Papers by Keyword: Chromium

Abstract: The increasing demand for metals has led to the growth of the metal industry in Indonesia. This has resulted in a rise in the amount of waste generated. Various methods can be used in the treatment of metal waste, such as flotation, flocculation-coagulation, and adsorption. One biopolymer that can be used for metal removal is chitosan. This study aims to synthesize chitosan from shrimp shell waste, which is then modified with silica to enhance its mechanical strength and stability in acidic conditions using the sol-gel method. The chitosan-silica composite is then immobilized using dithizone to increase the adsorption capacity through immersion variations of 4, 6, and 8 hours. The adsorbent, characterized using Fourier Transform Infrared, showed the presence of bonds in chitosan at wavenumbers 3454 cm^-1 (N-H) and 1647 cm^-1 (C=O), chitosan-silica at wavenumbers 966 cm^-1 (Si-O in Si-OH), 798 cm^-1 (Si-O in Si-O-Si), and 466 cm^-1 (Si-O-Si), and chitosan immobilized with dithizone at wavenumbers 2343 cm^-1 (S-H) and 1083 cm^-1 (S=C). Adsorption was performed by mixing the adsorbent with the waste for 1 hour, then the waste was added with 0.25 ml of phosphoric acid and analyzed using a UV-Vis Spectrophotometer. Based on the results of the study, the highest adsorption efficiency was obtained with the adsorbent variation of 8 hours immersion at 59%, while the adsorption efficiency for immersion times of 4 and 6 hours was 0.3% and 6%, respectively.

Abstract: The 45S Bioactive glass-ceramic (BG) and Chromium (Cr)-doped BG materials were successfully produced in this study. XRD, FTIR, and ICP-MS techniques were used to characterize the prepared materials. The XRD testing showed that all samples contained pure BG. Increased Cr ion inclusion shifted the BG diffraction peaks to a lower value of 2 Theta and increased crystallinity. FTIR was used to detect Si-O, P-O, and Ca-O functional groups. Cr ions steadily decreased the Ca-vibration mode area. The ultraviolet-visible spectrophotometry was used to measure the optical characteristics of pure and Cr BG-doped materials. The Cr-doped BG was green in colour, whereas the lab-synthesized BG was white. Two additional bands formed at 433 and 615 nm when Cr ions were doped into the BG structure. These bands may be caused by ⁴A₂ → ⁴T₁ and ⁴A₂ → ⁴T₂ electronic d-d transitions. The findings show that biomedical applications may exist for fluorescent probes manufactured from Cr-BG materials.

Abstract: Titanium and its alloys are the 5th most common metallic materials used world wide but the markets volume of titanium materials, is difficult to expand due to associated production costs, and the decrease of those costs are critical in order to expand their markets. A possible option is the alloy design, i.e. using low price alloying element, such as iron, chromium, manganese and oxygen, and the selection of other raw materials, i.e. grade of sponge titanium. In beta titanium alloy, Ti-Mo system alloy using ferro-molybdeum was developed by USA company or Ti-Cr-Fe-Al beta alloy were also developed by Japan company. In this paper, those developed alloys were explained. Furthermore, substitution of Ti-10V-2Fe-3Al near beta alloy, presenters are studying about Ti-Mn-Fe-Al alloy.

Abstract: Chromium carbide coatings deposited on mechanical parts by different techniques have an interesting hardness, wear-resistant and corrosion resistance. Some studies show that chromium carbides produced by physical vapor deposition methods and revealed a superior hardness present a poor adherence to their substrates. The objective of this study is to indirectly obtain a hard, and adherent coating of chromium carbide by using a conversion treatment including carburizing treatment of steel substrate, deposition of a pure chromium layer, and annealing treatment of coated carburized steel under a carbonic gas atmosphere. Treatment temperature has an effect on the partial or complete conversion of chromium film as a result of the diffusion and precipitation process. The transformation rate of chromium into both chromium carbide layers was investigated. For 1 h of holding treatment, chromium film was totally transformed at 900 °C into chromium carbide film which presented high hardness and excellent adhesion.

Abstract: Gold nanoparticles (AuNPs) have been successfully synthesized using L-Ascorbic Acid as a reducing agent and p-Aminobenzoic Acid as a capping agent. These AuNPs were used to detect and quantify Chromium(III) as a pollutant utilizing its unique characteristic called surface plasmon resonance (SPR). The change of SPR and color of AuNPs then was employed to determine the concentration of Cr(III) by using colorimetric and Digital Image Colorimetric methods. Digital Image Colorimetry allowed to development of an easier and cheaper way to detect and quantify Cr(III). AuNPs capped p-aminobenzoic acid (AuNPs-PABA) were synthesized at room temperature without using any heating method. Then synthesized AuNPs-PABA were characterized using UV-Visible spectrometer and Transmission Electron Microscope. This AuNPs-PABA then got contacted to Cr(III) and color-changing happened in AuNPs-PABA was analyzed using UV-Vis Spectrometer and captured for Digital Image Colorimetric. The result showed that Digital Image Colorimetric method has a very big potential to be developed for AuNPs-based detection and quantification of Cr(III) as confirmed by good linearity of AuNPs-PABA-Cr(III) respect with Difference Intensity of Red Color Component, wider dynamic range, and Lower Limit of Detection (LoD).

