Suppression Effect and Mechanism of Platinum and Nitrogen

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Suppression effect and mechanism of platinum and nitrogen-containing silane on the tracking and erosion of silicone rubber for high voltage insulation Wan Juan Chen, Xingrong Zeng, Xuejun Lai, Hongqiang Li, Wei Zhen Fang, and Fei Hou ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b05580 • Publication Date (Web): 27 Jul 2016 Downloaded from http://pubs.acs.org on August 2, 2016

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ACS Applied Materials & Interfaces

Suppression effect and mechanism of platinum and nitrogen-containing silane on the tracking and erosion of silicone rubber for high voltage insulation Wan Juan Chen, Xingrong Zeng*, Xuejun Lai, Hongqiang Li, Wei Zhen Fang, Fei Hou College of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, P. R. China

ABSTRACT: How to effectively improve the tracking and erosion resistance of silicone rubber was an urgent topic in the field of high-voltage insulation. In this work, the tracking and erosion resistance of silicone rubber (SR) was significantly improved by incorporating platinum (Pt) catalyst and nitrogen-containing silane (NS). The suppression effect and mechanism of Pt/NS on tracking and erosion were studied by inclined plane (IP) test, thermogravimetry (TG), thermogravimetry-Fourier

transform

infrared

spectrometry

(TG-FTIR),

laser

Raman

spectroscopy (LRS) and scanning electron microscopy (SEM). It revealed that when 1.4 phr of NS and 6.7 ppm of Pt were added, the tracking resistance of SR was improved from 2.5 kV to 4.5 kV level in the IP test and the eroded mass was significantly reduced. This might be attributed to the synergistic effect of Pt/NS on silicone chains. At a high temperature produced by arc discharge, Pt/NS would catalyze radical crosslinking, meanwhile suppressing oxidation and depolymerization of silicone chains. Hence, a tightly crosslinked network was formed and

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protected inner materials from arc ablation. Moreover, carbon deposit during pyrolysis was suppressed by Pt/NS, which served as the secondary mechanism of tracking suppression.

KEYWORDS: Silicone rubber; Tracking and erosion resistance; Inclined plane test; TG-FTIR; Platinum; Nitrogen-containing silane

INTRODUCTION In the last decade, silicone rubber is gradually replacing traditional inorganic materials in highvoltage insulation, due to its light weight, high vandal resistance, wide temperature adaptability and superior hydrophobicity and self-recovery of hydrophobicity.1-3 However, silicone rubber may lose its hydrophobicity in polluted environment and under electrical stress.4 On such condition, moisture can dissolve conductive salt and dust on the hydrophilic surface, thus resulting in leakage current along the formed conductive layer.5 Leakage current generates heat which evaporates water and leads to formation of local dry bands.6 Under a nonuniform electric field induced by high voltage, arc discharge happens intermittently on those bands. While subjected to dry band arcing, silicone rubber is rapidly heated up to 1200 oC at local position.7 Consequently, silicone chains are thermally degraded and even carbonized, which are the main reasons for the tracking and erosion of silicone rubber.8 Currently, power transmission tends to run at higher voltage level. As a result, dry band arcing is more frequent and destructive at present than ever before, which leads to more insulation failures of silicone rubbers by tracking and erosion. Nowadays, it is required that insulation materials must pass inclined plane (IP) test at higher voltage level for high voltage application. Especially, many of the national standards


