Thermodynamics of adsorption of light hydrocarbons on microporous active carbons at supercritical temperatures

Methods for describing adsorption isotherms and the thermodynamic characteristics of adsorption of methane, ethylene, propane, and butane on active carbons are considered in a wide range of temperatures below and above the critical ones.     

Thermodynamics of adsorption of methane and carbon dioxide on microporous adsorbents at temperatures above critical values

The earlier-shown possibility that the isotherms of adsorption on microporous adsorbents at temperatures above the critical values can be described with the Dubinin-Radushkevich and Tolmachev-Aranovich equations is confirmed by describing the experimental isotherms of adsorption of methane and carbon dioxide on microporous AUK and PAU-10 coals at temperatures above critical values; in the above-mentioned equations, the pressure of saturated adsorbate vapors used as a standard pressure at temperatures below critical values is substituted for the standard pressures (P*) that are determined through extrapolating the dependences of the logarithm of the saturation vapor pressure for the adsorptive on an inverse temperature over the supercritical temperature range.     

Thermodynamics of adsorption on microporous adsorbents above critical temperatures

The possibility of describing the isotherms of adsorption on microporous adsorbents at supercritical temperatures using the Dubinin-Radushkevich, Dubinin-Astakhov, and Tolmachev-Aranovich equations, in which the adsorbtive saturated vapor pressures that serve as the standard pressures below critical temperatures are substituted for the standard pressures (P _s ^*) found by the linear extrapolation of the dependences of adsorbtive saturated vapor pressure on the inverse temperature to the supercritical region, is shown. The possibility of linear extrapolation is substantiated by the data of a numerical experiment.     

Adsorption of methane on an MOF-199 organometallic framework structure at high pressures in the range of supercritical temperatures

Synthesis of an adsorbent based on an organometallic framework of the MOF-199 type is performed. The Dubinin–Radushkevich equation is used to calculate the structure–energy characteristics of adsorbents on the basis of data on nitrogen adsorption at 77 K as per benzene. Methane adsorption is studied on the obtained MOF-199 adsorbent, and adsorption isosteres are plotted. The capacitive characteristics of the adsorption system for methane storage with the synthesized adsorbent are determined. Differential molar isosteric and integral adsorption heats are calculated.     

Nitrogen adsorption by microporous adsorbents in the range of high pressures and supercritical temperatures

The nitrogen adsorption isotherms for the AUK microporous carbon adsorbent are measured at pressures of 1 Pa to 6 MPa and temperature of 177.7–393 K. In terms of the adsorption isotherms, in the same range of pressures and temperatures, the nitrogen adsorption isosteres are calculated. The resultant dependences are adequately approximated by linear functions. By the adsorption isosteres, the dependences of differential molar isosteric heat of adsorption on the value of adsorption and temperature are plotted. The results are compared with the literature data on nitrogen adsorption by zeolite NaX and activated carbon SKT.     

Fatigue behavior of X40CrMoV 51 at high temperatures

The fatigue characteristics of the hot work tool steel X40CrMoV 51 (UNS number T20811) at high temperatures is presented. The temperatures for the experiments were chosen between 50–600 °C. The experiments used B-type cylindrical specimens machined from X40CrMoV in an R.R. Moore rotating bending type fatigue test machine obeying the high cycle principle. The temperature intervals for the experiments were chosen as 50, 100, 200, 300, 400, 500, and 600 °C, for which the fatigue limit for each interval at 2 × 10⁶ cycles was determined. The fatigue limit of the material at room temperature (RT) is observed as 432 MPa, whereas it drops to 383 MPa at 400 °C. On the other hand, it stays almost constant between 400–600 °C, indicating that the material includes the elements forming strong carbides such as V, Mo, and Cr, which prevent the decrease of the fatigue limit due to higher temperatures.     

