Rotating Disk Method Research Articles

Reaction kinetics of molybdenum dissolution by hydrogen peroxide in acidic and alkaline solutions using tartaric acid and sodium hydroxide: A semi‐empirical model with rotating disc method

AbstractMolybdenum is an amphoteric metal that dissolves in both acidic and alkaline solutions. This fundamental study explores a sustainable process for the dissolution of molybdenum, focusing on the reaction kinetics in H2O2, H2O2‐NaOH, and H2O2‐C4H6O6 solutions. A rotating disc method was applied with the Levich's equation. Semi‐empirical models with activation energy were developed for the H2O2‐NaOH and H2O2‐C4H6O6 solutions. The study examined the effects of rotating speed, disc surface area, temperature, H2O2, NaOH, and C4H6O6 concentrations, along with rotating speed, disc surface area, and temperature. Hydrogen peroxide significantly impacted molybdenum dissolution rates across all three solutions. The reaction order of hydrogen peroxide concentration in the H2O2 solution was greater than that of the H2O2‐NaOH and H2O2‐C4H6O6 solutions. The complex of molybdenum peroxo was formed in H2O2 and H2O2‐NaOH solutions but decomposed at a temperature ≥50°C. The activation energies were determined to be 49.90, 43.60, and 41.10 kJ/mol for the H2O2, H2O2‐NaOH, and H2O2‐C4H6O6 solutions.

The influence of sodium fluoride on the dissolution kinetics of metallic titanium in citric acid solution using the rotating disc method

This study reports the effect of sodium fluoride on the dissolution kinetics of pure metallic titanium in a citric acid solution. The effects of sodium fluoride concentration, citric acid concentration, temperature, stirring speed, and disc surface area were examined. The dissolution rate of titanium increases strongly with increasing citric acid and sodium fluoride concentrations. Fluoride ions react with hydrogen ions to form hydrofluoric acid, which removes the passive layer of titanium dioxide. An increase in the concentration of NaF and acid causes the formation of a brown layer on the surface of titanium. X-ray diffraction and SEM-EDX analyses showed that the layer composition is mostly of titanium fluoride (TiF3) and titanium fluoride oxide (TiOF2). A mixed kinetic model with an activation energy of 26.4 kJ/mol can be used to explain the reaction kinetics.

Rotating disc method to study the dissolution kinetics of copper metal in citric acid and hydrogen peroxide

This study reports the kinetics of copper metal dissolution in citric acid-hydrogen peroxide solution using the rotating disc method. The effect of the concentration of citric acid as well as hydrogen peroxide, stirring speed, disc surface area, and temperature was investigated. The concentration of hydrogen peroxide (0.25–1.5 mol/L) has a strong effect on the dissolution rate (mg/min) of copper with a reaction order of 0.92, compared to a reaction order of 0.42 with respect to the concentration of citric acid (0.125–1.5 mol/L). The reaction rate is directly proportional to the disc area (A) and square root of the disc rotation speed (ω1/2), as expected from the Levich equation. The activation energy of 33 kJ/mol, in the temperature range 30-60 °C is also comparable with the values reported in previous studies.

A study of cavitation erosion resistance of an ion nitrided titanium alloy by means of the vibration and rotating disk methods

In this work, a comparative analysis of the cavitation erosion resistance of the Ti–6.7Al–2.5Mo–1.8Cr–0.5Fe–0.25Si alloy (known as brand VT3-1) before and after low-temperature ion nitriding is carried out. Two test methods were applied, using vibrative (ASTM G-32) and rotating disk rigs, respectively. The kinetic dependences of the erosive destruction of samples of titanium alloy VT3-1 in the initial state, after ion nitriding and stainless steel AISI 321 were obtained. A study of the microstructure, hardness and surface morphology was carried out. The samples were examined using optical and scanning electron microscopy. The relationship between mass loss and cavitation erosion duration was experimentally determined and analyzed. The erosion rate on a rotating disk stand is much higher than during vibration tests. A large cavitation load gradient provides additional opportunities for analyzing the durability of materials and coatings using this method.

