摘要:

The anisotropic thermal expansion of U2PtC2(tetragonal), and UMoC2(orthorhombic) has been measured using a high‐temperature neutron diffractometer. Coefficients of thermal expansion (units of 10−6/°C) are U2PtC2, &agr;11=9.3±0.1, &agr;33=10.1±0.8; UMoC2, &agr;11=8.6±0.2, &agr;22=15.5±0.5, &agr;33=10±3.

ISSN:0021-8979    

DOI:10.1063/1.1658604

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The thermal expansion of niobium monocarbide, hafnium monocarbide, and tantalum monocarbide was determined from room temperature to 2700°C by dilatometric measurements. The apparatus and experimental procedure were described earlier by Miccioli and Shaffer.1All carbides used in the present investigation were prepared at The Carborundum Company by hot pressing at 3150°C and 3000 psi. The bulk thermal expansion results of these three monocarbides are compared with other published dilatometric data1–3and also with x‐ray lattice expansion data.4–6The high‐temperature divergence between the bulk thermal expansion data and the lattice expansion data is due to the effect of nonstoichiometry, caused by noncongruent vaporization7–9at high temperature in these cubic monocarbides. The previously reported inversion phenomena were observed in the vicinity of 2000°C on several refractory monocarbides which were prepared by hot pressing at about 2000°C. This inversion was not detected in the present investigation. The inversion is due to the densification at the temperature apparently at which the specimens were fabricated.

ISSN:0021-8979    

DOI:10.1063/1.1658606

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The thermal expansivity and isothermal compressibility atp=0 of solid rare gases can be measured interferometrically in the temperature region between 2° and 150°K. The experimental errors are about 1% in the whole temperature region. First measurements have been done on solid Kr. We have found that the volume thermal expansion coefficient varies from (3.80±0.02)×10−5°K−1at 5°K to (1.82±0.012)×10−3°K−1at 115°K (triple point). The isothermal compressibility atp=0 varies from (2.93±0.022)×10−11dyn−1cm2at 5°K to (8.83±0.10)×10−11dyn−1cm2at 115°K.

ISSN:0021-8979    

DOI:10.1063/1.1658607

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Recent theoretical developments dealing with the equation of state of polymers make it possible to obtain some estimate of the volume dependence of the thermal expansion &agr; of these materials. It is clear at this point that &agr; should depend not only on the volumeVand temperatureT, but also on the degree of crystallinityFcof the polymer in question. The calculations presented take this latter parameter into account and theoretical values of &agr; for polyethylene (PE) are given as a function ofV, T, andFc. The values of &agr; for crystalline PE are converted into values for poly chloro tri fluoro ethylene (Kel F) by simple corresponding states relations. The efficacy of these relations is shown by accurately convertingP‐Vdata on PE toP‐Vdata on Kel F.

ISSN:0021-8979    

DOI:10.1063/1.1658608

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Interferometric measurements of the linear thermal‐expansion coefficients &agr;∥ and &agr;⊥ in the ``c'' and ``a'' axial directions of well‐oriented pyrolytic graphite between approximately 20° and 270°K are reported. Gru¨neisen parameters &ggr;∥ and&ggr;⊥, defined for strain coordinates parallel and perpendicular to the ``c'' axis, respectively, have been calculated from the present thermal expansion coefficients and related data. Between 30° and 270°K &ggr;∥ is positive, indicating the preponderance of longitudinal modes of vibration, while&ggr;⊥is negative, indicating the predominance of transverse modes. The quasiharmonic approximation has been applied to calculate the characteristic temperatures &thgr;(n) corresponding to the maximum frequencies &ohgr;D(n) of the Debye distributions having the samenth moments⟨&ohgr;n⟩as the specimens, which vary between approximately 420° and 2270°K asnincreases from −3 to +6. The dimensional dependence of the moments, defined by &ggr;(n) =&Sgr;&ggr;j&ohgr;jn/&Sgr;&ohgr;jncorresponding to &ggr;∥(n) and&ggr;⊥(n), and their variations withn, are consistent with the existence of low‐frequency modes of vibration between planes of atoms perpendicular to the ``c'' axis, and high‐frequency modes within the planes, a result supported by calculations of the rms displacements of the atoms.

