Papers by Keyword: Reduction

Abstract: The main problem of processing of ores with a high content of titanium oxides is refractory slag based on TiO₂, which makes it difficult to melt. The methods of processing of titanomagnetite and ilmenite ores were analyzed. It is shown that the existing scheme of processing does not meet the requirements of complex use of materials. The paper presents the results of laboratory studies on reduction of ilmenite concentrate and subsequent pyrometallurgical separation of reduction products without addition of flux or slag-forming materials. Solid-phase reduction of iron enabled to extract iron selectively from the ilmenite crystal lattice, not diluting the oxide phase with the reducing agent ash. Using the advantages of solid-phase reduction, the possibility of obtaining pure iron and slag with a high content of titanium oxides was shown.

Abstract: The use of hydrogen peroxide and hydrazine sulfate for the treatment of chrome-containing rinsing waters of galvanic production of machine-building enterprises is proposed. The process of reducing chromium (6+) to (3+) from rinsing waters with a concentration of 8.55 mg/dm³ was studied. These reagents allow reducing more than 99% of chromium (6+) to chromium (3+) and maintaining a low salt content of treated wastewater. The consumption of hydrogen peroxide is 1.5 mg/dm³, and the consumption of hydrazine sulfate is 10 mg/dm³. The current situation in the treatment of galvanic wastewater leads to pollution of the environment with dangerous substances (CN^-, Cr⁶⁺, F^-, Cd²⁺), irrational use of raw materials and significant economic losses. The possibility of extracting valuable components from wastewater, in order to recycle them and return the treated water to production, is considered. Hydrogen peroxide is effective for treating acidic wastewater, and hydrazine sulfate can be used for both acidic and alkaline wastewater. Removal of excess hydrogen peroxide from the solution after reduction of chromium (6+) before precipitation of chromium (3+) hydroxide is required. The toxicity of hydrazine compounds must be taken into account.

Abstract: In real industrial environment there is always a difference between ideal theoretical condition and real production condition which bears the risk of producing defective or low quality parts. Getting closer to this ideal situation requires more effort and investment which tends to increase the production cost. In the P/M production lines, the sintering stage is one of the most critical processes. Maintaining an open continuous sintering furnace in an ideal condition is a challenge, and this issue gets more pronounced when using alloy powder containing oxygen-sensitive elements such as Cr or Mn which provide good hardenability at low cost but on the other hand form stable oxides that weaken the sintering contacts if they are not reduced properly. In the present study, using a carbon master alloy as a sintering enhancer in the sintering process of Cr-Mo alloyed powder compacts has been investigated. For clearly depicting the effect of carbon master alloy addition on carbon dissolution and deoxidation, sintering was done in argon as inert atmosphere to avoid other reducing agents such as H₂. The physical and mechanical properties of the sintered specimens were investigated, and thermal chemical analysis by DIL/MS and carbon/oxygen measurements were performed. The experiments showed that adding iron-carbon masteralloys promote the sintering processes such as reduction of oxides and carbon dissolution in the early stages of sintering, resulting in better properties after final sintering.

Abstract: The microstructure and magnetization of SmCo₅ micro-particles may be used as feedstock for 3D printing to make miniature strong magnets. Thus, the magnetic response and microstructures of commercially available SmCo₅ micro-particles were studied under various heat treatments using a high wattage laser. The magnetization of laser heat treated powders at 50-watt showed an increase in magnetization, while the 75-watt melt showed a little to no change. Unfortunately, the coercivity of both laser heat treated samples decreased significantly. Oxidation during the heat treatment is suspected to result in low coercivity. Purging with argon-gas prior to laser heating showed improved coercivity. To further minimize the oxidation problem a set of SmCo₅ powder was reduced prior to laser heat treatment using a constant flow of hydrogen gas while being heated at various temperatures from 100 oC to 400 oC for a period of ~4 hours. The results show that the magnetization generally increases with the temperature, while the coercivity decreases significantly. Another set of SmCo₅ was annealed in a vacuum furnace for one hour at temperatures between 200 oC and 400 oC in order to confirm that no hydride phases were formed during reduction. The magnetization and coercivity showed similar variations with annealing temperature to those for the reduced powders confirming that these variations may be due to change in crystal structure rather than formation of hydrides. X-ray Diffraction (XRD) studies were performed to identify the changes in crystal phases.

