Surface Diffusion of Deuterium and Light Hydrocarbons in Microporous Vycor Glass

Abstract

The significance of the surface diffusion of helium through a microporous Vycor glass is emphasized, and the experimental evidence is presented. New permeability data of D₂, CH₄, C₂H₆, and C₃H₈ are reported over a wide temperature range, and the results are analyzed numerically. Interesting comparisons are made for D₂-H₂ and C₃H₈-CO₂ systems. Finally, the separation factors for CO₂-C₃H₈ and CH₄-C₃H₈ systems are discussed.

All the experimental work has been carried out with porous Vycor glass as the microporous medium. However, there is good reason to believe that the basic findings will hold for any other microporous barrier. Differences will only be a matter of magnitude and will be determined by the adsorption interaction of the respective gas-solid system.     

Crystallization and Densification of Nano-Size Amorphous Cordierite Powder Prepared by a PVA Solution-Polymerization Route

A homogeneous and stable amorphous-type cordierite (2MgO2Al₂O₃5SiO₂) powder was prepared by a solution-polymerization route employing a Pechini resin or a poly(vinyl alcohol) (PVA) solution as the polymeric carrier. After calcination at 800°C for 1 h under atmospheric conditions, the bulky precursor changed into a very soft and porous powder. A 30 nm size, amorphous-type cordierite powder was prepared by attrition milling the calcined powder, which was made using a PVA precursor solution. The nano-size powder, which had a high specific surface area of 181 m²/g, was obtained after milling for <1 h. The sintered cordierite grains did not show the presence of any amorphous SiO₂ phase and had a dense microstructure with a relative density of 99% and a thermal expansion coefficient of 2.1 10^-6/°C.     

Experimental Studies on the Separation of Deuterium Oxide in Continuous Thermal Diffusion Column for Low Concentration Range

Abstract

Separation equations for the enrichment of heavy water in a continuous-flow thermal diffusion column have been derived for low-concentration operations. Experimentals on two feed concentrations of the H₂O-HDO-D₂O system have also been conducted, and the results quantitatively confirm the predictions of theory.     

Deuterium Recovery from H-D Gas Mixture by Thermal Diffusion in the Device of Branch Columns for Improved Performance

The strength of forced convection currents, as well as the remixing effect in a continuous-flow thermal diffusion column for recovery of deuterium from H-D gas mixture, can be reduced by employing the device of branch columns, instead of the device of single column, with the same total column length. The improvement in separation increases when the flow rate or the total column length increases. It is found that the improvement in recovery can reach about 50% for the numerical example given.     

Molecular Dynamics Study of Atomic Structure and Diffusion Behavior in Amorphous Silicon Nitride Containing Boron

We have performed molecular dynamics simulations of amorphous Si₃N₄ containing boron (Si-B-N). We have examined short-range atomic arrangements and self-diffusion constants of amorphous Si-B-N systems with various boron contents. Our simulations show that boron atoms are threefold coordinated by nitrogen atoms and that nitrogen atoms are bonded to both silicon and boron atoms in the amorphous network of Si-B-N. Also, the self-diffusion constant of nitrogen in Si-B-N is much decreased compared with that in amorphous Si₃N₄. This suggests that boron is important in decreasing the mobility of atoms in amorphous Si-B-N, which may explain the improved thermal stability of amorphous Si-B-N relative to amorphous Si₃N₄ observed experimentally.     

