Coalbed methane adsorption and desorption characteristics related to coal particle size

Effects of particle size on CH_4 and CO_2adsorption and desorption characteristics of coals are investigated at 308 K and pressures up to 5.0 MPa.The gas adsorption and desorption isotherms of coals with particle sizes ranging from 250 μm to 840 μm are measured via the volumetric method,and the Langmuir model is used to analyse the experimental results.Coal particle size is found to have an obvious effect on the coal pore structure.With the decrease of coal particle size in the process of grinding,the pore accessibility of the coal,including the specific surface area and pore volume,increases.Hence,coal with smaller particle size has higher specific surface area and higher pore volume.The ability of adsorption was highly related to the pore structure of coal,and coal particle size has a significant influence on coal adsorption/desorption characteristics,including adsorption capacity and desorption hysteresis for CH_4 and CO_2,i.e.,coal with a smaller particle size achieves higher adsorption capacity,while the sample with a larger particle size has lower adsorption capacity.Further,coal with larger particle size is also found to have relatively large desorption hysteresis.In addition,dynamic adsorption performances of the samples are carried out at 298 K and at pressures of 0.1 MPa and 0.5 MPa,respectively,and the results indicate that with the increase of particle size,the difference between CO_2 and CH_4adsorption capacities of the samples decreases.     

Electron-probe X-ray microanalysis of individual particles of solid snow sediment with size factor correction

A technique is proposed for X-ray electron-probe microanalysis (EPMA) of individual particles of solid snow sediment. Two sample preparation procedures were used to analyze the sediments. The PAP-method and the original bi-exponential model were used for matrix correction and the calculation of elemental composition. A method of calculating composition has been developed for approximately spherical individual particles, comparable in size with an area of X-ray generation. An analytical expression is proposed for determining the composition of these particles, taking account of their size. Including the size factor reduces the error of composition determination from 0.5-45 to 0.2-22% relative percent, for particles in the size range 1-3 microm.     

Simultaneous, single particle, magnetization and size measurements of micron sized, magnetic particles

Single particle magnetization and size measurements of micron and nano sized, magnetic particles were made using a previously described device referred to as Cell Tracking Velocimetry, CTV. Three types of commercially available, and commonly used, magnetic particles were studied in this report. While the CTV instrument provides individual particles measurements, the average magnetization and size measurements were found to have reasonable agreements with reported values from instruments which measure bulk values. In addition, the CTV instrument, using electromagnets, can also determine magnetization curves, which also proved to have reasonable agreement with other published studies. Given that magnetic separation and analysis technology is dependent on the quality of the magnetic particles used, studies such as this one using CTV provide not only average data, but also provides information with respect to the distribution of the properties such as magnetization and size. For example, the spread of the data in magnetic and settling velocities were found to be predominately due to the size distribution of the analyzed particles.     

Speckle reduction of synthetic aperture imaging ladar based on wavelength characteristics

We propose a speckle-reduction method based on wavelength characteristics of speckle effect in synthetic aperture imaging ladar （SAIL）. The return signal, which is the back scattering field with speckle effect from the rough surface of target, can be integrated over N chirp periods and heterodyne detected with a local-oscillator signal. After performing image processing respectively, the final image can be regarded as the incoherent superposition of the N sub-images. Numerical simulations indicate the effectiveness of this method. Our research may facilitate practical applications of SAIL.     

The effect of particle size on the characteristics of FeCo nanoparticles

Some size-dependent characteristics of FeCo nanoparticles are investigated in this paper. The nanoparticles are fabricated using a coprecipitation route and their sizes are controlled by changing the reaction time. Transverse electron microscopy (TEM) images show that the nanoparticles are all spherical with an average size of 2–6 nm. The average size obtained from X-ray diffraction (XRD) measurements is in the range 1–3 nm. Magnetic measurements reveal that the nanoparticles are ordered ferromagnetically and have a high coercivity of about 500 Oe. In our measurements, the coercivity was decreased with decreasing particle size, indicating that the nanoparticles were in a single-domain region. Production of FeCo nanoparticles with high coercivity and fine dimension is highly promising for future recording media technology.     

粒子成像测速法中询问域大小的选择与粒子位移量的关系

通过分析询问域大小对底片乳剂颗粒产生的散斑噪声及其散斑噪声对干涉条纹识别的影响,推导出了询问域大小的选择与被测粒子位移量之间的关系,并详细讨论和分析了询问域的大小对所能探测的粒子位移量最大值的限止,以及合理选择询问域大小的依据.     