Study of the basic laws of dissolution of gold and copper in solutions with an ultra-low concentration of sodium cyanide

The work sets out to study the basic physicochemical dissolution patterns of gold, copper, and natural copper-containing minerals (chalcopyrite, bornite and azurite) in solutions with an ultra-low concentration of sodium cyanide (from 0.102∙10-3 to 4.08∙10-3 mol/L). The influence of various factors on the rate of dissolution of Au and Cu in solutions with ultra-low NaCN concentrations was studied by the rotating disk method; for natural copper minerals, the powder diffraction method was used. The concentration of gold and copper in solutions was determined by atomic absorption analysis. The chemical composition of the studied copper minerals was determined using the X-ray phase method, while the specific surface of the minerals was detected using a laser granulometer. The process of gold dissolution is shown to proceed in both diffusion and kinetic regions. In the diffusion region, the rate constant was 0.334∙10-6 L∙cm-2∙s-1/2∙rad-1/2; in the kinetic region – 0.919∙10-6 L∙cm-2∙s-1/2. The calculated value of the apparent activation energy for the diffusion region was 22.5 kJ/mol; for the kinetic region – 40.1 kJ/mol. The addition of glycine to a solution with an ultra-low concentration of sodium cyanide is shown to increase the specific dissolution rate of gold by 1.2 times: from 0.692∙10-9 to 0.82∙10-9 mol/cm2∙s. The process of copper dissolution is shown to take place in the diffusion r egion. The rate constant was 0.496∙ 10-6 L∙cm-2∙s-1/2∙rad-1/2 at an activation energy of 17.0 kJ/mol. With a fractional supply of sodium cyanide, the dissolution rate of copper minerals is reduced by 10–30% compared to a single load. The calculated apparent activation energy values for chalcopyrite, bornite, and azurite were 22.03, 24.2, and 24.1 kJ/mol, respectively. Thus, the use of ultra-low concentrations of NaCN in the process of cyanidation of gold and copper has a positive effect, which can be used i n the processing of gold-copper raw materials to significantly reduce the consumption of sodium cyanide.

Corrosion Rate of Steel in Liquid Zn, Zn-Bi and Zn-Sn Baths

In the hot dip galvanizing process, steel products are immersed in a liquid zinc bath. The contact of steel with liquid zinc causes the corrosion of the steel as a result of Fe dissolution processes in the liquid. If the dissolution process is carried out in a controlled manner, it results in the formation of a coating. Uncontrolled dissolution leads to the degradation of the steel surface. This article presents the results of research into the influence of Bi and Sn additions to zinc baths on the corrosion of steel in liquid zinc. Corrosion tests were carried out under conditions of kinetic dissolution using the rotating disc method. The kinetic dissolution constants of steel with different Si contents in Zn, Zn-0.5Bi and Zn-2Sn baths were determined. It was found that the addition of Bi and Sn lowers the value of the dissolution constant and may act as an inhibitor of Fe dissolution in liquid zinc. Based on the measurements and the determined value of the dissolution constant, the activation energy of kinetic dissolution was determined. It was found that in the temperature range of 440–480 °C, the addition of Bi and Sn increases the value of dissolution activation energy, which reduces the intensity of Fe transfer to the zinc bath.

Effect of carbon content on resistance to cavitation erosion of Cr-C coatings deposited by Arc PVD method

The aim of the study is a comparative analysis of effect of the carbon content in the range from 2 to 25 at.% on the resistance to cavitation erosion of Cr-C coated samples by means of the rotating disk method. The effect of carbon concentration in the range from 2 to 25 at % on the structure, properties and cavitation resistance of Cr-C vacuum-arc coatings deposited in argon with toluene at a pressure of 0.08 to 0.23 Pa on 12Cr18Ni10Ti stainless steel samples has been studied. It has been established that the application of coatings leads to a decrease in the rate of cavitation erosion of steel from 4 to 6 times. Chromium coatings with a two-phase structure containing carbide Cp7C3 show maximum durability.

