Analysis of the Corrosion Behavior of the TiNi Alloy in the Coarse-Grained State

In this work was investigate the corrosion behavior of the TiNi alloy in a coarse-grained state in inorganic field with different concentration and holding time. An increase in the concentration of the solution leads to a significant acceleration of corrosion processes in the Ti49.1Ni50.9 alloy with a high Ni content, including until the samples are completely dissolved. It was revealed that solutions of 1 M sulfuric and hydrochloric acids after a month's exposure did not change in color and no precipitations were found, while solutions of 5 M hydrochloric and sulfuric acids acquired a violet and then green color, which is due to the predominant release of titanium ions (+4) and nickel (+2).

Dispersion of watermelon rinds as secondary raw materials in technologies of pectin-containing extracts and film structures

The development of protective coatings based on pectin substances that serve as natural structure-forming agents developed from a secondary resource base is focused on removing a complex problem in the production of finished products by deep processing of basic raw materials and developing an original film material. At the same time, the technical result of obtaining pectin-containing film structures is their ability to protect food products from microbiological spoilage, natural losses during storage and the preservation of quality and safety indicators. An important preparatory procedure that determines the efficiency and intensity of extraction processes can be attributed to the operation of dispersing the feedstock, since it directly affects the size of the contact surface area of the phases involved in mass transfer. However, it is clear that the greater the degree of grinding, the higher the efficiency of the process, but an excessive increase can lead to additional unjustified energy costs and, as a result, to an increase in the cost of the finished products sold. In this regard, the purpose of the research is to analyze existing technologies for producing pectin-containing extracts, in which watermelon rinds can be used as secondary resources and to intensify the extraction process by conducting a rational preparatory procedure for grinding the raw materials. The object of the research are watermelon rinds as non-recyclable waste from processing watermelon raw materials. According to the obtained graphs, and taking into account the high rates of gelatinization of the obtained pectin extracts, it is possible to recommend a complex treatment of watermelon rinds, including, in addition to the operations of preliminary preparation of raw materials, ultrasonic exposure and acid hydrolysis, and it is desirable to use food acids, for example, acetic or citric, instead of aggressive sulfuric and hydrochloric acids. As a result of the study of the dispersed composition, it has been concluded that the average equivalent particle size of the dispersed raw materials does not exceed the recommended limits, that is, the result obtained can be considered acceptable.

Extraction of Alumina from Nawan Kaolin by Acid Leaching

This paper investigated the production of alumina from Nawan kaolin by acid leaching with sulfuric and hydrochloric acids. Kaolin was calcined at 850°C and was leached with 6 M acid at 90°C, 5M NaOH followed by HCl solutions were added to the leaching liquor, and the precipitated aluminum hydroxide was converted to alumina by calcination at 900°C. Materials were characterized by FTIR, XRD, and SEM techniques. The alumina extraction percent was determined at different leaching times (30-180 min) and solid/liquid ratios (0.05-0.15 g/ml). The purity of kaolin is about 95%. The percent of extraction of alumina rapidly increases with the solid/liquid ratio up to 0.1 g/ml then decreases thereafter. The percent of extraction of alumina is higher for HCl than H2SO4. The size of the chloride and sulfate ions is the key factor that controls the percent of extraction of alumina from calcined kaolin under the studied conditions.

Vanadium Electrolyte for All-Vanadium Redox-Flow Batteries: The Effect of the Counter Ion

In this study, 1.6 M vanadium electrolytes in the oxidation forms V(III) and V(V) were prepared from V(IV) in sulfuric (4.7 M total sulphate), V(IV) in hydrochloric (6.1 M total chloride) acids, as well as from 1:1 mol mixture of V(III) and V(IV) (denoted as V3.5+) in hydrochloric (7.6 M total chloride) acid. These electrolyte solutions were investigated in terms of performance in vanadium redox flow battery (VRFB). The half-wave potentials of the V(III)/V(II) and V(V)/V(IV) couples, determined by cyclic voltammetry, and the electronic spectra of V(III) and V(IV) electrolyte samples, are discussed to reveal the effect of electrolyte matrix on charge-discharge behavior of a 40 cm2 cell operated with 1.6 M V3.5+ electrolytes in sulfuric and hydrochloric acids. Provided that the total vanadium concentration and the conductivity of electrolytes are comparable for both acids, respective energy efficiencies of 77% and 72–75% were attained at a current density of 50 mA∙cm−2. All electrolytes in the oxidation state V(V) were examined for chemical stability at room temperature and +45 °C by titrimetric determination of the molar ratio V(V):V(IV) and total vanadium concentration.