堇青石红外特性的研究

参考国内外资料,结合红外辐射产生的条件、发射率的基本概念综述了堇青石具有高红外发射率的机理,从合成原料、合成方法和添加剂的加入等方面分析了对堇青石红外发射率产生影响的因素。对堇青石红外陶瓷材料的发展方向进行了展望。     

Low-Expansion Cordierite Porcelains

The crystalline nature and expansion characteristics of compositions in the region surrounding the cordierite area of the system MgO–Al₂O₃–SO₂ were investigated. The selected compositions were fired to temperatures of 1250°, 1300°, 1350°, and 1400°C., and the thermal expansion characteristics were determined with the interferometer. Coefficients of linear thermal expansion were determined in the temperature range of 20° to 300°C. and were found to lie between 9.8 ± 10^–7 and 50.5 ± 10^–7. The qualitative, as well as the quantitative, determination of crystalline constituents was made utilizing strontium fluoride as an internal standard in the X-ray spectrometer. In the compositions studied crystalline cordierite ranged from 38 to 97%. There was a close correlation between the linear thermal expansion coefficient and the crystalline cordierite content of the bodies.     

堇青石棚板的试制

叙述了利用镁质粘土和高岭土原料人工合成堇青石 ,再与其它原料配合制成的堇青石棚板 ,取代了高价外购的堇青石棚板 ,进一步降低了生产成本 ,提高了企业的经济效益     

合成温度对堇青石—莫来石复相材料中堇青石、莫来石生成量的影响

以MgO-Al2O3-SiO2三元相图为依据,在M2A2S5－A2S3连线上进行了堇青石－莫来石复相材料组成点的设计,并在高温下合成了堇青石与莫来石比例为1：1的复相材料,重点讨论了烧成温度对堇青石－莫来石复相材料中堇青石,莫来石生成量的影响,XRD定量分析结果表明,当合成温度范围约在1380－1420℃之间时,可在复相材料中得到接近理论的相组成。     

Alkoxide Sol-Gel-Processed Cordierite Fiber

An alkoxide sol-gel route was developed to prepare stoichometric cordierite fibers. The influences of the aging treatment and heating rate on the sinterability of the gel fibers were also examined. X-ray diffraction analysis revealed that the unaged and aged fibrous gels all remained amorphous <800&, but began crystallization into μ-cordierite and α-cordierite at ∼900°C and 1050°C, respectively; single-phase α-cordierite fibers were obtained at 1300°C. Heating the unaged fibers yielded denser microstructures, with fine grain sizes of ∼0.2–0.4 μm, whereas the aged fibers exhibited porous microstructures following heating at 1300°C. A higher heating rate and aging treatment resulted in a higher open porosity of the fired fiber.     

含锂辉石添加物的堇青石陶瓷

研究了β-锂辉石添加物对生料、预合成堇青石料工艺特性和所生产样品性能的影响。添加1％锂辉石可以改进以生料为基础的泥浆的流变特性并能显著地提高烧结制品的强度。     

低温合成堇青石

本研究采用废玻璃纤维和高纯Ａｌ_２Ｏ_３、ＳｉＯ_２、ＭｇＯ，在常压下于＜１２００℃，４～８ｈ人工合成高纯堇青石。废玻璃纤维中的ＣａＯ、Ｆｅ_２Ｏ_３、Ｒ_２Ｏ能溶入堇青石的晶体结构，并可有效地扩大烧结范围，降低热膨胀系数。讨论了试样的配方组成、合成温度、保温时间和冷却条件等对堇青石的合成量和晶粒大小的影响。     

堇青石合成过程的研究

采用高岭土、滑石和氧化铝作原料合成堇青石,通过对高岭土和滑石的ＤＴＡ分析,并结合前人所做的工作对高岭土和滑石在１０００℃以前的加热变化过程进行了阐述,同时通过对不同烧成温度下的试样做ＸＲＤ分析及ＳＥＭ观察,重点研究了堇青石的合成过程。     

堇青石整体式催化剂的研究进展

近年来,堇青石整体式催化剂由于具有低热膨胀性、比表面积大、优良的机械强度和高熔点等特点,在尾气废气处理、化工产品的合成、新能源处理、生化等多个领域得到了广泛应用,并表现出了良好的性能。综述了堇青石整体式催化剂制备的过程及研究进展,并对堇青石整体式催化剂的前景做了展望。