Investigation of Permeation Tubes for Temperature-Compensated Gas-Sensor Calibrators

Ethanol permeation tubes have been proposed for a possible use in temperature-compensated gas-sensor calibrators. Two commercial tubes with a different geometric configuration of the polymeric membrane (wafer- and EL-type) have been tested. First, their permeation characteristics have been evaluated and, subsequently, their performances tested in an apparatus simulating programmed temperature cycles. Both tubes have shown a linear permeation rate in the range of temperature investigated and a low permeation temperature coefficient, with the EL-type tube showing also a very fast response to temperature variation. The integration of this latter tube with a flow-compensation controller has lead to the realization of a temperature-compensated calibrator device, allowing to maintain the ethanol concentration constant at the calibrator outlet by simply modulating the carrier flow through the permeation tube to compensate the temperature fluctuation. Results obtained in the generation of calibrated gas-phase ethanol concentrations, in the range from 1 to 500 ppm, suggest a promising use of these temperature-compensated permeation tubes as calibrators in portable gas-sensor devices.     

氢渗透电流法监测海洋大气中钢材的腐蚀速率

用Devnathan-Stachurski双电解池技术,对16Mn钢表面干湿循环时氢渗透现象进行了研究,结果表明不同表面液膜下,都有氢渗透电流的存在.氢离子渗透量与试样腐蚀失重之间存在线性关系.利用此线性关系制作的实时监测氢渗透电流的传感器,用以记录实际海洋大气中氢渗透电流,并根据氢离子渗透量与腐蚀失重之间的线性关系对海洋大气中钢材的腐蚀速率进行预测.结果表明,实际海洋大气中,氢渗透电流与环境湿度存在着对应关系,环境湿度由大变小时,氢渗透电流由小变大.环境湿度交替变化,在试样表面完成干湿循环,促进了氢的渗透,实际海洋大气与摸拟海洋大气失重取得了较好的一致性.可以用氢渗透电流传感器实时监测海洋用钢在大气中的氢渗透情况及腐蚀失重情况.     

The permeation resistance of polyethylene, polyethylene/polyamide and polyethylene/modified polyamide blown tubes against unleaded gasoline

The barrier resistance of polyethylene (PE), polyethylene/polyamide (PE/PA) and polyethylene/modified polyamide (PE/MPA) blown tubes against gasoline permeation is reported. The blown tubes prepared from pure PE exhibited much poorer gasoline permeation resistance than PE/PA and PE/MPA blown tubes. About 93% of the filled gasoline permeated out of PE blown tubes in 14 days at 40°C. In contrast, the gasoline permeation resistance of the blown tubes improved significantly by blending MPA (or PA) before tube blowing. PE/MPA blown tubes exhibited significantly better gasoline permeation resistance than PE/PA blown tubes of the same PE contents. The order of gasoline permeation resistance of PE/MPA blown tubes is the same as the order of the barrier resistance of MPA resins against gasoline permeation before blending with PE. In fact, by using proper compositions and carefully controlling the MPA morphology, the gasoline permeation resistance of the PE/MPA blown tubes can reach about 360 times better than that of pure PE blown tubes at 25°C. These interesting phenomena were investigated in terms of the morphology, thermal and rheological properties of the base resins and/or blown tubes of PE/PA and PE/MPA blends.     

A Predictive Instrument for Sensitive and Expedited Measurement of Ultra-Barrier Permeation

The reliable operation of flexible display devices poses a significant engineering challenge regarding the metrology of high barriers against water vapor. No reliable results have been reported in the range of 10^–6 g∙(m²∙d)⁻¹, and there is no standard ultra-barrier for calibration. To detect trace amount of water vapor permeation through an ultra-barrier with extremely high sensitivity and a greatly reduced test period, a predictive instrument was developed by integrating permeation models into high-sensitivity mass spectrometry measurement based on dynamic accumulation, detection, and evacuation of the permeant. Detection reliability was ensured by means of calibration using a standard polymer sample. After calibration, the lower detection limit for water vapor permeation is in the range of 10^–7 g∙(m²∙d)⁻¹, which satisfies the ultra-barrier requirement. Predictive permeation models were developed and evaluated using experimental data so that the steady-state permeation rate can be forecasted from non-steady-state results, thus enabling effective measurement of ultra-barrier permeation within a significantly shorter test period.     