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have proposed the requirement that polymeric insulation materials are able to pass IP test at 4.5 kV level.9,10 General method to improve tracking and erosion resistance of silicone rubbers is to incorporate inorganic fillers. Those effective fillers include alumina trihydrate,11 alumina,12 silica,13 boron nitride14 and barium titanate.15 Blended with such fillers, silicone chains are diluted and physically bound to the surface of fillers. Moreover, high thermal conductivity of those fillers facilitates thermal dissipation.16,17 Thus, the tracking and erosion of silicone rubber initiated by arc discharge are reduced. The most commonly used filler was alumina trihydrate (ATH) which decomposed and released water vapor at temperature above 220 oC.18 Released water can react with deposit carbon and consume it, so as to retard tracking.19 Nevertheless, a large amount of inorganic filler is required to achieve satisfactory tracking and erosion resistance, which may lead to loss in nature of silicone rubber.20 Besides, mechanical properties and processability of silicone rubber are generally deteriorated. Other solutions include introducing arc-quenching substances, such as melamine compound, urea compound and guanine compound,21 whose effectiveness is attributed to the rapid generation of arc-quenching gases under the arcing.22 Schmidt used 15 phr of melamine cyanurate, in combination with silica, to substitute 100 phr of ATH in silicone rubber. All samples passed tracking and erosion test at 4.5 kV.23 However, melamine cyanurate was imcompatible with silicone rubber and also had negative effect on mechanical properties. Our previous study indicated that incorporating a small amount of urea-containing compound could realize tracking and erosion resistance at 4.5 kV as well as enhanced mechanical properties in addition-cure liquid silicone rubber.24 This gave a new method to prepare silicone rubber with excellent tracking and erosion resistance. However, our further investigation found that it was


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ineffective for high temperature vulcanized silicone rubber (HTVSR). Recently, we found that there existed synergistic effect between platinum and nitrogen-containing silane on significantly enhancing the thermal stability of HTVSR.25 Therefore, it may have great potential for combining platinum and nitrogen-containing silane to improve tracking and erosion resistance of HTVSR. In this work, nitrogen-containing silane (NS) and platinum (Pt) catalyst were introduced into HTVSR. The separate and synergistic effects of NS and Pt on tracking and erosion resistance were investigated via inclined plane (IP) test. Then, the thermal stability, characterization of pyrolysis gases and residues were investigated by thermogravimetry (TG), thermogravimetryFourier transform infrared (TG-FTIR), laser Raman spectroscopy (LRS) and scanning electron microscopy (SEM). Through the investigation, the possible mechanism of Pt/NS resisting tracking and erosion of silicone rubbers was proposed.

EXPERIMENTAL SECTION Materials. Polydimethyl/methylvinylsiloxane (PMVS) gum with an average molecular weight of 600,000 g/mol and a vinyl content of 0.18 mol% was supplied by Nanjing Dongjue Silicone Group Co. Ltd., China. Fumed silica possessing a specific surface area of 200 m2/g was the product of Tokuyama Chemical Co. Ltd., China. Hydroxyl silicone oil containing 6 wt% hydroxyl and methyl hydrogen silicone oil containing 1.2 wt% hydrogen were provided by Nanjing Dongjue Silicone Group Co. Ltd., China. The platinum(0)-1,3-divinyl-1,1,3,3tetramethyldisiloxane, i.e. Karstedt catalyst, contained 3300 ppm of platinum (Pt) and was obtained

from

Guangzhou

Tinci

Silicon

Technology

Co.

Ltd.,

China.

γ-

Ureidopropyltrimethoxysilane (US) and γ-aminopropyltriethoxysilane (AS), selected as the


4

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nitrogen-containing silanes (NS) in this case, were purchased from Hubei Jusheng Technology Co. Ltd., China. The molecular structures of AS and US were shown in Scheme 1. Radical generator, 2,5-Bis(tert-butylperoxy)-2,5-dimethylhexane (DBPMH), was produced by ShinEtsu Chemical Corporation, China. All of the materials were used as received.

Scheme 1. Molecular Structures of AS and US

Table 1. Compounding Formulaa of Silicone Rubbers and their Characteristic Data of Thermogravimetric Curves NS (g)b AS US

T10c (oC)

Rmaxd (wt%/min)

0

0

0

461

12.3

44

100

6.7

0

0

453

14.4

48

SR/AS

100

0

1.4

0

459

11.8

49

SR/US

100

0

0

1.4

459

11.3

46

SR/Pt/AS

100

6.7

1.4

0

472

5.2

68

SR/Pt/US

100

6.7

0

1.4

465

5.8

64

PMVS gum (g)

Pt (ppm)

SR

100

SR/Pt

Samples

Residue at 900 C (wt%)

o

a

The other ingredients of silicone rubber samples were fixed as: 40 phr (parts per 100 parts of gum) of silica, 8 phr of hydroxyl silicone oil, 0.5 phr of methyl hydrogen silicone oil and 2 phr of DBPMH. b The amount of NS was determined by the result of IP test, as shown in Figure S1-3 in Supporting Information. c T10 represented the temperatures of 10% weight loss. d Rmax represented maximum degradation rate.


