Passive and transpassive anodic behavior of chalcopyrite in acid solutions

The electrochemical oxidation of CuFeS₂ in various acid solutions was studied using electrodes made from massive samples. The primary techniques employed were potentiodynamic polarization and constant potential experiments supplemented by capacitance measurements. It was the purpose of this study to investigate the behavior of: (1) several sources of CuFeS₂ in H₂SO₄ electrolytes, and (2) a single source of CuFeS₂ in various dilute acids. Electrochemical characterization of CuFeS₂ from various locations was performed in 1 M H₂SO₄ which showed significant differences in their behavior. All samples exhibited passive-like response during anodic polarization. The current density in this passive region was reproducible and showed differences of up to two orders of magnitude between samples from different sources which has been attributed mainly to the presence of impurities in some of the samples. During anodic polarization CuFeS₂ was found to be sensitive to pH at higher potential, but insensitive at low potential in sulfate solution. In addition, current decay measurements at constant potential in the low potential-passive region were found to follow the Sato-Cohen (logarithmic) model for solid film formation. Based on current and mass balance measurements, two intermediate sulfide phases appeared to form in the sequence CuFeS₂→S₁→S₂. At higher potentials, in the transpassive region, the observed increase in current is compatible with the decomposition of water to form chemisorbed oxygen which releases copper and forms sulfate ions.     

Distribution of cell wall components in potato tubers: a new titrimetric procedure for the estimation of total polyuronide (pectic substances) and its degree of esterification

Total esterified polyuronide in plant tissue can be assayed by titrating the uronic acid liberated from the alcohol-insoluble fractions of the tissue by alkaline hydrolysis. The total polyuronide can be determined in a similar manner if the carboxyl groups are initially esterified with methanolic hydrochloric acid. Comparison of the two results gives the degree of esterification of the total polyuronide. The divalent metals present in the same alcohol-insoluble fractions are assumed to be bound to the uronide groups and their assay gives a measure of the extent of interchain cross-linking by metal salt formation. Application of these procedures to samples from different parts of potato tubers showed that polyuronide generally had a low degree of esterification (about 40%) and was present in higher concentrations (about 4.6% a.i.s.) in the cortex and periderm than in the interior tissues (about 2.7% a.i.s.). The degree of crosslinking due to calcium and magnesium ions is lowest in the outer layers of the potato tuber and may be the reason that sloughing occurs in this area.     

Brain areas controlling thermoregulatory grooming prone extension, locomotion, and tail vasodilation in rats.

In an experiment with 134 male Long-Evans rats, localized diathermic warming elicited the principal hyperthermic responses of the rat: grooming, body extension, locomotion, and tail vasodilation. Failure of diathermy to elicit nonthermoregulatory responses evoked by electrical stimulation ruled out nonspecific excitation. The largest zone extended from the septal area through the preoptic area and hypothalamus into the midbrain, and a smaller zone was located in the medulla. Grooming, extension, and locomotion were obtained from differentiated though partially overlapping subareas, all of which elicited vasodilation. Fewer than 3% of the electrodes induced all responses, while the remainder produced incomplete combinations, indicating that the rat's hyperthermic repertoire results from largely independent channels from thermal detector to motor effector, and does not require an integrative center or mutually excitatory collaterals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A new technique for precedence-ordering chemical process equation sets

An algorithm that combines structural equation analysis with algebraic rearrangement and substitution has been developed to precedence-order algebraic chemical process equations. The SWS (Structural Analysis with Substitutions) algorithm selects an output variable for each equation, rearranges the equation to solve for that variable, and reduces the number of equations by substitution. The algorithm has been used for computer generation of Fortran programs to perform meterial and energy balances in the design of chemical processes.     

The government <Emphasis Type="Italic">is</Emphasis> here to help: a small business perspective

Public-private partnerships between government and industry have been increasingly used as a vehicle for defining and executing R&D activities. Stimulus of smaller technology enterprises in particular is important, and this article explores this topic from the policy level as well as from organizations “on the ground.” The story in brief: challenges and opportunities. Editor’s Note: A hypertext-enhanced version of this article is available on-line at www.tms.org/pubs/journals/JOM/0412/Hunt-0412.html Warren H. Hunt, Jr. is technical consultant at TMS.     

The China factor: Aluminum industry impact

The emergence of China as a global economic force has influenced the technical enterprise generally and a number of industries specifically. The aluminum industry is an example, with effects on consumption and demand as well as production and supply. This article reviews these areas from both a historical and future perspective. For more information, contact W.H. Hunt, Jr., TMS, 184 Thorn Hill Road, Warrendale, PA 15086; (724) 776-9000, ext. 226; (724) 776-3770; e-mail whunt@tms.org.     

Cadmium sulfide and cadmium selenide/cadmium sulfide nanoparticles stabilized in water with poly(cysteine acrylamide)

Cysteine acrylamide (N-acryloyl L-cysteine) stabilizes CdS nanoparticles as the particles form in aqueous dispersions. Cysteine acrylamide also exchanges for citrate on the surfaces of CdSe and core/shell CdSe/CdS nanoparticles to provide greater stability. Heating of the nanoparticle dispersions polymerizes the cysteine acrylamide on the surface to form a more efficient polydentate stabilizer. The polymer-coated nanoparticle dispersions are colloidally stable even after removal of low molecular weight solutes by dialysis. Emission quantum yields of the polymer-coated CdSe and CdSe/CdS samples were 0.9% and 2.6%, respectively, after aging of the samples in light. CdSe/CdS coated with poly(cysteine acrylamide) is colloidally stable for at least two years in the dark at 5 degrees C.