压缩热效应对单晶硅密度测量的影响

为了探究压缩热效应对近单晶硅液体(DSL-2329)温度的影响,可采用理论推导与实验结果相结合的方式分析计算DSL-2329液体恒温压缩系数与恒熵压缩系数的比值,比值越大,则液体温度对压强越敏感。在0.1mK的恒温液体测量环境中,通过对液体温度与所受压强的微量调节,实现单晶硅球特定的3种悬浮状态,这3种状态之间包括液体密度分别在恒温与恒熵条件下的变化过程,利用这3种特定悬浮状态之间的压强关系计算出液体等温压缩系数与等熵压缩系数的比值。实验数据表明,压强变化量越小,测得的恒熵压缩系数与液体恒温压缩系数的比值与理论值0.72越接近。     

液体密度量传中大气压强影响的研究

为了探究并修正大气压强对液体密度的影响,提出了一种在低压条件下测量密度标准液体压缩系数的方法。通过纯水和空气标准密度的校准测量设备,建立压强和液体密度之间的关系。在不同温度点下对标准液体的压缩系数进行测量,得出每100m的海拔差距引起的液体密度相对变化量大约为1×10-6,验证了密度修正的必要性。     

流量计现场检定方法及自动检定系统

介绍设计及构建的流量计现场检定方法及检定系统,在线检测被检定流量计内液体温度以及标准金属量器内的液体温度、液体密度、液体体积和几何中心处压力;计算标准金属量器内液体经过温度修正后的液体体积;检测在检测过程中挥发的油气体积及质量;计算实际液体质量或体积与被检定流量计现场示值的相对误差。检定系统包括控制器、数据采集单元、标准金属量器、高精度质量流量计、磁致伸缩液位传感器、温度传感器、密度传感器、压力传感器、溢流报警器和打印机。在标准金属量器的计量颈内安装高精度磁致伸缩液位传感器,用于测量计量颈处的液位高度,得出一定容积值,通过在线温度传感器的测量与修正,引入在线密度检测,检测精度和测量效率高。     

阿伏加德罗常数测量中单晶硅密度的绝对测量

基于改进型五幅算法,利用压力扫描原理设计出腔长可变式法-珀标准具和柔性铰链微位移平台,实现了标准具腔长和硅球表面与标准具之间的相移测量,建立了一套技术原理新颖、提高潜力较大的相移法精密测长系统.该测量系统对硅球直径的测量准确度优于3 nm,单晶硅密度的测量不确定度达到1×10-7.     

利用电容式传感器测量液位的研究

采用差动电容差压传感器测量液体的压力,利用液体的压力公式计算液位,设计了一种便携式低功耗液位仪。该仪器可以实现液位信号的采集和运算,同时还配有温度检测系统,通过软件编程对液位进行温度补偿,同时计算出液位值,最后结果由LCD显示。     

基于静力称重法的玻璃浮计校准方法研究

采用单晶硅环作为参考标准固体密度,以密度稳定、表面张力低的正十三烷为标准工作液体,选用CCD图像测量系统进行玻璃浮计刻度和液面位置的对准,设计了玻璃浮计校准系统。根据空气中和液体中两次玻璃浮计称重测量值可以计算出当前刻度对应的修正值。对密度测量范围为770~790kg/m³,最小分度为0.2kg/m³的玻璃浮计进行了测量,并与德国国家物理技术研究院进行了双边比对,验证了玻璃浮计校准系统的有效性。     

基于液体静力称量法的纯水密度测量

分析了液体静力称量法测量密度的原理和体积测量中纯水密度的特性公式,推导了由己知密度的固体标准来测量液体密度的计算公式。利用固体密度基准量传装置,通过静力称量法为固体密度标准硅球赋值,其相对测量不确定度3×10^-6(k=2)。在20℃时利用高精度液体密度测量装置,通过静力称量法将固体标准(硅球)密度传递至纯水密度,与Tanaka模型比对,E_n值为0.059,比对结果等效。实验结果不仅验证了高精度液体密度测量装置,还验证了20℃纯水密度模型的理论值。     

