Room Temperature Vulcanized Silicone Rubber Research Articles

Breakdown mechanism of RTV silicone rubber coated insulators under steep-front impulse voltage

Insulators play the vital role in the power transmission, including traditional porcelain/glass insulator and silicone rubber based polymeric insulator. By coating the glass/porcelain insulators with silicone rubber, the advantages of organic and inorganic dielectrics are integrated. However, it was found that the breakdown probability of coated insulators under steep-front impulse increases significantly. It suggests the possible degradation of insulator material and might become the hidden danger of power system. Therefore, in this research, a great deal of steep-front impulse voltage tests are carried out over various types of insulators. It demonstrates that the performance degradation is introduced by RTV coating instead of intrinsic defects. Then, based on the analysis of flashover paths and breakdown locations, the breakdown mechanism of coated insulator under steep-front impulse is illustrated. Also, numerical simulation of electric field distribution is performed for verification, taking the surface arc development into account. It indicates that the development of surface arc is distorted by the coating which results in the intense local field and dielectric breakdown. Next, different controlled experiments are designed and conducted to validate the theory. Besides, the corresponding modification towards the current coating method is proposed.

The Glaze Icing Performance of a Robust Superhydrophobic Film Composed of Epoxy Resin and Polydimethylsiloxane

Ice accretion on transmission lines can cause operational difficulties and disastrous events. In this study, a micro/nano-structured epoxy resin/polydimethylsiloxane (EP/PDMS) film on glass, with water droplet contact angles (CA) observed as high as 160° and the water droplet sliding angle (SA) < 1° was fabricated by aerosol-assisted chemical vapor deposition (AACVD). The glaze icing performance of the superhydrophobic EP/PDMS films have been investigated by comparing the bare glass and room temperature vulcanized (RTV) silicon rubber-coated glass substrate representing the glass insulators and silicone rubber insulators, respectively. Compared with the bare glass and the RTV silicon rubber coating, the EP/PDMS superhydrophobic coating showed excellent performance in delaying glaze icing, especially in the early stages of icing. After 20 min of glaze icing with tilting angle of 90° at −5 and −10 °C, 38.9% and 85.7% of the RTV silicon rubber coating were covered, respectively, and less than 3% of the EP/PDMS coating was covered by ice when the blank glass sheet was completely covered. The EP/PDMS films also showed good mechanical robustness and long-term stability, which are important considerations in their widespread real-world adoption.

Characteristics stability assessment of silica/alumina trihydrate based silicone elastomer composites subjected to long-term weathering under bipolar direct current for industrial electrical insulation

Room temperature vulcanized silicone rubber (RTV-SiR) coatings co-filled with silica (SiO2) and alumina trihydrate (ATH) fillers were subjected to long-term accelerated weathering under bipolar direct current (DC). Experimentations were conducted on fabricated samples of RTV-SiR with 5% nano-silica and RTV-SiR with 20% ATH in a specially designed weathering chamber. An extended aging (10,000 h) was conducted on samples energized equally under both polarity voltages to evaluate the effect of positive and negative voltages on the performance of RTV coating under bipolar high voltage DC. The electrical stability of specimens was assessed using online leakage current measurement, hydrophobicity, volume, and surface resistivity analysis. For mechanical characteristics of test samples hardness shore-A, tensile strength, weight loss, and elongation-at-break were measured and analyzed. Variations in chemical, morphological, and thermal degradation of the samples with aging were assessed using characterization tools like Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Thermal Gravimetric Analyzer (TGA), respectively. Findings explicated that samples with nano SiO2, offer better hydrophobic recovery and hence better leakage current suppression while ATH-filled composites exhibited enhanced thermal stability and better resistance to mechanical alterations. Furthermore, the comparative analysis of voltage polarity elucidates that the impact of positive DC was more profound in aging.

