Kinetics of the oxidation of model toxicants during photolysis of nitrites and nitrates in an aqueous medium

Quantitative toxicology methods with the use of the enzymic activity of luminescent bacteria and the reproductive function of Tetrahymena pyriformis infusoria as test functions were employed to study the kinetics of the detoxication of model toxicants during photolysis of nitrite and nitrate. The model objects were the para-nitrosodimethylaniline (p-NDA) dye and a 2000-fold diluted solution of black liquor, which is formed during the sulfate boiling of cellulose. It was established that, irrespective of the wavelength of photolyzing UV radiation, be it 220 or 365 nm, the reactive product of NO ₂ ^? and NO ₃ ^? photolysis is the hydroxyl radical, which causes a symbatic decrease in the concentration of the toxicant and its toxicity. It was demonstrated that nitrite and nitrate ions can be used as initiators of free radicals during the destructive UV-light-induced purification of wastewater.     

Moderate micro-explosion during the combustion of iron wire in atmospheric air

The combustion of a thin iron wire in atmospheric air was investigated through the in-situ high-speed videography and the sampled product characterization. During the iron wire burning, a hot spherical ball was found to form at the wire tip and propagate with a speed of around 3.5 cm/s along the wire. Meanwhile, small bright droplets were randomly ejected from the burning ball. In fact, the burning spherical ball is hollow to be a ferric bubble according to the SEM image of sampled product. The high-speed videography further indicates that the small droplet ejection occurs largely owing to the bubble bursting, that is called the moderate micro-explosion to be different from the conventional micro-explosion process. For this bubble bursting process, the volume expansion rate inside the burning bubble needs not to be very fast but the bubble size should be adequate. If the bubble is too small (e.g. <50 μm), the droplet ejection during bubble bursting may be difficult to occur. Furthermore, the bubble formation is mainly attributed to the fact that carbon dissolved in iron can be preferentially oxidized to produce CO₂, which nucleates to generate a large bubble inside the ferric ball. It is noted that less than 0.05%wt of carbon content is enough for the bubble formation. It thereby suggests that carbon content should be accurately measured to predict the micro-explosion phenomena during iron combustion.     

XPS study of cadmium oxidation in air

The progressive oxidation of polycrystalline cadmium in air has been followed by XPS. In all the analyzed range of air exposures, two components have been observed in the O1s peak. The first one has been assigned to oxide, while the second one is probably due to hydroxide. Up to 5000 L air exposure, the two species are formed and grow simultaneously, with CdO as the main component.     

Rapid oxidation of InP nanoparticles in air

InP nanoparticles (NPs) in the size range of 1.5-3 nm were synthesized using colloidal chemistry methods. Exposure of these NPs to air resulted in rapid oxidation, as shown by transmission electron microscopy. Diffraction and spectroscopic measurements confirmed the formation of In₂O₃. Similar behavior was observed for commercial InP NPs, even when capped with a ZnS shell. Photoluminescence studies suggest that the oxidation occurs even while InP NPs are still dispersed in hexane, albeit at a much slower rate.     

Oxidation of iron within the scanning electron microscope: Oxide crystallite growth kinetics during the oxidation of iron in CO2

The growth of magnetite (Fe₃O₄) on a polycrystalline iron substrate has been continuously followed in situ in the S.E.M. at 500°C in 13.3 N m^?2 CO₂. Medium resolution (250 Å) micrographs of the same area have been taken at time intervals over periods of oxidation in excess of 200 hr. Successive layers of oxide crystallites grow according to the same logarithmic rate law, but the overall thickening rate of the oxide film conforms to the parabolic rate law. A theoretical analysis of this situation suggests that the dominant factor determining the overall growth kinetics is the frequency of oxide nucleation steps. It can be shown that the basic logarithmic growth of individual oxide crystallites could lead to a variety of overall growth processes, depending upon the conditions required for nucleation.     

