摘要:

Comparison of the National Institute of Standards and Technology’s Standard Reference Material 720 certificate values for heat capacity with those obtained from recent experimental determinations indicated the possibility of a systematic error in the certificate values. Selected experimental determinations of enthalpy increments and heat capacities were fitted in order to obtain a representation of the thermodynamic properties of &agr;‐Al2O3, a sample of which is the standard reference material (SRM‐720) for calibration of some types of calorimeters. The fitted equation and calculated values of the heat capacity, the relative enthalpy, and the entropy are given. The new values are more accurate and result from a better representation of the experimental values than did the 1982 SRM‐720 certificate values. Additionally, the general problem of the effect of changes in practical temperature scales on thermodynamic properties is briefly discussed, using the results for &agr;‐Al2O3. A recent report from the I.U.P.A.C. Commission on Thermodynamics gave a method for the conversion of thermodynamic properties for changes in practical temperature scale. The I.U.P.A.C. method is shown to be not generally correct. A better method for estimation of these changes is given.

ISSN:0047-2689    

DOI:10.1063/1.555931

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Statistical‐thermodynamic calculations have been combined with the results of high‐temperature Knudsen‐effusion studies of the vaporization of Si2Te3to calculate the thermodynamic properties of SiTe(g) fromT→0 toT=2000 K. The dissociation enthalpyD○m(SiTe,T→0) is (448±8) kJ⋅mol−1; its value is discussed vis‐a‐vis the other silicon monochalcogenides.

ISSN:0047-2689    

DOI:10.1063/1.555932

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A critical evaluation is presented of the thermodynamic properties of six disilicides and one monosilicide that are important in the manufacture of very large scale integrated circuits. Values of the standard molar enthalpies of formation &Dgr;fH○matT=298.15 K andp°=0.1 MPa are recommended as follows: WSi2, −(79±5) kJ⋅mol−1; MoSi2, −(137±4) kJ⋅mol−1; TiSi2, −(171±11) kJ⋅mol−1; CoSi2, −(103±15) kJ⋅mol−1; NiSi2, −(88±12) kJ⋅mol−1; TaSi2, −(120±20) kJ⋅mol−1; and PtSi, −(119±7) kJ⋅mol−1. Equations are given for the molar enthalpy increments of some of the silicides along with a few evaluated standard Gibbs free energies of formation. Brief descriptions of methods of synthesis and limited structural information have also been included.

ISSN:0047-2689    

DOI:10.1063/1.555922

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Recommendations of reaction rate coefficients and product distributions for bimolecular positive ion‐molecule reactions of importance in planetary atmospheres, cometary comae, and interstellar clouds are presented. Two publications Anicich and Huntress, 1986, Ap. J. Supplement Series62, 553 and Anicich, 1993, Ap. J. Supplement Series84, 215 served as the basis for this evaluation, which covers the literature from 1965 through 1991 with some additional citations missed in the original surveys.

ISSN:0047-2689    

DOI:10.1063/1.555940

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The biennial review of atomic weightAr(E), determinations, and other cognate data has resulted in changes for the standard atomic weight of indium from 114.82±0.01 to 114.818±0.003, for tungsten from 183.85±0.03 to 183.84±0.01, and for osmium from 190.2±0.1 to 190.23±0.03 due to new high precision measurements. Recent investigations on silicon and antimony confirmed the presently acceptedArvalues. The footnote ‘‘g’’ was added for carbon and potassium because it has come to the notice of the Commission that isotope abundance variations have been found in geological specimens in which these elements have an isotopic composition outside the limits for normal material. The value of 272 is recommended for the14N/15N ratio of N2in air for the calculation of atom percent15N from measured &dgr;15N values. Because many elements have a different isotopic composition in nonterrestrial materials, recent data on nonterrestrial material are included in this report for the information of the interested scientific community.

ISSN:0047-2689    

DOI:10.1063/1.555933

出版商:AIP    

年代:1993

数据来源: AIP