不同温度下HNO3改性对活性炭吸附银的影响

使用浓HNO3分别在常温和沸腾状态下对活性炭进行改性，用FTIR和N2吸附法对活性炭进行表面分析，使用AAS，SEM和XRD研究银在活性炭表面的吸附和分布特征。研究结果表明：活性炭经常温浓HNO3改性后，比表面积和孔容都明显提高，而经沸腾浓HNO3改性后，比表面积和孔容却明显减小，但2种改性方式都使活性炭表面产生更多的含氧基团，为[Ag（NH3）2]^＋的吸附还原提供更多的活性点，从而使活性炭表面银颗粒更加密集；常温浓HNO3改性极大地促进了[Ag（NH3）2]^＋的吸附还原，当银离子初始质量浓度为600mg／L时，活性炭对银的吸附量是原炭的5倍多；而活性炭沸腾浓HNO3改性使银的吸附量略有下降，但银颗粒却更加细小而密集，有利于活性炭表面纳米银颗粒的形成。     

The energy of adsorption of methane on microporous carbon adsorbents

Differential molar isosteric and integral heats of methane adsorption on a range of microporous carbon adsorbents of different origin have been calculated. The values of densities of integral heats Ω of methane adsorption on the sorbents under study Ω have been determined as the ratio between integral heat of adsorption and micropore volume. The dependence of density of integral heat of adsorption on standard characteristic energy of adsorption E ₀ has been estimated. It has been shown that the value of density Ω increases as E ₀ increases. The results of calculation of specific amount of accumulated methane V _sp depending on energy and structural parameters of adsorbents have been presented.     

Low-temperature adsorption of methane on microporous AU-1 carbon adsorbent

In this work, isotherms of absolute adsorption of methane on microporous AU-1 carbon adsorbent have been measured in the pressure range from 30 Pa to 6 MPa and temperature range from 178 to 273 K. Adsorption isosteres of methane have been plotted according to experimental data. Isosteres are approximated well by lines in lnp = f(1/T)a coordinates. Differential molar heats of adsorption of methane on this adsorbent have been calculated on the basis of experimental isotherms. Theses regarding the structure of adsorbed substance based on thermodynamic analysis have been proved by molecular-dynamic calculations.     

Y型分子筛的红外光谱

研究了ＣｏＮａＹ, ＮｉＮａＹ, ＣｄＮａＹ,ＣａＮａＹ 及晶体结构已被破坏的“ＣｒＮａＹ”, 在５２３ Ｋ 和１０ － １Ｐａ条件下处理后及其吸附苯后的红外光谱, 认为４１５ｃｍ － １ 谱带归属于六元环的振动, ４０３ｃｍ － １ 归属于十二元环的振动, ５１１ｃｍ － １ 吸收谱带归属于 Ｏ１Ｓｉ Ｔ 的弯曲振动。解释了Ｙ 型分子筛的 Ｏ１Ｓｉ Ｔ 易于断裂及５１１ｃｍ － １ 谱带频率大于４６２ｃｍ － １ 谱带频率的原因。     

Thermodynamics of initial stage of oxygen adsorption on surface of amorphous aluminum-cerium alloy

An equation is proposed to connect the characteristics of the energy and the surface level population on pure and oxidized metal surface with the value of heat of the physical absorption of oxygen. The electron structure is studied of pure and oxidized surface of the amorphous Al-8 at. % Ce alloy by analyzing the results of modeling the optical conductivity obtained from the optical experiment data. The conductivity band of the alloy is shown to be split. The heat value is calculated from the oxygen absorption on the amorphous alloy surface.     

A spectroscopic investigation for the adsorption of 4-nitrophenol onto synthetic zeolites

In this study, the characterization and environmental applications of faujasite type zeolites (NaX, NaY) are investigated using different instruments. Vibrational spectroscopy is used to a large extent in this research to characterize the zeolite materials and after the adsorption process. 4-nitrophenol was adsorbed on NaX and NaY zeolite and adsorption process was investigated by vibrational spectroscopy and scanning electron microscopy. Vibrational spectroscopic results showed that source of the adsorption is weak hydrogen bonding between zeolite surface silanol groups and OH group of 4-nitrophenol. This study was made to remove phenolic organics as possible substitutes for synthetic zeolites. SEM studies revealed the morphological observations of the unloaded zeolites and thereby changes in the adsorbed zeolites.     

