High Temperature Vulcanized Silicone Rubber Research Articles

Recovery of Hydrophobicity of HTV Silicone Rubber after Accelerated Aging in Saline Solutions

A study of the recovery of the hydrophobicity of high temperature vulcanized (HTV) silicone rubber (SIR) after immersion for 3000 h in saline solutions of different conductivities (0.005-100 mS/cm) and at different temperatures (0-98degC) as a function of time (0 to 3000 h) is reported. The hydrophobicity characterized as the ability of the material to bead water is determined by measuring the static contact angle thetas between the tangent to the droplet of distilled water and the horizontal surface of the HTV SIR. After removal from the saline solution the recovery of the contact angle was determined at 22 plusmn 3degC in air. The contact angle recovered from its lowest value of 15deg after immersion in distilled water at 98degC for 3000 h to 100deg after 3000 h of recovery. The percentage reduction in weight during recovery due to drying of the specimens at 22degC was determined. The surface roughness which affects the hydrophobicity was monitored during the recovery period. The changes in the weight and surface roughness of the specimens are correlated with the contact angle and hence with the recovery of the hydrophobicity of HTV SIR. The surface properties during recovery were examined using scanning electron microscopy (SEM), energy dispersive X-ray (EDS) spectroscopy and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy.

Low acoustic attenuation silicone rubber lens for medical ultrasonic array probe

Effects of heavy density (rho = 9.2 x 10(3) kg/m(3)) Yb(2)O(3) fine dopant (16 nm in diameter) on the acoustic properties of a high-temperature-vulcanization (HTV) silicone rubber have been investigated, to develop a new acoustic lens material with a low acoustic attenuation (alpha) for the medical array probe application. The HTV silicone rubber has advantages in that it shows a lower alpha than that of a room-temperature-vulcanization (RTV) silicone rubber and it can be mixed by applying shear stress, using roll-milling equipment. Roll-milling time dependence of the HTV silicone rubber indicates that the alpha is closely affected by the dispersion of nanopowders in the rubber matrix. The 8 vol% Yb(2)O(3)-doped HTV silicone rubber mixed for 30 min showed the lowest alpha of 0.73 dB/mm MHz with an acoustic impedance [AI = sound speed (c) x density (rho)] of 1.43 x 10(6) kg/m(2)s at 37 degrees C. Moreover, simulation results reveal that a 5 MHz linear probe using the HTV silicone rubber doped with Yb(2)O(3) powder showed relative sensitivity around 2.6 to 3.0 dB higher than a probe using RTV silicone rubber doped with Yb(2)O(3) powder or SiO2-doped conventional silicone rubber for the ultrasonic medical application.

Effects of saline water and temperature on surface properties of HTV silicone rubber

A study of the loss of hydrophobicity of high temperature vulcanized (HTV) silicone rubber (SIR) after immersion in saline solutions as a function of time (0 to 3000 h) at different temperatures is reported. The hydrophobicity is determined by measuring the static contact thetas between the tangent to the droplet of distilled water and the horizontal surface of the HTV SIR. The conductivity of the saline solution was varied from 0.005 to 100 mS/cm and the temperature from 0 to 98°C during immersion. The contact angle decreased from the original value of 100±4.6deg to low value of 15deg after 3000 h of immersion at 98°C in a solution of 0.005 mS/cm. The lower the conductivity, the larger was the decrease in the contact angle. The changes in the weight of the HTV SIR due to the uptake of water and the average surface roughness (ASR) are determined during the immersion. The increase/decrease in the weight and surface roughness of the HTV SIR are correlated with the contact angle and hence with the loss of hydrophobicity. The surface free energies Γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sd</sub> , Γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sh</sub> and Γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , the interfacial energy of HTV SIR and water Γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sl</sub> , and the energy of adhesion W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">si</sub> of water on HTV SIR are determined as a function of time during the immersion and related to the loss of hydrophobicity.

