Ensinger, W.

Fasel, C.

Hossain, U. H.

Seidl, T.

Severin, D.

GSI Repository

GSITemplate2007 Ion induced weight loss and thermal gravimetric analysis of ion-irradiated poly-vinyl formal U. H. Hossain1, 2#, T. Seidl1, 2, C. Fasel1 , D. Severin2 and W. Ensinger11Technische Universität Darmstadt, Germany; 2GSI, Darmstadt, Germany.Polyvinyl polymers are high-performance insulating materials used in many applications. At the new Facility for Antiproton and Ion Research (FAIR) polyvinyl poly-mers are foreseen as wire insulation in some parts of the superconducting magnets [1]. During the operation of FAIR, beam losses will result in secondary radiation fields consisting of various energetic particles and gamma radiation. Ion-induced radiolysis of polymers involves bond scission, cross-linking and other chemical reactions leading to outgassing of small volatile degradation prod-ucts and finally to loss of functional properties. At opera-tional cryogenic temperatures, these gases may accumu-late and raise problems during thermal cycling of the su-perconducting magnets [2]. This study extends existing data of beam-induced weight loss in polymers and shows results of thermal gravimetric analysis (TGA) of irradi-ated polyvinyl formal. Results are complementary to pre-vious reports on infrared spectroscopy (IR) and qualita-tive interpretation of residual gas analysis [3]. 20-μm thick Formvar® foils were synthesized and irra-diated at the X0 beamline of the UNILAC with Au and U ions of 11.1 MeV/u. The applied fluences were 1×109 - 6×1011 Au/cm2 for TGA measurements and 1×1010 - 1×1012 U/cm2 for weight-loss measurements. TGA was performed using a Netzsch TG209 F1 instrument with a heating rate of 4 K/min in argon atmosphere. For weight loss analysis a chemical balance with a resolution of about 0.1 mg was used. TGA measures the weight of a material as a function of temperature in a controlled atmosphere. Figure 1 com-pares the decomposition behavior of a pristine and an ion-irradiated polyvinyl formal sample from room tempera-ture to 650 °C. The pristine Formvar® foil shows two steps, first a small initial weight loss occurring between 104 and 153ºC which is commonly attributed to the re-lease of water absorbed in the polymer. Between ~300 and 420°C a significant weight loss occurs with a 5% of char residue. The decomposition of nearly the entire poly-mer indicates that the thermal degradation follows a de-polymerisation process and not a so-called random scis-sion process, which would lead to a great amount of char. The TGA curve of the irradiated sample shows only one broad degradation phase occurring between 110 and 420°C with a residual char of 10%. The temperatures for maximum mass loss rate (Td (max)) of both samples are indicated in the derivative curves (Fig. 1, bottom). The ion irradiation leads to a slight increase of Td (max). Both effects are explained by ion induced synthesis of carbon clusters which are not decomposed at the used tempera-tures. Figure 1: TGA curves of Formvar® foils (black) before and (red) after irradiation with 6×1011 Au-ions/cm2 (top) and their derivatives (bottom). Figure 2: Residual mass as a function of ion fluence for polyvinyl formal (black) and polyimide (red) [2] irradi-ated with 11.1-MeV/u U ions. Figure 2 depicts the residual mass of irradiated polyvi-nyl formal in comparison with results from irradiated polyimide samples from previous work [2]. All irradiated samples show a strong decrease in weight with increasing ion fluence. Compared with polyimide a greater decrease is found for polyvinyl formal. Polyimide insulation obvi-ously forms less outgassing radiolysis products which could accumulate when used in cryogenic environment. [1] T. Seidl et al. Nucl. Instr. Meth. B 272, (2012), 400. [2] D. Severin, PhD thesis, Univ. Marburg (2008). [3] U.H. Hossain et. al., GSI Scientific Report; PNI-MR-20 (2011). * work was partially financed by BMBF 06DA7027# u.h.hossain@gsi.de GSI SCIENTIFIC REPORT 2012 PNI-INHOUSE-EXP-36405

Ion induced weight loss and thermal gravimetric analysis of ion-irradiated poly-vinyl formal

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Ion induced weight loss and thermal gravimetric analysis of ion-irradiated poly-vinyl formal

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