The adsorption and decomposition of methanol on tungsten. II

A clean tungsten filament adsorbs methanol rapidly at room temperature, the initial sticking probability being 0.8. At saturation, the composition of the adsorbed layer is roughly CO:H = 1:1 and it is suggested that the hydrogen may be in the form of a surface complex. The continuous decomposition of methanol by the hot filament under steady-state conditions, or when the filament had been previously oxygenated, followed a different course from that previously reported for the newly-cleaned filament. Rather than a rapid rise in the rate of decomposition (to CO + H₂) for 600 < T_fil < 1300 K to a high plateau above 1300 K, decompositon to formaldehyde, carbon monoxide and methane was observed. The rates at which these products appeared passed through low maxima between 900 and 1100 K. The change in the relative importance of formaldehyde and carbon monoxide production with filament temperature within this range is attributed to a temperature-dependent life-time of formaldehyde molecules on the oxygenated surface. At the highest temperature (> 1500 K) the reactivity increased rapidly to join that of the clean surface, probably due to the desorption of surface oxygen.     

Properties of the incandescent light emitted fromdouble-walled carbon nanotube filament

We have studied the radiation of a double-walled carbon nanotube (DWNT) filament with a length of 4.5\,mm and a diameter of 10\,$\mu$m by applying an electric current through the filament. The DWNT filament starts emitting incandescent light at voltage $U=6$\,V. Emission spectra of the DWNT below temperature 1250\,K can well be fitted to those of the blackbody radiation. The intensity of the incandescent light shows an exponential dependence on the voltage applied on the DWNT filaments. The resistance of the DWNT filaments is very stable at high temperatures between 900 and 1250\,K during the emission of light in the experiments.     

Oxygen and carbon monoxide isotope exchange reactions on rhenium

The catalytic efficiency, E, of rhenium at high temperatures for the equilibration of a mixture of carbon monoxide isotopes (¹²C¹⁸O + ¹³C¹⁶O) is reduced by pre-adsorbed oxygen; E at 1300 K declines linearly to zero at an oxygen uptake of about 5 × 10¹⁴ atoms cm^?2. The replacement of one pre-adsorbed carbon monoxide isotope by another can be correlated with the characteristic desorption temperatures of the two main states (α and β) of CO on Re. The observation that a considerable fraction of CO is non-replaceable at filament temperatures below 700 K suggests a high activation energy for migration of some adsorbed CO. The probability of exchange of ¹⁶O between an oxygenated rhenium filament and gaseous ¹²C¹⁸O for oxygen coverages ?4 × 10¹⁴ O atoms cm^?2 is 0.012 per 10¹⁴ O atoms cm^?2 per collision with the filament at 900 K. The surface reaction $\text{Re-}{}^{16}\text{O +}{}^{12}\text{C}{}^{18}\text{O}{}_{\mathrm{(g)}}\text{= Re-}{}^{18}\text{O +}{}^{12}\text{C}{}^{16}\text{O}{}_{\mathrm{(g)}}$ is completely reversible. However, in the presence of nitrous oxide no reaction is observed until the filament temperature exceeds 1600 K, when continuous decomposition of N₂O is appreciable. Possible transition states for isotope exchange are discussed.     

Adsorption and decomposition of triethylsilane on Si(1 0 0)

The adsorption and decomposition of triethylsilane (TES) on Si(1 0 0) were studied using temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), electron stimulated desorption (ESD), and X-ray photoelectron spectroscopy (XPS). TPD and HREELS data indicate that carbon is thermally removed from the TES-dosed Si(1 0 0) surface via a β-hydride elimination process. At high exposures, TPD data shows the presence of physisorbed TES on the surface. These species are characterized by desorption of TES fragments at 160 K. Non-thermal decomposition of TES was studied at 100 K by irradiating the surface with 600 eV electrons. ESD of mass 27 strongly suggests that a β-hydride elimination process is a channel for non-thermal desorption of ethylene. TPD data indicated that electron irradiation of physisorbed TES species resulted in decomposition of the parent molecule and deposition of methyl groups on the surface that desorbed thermally at about 900 K. Without electron irradiation, mass 15 was not detected in the TPD spectra, indicating that the production of methyl groups in the TPD spectra was a direct result of electron irradiation. XPS data also showed that following electron irradiation of TES adsorbed on Si(1 0 0), carbon was deposited on the surface and could not be removed thermally.     