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Preparation of Silicone Vulcanizates. PMVS gum, silicone oil and silica were intensively mixed in a kneading machine for six hours. Then, two hours of kneading at 150 oC were conducted for the mixture, followed with one hour of kneading under vacuum. After that, silicone compound was cooled down and taken out from the kneader. Pt catalyst, NS and DBPMH were blended into silicone compound via the two-roll mill (XK-168, an open mixing mill, Dongguan Lina Machinery Industrial Co. Ltd., China), according to ISO 2393. Then, obtained compound was placed into a mold and compression-molded at 165 oC and 8 MPa for an optimal cure time that determined by UR-2030 rheometer. The post vulcanization was conducted in a ventilated oven at 180 oC for four hours. Compounding formula was listed in Table 1. Measurements. According to IEC 60587, the tracking and erosion resistance of silicone rubber was measured by an inclined plane (IP) tracking and erosion test apparatus (DX8427, Dongguan Daxian Instruments Co. Ltd., China). Figure 1 depicts the schematic diagram of IP test and sample setup. The testing specimen with sample dimension of 120 × 50 ×6 mm3 was mounted at an angle of 45o, fixed by two electrodes. The distance between upper and bottom electrodes was 50 mm. During test, a certain voltage was applied to samples through electrodes, along with standardized conductive solution (aqueous solution containing 1 wt% ammonium chloride and 0.2 wt% isooctylphenoxypolyethoxyethanol, 3.95 Ω·m tested according to IEC 60587) flowing from upper electrode to bottom electrode. The selected flow rate depended on the applied voltage, according to IEC 60587. Five specimens were needed for each test. When the leakage current exceeded 60 mA for 2 seconds, the test apparatus would recognize this moment as the time to failure. After six hours of IP test, specimen without excess current and burnthrough would be regarded as passed one. The eroded compound of tested specimen was cleared away after IP test and the decreased mass of specimen was recorded as the eroded mass.


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Figure 1. Schematic diagram of the IP test and sample setup. The thermogravimetry (TG) of silicone rubber was carried out via TG209 analyzer (Netzsch Instruments, Germany) from 30 to 900 oC with a linear heating rate of 20 oC/min. 5~10 mg of each sample was tested for thermal stability in an alumina crucible under a synthetic air flow of 40 mL/min. The volatile products of silicone rubber during thermal degradation were investigated by using thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR) which consisted of a TG209 analyser, a Fourier transform infrared spectrometer (Tensor 27, Bruker Optics, Germany) and a transfer tube connecting these two parts. About 15 mg of samples suffered from heating from 30 to 900 oC with a linear heating rate of 20 oC/min and under a synthetic air flow of 40 mL/min. Meanwhile, the pyrolysis gases were continuously transferred to Tensor 27 for FTIR test though the transfer tube with a temperature at 230 oC. Laser Raman spectroscopy (LRS) of the residues of silicone rubbers after IP test and after heating to 900 oC in a muffle furnace were determined by a Raman microspectrometer (Renishaw inVia, Renishaw Co., Britain) at optical range from 3000 to 100 cm-1 and with a 532 nm helium-neon laser source.


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The morphology of the residues of silicone rubbers after IP test and after heating to 900 oC in a muffle furnace were investigated via scanning electron microscopy (SEM, EVO18, Carl Zeiss Jena, Co., Germany) with an accelerating voltage of 10.0 kV. A thin layer of gold was sprayed on the surface of samples before observation.

