Use of Ring-Disk Equipment in Coulometry

Abstract

We have found it difficult to implement coulometry on small volumes and yet react the sample quantitatively in a reasonable time. We describe here a simple and satisfactory solution, making use of a commercial ring-disk electrode system.¹ A small cup-like cell is constructed with dimensions such that the ring-disk assembly can rotate freely inside it at a small distance from the bottom, as shown in the figure. The ring is used as the counter-electrode, and appears to be acceptable in spite of a much smaller area than the working electrode (the disk). The reference electrode is provided by a capillary connection at the bottom. The capillary is filled with a solution of supporting electrolyte and agar, which in turn is connected through a salt-bridge (containing electrolyte only) to a calomel electrode. The level of the electrolyte in the reference arm is higher than that in the cell, so that a very small positive flow is ensured to prevent contamination of the agar with the sample. The very smooth rotation of the ring-disk system permits speeds up to about 2000 RPM. It was found that for electrolysis of metals such as Cd and Pb on a mercury-coated glassy carbon electrode, the half-time for electrolysis is about 2.5 min at the optimum rotation speed of 800 RPM, with a sample volume of 10 μL.     

Improved wear performance by the incorporation of solid lubricants during thermal spraying

For components that are required to function in sliding or rubbing contact with other parts, degradation often occurs through wear due to friction between the two contacting surfaces. Depending on the nature of the materials being used, the addition of water as a lubricant may introduce corrosion and accelerate the degradation process. To improve the performance and increase the life of these components, coatings may be applied to the regions subject to the greatest wear. These coatings may be engineered to provide internal pockets of solid lubricant in order to improve the tribological performance. In the present study, coatings containing a solid lubricant were produced by thermal spraying feedstock powders consisting of a blend of tungsten carbide-metal and a fluorinated ethylene-propylene (FEP) copolymer-based material. The volume content of this teflon-based material in the feedstock ranged from 3.5 to 36%. These feedstocks were deposited using a high velocity oxy-fuel (HVOF) system to produce coatings having a level of porosity below 2%. Sliding wear tests in which coated rotors were tested in contact with stationary carbon-graphite disks identified an optimum level of teflon-based material in the feedstock formulation required to produce coatings exhibiting minimum wear. This optimum level was in the range of 7 to 17% by volume and depended on the composition of the cermet constituent. Reductions in mass loss for the couples on the order of 50% (an improvement in performance by a factor of approximately 2) were obtained for the best performing compositions, as compared to couples in which the coating contained no solid lubricant.     

Graded Casting of Materials with Continuous Gradients

A process is introduced for producing continuously graded materials by slip casting with a continuous flow of slip of changing composition. The approach has been tested using alumina and zirconia slips to produce alumina/zirconia composites with a graded composition. Observation of the microstructure has shown that the phases are relatively well dispersed. Compositional analysis revealed a relatively smooth transition in composition through the thickness of sintered bodies. Results have also indicated that for flow rates up to ∼ 60 cm/min, the highest linear flow rate tested, the casting rate of alumina slips containing 38.6 vol% solids was not affected.     

Graded Casting: Process Control for Producing Tailored Profiles

The concept of graded casting for processing composite materials having a smooth through-the-thickness transition in composition is further developed and refined. An empirical model is presented that uses data from the casting of constant composition slips to predict casting rates for slips of changing composition. The model was tested by producing A1₂O₃–ZrO₂ composites having tailored composition profiles. Both linear- and nonlinear-graded compositions were processed, and it was shown that the model could correctly predict the changes necessary during casting to produce the selected contours. Analysis of the composites by EDS and SEM revealed a smooth transition in composition through the thickness of sintered bodies and a relatively good distribution of the phases.     

Partially Water-Soluble Binder Formulation for Injection Molding Submicrometer Zirconia

A binder system containing 60% by volume of a water-soluble major constituent was formulated and tested for powder injection molding ceramic materials. The main components of the binder phase were a low molecular weight polyethylene glycol, an oxidized high density polyethylene, polyvinyl butyral and stearic acid. Ceramic powder-binder mixes containing these binder components and up to 45% by volume of a submicrometer stabilized zirconia powder were prepared and characterized. The apparent viscosity of these mixes at a temperature of 190°C and a shear rate of 100 s^-1 was determined to be 700–800 Pa·s. Binder removal from parts produced by injection molding these feedstocks was accomplished using a two-stage process. The water-soluble constituent, polyethylene glycol, was removed by dissolution in water at 50°C. Tests showed that approximately 90% of the polyethylene glycol could be removed from a 2-mm thick part during a 2 h immersion in water. The remaining binder constituents were removed using a thermal treatment to 500°C at a heating rate of 100°C/h. Thermogravimetric analysis revealed a good separation of the decomposition regions for the various components when heated in an argon atmosphere. A final sintering step in air at 1500°C produced parts having a density above 99%.     