聚二羟基甲基硅氧烷改性聚醚酯弹性体的合成与表征

以对苯二甲酸二甲酯(DMT)、1,4丁二醇(BD)、聚乙二醇(PEG)和聚二羟基甲基硅氧烷(PDMS)为原料,采用熔融缩聚法一步合成了聚硅醚酯弹性体(PBT-co-PEG/PDMS)。通过红外光谱、核磁共振和凝胶色谱等分析方法对其分子结构和分子量进行了表征,用差示扫描量热(DSC)和热重分析(TG)研究了耐热性能,结果发现,PEG和PDMS参与了共聚反应,随着聚合物中聚二羟基甲基硅氧烷含量的增加,聚合物的数均分子量相应减小,PDMS含量为10%的共聚物数均分子量仅为3万;热分析结果表明,随着PDMS含量的增加,聚合物的熔点从175℃逐渐升高到200℃,同时起始降解温度也逐步提高。     

Thermal processing of multilayer PLZT actuators

Cofired multilayer actuators (MLAs) can suffer from reliability problems due to internal cracking, resulting from imperfections formed during binder extraction or sintering. Thermal processing methodology was developed to optimize manufacturing output of defect-free multilayer actuators. Rate-controlled thermogravimetry (RCT), in which furnace power is adjusted to maintain a constant specimen weight loss rates, was used for organic binder burnout in MLAs. The effectiveness of the various thermal schedules in eliminating MLA damage was determined through image analysis of depth profiles, ground perpendicular to the layers. The damage resulting from RCT schedules were compared to those produced using conventional temperature-controlled thermogravimetry (TCT). Specimens heat-treated with mass loss rates of 0.003 to 0.03 wt%/min showed fewer microstructural defects than all evaluated TCT schedules. Under RCT, furnace power was adjusted to mitigate the effects of rapid burnout of the multicomponent binder, which surged at specific temperature ranges. The effect of introducing a modified atmosphere of MLAs was also investigated using thermogravimetry in conjunction with mass spectrometry.     

一种多路外渗式湿度发生器的研制

介绍了一种多路外渗式湿度发生器的工作原理及研制过程.详细阐述了多路外渗式湿度发生器的渗透管选择、多渗透管气路选通方法及硬件结构.通过试验验证,证明了该装置工作准确可靠.     

Gel permeation chromatography coupled to fourier transform mass spectrometry for polymer characterization

We report an on-line coupling of gel permeation chromatography (GPC) to Fourier transform mass spectrometry (FTMS) using a modified commercial electrospray ionization (ESI) interface. Selected oligomer profiles for the sodiated (1+ through 5+ charge states) oligomer ions of a narrow-molecular-weight poly(methyl methacrylate) were generated and used for obtaining a calibration curve. Using the MS-generated calibration curve and the refractive index response for quantification, an accurate molecular weight distribution was calculated and showed an excellent agreement with the value specified by the supplier. GPC/ESI/FTMS also allowed for an unequivocal end-group determination and characterization of a secondary distribution due to the formation of cyclic reaction products. We analyzed a glycidyl methacrylate/butyl methacrylate copolymer with a broad molecular weight distribution, where fractionation and high resolving power were required for adequate characterization. Molecular weight distribution data showed the advantage of coupling high-resolution MS and GPC to overcome the difficulty of analyzing polydisperse polymers with MS alone.     

Reducing the Uncertainty of Industrial Trace Humidity Generators through NIST Permeation-Tube Calibration

Permeation-tube moisture generators (PTGs) are commonly used by the semiconductor industry as transfer standards for the calibration of hygrometer systems measuring trace amounts of water vapor in gases (water vapor mole fractions typically below 1 × 10⁻⁶). They are relatively simple devices that generate a steady stream of humidified gas by diluting water vapor delivered at a constant rate from a permeable capsule with precisely metered purified gas, usually nitrogen. Here a new calibration service enabling the measurement of PTG permeation rates directly in terms of NIST primary standards of trace humidity generation is described. Rather than using commonly employed gravimetric methods for permeation-tube calibration, the method applied here links the permeation rate of the permeation tube to the thermodynamic properties of ice. Using a hygrometer based on cavity ringdown spectroscopy, we compare the water vapor concentrations produced by the NIST low frost-point generator (LFPG) and a specially constructed PTG containing the permeation tube undergoing calibration. A least squares fit of the data determines the permeation rate of the tube under test. We describe the calibration system, experimental procedure and present sample calibration data. The expanded relative uncertainty of NIST permeation-tube calibrations is 1.8% with a coverage factor k = 2, dominated by the Type A uncertainties.     