RESULTS AND DISCUSSION Inclined Plane (IP) test. Figure 2 shows the result of IP test for silicone rubbers. It revealed that SR could only pass the IP test at 2.5 kV. At both 3.5 kV and 4.5 kV, SR failed within 100 minutes due to excess current. SR containing either Pt or NS still failed at 4.5 kV, though the time to failure was delayed for SR/AS and SR/US. However, SR added with both Pt and NS passed IP test at 4.5 kV for all the samples. The eroded mass of sample after the IP tests at 4.5 kV was calculated and also shown in Figure 2. The lower eroded mass of SR/Pt than that of SR was likely due to the shorter time under the dry band arcing. On the contrary, the eroded mass of SR/AS and SR/US was higher than that of SR, due to the longer time. Nevertheless, the eroded mass of SR/Pt/AS and SR/Pt/US was significantly lower than that of SR. This indicated that the cooperation of Pt and NS contributed to high erosion resistance of silicone rubbers. It might because that Pt and NS synergistically catalyzed silicone chains to form firm network on the surface,26,27 which prevented inner silicone rubber from arc ablation. This could be confirmed by the photographs in Figure 3.


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Figure 2. The tracking and erosion performance of silicone rubbers in the IP test.

Figure 3 exhibits the photographs of silicone rubbers after the IP test. As was shown, the surface of SR was covered with a thin layer of white silica ash which was the degradation products of silicone rubber. Under the silica ash, a carbonaceous track linked through top and bottom electrodes, which acted as the carrier of excess leakage current. Both the white ash and carbonaceous track loosely covered the surface and were easy to be blown away. Instead, SR/Pt/NS showed relatively intact surface with only a small area turning black. Besides, this area was compact and tightly bound to inner parts, which might serve as the barrier to protect underlying materials.


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Figure 3. Photographs of silicone rubbers after the IP test at 4.5 kV.

Thermogravimetric Analysis. Thermal degradation is the main reason for the tracking and erosion of silicone rubber. Under dry band arcing, local temperature of silicone rubber increases to even above 1200 oC due to the continual discharge.7 Such high temperature causes thermal oxidative degradation on the surface of silicone rubber. Figure 4 illustrates thermogravimetric curves of various samples under air atmosphere. The corresponding characteristic data are shown in Table 1. It revealed that SR/Pt and SR/NS showed slightly higher residue weight than SR. However, SR/Pt/AS and SR/Pt/US showed 68% and 64% residue at 900 oC, far higher than that of SR. Incorporation of Pt/AS or Pt/US reduced maximum degradation rate (Rmax) by half, though degradation rate didn’t show obvious change after adding either Pt or NS. Besides, the temperature of 10% weight loss (T10) of SR/Pt/AS and SR/Pt/US was also higher than T10 of SR, in spite of lower T10 for SR/Pt and SR/NS. The result indicated that Pt and NS contributed to


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improved thermal stability of silicone rubber in synergy, which might explain the result of IP tests.

Figure 4. The thermogravimetric curves of silicone rubbers under air atmosphere.

Evolved Gases Analysis. To investigate the thermal degradation of silicone rubber under air atmosphere, TG-FTIR was used to investigate the volatile products. Figure 5 shows FTIR spectra of total volatile products for various samples. For all samples, cyclic oligomers (2964 cm-1, 1264 cm-1, 1084 cm-1, 1026 cm-1 and 815 cm-1) were the main products, according to the assignment of absorbance peaks (Table S1).24,28 Besides, carbonyl compounds (CH2O, 1745 cm-1 and 26003200 cm-1), CO (2179 cm-1 and 2114 cm-1), CO2 (2359 cm-1 and 2314 cm-1), H2O (3500-3700 cm-1 and 1590 cm-1) and CH4 (3017 cm-1 and 1304 cm-1) were also detected.25,28 Those products were generated from oxidation and degradation of silicone chains.


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Figure 5. FTIR spectra of total pyrolysis gases of silicone rubbers under air atmosphere.

As demonstrated in Scheme 2a, alkyl groups in silicone chains were oxidized to yield CH2O and turned into silanol groups themselves at high temperature.29 Such silanol groups would easily induce unzipping depolymerization of silicone chains that contributed to a fast degradation via volatilization of cyclic oligomers.30 Furthermore, cyclic oligomers, CH2O and CH4 could be oxidized into CO, CO2 and H2O at high temperature. The yield of CH4 was a result of radical mechanism (Scheme 2b) that could be catalyzed by platinum.28 It revealed that SR/Pt/US and SR/Pt/AS showed significantly lower fraction of CH2O, H2O and cyclic oligomers in total products than other samples, along with higher fraction of CH4 and CO2. This suggested that the presence of Pt/US or Pt/AS suppressed oxidation of silicone chains, whilst enhancing radical mechanism. Therefore, the degradation was retarded by Pt/US and Pt/AS.