Psychological and social indicators of suicide ideation and suicide attempts in Zuni adolescents.

Suicide behavior is a significant problem for many American Indian populations, often more so than in the general population, but little tribal-specific data is available. In this study, baseline data on the correlates of suicide ideation and the social and psychological differences between suicide attempters and nonattempters were collected on a sample of 84 Zuni adolescents. Results show significant correlations between a measure of suicide ideation and past suicide attempt behavior, drug use, depression, hopelessness, stress, psychological symptomatology, social support, liking for school, and interpersonal communication. Significant differences between the 30% of the students who reported having previously attempted suicide and the nonattempters were also found on these measures. Areas for education and prevention efforts are suggested. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hierarchical information and the synthesis of distributed strategies

Acta Informatica - Infinite games with imperfect information are known to be undecidable unless the information flow is severely restricted. One fundamental decidable case occurs when there is a...     

Grain Growth in CaO-Stabilized ZrO2 in the Presence of a Liquid Phase

Calcia-stabilized zirconia, CSZ (7.5 wt% CaO), with impurities of A1₂O₃, SiO₂, MgO, Fe₂O₃, and TiO₂, was sintered in air at 1783 K for times (t) up to 230 h. The microstructure consisted of grains of CSZ with small amounts of pores and a CaO-Al₂O₃-SiO₂ eutectic. Grain diameters grew in proportion to t^1/3. The results are consistent with a mechanism in which grain growth is limited by diffusion of Zr⁴⁺ ions through the liquid eutectic.     

Coke formation during simultaneous hydrocracking of bitumen and hydrogenation of coal

Conventional catalysts are rapidly fouled with coke deposits when they are used to hydrocrack residual oils. The work reported here was part of an investigation on the removal of coke-forming compounds from residual oils prior to their contact with catalysts. Semianthracite coal particles have been added to a reaction mixture of hydrogen and Athabasca bitumen at 13.9 MPa and 723 K, to provide a large surface area on which coke could deposit. Agglomeration of coal particles occurred during hydrogenation in the absence of bitumen, but did not occur when bitumen, coal, and hydrogen were all present together in the reaction system. A solid mass of coke formed when bitumen was hydrocracked in the absence of coal particles, but did not form when the bitumen was present with coal and hydrogen. These observations illustrate one of the advantages of processing bitumen and coal simultaneously. The solid particles from hydrocracking experiments, coal hydrogenation experiments, and experiments on coal carbonization were examined petrographically. It was found that coke formed from Athabasca bitumen has a different microstructure from that formed from semi-anthracite coal. On the basis of these studies it was concluded that semi-anthracite coal was converted to coke similar to that normally made from low-volatile bituminous coal. Simultaneously coke formed from the bitumen was deposited on the exterior of the particles.     

Characteristics and composition of melon and grape seed oils and cakes

Watermelon (Citrullus vulgaris) and grape (Vitis vinifera) seeds were investigated for their nutritional quality and oil characteristics. The yields of seeds on an as is basis (edible portion) were 1.6 and 1.8% for grape and melon, respectively. The melonseed on a dry weight basis consisted of 53.6% testa and 46.4% kernel. The crude protein, fat and fiber content were 16.4, 23.1 and 47.7% for melon and 8.2, 14.0 and 38.6% for grape (dry weight basis). Both seeds were found to contain significant levels of Ca, Mg, P and K. The fatty acid profiles showed an unsaturated fatty acid content of 76.1% for melonseed oil and 88.6% for grapeseed oil. The predominant fatty acid in both seeds was linoleic acid. The iodine value, saponification number and acid value were 116, 248 and 0.97 for melonseed oil and 132, 194 and 1.59 for grapeseed oil. The amino acid profiles of both seed cake proteins were determined and compared with hen’s egg protein.