Intercomparison of the LBIR Absolute Cryogenic Radiometers to the NIST Optical Power Measurement Standard

The Low Background Infrared calibration (LBIR) facility at the National Institute of Standards and Technology (NIST) presently maintains four absolute cryogenic radiometers (ACRs) which serve as standard reference detectors for infrared calibrations performed by the facility. The primary standard for optical power measurements at NIST-Gaithersburg has been the High Accuracy Cryogenic Radiometer (HACR). Recently, an improved radiometer, the Primary Optical Watt Radiometer (POWR), has replaced the HACR as the primary standard. In this paper, we present the results of comparisons between the radiometric powers measured by the four ACRs presently maintained by the LBIR facility to that measured by the HACR and POWR. This was done by using a Si photodiode light-trapping detector as a secondary transfer standard to compare the primary national standards to the ACRs maintained by the LBIR facility. The technique used to compare an ACR to the trap detector is described in detail. The absolute optical power measurements are found to be within 0.1 % of the primary standard for all the ACRs examined in this study.     

A Mathematic Model for Direct Causticization of Na2CO3 with TiO2 in a Semi‐batch Reactor

A mathematic model was developed for direct causticization of sodium carbonate with titanium dioxide in a semi‐batch reactor. The model predictions of the titanate yield and pentatitanate yield showed a reasonable agreement with the experimental data from a pilot‐scale fluidized bed operating in semi‐batch mode. The rate constant of the present model was generally consistent with those obtained from the small‐scale batch experiments in the literature. A new rate constant considering carbonate conversion to pentatitanate was introduced. All the results provided support that the solid‐state direct causticization of sodium carbonate with titanium dioxide in a semi‐batch fluidized bed follows the shrinking‐core diffusion model.     

基于圆环和等强度截面的纤维缠绕环形容器设计与分析

复合材料环形压力容器以其特有的结构形状得到了日益广泛的应用.目前关于纤维缠绕环形容器的研究主要局限于测地线缠绕圆环截面容器.由于环形容器的结构效率取决于它的管截面形状,所以使用圆环截面的环形容器无法实现等强度结构.本文提出了分别使用圆环截面和等强度截面的环形压力容器设计方法,并对二者进行了比较.基于最小应变能准则,得到了缠绕层铺设角和环壳内力间的最优化关系.根据网格理论,考虑截面缠绕层的厚度变化,导出了圆环容器缠绕的最优线型.引入应力比,分析了环壳上纤维的应力分布.描述了等强度经线曲线的一般形状,分析了轴向截荷对等强度曲线形状的影响.计算结果表明当轴向载荷达到一定数值时,等强度曲线能够实现闭合形成环形容器.进一步计算和比较了两种截面形状的环形压力容器在不同相对弯曲半径下的结构质量.研究表明,使用等强度截面设计的环形容器比使用圆环截面的环形容器要轻的多.通过等强度截面设计,环形压力容器的结构性能得到了明显的提高.     

基于圆环和等强度截面的纤维缠绕环形容器设计与分析EI

复合材料环形压力容器以其特有的结构形状得到了日益广泛的应用.目前关于纤维缠绕环形容器的研究主要局限于测地线缠绕圆环截面容器.由于环形容器的结构效率取决于它的管截面形状,所以使用圆环截面的环形容器无法实现等强度结构.本文提出了分别使用圆环截面和等强度截面的环形压力容器设计方法,并对二者进行了比较.基于最小应变能准则,得到了缠绕层铺设角和环壳内力间的最优化关系.根据网格理论,考虑截面缠绕层的厚度变化,导出了圆环容器缠绕的最优线型.引入应力比,分析了环壳上纤维的应力分布.描述了等强度经线曲线的一般形状,分析了轴向截荷对等强度曲线形状的影响.计算结果表明当轴向载荷达到一定数值时,等强度曲线能够实现闭合形成环形容器.进一步计算和比较了两种截面形状的环形压力容器在不同相对弯曲半径下的结构质量.研究表明,使用等强度截面设计的环形容器比使用圆环截面的环形容器要轻的多.通过等强度截面设计,环形压力容器的结构性能得到了明显的提高.     

Oxidized wax as compatibilizer in linear low-density polyethylene-clay nanocomposites: x-ray diffraction and dynamic mechanical analysis

Oxidized paraffin wax was used as a compatibilizer in composites of linear low-density polyethylene and layered nano silicate clays. X-ray diffraction analyses were carried out to investigate the crystalline morphology of five types of clays, oxidized wax, and their composites with LLDPE. The composites exhibited different X-ray diffraction and dynamic mechanical behaviour in the presence of different clays. Generally, the composites retained the partially crystalline behaviour of LLDPE, and no exfoliation was observed. Increased amount of wax did not change the morphology in most cases. The incorporation of clay resulted in an observable increase in the storage modulus of LLDPE. These values also increased with the addition of oxidized wax for most of the composites. The loss modulus increased with the amount of clay, irrespective of its nature. In most cases these values also increased with the incorporation of wax. The composites with 10% clay and 10% oxidized wax showed the highest storage and loss moduli, irrespective of the nature of the clay. The tan delta values did not change considerably with the addition of clay or wax.     