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Scheme 2. Oxidation Mechanism (a) and Radical Mechanism (b) of Silicone Rubbers during Thermal Degradation

Figure 6 shows the evolution of volatile products of silicone rubbers as the temperature increases, according to the absorbance at 1745 cm-1, 1026 cm-1, 3018 cm-1, 3500 cm-1, 2179 cm-1 and 2359 cm-1. For SR, CH2O firstly emerged at 290 oC. Then, CH4 and cyclic oligomers were detected. It implied that the silanol groups (generated according to Scheme 2a) might induce release of CH4 and cyclic oligomers. Incorporation of Pt enhanced the maximum release of CH2O, cyclic oligomers, and CH4, though the total release hardly changed by addition of Pt (Figure 5). This might explain the shorter time to failure and lower T10 of SR/Pt than those of SR (see Table 1 and Figure 2). However, the presence of Pt/AS significantly reduced the release of volatile products except CO2 and CH4 (Figure 6), indicating suppressed oxidation and depolymerization of silicone chains. Besides, the maximum release of CH4, CO and CO2 was shifted to higher temperature after adding Pt/AS. This was because Pt/AS performed catalytic effect at high temperature. The release of CO2 and CH4 was much larger for SR/Pt/AS than SR.


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It was due to the catalytic action of Pt/AS on radical mechanism.25,26 The enhancement in radical mechanism facilitated the formation of tight silicone network, so that a residue with high strength and thermal stability was formed.27 Finally, the generation of CO and CO2 was the result of pyrolysis and oxidation of CH2O and CH4. A higher ratio of CO2 versus CO for SR/Pt/AS suggested a tendency of complete oxidation in the presence of Pt/AS.

Figure 6. The evolution of characteristic absorbance of volatile products during thermal degradation.


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Residues Analysis. To investigate the effect of Pt/NS on tracking resistance and thermal degradation of silicone rubber, laser Raman spectroscopy (LRS) was adopted to characterize the residues of SR and SR/Pt/NS after IP test and after heated to 900 oC. Figure 7a shows the spectra of black residue after IP test. It revealed that failed samples for SR possessed carbon characteristic peak of D and G bands, which supported that the carbon deposits could account for the conductive track.31 However, the passed sample for SR/Pt/NS exhibited totally different spectrum, which reserved Si-C peaks and lost the carbon peaks. This indicated that high stability of Si-C and low carbon deposit might contribute to high tracking resistance. The LRS spectra of residues after heated to 900 oC were shown in Figure 7b. The strong peak at 488 cm-1 was attributed to the bending of Si-O-Si.32 It was likely that silica was produced after degradation of silicone rubber in air. The peak at 800 cm-1 was assigned to Si-C. An obvious difference of SR/Pt/NS from SR was the disappearance of the peak at 1317 cm-1 that belonged to the carbon peak.33 This result implied that the incorporation of Pt/NS suppressed the generation of carbon. This agreed with the tendency of complete oxidation in the presence of Pt/NS, as mentioned in TG-FTIR result. Besides, it was reported that platinum promoted oxidation of carbon,34 which might be another reason of suppressed carbon deposit. The SEM images of SR and SR/Pt/NS residues were illustrated beside the corresponding Raman curves. It showed that residue of SR was loose and porous, while residue of SR/Pt/NS was compact. Such structure indicated that the presence of Pt/NS reduced pyrolysis of silicone chains and thus suppressed deposit of carbon and silica. The morphology of SR/Pt/NS suggested an improved thermal stability and the formation of tight network barrier on the surface.


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Figure 7. LRS spectra of silicone rubbers after IP test (a) and heat treatment (b).