Electrical Performance Study of 11kV Coated Porcelain, Coated Glass, and Polymer Outdoor High Voltage Insulators

The study in this paper investigates how contaminations and different types of pollutants affect the electrical performance of outdoor coated porcelain, coated glass, and composite insulators when subjected to an 11 kV AC voltage. The ceramic insulators (porcelain and glass) coating layer is assumed to be RTV silicon rubber material with a 0.5 mm thickness. The effect of these three pollution cases on the electrical performance were investigated using a commercial software called COMSOL Multiphysics based on the finite element method (FEM). The three pollution cases were uniform, non-uniform pollution, and water droplets. In the uniform pollution condition, the pollution layer over the surface of the insulators was assumed to be 0.5 mm; however, in non-uniform pollution condition, water patches with a thickness varying from 0.5 to 1.5 mm was used. In water droplets condition, hemispherical shapes were used to model water droplets with a diameter of 1 mm. Voltage, electrical field distributions, and dissipated power were computed along the creepage distance of the three insulators models. The simulation results indicated that for the uniform case, the lowest electrical field appeared on the silicon rubber insulator. For the non-uniform case, the electrical field distribution became more non-uniform for the three models. In the water droplets case, more fluctuations appeared in the metal end fittings where the water droplets were located. The analysis indicated that the maximum dissipated power was found to be for the coated glass. The obtained results showed that the silicon rubber insulator offered better performance compared with coated porcelain and glass. Coated porcelain offered better performance compared with the coated glass insulator.

Flame retardancy, combustion, and ceramization behavior of ceramifiable flame‐retardant room temperature vulcanized silicone rubber foam

AbstractTwo types of ceramifiable flame‐retardant room temperature vulcanized (RTV) silicone rubber foam containing mica power (MP) were prepared by using glass powder (GP) as fluxing agents and aluminum hydroxide (ATH) as flame‐retardant agent, respectively. The flame retardant, combustion behavior, and thermal stability of ceramifiable flame‐retardant RTV silicone rubber foams were investigated. The results show that GP is not conducive to the flame retardancy and thermal stability improvement of the foams. On the contrary, MP and ATH can significantly improve the flame retardancy and thermal stability at high temperatures of the foams. The foams with addition of MP and ATH can reach to a high limiting oxygen index value of 35.8 with V‐0 rating in the vertical combustion test, and the total heat release and total smoke production of the foams are 21.0% and 61.7% lower than of the pure RTV silicone rubber foam, respectively. Furthermore, the structural and morphological changes of the foams under different pyrolysis conditions were studied, so as to reveal its ceramifiable mechanism under different fire scenarios. The results show that GP does not promote the formation of more char residue during pyrolysis, but it can greatly lower the ceramifiable temperature, resulting in a superior ceramic phase char residue. The foams including MP and ATH have a high char residue content; nevertheless, a comparatively higher temperature is necessary to create ceramic phase char residue.

Application of Magnesium Hydroxide/Diphenoxy Phosphate in Silicone Rubber Flame Retardant Cable Material

Deketoxime–type room–temperature vulcanized silicone rubber cable materials were prepared using α, ω–dihydroxy polydimethylsiloxane, carbon black, calcium carbonate, magnesium hydroxide, piperazine bis (diphenoxy phosphate) salt (PBDP), and melamine diphenoxy phosphate (MDP). The effects of carbon black and flame retardants on the mechanical properties, flame–retardant properties, and electrical insulation properties of silicone cable coatings were investigated. The research results showed that the products obtained had good mechanical and electrical insulation properties, with tensile strength greater than 3.0 MPa, dielectric strength greater than 22 kV/mm, and volume resistivity higher than 6.5 × 1014 Ω·cm. When 30 parts of Mg(OH)2:MDP = 2:1 are added to 100 parts of resin, the flame–retardant performance of wire and cable materials can be significantly improved. Under the thermal radiation illumination of 50 kW/m2, the ignition time (TTI) of the Mg(OH)2/MDP coating increased by 16 s, and the maximum heat release rate (pkHRR) and total heat release rate (THR) decreased by 29.7% and 68.8%, respectively, compared with silicone rubber without flame retardant. The silicone rubber coatings prepared were flame retardant up to the FV–1 level.

