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CSIRO PUBLISHING Aust. J. Chem. 2019, 72, 633–636 https://doi.org/10.1071/CH19239 The Position of Solid Carbon Dioxide in the Triboelectric Series* Jinyang ZhangA and Simone Ciampi A,B ASchool of Molecular and Life Sciences, Curtin Institute of Functional Molecules and Interfaces, Curtin University, Bentley, WA 6102, Australia. BCorresponding author. Email: simone.ciampi@curtin.edu.au Communication RESEARCH FRONT The process of releasing liquid carbon dioxide from a fire extinguisher is accompanied by a strong static charging of the plastic material making up the extinguisher discharge horn. Firefighters often report an electric shock when operating CO2 extinguishers, but the origin of this electrostatic hazard is largely unknown. Here, we begin to investigate this phenomenon, and test the hypothesis of plastic samples being tribocharged on contact with rapidly flowing solid CO2. Using Faraday pail measurements, we show that non-conductive polymers gain a net static charge when brought in and out of contact with dry ice (solid CO2). These measurements of charge sign and magnitude give indirect evidence helping to place solid CO2 for the first time on the triboelectric series. Polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE), and polyvinyl chloride (PVC) samples acquire a negative charge when rubbed against dry ice, whereas poly(methyl methacrylate) (PMMA), glass, and nylon surfaces become positively charged. Therefore, we suggest the position of dry ice in the triboelectric series to be close to that of materials with stable cations and unstable anions, possibly locating it between PMMA and PVC. Manuscript received: 28 May 2019. Manuscript accepted: 12 July 2019. Published online: 1 August 2019. Introduction Contact electrification[1] is a process in which two materials that are brought in and out of contact acquire a net charge of opposite sign. Although contact electrification is exploited in several important technologies, such as photocopying and laser print- ing,[2] electrostatic painting,[3] industrial separations,[4] and new forms of alternating current generation,[5] when uncontrolled it remains a detrimental, or even dangerous, phenomenon.[6] For examples, in industries such as textiles, manufacturing of explosives, and storage of grains and flour, static electricity is a well-known hazard.[6b,7] Contact charging is, however, not lim- ited to contact between polymers, as the flow of water or of liquid and gaseous hydrocarbons[8] is known to generate static charge.[7a,9] Analogously, when a CO2 extinguisher is operated, the liquefied gas expands and rapidly moves across the surface of the discharge horn, generating a large amount of electrostatic charge.[10] Major accidents have been associated with static charging created by the release of CO2 extinguishers, such as an explosion in Germany in 1966.[11] Electrification induced by solid CO2 has been studied by several groups,[12] and as early as in 1954 Heidelberg and coworkers investigated charge generation during release of CO2 from a large fire-snuffing installation.[11] They reported a highly variable rate of charge generation, but to date, how different dielectrics respond to contact with solid CO2 and how the environment influences CO2-related tribocharging events are still largely unexplored. *Simone Ciampi is the winner of the 2017 RACI Alan Bond Medal. Here, we have begun to quantify the magnitude and sign of static electricity that develops on polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), poly(methyl methacrylate) (PMMA), nylon, and glass surfaces that were rubbed against dry ice under either an air or argon atmosphere, and tried for the first time to tentatively place CO2 in the triboelectric series. Results and Discussion We first considered experiments in which solid CO2 is allowed to slide down an inclined plane made of a sheet of the polymer under test (Fig. 1a). This system is especially convenient in terms of reproducibly controlling the contact force. Solid CO2 is not found in any available triboelectric series,[13] and therefore, we performed experiments where dry ice was in contact with different polymers whose position in these charts is known. Fig. 1a illustrates the experimental set-up in which PDMS, PTFE, PVC, PMMA, nylon, and glass plates were rested on an inclined plane made of a wood surface tilted 308 away from the horizontal plane. Wood was used as to hold the samples because it is known to gain negligible charge after contact with any other polymer. The choices of the polymer materials were motivated as follows: (i) PDMS, PTFE, PVC, and PMMA are known to be close to the bottom (i.e. negative end) of the triboelectric series,[14] and (ii) glass and nylon are found towards the top (i.e. positive) end of the series. After contact with CO2, Journal compilation ! CSIRO 2019 www.publish.csiro.au/journals/ajcPDF Image | Position of Solid Carbon Dioxide in the Triboelectric Series
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