The SEM images of SR and SR/Pt/NS after IP test were shown in Figure 8. Figure 8a was the morphology of black tracked compound of SR, which was similar to the morphology of SR after heat treatment (Figure 7b). This implied that the tracked compound was the product of thermal degradation to a large extent, though the LSR spectra were not absolutely consistent. It was because dry band arcing resulted in the development of hot spots on the samples’ surface, which induced thermal degradation of silicone rubber. However, temperature rise induced by dry band acing was much faster than the condition of heat treatment. Thereby, tracked compound contained larger content of carbon than residue after heat treatment as demonstrated in LSR spectra. Figure 8b was the morphology of silicone rubber under tracked compound. It showed that there were lots of ravines on the undulating surface, which suggested severe damage on the materials. Figure 8c exhibited the morphology of most damaged point (as was marked in Figure 7a) in SR/Pt/NS after IP test. The total surface was almost continuous, which could support the formation of tight network barrier. Thus, inner material could be protected from arcing ablation.


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Figure 8. SEM images of silicone rubbers after IP test: (a) tracked compound, (b) silicone rubber under tracked compound and (c) the surface of passed sample.

Suppression Mechanism. According to the discussion mentioned above, the suppression mechanism of Pt/NS on tracking and erosion of silicone rubber was proposed and displayed in Figure 9. For SR, the thermal degradation of silicone chains was induced by large heat from dry band arcing, via predominant unzipping depelymerization and secondary molecular mechanism. During degradation, cyclic oligomers, CH2O and CH4 were evolved and were further carbonized to form tracking compounds. Such conductive tracking compounds deposited on the surface, which further aggravated arcing and led to degradation. As a result, silicone rubber would lose properties of electrical insulation due to tracking and erosion. However, for SR/Pt/NS, Pt/NS suppressed oxidation of silicone chains. Besides, at high temperature, the catalytic effect of Pt/NS on radical crosslinking promoted the formation of tightly crosslinked network, which protected silicone chains from further degradation. Moreover, the volatile products tended to be completely oxidized into CO2, in the presence of Pt/NS. Thus, the tracking of SR/Pt/NS was restrained.


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Figure 9. Suppression mechanism of Pt/NS on tracking and erosion of silicone rubber.

CONCLUSIONS Nitrogen-containing silane (NS) and platinum (Pt) were introduced to improve the tracking and erosion resistance of silicone rubber. It revealed that when 1.4 phr of NS and 6.7 ppm of Pt were added, the tracking resistance of silicone rubber was improved from 2.5 kV to 4.5 kV level in the IP test and the eroded mass was significantly decreased. The TG results revealed that there existed synergism between NS and Pt on enhancing thermal stability of the silicone rubber,


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which contributed to a high residue of 68 wt% at 900 oC and reduced the degradation rate by a half. TG-FTIR results, LRS spectra and SEM images further revealed the suppression mechanism of Pt/NS on tracking and erosion of silicone rubber. At high temperature, silicone rubber could develop tight silicone network on the surface by the catalytic action of Pt/NS. This tight network acted as a barrier to protect inner part from degradation. Moreover, the presence of Pt/NS facilitated complete oxidation of evolved gases during pyrolysis and suppressed the carbon deposit on silicone rubber. Therefore, the tracking of SR/Pt/NS was hard to develop.

ASSOCIATED CONTENT Supporting Information. The result of IP test of silicone rubbers with different formulation; the thermogravimetric curves of silicone rubbers used in this paper under nitrogen atmosphere; the assignment of absorbance peaks of cyclic oligomers. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author * Tel&Fax: +86-20-8711-4248. E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT The authors appreciate for the financial support of the National Natural Science Foundation of China (No. 51573052 and No. 51403067).