Abstract: The article considers the possibility of controlling the macromolecular structure of ternary alloys in the form of compact coatings, which are obtained by electrochemical means. This method of obtaining metal clusters is more economical than from plasma one. The influence of the cluster structure of the synthesized coatings in the form of a triple alloy of polyligand complex electrolytes on their functional properties is shown. There are presented the results of testing coatings from this ternary alloy of different elemental and cluster composition for microhardness according to Vickers. The highest microhardness was obtained by the coating with the lowest molecular weight of the cluster, which provided a denser packing of atoms.

Abstract: Treatment of rich chromium effluent is a matter of concern in many leather industries. Nano zero valent iron (NZI) is considered as one of the promising adsorbent materials due to its large surface area. Also, biomaterials have great remediation efficiency because of their surface-active groups such as hydroxyl and carboxyl groups. In this paper, we study the use of nano-bio polymer complex (NBPC) in chromium removal. Batch experiments were carried out in terms of operating medium pH, contact times, initial chromium concentrations, and speed rates. The maximum chromium removal of 88% was observed at pH values 7.0, contact time 30 min, and speed rate 150 rpm for chromium concentration 100 mg/L. The adsorption linear isotherms fitted well to Freundlich’s model compared to Langmuir’s model. Treatment of tannery wastewater through NBPC beads showed a decrease in heavy metal concentrations at equilibrium with removal orders of Mn > Cu > Ni > Cr > Pb > Fe > Cd. The removal efficiency of chromium ions is 52% with specific uptake of 25.6 mg(Cr)/g(NBPC). Results showed a decrease in the organic loads represented in COD, BOD, ammonia nitrogen, nitrate, and phosphorous with removal efficiencies 51.8, 48.6, 66.1, 63, and 43.3%, respectively. The reusability of NBPC beads was studied for three subsequent cycles. Results revealed that the availability of NBPC beads for reuse but with removal efficiencies is less than that of the first cycle. X-ray diffraction, SEM micrograph with EDAX analysis, and FT-IR spectroscopy for NBPC beads were studied for surface characterizations.

Abstract: Corn Cob ash was used in competitive adsorption of copper, zinc, and chromium from wastewater. The central composite design; a sub-set of response surface methodology was used to optimize the adsorption of the heavy metals. The result of the statistical parameters showed the coefficient of determination (R²) of 1.000, 0.999, and 1.000 for copper, zinc, and chromium respectively. The optimal conditions obtained for adsorbent dosage, initial concentration, temperature, contact time, and particle size were 13.20 mg, 79.72 mg/l, 34.95 °C, 40.38 min, and 1400 µm, respectively with the desirability of 1.000. The predicted and the actual values of metal removal obtained were 69.41%, 76.37%, as well as 70.44%, 72.50%, 77.90 % and 71.00% for copper, zinc, and chromium respectively. The ressult indicated a good conformity between the model predicted values and the actual values, thus having small errors of 3.09%, 1.53 % and 0.56 % for copper, zinc, and chromium respectively.

Abstract: The conditions for the synthesis of Al-Cr-W alloys during the aluminothermic reduction of a mineral tungsten concentrate - scheelite were considered. The alloys were identified as an aluminum matrix by the methods of elemental and X-ray phase analyzes. It is shown that the alloy synthesized from scheelite concentrate contains small amounts of iron and oxygen impurities (1.2 wt. %). It has been established that the alloys have a composite structure: inclusions of continuously solid solutions based on chromium and tungsten, as well as chromium aluminides Al₃(Cr, W, Fe)2, which have increased microhardness values (12.9 GPa) are distributed in the aluminum matrix.

Abstract: In the present work, Cr-Al₂O₃ nanocomposite coatings were electrodeposited onto a copper substrate using a modified trivalent chromium electroplating bath with the addition of 80nm Al₂O₃ powder. The effects of mechanical agitation of electrodeposition bath on Al₂O₃ particles dispersion and particles embedment were studied. The Cr-Al₂O₃ nanocomposite samples were subjected to different tests to characterize their surface morphology, crystalline structure, and mechanical properties. The crystalline structure, composition and surface morphology of the deposits were studied by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and field emission scanning electron microscopy (FESEM). The corrosion resistance test was carried out by electrochemical polarization method. The microhardness was studied via Vickers Microhardness Test. The variation in the microhardness as a main property to achieve enhancement of Al₂O₃ incorporations with Cr matrix. From the EDX analysis, Cr-Al₂O₃ nanocomposite deposited at 200 rpm stirring speed showed the highest weight percentage (wt%) of alumina. The hardness results showed the Cr-Al₂O₃ composite coating has the best performance at 200 rpm stirring speed which the hardness increased 32.3 % compared to that of Cr coating. The corrosion current density (i_corr) of Cr-Al₂O₃ coating achieved highest value at 200 rpm. This result revealed that the corrosion resistance of Cr-Al₂O₃ coating decreases with increasing Al₂O₃ particles content.