Stability oxidation

Very many oxidation tests for transformer oils have been used at one time or another. Most of these tests are of a similar pattern The oil is heated and subjected to oxidation by either air or oxygen and usually in the presence of a metallic catalyst, almost invariably copper, which is the main active metal in transformer construction. Temperatures and duration have varied within wide limits, from 95 to 150°C (203-302°F) and from 14 to 672 h. 

In one test method (ASTM D-943), the oil is maintained at 100°C (212°F) for up to 1 week, during which time oxygen is passed through the oil, in which metallic copper is immersed. At the end of the oxidation period the amount of solid deterioration products sludge) is measured, after such sludge has been precipitated by dilution of the aged oil with n-heptane, and the soluble acid) decomposition products are also measured by determination of the neutralization value of the aged oil. 

To shorten the time for the oxidation test method, a test for sludge formation in transformer oil by high-pressure oxidation bomb has been devel- 

A transformer oil should not contain levels of unsaturated components (aromatics and/or olehns) that affect the oxidation resistance of the oil (ASTM D-2300). Another type of test (ASTM D-2298) exposes the degassed oil to electric stress, in a vacuum and at room temperature, the amount of gas evolved at the end of 1000 min being measured. 

Acidity (ASTM D-974, IP 1, IP 139) after oxidation is another criterion by which the extent of oil deterioration is judged. 

---

The procedure most commonly employed (NF M 07-047 or ASTM D 2274) Is to age the diesel fuel for 16 hours while bubbling oxygen into it at 95°C. The gums and sediment obtained are recovered by filtration and weighed. There is no official French specification regarding oxidation stability however, in their own specifications, manufacturers have set a maximum value of 1.5 mg/100 ml. 

Oxidation stability (distillate fuel oil) NF M 07-047 ISO/DlS 12205 ASTM D 2274 Measurement of precipitate after 16 h of oxygen sparging at 95°C... 

Oxidation stability (gasoline) (induction period) NFM 07-012 ISO/DlS 7536 ASTM D 525 Time necessary for a sample bomb under oxygen pressure to reach the critical induction point... 

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). 

Oxidative Stability. Ben2otrifluoride resists ring oxidation. In contrast, chromic acid readily oxidi2es 3-aminoben2otrifluoride to ttifluoroacetic acid in 95% yield (287). 

HalogenatedFluids. Chlorocarbons, fluorocarbons, or combinations of the two are used to form lubricating fluids (see Chlorocarbons and CHLOROHYDROCARBONS Fluorine COMPOUNDS, ORGANIC). Generally, these fluids are chemically inert, essentially nonflammable, and often show excellent resistance to solvents. Some have outstanding thermal and oxidation stability, because they are completely unreactive even in Hquid oxygen, and extremely low volatility. 

Hydroxyethyl cellulose (HEC), a nonionic thickening agent, is prepared from alkali cellulose and ethylene oxide in the presence of isopropyl alcohol (46). HEC is used in drilling muds, but more commonly in completion fluids where its acid-degradable nature is advantageous. Magnesium oxide stabilizes the viscosity-building action of HEC in salt brines up to 135°C (47). HEC concentrations are ca 0.6—6 kg/m (0.2—21b/bbl). 

The greatest source of contamination is extraneous matter. Atmospheric dirt, for example, is always a serious threat. It can enter the oil system through vents, breathers, and seals. Its primary effect is equipment wear, but plugging of oil lines and ports, and reduced oxidation stability of the oil are also serious effects. 

Impurities in mineral fillers can have serious effects. Coarse particles (grit) will lead to points of weakness in soft polymers which will therefore fail under stresses below that which might be expected. Traces of copper, manganese and iron can affect the oxidative stability whilst lead may react with sulphur-containing additives or sulphurous fumes in the atmosphere to give a discoloured product. 

In terms of processing there is no need for pre-drying PCHE granules, a standard extruder screw as used for polycarbonate may be used and discs are said to release well from the mould. Question marks remain on the oxidative stability of the polymer and on the quality of adhesion of the reflective layer but Dow claim that metallising is possible. 

In addition to the elastomers already described, others, have been produced on an experimental scale. These include the perfluoroalkylenetriazines with their unsurpassed thermal oxidative stability for an elastomer but with many offsetting disadvantages, and polyfthiocarbonyl fluoride). It is probably true to say that material does not have any outstanding desirable property that cannot now be matched by an alternative and commercially available material. 