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(8) Bolliger, D. A.; Boggs, S. A. The Chemistry of Interfacial Tracking. IEEE T. Dielect. El. In. 2012, 19, 996-1006. (9) Guan, Z. C.; Liu, Y. Y.; Zhou, Y. X.; Jia, Z. D.; Wang, L. M.; Shi, W. D. Insulators and Insulation Materials in Power Transmission and Transformation System, 1st ed. Tsinghua University Press: Bei Jing, 2006; pp 261-311. (10) Farzaneh, M.; Chisholm W. A. Insulators for Icing and Polluted Environments, 1st ed. John Wiley& Sons: Hoboken, 2009; pp 155-240. (11) Ghunem, R.; Jayaram, S.; Cherney, E. Suppression of Silicone Rubber Erosion by Alumina Trihydrate and Silica Fillers From Dry-band Arcing under DC. IEEE T. Dielect. El. In. 2015, 22, 14-20. (12) Venkatesulu, B.; Thomas, M. J. Erosion Resistance of Alumina-filled Silicone Rubber Nanocomposites. IEEE T. Dielect. El. In. 2010, 17, 615-624. (13) Liu, Y.; Li, Z.; Du, B. Effects of Nano-SiO2 Particles on Surface Tracking Characteristics of Silicone Rubber Composites. Appl. Phys. Lett. 2014, 105, 102905. (14) Du, B.; Xu, H. Effects of Thermal Conductivity on DC Resistance to Erosion of Silicone Rubber/BN Nanocomposites. IEEE T. Dielect. El. In. 2014, 21, 511-518. (15) Wang, Z.; Nelson, J. K.; Miao, J.; Linhardt, R. J.; Schadler, L. S.; Hillborg, H.; Zhao, S. Effect of High Aspect Ratio Filler on Dielectric Properties of Polymer Composites: a Study on Barium Titanate Fibers and Graphene Platelets. IEEE T. Dielect. El. In. 2012, 19, 960-967.


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Hayashida,

K.;

Tsuge,

S.;

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Polydimethylsiloxane Material Containing Platinum Compound Studied by Analytical Pyrolysis Techniques and Alkaline Hydrolysis Gas Chromatography. Polymer 2003, 44, 5611-5616. (27) Delebecq, E.; Hamdani-Devarennes, S.; Raeke, J.; Lopez Cuesta, J. M.; Ganachaud, F. High Residue Contents Indebted by Platinum and Silica Synergistic Action during the Pyrolysis of Silicone Formulations. ACS Appl. Mater. Interfaces 2011, 3, 869-880. (28) Camino, G.; Lomakin, S.; Lageard, M. Thermal Polydimethylsiloxane Degradation. Part 2. The Degradation Mechanisms. Polymer 2002, 43, 2011-2015. (29) Camino, G.; Lomakin, S.; Lazzari, M. Polydimethylsiloxane Thermal Degradation. Part 1. Kinetic Aspects. Polymer 2001, 42, 2395-2402. (30) Hamdani, S.; Longuet, C.; Perrin, D.; Lopez-cuesta, J. M.; Ganachaud, F. Flame Retardancy of Silicone-based Materials. Polym. Degrad. Stabil. 2009, 94, 465-495.


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Table of Content graphic


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Scheme 1. Molecular Structures of AS and US Scheme 1 85x20mm (300 x 300 DPI)


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Figure 1. Schematic diagram of the IP test and sample setup. Figure 1 109x56mm (300 x 300 DPI)



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Figure 2. The tracking and erosion performance of silicone rubbers in the IP test. Figure 2 116x70mm (300 x 300 DPI)


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Figure 3. Photographs of silicone rubbers after the IP test at 4.5 kV. Figure 3 85x85mm (300 x 300 DPI)



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Figure 4. The thermogravimetric curves of silicone rubbers under air atmosphere. Figure 4 85x58mm (300 x 300 DPI)


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Figure 5. FTIR spectra of total pyrolysis gases of silicone rubbers under air atmosphere. Figure 5 73x63mm (300 x 300 DPI)



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Scheme 2. Oxidation Mechanism (a) and Radical Mechanism (b) of Silicone Rubbers during Thermal Degradation Scheme 2 150x78mm (300 x 300 DPI)


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Figure 6. The evolution of characteristic absorbance of volatile products during thermal degradation. Figure 6 85x157mm (300 x 300 DPI)



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Figure 7. LRS spectra of silicone rubbers after IP test (a) and heat treatment (b). Figure 7 175x68mm (300 x 300 DPI)


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Figure 8. SEM images of silicone rubbers after IP test: (a) tracked compound, (b) silicone rubber under tracked compound and (c) the surface of passed sample. Figure 8 177x40mm (300 x 300 DPI)



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Figure 9. Suppression mechanism of Pt/NS on tracking and erosion of silicone rubber. Figure 9 136x121mm (300 x 300 DPI)


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Table of Content Graphic Table of Content graphic 35x15mm (300 x 300 DPI)


Suppression Effect and Mechanism of Platinum and Nitrogen

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