Characteristics of Electrical Insulation in PDMS-ATH Composite for High Voltage Insulators

The electrical insulation properties and the tracking and erosion resistances of high-temperature vulcanized silicone rubber were investigated as to the concentration of alumina trihydrate (ATH) therein for the fabrication of silicone rubber with optimum ATH content. Controlling the ATH concentration has been found to be an important factor in the enhancement of the tracking and erosion resistances of silicone rubber. In addition, the silicone rubber showed constant electrical resistivity and dielectric breakdown voltage without any decrease due to the interfacial problems with the addition of ATH to the silicone rubber. Therefore, this fabricated silicone rubber that contains an optimum ATH concentration can be applied to outdoor high-voltage insulators.

PREPARATION OF HIGH-TEMPERATURE VULCANIZED SILICONE RUBBER OF EXCELLENT MECHANICAL AND OPTICAL PROPERTIES USING HYDROPHOBIC NANO SILICA SOL AS REINFORCEMENT

Hydrophobic nano silica sol (HNSS) was incorporated into polyvinylmethylsiloxane to prepare reinforced high-temperature vulcanized (HTV) silicone rubber. HTV silicone rubber filled with 40 phr HNSS showed excellent mechanical and optical properties: the tensile strength reached 11.7 MPa and the optical transmittance was higher than 90%. Possible reasons for reinforcement and transparency were discussed on the basis of the bound rubber percentage, total crosslink density, and SEM analysis. Our work suggests that HNSS is effective for reinforcement of HTV silicone rubber to endow excellent mechanical and optical properties.

Preparation of an organomontmorillonite master batch and its application to high‐temperature‐vulcanized silicone‐rubber systems

AbstractN,N‐Di(2‐hydroxyethyl)‐N‐dodecyl‐N‐methyl ammonium chloride was used as an intercalation agent to treat Na+‐montmorillonite and form a novel type of organic montmorillonite (OMMT). An OMMT master batch (OMMT‐MB) was prepared by solution intercalation and was used in the preparation of high‐temperature‐vulcanized silicone rubber (HTV‐SR)/OMMT‐MB nanocomposites. The properties, such as the tensile and thermal stability, were researched and compared with those of composites directly incorporated with OMMT or aerosilica. A combination of Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, and transmission electron microscopy studies showed that HTV‐SR/OMMT‐MB composites were on the nanometer scale, and their structure was somewhat hindered by the presence of OMMT. The results showed that the tensile properties of HTV‐SR/OMMT‐MB and HTV‐SR/OMMT systems were better than those of pure HTV‐SR. Compared with those of HTV‐SR/OMMT‐20%, the tensile strength and elongation at break of HTV‐SR/OMMT‐MB‐20% were improved about 1.5 and 0.9 times, respectively. This was probably due to the nanoeffect of the exfoliated silicate layers. Moreover, the tensile strength of HTV‐SR/OMMT‐MB‐20% was nearly equal to that of HTV‐SR/aerosilica‐20%, and the elongation at break even showed much improvement. Additionally, the thermal degradation center temperature of the HTV‐SR/OMMT‐MB‐20% nanocomposite was increased by 30°C compared with that of the HTV‐SR/OMMT‐20% composite. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Leakage current suppression and resistance to tracking and erosion of HTV silicone rubber with added silicone plasticizer

The present study evaluated the leakage current suppression and the resistance to tracking and erosion of high-temperature vulcanized silicone rubbers (HTV-SIRs) containing different levels of silicone plasticizer. Slab HTV-SIRs unfilled and filled with alumina trihydrate (ATH, 50 wt%) and with added linear silicone plasticizer (0-6.0 wt%), which was terminated with hydroxyl groups and of which repetition number was 13-18, were tested. Evaluation using the IEC 60587 inclined-plane method indicated that the plasticizer had no influence on the tracking and erosion behavior. Salt-fog test results indicated that a higher level of plasticizer in the ATH-filled HTV-SIR showed smaller leakage current. Gas chromatography and mass spectrometry suggested that the enhanced suppression of the leakage current for ATH-filled HTV-SIR can be attributed to migration of the linear silicone plasticizer onto the surface contaminants. It was concluded that the addition of silicone plasticizer is useful for improving the leakage current suppression ability of HTV-SIR without reducing its tracking and erosion resistance in the above laboratory tests

