Polysulfide stability

The decomposition of dithionite in aqueous solution is accelerated by thiosulfate, polysulfide, and acids. The addition of mineral acid to a dithionite solution produces first a red color which turns yellow on standing subsequentiy, sulfur precipitates and evolution of sulfur dioxide takes place (346). Sodium dithionite is stabilized by sodium polyphosphate, sodium carbonate, and sodium salts of organic acids (347). 

Ozonc-rcsjstant elastomers which have no unsaturation are an exceUent choice when their physical properties suit the appHcation, for example, polyacrylates, polysulfides, siHcones, polyesters, and chlorosulfonated polyethylene (38). Such polymers are also used where high ozone concentrations are encountered. Elastomers with pendant, but not backbone, unsaturation are likewise ozone-resistant. Elastomers of this type are the ethylene—propylene—diene (EPDM) mbbers, which possess a weathering resistance that is not dependent on environmentally sensitive stabilizers. Other elastomers, such as butyl mbber (HR) with low double-bond content, are fairly resistant to ozone. As unsaturation increases, ozone resistance decreases. Chloroprene mbber (CR) is also quite ozone-resistant. 

Figure 3 Thermal oxidative breakdown of polypropylene (temperature 200°C Poj = 350 Tor stabilizer concentration 0.5 mass percent). 1-without stabilizer 2-Santanox 3-polythiosemicarbazide disulfide 4-polyamineaniline disulfide 5-polydi-iminodiphenyloxide disulfide 6-polyaniline disulfide 7-polydiiminodiphenylmethane disulfide 8-hydrorubeanicpoly disulfide 9-thiocarbamide polysulfide 10-polyiminoazobenzene disulfide.

In the Pourbaix diagram, solid sulfur appears to be stable in a very narrow triangular domain, which lies completely within the stability domain of water. Sulfur is therefore stable in the presence of water and in acid solutions free from oxidizing agents. It is unstable, however, in alkaline solutions, in which it tends to disproportionate to give HS , (and polysulfides), SO , and other oxidation products. In... 

The reaction occurring at the photoanode (CdS or CdSe) is the oxidation of sulfide or polysulfide, while at the cathode (Pt) some polysulfide species are reduced, so that the electrolyte undergoes no net chemical change. Here, the previous problem of poor stability in Fe(CN)g solutions could be minimized, at the expense of lowering the driving potential (and thus the conversion efficiency), by using fhe... 

Photovoltaic response parameters for electrodeposited (polycrystalline) CdTe thin film electrodes in sulfide-polysulfide or alkaline sodium telluride PEC have been reported, primarily with no reference to the stability of the cells [100], In view of the instability of CdTe in aqueous solutions, Bhattacharya and Rajeshwar [101] employed two methods for the characterization of their electrodeposited CdTe-based PEC. In the first one, a coating of Pb02 (-100 nm thick) was deposited on the CdTe film surface by electroless deposition, and the coated films... 

Importantly, Licht [104], using the optimized polysulfide elecfrolyfes developed for CdX PEC (described in a preceding paragraph), was able fo demonsfrafe frue long-term stability for a polycrystalline pasted thin film Cd(Se,Te)/aqueous polysulfide system. In specific, complete stability was exhibited for an 8-month outdoors operation at 4.1% conversion efficiency. 

Licht S, Tenne R, Flaisher H, Manassen J (1984) A pronounced cation effect on performance and stability of Cd- chalcogenide/polysulfide photoelectrochemical cells. J Electrochem Soc 131 950-951... 

Sealants obtained by curing polysulfide liquid polymers with aryl bis(nitrile oxides) possess stmctural feature of thiohydroximic acid ester. These materials exhibit poor thermal stability when heated at 60°C they soften within days and liquefy in 3 weeks. Products obtained with excess nitrile oxide degrade faster than those produced with equimolar amounts of reagents. Spectroscopic studies demonstrate that, after an initial rapid addition between nitrile oxide and thiol, a second slower reaction occurs which consumes additional nitrile oxide. Thiohydroximic acid derivatives have been shown to react with nitrile oxides at ambient temperature to form 1,2,4-oxadiazole 4-oxides and alkyl thiol. In the case of a polysulfide sealant, the rupture of a C-S bond to form the thiol involves cleavage of the polymer backbone. Continuation of the process leads to degradation of the sealant. These observations have been supported by thermal analysis studies on the poly sulfide sealants and model polymers (511). 

However, Wrighton et al (2-6) showed that the photoelectrodes could be stabilized in a polysulfide medium. The recognition that these devices could show hi stability, large area, and low cost, spurred on further investigation of the factors involved in producing working devices. 

A number of plastics are condensation polymers and include polyesters and nylons that are not as highly oriented as the same materials but in fiber form. Other plastics have been developed that have outstanding heat stability, strength, and other properties that allow their wide use. These plastics include polycarbonates, polyimides, polybenzimidazoles, polysulfides, polyethers, polysulfones, and polyketones. 

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