Sonolysis of levodopa and paracetamol in aqueous solutions

Pharmaceutical products are often present in wastewater treatment effluents, rivers, lakes and, more rarely, in groundwater. The advanced oxidation methods, like ultrasound, find a promising future in the area of wastewater treatment. The aim of this paper is to evaluate the influence of several parameters of the ultrasound process on the degradation of paracetamol, a widely used non-steroidal anti-inflammatory recalcitrant drug found in water and levodopa, the most frequently prescribed drug for the treatment of Parkinson disease. Experiments were carried out at 574, 860 and 1134 kHz of ultrasonic frequency with horn-type sonicator and actual power values of 9, 17, 22 and 32 W at 20 °C. Initial concentrations of 25, 50, 100 and 150 mg L^?1 of both products were used. Treatment efficiency was assessed following changes in pharmaceuticals concentration and chemical oxygen demand.The sonochemical degradation of both products follows a pseudo-first-order reaction kinetics. Complete removal of pharmaceuticals was achieved in some cases but some dissolved organic carbon remains in solution showing that long lived intermediates were recalcitrant to ultrasound irradiation. Pollutants conversion and COD removal were found to decrease with increasing the initial solute concentration and decreasing power. The best results were obtained with 574 kHz frequency. Investigations using 1-butanol as radical scavenger and H₂O₂ as promoter revealed that pollutants degradation proceeds principally through radical reactions, although some differences were observed between both molecules. Addition of H₂O₂ had a positive effect on degradation rate, but the optimum concentration of hydrogen peroxide depends on the pollutant.     

水云增长过程中的云滴谱及散射特性分析

基于大气物理学研究了水云云滴增长过程中的粒谱及散射特性.研究结果表明,凝结增长使粒谱半高宽和有效半径不断增加,碰并增长使粒谱出现多峰分布,有效半径增加.在凝结增长和碰并增长共同作用下,有效半径的平均增长速率为8 nm/s.凝结增长和碰并增长单独作用下,消光系数和散射系数随时间呈线性变化.在二者共同作用下,除3.2 mm波长外,消光系数和散射系数随时间呈指数增长;1.064, 2.2, 3.7, 12和22μm波长的不对称因子逐渐趋于稳定,200μm的不对称因子呈指数增长,3.2 mm的不对称因子基本保持不变;1.064和2.2μm波长的雷达比在20 sr附近波动,3.7μm波长的雷达比呈大幅振荡.云滴增长过程中,水云在1.064, 2.2和3.7μm波长的单次散射反照率逐渐降低,在12μm, 22μm, 200μm和3.2 mm波长的单次散射反照率逐渐增加,波长指数的绝对值逐渐减小.研究结果可为天气预报、地气辐射平衡研究和遥感数据校正提供重要的参考.     

Sonolysis of chlorobenzene in aqueous solution: organic intermediates

The ultrasonic degradation of 1.72 mM chlorobenzene was investigated. The sonolysis of chlorobenzene followed first-order kinetics. The influence of the pH of the aqueous solution and the effect of the saturating gás, air or argon, was measured. No pH effect was noticed, and saturation with the monoatomic argon accelerated the degradation. Furthermore, the addition of the radical scavenger benzoate demonstrated that no significant degradation took place in the bulk solution. For air-saturated solutions, the following organic degradation products were identified: methane, acetylene, butenyne, butadiyne, benzene, chlorophenols, phenylacetylene and other chlorinated and non-chlorinated monocyclic and dicyclic hydrocarbons. For argon-saturated solutions, the same products were found, except for the chlorophenols. The presence of the chlorophenols in the case of air-saturation only demonstrated the interaction between the radicals formed and oxygen, and no direct degradation by OH. radicals. The kinetics of several organic degradation products and chloride were determined for the sonolysis of air- and argon-saturated solutions.     

Interplay of surface conditions, particle size, stoichiometry, cell parameters, and magnetism in synthetic hematite-like materials

We have studied several synthetic hematite-like materials, produced via different reactions using various hydrothermal conditions and various temperatures of annealing in air, by bulk elemental analysis, weight loss measurements, scanning electron microscopy, powder X-ray diffraction, Mössbauer spectroscopy, and SQUID magnetometry. We conclude that hematite-like materials cannot be related to pure stoichiometric hematite via a single stoichiometric or physical parameter and that at least two degrees of freedom are required. This is most clearly seen when we introduce a plot of the cell parameter c versus the cell parameter a on which hematite-like materials do not fall on a single line but occupy an entire region that is bounded by hydrohematite-hematite and protohematite-hematite lines. A Morin transition boundary on this c-a plot separates a region where Morin transitions occur from a larger region where Morin transitions do not occur down to 4.2 K. Previous claims that particle size is the dominant factor controlling the Morin transition are understood in terms of correlations between stoichiometry and particle size that are produced at synthesis. Changing contents of incorporated molecular water and structural hydroxyls with associated cation vacancies have different characteristic effects on the crystal structure and move the sample coordinates in different directions on a c-a plot. It is also shown that an accessory sulphate content is adsorbed on the individual hematite crystallites and is not structurally incorporated. Mössbauer spectroscopy is used, as usual, to identify and characterize the spin structure. In addition, hyperfine field distributions from room temperature spectra, extracted by a new method, give a sensitive measure of sample conditions but not a unique one since several factors affect the extracted distributions in similar ways.     