Kinetic study on arsenopyrite dissolution in nitric acid media by the rotating disk method

The kinetics of arsenopyrite compact samples dissolution in nitric acid media was investigated using the full factorial experiment model (FFEM). The effects of nitric acid concentration (2–5 M), temperature (303–348 K), disk rotation frequency (3.33–10 rps) on the arsenopyrite dissolution rate were studied. Nitric acid concentration and temperature have a significant effect, and disk rotation frequency does not. With an increase in nitric acid concentration from 4 M to 5 M and temperature from 318 K to 333 K, the dissolution rates of iron and arsenic increase by 30.1–30.4 times, from 0.26–0.27 × 10–6 mol dm−2 s−1 to 7.83–8.21 × 10–6 mol dm−2 s−1. Increasing temperature to 348 K does not lead to a significant increase in the dissolution rate. The data obtained were processed using the FFEM to obtain kinetic equations (R2 = 0.95): WFe=0.04CHNO31.8e-4419Tω0.1, WAs=0.04CHNO31.8e-4420Tω0.1. Using SEM–EDS and XPS analyses, the mechanism of arsenopyrite passivation was determined. Under mild conditions (nitric acid concentration of 3 M and temperature of 303 K), local conglomerates containing iron polysulphides (Fe2Sx) are formed on the arsenopyrite surface. They do not create diffusion difficulties when dissolving arsenopyrite. Under harsh conditions (nitric acid concentration of 5 M and temperature of 333 K), polysulphides begin to aggregate. It leads to the formation of the passivating film containing elemental sulphur. The film is thin (20–30 μm) and porous. While the arsenopyrite dissolution rate is high. Further increase of parameters leads to thickening and compaction of the passivating film and decrease in the arsenopyrite dissolution rate.

Study of the Kinetics of Arsenopyrite Dissolution in Nitric Acid Media by the Rotating Disk Method

Study of the Kinetics of Arsenopyrite Dissolution in Nitric Acid Media by the Rotating Disk Method

The dissolution kinetics of natural gypsum: a case study of Eocene facies in the north-eastern suburbs of Paris

The dissolution kinetics of different varieties of natural gypsum samples with different porosity and content of insoluble impurities are experimentally investigated under unsaturated conditions. The main goal of this work is to verify whether and how the petrophysical and petrographic nature of gypsum influence its dissolution rate. Gypsum samples were taken from Priabonian (Ludian) and Lutetian formations located in the north-eastern suburbs of Paris, where the development of sinkholes due to gypsum dissolution is a common phenomenon. Experiments using the rotating disk technique allow us to determine the kinetic rate model parameters of each sample in pure water following the empirical rate expression derived from mixed kinetic theory. The kinetic order n shows a dispersion around a mean value \(n=1.2\) and k, the pure dissolution rate coefficient varies according to the facies and the experimental conditions (k \(\approx \,1\times 10^{-6}\) to 8\(\times 10^{-6}\) mmol/\(\hbox {cm}^2/\hbox {s}\)). These results are adjusted according to the specific roughness and texture of each sample, for the results to be more representative of in situ conditions. Batch experiments are also performed to evaluate the extremely low dissolution rates when the solution is close to equilibrium. The results reveal a double kinetics: far from equilibrium, the dissolution rates show that the linear behavior and the kinetic parameters are relatively close with the values found using the rotating disk method. For concentrations greater than 0.94 ± 0.02 of the equilibrium concentration \(C_\mathrm{{ref}}\), the dissolution rates show a linear behavior but with greater slope depending on the texture of the mineral. No changes of the dissolution rates were observed on pure gypsum crystals when non soluble solid impurities are added. However, a small degree of uncertainty around the value of \(C_\mathrm{{ref}}\) show a significant effect on the parameters of the second kinetics.

