One-pot, high-yield synthesis of size-controlled gold particles with narrow size distribution

Here, we first report a facile one-step one-phase synthetic route to achieve size-controlled gold micro/nanoparticles with narrow size distribution by using o-diaminobenzene as a reducing agent in the presence of poly(N-vinyl-2-pyrrolidone) via a simple wet-chemical approach. All experimental data including that from scanning-electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction techniques indicates that the gold micro/nanoparticles with a narrow size distribution were produced in high yield (similar to 100%).

EFFECT OF PARTICLE-SIZE ON IMPACT STRENGTH OF POLYMER BLENDS

The effect of particle size on impact strength of polymer blends with ductile fracture was studied. The results are in agreement with the experiments. (C) 1995 John Wiley & Sons, Inc.

Modification to the Hardisty equation, regarding the relationship between sediment transport rate and particle size

Bagnold-type bed-load equations are widely used for the determination of sediment transport rate in marine environments. The accuracy of these equations depends upon the definition of the coefficient k(1) in the equations, which is a function of particle size. Hardisty (1983) has attempted to establish the relationship between k(1) and particle size, but there is an error in his analytical result. Our reanalysis of the original flume data results in new formulae for the coefficient. Furthermore, we found that the k(1) values should be derived using u(1) and u(1cr) data; the use of the vertical mean velocity in flumes to replace u(1) will lead to considerably higher k(1) values and overestimation of sediment transport rates.

Grain size distribution of quartz isolated from Chinese loess/paleosol

Grain size distribution of bulk loess-paleosol and quartz chemically extracted from the loess/paleosol shows that mean size of the bulk samples is always finer than that of the quartz, The original aeolian depositions have been modified to various degrees by post-depositional weathering and pedogenic processes. The grain size distribution of the isolated quartz should be close to that of the primary aeolian sediment because the chemical pretreatment excludes secondary produced minerals. Therefore, the grain size of the quartz may be considered to more clearly reflect the variations of winter monsoon intensity.

Ultrasonic synthesis of silica-alumina nanomaterials with controlled mesopore distribution without using surfactants

A novel sol-gel process has been developed for the synthesis of amorphous silica-aluminas with controlled mesopore distribution without the use of organic templating agents, e.g., surfactant molecules. Ultrasonic treatment during the synthesis enables production of precursor sols with narrow particle size distribution. Atomic force microscopy analysis shows that these sol particles are spherical in shape with a narrow size distribution (i.e., 13-25 nm) and their aggregation during the gelation creates clusters containing similar sized interparticle mesopores. A nitrogen physiadsorption study indicates that the mesoporous materials containing different Si/Al ratios prepared by the new synthesis method has a large specific surface area (i.e., 587-692 m(2)/g) and similar pore sizes of 2-11 nm. Solid-state Al-27 magic angle spinning (MAS) NMR shows that most of the aluminum is located in the tetrahedral position. A transmission electron microscopy (TEM) image shows that the mesoporous silica-alumina consists of 12-25 nm spheres. Additionally, high-resolution TEM and electron diffraction indicate that some nanoparticles are characteristic of a crystal, although X-ray diffraction and Si-29 MAS NMR analysis show an amorphous material.

Detection and Characterization of Long-Pulse Low-Velocity Impact Damage in Plastic Bonded Explosives

Damage not only degrades the mechanical properties of explosives, but also influences the shock sensitivity, combustion and even detonation behavior of explosives. The study of impact damage is crucial in the vulnerability evaluation of explosives. A long-pulse low-velocity gas gun with a gas buffer was developed and used to induce impact damage in a hot pressed plastic bonded explosive. Various methods were used to detect and characterize the impact damage of the explosive. The microstructure was examined by use of polarized light microscopy. Fractal analysis of the micrographs was conducted by use of box counting method. The correlation between the fractal dimensions and microstructures was analyzed. Ultrasonic testing was conducted using a pulse through-transmission method to obtain the ultrasonic velocity and ultrasonic attenuation. Spectra analyses were carried out for recorded ultrasonic signals using fast Fourier transform. The correlations between the impact damage and ultrasonic parameters including ultrasonic velocities and attenuation coefficients were also analyzed. To quantitatively assess the impact induced explosive crystal fractures, particle size distribution analyses of explosive crystals were conducted by using a thorough etching technique, in which the explosives samples were soaked in a solution for enough time that the binder was totally removed. Impact induces a large extent of explosive crystal fractures and a large number of microcracks. The ultrasonic velocity decreases and attenuation coefficients increase with the presence of impact damage. Both ultrasonic parameters and fractal dimension can be used to quantitatively assess the impact damage of plastic bonded explosives.

Influence of 5A-Type Zeolite Powder on Tetrahydrofuran Hydrate Formation and Dissociation Process

Visual observations of tetrahydrofuran (THF) hydrate formation and dissociation processes with 5A-type zeolite powder were made at normal atmospheric conditions and below zero temperature by microscope. Results indicate that 5A-type zeolite powder can promote THF hydrate growth. At the same time, in the presence of 5A-type zeolite, agglomerated crystals and vein-like crystals of THF hydrate were also formed. SA-type zeolite powder increases the crystallization temperature and decreases the dissociation temperature. The particle size distribution of 5A-type zeolite powder influences THF hydrate formation and its dissociation characteristics significantly.

激光衍射法与吸管法对东北黑土区土壤粒径分布测定的差异性研究

目前激光衍射法(laser diffraction method,LD)逐步被用于土壤颗粒粒径分布(particle size distribution, PSD)的分析,为了对比LD法和吸管法测定东北黑土区土壤PSD的差异性,采用LD法和吸管法分别对东北黑土区宾州河流域36个土壤剖面不同层次178个土壤样品的PSD值进行了测定与分析。结果表明,同吸管法相比,LD法低估了土壤的黏粒含量,平均低估幅度19.69%,而高估了土壤的粉粒和砂粒含量,平均高估幅度分别为14.66%和5.13%。LD法所得PSD结果依据美国土壤质地分类制判定的土壤质地,相对于吸管法总体由粉黏质偏向粉砂质方向。建立了LD法与吸管法测定PSD结果的转换模型,将LD法测定的PSD结果利用转换模型校正后,其测定的各土壤粒级同吸管法相比,准确度达96.97%～98.71%,判定土壤质地的准确率也达83.15%。

两种土壤水分特征曲线间接推求方法对黄土的适应性评价

土壤水分特征曲线(SWCC)是模拟土壤水分运动和溶质运移的一个重要参数,利用土壤的基本物理性质来间接推求SWCC的方法已经成为当今土壤物理学领域的研究热点。为了比较两种SWCC间接推求方法——Arya-Paris物理经验方法(简称AP方法)和Tyler-Wheatcraft分形几何方法(简称TW方法)对黄土的适应性,该文分析了黄土高原296组土壤颗粒分布、容重和水分特征曲线等资料,利用简化的Fredlund(Fred3P)模型模拟得到连续的土壤颗粒分布曲线,然后应用AP和TW方法预测出相应吸力下的土壤含水量。研究结果表明,对于黄土性土壤,AP和TW两种方法的预测结果均达到了一定的精度,相比较而言AP方法的预测效果明显优于TW方法,且受质地影响小。