McLeod Gauge Research Articles

三極管型電離真空計の比感度係数に及ぼす空間電荷の影響

Secondary standard ionization gauges (VS-1) had been calibrated by using the primary standard McLeod gauge at former Electrotechnical Laboratory for about twenty years around 1980's. VS-1 is a triode gauge. Sensitivity coefficient of VS-1 was measured experimentally and reported by Hirata et. al. Simulation of the electrical potential profile of the gauge, electron trajectory emitted from a hot filament, and ion current produced by electron impact ionization of gas assuming a simple electrode geometry was done. The space charge is also taken into consideration in the simulation. In the simulation results in the pressure range above 10−2 Pa the relative sensitivity coefficient of Ar increased with pressure and that of He decreased with pressure. In the pressure range between 10−3 Pa and 10−2 Pa the relative sensitivity coefficient of Ar and He were constant respectively. These features are similar to the experimental results. Taking the characteristics of the relative sensitivity coefficient into account, it is recommendable to use this gauge in the pressure range between 10−3 Pa and 10−2 Pa.

K-Ar and Ar-Ar Dating

The aim of this chapter is to present the K-Ar and Ar-Ar dating techniques in the context of noble gas studies, since there are already several recent texts on K-Ar and Ar-Ar dating (Dickin 1995; McDougall and Harrison 1999). The focus of this section will be aspects of argon transport and storage in the crust, which affect K-Ar and Ar-Ar dating including Ar-loss from minerals by diffusion and Ar-gain by minerals or “excess argon.” The K-Ar dating technique was one of the earliest isotope dating techniques, developed soon after the discovery of radioactive potassium, and provided an important adjunct to U-Pb and U-He dating techniques. The ease of measurement and ideal half-life (1250 million years; see Table 2⇓ below), for dating geological events has made this the most popular of isotopic dating techniques. Aldrich and Nier (1948) first demonstrated that 40Ar was the product of the decay of 40K, and soon after K-Ar ages were being measured in several laboratories most often using an absolute method such as a McLeod gauge to measure argon concentrations. The first published K-Ar results by such a technique were those of Smits and Gentner (1950) who analyzed sylvite from the Buggingen Oligocene evaporite deposits, obtaining an age of 20 million years. Mass spectrometers, which simultaneously measured very small amounts of gas, and the isotope ratios necessary to make corrections for atmospheric contamination, quickly replaced manometric techniques. Crucially the use of static vacuum techniques, pioneered by John Reynolds at the University of California-Berkeley, meant that mass spectrometers were sufficiently sensitive to analyse the small amounts of gas released from common rocks and minerals. Although the earliest mass spectrometers were built ‘in house’, the introduction of the commercially available MS10 (Farrar et al. 1964), a small 180° metal mass spectrometer built for …

Safety and health considerations related to vacuum gauging

Safety or health hazards exist with some common types of vacuum gauging including mercury manometers, thermal conductivity gauges, and ionization gauges. Mercury filled manometers and McLeod gauges have been replaced by other gauging in most applications. The difficulty with thermal conductivity gauges arises because the calibration curves for various gases diverge widely at the upper end of the range, from 10 to 1000 Torr. When they are used to monitor backfilling to atmospheric pressure, dangerous over or under pressure situations may exist if the identity of the gas is not known. The greatest danger with hot cathode ionization gauge systems is electric shock from the high voltages supplied by the control unit. Especially with gauges using electron bombardment degas, proper use of grounds, cables, and connectors is necessary. A concern with many hot cathode ionization gauge sensors is the thorium oxide electron emitting coating on the cathode. Natural thorium is an alpha emitter with a half-life of 1.4×1010 years. Yttrium oxide is a safe alternate coating material now available in ionization gauges.

Residual gas pressures in sealed fused silica glass ampoules

The residual gas pressures in sealed and annealed ampoules made from silica glass have been determined using different methods including a McLeod gauge. It has been found that the gas build-up in the ampoule is mainly the result of the ampoule heat treatment; the amount of gas released and trapped during sealing the ampoule under vacuum is much less. The pressures in the ampoules after heat treatment range from a few mTorr to a few Torr, depending on the silica glass and on the outgassing and annealing procedures.

