Quantifying secondary reactions in VRLA batteries. What purity standards and other factors are necessary to prevent negative plate discharge?
In a VRLA cell with a fully developed oxygen cycle, the negative plates will suffer discharge during float service if their self-discharge rate is too high to be balanced by the corrosion rate of the positive grids. Positive grids have been developed with very low corrosion rates. However, there is little quantitative data available on negative plate self-discharge rates that are required to balance such low corrosion rates. This paper presents values measured from several different battery brands, American and European. The data shows clearly that some production batteries have high negative self-discharge rates that account for the observed tendency for self-discharge in service. Surprisingly, the data also shows that other brands have achieved extremely low self-discharge rates-low enough to be compatible with the best positive grids that the authors have tested. These results are very encouraging for VRLA technology and confirm that the principle can be realized. The focus now shifts to the practical issues: finding the source of the impurities that increase hydrogen evolution and weighing the cost and practicality of reducing them.
Monobloc Batteries: High Temperatures, Life and Catalysts
12-Volt Monobloc batteries have become very popular in recent years due to their high power density and compact form. With the advent of the front terminal design this battery has become easy to install and support and its compact form allows it to be used in a wide variety of space constrained applications where larger 2-volt VRLA cells will not fit. The Monobloc VRLA battery, while not new, has become the preferred battery to be used in outside plant (OSP) applications due to the features just outlined. As is being dis covered, the high temperatures of the outside plant environment are not conducive to the life of these batteries. This paper will review the life expectations of Monobloc VRLA batteries, explore the effects of high temperatures on these batteries and explain why high temperature can drastically shorten the life of VRLA batteries. Finally the paper will present a possible application of catalysts to 12-volt Monobloc batteries in order to mitigate the effects of high temperature.
Determination of metals in urine by direct injection of sample, high-performanc liquid chromatography and electrochemical or spectrophotometric detection
Abstract A method for the rapid and simultaneous determination of copper, nickel and lead in urine is described. Direct injections of freshly acidified and filtered (0.45-μm) urine samples were made onto a reverse-phase separator column with a guard column for sample clean-up. By complexing the metals with a dithiocarbamate ligand included in the mobile phase, the metal complexes could be detected electrochemically (copper and nickel) or spectrophotometrically (copper, nickel and lead). The procedure is shown to provide a convenient method for the determination of copper and nickel at normal to occupationally exposed levels of urinary output (electrochemical detection) after direct injection of samples. Spectrophotometric detection methods were insufficiently sensitive for direct determinations of copper and nickel at some of the lower levels found in urine. The spectrophotometric detection of lead is subject to interference by u.v.-absorbing constituents present in urine and is restricted to detection of lead in persons over-exposed to lead, unless additional clean-up procedures are applied.