Structure and mechanical properties of polycarbonate modified clay nanocomposites

Polycarbonate (PC)/modified clay nanocomposites were prepared, in the absence and presence of different amounts of maleic anhydride grafted polypropylene (PP-g-MA), by direct melt blending. Their structures, as well as mechanical, morphological and thermal properties, were characterized by X-ray diffractometry (XRD), tensile testing, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The XRD results of the PC/clay nanocomposites showed that they had intercalated structures, although some exfoliation was visible at low clay contents, that the gallery heights of the PC/clay nanocomposites were almost the same, and that some of the clay layers collapsed as a result of modifier decomposition at the high processing temperature. The XRD patterns of the PC/PP-g-MA/clay nanocomposites clearly show less intercalation and more exfoliation with increasing PP-g-MA content. These results were supported by TEM observations. Both the tensile strength and modulus show substantial improvements with both increasing clay and PP-g-MA contents, while the elongation at break substantially decreases, although the presence of PP-g-MA somewhat improves these values. All the nanocomposites have lower thermal stability than pure PC, but the presence of PP-g-MA seems to improve the thermal stability of these samples.     

Investigation of the physico‐mechanical properties of electrospun PVDF/cellulose (nano)fibers

The electro‐activity and mechanical properties of PVDF depends mainly on the β‐phase content and degree of crystallinity. In this study, cellulose fibers were used to improve these characteristics. This could be achieved because the hydroxyl groups on cellulose would force the fluorine atoms in PVDF to be in the trans‐conformation, and the cellulose particles could act as nucleation centers. Electrospinning was used to prepare the PVDF/cellulose (nano)fibrous films, and this improved the total crystallinity and the formation of β‐crystals. However, the presence and amount of cellulose in PVDF were found to have little influence on the β‐phase content and on the total crystallinity of PVDF. Improvements in the extent of crystallinity and the β‐phase content were primarily brought about by the chain‐ and crystal orientation as a result of electrospinning. The thermal stability of PVDF in the composites slightly increased with increasing cellulose content in the composites up to 1.0 wt %, while the modulus and tensile strength significantly increased up to the same filler level. The dielectric storage permittivity also increased with increasing cellulose content, but the presence of cellulose had no influence on the dynamics of the γ‐ and β‐relaxations of the PVDF. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43594.     

Minimum weight design of helically and hoop wound toroidal hydrogen storage tanks with variable slippage coefficients

This article determines the optimal winding parameters for helically and hoop overwound toroidal hydrogen storage tanks, based on the application of variable slippage coefficients. First, an optimality condition between helical winding angle and hoop‐to‐helical thickness ratio is derived from the minimum strain energy density criterion. The winding angle distributions are then obtained with the aid of the optimality condition, taking into account the shell thickness variation along the meridional direction. The general criteria for fiber trajectory stability on a torus are presented, and the relationship for the slippage coefficient and the helical winding angle is formulated according to the windability and manufacturability. The helical winding angle and thickness at the equator are considered as design variables, whereas the minimum weight acts as the objective function. A design example with a toroidal hydrogen storage tank is outlined to demonstrate the favorable performance of the present method. The results show that the present method using variable slippage coefficients leads to a better distribution of the fiber stress in the toroidal shell and an efficient utilization of the laminate strength. The obtained winding parameters can thus be regarded as optimal for filament‐wound toroidal hydrogen storage tanks. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Dynamic mechanical and thermal properties of the composites of thermoplastic starch and lanthanum hydroxide nanoparticles

Nanostructured lanthanum (III)‐oxide (La₂O₃) particles were prepared by a polymer complex solution method and further used for the preparation of lanthanum hydroxide (La(OH)₃) nanoparticles. The La(OH)₃ nanopowder was mixed with glycerol‐plasticized maize starch and the effect of the filler on the thermal, mechanical, and viscoelastic properties of the matrix was investigated. It was expected that this nanofiller, which shows an affinity toward OH groups, would strongly affect the physical properties of thermoplastic starch (TPS). The pure TPS and the TPS‐La(OH)₃ nanocomposite films (with 1, 2, and 3 wt % filler) were conditioned at various relative humidities (RHs) (35, 57, 75, and 99% RH). After conditioning at 99% RH, the pure TPS films exhibited higher affinity toward water than the nanocomposites. Differential scanning calorimetric measurements showed that, due to retrogradation effects, the melting enthalpies of the films increased with increasing RH. Dynamic mechanical analysis revealed that the mechanical properties in the linear range strongly depend on both the humidity conditions and the concentration of the filler. The results also show that La(OH)₃ nanoparticles are good reinforcement for TPS films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013