Streaming Electrification of Nycodiel 1255 Synthetic Ester and Trafo EN Mineral Oil Mixtures by Using Rotating Disc Method

Power transformers are the main element of an electric power system. The service life of these devices depends to a large extent on the technical condition of their insulation system. Replacing mineral oils with natural or synthetic ester (retrofilling process) may increase the efficiency and operational safety of transformers, and also limit their adverse environmental impact. It is technically unfeasible to completely remove mineral oil from a transformer. Its small residues form a mixture with fluid ester, with different physicochemical and electric properties. Streaming electrification is one of the phenomena which, under unfavorable conditions, may damage the insulation system of a forced oil cooled transformer. It is necessary to run prophylactic tests for the ECT (electrostatic charging tendency) of insulating liquid mixtures from the point of view of transformer retrofilling, which is being used more often than before. The article presents the results of studies on selected physicochemical, and electrical properties, and the ECT of mixtures of fresh and aged Trafo EN mineral oil with Nycodiel 1255 synthetic ester. In this regard, the density, the kinematic viscosity, the conductivity, and the relative dielectric constant were measured. The molecular diffusion coefficient was determined using Adamczewski’s empirical dependency. The streaming electrification was tested in a rotating disc system. The impact of the rotation time, the diameter, and the disc’s rotation speed on the amount of the electrification current generated were analyzed. In addition, the co-relation between the electrification current and the composition of the mixture was determined using fresh and aged mineral oil. On the basis of the electrification model, the volume density of the qw charge was calculated, which is a parameter defining the ECT of insulating liquids. Based on the results, it was concluded that the synthetic ester is characterized by a higher susceptibility to electrification than the mineral oil. However, combining synthetic ester with a small amount (up to 20%) of fresh or aged mineral oil significantly reduces its ECT, which is beneficial from the point of view of retrofilling power transformers.

Дослідження кінетики розчинення мінералів методом обертового диску

Дослідження кінетики розчинення мінералів методом обертового диску

Kinetics Study of Surface Reaction Between Acid and Sandstone Based on the Rotation Disk Instrument

The chemical reaction between acid and rock mineral during the acidizing process is the key point for the acidizing technique. In this study a rotating disk method is used to simulate strata conditions, such as high temperature, high pressure, and acid shear flow reaction. The work investigates the kinetics of the rock acidizing reaction and analyzes the factors effecting the reaction rate, including mineral composition, temperature, pressure, acid concentration, shear velocity, and common-ion effect. The kinetic parameters, such as velocity constant, reaction order, activation energy, and frequency factor, were successfully extracted by curve fitting and the linear regression method. In was shown that hydrochloric acid does not participate directly in the reaction between mud acid (which is a mixture of hydrochloric and hydrofluoric acids) and sandstone mineral but catalyzes the reaction between hydrofluoric acid and sandstone. In this work, the acid rock reaction rate equation has been established, and the impact of the hydrochloric acid catalytic effect has been considered.

