpose of the experiment presented here is to characterize the adherence of thermal sprayed coating Cr₂O_3. Because, the main problem of metalspraying layers is adhesion to the base material, there were subjected to tensile testing 2 samples made by 1C45 steel, which were previously bonded with an epoxy glue. The adhesion of the deposited layer on the basic material is important for ensuring the quality of products. The results show that the quality of surfaces and the existence of accidental defects at the interface lead to a decrease of adherence.

Abstract: Chromium oxide is a promising material for applications where excellent corrosion resistance, high hardness, and high wear resistance are needed. However, its use is limited because of low fracture toughness. Improvement of fracture toughness of chromium oxide while maintaining its afore mentioned key properties is therefore of high interest. In this communication we study the possibility of increasing the toughness of pulsed electric current sintered (PECS) chromium oxide by the addition of graphene oxide (GO). The indentation fracture toughness was improved markedly with the addition of graphene oxide. Materials prepared by direct chemical homogenization had better fracture toughness. In composites with 10 vol.% GO piling of thin graphene oxide layers resulted in the formation of graphite layers between Cr₂O₃ and in carbide formation, which were observed to be the main reasons for the degradation of the mechanical properties. The distribution of graphene oxide was more homogeneous, when the GO amount was 0.1 vol.% and the formation of graphitic layers were avoided due to lesser amount of GO as well as ultrasonic treatment following the ball milling.

Abstract: 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.

Abstract: The intense violet color and the high catalyst activity of Cr-doped SnO₂ nanoparticles have motivated several authors to understand the solid solution formation and the oxidation state of chromium ions after synthesis. Recent work has demonstrated the ability of surface segregation in chromium-doped tin oxide system but the oxidation state is still misunderstood. Calcium oxide addition changes the color of (Cr,Ca) codoped nanocrystalline tin dioxide pigments from violet to yellow simultaneously to a high particle size stabilization demonstrating that co-segregation could be associated to color change due to chemical environment change of chromium ions and specific surface area increase. High solubility of Cr⁺⁶ and Ca⁺² allow us to determine the surface excess of both cations by ionic chromatography and the color change after surface solubilization.

Abstract: In this paper, the effects of Surface Mechanical Attrition Treatment on the high-temperature oxidation of AISI 316L austenitic stainless steel are investigated. Samples treated with different conditions were oxidized at 650°C in order to study the effect of this type of nanocrystallisation on the oxidation resistance of the alloy concerned. X-ray diffraction and in-situ Raman spectroscopy were used to identify the oxides formed at the surface. The results indicate the presence of hematite and chromium oxides. Experimental results obtained by Raman spectroscopy were also used to study the stress evolution in Cr₂O₃ films during isothermal conditions.

Abstract: The presence of residual stresses in thermal oxide layers has been recognized for a long time. In the present work, the mechanical fields for chromia oxide are determined either by XRD or Raman spectroscopy. In addition, the microstructure of the chromia films is investigated ant its influence on the evolution of the stress release processes is analyzed.