Experimental study on electrostatic removal of high-carbon particle in high temperature coal pyrolysis gas

A high-temperature electrostatic precipitator (ESP) presents a good solution for hot gas cleaning, which can remove fly ash from pyrolysis gas at temperatures higher than the tar dew point. In this paper, the characteristics of negative DC corona discharge in air and simulated coal pyrolysis gas were studied. The removal of coal pyrolysis furnace fly ash (ash A) was investigated and compared with that of coal-fired power plant fly ash (ash B) in ESP with a temperature ranging from 300?K to 900?K. The current density of simulated gas was higher than that of air under the same discharge voltage and at different temperatures. The simulated gas also had a higher spark voltage and a lower onset voltage compared with air. The fractional collection efficiency of ash A was lower for particles with diameters of larger than 0.1?µm at high temperature, compared with ash B. A lower collection efficiency in simulated gas was obtained for particles with diameters of less than 0.1?µm compared with air. The collection efficiency of submicron particles in simulated gas was usually higher than it in air, especially for particles with diameters of less than 0.04?µm. In simulated gas, the overall collection efficiency of ash A was obviously lower than that of ash B, especially at high temperature. From 300?K to 700?K, the collection efficiencies of both ash samples were as high as above 93%, but the collection efficiency of ash A in simulated gas decreased to 78.7% at 900?K.     

Fluorescence spectroscopy of 1,2,4-trimethylbenzene at high temperatures and pressures: application to temperature measurements

Fluorescence of the S₁→S₀ transition of 1,2,4-trimethylbenzene vapour after laser excitation at 266 nm was investigated in a heated cell. Experiments were performed for temperature between 350 and 900 K, at pressure between 0.1 and 3.0 MPa and for oxygen molar fraction between 0 and 21%. The absorption cross section was found to reduce by about 20% between 350 and 900 K. 1,2,4-trimethylbenzene fluorescence exponentially decreased by three orders of magnitude as temperature increased. A similar behaviour was observed with pressure, although fluorescence reduced only by a factor of 2.5 between 0.1 and 3.0 MPa. Additionally, Stern–Volmer plots were found to be linear for temperatures between 450 and 750 K. Using the dependence of 1,2,4-trimethylbenzene fluorescence on temperature, potential use of this molecule for temperature measurements in turbulent flows is suggested.     

In-situ study on thermal decomposition of 1,3-disilabutane to silicon carbide on Si(1 0 0) surface

The intermediates of thermal decomposition of 1,3-disilabutane (SiH₃CH₂SiH₂CH₃, DSB) to form SiC on Si(1 0 0) surface were in situ investigated by reactive ion scattering (RIS), temperature programmed reactive ion scattering (TPRIS), temperature programmed desorption (TPD), and auger electron spectroscopy (AES). DSB as a single molecular precursor was exposed on Si(1 0 0) surface at a low temperature less than 100 K, and then the substrate was heated up to 1000 K. RIS, TPD, and AES investigations showed that DSB adsorbed molecularly and decomposed to SiC via some intermediates on Si(1 0 0) surface as substrate temperature increasing. Between 117 and 150 K molecularly adsorbed DSB desorbed partially and decomposed to CH₄Si₂, which is the first observation on Si(1 0 0) surface, and further decomposed to CH₄Si between 150 and 900 K. CH₄Si lost hydrogen and formed SiC over 900 K.     

用红外测温仪观察二极管板流引起的阴极降温现象

为了观察由板流引起的灯丝温度下降现象,利用红外测温仪对理想二极管灯丝温度作了精密测量。由于忽略了板流,导致阴极灯丝温度下降,致使测得的金属逸出功存在着大约-1.86%的系统相对误差。实验验证了当灯丝电流和板流较小时,测不出灯丝温度随板流的变化。当灯丝电流为0.74A以上时,可以明显地观察到输出板流后,灯丝温度要比板流为0时低（1～2）K,此结果与预测值十分相符。     