Products of carbon disulfide oxidation in ionized air

Products of plasmochemical reactions proceeding in gas mixtures containing toxic CS₂ impurity were studied. The mixtures were excited by 180-and 300-keV electron pulses of duration 3 ns and 48 μs, respectively.     

Kinetics of isothermal nucleation in a supercooled iron melt

An isothermal kinetic diagram for the beginning of homogeneous nucleation is constructed using the molecular-dynamics model of an instantaneously supercooled iron melt near the icosahedral percolation transition temperature identified with the glass transition temperature T _g . This diagram is compared with the theoretical one calculated using quantitative information obtained by analyzing the kinetics of the initial stage of growth of supercritical nuclei at temperatures higher than T _g . A satisfactory coincidence of the theoretical curve with computer simulation data at temperatures higher than T _g and substantial disagreement with these data below T _g , where crystallization is necessarily preceded by the formation of an icosahedral percolation cluster, demonstrate the substantive influence of an icosahedral substructure on the nucleation rate predicted by the classical theory.     

On the early stages of oxidation of iron borides

Pure Fe₂B and FeB powders were compacted and oxidized for 1 h in flowing oxygen in the 300°–450°C temperature range. The reaction products were analyzed by X-ray diffraction, surface Mössbauer spectroscopy and scanning electron microscopy. Thermogravimetric analysis was carried out on powders treated under the same conditions. Iron borides undergo oxidation at low temperatures, with formation of both oxides and oxygen-free products.     

SEM-EDX study of the crystal structure of the condensed combustion products of the aluminum nanopowder burned in air under the different pressures

The experimental results of combustion of aluminum nanopowder (ANP) in air and AlN crystals formation process were studied. The air pressure during the combustion process significantly affected the crystals growth mechanism. Crystals with the different morphology (whiskers, hexagonal crystals, rods) were found in the condensed combustion products.     

Kinetics of the thermal oxidation of Fe(2+) in talc

The thermally induced oxidation of Fe²⁺ in talc has been investigated by Mössbauer spectroscopy. The heating temperature range of the samples was from 600°C to 750°C with variable times of treatment going from 6 hours up to 192 hours. The obtained isothermals could be well fitted by a first order kinetic model. The activation energy deduced from an Arrhenius plot is 178 kJ/mol.     

双热源空调-热水器一体机冬季制热的实验研究

冬季室外温度低时,空气源热泵系统的蒸发器会结霜,使系统COP降低。所设计的空调-热水器一体机可以制冷、制热、一年四季提供生活用热水。冬季室外温度低时,用太阳能加热后的水作为热泵的低温热源,可以提高热泵的效率。分别用空气源蒸发器和水源蒸发器独立工作使系统给房间制热,实验结果发现水源蒸发器工作时系统的COP平均值为3.56,空气源蒸发器工作时的COP平均值为2.51。     

Characteristics of gas heating in a transverse discharge in air flow

The thermal instability of discharge plasma in air is analyzed. The contributions of specific mechanisms of instability are examined, including VT relaxation, the increase in the fractional energy dissipation via rapid heating due to an increase in reduced field strength, and ionization thermal instability. The effects of acoustic wave generation caused by heating and of charged particle motion relative to the neutral gas on both the length scale and the growth rate of unstable fluctuations are taken into account.     

Kinetics of CW laser-induced crystallization and oxidation of thin,Sb, Se,and Sb2Se3 films in air

Thin films of Sb, Se and Sb₂Se₃ are deposited onto glass and irradiated by a cw-Ar⁺ laser beam. The kinetics of crystallization and oxidation are traced via the time dependence of optical reflectivity and temperature, T, of the irradiated zone. For Sb₂Se₃, transformations start abruptly when T attains a critical value, T _c, independently of the laser beam power. These T _c values are comparable to the ones observed under furnace annealing conditions.     