ISSN:0021-8979    

DOI:10.1063/1.1658609

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Neutron scattering techniques have been used to measure phonon dispersion relations in a 1‐ml single crystal of36Ar. Data were taken along the 100 crystallographic direction for the transverse mode at 4°, 40°, and 77°K. The measurements were performed on a free‐standing crystal in equilibrium with its own vapor pressure. Preliminary analysis of the results yields mean shifts of the frequency of the transverse mode of 7% at 40°K and 21% at 77°K, relative to the 4°K value. These frequency shifts appear to decrease slightly with increasing wave vector. The mean Gru¨neisen parameter for this mode between 4° and 77°K is then 3.2±0.4 if it is assumed that the frequency shifts are due to the change in volume alone. Good agreement is found between the experimental frequency shifts and those predicted using a classical lattice dynamical model.1

ISSN:0021-8979    

DOI:10.1063/1.1658612

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Thermal expansion characteristics of a group of polycrystalline graphites have been measured to 2400°C by a method which permits acquisition of meaningful expansion data without resorting to reference standards. Direct measurements on specimens while in the furnace were accomplished by using two 8‐in. focal length Gaertner optical micrometers. Thermal expansion behavior is discussed in relation to orientation, impurity, degree of crystallinity, and grain size. Specimens were heated from room temperature to 2400°C, then cooled to room temperature, taking measurements of thermal expansion throughout both heating and cooling cycles. The existence of hysteresis is observed and discussed.

ISSN:0021-8979    

DOI:10.1063/1.1658613

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Copper is the first of a series of materials that will be certified as thermal‐expansion standards by the National Bureau of Standards. The results of tests on five specimens indicate the stock is of consistent quality so that it may be certified as Standard Reference Material 736. A Fizeau interferometer was used for the expansion measurements. Above room temperature a controlled‐atmosphere furnace using a calibrated Pt vs Pt‐10% Rh thermocouple was used. Below room temperature a cryostat capable of operation with both liquid nitrogen and helium was used with a calibrated platinum resistance thermometer. Values of expansivity were calculated between equilibrium temperatures. The expansivity was used in the analysis of the data. Third‐order polynomials were fitted to the data for each of the five specimens in the overlapping temperature ranges from 0 to 70 K, 50 to 270 K, and 210 to 800 K to test for variations between the specimens. The deviations between the five equations were well within the standard deviations of the data for each of the specimens in the respective temperature intervals. All the expansivity data were then pooled and used to obtain an equation for each of the temperature ranges given above. These equations and their integrals were used to calculate the final values of expansivity and expansion, respectively. The results of the statistical analysis of the expansion and expansivity data are presented. A comparison is made with the data in the literature.

ISSN:0021-8979    

DOI:10.1063/1.1658614

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A theoretical technique for determining the volume dependence of the thermal expansion coefficient &agr; along an isotherm is developed for solids which exhibit a linearUs‐up(i.e., shock velocity‐particle velocity) relationship. The method is founded on an accurate Gru¨neisen equation of state utilizing the temperature‐independent Gru¨neisen parameter &ggr; which has been calculated from experimental shock data. Detailed results are presented for several isotherms at pressures as high as 1 Mbar. Based on the accuracy of the Gru¨neisen parameter, the accuracy of the calculated thermal coefficient &agr; is estimated to be within ±10% down to 20% compression with greater accuracy for lower compressions.

ISSN:0021-8979    

DOI:10.1063/1.1658615

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The purpose of this paper is to encourage agreement as to where we are and suggest a few ways that this symposium can contribute to some future requirements. Thermal expansion of solids is a subject of interest to a wide range of disciplines from those conducting basic studies of lattice behaviors to those analyzing temperature stresses on re‐entry. Temperatures of interest range from cryogenic to 6500°F. Pressures range from 10−12Torr to several atmospheres. The chemistry of the environment is also concerned. Thus the total environment is important. As a result of this broad scope, many different test methods are involved, different precisions and accuracies are required, and data are difficult to relate. This paper describes the applicability of some of the major test methods in terms of some of the above requirements, the standards that are available, and some sources of data for the different regimes. Particular emphasis is placed on engineering behavior since that represents the bulk of the authors experience. The observations are made that we need some base line understanding as to where we now stand and as to the areas where the thermal expansion symposium could systematically attack the problems by (1) encouraging papers and discussions of the various test methods, their environments, and limitations, (2) resolving by discussion and by encouraged personal round robins the obtainable precision and accuracy of methods and standards, (3) making known sources of data through author references, (4) communicating needs to groups that develop standards, (5) providing a forum where the facts can emerge and (6) publishing informal bound proceedings for a few years to gather the existing information and then bound abstracts eventually to provide references of more detail. After this sorting of information, more sophisticated studies will be possible by more people.

ISSN:0021-8979    

DOI:10.1063/1.1658616

出版商:AIP    

年代:1970

数据来源: AIP