Siro Nagai

Surface structural change of alumina induced by electron impact in CO2, CO, O2 and D2O

Change of surface structure of alumina by electron impact in CO2, CO, O2 and D2O has been compared with that in ultra-high vacuum (UHV) using Auger electron spectroscopy (AES). Electron impact in CO2, O2 or D2O suppresses the formation of Al metal on the surface which proceeds in UHV while the impact in CO has no effect on the reduction from alumina to Al metal and produces aluminium carbide on the surface. Experiments on the reaction of the Al metal produced by electron beams with CO2 and CO showed that the observed effects due to CO2 and CO were caused by reaction of the produced Al metal with O atoms from CO2 and with C atoms from CO, respectively.

Effect of irradiation temperature on the radiolysis of methane

Abstract The G-values of most products increase with temperature in the radiolysis of methane in a flow-type experiment over the temperature range 50–280°C at atmospheric pressure. The apparent activation energies of most products are higher at higher temperature region above 150°C than those obtained below about 100°C. Irradiation at higher temperature favors the formation of olefins. The results are qualitatively understood on the basis of known nature and reactivity of free radicals.

Electron and Ar+ ion impact effects on SiO2, Al2O3 and MgO

Abstract Surface defects and secondary ion formation by electron and Ar+ ion impact on SiO2, A12O3 and MgO have been studied using a combined equipment of Auger electron spectroscopy and secondary ion mass spectrometry. Both electron impact and simultaneous impact with Ar+ ions and electrons produced reduced species on the surface of SiO2and A12O3, which were not stable in the vacuum conditions employed. The Ar+ ion impact desorption cross sections of water from SiO2 and A12O3 were obtained from time dependence of the currents of the hydrogenated secondary ions, SiOH+ and AlOH+, respectively, produced by simultaneous impact with Ar+ ions and electrons.

Radiolysis of methane containing small amounts of carbon monoxide—formation of organic acids

Electron beam irradiation of methane containing small amounts of carbon monoxide in a flow system at atmospheric pressure produced acetic and propionic acids in considerable yields. Propionic acid was formed in preference to acetic acid, especially at small molar ratios, [CO]/[CH4]. These acids were though to be formed via Koch-Haaf reactions CH3++CO→CH3CO+→H2OCH3COOH2+C2H5++CO→C2H5CO+→H2OC2H5COOH2+ The decrease in G(H2) observed by the addition of CO to methane was interpreted on the basis of the following reaction H+CO→k2HCO The estimated values of k2 were close to the reported value.

Radiation effects on COH2 gas mixture in the presence of silica gel

Abstract Electron beam irradiation of gas mixture of CO and H2 (1:6) in the presence of silica gel exclusively produces carbon dioxide and hydrocarbons in high yields. At the reaction temperature of 140°C, CO2 is preferentially produced, most of which are formed independently of hydrocarbons. The yields of hydrocarbons consisting predominantly of low molecular weight paraffins, obtained at 295°C, were higher by more than an order of magnitude than those by the homogeneous radiolysis and comparable to those by catalytic reactions over Fischer-Tropsch catalyst. Results obtained by irradiation of H2 over silica gel pre-irradiated under COHe gas stream indicate that secondary reactions between H2 and solid deposits produced from CO are responsible for the formation of hydrocarbons in the radiolysis of the COH2 mixture over silica gel.

Studies on the radiation-induced coloration mechanism of the cellulose triacetate film dosimeter

Abstract The species responsible for the coloration of the cellulose triacetate (CTA) film dosimeter have been studied using ultraviolet, electron spin resonance, infrared and gas chromatographic techniques. The post-irradiation change in the optical density at 280 nm indicates that the coloration occurs not only during irradiation ( in situ coloration) but also after irradiation (post-irradiation coloration) and that in situ coloration is due to unstable and stable components. The species responsible for the unstable component of in situ coloration are ascribed to the radicals produced from CTA molecules and those for the stable component to the radiolysis products from CTA and triphenyl phosphate contained in the dosimeter. On the other hand, post-irradiation coloration is attributed to the formation of carbonyl groups in CTA molecules, which is induced by reaction with NO 2 produced by irradiation of air.