The absence of both secondary and tertiary C—H bonds leads to a high measure of oxidative stability. Oxidation does take place when thin films are heated in air to temperatures above 300°C and causes cross-linking but this is of little practical significance. The absence of double bonds gives a very good but not absolute resistance to ozone. 

As with the polysulphones, the deactivated aromatic nature of the polymer leads to a high degree of oxidative stability, with an indicated UL Temperature Index in excess of 250°C for PEEKK. The only other melt-processable polymers in the same league are poly(phenylene sulphides) and certain liquid crystal polyesters (see Chapter 25). 

Matsumoto, T. and Mochida, I., Oxygen distribution in oxidatively stabilized mesophase pitch fiber, Carbon, 1993,31(1), 143 147. 

Hydrogenation of the conjugated C=C bonds to increase oxidative stability and... 

Solid SBR is often prefened to natural rubber because of its better thermal oxidative stability, higher abrasion resistance and easier processability. Solid SBRs are generally grouped into three families according to the production method. 

Resistance to weathering. Zinc oxide and magnesium oxide stabilize poly-chloroprene against dehydrochlorination. Further, zinc oxide helps vulcanize the rubber, and magnesium oxide reacts with /-butyl phenolic resin to produce a resinate which improves heat resistance of solvent-borne polychloroprene adhesives. 

Antioxidant activity is not a linear function of concentration. As the antioxidant level increases, less and less improvement in oxidative stability is noted. Therefore, only enough antioxidant should be added to rubber adhesives, typically 1 to 2 phr. 

Oxidative stability is highly important because it deals with the degradation of polymers under actual performance conditions. Oxidative stability, as applied to urethanes, refers to the combination of oxygen and heat or oxygen and light that causes degradation of urethanes. 

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

Lube oil extraction plants often use phenol as solvent. Phenol is used because of its solvent power with a wide range of feed stocks and its ease of recovery. Phenol preferentially dissolves aromatic-type hydrocarbons from the feed stock and improves its oxidation stability and to some extent its color. Phenol extraction can be used over the entire viscosity range of lube distillates and deasphalted oils. The phenol solvent extraction separation is primarily by molecular type or composition. In order to accomplish a separation by solvent extraction, it is necessary that two liquid phases be present. In phenol solvent extraction of lubricating oils these two phases are an oil-rich phase and a phenol-rich phase. Tne oil-rich phase or raffinate solution consists of the "treated" oil from which undesirable naphthenic and aromatic components have been removed plus some dissolved phenol. The phenol-rich phase or extract solution consists mainly of the bulk of the phenol plus the undesirable components removed from the oil feed. The oil materials remaining... 

A major development in fluoroplastks is the recent small scale production of Teflon AF, a noncrystaUme (amorphous) fluorocarbon polymer with a high glass transition temperature (240 °C) This optically transparent TFE copolymer is soluble m certan fluorocabons and has the same chemical and oxidative stability as crystallme TFE homopolymers [5]... 

Bismuth oeeurs mainly as bismite (a-Bi203), bismuthinite (Bi2S3) and bismutite [(Bi0)2C03] very oeeasionally it oeeurs native, in assoeiation with Pb, Ag or Co ores. The main eommereial souree of the element is as a byproduet from Pb/Zn and Cu plants, from whieh it is obtained by special processes dependent on the nature of the main product. Sulfide ores are roasted to the oxide and then reduced by iron or charcoal. Because of its low mp, very low solubiUty in Fe, and fairly high oxidative stability in air, Bi can be melted and cast (like Pb) in iron and steel vessels. Like Sb, the metal is too brittle to roll, draw, or extrude at room temperature, but above 225°C Bi can be worked quite well. 

Catalytic oxidation reactions in ionic liquids have been investigated only very recently. This is somewhat surprising in view of the well loiown oxidation stability of ionic liquids, from electrochemical studies [11], and the great commercial importance of oxidation reactions. Moreover, for oxidation reactions with oxygen, the nonvolatile nature of the ionic liquid is of real advantage for the safety of the reaction. While the application of volatile organic solvents may be restricted by the formation of explosive mixtures in the gas phase, this problem does not arise if a nonvolatile ionic liquid is used as the solvent. 

---