Intercomparison of vacuum standards between LIP and PTB

The Lanzhou Institute of Physics (LIP) with the McLeod gage and the Physikaalisch-Technische Bundesanstalt (PTB) with the static expansion standard, adopting the DL-2 hot cathode ion gage made in China as the transfer gage, twice carried out intercomparisons for He, Ar and N2 from 1987 to 1989, respectively. The deviation of the results was well within the range of uncertainties. During the two years, the reproducibilities of the DL-2 were 0.49% for the PTB and 0.88% for the LIP. The LIP purchased a SR-G gage calibrated by the PTB from MKS Co. When transported to China, the LIP conducted the careful calibration of it. The deviation of the data from the PTB and LIP was also within the range of uncertainties.

Thermocouple gauge for partial pressure measurements

We here present the design and testing of a thermocouple gauge with unique properties. Operating the gauge at different temperatures allows one to measure the partial pressure of different gases in a vacuum system. The gauge system consists of two parts, the detector and the control circuitry. The detector consists of a filament and a heat shield. A differential thermocouple measures the temperature difference between the filament and the heat shield. The control part consists of circuitry that keeps the temperature difference between the filament and heat shield constant by controlling the filament power. The gauge has been calibrated with a Mcleod gauge and with various gases, such as He, Ar, N2, and CO2 gas. This gauge measures pressure without ionizing the gases. Experimental results show that the gauge is very sensitive down to 10−4 Torr.

Multicapillary swivel-type McLeod

A multicapillary swivel-type McLeod of easy transport and operation, which is able to measure pressures from 10 3 down to 10 −3 Pa, was designed, built and finally tested in a high vacuum calibration system against a typical McLeod gauge.

Fabrication and calibration of integrated Cu–Cr thermocouple gauge

We report here the design, fabrication, and testing of an integrated thermocouple gauge. The gauge uses a thin-film Cr heater and a thin-film Cu–Cr differential thermocouple on a 5-×3-mm glass substrate. The thermocouple measures the difference between the heater and the substrate temperature. Calibration of the thin-film Cu–Cr thermocouple gauge was done by using a standard K-type thermocouple as reference. At a constant difference temperature the measured power input to the heater is a function of the surrounding vapor pressure. The thermocouple gauge was calibrated using a McLeod gauge with He, Ar, N2, H2O, and CO2 gases. Our measurements show that the range of the gauge can possibly be extended to the μTorr range. This gauge uses a standard thin-film processing technique for fabrication resulting in a lower cost of production. Also, small size makes this gauge versatile and unique in comparison to many commercial gauges.

Effect of measuring conditions on the accuracy of a spinning rotor gauge

The performance of a spinning rotor gauge was measured for nitrogen under various conditions. The effective accommodation coefficient was determined to be 1.05 by comparison with the standard McLeod gauge. The ratio of the reading of the gauge to that of a diaphragm gauge showed a variation ±1% at pressures from 0.1 to 10 Pa. The deviation of the ratio at 0.3 Pa was within ±1% for 7 months. The lower limit of the measuring pressure of the gauge was affected by fluctuations of its offset. The angular deviation of gauge positioning changed the offset up to 10−3 Pa (nitrogen equivalent). Just after starting the operation of the gauge at pressures less than 10−5 Pa, the offset changed by ±3×10−5 Pa from its final value. This was revealed to be due to a temperature variation of the rotor. And the offset depended not only on the amplitude of vibration but also on its frequency.

Mercury vapor streaming effect in McLeod gauges

In this paper the authors explain the experimental results, reported earlier, on the error made in measuring pressures below the vapor pressure of mercury with a McLeod gauge. Mercury vapor streaming effects the pressure measurement made by a cold trapped McLeod gauge. The percentage of errors in the pressure measured (i.e., Δp/P2%) agrees with Gaede’s transport theory and Takaishi’s kinetic theory of gas analysis of this problem. Below the vapor pressure of mercury the percentage error starts rising and rises to 10.3% forming a plateau and increases to 17%–19% below 2.67×10−3 Pa (2×10−5 Torr). This increase in pressure measurement error below 2.67×10−3 Pa (2×10−5 Torr) has been found to be in quantitative agreement with that predicted by Rambeau.

