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Automotive and Diesel Crankcase Lubricants
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
These additives control the oxygen-initiated degradation of the lubricant limited by the aging of the lubricant base oil. As lubricant aging advances, its viscosity begins to rise significantly and acidic oxidation products are formed. Antioxidants belong to three general classes: hydroperoxide decomposers, free radical scavengers, and metal deactivators. Hydroperoxide decomposers promote the decomposition of the hydroperoxides either to harmless materials or to free radicals. Common additives of this class include organo-sulfur and organophosphorus compounds.Free radical scavengers remove the free radicals that are primarily responsible for the oxidation chain reaction. Common additives of this class are zinc dialkyldithiophosphates (ZDTPs), hindered phenols, and alkylated aryl amines.Metal deactivators complex with metallic cations, which are oxidation catalysts, and make them inactive. Polyfunctional compounds, such as ethylenediaminetetraacetic acid (EDTA) and salicylaldoxime are often used in this capacity.
Degradation and Stabilization Issues of Polyethylene in Open air Applications
Published in A. K. Haghi, Ana Cristina Faria Ribeiro, Lionello Pogliani, Devrim Balköse, Francisco Torrens, Omari V. Mukbaniani, Applied Chemistry and Chemical Engineering, 2017
Güneş Boru Izmirli, Sevgi Ulutan, Pinar Tüzüm DEMIR
The UV stabilizers can be classified according to their chemical structure such as derivatives of 2-hydroxybenzophenone, esters of aromatic acids and aromatic alcohols and hydroxyphenyl benzotriazoles, substituted acrylonitriles, metallic complexes based on nickel and cobalt and inorganic pigments. Stabilizers are commonly defined with their protection mechanism as the primary antioxidants, which trap free radicals, and secondary antioxidants which decompose hydroperoxides into more stable molecules. The stabilizers mainly belong to four main groups: Hindered phenol, phosphites, thiosynergists, and HALS.13 As the CB is considered, its UV stabilizing ability is associated with both the UV absorbing capacity of CB and photo-generated ketonic species present on particles. It can be tolerated in some formulations where color is not a criterion. The pigment not only absorbs light, it is reactive with those free-radical species that might be formed.14
Environmental Oxidations
Published in Richard A. Larson, Eric J. Weber, Reaction Mechanisms in Environmental Organic Chemistry, 2018
Richard A. Larson, Eric J. Weber
Hydroperoxides are normally unstable to thermal or photochemical decomposition and often decompose to provide additional radical species. One such example is ultraviolet-induced homolysis of the O–O bond: () AOOH→hvAO·+·OH
Self-hardening thermoplastic foam for the inhibition of coal oxidation at low temperatures
Published in Combustion Science and Technology, 2019
Zhilin Xi, Xiaodong Wang, Xiaoli Wang, Li Wang, Ding Li, Xiangyu Guo, Liwei Jin
First, the activation energy and release of heat in Equation (1) are 0 and 140.35 kJ/mol, respectively, and in Equation (2) are 20.42 and 6.04 kJ/mol, respectively. Due to the activation energies of the two reactions both being less than 40 kJ/mol, the reactions spontaneously proceed at ambient temperature. Second, carbon radicals react with oxygen in only one step to form peroxides with a ~140.35 kJ/mol release of heat. The released heat can provide energy for other reactions, causing further coal oxidation. Third, the peroxides, where a portion decomposes to produce hydroxyl radicals and a portion interacts with hydrocarbons to generate hydroperoxides. In the coal oxidation process, hydroperoxides, which are considered as the first intermediate product, are always produced in the hydrocarbon oxidation process (Kudynska and Buckmaster, 1996). Forth, the methyne produces hydroxyl and carbon radicals in the oxidation process. The hydroxyl radical is one of the most active and it consumes R-H, R-C(=O)-OH, R-CH2-OH and R-C(=O)-H to produce carbon radicals, which, in turn, react with oxygen to form peroxides. Thus, the hydroxyl radical is considered as the chain carrier to form a cyclic chain reaction. Many researchers have shown that a rapid temperature increase occurs at 70°C in coal oxidation (Beamish, 2005; Beamish et al., 2001), which is also the temperature for forming a cyclic chain reaction. Therefore, it is crucial to seal coal body pores from oxygen ingress, expel heat generated by carbon free radicals reacting with oxygen and consume the active sites for inhibit coal self-oxidation.
Photoelectron angular distributions in photodetachment from polarised d-like states: the case of HO2 −
Published in Molecular Physics, 2021
Christopher C. Blackstone, Adam A. Wallace, Andrei Sanov
The hydroperoxide anion is readily produced through the deprotonation of hydrogen peroxide. This anion drives the solution-phase decomposition of ozone and production of OH radicals through the peroxone process, used, incidentally, as a means of disinfecting drinking water [14,15]. This chemistry and its application to new industrial processes were the subject of recent investigations [14,15]. Analogous processes may be possible in the atmosphere, as well, though their direct evidence is less abundant. Direct investigations of the hydroperoxide anion in the gas phase are therefore of crucial interest to understanding its chemistry in the atmosphere.