铠装贵金属热电偶测量端位置的确定方法

热电偶测量端位置的准确定位对于热电偶的校准和使用有着重要影响,特别对于铠装贵金属热电偶来说,由于无法通过肉眼准确识别保护管内部热电偶测量端的位置,因此在热电偶检定和使用过程中一般将其外保护管顶部作为测量端所在位置。然而通过现场试验发现,铠装贵金属热电偶测量端一般并不位于保护管顶部,本文提供了一种准确定位铠装贵金属热电偶测量端的方法。     

Investigation of Instability of Lattice of Bi_2Sr_2CaCu_2O_x

Bi2Sr2CaCu2Ox superconductor was studied by differential scanning calorimetry (DSC) and thermogravimetry (TG) in different atmospheres. It is discovered that there is a thermal anomaly in the DSC curve, associated with a weight loss in the TG curve before the melting of the sample. Careful thermal analysis and high temperature X-ray diffraction reveal that the thermal anomaly and the weight loss show an instability of the crystalline Iattice. By annealing the sample in oxygen and argon, respectively and then by TC measurement and thermal analysis, the coincidence of transition temperature with the instability is found. The coincidence is further confirmed by Y-doped 2212 phase.     

Calibration of permeation passive samplers with silicone membranes based on physicochemical properties of the analytes

Passive sampling is a very attractive alternative to active sampling due to its simplicity and low cost. Among the passive samplers used in air analysis, permeation passive samplers are the least affected by ambient conditions, including humidity, air currents, and temperature changes. The biggest drawback of permeation passive samplers is the need to calibrate them experimentally for each individual target analyte. The paper presents the results of research on the calibration of permeation passive samplers based on physicochemical properties of the analytes. Strong correlations were found between the calibration constants of the samplers and the number of carbon atoms among families of compounds (R2 ranging from 0.8507 for alcohols to 0.9995 for aromatic hydrocarbons), the molecular weights of the compounds (R2 = 0.8742), their boiling points (R2 = 0.8911), and linear temperature-programmed retention indexes (R2 = 0.9225). The last correlation makes it possible to estimate the calibration constants for unidentified analytes, which is impossible when the conventional procedure is used. This makes it possible to deploy permeation passive samplers in the same way in which active sampling is deployed.     

Gel permeation chromatography: A review

Gel permeation chromatography (GPC) enables the molecular weight distribution of a polymer sample to be determined in two or three hours. In the few years since its development it has revolutionised polymer characterisation. This review describes the essentials of the technique, its history and its relevance to polymer technology. Apparatus for GPC is also described with greatest emphasis being given to apparatus similar to that commercially available from Waters Associates Inc. The problems associated with chromatogram interpretation, instrumental broadening and calibration are discussed.     

Quantitative 1H NMR with external standards: use in preparation of calibration solutions for algal toxins and other natural products

We examine the use of external standards for quantitative measurement by 1H NMR of solution concentrations of natural products and other low molecular weight, hydrogen-containing compounds and show that precision and accuracy ca. 1% is obtainable with a commercial 11.7 T spectrometer when standards and analytes are contained in separate but identical sealed precision glass NMR tubes. Numerous factors contributing to the intensity of the NMR signals are evaluated. Precise measurements of 360 degrees pulse lengths for each sample provide direct corrections for variations in probe Q-factor that enable samples in different solvents to be compared, provided single-coil excitation and detection is used throughout. Samples need not be prepared in deuterated solvents if the 1H spectra of the solvents are simple enough for peak suppression by presaturation. The approach is particularly suitable for hazardous materials kept in sealed tubes and for the preparation of certified calibration solution reference materials for use with LC-MS and other techniques where deuterated solvents should be avoided.     

内高压成形波节管承载特性分析

内高压成形波节管作为目前应用最广换热设备,其变形特点以及成形后承载特性均备受关注.本文通过数值模拟和实验研究的方法,首先分析波节管内高压成形壁厚分布规律、成形精度以及残余应力分布情况,然后分析成形后波节管在承载时,典型区域应力应变分布情况,得出波节管在承受不同载荷时的变形特点.研究结果表明:在内高压成形过程,当整形压力为290 MPa时,成形精度较好,根部过渡区域减薄率达21.63%,且此处残余应力最大.在承载过程,当波节管承受内压力自由胀形时,波节管等效应力的最大值出现在波节根部过渡区域,此处为承载的薄弱区域;当波节管承受轴向压缩和拉伸载荷时,波峰及其附近区域与之对应的产生轴向拉应变和轴向压应变,体现出波节管具备很好的轴向位移补偿能力.     