The mercury vapour pumping effect for 3 He, 4 He, H 2 , D 2 , Ne, Ar, Kr, Xe, N 2 , O 2 , CO 2 , CH 4 , C 2 H 4 , and C 2 H 6 : its precise measurement and convenient application in McLeod gauge metrology

The McLeod gauge, an amplifying device for the mercury column, has been used since its inception in 1874 as the basic instrument for measurement of pressure or number density of gases at pressures below 1 Torr (1 Torr ≈ 133.32 Pa). In practically all cases for direct pressure measurement or for use in calibration of other gauges it must be used with a trap to remove mercury. In the 1960s it became generally known that the movement of mercury vapour from the gauge toward the trap increases the permanent gas pressure beyond the trap above that at the McLeod gauge, and that if this is overlooked the pressures assigned to the working region under common laboratory conditions may be in gross error, of a magnitude of up to hundreds of times the probable error of reading the gauge. We have found it quite impossible to gather from the literature the means for accurate correction of the McLeod pressure readings adequate for use in our clean surface thermal accommodation work, so have undertaken much more extensive sets of measurements than have previously been available. These are described in this paper. A new apparatus and method has been applied under carefully controlled conditions to supply 250 mercury pumping pressure measure­ments in 27 sets involving 14 gases over relevant ranges of pressure, temperature, and pumping tube radius and length. A semi-empirical equation has been developed for calculating the mercury pumping pressures for any set of conditions and has been thoroughly tested over the ranges and the gases used against our measurements, and comparison of results is made with other selected papers. The result of the work for us has been renewed confidence in the ability of the McLeod-gauge—cold-trap system to render precisely known pressures and, when applied in our measurements of thermal accommodation coefficients, it constitutes a ‘break-through’ in the accuracy and consis­tency of the measurements. Because of this, the paper is presented here as a necessary preliminary to two experimental papers on clean surface accommodation coefficients, which we intend to offer shortly in honour of and as an extension of the work of J. K. Roberts (1930), who first emphasized the importance of controlling surface conditions and first undertook bare surface measurements in this area. Our expression of appreciation for the work of Roberts belongs with these papers to follow.

Calibration of secondary standard ionization gauges

A McLeod gauge, designed, built and maintained by us, serves as the primary vacuum standard of Japan. We measure the sensitivities for nitrogen of the secondary standard ionization gauges (VS–1) with an accuracy of ±3% with the McLeod gauge in the pressure range from 0.01 to 0.3 Pa. The VS–1 gauge is a triode type that shows constant sensitivity from 1×10−4 to 0.3 Pa. 258 VS–1 gauges were calibrated since 1964. The average value of the sensitivities is 0.137 Pa−1. About 85% of the gauges have sensitivities with less than ±10% deviation from the average. The main reason for the spread of sensitivities was the electrode displacement. We discuss the technical problems connected with the use of the VS–1 gauge as a transfer gauge for international comparison of vacuum standards.

ＶＳ‐１の電極変位と感度との相間

Secondary standard ionization gauges (VS-1) have been calibrated by using the primary standard McLeod gauge at ETL for about twenty years. The average value of the sensitivities is 0.137 Pa-1. About 85% of the gauges have sensitivities with less than ± 10% deviation from the average. It was confirmed by the X- ray photograph of the gauge and the experiment of a nude type gauge with movable electrodes that the spread of the sensitivities are mainly caused by the electrode displacement. It is also discussed that the technical problems connected with the use of the gauge as a transfer gauge for the international comparison of vacuum standards.

Ultimate pressure of mechanical pumps and the effectiveness of foreline traps

The ultimate pressure attainable with two‐stage, rotary vane‐type mechanical pumps is often obscured by the presence of the lubricating oil. Its reported value depends on the method of measurement. Experimental results are presented with trapped and untrapped pumps using McLeod, ionization and diaphragm gauges (capacitance manometers). Partial pressure measurements performed with both zeolite and liquid nitrogen trapped pumps continuously monitored over a two month period indicate the possibility of maintaining ultimate pressure near 1×10−3 Pa for a few months. This depends on the frequency of atmospheric exposure and the duration of operation at higher pressures. However, the usefulness of mechanical pumps at such reduced pressure is limited by the relatively low pumping speed for a given size and cost. The primary benefit is in reducing the condensable vapors by approximately one hundred times.

