Effect of the O2 dissociation degree on the rate of anodic evaporation of Al in a low-pressure arc

The results of probe diagnostics and optical emission spectroscopy of Ar-O2 plasma of a low-pressure arc generated under anodic evaporation of Al and an increased (0.32 – 0.48) degree of O2 dissociation are presented. It is shown that an increase in the degree of O2 dissociation at a constant gas flow into the discharge gap leads to a significant (more than 1.5 times) decrease in the density of the evaporated atoms flux and a corresponding decrease in the coating deposition rate. The observed effect is due to the accelerated growth of the oxide film on the melt surface, which leads to the limitation of the flow of evaporated Al atoms by the rate of diffusion through the alumina.

Deposition of Al2O3 coatings in Ar-O2 low-pressure discharge plasma under a high dissociation degree of O2

The deposition of Al2O3 coating with a corundum structure was done by anodic evaporation in a low-pressure arc with a self-heated hollow cathode. The conditions were created for increasing the energy of plasma electrons and a corresponding increase in the frequency of O2 dissociation by contraction of the discharge in the anode region. The discharge was maintained in a combined mode with a constant current (70 – 100 A), on which current pulses (100 μs, 1 kHz) with adjustable amplitude (up to 220 A) were superimposed. This mode ensured a change in the degree of O2 dissociation in the range of 0.3 – 0.5 at constant average discharge current and Al evaporation rate. It is shown that an increase in the degree of O2 dissociation leads to an increase in the rate of coating deposition by a factor of 1.3 and promotion of the preferred (300) orientation of crystallites. The effect is due to the features of the adsorption of molecular and atomic oxygen on the Al2O3.

Dielectric Characteristics, Electrical Conductivity and Solvation of Ions in Electrolyte Solutions

Solvation and association of ions in solutions largely depend on the dielectric properties of the solvent, the distance between ions in solutions, and temperature. This paper considers the effect of temperature on static dielectric constant (DC), dipole dielectric relaxation (DR) time, and limiting (ultimate) high frequency (HF) electrical conductivity (EC) of water and some polar solvents. In the investigated temperature range (0–370 °C), the static DC and DR time of water decrease, and limiting HF EC passes through a maximum at 250–300 °C with temperature growth. The dielectric characteristics of methanol, ethanol, and propanol behave in a similar way. It is shown that the existence of an HF EC temperature maximum is due to the different nature of the temperature dependences of DC and DR time. It is suggested that the same dependences are responsible for the presence of a maximum in the temperature dependences of the dissociation degree and the ionic product of water. The influence of non-electrolytes concentration as well as metal salts on the dielectric properties of their aqueous solutions is considered. The limiting HF EC of water determines the specific EC value of aqueous electrolyte solutions. Analysis of the absorption of microwave energy by polar solvents, as well as aqueous solutions of non-electrolytes and electrolytes, at a frequency of 2455 MHz is carried out. The optimal conditions for high-frequency heating of solutions have been established. The distance between ions in aqueous solutions of inorganic salts and in non-aqueous solutions of ionic liquids is calculated. It is shown that the maximum on the concentration dependence of the specific EC can be related to ions association.

Research on the Increase of Mineral Dissociation Degree by High Pressure Water Jet

The traditional grinding technology of ball mill has many problems, such as high energy consumption, unable to maintain the original crystal shape, and it is difficult to obtain high quality and high purity ultrafine powder. The high-pressure water jet mineral dissociation technology is a new technology which is developed in response to these requirements. The experiment shows that the water jet technology has a strong ability of ultrafine grinding. With the increase of jet velocity, the crushing effect is more obvious. The high-pressure water jet pulverization is superior to ball milling for the separation of rare earth minerals, which has the characteristics of high dissociation degree and relatively uniform particle size. The water jet pulverization is more beneficial to the separation and recovery of rare earth minerals.

