Papers by Keyword: Sulfuric Acid

Abstract: Electrochemical research is devoted to the development of a method of processing secondary raw materials containing tungsten in the form of a pseudoalloy of the carbide type WC–Co in sulfate solutions. The target processing products are: powders of tungsten oxides of lower oxidation states, which can be reduced to metallic tungsten with lower costs. Using the methods of linear and cyclic voltammetry, it was established that the selective dissolution of the cobalt component of the pseudoalloy in the studied solutions occurs at potentials more positive than 0.2 V, carbon is removed from the working electrode at a potential > 0.8 V. At the same time, tungsten is oxidized to the higher oxide WO₃. It was determined that in sulfuric acid, with an increase in its concentration from 1 to 5 mol∙dm-3, the current density decreases, which is associated with the formation of a solid surface layer of tungsten oxide on the surface of the anode, which passivates the surface. It was established experimentally that when adding 1 mol∙dm^-3 of H₂SO₄ hexamine (C₆H₁₂N₄) with a concentration of 0.9 mol∙dm^-3 to a solution, it is possible to block the process of formation of a passivating film and obtain powders of tungsten oxides of lower oxidation states.

Abstract: Photoresist after implantation is commonly removed either by wet chemical dissolution with sulfuric acid, or by dry ash stripping followed with a wet cleaning. To prevent any photoresist residues, sulfuric acid is still conserved in post ash cleans as additional safety. However, by ensuring sufficient over ash time, SPM (Sulfuric acid Peroxide hydrogen Mixture) chemical need becomes less essential. This paper reevaluates the benefit of SPM after dry ash stripping regarding the environmental context. The advantages of dry ash stripping with clean, compared to wet stripping are outlined. The study introduces prior analyses on defectivity and material consumption. Finally, device matching and yield stability, defined as the main success criteria, are described.

Abstract: This research was conducted to determine the corrosion rate by varying the concentration of the solution against hydrochloric acid and sulfuric acid. The method used is open circuit potential (OCP) and Tafel plot. Based on the research conducted, Hastelloy C-276 was more prone to get oxidized in sulfuric acid rather than hydrochloric acid. It can be seen from the OCP value of sulfuric acid was much more negative than that of hydrochloric acid as of-1.5 V for 0.5 M sulfuric acid and-0.2 V for hydrochloric acid. The corrosion rate of Hastelloy C-276 in sulfuric acid was also higher compared to same alloy in hydrochloric acid. At the most concentrated solution, 0.5 M, the corrosion rate of sulfuric acid reached 0.39 mmpy and as for corrosion cate in hydrochloric acid, only at 0.16 mmpy. It is thought that there was a difference of passive film composition for both solutions. Keywords: Hastelloy C-276, Corrosion, Hydrochloric acid, Sulfuric acid.

Abstract: This paper investigates the valorization of slag in cement production in order to obtain a sustainable mortar and participate in protecting the environment. The study evaluated the setting time, hydration heat, mechanical strengths, drying shrinkage, sulfuric acid and sulfate attack of mortars. These mortars are based on Portland cement (PC), slag cements containing 10%, 30% and 50% slag and alkali-activated slag (AAS) using 6% and 9% of sodium hydroxide (NaOH). The results show that the increase in slag replacement rate increases the setting time accompanied by a drop in initial mechanical strength such that the compressive strength decreased by 30% at two days for a 50% slag substitution; also, it considerably reduces the shrinkage and hydration heat. The resistance to sulfate and sulfuric acid attack increases with the slag replacement rate. NaOH-activated slag mortar is the most resistant binder to sulfate attack and sulfuric acid, but it develops a lower mechanical strength and a more significant shrinkage than PC mortar. X-ray diffraction (XRD) analysis carried out on binder paste shows the formation of the same main hydration products in PC and slag cement with a small amount of portlandite in the last binder. Calcium silicate hydrate (CSH) and Hydrotalcite are the main hydration products of AAS.

Abstract: The aim of this work is to study the effect of nanoBentonite (NB) on the durability of concrete under normal and aggressive conditions. Different mixes were made with various amounts of NB at rates 10,15,20,25 and 30% as a partial mass replacement for cement. First group of samples were subjected to normal curing and tested after 7, 28, 90 and 180 days, while the second group of samples were subjected sulfuric acid of concentration 0.2 N and tested after the same ages. The hydration process and durability of samples was monitored using scanning microscope (SEM). The results of this study indicated that using NB as 15% partial replacement of cement improves durability and microstructure of concrete mixture against both normal and aggressive curing conditions.

