One-dimensional analytical model for oxide thin film growth on Ti metal layers during laser heating in air

This paper presents the theoretical and experimental results for oxide thin film growth on titanium films previously deposited over glass substrate. Ti films of thickness 0.1 μm were heated by Nd:YAG laser pulses in air. The oxide tracks were created by moving the samples with a constant speed of 2 mm/s, under the laser action. The micro-topographic analysis of the tracks was performed by a microprofiler. The results taken along a straight line perpendicular to the track axis revealed a Gaussian profile that closely matches the laser's spatial mode profile, indicating the effectiveness of the surface temperature gradient on the film's growth process. The sample's micro-Raman spectra showed two strong bands at 447 and 612 cm -1 associated with the TiO 2 structure. This is a strong indication that thermo-oxidation reactions took place at the Ti film surface that reached an estimated temperature of 1160 K just due to the action of the first pulse. The results obtained from the numerical integration of the analytical equation which describes the oxidation rate (Wagner equation) are in agreement with the experimental data for film thickness in the high laser intensity region. This shows the partial accuracy of the one-dimensional model adopted for describing the film growth rate. © 2001 Elsevier Science B.V.

Tocopherol content and fatty acid profile in soybean oil supplemented with salvia extract (Salvia officinalis L.) during heating

This paper aimed to assess the tocopherol content and evaluate the fatty acid profile in soybean oil supplemented with salvia extract during heating, so as to verify the isolated and synergistic effect of natural and synthetic antioxidants. In order to obtain the extract, the lyophilized and crushed salvia was subjected to extraction by ethyl alcohol for 30 min, with a 1:20 salvia:ethyl alcohol ratio, under continuous agitation. Afterwards, the mixture was filtered and the supernatant was subjected to the rotary evaporator at 40 °C. Later the control treatments, ES (3000 mg kg-1 salvia extract), TBHQ (50 mg kg-1), and mixture (ES+50 mg kg-1 TBHQ) were prepared and subjected to 180 °C for 20 h. Samples were taken in time intervals 0, 10, and 20 h and analysed in terms of tocopherol content and fatty acid profile. Regarding the tocopherol and fatty acid profile analysis, it was found that the extract proved efficient in oil protection, when added isolated to soybean oil subjected to thermo oxidation. According to the results, salvia extract is a viable alternative that might be applied in industrialized processing of oils as natural antioxidant.

Effect of the processing conditions on the microstructure and properties of rotational molded polyamide 11

Rotomolded containers for solvents and hydrocarbons require the use of high-permeability resins such as polyamide (PA). The published studies with this material are very scarce. In this work, a commercial grade of PA11 was rotational-molded using different processing temperatures and characterized with a range of techniques. The study aims at investigating the influence of the processing conditions on the microstructure and properties of molded parts. The results showed that the spherulitic morphology and the mechanical properties are affected by the processing temperature, the optimum processing range being between 220°C and 240°C. Overheating causes a decrease of the impact strength and a severe increase in the formation of pinholes at the outer surface due to polymer degradation and formation of volatile products. The thermo-oxidation reactions occurring at the inner surface of the samples result in the formation of products that absorb in the UV and visible light regions and cause the microhardness and the melt viscosity of the material to increase. The extent and severity of the degradation at the inner surface may be easily assessed by fluorescence microscopy. © 2008 Wiley Periodicals, Inc.

Thermal degradation studies on Edible Oil during Deep Fat Frying Process

Deep fat frying process is one of the widely followed cooking practices throughout the world. Cooking oils serve as a medium for frying food for transferring heat and makes fried food tasty and palatable. Frying process is a most complex process involving numerous physicochemical changes which are complicated to understand. Frying leads to thermal degradation of oil through thermo-oxidation, hydrolysis, and polymerization. Hydrolysis results in formation of free fatty acids whereas oxidation process produces hydroperoxides and small molecular carbonyl compounds. This whole process leads to the formation of polar compounds and degradation of antioxidants that further degrades frying oil. Eventually, through mass transfer process these degradation products accumulate into fried food and reduce the nutritional quality of both oil and food. Thus, the frying process is of research interest calls for detailed systematic study which is chosen for the present study. The primary objective of this study is to understand the mechanism of degradation and characterization ofdegraded products which helps in arriving at the limits for frying oil utilization in terms of number of frying cycles. The mechanistic studies and the knowledge on the degraded products help to understand the way to retard the deterioration of oil for stability and enhancement of frying cycles. The study also explores the formation of the predominant polar compounds and their structural elucidation through mass spectrometry. Oxidation of oil is another important factor that ignites the degradation phenomena. One of the best ways to increase thermal stability of any oil is addition of potent antioxidants. But, most of the natural and synthetic antioxidants are unstable and ineffective at frying temperatures. Therefore, it is necessary to screen alternative antioxidants for their activity in the refined oils which are devoid of any added antioxidants. In this context, this study discussed the efficacy of several natural and synthetic antioxidants to retard the formation of polar compounds and thermooxidation during prolonged frying conditions. Similarly, the advantage of blending of two different oils to improve the thermal stability was explored. The present study brings out the total picture on the type of degradation products formed during frying and the ways of retarding the determination to improve upon the stability of the oil and enhancement of frying cycles.