DISSOLUTION KINETICS OF GOLD IN SYSTEM THIOUREA–THIOSULFATE WITH OXIDANT OF Fe(III)EDTA

Cyanidation remains the predominant technology for the dissolution of gold from mineral raw materials. Environmental and technological disadvantages in the use of cyanides are the cause of the development of alternative systems, which include reagent-oxidant and reagent-complexant. A special place is occupied by the solvents, in which the formation of heteroligand complexes of gold is possible. Thus due to the formation of more durable compounds the rate of dissolution of the metal increases. In this work, as the ligands the thiourea and the ions of thiosulfate in the form of sodium salt were used, as the oxidant – complex of the iron (III) and EDTA. The influence of the mixed solvent composition on the kinetic characteristics and the reaction mechanism was studied by the rotating disc method. To confirm the role of different ligand complexes, the dependence of the dissolution rate of gold by the mixed system – thiosulphate and thiourea in the isomolar series, was determined. With a constant total ligands concentration, the molar ratio of reagents was changing. On the basis of the data obtained, a mathematical model of the process of oxidative dissolution of gold is proposed. A characteristic feature of the calculated results is a substantial increase in the reaction constants for the formation of heteroligand complexes, which confirms their role in the process of gold oxidation. The influence of pH and concentration of oxidant and ligand-forming substances on the kinetics of gold dissolution is established. To elucidate the mechanism of the limiting stage of the heterophase process, the experimental activation energy is calculated and the effect of the disk rotation frequency on the dissolution rate is studied. The experimental activation energy is 28.1 kJ/mol. The order by the disk rotation frequency is 0.35. Evaluation of the contribution of the diffusion and kinetic components of rate is estimated on the basis of the modified Levich equation for the mixed regime. Diffusion component of rate is almost an order of magnitude smaller than the kinetic one. Calculation of the diffusion flux of the supplied reagents showed that the only process that inhibits mass transfer is the diffusion of the reaction products from the surface of the rotating disc. The formation of more durable heteroligand complexes and a greater equilibrium constant of the oxidation reaction lead to an increase in the concentration of products at the surface and, consequently, to an increase in the rate of diffusion of the metal into the solution. An important factor affecting the oxidation of gold in the system studied is the formation of intermediate solid reaction products on the metal surface. To identify solid products, IR spectra of reflection of polished gold surface after etching in the system studied were obtained. A strong absorption band in the 808-762 cm-1 region is observed on the spectra. Absorption in this region is associated with valence symmetrical vibrations of the bond of the –C = S group adsorbed or chemically bound to the surface of the molecules of thiourea and its oxidation products. Depending on the composition of the solution and the temperature, the maximum of the peak shifts, and its intensity also changes. This can be explained by a change in the composition of the adsorbed compounds. The efficiency of regeneration of the oxidant Fe(III)EDTA by oxygen in thiourea-thiosulfate solution has been showed.

Study of the kinetics of dissolution of copper ferritic by the rotating disk method

Study of the kinetics of dissolution of copper ferritic by the rotating disk method

INFLUENCE OF FORMATION OF THE COMPLEXES WITH DIFFERENT KIND OF LIGANDS ON KINETICS OF OXIDATIVE DISSOLUTION OF METALS

Rotating disk method has been used to study the dissolution of gold in the presence of an oxidizer and a mixture of dissimilar ligandforming reagents. Kinetic regularities of gold dissolution were investigated in aqueous systems thiourea-thiocyanate with Fe (III) and Cu (II) ions as the oxidizer; thiosulfate-thiocyanatewithFe(III)EDTA oxidizing complex and thiosulfate-thiocyanate with ammonia complex [Cu(NH3)4]2+ asoxidizing agent. Peculiarities of these mixed systems is a possibility to form the monoligandas as well as geteroligand complexes of gold. The influence of gold complexes formation with different sorts of ligands on the metal dissolution rate have been considered. The dependence of the dissolution rate on the ratio of ligands concentrations and on the oxidizing agent nature was investigated. Interrelation was established: the use of dissimilar ligandforming reagents - the higher thermodynamic stability of the geteroligand complexes of gold (relative to the homoligand ones) - synergistic increase of the gold dissolution rate. It was found that the heterophase reaction makromechanism for the thiourea-thiocyanate-Fe(III) system is determined by the proximity of the rates of chemical and diffusion stages (experimental activation energy - 21.6 kJ/mol; the reaction order in respect to the disk rotation frequency – 0.23). Diffusive limitation is due to the slow withdrawal of the reaction products -Au (I) compounds - from the solid phase surface. The formation of stronger heteroligand complexes and the corresponding increase in the reaction products concentration at the surface increases a rate of the metal diffusion into the solution. For the thiourea-thiosulfate-Fe(III)EDTA system a film formation of the reaction solid products on the gold surface was observed. To identify it the infrared reflection spectra of the polished gold surface after the etching were obtained. There is a strong absorption band on the spectra at 804 cm-1. Absorption in this area has been associated with the stretching vibrations of C=S bond of the thiourea molecules joined to the surface and the products of their oxidation.