The tough and multi‐functional stretchable device based on silicone rubber composites

AbstractRecently, the advances in stretchable electronic devices have attracted great attention around the world. New technologies are constantly updated to obtain a stretchable device with high performance and robust durability. The stretchable device‐based rubber composites were prepared with the addition of room‐temperature‐vulcanized silicone rubber (RTV‐SR) and different types of nanofillers such as graphite nanoplatelets (GNP), molybdenum disulfide (MoS2), and their hybrid. The hybrid composites contain both nanofillers in 50:50 ratios. The mechanical performance of the stretchable device was studied and presented. For example, the compressive modulus was 1.86 MPa (virgin), and at 20 per hundred parts of rubber (phr) was 3.9 MPa (GNP), 2.3 MPa (MoS2), and 2.72 MPa (Hybrid). The mechanical stretching ability of the composites was 120% (virgin), and at 20 phr was 170% (GNP), 182% (MoS2), and 171% for (Hybrid). At end of the work, a novel stretchable device based on a piezo‐electric effect is presented which provides an output voltage of ~1.2 V and high durability of >0.1 million cycles without significant degradation. This device is based on a rubber composite with the inclusion of electro‐active and dielectric materials as described in the subsequent section of the paper.

Study on NO2 Barrier Properties of RTV Silicone Rubber by Incorporation of Functional Graphene Oxide.

In this study, functional graphene oxide (f-GO) nanosheets were prepared to enhance the NO2 resistibility of room-temperature-vulcanized (RTV) silicone rubber. A nitrogen dioxide (NO2) accelerated aging experiment was designed to simulate the aging process of nitrogen oxide produced by corona discharge on a silicone rubber composite coating, and then electrochemical impedance spectroscopy (EIS) was used to test the process of conductive medium penetration into silicone rubber. After exposure to the same concentration (115 mg·L-1) of NO2 for 24 h, at an optimal filler content of 0.3 wt.%, the impedance modulus of the composite silicone rubber sample was 1.8 × 107 Ω·cm2, which is an order of magnitude higher than that of pure RTV. In addition, with an increase in filler content, the porosity of the coating decreases. When the content of the nanosheet increases to 0.3 wt.%; the porosity reaches a minimum value 0.97 × 10-4%, which is 1/4 of the porosity of the pure RTV coating, indicating that this composite silicone rubber sample has the best resistance to NO2 aging.

Three-dimensional force detection using PVDF and room temperature-vulcanized silicone rubber layers

Three-dimensional force perception plays an extremely important role in human-computer interaction. The main objective of the present study is to propose a three-dimensional force detection sensor using room temperature-vulcanized silicone rubber, polyvinylidene fluoride (PVDF), and a silver coating layer. The sensor was designed in a cylindrical structure to detect the tangential force. The performed analyses reveal that the silver coating layer improves the surface charge output of the PVDF film. The output peak voltage of the sensing unit is 271.7% higher than that of the single PVDF film. The sensor has a response time of 40 ms. It is found that the angle detection error of the sensor along horizontal and vertical directions is less than 2.79° and 0.88°, respectively. In order to evaluate the performance of the proposed sensor, it is fixed on the mechanical hand to perform grasping and sliding tests. The tested results show that the proposed sensor can effectively identify the weight and slip of the object, and can be used in the field of manipulator clamping control.

Mechanical performance of composites reinforced with carbon black and different types of graphitic nanofillers for different applications

The piezo-electric energy harvesting devices based on rubber composites have attracted great attention in the field of flexible electronics. These devices have the ability to provide a voltage of ∼0.5 V when subjected to mechanical strain. In this work, carbon allotropes nanofillers were used to reinforce the room-temperature vulcanized silicone rubber (RTV-SR). The nanofillers added to the rubber matrix were found to improve the compressive modulus, tensile strength, fracture strain, and tensile modulus. For example, the compressive modulus was 1.29 MPa (Virgin) and improved to 1.4 MPa (graphene), 2.3 MPa (CB), 2.2 MPa (CB–graphite hybrid), 2.17 MPa (CB–Nano graphite hybrid), and finally 2.19 MPa (CB–graphene hybrid). Similarly, the fracture strain was 146% (Virgin) and improved to 149% (graphene), 156% (CB), 160% (CB–graphite hybrid), 151% (CB–Nano graphite hybrid), and lastly 178% (CB–graphene hybrid). Moreover, the effect of three different diameters of loading tips is used for voltage production. More areas of deformation during energy harvesting can be able to produce higher voltage output. For example, a 21 mm tip can produce higher energy output than 7 mm and 14 mm. In the end, it was found that formation of cracks in the electrode while repeated loading causes a reduction in voltage output.