Surface Modification of Silicone Rubber After Corona Exposure

This paper describes the surface modification of high temperature vulcanized silicone rubber (HTV-SR) resulting from corona discharges under atmospheric pressure. In this study, a plate-shaped HTV-SR specimen was exposed to corona stress generated by a needles-plane electrode system; further, physicochemical analyses were conducted on the surface layer of SR before and after corona discharge treatment. The results showed that the plasma impingement from the corona discharge can cause physical and chemical damages to the SR surface. In addition, it was demonstrated that instead of hydrophobic CH3 groups, hydrophilic OH groups that are byproducts of ageing may be formed on the surface of aged SR; further, the corona discharge plays an important role in the loss of hydrophobicity.

Surface Degradation of Silicone Rubber Exposed to Corona Discharge

This paper describes the surface degradation of unfilled high-temperature vulcanized silicone rubber (HTV-SR) resulting from creeping corona discharges under atmospheric pressure. In this paper, HTV-SR specimens were exposed to corona stress generated by a parallel needle-plate electrode system; furthermore, physicochemical analyses were conducted on the surface layer of SR before and after corona discharge treatment. The results showed that the plasma impingement from the corona discharge can cause physical and chemical damages to the SR surface. In addition, it was demonstrated that instead of hydrophobic CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> groups, hydrophilic OH groups that are by-products of aging may be formed on the surface of aged SR; furthermore, the corona discharge plays an important role in the loss of hydrophobicity

Effect of specimen configuration on deterioration of silicone rubber for polymer insulators in salt fog ageing test

The paper investigates the effects of specimen configuration on the deterioration of silicone rubber insulators in a salt fog ageing test. A cyclic salt fog ageing test was conducted on three types of high-temperature vulcanized silicone rubber (HTV SiR) specimens: two types of insulators having sheds, and plain rods without sheds. The test was based fundamentally on the CIGRE WG 15-04 specifications. After 50 test cycles, the three types of specimens showed different degrees of surface deterioration. Erosion on the straight shed insulator was more severe than that on the alternate shed insulator even though the two had the same leakage distance. No erosion was observed on the rod-type specimens, which had shorter leakage distances than the insulator-type specimens.

Corona Discharge from Water Droplet on Electrically Stressed Polymer Surface

This paper describes the results of experiments and simulations made to examine the corona discharges from water droplets on a polymer surface exposed to electrical stress. In this study, water droplets with different conductivities and volumes were placed on the surface of plate-shaped high temperature vulcanized silicone rubber (HTV-SR) energized with ac voltage, and the corona discharge phenomena were observed by a high-speed camera with an image intensifier. The electric-field distributions were calculated by the finite element method (FEM). It is demonstrated that the electric field is intensified at the triple junction of the water droplet, air and the insulating material due to the difference in their permittivities, which can ionize the surrounding air and trigger a corona discharge. It can also be confirmed that the contact angle, volume, conductivity and number of water droplets are shown to have a marked effect on the mode of the corona discharge development.

Loss and recovery in hydrophobicity of silicone rubber exposed to corona discharge

This paper describes the loss and recovery in the hydrophobicity of unfilled high temperature vulcanized silicone rubber (HTV-SR) resulting from corona discharge. In this study, HTV-SR specimens were exposed to corona stress generated by a parallel needle–plane electrode system, and physicochemical analyses on the surface layer of SR before and after corona discharge treatment were carried out by using Fourier transform infra-red (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It is demonstrated that hydrophilic OH groups that are by-products of ageing can be formed instead of hydrophobic CH 3 groups on the surface of aged SR and the corona discharge plays an important role on the temporary loss of hydrophobicity. After a substantial period of ‘rest’, the hydrophobic recovery of SR results from the diffusion of low-molecular weight (LMW) silicone fluid from the bulk onto the aged layer.

