Effects of Precipitation Hardening Variables on Al–Zn–Mg-Sn Alloy as Sacrificial Anode in Seawater: Experimental and Statistical Analysis

This research investigated the effects of tin composition and heat treatment variables on the Al-Zn-Mg alloy as sacrificial anode in seawater using gravimetric technique and statistical analysis. Tin was alloyed with Al-Zn-Mg in varied proportions (0%, 0.01%, 0.05% and 0.1%) to determine the optimum anode efficiency in the marine environment. Precipitation heat treatment was performed by first subjecting the samples to solution treatment at 5380C for 2 hours and later subjected to varying hardening temperatures and times. The samples were hardened for 4, 8 and 12 hours at each of the hardening temperatures of 1300, 1600 and 1900 centigrade. The anode efficiency increases as the tin concentration increases. The experimental result of this study showed that the Al-Zn-Mg alloy with 0.1% tin gives the optimum anode efficiency. It was revealed that the Al-Zn-Mg alloy without tin composition exhibited high output current capacity when hardened at 1900C for 4 hours. Predictive model developed in this work was in consonance with experimental observation except the following; at hardening temperature of 1600C, the model recommended 12 hours as against 4 hours of laboratory experiment and at hardening temperature of 1300C it advocated 8 hours as against 12 hours.Keywords - aluminum alloy, corrosion, precipitation hardening, regression and correlation analysis, and sacrificial anode

Параметрическое исследование двух устойчивых форм горения разряда в холловском двигателе

In this paper the behavior of the integral parameters of the Hall thruster (thrust, specific thrust impulse) in two stable discharge modes were experimentally investigated. This modes significantly different from each other in anode efficiency. The studies were carried out on a laboratory model of Hall thruster with the external discharge zone with the middle-line diameter equal to 77 mm. The discharge voltage was in the range of 500-900 V and a gas flow rate was from 2.0 to 5 mg/s. The most striking differences between the discharge modes are the shape of the plasma plume and the value of the discharge current at practically identical input parameters of operation (gas flow rate, discharge voltage, magnetic field). It is shown that in the entire studied range of input parameters during the transition from the optimal mode (in terms of the efficiency) to the suboptimal mode the main integral characteristics of the thruster suddenly change: the discharge current increases by 10-30% with the simultaneous relative drop of thrust by 5-15% and efficiency by 20-40%. A detailed study of the structure of the anode efficiency showed that when the transition between modes occurs the electron current efficiency (the ratio of the ion current to the discharge current) abruptly changes, that is, the electronic conductivity in the discharge channel of the thruster changes too.

ELECTROLYSIS OF GRANULATED COPPER-NICKEL MATTE

The paper justifies the method of processing sulfide-metal melts including their granulation and subsequent electrolysis of granules. High-speed crystallization ensures ultrafine structure formation and stabilizes non-stoichiometric high-temperature phases leading to an increase in the reactivity of granules during subsequent hydrometallurgical processing. Copper powder was isolated at the cathode, and sulfur-sulfide slime (NiS–Сu9S5–Cu7S4–S) was isolated at the anode in a sulfuric acid solution during the electrolysis of granular copper-nickel matte (Cu : Ni = 1 : 1). The influence of current density and process duration on electrolysis parameters and the quality of copper powder isolated was estimated. Sulfur sulfide slime (containing more than 50 % sulfur) forms a passivation layer on granule surfaces, which prevents reagent feeding and reaction product removal from the interaction zone. Anodic current density of up to 100 A/m2 ensures metal conversion into a solution and copper powder (PMS-1 grade) formation at the cathode. Powder is represented by 1 to 100 μm particles of dendritic and fragmented shapes. High-quality copper powder isolation was achieved when saturating electrolyte with nickel to 28,0 g/dm3 . In this case, anode efficiency was 37 % with respect to sulfur, and cathode efficiency was 92,8 % for copper. The process is recommended for copper and nickel separation when processing sulfide-metal alloys. Copper content of in the solution during electrolysis ranged from 0,4 to 2,0 g/dm3.

Corrosion Behavior of Al-Zn-In Sacrificial Anode Alloys Produced by Conventional Casting and Semi-Solid Metal Casting Processes

A challenge in producing a sacrificial anode through conventional casting method is that the alloying elements in casting segregate during solidification, which further causes non-uniform anode corrosion reducing anode performance. In this paper, we investigated the performance of Al-5Zn-0.02In anode produced by conventional casting compared with by semi-solid casting technique. The performance of produced anodes were measured in terms of anode potential, current capacity, consumption rate and anode efficiency in 3.5% NaCl solution for 14 days. We found that the microstructure of the conventional cast anode had dendrites and coarse grains and the corrosion caused pitting corrosion. In contrast, the semi-solid cast anode had fine grains without any dendrites. The corrosion attacked mainly the grain boundaries and less on the matrix. Surprisingly, the conventional cast anode has about 10% higher efficiency than that of semi-solid cast anode.

Experimental Investigations of a Krypton Stationary Plasma Thruster

Stationary plasma thrusters are attractive electric propulsion systems for spacecrafts. The usual propellant is xenon. Among the other suggested propellants, krypton could be one of the best candidates. Most studies have been carried out with a Hall effect thruster previously designed for xenon. The ATON A-3 developed by MSTU MIREA (Moscow) initially defined for xenon has been optimized for krypton. The stable high-performance ATON A-3 operation in Kr has been achieved after optimization of its magnetic field configuration and its optimization in different parameters: length and width of the channel, buffer volume dimensions, mode of the cathode operation, and input parameters. For a voltage of 400 V and the anode mass flow rate of 2.5 mg/s the anode efficiency reaches 60% and the specific impulse reaches 2900 s under A-3 operating with Kr. The achieved performances under operation A-3 with Kr are presented and compared with performances obtained with Xe.