Hydrogen generation by both acidic and catalytic hydrolysis of sodium borohydride

Sodium borohydride tablets have been employed as hydrogen-storage materials. Hydrogen release was performed by acidic hydrolysis where solutions of sulfuric and hydrochloric acids were added to the tablets, and by catalytic hydrolysis where water was added tablets of solid-state NaBH4/Co composite. In acidic solutions hydrogen evolution occurred instantaneously, and at high concentrations of acids the releasing hydrogen contained an admixture of diborane. Hydrogen evolution from the solidstate NaBH4/Co composite proceeded at a uniform rate of 13.8±0.1 cm3·min-1, water vapor being the only impurity in the evolving gas.

Chemical Attacks in Geopolymeric Materials by Sulfuric Acid and Hydrochloric Acid

The geopolymeric materials present a viable alternative as concretes, the durability of these materials is associated to expected environmental conditions and one of the problems is their corrosion. The objective of this study was to assess the durability of geopolymeric materials through the chemical attack by sulfuric and hydrochloric acids with 5% concentration. After synthesis of the geopolymeric materials, followed by curing at room temperature for 28 days and then the geopolymeric materials were subjected to cycles of chemical attacks, which consisted of periods of seven days of immersion and seven days of drying at room temperature, four cycles were provided. The geopolymeric materials were characterized and it was found that they exhibit adequate resistance to chemical attack, the adequate strength consisted of determining the mass loss in each cycle attack.

KINETIC STUDY ON ADSORPTION OF CHROMIUM(lIl) TO DIATOMACEOUS EARTH PRE-TREATED WITH SULFURIC AND HYDROCHLORIC ACIDS

In this research, the effect of Sangiran diatomaceous earth pre-treatment with sulfuric acid (H2SO4) and hydrochloric acid (HCl) on the kinetics of adsorption for Cr(III) in aqueous solution has been studied. The research has been carried out by mixing an amount of diatomeaeous earth with HCl or H2SO4 in various concentrations for two hours at temperature of 150 - 200°C. The mixture was washed with water until neutral, and the residue was dried at 70°C for four hours. The result then was used as adsorbent. Adsorption was carried out by mixing an amount of adsorbent with Cr(III) solution in various contact times. Ion adsorbed was determined by analyzing filtrate using atomic absorption spectrophotometry. The effect of pre-treatment on adsorption kinetics was evaluated based on kinetic parameters, i.e. constant of adsorption rate by using Langmuir-Hinshelwood kinetics and using two-process kinetics (fast and slow processes). Adsorption kinetics calculated using LH equation gave negative value for adsorption rate constant of zero order (k0). On the other words, the LH kinetics might not be applied for adsorption of Cr(III) to diatomaceous earth adsorbent. Results of kinetics study approached using two processes (fast and slow) showed that adsorption of Cr(III) occurred in two processes with rate constant of fast adsorption, kc, 0.041/min, rate constant of slow adsorption, kl, 0.0089/min, and of slow desorption, k'l, 0.089/menit. Pre-treatment with HCl up to 10 M decreased either kc, kl or k'l, while pre-treatment with H2SO4 1M increased kc to 0.061/min, decreased kl to 0.00424 and k'l to 0.0139/min. On pre-treatment with H2SO4 higher than 6 M significantly decreased three constants above. Based on the Gibbs energy change (4.31 - 6.79 kJ/mole) showed that adsorption involved physical interaction. Keywords: adsorption, chromium, diatomaceous earth, kinetics, Langmuir-Hinshelwood