Mechanism for change in leakage current waveform on a wet silicone rubber surface-a study using a dynamic 3-D model

This paper describes the results of experiments and simulations made to examine the waveform of leakage current flowing through the surface of HTV (high temperature vulcanized) silicone rubber specimen exposed to clean fog. Water droplets were placed on the surface of specimen energized with AC voltage and investigations of the surface state were done by a high-speed video camera in a wet condition produced by sprayed clean fog. Simultaneously, according to the experimental condition, a dynamic 3-D model was built to calculate the electric field and current density distribution on the specimen surface by a finite element software. A conducting water layer is formed due to the deformation of droplets and the development of dry band arcing. This caused large distortion and nonlinearly which increased the odd harmonic components in the leakage current waveform. This is in good agreement with the simulating calculation. The information from the leakage current frequency characteristic was extracted and correlated with the insulation surface condition. It can be considered as a diagnostic index for electrical characteristics and insulation state of polymer insulators in the wet condition.

Recovery of monomers and fillers from high-temperature-vulcanized silicone rubbers—combined effects of solvent, base and fillers

The depolymerization of high-temperature-vulcanized (HTV) silicone rubbers containing filler silica and alumina into cyclosiloxane monomers and spontaneous recovery of fillers were studied. First, HTV silicone rubber was treated with different types of solvents in the presence of KOH to find that a triad mixture of diethylamine, methanol and hexane was appropriate not only to dissolve the silicone rubber to a suspension but also to separate fillers completely by filtration. The filtrate was distilled to remove solvent first and then give pure cyclosiloxane monomers in 76–84% yields. Second, the rubbers were treated with other types of triad mixture of solvents and bases, e.g. tetramethylammonium hydroxide, hexane and diethylamine. After filtration, residue was again treated with the amine and hexane to recover clean fillers in 83–93% yields. Cyclosiloxane monomers were also obtained from the combined filtrates in 67–78% yields.

옥외용 실리콘 절연재료의 발수성에 미치는 표면전하의 영향과 표면 상태에 따른 표면전위 감쇠

This paper presents the effects of accumulation of surface charges on hydrophobic level and the changes of surface potential decay with various artificial environment treatments on high temperature vulcanized (HTV) silicone rubber used for outdoor insulating material. For this study, the charging apparatus by corona discharge, in which grid electrode was installed between the main corona and ground electrode, was used. From this study, it was found that the accumulation of surface charges above a critical surface potential on silicone insulating materials could lead to the temporary loss of surface hydrophobicity. In addition, corona stress and water absorption stress increase the decay rate of surface charges of HTV silicone rubber, while ultraviolet (UV) stress causes longer decay time. We could conclude that the effects of surface charges on hydrophobicity level and the changes of surface state by various artificial treatments were found through a trend of surface potential decay.

Tracking and erosion of HTV silicone rubber and suppression mechanism of ATH

Tracking and erosion of high temperature vulcanizing (HTV)-silicone rubber (SIR) and the suppression mechanism of alumina trihydrate (ATH) filler were investigated in the present study. The tracking and erosion resistance of HTV-SIR filled with 0 to 60%wt ATH was evaluated by employing an IEC 587 inclined plane (IP) tracking and erosion test, during which leakage current pulses on HTV-SIR were counted. Surface temperature distributions and the occurrences of thermal spots >400/spl deg/C also were observed by means of an infrared thermovision study. We employed thermogravimetry (TG)-differential thermal analysis (DTA)-mass spectrometer (MS) to observe the thermal degradation of unfilled and filled HTV-SIR in both air and argon. The test results indicate that 40%wt is a critical ATH level and whether tracking and erosion is allowed in the IP tracking and erosion test. Highly filling ATH (>40%wt) reduces the number of low unit silicone oligomer precursors which promote dry-band arcing as well as the presence of residual carbon which leads to carbonization. Chemical modifications of water vapor liberated from heated ATH to methyl groups, which occurs at the thermal decomposition temperature of silicone rubber, were found to result in the above process. The protection mechanisms of ATH for the tracking and erosion of HTV-SIR are formulated herein.