Aqueous peroxyl radical exposure to THP-1 cells causes glutathione loss followed by protein oxidation and cell death without increased caspase-3 activity

Protein oxidation within cells exposed to oxidative free radicals has been reported to occur in an uninhibited manner with both hydroxyl and peroxyl radicals. In contrast, THP-1 cells exposed to peroxyl radicals (ROO center dot) generated by thermo decomposition of the azo compound AAPH showed a distinct lag phase of at least 6 h, during which time no protein oxidation or cell death was observed. Glutathione appears to be the source of the lag phase as cellular levels were observed to rapidly decrease during this period. Removal of glutathione with buthionine sulfoxamine eliminated the lag phase. At the end of the lag phase there was a rapid loss of cellular MTT reducing activity and the appearance of large numbers of propidium iodide/annexin-V staining necrotic cells with only 10% of the cells appearing apoptotic (annexin-V staining only). Cytochrome c was released into the cytoplasm after 12 h of incubation but no increase in caspase-3 activity was found at any time points. We propose that the rapid loss of glutathione caused by the AAPH peroxyl radicals resulted in the loss of caspase activity and the initiation of protein oxidation. The lack of caspase-3 activity appears to have caused the cells to undergo necrosis in response to protein oxidation and other cellular damage. (c) 2007 Elsevier B.V. All rights reserved.

The oxidation behaviour of sintered iron

The oxidation behaviour of porous, sintered iron was studied by thermo-gravimetric analysis (TGA), at temperatures between 300oC and 700oC, in a flowing atmosphere of 20% O2/80% N2. Samples for TGA tests were compacted from pure iron powder, at 150MPa to 550MPa, and vacuum sintered at 1120oC. The mass gain of samples during oxidation was recorded continuously for a period of 24 hours. It was found that the oxidation mass gain of PM samples depended on the permeability of the pore structure and the temperature. At low temperatures, the oxidising gas was able to permeate through the pore structure, causing the oxidation of a large active surface area. At high temperatures the active surface area was smaller, because oxygen diffusing into the pore structure, from the external atmosphere, was adsorbed by pore surfaces close to the external surface of the compact. Although the weight of the external oxide scale on compacts increased with increasing oxidation temperature, the absence of oxide in the core porosity in compacts oxidised at higher temperatures resulted in smaller mass gains than were observed for compacts oxidised at lower temperatures. The heat generated by the oxidation of the large active surface areas of porous samples was studied by thermo-calorimetric analysis (TCA). It was determined that this phenomenon could raise the core temperature of samples significantly above the ambient furnace temperature, and affecting the morphology of the oxide scale formed. The effects (on oxidation behaviour at 500oC) of small, elemental alloy additions of Al, Cu, P and Si to pure iron powder were studied. It was found that elements that promote pore rounding during sintering caused a significant reduction in the mass gain rate of the PM alloys, compared to the PM pure iron. The oxidation resistance due to these elements prevented pore closure by oxide growth, so that the active surface area of these PM alloys remained high. The PM alloys were also studied by thermo-mechanical analysis (TMA, dilatometry), to determine their dimensional stability during sintering and subsequent elevated temperature service. The oxidation experiment was augmented with optical and electron microscopy, and X-ray analysis of alloy and scale compositions.

Metallocene ethylene-1-octene copolymers:effect of extrusion conditions on thermal oxidation of polymers with different comonomer content

Metallocene ethylene-1-octene copolymers having different densities and comonomer content ranging from 11 to 36 wt% (m-LLDPE), and a Ziegler copolymer (z-LLDPE) containing the same level of short-chain branching (SCB) corresponding to one of the m-LLDPE polymers, were subjected to extrusion. The effects of temperature (210-285 °C) and multi-pass extrusions (up to five passes) on the rheological and structural characteristics of these polymers were investigated using melt index and capillary rheometry, along with spectroscopic characterisation of the evolution of various products by FTIR, C-NMR and colour measurements. The aim is to develop a better understanding of the effects of processing variables on the structure and thermal degradation of these polymers. Results from rheology show that both extrusion temperature and the amount of comonomer have a significant influence on the polymer melt thermo-oxidative behaviour. At low to intermediate processing temperatures, all m-LLDPE polymers exhibited similar behaviour with crosslinking reactions dominating their thermal oxidation. By contrast, at higher processing temperatures, the behaviour of the metallocene polymers changed depending on the level of comonomer content: higher SCB gave rise to predominantly chain scission reactions whereas polymers with lower level of SCB continued to be dominated by crosslinking. This temperature dependence was attributed to changes in the different evolution of carbonyl and unsaturated compounds including vinyl, vinylidene and trans-vinylene. © 2007 Elsevier Ltd. All rights reserved.