Abstract: This study investigated the effect of activating agent on activated carbon preparation and potential chemical oxygen demand (COD) reduction using activated carbons (AC) prepared. Zinc chloride, phosphoric acid and potassium hydroxide were utilized in impregnation of bamboo and rice husk. Result of SEM-EDX, FTIR as well as COD reduction were compared and discussed. The SEM displayed highest porosity in AC using KOH activation. FTIR analysis displayed obvious difference for each activation. AC using KOH activation obtained highest COD reduction.

Abstract: The reduction behaviour of cobalt doped with nickel oxide and undoped nickel oxide (NiO) by hydrogen (H₂) in nitrogen (20%, v/v) and carbon monoxide (CO) in nitrogen (40%, v/v) atmospheres have been investigated by temperature programmed reduction (TPR). The phases formed of partially and completely reduced samples were characterized by X-ray diffraction spectroscopy (XRD). TPR results indicate that the reduction of Co doped and undoped nickel oxide in both reductants proceed in one step reduction (NiO → Ni) without intermediate. TPR results also suggested that by adding Co metal into NiO, the reduction to metallic Ni by both reductant gaseous give different intensity of the peak. The reduction process of Co and undoped NiO become faster when H₂ was used as a reductant. Furthermore, in H₂ atmosphere, Co-NiO give complete reduction to metallic Ni at 700 °C. Meanwhile, XRD analysis indicated that NiO without Co composed better crystallite phases of NiO with higher intensity.

Abstract: The chemical reduction behavior of NiO under various carbon monoxide (CO) concentration as a reduction agent was studied. The NiO and Ni⁰ transformations were identified using TPR and XRD techniques. It was shown that, the completed reduction occurred at temperature 700 °C for 40% CO and 900 °C for 10% and 20% CO. During the chemical reduction process, nickel carbide was formed at temperature 400 °C and another formation of carbon amorphous appeared at 500 °C and proved through diffraction of XRD pattern at 2θ: 22.86 under 20% CO/N₂ and and 2θ: 26.15 under 40% CO/N₂. The interpretation of physisorption data showed that the pore size after reduction with various CO concentration comprised as microporous size in the range of 6-40 nm. Therefore, CO as a mild reduction agent stated that as the concentration of CO high, the rate of reduction affected and formed a very crystalline of Ni⁰ particle.

Abstract: This paper describes the reduction of nickel oxide under different gas mixture. The influence of gas mixture on phase, density, morphology and pore size of reduced nickel oxide were studied. Nickel oxide pellets sintered at 1400 °C were reduced under various hydrogen-nitrogen gas mixtures, namely 40% H₂-60% N₂, 60% H₂-40% N₂, 80% H₂-20% N₂. Phase identification, density measurement and observation of morphology were conducted on samples before and after reduction process. Under all gas mixtures, nickel oxide was completely reduced to nickel. Density of the samples decreased in the range of 21% to 32% depends on H₂ percentage used. Results from the density shows that the higher the H₂ gas concentration, the smaller the density changes. Significant change in porosity of the sample before and after reduction was observed. Size of pore after reduction determined by H₂ concentration used during reduction where the higher the H₂ concentration resulted in large pore size.

Abstract: Azapropellanes have been extensively studied for their special application. Debenzylation of pentabenzylpentaaza[3,3,3]propellane was studied in this paper. The N-benzyl groups were removed by catalytic hydrogen transfer under the mild conditions with simple process. The yield of the debenzylation product was lower. Their structures of all compounds were confirmed by spectra.

Abstract: The content of elements in the main mineral components of the ore, such as serpentine, talc, and chlorites, were determined. It was shown that, during heat treatment of the ore, in addition to the decomposition of hydrates and carbonates, serpentine decomposes and new phases (forsterite and enstatite) form. On the bases of analysis of the properties of the ore, patterns of phase transitions during heated in inert and reducing atmosphere were identified. It was found that the coal-thermal reduction of nickel and iron from oxides begins at temperatures above 800 °C, and from serpentines begins at temperatures above 1250 °C. It was found that, when heating the ore above 1200 °C in a mixture with a reducing agent, the metals reduce and form iron-nickel alloy. During electro-thermal smelting, the mode of which was determined by the melting points of slag (SiO₂ – MgO – FeO – CaO – Al₂O₃ system) and ferronickel, the ratio of Ni / Fe in the metallic phase was determined by the consumption of reducing agent (coal, coke).