Electrodeposition of nickel from alkaline NH_4OH/NH_4Cl buffer solutions

The electrodeposition of nickel on steel and copper from alkaline NH4OH/NH4Cl buffer solutions was investigated by cyclic voltammetry (CV), chronopotentiometry (CP), chronoamperometry (CA) as well as an opto-digital microscope, glow-discharge optical emission spectroscopy (GD-OES), XRF, and SEM-EDS techniques. The aim was to obtain Ni coatings from weak alkaline solutions and to optimize the process. The electrolyte composition, pH, temperature as well as current and potential parameters of the process were optimized using the quality of Ni deposit as a criterion. The role of hydrogen evolution in the process was discussed. An influence of Co as an additive was also investigated. It was found that a small amount of Co catalyzes Ni deposition process and improves the quality and color of the deposit. Therefore, in the possible application, the Ni/Co codeposition should be seriously considered. It was also shown that for constant current deposition mode, the width of self-established potential range, revealed at the very beginning of the process by the chronopotentiometric E=f(t) curves, is related to the quality of the coating.

CORRELATION BETWEEN STRESS COMPONENTS AND STRESS CORROSION CRACKS IN BRASS Lecturer,Department of Materials Physics,University of Science and Technology Beijing,Beijing 100083,China

The effects of stress components on nucleation sites and propagation directions of stress cor- rosion cracks in brass were investigated with specimens under mode Ⅱ and mode Ⅲ loadings. The results indicated that under mode Ⅱ loading,stress corrosion cracks nucleated on the site with maximum normal stress component and propagated along the plane perpendieular to the maximum normal stress,under mode Ⅲ loading,the stress corrosion crack was not evident on the 45°plane due to the general corrosion in aqueous solution with high NH_4OH concentra- tion,while stress corroded in aqueous solution with low NH_4OH concentration, numerous cracks with spacings of 10—150μm were found on the 45°plane with maximum normal stress and no stress corrosion cracks was observed on the plane with maximum shear stress.

Removing ammonia from air with a constant pH, slightly acidic water spray wet scrubber using recycled scrubbing solution

Previous research on wet scrubbers has only studied highly acidic scrubbing solutions because of their high ammonia capture efficiencies; however, the high acidity created practical problems. Lower acidity solutions would reduce corrosion, maintenance, and cost; however, designers may need to use strategies for increasing scrubber effectiveness, such as using lower air velocities. The objective of this studywas to determine if a spray scrubber with slightly acidic and higher p H scrubbing solution （pH from 2 to 8） could effectively remove NH3 from NH3 laden air （such as animal building exhaust air）, and also collect this valuable resource for rater use as a fertilizer. A bench-scale spray wet scrubber treated 20 ppmv NH3/air mixture in a countercurrent contact chamber. First, the solution pH was varied from 2 to 8while maintaining constant air velocity at 1.3 m. s-1. Next, air velocity was increased （2and 3 m.s-1） while solution pH remained constant at pH6. At 1.3 m.s -1, NH3 removal efficiencies ranged between 49.0% （pH8） and 84.3% （pH2）. This study has shown that slightly acidic scrubbing solutions are a practical means of removing ammonia from air especially if the scrubber is designed to increase collisions between solution droplets and NH3 molecules. The NH3 removed from the air was held in solution as NH4＋ and accumulates over time so the solution should be an excellent fertilizer.