Abstract: The conversion of silica gels into sulfated silicas (SO₄/SiO₂) have been carried out. The sulfation process of the catalysts was carried out by impregnation of sulfuric acids at concentrations of 1; 2; and 3 M and calcination temperatures of 500, 600, and 700 °C. Sulfation with 2 M H₂SO₄ and calcination temperature of 600 °C (SS2-600) produced a catalyst with the highest acidity value (5.13 mmol NH₃ g^-1). XRD analysis showed the formation of amorphous SiO₂ phase, whereas SSA analysis showed that the SS2-600 catalyst had a mesoporous structure with a surface area of 147.728 m²/g, a total pore volume of 0.25 mL/g and a pore diameter of 6.439 nm. Characterization results show that sulfated silica gels have potency as solid acid catalysts.

Abstract: The spread of disease by bacteria and viruses is very susceptible to outbreaks in public facilities through direct and indirect contact. Indirect contact occurs through intermediate such as housing equipment made of aluminum. One thing that people touch the most is door handles and frames. Aluminum frames are generally anodized to give a color effect because painted directly is difficult. Anodized products generally have a pore structure so that they can easily become an ideal place to grow and colonize bacteria and viruses. To overcome this, the coating process is carried out by electroplating. In this study, aluminum was treated with anodization and non-anodization. The concentration of sulfuric acid solution used was 0.5 M; 1M and 2M. The current used is 0.6A; 0.9A and 1.2M. Increasing the sulfuric acid concentration will increase the efficiency of the cathodic current and increase the mass of the deposit per unit area. Observation of the microstructure with an optical microscope shows the structure formed is dendritic in which the nucleus is continuous. The smooth and flat surface makes aluminum safe to be used and does not become a medium for bacteria or viruses to stick at aluminum surfaces.

Abstract: The production of aluminum by electrolysis of cryolite-alumina melts is associated with generation of process waste including gas cleaning sludge, electric filter dust, coal flotation tailings, and spent pot lining (SPL). Most of this waste is then stored in sludge fields, deteriorating the environment near aluminum works. 30 to 50 kg of spent pot lining is produced per ton of Al. The authors’ research was dedicated to finding the best reagent for solvent extraction of valuable components (fluorine in particular) in the process of SPL hydrometallurgy. To that end, the research team sampled carbon parts of lining at the RUSAL Bratsk facility in Shelekhov, Irkutsk Oblast. The following reagents were tested: 2 wt.% solutions of sulfuric acid and sodium hydroxide. Leaching lasted 60 minutes in each experiment. 2% H₂SO₄ solution was found to release fluorine at a higher rate. However, the resulting liquors contained sulfates, which might negatively affect the service life of equipment; for this reason, 2% NaOH solution was chosen for further leaching of fluorine from spent carbon parts of lining.

Abstract: Sulphated zirconia (SZ) is one of the most important solid acid catalysts was synthesize at different operating conditions,different calcination temperature and sulfonating time has been used. The prepared catalyst was distinguished by X-ray Diffraction (XRD), particle size and morphology of catalyst were checked by atomic force microscopy (AFM) and scanning electron microscopy (SEM) respectively, in addition to analysis by (DTA) Differential thermally and Energy Dispersive X-Ray (EDX). Finally, the N2 adsorption-desorption was used to measure the surface area (BET) and pore volume. High degree of tetragonal crystallinity was obtained 90 %, and surface area of 169 m²/g and pore volume of 0.39 cm³g^-1 at 600°C calcination temperature for 3 hrs and 6 hrs time of impregnation in H₂SO₄. nanoparticle size of sulphated zirconia was produced with an average of 73.48 nm.

Abstract: A white light, i.e., Fabry-Perot, interferometry was unprecedently applied to determine the rate change of the current density (J) of aluminum samples during the anodization processes of the samples in aqueous solutions. The current density(J) values were obtained by Fabry-Perot interferometry rather than the direct current (DC) or alternating current (AC), methods. Therefore, the abrupt rate change of the J was called electrochemical-emission spectroscopy. The anodization of the aluminum samples was conducted by an external DC source in 0.0,2,4,6,8,10% sulfuric acid (H₂SO₄) solutions at room temperature. In the meantime, the Fabry-Perot interferometry was used to determine the difference between the J of two subsequent values, dJ, as a function of the elapsed time of the DC experiment for the aluminum samples in 0.0,2,4,6,8,10% H₂SO₄ solutions. The Fabry-Perot interferometry was based on a fiber-optic sensor in order to make real time-white light interferometry possible at the aluminum surfaces in the sulfuric acid solutions. As a result, a new spectrometer was developed based on the combination of the Fabry-Perot, i.e., white light, interferometry and DC method for studying in situ the electrochemical behavior of metals in aqueous solutions.