Structure and decomposition of the carbonaceous solid produced on the surface of molecular sieve 5A by irradiation of methane

Abstract The structure and the behavior of decomposition of the carbonaceous solid which was formed on the surface of molecular sieve 5A by electron beam irradiation of methane at 300°C have been studied by Auger electron spectroscopy and X-ray powder diffraction, and have been examined using volatile product analyses during electron impact under an H2 atmosphere and during H+2 ion bombardment on the solid using a quadrupole mass filter. The carbon KLL Auger spectrum of the solid is similar to that of amorphous/graphitic carbon. The X-ray diffraction pattern of the solid did not give the diffraction peak corresponding to the interlayer spacing of the graphite crystal structure, indicating that the solid has an amorphous carbon structure. Both electron impact under an H2 atmosphere and H+2 ion bombardment on the solid near 50°C produced hydrocarbons such as methane and ethane, the yields of which all increased with increasing impact temperature, and raising the impact temperature to 200°C resulted in the formation of ethylene and propylene together with methane, ethane and propane. These results are compared with the results for graphite, and also are discussed in connection with the results obtained by the hydrogenolysis of a carbonaceous solid under electron beam irradiation.

Radiation effects on methane in the presence of molecular sieves

Product analysis has been carried out for the radiation-induced reaction of methane in the presence of molecular sieves (MS) 3A, 4A, 5A and 13X. Irradiation of methane over MS 4A selectively produces C2 hydrocarbons, while the use of MS 5A leads to C2 and C3 hydrocarbons. The selectivity and yields of these hydrocarbons, however, decrease with irradiation time, owing to deposition of carbonaceous solid produced from methane on the surface of the molecular sieves. The carbonaceous solid is decomposed to low-molecular-weight hydrocarbons when irradiated in an H2 atmosphere. Material balance estimated for the radiation-chemical reaction of argon containing 2 mol% methane over MS 5A reveals that the carbonaceous solid is highly abundant in carbon atoms. On the other hand, the formation of carbonanceous solids plays a less important role in the radiation-chemical reaction of methane in the presence of silica gel, which is found to exhibit greater activity for the formation of hydrocarbons than the molecular sieves.

Radiolysis of methane by electron beam irradiation over wide ranges of dose and dose rate

Abstract Radiolysis of methane has been carried out using electron beams in the dose range from 0.05 to 3 × 10 4 Mrad and dose rate range from 0.024 to 2.4 Mrad/s. The G -values of alkanes are almost independent of dose and dose rate except dose regions below 0.2 Mrad and above 5000 Mrad, while those of unsaturated hydrocarbons strongly depend on dose and dose rate.

Radiation-induced reactions of COH2 gas mixtures over various solid catalysts

Abstract Studies have been carried out of radiation-induced reactions of COH 2 gas mixtures in the presence of various solid catalysts in order to find possibilities of synthesizing organic raw materials from COH 2 by radiation for the future. The solid catalysts studied include Fischer-Tropsch catalyst (FeCu supported by diatomaceous earth), titania(TiO 2 ), and silica gel. Analysis of the reaction products over Fischer-Tropsch catalyst or semiconductors such as TiO 2 and ZnOCr 2 O 3 reveals that these solid catalysts do not sensitize the radiation chemical reaction of COH 2 but show the secondary effects on the reaction so as to induce the hydrogenation of olefins produced by the catalytic reaction and of aldehydes produced in gas phase by radiation. On the other hand, silica gel and other insulators such as alumina have been found to exhibit high catalytic activity in the formation of hydrocarbons from COH 2 under electron beam irradiation at 300°C. It has been shown experimentally that secondary reactions between H 2 and carbonaceous solid produced from CO make a substantial contribution to the formation of hydrocarbons from COH 2 over silica gel. In an attempt to find the role of silica gel in the reaction to produce hydrocarbons, radiation-induced reactions have been studied of H 2 with the carbonaceous solid that had been produced by irradiation of CO in the absence of solid catalyst, over TiO 2 , or over silica gel. The results indicate that silica gel not only enhances the yields of CO 2 and carbonaceous solid from CO but also promotes hydrogenation reactions of the carbonaceous solid under electron beam irradiation.