掺铒GaN薄膜的背散射/沟道分析和光致发光研究

采用背散射（RBS）/沟道（channeling）分析和傅里叶变换红外光谱（FT-IR）研究了掺铒G aN薄膜的晶体结构和光致发光（PL）特性.背散射/沟道分析结果表明：随退火温度的升高， 薄膜中辐照损伤减少；但当退火温度达到1000℃，薄膜中的缺陷又明显增加.Er浓度随注入 深度呈现高斯分布.通过沿GaN的<0001>轴方向的沟道分析，对于900℃，30min退火的GaN:Er 样品，Er在晶格中的替位率约76％.光谱研究表明：随退火温度的升高，室温下样品的红外P L峰强度增加；但是当退火温度达到100 关键词： GaN Er 离子束分析 光致发光     

A theory for filamentation in semiconductor lasers including the dependence of dielectric constant on injected carrier density

A model for the self-focusing mechanism in semiconductor lasers is analysed and applied to the formation of lasing filaments in p-n junction devices. The self-focusing is attributed to an increase of dielectric constant in the semiconductor in regions of high light intensity due to a depletion of the injected carrier concentration. Two mechanisms are postulated for the dependence of dielectric constant on carrier concentration; the free carrier effect and the band-to-band interaction. The band-to-band interaction is computed as a function of photon energy, and found to give the major contribution to a total dielectric constant perturbation of typically −0.05 at threshold. This agrees with experiment. A single-mode solution is obtained for the waveguide equation of an isolated filament or a set of coupled filaments. This shows that the filament width contracts with current. Expressions are obtained for the optical intensity distribution, for the guided wavelength, for the effect of carrier diffusion, and for the higher-order mode cut-offs. The calculated filament width at 300 K varies typically between 12 and 3 microns for currents from 1 to 60% above threshold; at 77 K the width is almost doubled. This agrees reasonably with experiment. In general the analysis shows that the strength of self-focusing in heterostructure lasers depends on the number of carriers injected at threshold per cm² per micron thickness of the optical confinement region.     

The influence of substrate temperature on femtosecond laser micro-processing of silicon,stainless steel and glass

We report the influence of substrate temperature on femtosecond laser ablation of silicon, stainless steel, and glass. Remarkable decrease in surface roughness was observed under high substrate temperature for silicon and stainless steel. While the ablation efficiency of glass as a typical wide band-gap material is scarcely altered at 900 K, the efficiency for stainless steel as a conductor apparently increased about 20% accompanied to the elevation of substrate temperature from 300 to 900 K. Silicon wafer results in slight increase of the ablation efficiency with decreasing the ablation threshold. Considering that the melting temperature of glass is much lower than those of silicon and steel, the observations from this work suggests that the material ablation caused by the ultrafast laser irradiation could not be explained in term of only laser-induced thermal excitation.     

Über Zusammenhänge zwischen Elektronenspinresonanz,elektrischer Leitfähigkeit und Photoleitung bei reinem und dotiertem Bor

The conductivity mechanism in pure and doped, β-rhombohedral, polycrystalline boron between 1.5 °K and 900 °K is clarified by measurements of electrical conductivity, photoconductivity, electron paramagnetic resonance and thermoelectric effect. The semiconductor behaviour of boron between 1.5 and 900 °K is similar to that of doped and compensated germanium and silicon at helium temperatures concerning the temperature-independent number of carriers and the thermally activated conduction process at low and high carrier concentrations. The paramagnetic centres are nearly localized electrons at 1.5 °K and nearly free electrons at 900 °K with a continuous transition between these two extreme kinds of behaviour. Mobilities of charge carriers in carbon doped boron over a range from 10¹⁶ cm^?3 to 10²⁰ cm^?3 and 77 °K to 900 °K were measured for the first time and were found to obey an exponential law.     

灯丝温度对原位吸收光谱和金刚石薄膜生长的影响

 报道了原位红外吸收光谱在气相合成金刚石薄膜生长过程中的应用，研究了灯丝温度对原位红外吸收光谱和金刚石薄膜生长的影响。较高的灯丝温度使甲烷分解更充分，从而产生更多诸如C₂H₂等可能对金刚石薄膜生长有利的基团，导致金刚石薄膜质量和生长速率的提高。     

具有红外反射膜的节能卤素灯

研究了节能卤素灯的技术和设计问题.给出了红外反射膜的厚度对近红外波段的反射率分布以及该涂层对2 850 K照明光源在可见光范围内的影响,讨论了灯丝和泡壳的几何形状,以及钨丝对红外反射能量的吸收.实验表明：1）当选用9层膜时,实验数据与计算值偏差很微小.当灯的管径为10 mm,而灯丝外径为1.5 mm时,节能可达12%到13%.2）对圆柱形灯外壳,在不考虑端面影响时,光源的灯丝若处于外壳的中心轴上,则反射的能量会有效地返回灯丝.3）螺旋结构的灯丝比表面光滑的直钨丝有更高的吸收率,灯丝绕成螺旋后在现行的螺距尺寸下吸收率能达到0.6~0.7.     

