摘要:

A technique has been developed for measurement of small displacements. The method relies on multiple beam optical interference, with the sample used as a Fabry‐Perot etalon spacer. Extreme precision is made possible by monitoring in the electrical domain the thermally induced changes in optical interference. The method is as follows: A frequency stable laser is used to probe the resonances of a Fabry‐Perot etalon whose mirrors are optically contacted to the ends of the sample. The incident beam is electro‐optically modulated to impress sidebands on it which can be moved in frequency until one coincides with a Fabry‐Perot transmission peak. When the sample temperature is changed an amount &Dgr;T the subsequent length change &Dgr;L causes the Fabry‐Perot resonances to shift an amount&Dgr;&ngr; = (&ngr;/L)&Dgr;L. This change in modulation frequency is related to the thermal expansion coefficient&agr; ≡ (1/&Dgr;T) (&Dgr;L/L) = (1/&Dgr;T)(&Dgr;&ngr;/&ngr;). For small values of &agr; the precision of measurement is limited by the laser's frequency stability, which is approximately one part in 109. Measurements have been made in the temperature range 0 – 300°C. A proposal is outlined for increasing the laser's stability and hence the precision of measurement by at least 3 orders of magnitude. Applications for such high precision are discussed.

ISSN:0094-243X    

DOI:10.1063/1.2948558

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Fused silica is the second of a series of materials to be certified as thermal expansion standards by the National Bureau of Standards. The results of tests on five samples indicate the stock to be consistent quality suitable for certification as Standard Reference Material 739. The same interferometer apparatus was used as in the certification of copper SRM 736. Expansivity values from each of the five samples were fitted using a least squares third order spline polynomial with three separate temperature intervals. The data from all the samples were then pooled and fit with the same type spline polynomial. Values calculated from these equations and their integrals are presented and also compared to literature data on fused silica.

ISSN:0094-243X    

DOI:10.1063/1.2948551

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

As a part of a major AGARD project concerning thermophysical properties of solid materials at high temperatures, cooperative thermal expansion measurements up to 1000°C were carried out using pushrod techniques. Sixteen laboratories have contributed results. Parallel samples having the same history were used for all tests. Materials investigated were very pure gold and platinum, an austenitic alloy, alumina, and three types of graphite. From the mean values of the individual contributors, band widths of group scatter as well as group averages were derived. In addition, error analyses were carried out to show if the errors involved were predominantly of a systematic or of a non‐systematic nature. For gold and platinum, the absolute accuracy of the group averages amounting to 0.005 per cent expansion was found to be no worse than that of individual averages by X‐ray and optical measurements. Of the technical materials investigated, the austenitic alloy, alumina, and a special ultrafine‐grain graphite were found to be very suitable materials. In the case of alumina, a correction of the originally submitted individual averages by calibrating the apparatuses with platinum was found to decrease the band width of group scatter to any significant extent but again the group averages remained unchanged. Regarding the accuracy obtained by the pushrod dilatometers used in this cooperative program it was observed that it is possible for an individual calibration to be less reliable than a statistical evaluation of a group effort. This surprising result indicates that the individual measurement conditions differ from those of the individual calibration runs. For the pushrod dilatometer reference system, up to 900°C silica glass was found to be acceptable but not better than alumina. Ultra‐fine‐grain graphite looks promising for the same application.

ISSN:0094-243X    

DOI:10.1063/1.2948565

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

To date, most applications of materials having very low thermal expansion have been near 20°C. In 1968 Plummer and Hagy reported measurements on some low‐expansion materials using Fizeau interferometry attaining high precision and accuracy. These measurements were limited to a maximum temperature of 80°C. In response to interest in expansion of these materials at somewhat higher temperatures, the apparatus has been modified to permit measurements to 130°C. Results of these measurements are reported.

ISSN:0094-243X    

DOI:10.1063/1.2948571

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

An electrical method has been developed for estimating the coefficient of linear expansion of a solid. Application of longitudinal stress on wires results in typical lattice distortions. Measured adiabatic and isothermal stress coefficients of resistance, Poisson's ratio, Young's modulus along with standard values of density and specific heat of the material allow us to calculate its desired linear coefficient of expansion to quite a good accuracy.

ISSN:0094-243X    

DOI:10.1063/1.2948572

出版商:AIP    

年代:1972

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.2948573

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Copper samples which have been measured in the capacitance dilatometer include Asarco (6N), OFHC, deformed, electrolytic tough‐pitch, phosphorus‐deoxidized, tellurium‐copper, and alloys containing 0.2% Fe and Mn. At room temperature and oxygen temperature they differ in linear coefficient a from the dilatometer cell (itself OFHC copper) by< ½% (<0.1 × 10−6 K−1). Below 30 K differences between annealed and 70% deformed material, and between Asarco and OFHC, are <1%, but the magnetic impurities inCuFe andCuMn alloys do have an increasing and marked effect on the expansion, a being increased byca4% at 20 K and 40% at 10 K.

ISSN:0094-243X    

DOI:10.1063/1.2948574

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Measurements of a for the N.B.S. standard copper from 30K to 2K are presented.

ISSN:0094-243X    

DOI:10.1063/1.2948575

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

The low temperature thermal expansion of pure zinc and a dilute (40 ppm) zinc manganese alloy have been measured. Results confirm the oscillatory behavior of pure zinc and show the effect of a magnetic impurity. The pure zinc results can be accounted for by a possible c/a effect on the electronic contribution to the thermal expansion.

ISSN:0094-243X    

DOI:10.1063/1.2948576

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Measurements, using the optical dilatometer described by Bunton and Weintroub, of the linear expansivities&agr;&psgr;between the temperatures 200 K and 6 K of four single crystal specimens of Te of orientations&psgr; = 0°, 45.5°, 86.5° and 90°are reported. It is shown that Voigt's law&agr;&psgr; = &agr;⊥ + (&agr;∥−&agr;⊥) cos2&psgr;is obeyed, where&agr;∥and&agr;⊥are the principal expansivities in the directions parallel and perpendicular respectively to the trigonal axis. Values of&agr;∥and&agr;⊥as a function of temperature are tabulated and shown graphically. Throughout the whole temperature range&agr;∥is negative and&agr;⊥positive. The Gru¨neisen parameters&ggr;∥and&ggr;⊥are calculated and are shown graphically as a function of temperature. Below 70 K,&ggr;∥ < &ggr;⊥, but at higher temperatures&ggr;∥remains> &ggr;⊥. An explanation for this behaviour in terms of the known lattice structure of Te is suggested.

ISSN:0094-243X    

DOI:10.1063/1.2948577

出版商:AIP    

年代:1972

数据来源: AIP