Thermal oxidation studies

Thermal oxidation studies of unnotched and uncracked specimens of Al203/SiC composites also reveal the formation of carbon-rich and silicon-rich reaction layers via solid-state oxidation of the SiC whisker according to the reaction 56... 

In this chapter the experimental techniques used to obtain rate constants for the reactions of OH radicals with organics are described, and the resulting data and chemical mechanisms are presented. Discussion has been limited to data obtained at temperatures 6500 K, and hence flame, shock-tube, and hlgh-temperature thermal oxidation studies are not dealt with. 

Thermal Oxidation Studies. Another example of a detailed study of the oxidation of aluminum metal was provided in the Cornell Ph.D. Dissertation by Eric Johnson [68], and in a subsequent review of various AI2O3 studies the he coauthored with Cocke and Merrill [65]. They reported prominent Al (2p) peaks... 

In most cases thermal oxidation studies in polymers would be conducted under an inert gas such as nitrogen or helium in order to avoid the formation of secondary oxidation products that would complicate interpretation. In some cases, however, information is required on the stability to oxidation of polymeric materials and in these instances the thermal experiment would be carried out in an atmosphere of oxygen or air. Applications of the various techniques listed above to the determination of oxidative stability are discussed next. 

Thermal Oxidative Stability. ABS undergoes autoxidation and the kinetic features of the oxygen consumption reaction are consistent with an autocatalytic free-radical chain mechanism. Comparisons of the rate of oxidation of ABS with that of polybutadiene and styrene—acrylonitrile copolymer indicate that the polybutadiene component is significantly more sensitive to oxidation than the thermoplastic component (31—33). Oxidation of polybutadiene under these conditions results in embrittlement of the mbber because of cross-linking such embrittlement of the elastomer in ABS results in the loss of impact resistance. Studies have also indicated that oxidation causes detachment of the grafted styrene—acrylonitrile copolymer from the elastomer which contributes to impact deterioration (34). 

A study was done measuring the thermal oxidative stability of polyurethanes made from PPG polyols, varying the isocyanate curative. Oxygen absorption was... 

A study of the thermal oxidative breakdown of polyethylene under static conditions has revealed that polyamine disulfides are stabilizers, yet to varying degrees (Fig. 1). 

Thermal-oxidative decomposition has been studied by Beachell and Nemphos (B5), Grassie and Weir (G2), Notely (N3), Parker (PI), and Ryan (R4) for a variety of polymer systems. The principal results of these studies are ... 

Miller et al. (1996) give examples of APFIM studies of the surface oxides formed on silicon, and studies of the stoichiometry of thermal oxide layers of this element, as well as a wide range of binary III-IV semiconducting materials. 

A typical synthetic route to the incorporation of pendent carboranyl units into a polymer chain is shown in scheme 3. Poly(o-carboranyl-organo-siloxane)s have been successfully prepared through hydrolysis of dimethyldichlorosilane in the presence of carboranedichloromethylsilane. The polymer has some of the elastomeric characteristics of the parent poly(siloxane) however, the thermal-oxidative cleavage of the o-carboranyl pendent group is reported to occurat lower temperatures than that for the thermooxidative cleavage of Si—O and Si—C bonds.10 Thermal studies have... 

Specific structural features are observed in the formation of composite oxides. Kobayashi, Shimizu, and their co-workers have, in a series of papers, reported studies of the structure of barrier alumina films, anodically formed on aluminum covered by a thin (5 nm) layer of thermal oxide.198,199 Their experiments have shown that the thermally oxidized thin layer generally contains y- alumina crystals of about 0.2 nm size. This layer does not have a pronounced effect on ionic transport in the oxide during anodization. Also, islands of y -alumina are formed around the middle of anodic barrier oxides. They are nucleated and developed from tiny crystals of y -Al203 and grow rapidly in the lateral direction under prolonged anodization.198,199... 

As part of a multi-technique investigation (see also discussion under mid-infrared spectroscopy later), Corrales et al. [13] plotted the carbonyl index for films prepared from three grades of polyethylenes a high-density PE (HDPE), a linear low-density PE (LLDPE) and a metallocene PE (mPE) (see Figure 5). In this study, the data trend shown in Figure 5 correlated well with activation energies derived from the thermal analysis, which showed that the thermal-oxidative stability followed the order LLDPE > mPE > HDPE, whereas the trend... 

Imaging chemiluminescence technique. Chemiluminescence analysis is suitable for studying the early stages of the thermal oxidation of rubbers. A weak emission of light formed by chemical reactions appears during the oxidative degradation of hydrocarbons. This technique can be used to depth profile the oxidation of rubbers. MR... 

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). 

Tang, S.L.Y., McGarvey, D.J. and Zholobenko, V.L. (2003). Photooxidation and dark thermal oxidation of 1-butene on cationic forms of zeolite Y a spectroscopic study. Phys. Chem. Chem. Phys. 5, 2699-2705... 

During processing polypropylene melts under the action of transverse strain there occur strain-chemical conversions which can result in both decrease and increase in their molecular masses the mechanical effect on the rapidity and level of the occurring processes is considerably more prominent than the mere contribution of thermal and thermal-oxidative breakdown. These data necessitate studying the process of polymer destruction. For this purpose it would be most effective to apply the criterion of assessment of the intensity with which destructive processes happen in polymer melts. 

Microporous and mesoporous silicon can be partly oxidized by chemical or electrochemical methods, while thermal oxidation is needed for a complete conversion of the porous layer to oxide. This complete conversion was the aim of the first studies in this field. 

Apart from titanium oxide, two other carbon-modified semiconductors were studied in water photoelectrolysis due to their low band gap energy, namely iron (Fe203) and tungsten oxide (W03) [70,90]. Carbon-modified iron oxide demonstrated promising photoconversion efficiency, 4 % and 7 % for modified oxides synthesized in oven and by thermal oxidation respectively [90]. Also, carbon-modified tungsten oxide (C-W03) photocatalysts exhibited a 2 % photoconversion efficiency [70],... 

Thermal degradation studies might be required to determine the decomposition characteristics of of the subject pesticide vAien heated alone or In the presence of oxidizers and/or binders In both closed and open systems and at various temperatures. 

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