Accelerated weatherability of shed materials for composite insulators

Shed materials for hollow composite insulators (low temperature vulcanized silicone rubber, high temperature vulcanized silicone rubber, ethylene vinyl acetate and ethylene propylene diene monomer) were examined through accelerated weathering tests and their weathering resistances were evaluated from changes of surface and bulk properties. For silicone rubber, changes in the content of low molecular weight silicone (silicone oil) related to maintaining water repellency were investigated. The results showed that silicone rubbers had excellent weathering resistance and kept high water repellency during long term weathering tests. Using an equivalent model, an investigation was also carried out on how non-soluble contaminations deposited on the surfaces of sheds in outdoor service could cut off UV rays.

Loss and recovery of hydrophobicity and surface energy of HTV silicone rubber

The loss of surface hydrophobicity of high temperature vulcanized (HTV) silicone rubber (SIR) due to immersion in saline solutions (0.005 to 100 mS/cm) has been studied as a function of immersion time (0 to 576 h) and temperature (0 to 98/spl deg/C). The subsequent recovery of the hydrophobicity in air is determined also. The loss and recovery of the hydrophobicity is correlated with the absorption of water during immersion and its subsequent desorption in air. The hydrophobicity is determined by measuring the static contact angle /spl theta/ between the tangent to a droplet of distilled water and the horizontal HTV-SIR surface. The surface energies /spl gamma//sub S/, /spl gamma//sub SD/ and /spl gamma//sub SH/ of HTV-SIR, the energy of adhesion W/sub SL/ and the surface tension /spl gamma//sub SL/ of water to HTV-SIR were determined as a function of time of immersion (loss of hydrophobicity), the time of recovery of hydrophobicity and the contact angle of water. For virgin HTV-SIR at 24.5/spl plusmn/3.5/spl deg/C the surface energies were determined to be /spl gamma//sub S/=31.6 mJ/m/sup 2/, /spl gamma//sub SD/=28.5 mJ/m/sup 2/, /spl gamma//sub SH/=3.1 mJ/m/sup 2/, W/sub SL/=61.4 mJ/m/sup 2/ and /spl gamma//sub SL/=43.0 J/m/sup 2/. These values are in reasonable agreement with the literature.

Tracking and erosion of HTV silicone rubbers of different thickness

Tracking and erosion behaviors of high temperature vulcanized (HTV)-silicone rubber (SIR) of 0.5 to 6.0 mm thicknesses were investigated in order to obtain the optimum thickness for enhancing tracking and erosion resistance under various leakage current levels. Under low leakage current, thinner samples showed a higher tracking and erosion resistance, while under medium and high leakage current, thicker samples showed better resistance to these behaviors. The optimum thickness to prolong the time to tracking and erosion failure appeared in the range of 1.0 to 3.0 mm thickness. The content of an initial low molecular weight (LMW) silicone fluid was shown to be closely related to the development of leakage current and high temperature thermal spots. The results indicate that the sample thickness is crucial to the ability of HTV-SIR to withstand a large number of high temperature thermal spots under condition of high level leakage current.

Resistance to Tracking and Erosion of Silicone Rubber Material under Various Types of Precipitation

Environment stress and contaminants have become more and more severe due to the development of industry. Outdoor polymer insulating materials in use may suffer from rainwater containing various chemical contaminants so that their resistance to tracking degrades. In this paper, the tracking resistance of high-temperature vulcanized silicone rubber (HTVSR) under various types of precipitation is evaluated by the incline-plane method, using artificial rainwater as a contaminant. The influences of ion concentration, acidity, and conductivity of rainwater on the energized silicone rubber material are studied. Experimental results reported here show that the degradation of the energized material increases with the ion concentration of the rainwater; the discharge current and the erosion of material increase. The conductive ions in rainwater could induce more tracking and discharge on the energized material surface, and acidic rainwater could accelerate the electrolyte process in the materials and dissolve the inorganic filler in silicone rubber. Although silicone rubber degrades under our process of accelerated aging using artificial rainwater, the ion concentration, acidity and conductivity of actual precipitation is insufficient to exert a significant degradation effect on silicone rubber. Silicone rubber can resist the erosion of even the most corrosive rainwater and does not fail.