July/August_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 2 0 3 4 Lead image: 2019-nCoV spike protein, courtesy of Jason McLellan/University of Texas at Austin. MATERIALS SCIENCE AND CORONAVIRUS SERIES COPPER’S CONDUCTIVITY AND ANTIMICROBIAL PROPERTIES INSPIRE RENEWED INTEREST As copper’s antimicrobial benefits spur new applications, the metal’s other properties are also worth reviewing. T oday, copper and its alloys re- main one of the major groups of commercial metals, ranking third behind only iron/steel and alumi- num in production and consumption. Copper is widely used due to its excel- lent electrical and thermal conductivi- ty, outstanding resistance to corrosion, ease of fabrication, and good strength and fatigue resistance. It can be readily soldered and brazed, is generally non- magnetic, and can be welded by vari- ous gas, arc, and resistance methods. For decorative parts, standard alloys ELECTRICAL AND THERMAL CONDUCTIVITY A majority of copper and copper alloys consumed in the United States are used because of electrical conduc- tivity. The bulk of these applications are wire and cable, for example, telecom- munications wire and cable, electronic wire and cable, building wire, magnet wire, power cable, and automotive wire and cable. The electrical conductivity scale established in 1913 was based on a ANTIMICROBIAL PROPERTIES OF COPPER ALLOYS The ASM Specialty Handbook: Copper and Copper Alloys, published in 2001, contains a wealth of information on the prop- erties of copper alloys. The reference volume lists the following as important properties: electrical conductivity, thermal con- ductivity, corrosion resistance, color, and fabrication characteristics. However, a few less recognized but nevertheless important properties include: highly recyclable, antifouling, and antimi- crobial. Of particular current interest are the antimicrobial properties of copper alloy surfaces, which were not characterized in the scientific literature when the specialty handbook was published in 2001. However, over the last two decades, their anti- microbial properties began to emerge and have grown in recognition, especially since emergence of the COVID-19 pandemic. Copper alloy surfaces have been shown to be effective on a broad spectrum of microbes, including bacteria, fungi, and viruses. Published studies carried out in several research laboratories around the world repeatedly demonstrated that expo- sure of microbes to copper alloy surfaces causes significant killing and inactivation. In addition, several clinical trials yielded marked reduction in bacteria in real world settings, and in one case, over 50% reduction in infections in hospital intensive care units. An overview of these studies is summarized elsewhere [1] . However, in view of the emergence of SARS-CoV-2, the virus that causes COVID-19, it is important to note the viruses that have been tested and found to be destroyed by copper alloy sur- faces. These include: Coronavirus 229E (human), which is genetically highly similar to SARS-CoV-2; Influenza A; Norovirus (hu- man, murine); T2 bacteriophage; and Vaccina, Monkeypox (Herpes viruses). The Copper Development Association obtained an US-EPA registration after demonstrating in a third-party EPA approved and audited laboratory that a range of copper alloys down to 60% Cu killed the following six bacteria: MRSA, Staphylococcus aureus, VRE, Enterobacter aerogenes, Pseudomonas aeruginosa, and E. coli O157:H7. These bacteria, which include two antibiotic resistant “superbugs” MRSA and VRE, were selected because they cause se- rious human infections. Copper alloys hold EPA Public Health Registration because they demonstrated the ability to kill the with specific colors are readily avail- able. This article, adapted from “Intro- duction and Overview,” ASM Specialty Handbook: Copper and Copper Alloys, describes some of the more significant properties of copper. Along with strength, fatigue resis- tance, and ability to take a good finish, the primary selection criteria for cop- per and its alloys are electrical conduc- tivity, thermal conductivity, corrosion resistance, color, ease of fabrication, and antimicrobial benefits (see “Anti- microbial Properties of Copper Alloys”).