基于Scheil方程的微量杂质对锌凝固点相变温度影响的评估方法

微量杂质是影响ITS-90国际温标定义固定点复现的最主要的不确定度来源。从凝固理论出发,建立基于Scheil方程的评估微量杂质对凝固点相变温度影响的数学模型,以国家温度基准中的锌凝固点为对象,利用最小二乘拟合法拟合实验数据评估了杂质对其相变温度的影响,并通过化学分析对该方法的有效性进行了验证,结果表明,全部杂质综合结果使相变温度增加0.56mK,化学分析结果中Ag及Cu在锌中存在一定量级证明该方法的有效性,该方法相对于SIE与OME方法具有较好的应用前景。     

SiCl4氨解法制备高纯度的Si3N4粉的研究

本文研究了影响Ｓｉ３Ｎ４粉中杂质氧和氯的含量的因素和如何提高粉料的纯度。实验表明：原料ＳｉＣｌ４（液）和ＮＨ３（气）的纯度对粉料中杂质氧和氯的含量影响不大。制备粉料过程中，加热温度越高，加热时间越长，粉料中杂质氯的含量越低；不同的保护气氛对粉料中杂质氧和氯的含量的影响大，保护气氛为真空，得到的粉料质量很差，粉料中杂质氧和氯的含量均很高。在高纯Ｎ２气氛中制粉，得到的粉料其纯度亦很低，含氧量达４％￣６     

ZnS：Mn^2＋薄膜电致发光器件中电子散射过程的研究

研究了薄膜电致发光器件中的电子散射过程，计算了ＺｎＳ：Ｍｎ＾２＋中声学声子，极化光学声子，电离杂质及谷间散射的几率随电子能量的变化关系，对各种散射这程了比较，发现极化光学声子散射及谷间散射较为重要，杂质散射的重要性取决于浓度的大小。同时研究了它们在不同能谷中的行为，进而研究了温度对散射过程的影响。     

复现90温标定义固定点时杂质引起的偏差估算

本通过介绍一种计算杂质在复现各定义固定点温度时引起的偏差的方法,从实验及理论分析计算的角度讨论了在高纯金属凝固（或熔化）过程中,样品中的杂质对相变温度的影响。     

常压CVD法制备Si—N—O薄膜及其电性能

本文利用常压ＣＶＤ设备在较低温度下制备得到了Ｓｉ－Ｎ－Ｏ薄膜，探讨了反应温度，反应时间，ＮＨ３中杂质水汽薄膜生成的影响。制得的薄膜具有较大的体积电阻。     

高浓度补偿掺砷锗的电离杂质密度分析

对含净杂质浓度(N_D-N_A)高于7×10~(16)cm~(-3)的补偿掺砷锗进行了电离杂质密度的分析。霍尔分析和二次离子质谱含杂相对量的分析结果与在霍尔迁移率峰值温度下的电离杂质密度分析结果相一致,证实 Brooks-Herring 电离杂质散射迁移率分析式,对于高浓度补偿掺砷锗的分析仍是适用的。最佳分析温度因杂质浓度而有所差异,不宜简单采取两个温度(如300K 和77K 两个温度点)测量法,应取测量迁移率出现峰值的温度为最佳分析温度。     

毛细管色谱法分析2，6-二叔丁基对甲酚的纯度

采用毛细管气相色谱技术，使用OV1大口径石英毛细管柱，在稳定的温度、压力操作条件下对样品进行测定，并筛选最佳分析操作条件，成功分离了8种杂质，测定出了异丁烯和对甲酚合成的2，6二叔丁基对甲酚及游离甲酚含量。     

杂质对磷石膏应用性能的影响

磷石膏是一种含有磷、氟等杂质的化学石膏,其中杂质对磷石膏的应用性能产生了不利影响,限制了其实际应用.由于杂质的存在,磷石膏脱水温度较天然石膏低,当其用作水泥缓凝剂时,在粉磨温度下可能脱水生成半水石膏和无水石膏,影响水泥性能;磷石膏和天然石膏制备的半水石膏胶结材料微观结构与物理性能之间存在较大差异.现有磷石膏预处理研究大多偏重于宏观性能的比较,而对杂质影响机理的研究较为欠缺,因此很有必要对其进行系统的基础研究.     