几种CPP树脂的pVT特性

利用PVT-100分析仅对几种不同牌号的流延聚丙烯(CPP)进行了pVT特性测量，得到了比容随温度和压力变化的关系．通过公式法计算出热膨胀系数α和等温压缩系数β与温度和压力的依赖关系，并与由Tait方程计算出的α和β结果进行了比较．另外从比容随温度和压力变化的关系图得到了各种牌号CPP熔融温度Tm与压力的关系。最后通过高温凝胶渗透色谱GPC法测量实验前后样品的分子量表明CPP在pVT特性测试过程中有部分降解。     

NRLM和IMGC固体硅密度基准双边比对的评述

为确定阿佛加德罗常数,意大利计量院(IMGC)和日本国家计量研究院(NRLM)分别建立各自的单晶硅球固体密度基准.本文介绍了两个硅球首次比对的结果NRLM以绝对法测量出IMGC硅球的质量和体积;IMGC采用液体静力法,通过比较两个硅球,测定NRLM硅球的密度.并且,双方还分别对IMGC硅球的直径进行了测量.测量结果的一致性很好密度不确定度＜0.16×10-6,质量不确定度＜0.1×10-6,体积不确定度＜0.06×10-6,直径不确定度＜0.04×10-6.     

单晶硅球密度的绝对测量

单晶硅球密度的绝对测量是阿伏加德罗常数测量的关键技术。综述了单晶硅球密度测量的最新进展,包括硅球密度测量的技术原理、测量领域、影响因素、测量装置及最佳测量能力等等,分析了硅球密度测量的主要难点和关键技术,预测了相关研究的技术前景及发展趋势。     

用于量值传递的高精度单晶硅球质量测量研究

基于单晶硅球与现行常用砝码的物理特性差异,提出空气浮力修正改进计算方法。通过对硅球质量测量时空气密度瞬态变化分析,得出单次测量序列中存在6种不同空气密度变化序列,根据不同精度等级测量对各环境参数变化限值的要求,利用CIPM公式计算环境条件动态变化下的空气密度变化量,分析得出即使在恒温恒湿精密实验室下开展测量,相邻2次测量间由于环境参数变化带来的空气密度变化幅度可达1×10^-4kg/m3。并以铂铱合金砝码作为参考砝码开展对标称质量值为1kg的高精度单晶硅球进行质量测量时,通过实验验证测量环境空气密度在单个测量序列中产生浮动变化时,采用改进后的空气浮力修正算法可减少15.1～30.2μg的计算误差。     

Surface layer impurities on silicon spheres used in determinationof the Avogadro constant

The Avogadro constant is required to be determined with an uncertainty of less than 1×10^-8 in order to allow an atomic definition of the kilogram. A single-crystal silicon sphere 93.6 mm diameter is used for this determination. A thin surface layer (typically 2 nm to 5 nm thick on flats and 10 nm or more on spheres) of contaminants such as oxide, water and hydrocarbons on the sphere can significantly affect the measurements due to corrections for density changes and to phase change on reflection in the diameter measurement by optical interferometry. The stability of this surface layer as a function of time is also of importance because of ongoing measurements. The nature of this contamination has been investigated using optical ellipsometry and ion beam analysis. It is concluded that the composition and structure of the surface layer are affected by a number of parameters and that the most appropriate method of achieving the desired accuracy is to remove the surface layer by etching and to form a hard stable coating of controlled thickness and composition. This coating may be either silicon dioxide or silicon nitride     

阿伏加德罗常数测量研究最新进展

综述了阿伏加德罗常数（N_A）测量研究的最新进展。介绍了目前测N_A准确度较高的方法—X射线晶体密度法,该方法通过测量单晶硅的摩尔质量、宏观密度和晶格常数得到N_A。采用X射线晶体密度法有望实现NA相对测量不确定度达到2×10^-8。分析了当前限制NA测量准确度提高的关键研究内容:单晶硅摩尔质量、硅球直径和表面氧化层厚度的测量。并展望了NA测量未来的工作方向。     