Physicochemical characterization and dissolution studies of acyclovir solid dispersions with Pluronic F127 prepared by the kneading method.

The dissolution rate of anhydrous acyclovir was improved by the preparation of physical mixtures and solid dispersions with the non-ionic polymer Pluronic F127 using the kneading method at different drug-to-polymer ratios. The obtained physical mixtures and solid dispersions were examined in terms of drug content and possible physical and chemical interactions between the drug and polymer using FTIR spectral studies, differential scanning calorimetry and powder X-ray diffraction analysis. The dissolution rate of acyclovir was determined using the rotating disk method. It was found that the minimal content of the polymer within the mixtures needed to increase the dissolution rate of the drug was 50 %.

Miniaturized rotating disc rheometer test for rapid screening of drag reducing marine coatings

Frictional drag from the submerged hull surface of a ship is a major component of the resistance experienced when moving through water. Techniques for measuring frictional drag on test surfaces include towing tanks, flow tunnels and rotating discs. These large-scale methods present practical difficulties that hinder their widespread adoption and they are not conducive to rapid throughput. In this study a miniaturized benchtop rotating disc method is described that uses test discs 25 mm in diameter. A highly sensitive analytical rheometer is used to measure the torque acting on the discs rotating in water. Frictional resistance changes are estimated by comparing momentum coefficients. Model rough surfaces were prepared by attaching different grades of sandpaper to the disc surface. Discs with experimental antifouling coatings applied were exposed in the marine environment for the accumulation of microbial fouling, and the rotor was capable of detecting the increased drag due to biofilm formation. The drag due to biofilm was related to an equivalent sand roughness.

Reproducibility of Obtaining thin Films of Polyaniline by Direct Doping

This paper presents the process of obtaining thin films of polymer polyaniline that has been doped directly in the production process. Samples of thin films were obtained using a rotating disk method at different speeds. Polyaniline synthesis (PANI) was performed at 0°C and room temperature of 20°C. Doping was made with hydrochloric acid (PANI-HCl). We have shown what were the important factors that had influence on obtaining reproducible patterns of about the same characteristics. As indicators of these properties we measured electrical resistance, on the basis of which was calculated specific electrical conductivity of the obtained samples of thin films of polyaniline from different series of production.

Magnetic colloid by PLA: Optical, magnetic and thermal transport properties

Ferrofluids of cobalt and cobalt oxide nanoparticles (NPs) have been successfully synthesized using liquid phase-pulse laser ablation (LP-PLA) in ethanol and double distilled water, respectively. The mechanism of laser ablation in liquid media and formation process for Co target in double distilled water (DDW) and ethanol are speculated based on the reactions between laser generated highly nascent cobalt species and vaporized solvent media in a confined high temperature and pressure at the plume-surrounding liquid interface region. Optical absorption, emission, vibrational and rotational properties have been investigated using UV–vis absorption, photoluminescence (PL) and Fourier transform-infra red (FT-IR) spectroscopy, respectively. In this study optical band gap of cobalt oxide ferrofluids has been engineered using different pulse energy of Nd:YAG laser in the range of (2.80–3.60eV). Vibrating sample magnetometer (VSM) is employed to determine the magnetic properties of ferrofluids of cobalt and cobalt oxide NPs while their thermal conductivities are examined using rotating disc method. Ferrofluids have gained enormous curiosity due to many technological applications, i.e. drug delivery, coolant and heating purposes.