Current fluctuations from various crystal faces of a clean tungsten field emitter

The temperature, frequency and current dependence of current fluctuations have been measured for the (310), (112) and (100) planes of a tungsten field emitter. The rms percent fluctuation of the current at 900 K was 8.7, 1.5 and 0.13% and the threshold temperature for current fluctuation was 300, 650 and 1000 K for the (310), (112) and (100) planes respectively. Based on the results reported here it is concluded that the current fluctuations arise from the generation of mobile atoms on net plane terraces.     

Ion-exchange resin decomposition in supercritical water

Abstract

Using supercritical water oxidation, the cation exchange resin was decomposed fast and completely to water, carbon dioxide and sulfuric acid. While the resin decomposition yield increased with the reaction time and the amount of hydrogen peroxide added as oxidizing agent, it was constant in the resin concentration from 0.14 to 1.9 dry resin weight percent to water. More than 99% of the cation exchange resin was decomposed with hydrogen peroxide added in the amount of 7 times the stoichiometric value at 673 K and 30MPa for 30 minutes of the reaction time. The cation exchange resin is decomposed through two main reaction pathways. One has a rate controlling intermediate such as acetic acid whose decomposition rate was very slow, and the other does not have stable intermediates. The decomposition of the acetic acid is a significant factor for the complete decomposition of the resin, although it does not dominate the whole resin decomposition. A simple kinetic model that estimates the resin decomposition yield was developed.     

Phase transition from asymmetric to symmetric dimer structure on the Si(001) surface at high temperature

The dimer configurations on the Si(001) surface at high temperatures have been investigated using the rocking curve of reflection high-energy electron diffraction. The Si(001) surface shows a displacive phase transition around 900 K, where a well-known asymmetric (tilted) dimer structure on the Si(001) at room temperature transforms to a symmetric dimer structure around 900 K. The metallic feature of the Si(001) surface above 900 K can be explained by the phase transition.     

Photochemical transformations of the azidonitroxyl radical in glassy media

The kinetic characteristics of the photochemical decomposition of the azido group of 3-azido-4-hydroxyimino-2,2,6,6-tetramethylpiperidine-1-oxyl in solid matrices at 293 and 77 K were studied. It was revealed that the presence of the nitroxyl radical center in the molecule is responsible for the realization of the radical mechanism of the decomposition of the azido group. The values of the quantum yield φ of the decomposition of the azido group were found to be 0.056 in toluene at 77 K, 0.14 in polystyrene at 77 K, and 0.16 in polystyrene at 293 K. It was demonstrated that the number of radicals remaining after photolysis correlates with the molecular mobility of the medium.     

Thermal Stability and Decomposition Kinetics of Poly(Methacryloyloxyethyl Trimethyl Ammonium Chloride-Co-Acrylamide)

Abstract

Poly(methacryloyloxyethyl trimethyl ammonium chloride-co-acrylamide) (P(DMC-AM)), is widely used for various applications under a wide range of conditions. In this work the thermal stabilities and decomposition kinetics of P(DMC-AM) with various intrinsic viscosities, synthesized in our laboratory, were studied by thermogravimetric analysis (TGA) at various heating rates, 5, 10, 20 and 40?K/min, and differential scanning calorimetry (DSC) at 10?K/min, all under a dynamic nitrogen atmosphere. The kinetic parameters were calculated using a model fitting method (Coats–Redfern, CR) and two model–free methods (Kissinger–Akahira–Sunose, KAS and Flynn–Wall-Ozawa, FWO). The result showed that all samples exhibited three steps of mass loss, one for the elimination of the adsorbed water and organic solvents and two for the thermal decomposition of P(DMC-AM). The first decomposition stage for the three samples was in the range of 5% to 45%, the second decomposition stage in the range of 65% to 95% and with 55% conversion separating the first and second decomposition stages. The E values increased with the increasing intrinsic viscosity of the samples. Hence, P(DMC-AM) had good thermal stability and the higher the molecular weight, the better the thermal stability was.