Statistical characteristics of quasi-elastically scattered light in analysis of size of aggregated biological particles

The spectra of the intensity fluctuations of light scattered by large (erythrocytes of whole blood) and small (vesicles of surgical bile) particles in natural conditions were studied. It is shown that photon correlation spectroscopy can be used in analysis of variations in the size of biological particles in normal and pathological conditions and as an express method of noninvasive diagnostics of diseases.     

Sonolysis induced decomposition of metal carbonyls: kinetics and product characterization

The decomposition kinetics of Fe(CO)₅ and Mo(CO)₆ induced by sonolysis in hexadecane solvent was studied as a function of temperature (303–343 K) under an inert atmosphere. The decomposition data, obtained over at least two half lives in most of the runs, yielded first-order rate constant (k) values with correlation co-efficient (R²)>0.95. The products were characterized by various spectroscopic techniques. The transmission electron microscopy (TEM) yielded images from which the mean particle diameter (MPD) of 10 nm for Fe and <3 nm for Mo were estimated. The generation of amorphous Fe and semi-crystalline Mo particles was determined from line broadening and corresponding d-spacing values in the X-ray diffraction (XRD) spectra. The XAFS/XANES data were consistent with the production of Fe(0) metal but carbided Mo (Mo₂C). The one-step production of high-yield pyrophoric products demonstrated the applicability of sonolysis to effectively produce gram-quantity of zero-valent metals.     

抛光颗粒尺度均匀性对射流去除特性的影响

基于单喷嘴射流抛光去除机理,研究了抛光颗粒尺度分布理想均匀时,颗粒直径和抛光液质量分数变化对冲击去除分布的影响。在此基础上,考虑到实际加工过程中,抛光粉颗粒不可避免地存在分布不均匀的情况,在非理想不均匀条件下,提出了一种分析颗粒尺度的材料去除特性模型,重点研究了不同颗粒尺度分布范围对材料去除特性的影响。结果表明：在理想状态下,冲击去除随着抛光颗粒直径的增大而减小,随着抛光液质量分数的增大而增大。当颗粒直径随机分布时,材料去除量将出现明显的波动,抛光液质量分数的增大使去除量波动也增加,去除量波动的大小与抛光粉颗粒的平均直径直接相关,且与理想均匀状态下的去除特性相比,颗粒分布不均匀性使得材料的去除量有所增大。     

对纳米微粒制备教学实验中微粒尺寸表征的探讨

讨论了纳米微粒制备教学实验的尺寸表征方法．用称重法得出纳米微粒的视比重，TEM法观测纳米微粒的粒径分布．发现视比重与粒径分布之间有定量的依存关系．可以将视比重换算成微粒尺寸，并对不同制备条件下的Cu纳米粉的物理参量与微粒尺寸之间的关系进行了探讨．     

Simultaneous measurement of moving particle size and velocity

An optical method that makes it possible to measure the size and velocity of particles in flows and mixtures independently and simultaneously is considered. Measurements are taken by analyzing a moving diffraction pattern using a multielement photodetector and a special signal processing algorithm. The shape of photocurrent pulses arising when the particle crosses a light beam is determined. Examples of applying this method to particles with internal optical inhomogeneities are given in comparison with other methods, such as the method of low-angle scattering.     

Hydrogen reduction of fine iron-oxide particles

Crystallographic, magnetic, and morphological changes induced by heating highly acicular -Fe₂O₃ particles (40 nm in diameter and an axial ratio of 8) under hydrogen have been observed. Reduction proceeds via a multi-phase process, and is not complete until 600°C. The -Fe particles produced are cylindrical in shape, 100 nm in diameter, and have an axial ratio of 1.7(3). Fourier analysis of x-ray profiles yielded a mean column length of 105(6) nm perpendicular to (110). Mössbauer spectra show two distinct hyperfine fields; at room temperature the values are 33.1(1) and 30.2(1)T. Evidence for diffusive particle motion is not present in 4.2–300 K spectra.