The Journal of Research of the National Note: The Journal was formerly published in NATIONAL BUREAU OF STANDARDS The National Bureau of Standards' was established by an act of Congress on March 3, 1901 THE NATIONAL MEASUREMENT LABORATORY provides the national system of Absolute Physical Quantities - Radiation Research - Thermodynamics and THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts Programming Science and Technology - Computer Systems Engineering. 'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; Some divisions within the center are located at Boulder, CO 80303. U.S. DEPARTMENT OF COMMERCE Order all publications from the Superintendent of Documents, JOURNAL OF RESEARCH of the National Bureau of Standards Contents Page Observations on the Mechanisms of High Resistance Junction Formation in Aluminum 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 449 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 |