Impact of Solvation on the Structure and Reactivity of the Co3O4 (001)/H2O Interface: Insights From Molecular Dynamics Simulations

The spinel Co3O4 has many beneficial properties for potential use in catalysis. In operando, water is always present and alters the properties of the catalyst. We have used ab initio molecular dynamics to understand the effect of water and solvation on the structure and reactivity of the Co3O4 (001) A-type and B-type surface terminations. Water adsorbs on both terminations via a partial dissociative mode, and the A-termination is seen to be more reactive. On this surface, a higher degree of dissociation is observed in the topmost layers of the crystal in contact with water. Water dissociates more frequently on the Co2+ sites (about 75%) than on the adjacent Co3+ sites, where the degree of dissociation is about 50%. Increasing water coverage does not change the degree of water dissociation significantly. OH− adsorption on the Co2+ sites leads to a reduction of the amount of reconstruction and relaxation of the surface relative to the clean surface at room temperature. Proton transfer within the water films and between water molecules and surface has localized character. The B-terminated interface is less dynamic, and water forms epitactic layers on top of the Co3+ sites, with a dissociation degree of about 25% in the contact layer.

ANALISIS MISKONSEPSI ASAM BASA CALON GURU KIMIA DENGAN METODE THREE-TIER TEST

This study aims to identify the misconceptions of a prospective chemistry teacher. The study population was all students of the Chemistry Study Program at the University of Riau, while the sample was 66 students at the Chemistry Study Program at the University of Riau, selected by cluster random sampling technique. Conception data of chemistry teacher candidates on acid-base subjects have been identified and obtained by providing valid acid-base TTT diagnostic tests to chemistry teachers candidates. The result of this research showed that chemistry teacher candidate who experienced misconception on acid-base subject were 66.5% from 4 main concepts studied, namely acid and base concepts (51.15%), pH and pOH concepts and their calculations (79.06%), the concept of acid-base dissociation degree (75.43%), and the concept of acid-base titration and indicator (58.13%). The study also revealed that some students have difficulties in performing mathematical operations using logarithms.

MENTAL MODEL OF PROSPECTIVE CHEMISTRY TEACHER ON EQUILIBRIUM CONSTANT AND DEGREE OF DISSOCIATION

MODEL MENTAL CALON GURU KIMIA PADA KONSEP TETAPAN KESETIMBANGAN DAN DERAJAT DISOSIASIAbstrakPenelitian ini bertujuan untuk mengeksplorasi model mental calon guru kimia pada konsep tetapan kesetimbangan dan derajat disosiasi. Penelitian ini menggunakan jenis penelitian kualitatif eksploratif. Penelitian dilaksanakan pada mahasiswa semester lima di Program Studi Pendidikan Kimia Universitas Riau. Hasil penelitian menunjukkan bahwa model mental mahasiswa sebagai calon guru kimia pada konsep tetapan kesetimbangan terbagi menjadi enam model yang tergolong mengalami miskonsepsi yaitu kekurangpahaman mengenai kesetimbangan heterogen, kesalahan penulisan persamaan Kp, pemahaman tentang nilai Kc bergantung pada pangkat dari koefisien reaksi pada kondisi reaksi yang sama, kesalahan menentukan satuan tetapan kesetimbangan, kesalahan menghitung Δn, dan tidak mengetahui koefisien reaksi zat yang tidak tertulis angka. Adapun model mental calon guru kimia pada konsep derajat disosiasi terbagi menjadi tiga yaitu model saintifik derajat disosiasi, model tanpa pengertian disosiasi, dan model kesalahan jumlah mol awal. Kata kunci: model mental, calon guru kimia, tetapan kesetimbangan, derajat disosiasiAbstractThis study was aimed at exploring the mental model of prospective chemistry teacher on the concepts of equilibrium constant and the degree of dissociation. This study used explorative qualitative research model. The research was conducted at the fifth semester students in the Chemistry Study Program at Riau University. The results show that the mental model of students as prospective chemistry teachers on the concept of the equilibrium constant is divided into six models that are classified as experiencing misconceptions: the lack of understanding about heterogeneous equilibrium, error writing in Kp equation, misunderstanding of the value of Kc depends on the rank of the reaction coefficient under the same reaction conditions, the error of determining the unit of equilibrium constant, the error of calculating Δn, and the lack of understanding regarding to the reaction coefficient of an unwritten number of substances. The mental model of prospective chemistry teachers on the concept of dissociation degree is divided into three: the scientific model of dissociation degree, the model without understanding dissociation, and the initial mole number error model.