Thermal oxidation induced during laser cleaning of an aluminium-magnesium alloy

During laser cleaning of metallic materials by pulsed lasers surface, modifications can be induced mainly by the transient thermal effect. In ambient conditions an oxidation of the cleaned surface can be detected. The aim of this work was to characterize this transient oxidation that can occur below the laser energy domain leading to any phase change (melting, ablation) of the cleaned substrate.A Q-switched Nd:YAG laser with pulse duration of 10 ns and wavelength of 1064 nm was used for the purposes of this study. For the surface analysis of the treated samples X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) were used.It was found that thermal oxidation took place on the aluminium-magnesium alloy during the irradiation in air with a laser energy ranged from 0.6 to 1.4 J cm^-2. It has been demonstrated that this thermal oxidation had the same mechanism as in the case of the steady state thermal oxidation of the aluminium-magnesium alloys even though the laser irradiation was applied only for the very short time of 10 ns. When the laser energy reached the value of 1 J cm^-2, the oxide formed by the thermal oxidation became in a large extent crystalline and its outer part was entirely covered by a continuous layer of magnesium oxide. PACS 61.82.Bg; 81.65.Mq; 61.80.Ba     

Controlled oxidation of iron nanoparticles in chemical vapour synthesis

Enteric-coated formulations can delay the release of drugs until they have passed through the stomach. However, high concentration of drugs caused by rapidly released in the small intestine leads to the intestinal damage, and frequent administration would increase the probability of missing medication and reduce the patient compliance. To solve the above-mentioned problems, aspirin-loaded enteric-coated sustained-release nanoparticles with core–shell structure were prepared via one-step method using coaxial electrospray in this study. Eudragit L100-55 as pH-sensitive polymer and Eudragit RS as sustained-release polymer were used for the outer coating and inner core of the nanoparticles, respectively. The maximum loading capacity of nanoparticles was 23.66 % by changing the flow rate ratio of outer/inner solutions, and the entrapment efficiency was nearly 100 %. Nanoparticles with core–shell structure were observed via fluorescence microscope and transmission electron microscope. And pH-sensitive and sustained drug release profiles were observed in the media with different pH values (1.2 and 6.8). In addition, mild cytotoxicity in vitro was detected, and the nanoparticles could be taken up by Caco-2 cells within 1.0 h in cellular uptake study. These results indicate that prepared enteric-coated sustained-release nanoparticles would be a more safety and effective carrier for oral drug delivery.     

The mechanism of the oxidation and passivation of iron by water vapour—an electron spectroscopic study

The interaction of water vapour with ‘clean’ iron surfaces at 290 K has been studied by X-ray photoelectron spectroscopy. Two distinct O(1s) pe     

Core and valence level photoemission studies of iron oxide surfaces and the oxidation of iron

The core and valence level XPS spectra of Fe_xO (x ~ 0.90–0.95); Fe₂O₃ (α and γ); Fe₃O₄; and FeOOH have been studied under a variety of sample surface conditions. The oxides may be characterized by a combination of valence level differences and core-level effects (chemical shifts, multiplet splittings, and shake-up structure). Fe^II and Fe^III states are distinguishable, but octahedral and tetrahedral sites are not. The O 1 s BE cannot be used to distinghuish between the oxides since it has a nearly constant value. Fe 3d valence level structure spreads some 10 eV below E_F, much broader than suggested by previous UPS and photoelectron-spin-polarization (ESP) measurements for Fe_xO and Fe₃O₄. Fe surfaces (films, foils, (100) face) yield predominantly Fe^III species when exposed to high exposures of oxygen or air, though there is evidence for some Fe^II also. At low exposures the Fe^II/Fe^III ratio increases.     

电加热融霜在冷风机融霜过程的优化

冷风机在低温工作环境下运行时的结霜是不可避免的问题。文中进行了电加热融霜实验,分析电加热元件的排布,合理选择电加热器的功率,使冷风机在经济运行成本的情况下,获得最优的制冷效果。