直流等离子体CVD金刚石膜的阴极发光性质的研究

本文研究了直流等离子体ＣＶＤ金刚石膜在常温和液氮温度下的阴极发光光谱，探讨了阴极发光谱中各峰的起因，并分析了光谱随测量温度和沉积条件的变化情况，讨论了造成这种变化的原因。研究表明，金刚石膜中缺陷和杂质以及金刚石膜的晶体结构对它的阴极发光光谱有重要的影响。     

冶金法制备高纯硅过程中石油焦粉的净化研究

为给高纯硅的制备提供一种高纯原料,详细研究了石油焦粉的酸浸除杂、超声酸浸除杂、真空高温除杂,考察了石油焦粉粒度、盐酸浓度、酸浸时间、酸浸温度、酸浸液固比和搅拌对除杂效果的影响.得到的最佳工艺条件为:石焦粉颗粒控制在150μm以下,盐酸质量分数5%,反应时间6 h,水浴温度70℃,浸出液固比10∶1,搅拌速度40 r/min.在此工艺条件下,石油焦粉中金属元素杂质的去除率可高达94.69%,非金属元素杂质的去除率达39.95%.实验同时探讨了超声场作用下酸洗时间对杂质去除效果的影响,以及在真空高温焙烧条件下杂质的去除效果,最终金属元素杂质和非金属元素杂质的去除率分别达到了99.55%和99.23%.     

A Solidification Approach to Correcting for the Effect of Impurities in Fixed Points

Uncertainty estimation for the effect of impurities on fixed points requires an accurate assay of the fixed-point material. To apply a correction also needs a knowledge of the liquidus slope of the solute binary system. Two methods are presented here for giving a realistic uncertainty and potential for correction without detailed knowledge of the impurities present. Both methods are based on the Scheil equation. The first method uses the gradient at about 50% solid; and where some limited knowledge of impurities is available, this method can, in cases where the bulk of impurities segregate preferentially into the liquid phase, be used to apply a correction. To apply an uncertainty simply knowing typical impurities for a particular metal may be considered sufficient. The second method involves a best fit for the four variables in the Scheil equation. It is shown that this second method can work even where multiple impurities are present, but that when applied to real data, problems arise due to deviations from Scheil behavior. This deviation is thought to be due to difficulties in maintaining a uniform solid/liquid interface at the end of a freeze.     

On the problem of superconductors containing polarized magnetic impurities

We investigate theoretically the influence of impurity polarization on the superconducting transition temperature of superconductors containing magnetic impurities. From previous theoretical work it is known that the pair-breaking effect of magnetic impurities is reduced when the impurity spins are fixed by an internal field. This spin-dynamic effect is studied in detail on two models of the magnetic state of the system based on a mean field theory. In some cases the critical concentration of magnetic impurities that destroys superconductivity atT=0 is increased, but we find that the polarization energy of the magnetic impurities must be very large compared to the gap energy of the pure superconductor in order to increase the critical impurity concentration by the factor (S+1)/S reported in the literature. We conclude that the anomalous dependence of the superconducting transition temperature on the concentration of magnetic impurities observed on some dilute alloys with rare-earth impurities can only be attributed to spin-dynamic effects if extraordinary strong polarizing forces between the magnetic impurities exist.Supported in part by Deutsche Forschungsgemeinschaft.     

Doping Experiments in Mercury Triple-Point Cells

Mercury is one of the fixed points that can be obtained with higher purity, and it also can be measured with high accuracy; this turns impurities into one of the dominant sources of uncertainty. This article summarizes the first steps that CEM has carried out to start an exhaustive study of the influence of impurities on the triple-point-of-mercury temperature by means of doping experiments. The basis to choose the doping elements are stated, the procedure to dope the cells is described together with the careful performance of the weighing of the alloy components, and the results obtained for Zn and Ag are also shown.     

High-Purity Fixed Points of the ITS-90 with Traceable Analysis of Impurity Contents

The International Temperature Scale of 1990 (ITS-90) is based on thermodynamic equilibrium states of ideally pure substances. The largest contribution to the uncertainty budgets of most metallic fixed points is the influence of impurities on the fixed-point temperature. Therefore, a traceable chemical analysis of the remaining impurities with small uncertainty is the basis of further progress. Further requirements are better knowledge of the phase diagrams at very low impurity contents, impurity segregation, and the quantification and correction of thermal effects during a fixed-point realization. In this article, current and future activities at PTB and BAM in order to develop improved metallic fixed-point cells of the ITS-90 are reviewed.     

Estimating the Contribution of Impurities to the Uncertainty of Metal Fixed-Point Temperatures

The estimation of the uncertainty component attributable to impurities remains a central and important topic of fixed-point research. Various methods are available for this estimation, depending on the extent of the available information. The sum of individual estimates method has considerable appeal where there is adequate knowledge of the sensitivity coefficients for each of the impurity elements and sufficiently low uncertainty regarding their concentrations. The overall maximum estimate (OME) forsakes the behavior of the individual elements by assuming that the cryoscopic constant adequately represents (or is an upper bound for) the sensitivity coefficients of the individual impurities. Validation of these methods using melting and/or freezing curves is recommended to provide confidence. Recent investigations of indium, tin, and zinc fixed points are reported. Glow discharge mass spectrometry was used to determine the impurity concentrations of the metals used to fill the cells. Melting curves were analyzed to derive an experimental overall impurity concentration (assuming that all impurities have a sensitivity coefficient equivalent to that of the cryoscopic constant). The two values (chemical and experimental) for the overall impurity concentrations were then compared. Based on the data obtained, the pragmatic approach of choosing the larger of the chemical and experimentally derived quantities as the best estimate of the influence of impurities on the temperature of the freezing point is suggested rather than relying solely on the chemical analysis and the OME method to derive the uncertainty component attributable to impurities.     

