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TS Department EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH ORGANISATION EUROPÉENNE POUR LA RECHERCHE NUCLÉAIRE CERN - TS Department EDMS Nr: 842110 TS-Note-2007-005 Chemical and radiolytical characterization of perfluorocarbon fluids used as coolants for LHC experiments Radiolysis effects in perfluorohexane fluids S. Ilie, R. Setnescu, B. Teissandier Abstract Perfluorohexane fluids, used as coolants within High Energy Physics Detectors in the Large Hadrons Collider (LHC) at CERN, were irradiated using gammas 60Co and characterized using different analytical techniques. The aim of this work was the assessment of radiation induced effects as a function of the chemical nature of these fluids and their impurity content. Were evidenced the radioinduced polymers and acidity, as well as different chemical by-products. Purification tests and measurements were carried out on different irradiated fluid samples to assess the efficiency of such purification treatments in view of their re-use in the HEP detector cooling systems. April 2007 i TABLE OF CONTENTS 1. INTRODUCTION ...................................................................................................................................................... 1 2. EXPERIMENTAL...................................................................................................................................................... 2 2.1 Experimental details.................................................................................................................................................... 2 2.1.1 Irradiated perfluorocarbons ........................................................................................................................................ 2 2.1.2 Irradiation doses.......................................................................................................................................................... 2 2.1.3 Irradiation conditions.................................................................................................................................................. 3 2.1.4 Analysis methods........................................................................................................................................................ 4 2.2 Radiation induced effects............................................................................................................................................ 6 2.2.1 Generalities on the fluorocarbons radiolysis.............................................................................................................. 6 2.2.2 Radiation induced acidity and the fluorine ions appearance ..................................................................................... 8 2.2.3 High molecular weight molecules .............................................................................................................................. 8 2.2.4 Low molecular weight products (LMwPs)................................................................................................................ 15 2.2.5 Correlation between the literature and the experimental data; qualitative and quantitative radiolytical effects.... 22 2.3 Purification of perfluorocarbon fluids...................................................................................................................... 25 2.3.1 Purification of the as received fluids........................................................................................................................ 25 2.3.2 Purification (cleaning) of the irradiated fluids types................................................................................................ 26 3. CONCLUSIONS....................................................................................................................................................... 29 ANNEX 1 - Pressure, acidity and fluorine ions content values for the irradiated perfluorocarbon samples..................... 32 ANNEX 2 - Pre-polymer content values for the irradiated perfluorocarbon samples........................................................ 33 ANNEX 3 - GC-MSD chromatograms of the gas phase of irradiated PP1......................................................................... 34 ANNEX 4 - GC-MSD chromatograms of the PF 5060 DL................................................................................................. 38 ANNEX 5 - GC-MSD chromatograms of PF 5060 irradiated fluid.................................................................................... 43 ANNEX 6 - GC-MSD chromatograms of the purified PF 5060 irradiated fluid ................................................................ 51 ANNEX 7 - FT-IR spectra of the radioinduced pre-polymers ............................................................................................ 55 ANNEX 8 - Mass evaluation of the radiation-induced deposits on the metallic strips surface.......................................... 60 ANNEX 9 - Optical (visual) inspection of the irradiated metallic strips ............................................................................ 61 ANNEX 10 - SEM and EDX inspection of the irradiated metallic strips ............................................................................. 66 ANNEX 11 - Perfluoroisobutylene properties....................................................................................................................... 75 ANNEX 12 - Carbonyl fluoride properties ............................................................................................................................ 78 ANNEX 13 - Purification tests on the as received PF 5060 fluid ......................................................................................... 80 ANNEX 14 - Purification tests on the irradiated fluids......................................................................................................... 85 ANNEX 15 - FT-IR spectra of irradiated and of purified fluids ......................................................................................... 105 ANNEX 16 - Thermal behavior of the radiation induced pre-polymer in PF-5060-28 fluid ............................................. 112 - 1 - 1. INTRODUCTION The previous work [1] was dedicated to the chemical characterization of the perfluorocarbon fluids received in CERN and to the quality control and the compliance tests. Were applied adequate methods for chemical characterization of these fluids; the obtained results confirmed the results from independent tests and confirmed also the validity of the laboratory procedures and methods settled-up [2 - 5]. This report deals with the investigation of the radiation-induced chemical effects (acidity - mainly HF, polymer & pre-polymers, new molecules, etc.) in perflurocarbon fluids of interest for CERN cooling applications (Table 1). These fluids were chemically characterized [1] and it was found that PP1 (F2 Chemicals, UK), PF 5060 DL (3M, USA) and C3F8 (ASTOR, RU) as received, met the CERN requirements [6]. The expected doses are roughly in the range of 40 Gy to 30 kGy, depending on the cooling application (Table 1) [7]. Table 1 – Irradiation doses expected for cooling fluids in various LHC Experiments [7] 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Experience Detector Fluid (Gy) (Gy) (Gy) (Gy) (Gy) (Gy) (Gy) (Gy) (Gy) (Gy) SCT ATLAS C F 40 240 1240 5240 9240 13240 17240 21240 25240 29240 Evaporative 3 8 ATLAS TRT C6F14 3 18 118 418 718 1018 1318 1618 1918 2218 ATLAS Cables C6F14 1 6 28 126 226 326 426 526 626 726 CMS Pixel C6F14 480 980 1440 1920 2400 2880 3360 3840 4320 4800 Silicon CMS C F 140 280 420 560 700 840 980 1120 1260 1400 Strips 6 14 Inner LHCb C F 7 40 73 106 139 223 306 389 472 556 Tracker 6 14 Trigger LHCb C F 4 25 47 68 89 142 195 248 301 353 Tracker 6 14 LHCb Rich 1&2 C6F14 1 3 6 9 12 19 26 33 39 48 The present investigation was necessary to understand the chemistry of the radiation induced processes, to evaluate the use limits of the fluids and the possibilities of their recovery (cleaning), as well. There are known the detrimental impurities for perfluorocarbon radiation hardness, namely H-and double bonds containing molecules, water and air. H and double bonds containing molecules can be removed using an adequate production technology by different producers and CERN requirements [6] established very low levels for these "evitable impurities". Water and oxygen are more or less inevitable due to manipulation, leaks, etc. Therefore, water and oxygen, as well as the eventual traces of greases have to be removed when the cooling plants are filled and on line when in use. PF 5060 (3M, USA) in the as received state was found not compliant, as H-containing molecules exceeded significantly the required limits. This fluid was however included in the irradiation program to check the influence of the relative high level of impurities on the radiation behavior and on the post-irradiation cleaning efficiency, as well. A specially purified fluid by a laboratory treatment of the as received PF 5060, which fulfilled the requirement of H-containing molecules, was also investigated for its radiation and cleaning behavior. The fluids tested in the present work are listed in Table 2. - 2 - Table 2 - Perfluorocarbon fluids types studied within this work No. Product name Supplier Composition mainly iso-C F 1 Flutec PP1 F2 Chemicals Ltd., UK 6 14 (iso-perfluorohexane) mainly n-C F 2 PF 5060 DL 3M Chemicals, USA 6 14 (n-perfluorohexane) mainly n-C F 3 PF 5060 as received 3M Chemicals,
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