Properties of ceramic injection moulding formulations

The oxidative and thermal degradation of nine suspensions, with polypropylene as the main organic component and a fixed silicon powder loading, were studied by thermogravimetry. Samples were in the form of finely divided shavings and moulded bodies. The acceleration of weight loss in oxidizing atmospheres was dependent on sample size, indicating oxygen diffusion control. Minor additions in the formulations exerted considerable influence on the form of the thermograms. Samples heated in nitrogen presented an exfoliated skin defect which did not appear in oxidizing atmospheres. An important observation was that the form of the thermogram could not be directly related to the incidence of defects in the powder assembly and was therefore an incomplete guide in the screening of potential blends. Nevertheless, a low temperature dependence of weight loss was shown to be desirable for process control.     

On Parameters Affecting the Sensitivity of Ultrasonic Testing of Tubes: Experimental and Simulation

The response (amplitude) of the reference notch during ultrasonic testing of tubes is dependent on several parameters like (1) size, shape and location of notch in the material (2) operating parameters like pitch, incidence angle, focusing, beam profile etc (3) Electronic parameters like PRF, pulse width etc. A thorough analysis of several parameters is made in this paper which affects the calibration sensitivity and its repeatability. Calibration during ultrasonic testing of tubes is carried out by using reference notches made on the tubes. The size and shape of the reference notches are defined in the specification of the tube. Different specifications like ASTM, ASME, AMS, BS etc recommend the type of notch to be used for calibration. These are varying from one standard to another and there is no comparison available for the achieved sensitivity during calibration. This paper deals with a comparison of the recommended size and shape of the notches in different codes and specifications. The sensitivity of test is dependent on the calibration notch size and shape. In the present work a comparison is made on the sensitivity (in terms of gain level) for different size and shape of notches used during calibration of a tube. Usually, these notches are made on the ID and OD surface of the tubes which are generally equal in size. During calibration equalization of the amplitude of indication from the ID and OD is recommended. However no sound basis is available for the reason for unequal amplitude indication from ID and OD notch. In the present work, response from the notches at ID and OD is experimentally determined and compared with modeling of the response from the ID and OD notches. The repeatability of the calibration is demonstrated by carrying out a series of repeated measurements of the gain of the response from the notch. Different specifications recommend different tests for demonstrating the repeatability of the calibration. A comparison is made here for the repeatability requirements in different specifications. An analysis of the operating and electronic parameters responsible for variation in gain during a repeatability test is made.     

一种制定非线性GPC校准线的新方法

校准曲线是凝胶渗透色谱仪进行各种计算的基础,但往往最小两乘多项式拟合结果的精确性不理想。本文介绍一种用非线性逐步回归的拟合方法,可以得到很满意的精度。     

新型含铱共聚物的合成及表征

利用2-对甲苯基吡啶(ptpy)、对乙烯基苯甲酸(VBA)和三水合氯化铱(IrCl_3·H_2O)配位,得到了铱配合物单体Ir(ptpy)_2(VBA),再将其与乙烯基咔唑共聚制得了一种含铱配合物的新型聚合物.通过元素分析、FT-IR光谱和~1H NMR谱等对Ir(ptpy)-2(VBA)和聚合物的结构进行了表征.凝胶色谱仪(GPC)测试结果表明,聚合物的数均分子量(Mn)为8230.此外还研究了Ir(ptpy)_2(VBA)和聚合物的紫外-可见(UV-vis)吸收光谱和光致发光(PL)光谱.光致发光光谱测试结果表明,聚合物在固态时,主体咔唑基团向客体铱配合物基团有着较为有效的能量转移.聚合物在501nm处有较强的金属配合物三重态的磷光发射峰,是一种绿色磷光材料.     

Proton-recoil detectors for time-of-flight measurements of neutrons with kinetic energies from some tens of keV to a few MeV

For experiments at the superconducting electron accelerator ELBE, where neutrons in the kinetic energy region from some tens of keV to a few MeV will be produced by bremsstrahlung, neutron-time-of-flight detectors have been developed. These detectors are made from the plastic scintillator material EJ-200. Efficiency calibration showed more than 10% efficiency for kinetic energies down to 30 keV. The calibration was done at the “accelerator facility for fast neutron research” at Physikalisch-Technische Bundesanstalt in Braunschweig, using pulsed quasi-monoenergetic neutron fields with a well-determined fluence. The low detection threshold was obtained by coincident readout of two Hamamatsu R2059-01 photomultiplier tubes per scintillator and by triggering just below the single-photo-electron peak of these photomultiplier tubes, which additionally gives a well-reproduceable detection threshold.