気体透過膜の性能評価法

Various methods of test for gas transmission rate of polymer membranes were summerized, which cover the determination of the steady state rate of transmission of a gas through polymers in the form of film, sheeting, laminates and polymer coated papers. They provide for the determination of (a) gas transmission rate (GTR), and (b) permeability coefficient in the case of homogeneous materials, and (c) diffusion coefficient.Methods are divided into two main groups; A) non-equable pressure method and B) equable pressure method. In the non-equable pressure method, the pressure difference exists across the sample and the permeated gas through the sample is measured by a monometric method or volumetric method. In the manometric method, when the lower pressure side of the sample is initially evacuated at 10 -5 -10 -6 mmHg, the transmission of the gas through the test specimen is indicated by a change in pressure which is measured by Mc Leod gauge or an MKS Baratron pressure transducer. This method is called “high-vacuum technique ”. When the lower pressure side of the sample is initially evacuated at 10 -1-10 -2 mmHg, the transmission of the gas is measured by a cell manometer, namely a closed end U-tube manometer. This method is called “low-vacuum technique ”. In the volumetric method, the low pressure side of the sample is maintained near atmospheric pressure and the transmission of the gas is indicated by a change in volume. In the equable pressure method, the total pressures of the both sides of the sample are equal. The permeated gas is measured by a detector system, for example, cas chromatography, thermal conductivity. When oxygen is a test gas, the oxygen electrode is available.In both methods (A) and (B), the principles, apparatus and calculations were described here in detail.

Solid state decomposition studies of fluoroperoxo species of transition metals VIII: photodecomposition of Rb 3Zr 2(O 2) 2F 7·H 2O and Cs 3Zr 2(O 2) 2F 7·2H 2O

The kinetics of photodecomposition of the solids Rb 3Zr 2(O 2) 2F 7·H 2O and Cs 3Zr 2(O 2) 2F 7·2H 2O were studied under vacuum as a function of both intensity and temperature by measuring the pressure of the oxygen evolved with a McLeod gauge. Similar to other fluoroperoxozirconates the photolysis kinetics of these compounds are deceleratory throughout the decomposition reaction. The pressure—time curves are parabolic and the data fit the rate equation p = kt 1 2 . Also the rate of photodecomposition is a linear function of the intensity, indicating a monoexcitation process for the photolysis. The probable mechanism of photodecomposition can be visualized as the interaction of peroxo groups in excited states at special sites: ▪

A simple graphical method of pressure determination in a McLeod gauge

This paper describes a simple graphical approach for pressure determination using a conventional McLeod gauge. This method also permits a simultaneous detection of the presence of condensable vapours and gases present in the gauge or the system. The pressures thus determined are compared 4.

McLeod gauge: Investigations of capillary depression phenomena and mercury vapor drag effect

This paper describes the accurate determination of pressure in the range 10−3–10−6 Torr (∠10−1–10−4 Pa) by a bakeable McLeod gauge using variable compression technique. A thorough investigation of two major aspects of pressure determination by a McLeod gauge, i.e., capillary depression phenomena and mercury vapor stream effect, has been made. The capillary depression phenomena in the wide bore reference arm tube has also been taken into account in determining the capillary depression correction in the compression capillary. The minimization of the error due to the vapor stream effect of mercury has been studied by cooling the cutoff point in the McLeod gauge at different temperatures, i.e., 0°, −15°, and −78 °C. The pressures thus determined are found to be accurate to ±2% or better.

Solid state decomposition studies on fluoroperoxo species of transition metals. IV. Photodecomposition of K 3Zr 2(O 2) 2F 7 · 2H 2O

The kinetics of photodecomposition of solid K 3Zr 2(O 2) 2F 7 · 2H 2O have been studied under vacuum as a function of intensity and temperature by measuring the evolved oxygen with the help of a McLeod Gauge. Pressure-time curves are parabolic in nature and the data fit the empirical equation p = kt 1 2 . The rate of photodecomposition is a linear function of intensity. The activation energy determined from an Arrhenius plot, in the temperature range 15–55°C, of the title compound is 2.15 kcal mole −1 (9.00 kJ mole −1).

Solid-state decomposition studies on fluoroperoxo species of transition metals part II

The kinetics of isothermal decomposition of solid K2Zr2(O2)2F6·2H2O have been studied in the temperature range 100–226° under vacuum. The fractional decomposition α has been determined by measuring the pressure of evolved oxygen during pyrolysis with the help of a McLeod gauge. The α values ranged from 0.05 to 0.62. The αvs. t data showed that the kinetics are deceleratory throughout the course of the reaction. The initial part of the decomposition reaction could be best described by a unimolecular decay law, while the later stages obey contracting volume kinetics. The activation energies have been determined and the respective values for the above stages are 13.6 and 6.9 kcal·mole−1.