Effect of nickel equivalent on hydrogen gas embrittlement of austenitic stainless steels based on type 316 at low temperatures

The effect of nickel equivalent on hydrogen gas embrittlement (HGE) of austenitic stainless steels of Fe–(10–20)Ni–17Cr–2Mo alloys vacuum-melted in a laboratory, based on type 316 stainless steel, was investigated. Tensile tests were conducted in hydrogen and helium at 1 MPa in the temperature range from 80 to 300 K. It was found that HGE of the alloys below a nickel equivalent of 27% increased with decreasing temperature, reached a maximum at 200 K, and then decreased with further decreasing temperature, whereas no HGE occurred above the nickel equivalent of 27%. It was observed that the content of strain-induced α′ martensite increased with decreasing temperature and nickel equivalent, and hydrogen-induced fracture occurred mainly along α′ martensite structure. Thus, the susceptibility to HGE depended on nickel equivalent. It was discussed that HGE was controlled by strain-induced α′ martensite above 200 K, whereas it was controlled by hydrogen transport below 200 K.     

The effect of carbon and silicon additions on the creep properties of Fe-40 at. % Al type alloys at elevated temperatures

The mechanical properties of Fe–Al alloys with 39–43 at.% Al, C contents up to 4.9 at.% and Si contents up to 1.2 at.% were studied using uniaxial compressive creep at temperatures from 600 to 800 °C. The stress and temperature dependence of the creep rate were determined by stepwise loading and evaluated in terms of the stress exponent n and the activation energy Q, respectively. These quantities can be interpreted by means of dislocation motion controlled by climb and by the presence of second-phase particles. The dislocation motion is obstructed by precipitates of carbide κ in alloys E and F and by particles of Al₄C₃ in the alloys with either higher content of C or of C and Si. Both carbon and silicon improved the creep resistance, but the effect of silicon was more significant.     

Recent developments of nanomaterials-based conductive type methane sensors

Methane is an explosive gas in coalmines and needs to be monitored by methane sensors.Conductive-type methane sensors are small,simple and stable,and they are v...     

Scale development on impure nickel at high temperatures

The growth of scales on impure Ni at 1373 and 1473 K was examined by microscopy and by oxygen-tracer-imaging techniques. The outward transport of cations was the basic rate-controlling step, and on the simple initial columnar scales such cation movement was the only kinetic process. However, oxygen movement was essential for the continued growth of more complex scales. Three types of sub columnar oxide were observed: (1) relatively coarse equiaxed crystals, (2) fume-like crystals, and (3) oxide that filled the pores between the crystals of the first two types. The oxygen for the first two types was provided by dissociation of the base of the columnar layer and also from voids that developed in the columnar layer. Oxygen for the third type came directly from the atmosphere following scale cracking. Such cracks healed after forming. The origin of the major features of scales was accounted for.     

Non-contact ultrasonic measurements on steel at elevated temperatures

Non-contact ultrasonic measurements have been made on ferritic and austenitic steel specimens as a function of temperature from ambient to 1200°C, using a pulsed laser to generate and a reference beam laser interferometer to receive the ultrasound. The generation efficiency is found to remain surprisingly constant in both thermoelastic and ablation regimes over a wide temperature range. The sensitivity of the laser interferometer is also found to be temperature independent to a first approximation. However, it is typically reduced by 3–6 dB by convection currents above 900°C. Both the compression and shear velocities decrease with rising temperature. The former is measured with a precision of 1 in 10³, the latter rather less accurately with the present configuration. Compression wave attenuation increases steadily below 600°C in both materials. There is a peak in attenuation in ferritic steel between 600 and 750°C, which is absent in austenitic steel. It coincides with a steeper decrease in ultrasonic velocity and is believed to be due to the martensitic structural phase transformation.The attenuation rose more rapidly in both materials as 1000°C was approached. The material attenuation varied with heat treatment, a value in the range 1–1.5 dB cm⁻¹ being recorded at 1000°C. Complicated effects were observed during heat treatments at 1000°C and above. Both attenuation and forward scattering data were consistent with some annealing out of sub-structure, in addition to austenitic grain growth. Finally, there was evidence of lattice softening at the highest temperatures investigated. The data suggest that thicknesses of steel in the range 100–250 mm should be inspectable with a scaled-up system, depending upon various factors such as the presence of oxide scale, provided high power lasers are employed for generation and reception and an optimum bandwidth is chosen.