Vapor pressure data obtained by the torsion-effusion method provides the thermodynamic properties of several transition-metal alloy systems. The vapor pressure of silver over solid silver and over palladium-silver alloys was measured and the results were more accurate than those found previously by other techniques

Myles, K. M.

English

NASA Technical Reports Server

September 1967	 .	 Brief 67-10324 
. 
TES 
icy
AEC-NASA, TECH BRIEF 
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Thermodynamic Properties of Solid Palladium—Silver Alloys and Other
Alloys Are Investigated by Torsion—Effusion Technique 
.
Protractor-
Torsion Wire 
Window... 
Connector Tube 
Ionization Gage 
Magnetic...........-
Dampener 
Thermocouple / 
Port 
To Vacuum
Pumps
Electronic 
Vacuum Pump 
Mirror 
Chevron Baffle 
To Vacuum Pumps 
Tantalum Bucket 
Effusion Cell 
Furnace Element 
Jackscrew 
The problem: 
To obtain the thermodynamic properties of transi-
tion-metal alloys in order to study the contributions 
to these properties associated with changes in the 
electronic structure upon alloying. The electromotive-
force method was rejected because the desired emf 
is often masked by interfering side reactions. The 
Knudsen vapor-pressure method also was rejected 
because of the possibility of surface depletion and 
contamination during the long experimental runs. 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
The solution: 
The thermodynamic properties of several transition-
metal alloy systems were derived from vapor pressure 
data obtained by the torsion-effusion method. For 
example, the vapor pressure of silver over solid silver 
and over palladium-silver alloys was measured by this 
method in the temperature range of 1100° to 1300°K. 
The results were more accurate than those found 
previously by the emf technique, and enabled the 
computation of the chemical activities, free energies, 
(continued overleaf) 
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19670000324 2020-03-11T20:40:06+00:00Z
entropies, and enthalpies of formation of the alloys at 
1200° K. 
The activities of silver exhibit large deviations from 
ideal behavior over the entire compositional range. 
The activities of palladium deviate positively in the 
palladium-rich alloys and negatively in the silver-rich 
alloys. Since the excess entropies and enthalpies, both 
of which are negative, agree with the values found by 
calorimetric methods, it is evident that the data are 
quite reliable. The palladium—silver alloy system was 
selected for the investigation because the band struc-
ture is known and other information related to the 
properties of the electrons is available. 
How it's done: 
The alloys were prepared by arc-melting the re-
quired amounts of pure palladium and silver on a 
water cooled hearth in a helium—argon atmosphere. 
The specimens were homogenized, quenched, and 
machined into coarse turnings, which were then 
cleaned and loaded into tantalum effusion cells. The 
cells, which have two eccentrically located orifices, are 
suspended vertically from a fine tungsten wire. An 
elastic torsional strain is induced in the wire as the 
metal vapor effuses through the orifices. The vapor 
pressure, p, is related to the angle through which the 
cell rotates, 0, by the expression p = 2TO/I Adf, where 
T is the torsion constant of the wire, A is the cross-
sectional area of the orifice, d is the horizontal 
distance of the orifice from the suspension axis, and f 
is the orifice correction factor.
Notes: 
I. Additional information is contained in: 
(a) Ada Mezallurgica, vol. 13, Feb. 1965, p. 109-
113 
(b)Jour. Phvs. Chem., vol. 68, no. 1, Jan. 1964, 
p. 64-69. 
(c) A Study of the Thermodynamic Properties of the 
Vanadium-Iron Alloy System, by Kevin Michael 
Myles, ANL-6657, Argonne National Labora-
tory, Feb. 1963. This report is available from 
the Clearinghouse for Federal Scientific and 
Technical Information, Springfield, Virginia 
22151, $3.00 each (microfiche, $0.65). 
2. Inquiries concerning this innovation may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B67-10324 
Source: K. M. Myles,
Metallurgy Division
(ARG-277) 
Patent status: 
Inquiries about obtaining rights for commercial 
use of this invention may be directed to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
• 9800 South Cass Avenue 
Argonne, Illinois 60439 
Brief 67-10324	 Category 03


Thermodynamic properties of solid palladium-silver alloys and other alloys are investigated by torsion-effusion technique

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