Metallocene ethylene-1-octene copolymers:influence of comonomer content on thermo-mechanical, rheological, and thermo-oxidative behaviours before and after melt processing in an internal mixer

The influence of the comonomer content in a series of metallocene-based ethylene-1-octene copolymers (m-LLDPE) on thermo-mechanical, rheological, and thermo-oxidative behaviours during melt processing were examined using a range of characterisation techniques. The amount of branching was calculated from 13C NMR and studies using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were employed to determine the effect of short chain branching (SCB, comonomer content) on thermal and mechanical characteristics of the polymer. The effect of melt processing at different temperatures on the thermo-oxidative behaviour of the polymers was investigated by examining the changes in rheological properties, using both melt flow and capillary rheometry, and the evolution of oxidation products during processing using infrared spectroscopy. The results show that the comonomer content and catalyst type greatly affect thermal, mechanical and oxidative behaviour of the polymers. For the metallocene polymer series, it was shown from both DSC and DMA that (i) crystallinity and melting temperatures decreased linearly with comonomer content, (ii) the intensity of the ß-transition increased, and (iii) the position of the tan δmax peak corresponding to the a-transition shifted to lower temperatures, with higher comonomer content. In contrast, a corresponding Ziegler polymer containing the same level of SCB as in one of the m-LLDPE polymers, showed different characteristics due to its more heterogeneous nature: higher elongational viscosity, and a double melting peak with broader intensity that occurred at higher temperature (from DSC endotherm) indicating a much broader short chain branch distribution. The thermo-oxidative behaviour of the polymers after melt processing was similarly influenced by the comonomer content. Rheological characteristics and changes in concentrations of carbonyl and the different unsaturated groups, particularly vinyl, vinylidene and trans-vinylene, during processing of m-LLDPE polymers, showed that polymers with lower levels of SCB gave rise to predominantly crosslinking reactions at all processing temperatures. By contrast, chain scission reactions at higher processing temperatures became more favoured in the higher comonomer-containing polymers. Compared to its metallocene analogue, the Ziegler polymer showed a much higher degree of crosslinking at all temperatures because of the high levels of vinyl unsaturation initially present.

The influence of surface functionalization of activated carbon on palladium dispersion and catalytic activity in hydrogen oxidation

Stone-fruit activated carbon (SAC) and modified versions containing acidic oxygen and basic nitrogen groups have been used to prepare palladium catalysts by wet impregnation. Carbon supports and catalysts are investigated by thermo-gravimetric analysis, TPD, oxygen chemisorption, TEM and XPS. The influence of the nature of the functional groups on the dispersion and oxidation state of palladium and its activity in hydrogen oxidation is investigated. Pd dispersion is found to increase with the basic strength of functional groups on the support. XPS reveals that introduction of amine groups in SAC results in an increased proportion of Pd0, resistant to re-oxidation. Palladium catalysts supported on activated carbon modified by diethylamine groups are found to exhibit the highest metal dispersion and greatest activity in hydrogen oxidation. © 2007 Elsevier B.V. All rights reserved.

Thermo-oxidative stabilization of poly(lactic acid) with antioxidant intercalated layered double hydroxides

Two antioxidant modified layered double hydroxides (AO-LDHs) were successfully prepared by theintercalation of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (IrganoxCOOH) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) in the layered structure of LDH. It was foundthat by anchoring the phenolic moieties to the LDH layers the antioxidant power is retained in the caseof Trolox, and even amplified in the case of IrganoxCOOH. A small amount of the two AO-LDHs wasincorporated into poly(lactic acid), PLA, by solution mixing and melt extrusion. The thermo-oxidativestability of the composites was compared with that of the neat PLA and PLA containing free AOs. SECanalysis indicates that, after a controlled period of ageing, both the AO-LDHs protect the PLA fromchain scission. The oxidation induction time (OIT, DSC) at 230 °C shows also the beneficial effects ofthe presence of the functional filler in the polymer matrix. Further, results from a preliminary migrationtest suggest that the AO species have a low tendency to migrate away from the AO-LDHs embedded inthe polymer matrix thus keeping the AO protected inside the nanofiller layers thereby remaining activefor a longer time.

Electrochemical Oxidation Of Landfill Leachate In A Flow Reactor: Optimization Using Response Surface Methodology.

