Lead peroxide paste

The disk surface is thus exposed only to gaseous SO, not particulates. The American Society for Testing of Materials (ASTM) procedure suggests a 30-day exposure, followed by a standard sulfate analysis [16]. The other method sometimes used is the peroxide candle, similar in its function to the chloride candle, but again using lead peroxide to capture SOy In this procedure, a lead peroxide paste is applied to a paper thimble in the laboratory, and allowed to dry thoroughly before exposure. The thimble is then exposed in an instrument shelter to the test yard environment. In both cases, the SOj deposited results are appropriately reported in terms of deposition rate on the surface in units of mg/m /day. 

Lead Peroxide.—100 gms. of bleaching powder are shaken up with 1,500 c.cs. of water and filtered. The filtrate is added gradually to a hot solution of 50 gms. lead acetate in 250 c.cs. of water the addition is continued until the precipitate turns dark brown, and until no precipitate is formed by further addition of bleaching powder solution to a filtered test portion. The liquid is decanted, and the precipitate washed several times with water, then filtered and washed with water. It is preserved in a well-stoppered bottle in the form of a thick paste. 

The product is then transferred to a large flask and distilled with steam to remove unchanged dimethyl-aniline the leuco-base is filtered when cool and recrystallised from alcohol. Almost a quantitative yield is obtained. The zinc chloride double salt of the dye is prepared as follows Ten. gms. of the base is dissolved in dilute hydrochloric acid containing 2 7 gms. of HC1 the liquid is diluted with 800 c.c. of water and 10 gms. of 40 per cent, acetic acid added it is then cooled with ice, and a thin paste of 7 5 gms. of lead peroxide added gradually with shaking. After standing a few minutes, the lead is precipitated by adding 20 per cent, sodium sulphate, and to tho filtrate from lead sulphate is added 8 gms. of zinc chloride dissolved iu a little water. The dye is then salted out by addition of common salt. Yield, abont 7 gms. 

The early 1980s saw considerable interest in a new form of silicone materials, namely the liquid silicone mbbers. These may be considered as a development from the addition-cured RTV silicone rubbers but with a better pot life and improved physical properties, including heat stability similar to that of conventional peroxide-cured elastomers. The ability to process such liquid raw materials leads to a number of economic benefits such as lower production costs, increased ouput and reduced capital investment compared with more conventional rubbers. Liquid silicone rubbers are low-viscosity materials which range from a flow consistency to a paste consistency. They are usually supplied as a two-pack system which requires simple blending before use. The materials cure rapidly above 110°C and when injection moulded at high temperatures (200-250°C) cure times as low as a few seconds are possible for small parts. Because of the rapid mould filling, scorch is rarely a problem and, furthermore, post-curing is usually unnecessary. 

Particles of lead dioxide in lead monoxide, such as those formed in a ball-mill, can be formed by treating the oxide with ozone before paste mixing [49]. The use of persulfate [50-53] and peroxides [54] to effect the partial conversion of lead oxide in the paste to lead dioxide has also been proposed. A proprietary process for treating the surfaces of unformed plates with ozone gas produced a thin coating of lead dioxide, which enhanced formation [55,56]. Much lower quantities of lead dioxide are needed with this approach than when red lead is added to the plate, and the normal battery paste mix can be used. Dipping or spraying the plate with a persulfate solution has also been adopted to oxidize the surface PbO to conductive Pb02 [57]. 

Within the past few years, the Stadtman group at NIH has provided an elegant elucidation of the chemistry of Mn(II)-cataIyzed radical reactions that lead to catalase-like disproportionation and dismutation of hydrogen peroxide [276-278], The key complex involves inner-sphere coordination of 3 HCO3 moieties per Mn(II) ion, which catalyzes the following inter-related redox reactions ... 

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