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The Journal of Research of the National
Bureau of Standards reports NBS research
and development in those disciplines of the
physical and engineering sciences in which the
Bureau is active. These include physics, chem-
istry, engineering, mathematics, and com-
puter sciences. Papers cover a broad range of
subjects, with major emphasis on measure-
ment methodology, and the basic technology
underlying standardization. Also included
from time to time are survey articles on topics
closely related to the Bureau's technical and
scientific programs. As a special service to
subscribers each issue contains complete cita-
tions to all recent NBS publications in NBS
and non-NBS media. Issued six times a year.
Annual subscription: domestic $13; foreign
$16.25. Single copy, $3 domestic; $3.75
foreign.

Note: The Journal was formerly published in
two sections: Section A "Physics and Chem-
istry" and Section B "Mathematical Sciences."

NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on March 3, 1901
The Bureau's overall goal is to strengthen and advance the Nation's science and technology
and facilitate their effective application for public benefit. To this end, the Bureau conducts
research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific
and technological services for industry and government, (3) a technical basis for equity in
trade, and (4) technical services to promote public safety. The Bureau's technical work is per-
formed by the National Measurement Laboratory, the National Engineering Laboratory, and
the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of
physical and chemical and materials measurement; coordinates the system with measurement
systems of other nations and furnishes essential services leading to accurate and uniform
physical and chemical measurement throughout the Nation's scientific community, industry,
and commerce; conducts materials research leading to improved methods of measurement,
standards, and data on the properties of materials needed by industry, commerce, educational
institutions, and Government; provides advisory and research services to other Government
agencies; develops, produces, and distributes Standard Reference Materials; and provides
calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities - Radiation Research - Thermodynamics and
Molecular Science - Analytical Chemistry - Materials Science.

THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser-
vices to the public and private sectors to address national needs and to solve national
problems; conducts research in engineering and applied science in support of these efforts,
builds and maintains competence in the necessary disciplines required to carry out this
research and technical service; develops engineering data and measurement capabilities;
provides engineering measurement traceability services; develops test methods and proposes
engineering standards and code changes; develops and proposes new engineering practices.
and develops and improves mechanisms to transfer results of its research to the ultimate user
The Laboratory consists of the following centers:

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THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts
research and provides scientific and technical services to aid Federal agencies in the selection,
acquisition, application, and use of computer technology to improve effectiveness and
economy in Government operations in accordance with Public Law 89-306 (40 U.SC. 7591.
relevant Executive Orders, and other directives; carries out this mission by managing the
Federal Information Processing Standards Program, developing Federal ADP standards
guidelines, and managing Federal participation in ADP voluntary standardization activities
provides scientific and technological advisory services and assistance to Federal agencies; and
provides the technical foundation for computer-related policies of the Federal Government
The Institute consists of the following centers:

Programming Science and Technology - Computer Systems Engineering.

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted;
mailing address Washington, DC 20234.

Some divisions within the center are located at Boulder, CO 80303.

U.S. DEPARTMENT OF COMMERCE
Philip M. Klutznick, Secretary
NATIONAL BUREAU OF STANDARDS
Ernest Ambler, Director

Order all publications from the Superintendent of Documents,
U.S. Government Printing Office, Washington, DC 20402
The Secretary of Commerce has determined that the publication of this
periodical is necessary in the transaction of the public business required
by law of this Department. Use of funds for printing this periodical has
been approved by the Director of the Office of Management and Budget
through June 30, 1981.

JOURNAL OF RESEARCH of the National Bureau of Standards
Vol. 85, No. 6, November-December 1980

Contents

Page

Observations on the Mechanisms of High Resistance Junction Formation in Aluminum
Wire Connections.

429

On the Calculation of Critical Liquid-Vapor Lines of Binary Mixtures. P. Wielopolski......

441

Systematic Errors in an Isoperibol Solution Calorimeter Measured with Standard Reference
Reactions. Marthada V. Kilday

449

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JOURNAL OF RESEARCH of the National Bureau of Standards

Vol. 85, No. 6, November-December 1980

bservations on the Mechanisms of High Resistance Junction Formation in Aluminum Wire Connections

Dale Newbury* and S. Greenwald

National Bureau of Standards, Washington, D.C. 20234

June 19, 1980

The basic mechanism of high resistance junction formation in duplex connectors wired with aluminum was investigated. Laboratory experiments to simulate loose connections were made both in actual duplex connectors and in an experimental apparatus. Microstructural observations were made by scanning electron microscopy and x-ray microanalysis of the structures formed at the interfaces between the circuit components during high resistance junction formation. At the iron screw/aluminum wire interface, the arcing process which occurs in a loose connection causes high temperatures in excess of 1500 °C and material transport between the components. Under these conditions, aluminum and iron react to form intermetallic compounds such as Fe3 Al and FeAl. The formation of an extensive zone of these compounds adjacent to the iron-aluminum interface in duplex connectors was revealed by electron metallography. In duplex connectors tested to glow failure, the formation of intermetallic compounds such as CuAl2 and Cu2ZnAl was observed at the brass plate/aluminum wire interface. These intermetallic compounds have a resistivity of the order of 100×10-6 ohm-cm or higher which may provide sufficient resistence at the current-carrying interface to lead to significant I2R heating losses at the interface. Key words: Aluminum wiring; duplex connectors; high resistance junctions; junction resistance; scanning electron microscopy; x-ray microanalysis.

1. Introduction

Overheating of electrical connections has been observed various studies of aluminum wiring used in residential inch circuits [1]'. The implications of this overheating for maging the connection, destroying the device, and sibly causing fire have been established. It is not ious however why the components involved, which ically include aluminum wire, a steel screw with a thin ss, tin or zinc plating, and a brass plate, should produce erheating since all are good conductors. Engineering dies have revealed that the overheating occurs mainly in se connections [2,3]. The overheating is often ompanied by the emission of visible light, the so-called w phenomenon, an apparent result of electrical arcing. Loose screw connections in the receptacle may result m one or more of the following causes:

a) Expansion and contraction of the connection. Heating sed by the FR losses in the connection is the principal ans of expansion and contraction [2,3]. Receptacles ated in outer walls are also subject to heating and -ling without the need for any electric current in the

enter for Analytical Chemistry, National Measurement Laboratory. nter for Consumer Product Technology, National Engineering Laboratory, red, 1980.

gures in brackets refer to literature references at the end of this paper.

branch circuit. Such temperature swings cause an alternate compression and relaxation of the connection mainly because of the difference in expansion rates of aluminum and steel.

(b) Creep. Aluminum is a metal which may exhibit creep or relaxation under stress at ambient temperatures. This effect in the aluminum wire is dependent on its composition and heat treatment during manufacture and on the temperature at which the connection operates. Related to this problem is the very limited mechanical compliance of the screw-wire-brass plate system found in these receptacles [2,3].

(c) Workmanship. A receptacle in which the screws are not sufficiently tightened during installation is a source of potential problems. Even when the screws are satisfactorily tightened outside the wall box during installation, some of the screws may be loosened in the act of pressing the receptacles back in their box. The stiffer the wire, the more likely this will occur [2,3].

In a tight connection very little heat is dissipated at the electrical interface. With 15 A of current flowing across the junction, the power consumed is on the order of 80 mW. With the same current flow, power dissipation as high as 36 W has been reported with a glowing connection [1]. One particular glow situation was reported to have been sustained for over 100 h although the time duration is

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