Response surface methodology based on Box-Behnken (BBD) design was successfully applied to the optimization in the operating conditions of the electrochemical oxidation of sanitary landfill leachate aimed for making this method feasible for scale up. Landfill leachate was treated in continuous batch-recirculation system, where a dimensional stable anode (DSA(©)) coated with Ti/TiO2 and RuO2 film oxide were used. The effects of three variables, current density (milliampere per square centimeter), time of treatment (minutes), and supporting electrolyte dosage (moles per liter) upon the total organic carbon removal were evaluated. Optimized conditions were obtained for the highest desirability at 244.11 mA/cm(2), 41.78 min, and 0.07 mol/L of NaCl and 242.84 mA/cm(2), 37.07 min, and 0.07 mol/L of Na2SO4. Under the optimal conditions, 54.99 % of chemical oxygen demand (COD) and 71.07 ammonia nitrogen (NH3-N) removal was achieved with NaCl and 45.50 of COD and 62.13 NH3-N with Na2SO4. A new kinetic model predicted obtained from the relation between BBD and the kinetic model was suggested.

Myoglobins: the link between discoloration and lipid oxidation in muscle and meat

Aerobic metabolism changes rapidly to glycolysis post-mortem resulting in a pH-decrease during the transformation of muscle in to meat affecting ligand binding and redox potential of the heme iron in myoglobin, the meat pigment. The inorganic chemistry of meat involves (i) redox-cycling between iron(II), iron(III), and iron(IV)/protein radicals; (ii) ligand exchange processes; and (iii) spin-equilibra with a change in coordination number for the heme iron. In addition to the function of myoglobin for oxygen storage, new physiological roles of myoglobin are currently being discovered, which notably find close parallels in the processes in fresh meat and nitrite-cured meat products. Myoglobin may be characterized as a bioreactor for small molecules like O2, NO, CO, CO2, H2O, and HNO with importance in bio-regulation and in protection against oxidative stress in vivo otherwise affecting lipids in membranes. Many of these processes may be recognised as colour changes in fresh meat and cured meat products under different atmospheric conditions, and could also be instructive for teaching purposes.

Screening process for activity determination of conductive oxide electrodes for organic oxidation

A modified method for the calculation of the normalized faradaic charge (q fN) is proposed. The method involves the simulation of an oxidation process, by cyclic voltammetry, by employing potentials in the oxygen evolution reaction region. The method is applicable to organic species whose oxidation is not manifested by a defined oxidation peak at conductive oxide electrodes. The variation of q fN for electrodes of nominal composition Ti/RuX Sn1-X O2 (x = 0.3, 0.2 and 0.1), Ti/Ir0.3Ti0.7O2 and Ti/Ru0.3Ti0.7O2 in the presence of various concentrations of formaldehyde was analyzed. It was observed that electrodes containing SnO2 are the most active for formaldehyde oxidation. Subsequently, in order to test the validity of the proposed model, galvanostatic electrolyses (40 mA cm-2) of two different formaldehyde concentrations (0.10 and 0.01 mol dm-3) were performed. The results are in agreement with the proposed model and indicate that this new method can be used to determine the relative activity of conductive oxide electrodes. In agreement with previous studies, it can be concluded that not only the nature of the electrode material, but also the organic species in solution and its concentration are important factors to be considered in the oxidation of organic compounds.

Effect of temperature on the electro-oxidation of ethanol on platinum

We present in this work an experimental investigation of the effect of temperature (from 25 to 180 ºC) in the electro-oxidation of ethanol on platinum in two different phosphoric acid concentrations. We observed that the onset potential for ethanol electro-oxidation shifts to lower values and the reaction rates increase as temperature is increased for both electrolytes. The results were rationalized in terms of the effect of temperature on the adsorption of reaction intermediates, poisons, and anions. The formation of oxygenated species at high potentials, mainly in the more diluted electrolyte, also contributes to increase the electro-oxidation reaction rate.

Electrocatalytic oxidation of methanol by the [Ru3O(OAc)6(py)2(CH3OH)]3+cluster: improving the metal-ligand electron transfer by accessing the higher oxidation states of a multicentered system

The [Ru3O(Ac)6(py)2(CH3OH)]+ cluster provides an effective electrocatalytic species for the oxidation of methanol under mild conditions. This complex exhibits characteristic electrochemical waves at -1.02, 0.15 and 1.18 V, associated with the Ru3III,II,II/Ru3III,III,II/Ru 3III,III,III /Ru3IV,III,III successive redox couples, respectively. Above 1.7 V, formation of two RuIV centers enhances the 2-electron oxidation of the methanol ligand yielding formaldehyde, in agreement with the theoretical evolution of the HOMO levels as a function of the oxidation states. This work illustrates an important strategy to improve the efficiency of the oxidation catalysis, by using a multicentered redox catalyst and accessing its multiple higher oxidation states.