Density Determination of a Small Isotopically Enriched Silicon Single Crystal

For a new determination of the Avogadro constant using small crystals of isotopically enriched silicon, the density of a sample was determined at Physikalisch-Technische Bundesanstalt. The sample has a mass of 58 g and a ²⁸Si enrichment of about 99.98%. Its density was compared by the pressure-of-flotation method to the density of a large hollow transfer standard that was manufactured from natural silicon, to have the same density. The flotation measurement yielded a relative density difference of 0.64(10) 10^-6. The density of the transfer standard was then measured by hydrostatic weighing, which is traceable to a primary density standard. Thus, the density of the small ²⁸Si sample was determined to be 2320.08031(40) kg/m ³, i.e., with a relative standard uncertainty of 0.17 10^-6     

高精度单浮子磁悬浮密度测量系统研制

研制了一套高精度的流体压力-密度-温度(p,ρ,T)测量系统,其适用温度、压力和密度范围分别为90—290 K,0—3 MPa,0—2 000 kg/m3。该系统基于阿基米德原理,采用单浮子磁选耦合力传递方法,实现密度的高精度测量。该系统的温度、压力测量标准不确定度分别为5 mK、250 Pa(1.5 MPa量程)/390 Pa(3 MPa量程),密度测量最大相对标准不确定度为0.1%。用新研制的密度测量系统,对190—276 K温度区间和0—3 MPa压力区间的甲烷气体密度进行了测量,实验结果与REFPROP密度值有较好的一致性,验证了该系统的可靠性。     

Linear Thermal Expansion Coefficient of Silicon from 293 to 1000 K

As a part of the program to establish a thermal expansion standard, the linear thermal expansion coefficients of single-crystal silicon have been determined in the temperature range 293 to 1000 K using a dilatometer which consists of a heterodyne laser Michelson interferometer and gold versus platinum thermocouple. The relative standard deviation of the measured values from those calculated from the best least-squares fit was 0.21%. The relative expanded uncertainty in the measurement was estimated to be 1.1 to 1.5% in the temperature range, based upon an analysis of thirteen standard uncertainties. The present data are compared with the data previously obtained by similar dilatometers and the standard reference data for the thermal expansion coefficient of silicon, recommended by the Committee on Data for Science and Technology (CODATA). The present data are in good agreement with the most recently reported data but not with the earlier high-temperature data used to evaluate the standard reference data, which suggests a need for the reevaluation of the standard reference data for the thermal expansion coefficient of silicon at temperatures above 600 K.     

Mesoporous carbon spheres produced by hydrothermal carbonization from rice husk: Optimization,characterization and hydrogen storage

In this study, carbon spheres were synthesized from rice husk with hydrothermal carbonization method at different temperatures and different reaction times. Surface areas and pore size distributions of carbon spheres were characterized by BET surface area device, sphere morphology by SEM, structural characterization by FTIR-ATR and XRD, and thermal properties and degradation mechanism by DTA/TG. In addition, hydrogen gas adsorption measurements of the samples were also carried out with the Hiden IMI PSI gas storage device. It can be said that the required temperature is 280 °C and the required reaction time is 6 h in order to obtain homogeneous and ideal sphere morphology carbon spheres from a lignocellulosic biomass in experiments carried out under different conditions in an acidic reaction medium. This is clearly seen from the SEM images. In addition, FTIR spectra and XRD patterns confirm that the sphere was obtained. According to the BET surface area and pore size distribution results, it can be said that the main significant difference is in the mesopore structure of the carbon spheres, even if the surface area values of the samples obtained at different temperatures and different reaction times increase linearly with temperature. In order to determine the usability of carbon spheres obtained in different conditions in the energy field, the gravimetrically measured H₂ storage capacities at cryogenic temperature (77 K) and pressure range of 0–30 bar were determined as maximum 1.1% by weight. When the hydrogen storage capacities of the samples are evaluated together with the BET surface area values and pore size distributions, it shows that the hydrogen storage capacity in carbon spheres is directly proportional to the mesopore volumes. In addition, Langmuir and Freundlich isotherms related to adsorption equilibrium were investigated in order to better define the H₂ adsorption that took place in these samples. Considering the regression coefficients of the obtained isotherms, it was determined that some of the carbon spheres were more compatible with the Langmuir isotherm and some with the Freundlich isotherm.