Aluminum Fixed Point: Impact of the Time Spent in the Liquid Phase on the Liquid�CSolid Transition and Obviousness of the Pollution of the Ingot

In order to improve the uncertainty on the aluminum fixed point, a study was launched by Laboratoire Commun de Métrologie LNE-CNAM in the frame of the EURAMET Project 732 ??Toward more accurate temperature fixed points?? (coordinating laboratory: France, 17 partner countries). An earlier study completed in this laboratory showed that in regular realization of the melting?Cfreezing plateaus, there is no diffusion of impurities in the thickness of the ingot, or the diffusion is excessively slow and cannot allow a uniform distribution of the impurities. On the other hand, it is frequently noticed that the experimental conditions before the freezing plateau have an impact on its characteristics (value, slope,??). Up to now, no systematic study was performed on the influence of this parameter. So, the objective of the task started recently in this laboratory is to investigate the influence of the time spent in the liquid phase on the phase transition. As a final result, it is demonstrated that in order to reach the equilibrium of the concentration of impurities, it is necessary to ensure that the metal remains in the liquid phase at least 24 h before initiating the freeze. At the end of the process, the aluminum ingot was chemically analyzed. The analyses reveal large contaminations of the surface of the ingot (sodium, sulfur, and phosphorus). One of the important outputs of this study is that the conditions of usage of the cells should be given important attention since large contaminations can be brought by the furnace.     

Impurity Effect in Silver-Point Realization

CCT-WG1 has recommended the sum of individual estimates (SIE) method to correct for the influence of impurities on the realization of temperature fixed points when a detailed impurity analysis is available. The method to estimate the uncertainty of the SIE has also been reported. On the other hand, most cells are fabricated from commercial fixed-point metals that often have no detailed impurity analysis, so the SIE calculation is impossible in that case. Due to this circumstance, and with the focus on the silver fixed point, a new fixed-point cell was fabricated in such a way that a portion of the silver ingot used was extractable during the silver casting. This portion was then analyzed by glow discharge mass spectrometry (GDMS), and the result used to calculate the SIE correction and its uncertainty. Temperature measurements during melting and freezing were collected using new and existing silver fixed-point cells under various conditions. These measurements were used to derive the slope of the silver freezing curve, from which the effect of impurities was evaluated by thermal analysis. The difference between the SIE and the thermal analysis method was evaluated to check the inaccuracy of the thermal analysis from the SIE point of view.     

Establishment of NIMT Zinc Fixed-Point Cell

One of the research programs for the Thermometry Metrology Department at the National Institute of Metrology (Thailand), NIMT, is establishment of its own fixed-point cells. Among the fixed-point cells adopted for the realization of the International Temperature Scale of 1990 (ITS-90), NIMT has chosen the zinc fixed point to start the program. The fabrication and the initial evaluation of the zinc fixed-point cell were conducted at the National Metrology Institute of Japan, NMIJ. The cell fabrication was following the design and procedures developed by the NMIJ. In the cell fabrication, a 6N nominal purity zinc metal cylinder ingot was used. The metal ingot was collected in a graphite crucible under an argon gas atmosphere. The new fixed-point cell was compared with the old fixed-point cells already owned by NIMT, namely, one open-type cell and one sealed-type cell by direct cell comparisons. Since the ingot was equipped with a detail impurity element analysis, it is possible to calculate the effect coming from the existence of the impurities based on, for example, the sum of individual estimates (SIE) method. This effect can then be used to correct for the influence impurities on the realization of the temperature fixed point.     

Survey of Key Parameters of Impurities in Aluminum: Diffusion Coefficients,Solubility, and Liquidus Slopes

Impurities represent in many cases the largest contribution to the uncertainty associated with fixed points of the International Temperature Scale of 1990 (ITS-90). The effect of impurities on the solidification temperature of ITS-90 metals can be characterized by the liquidus slope, the values of which have recently been characterized for a large number of systems. Two other key parameters are the diffusion coefficient, which provides information on how rapidly diffusion, and hence mixing, proceeds, as well as on the validity of the Scheil model of solidification; and the solubility, which provides information on how much impurity is actually dissolved and hence participates in affecting the solidification temperature. In this study, a comprehensive survey is presented of liquidus slopes, together with a survey of 237 diffusion coefficients and 274 values for the solubility of impurities in both liquid and solid aluminum.