Preparation and Properties of Flexible Cushioning Composites Based on Silicone Rubber and Warp—Knitted Spacer Fabric

This paper aims to develop a new type of flexible cushioning composite material that can be applied to cushioning protective appliances. Room temperature vulcanized silicone rubber (RTV silicone rubber) was filled into five groups of warp knitted spacer fabrics with different structural parameters, and flexible cushioning composites with filling rates of 30%, 50% and 70% were prepared. At the same time, there was a group of warp knitted spacer fabrics without silicone rubber as control. Then the infrared spectrum of silicone rubber was analyzed to test the compression and impact properties of flexible cushioning composite. It is found that the increase of filling rate enhances the compressive and impact properties of flexible cushioning composites. The flexible cushioning composite material can show better compression performance at a larger compression ratio. The structural parameters affecting the impact properties of flexible cushioning composites are arranged in descending order as fabric thickness, spacer tilt angle, spacer density, mesh number. The established mathematical model can provide a theoretical basis for the performance study of such composite materials. The compressive properties and impact properties of flexible buffer composites are not correlated.

Great new generation carbon microsphere-based composites: Facile synthesis, properties and their application in piezo-electric energy harvesting

In this work, new generation carbon microspheres (CMS) based rubber composites have been obtained for flexible electronics applications such as stretchable piezo-electric energy harvesting devices. The rubber matrix used was room-temperature-vulcanized silicone rubber (RTV-SR). Herein, the CMS was exploited as a source of reinforcement and conductive material for improving mechanical and electrical properties. For example, the compressive modulus was 2.1 MPa (virgin) and increased to as high as 3.3 MPa (5 phr CMS). Similarly, the Shore A hardness was 26 (virgin) and increased to 40 (5 phr CMS). The electrical properties were also influenced significantly with electro-chemical resistance of 22.05 kΩ (virgin) and decreased to 15.91 kΩ (5 phr CMS). CMS's XPS spectrum revealed a high carbon-to-oxygen atomic ratio (74.47 and 25.53 %). The carbon and oxygen-containing functional groups of CMS acted as a catalyst to improve interfacial interaction of the composites thereby leading to higher mechanical properties. These improved properties were explored in the real-time device and output voltage generation with high durability was tested. From measurements, it was found that the output voltage from the piezo-electric energy harvesting device was around 1.25 V and high durability of 0.5 million cycles was reported.

Analysis of High-Temperature Wideband Dielectric Properties of ATH-Filled Silicone Rubber Used for On-Site Insulation of Bare Overhead Conductors

Due to its excellent electrical and mechanical properties, and easy to cure at room temperature, room temperature vulcanizing silicone rubber is currently used in the on-site insulation of bare overhead conductors in the distribution system. The dielectric properties of silicone rubber materials have a great impact on power loss, which is vital to the transmission lines. Therefore, in this article, the dielectric properties of silicone rubber with the addition of different aluminum hydroxide contents are investigated by broadband dielectric spectroscopy in wide broadband range and wide temperature ranges, and the influence of aluminum hydroxide filler on the dielectric response is analyzed using a modified Cole–Cole model which takes the low-frequency dispersion process into account. It is found that the relationship of the dc conductivity and the low-frequency dispersion strength with temperature follows the Arrhenius equation law. The low-frequency dielectric response is influenced by dipoles’ polarization and electrode polarization. Moreover, the relaxation time decreases with the increase in temperature, and its mechanism can be revealed by the double-well model. The characteristic parameters obtained in this article can provide a reference for on-site insulating of bare overhead conductors.

Ultraviolet-Sensitive Photoluminescent Spray-Coated Textile

The target of the presented research work was the development of new smart textiles with photoluminescence properties which maintain light emission for a prolonged time period, even when the illumination source is turned off. Phosphorescence has been frequently used to improve the reliability of various safety products. Thus, simple and photoluminescent and superhydrophobic smart cotton fibers were fabricated. Rare-earth-doped aluminate (REA) nanoparticles (NPs) were immobilized into room-temperature vulcanizing silicone rubber (RTV) and spray-coated onto cotton fibers. The coated fabrics were excited at 365 nm, while the emission peak was detected at 518 nm. Various concentrations of REA nanoparticles in the REANPs@RTV composite formula were used to create a homogeneous phosphorescent coating on the surface of the cellulosic fabrics. CIE (Commission Internationale de L’éclairage) lab values and emission spectra confirmed that the fabric had a white color under visible light, green color under UV rays, and greenish-yellow color in darkness. The lifetime of phosphorescence and decay time were examined. The findings also displayed an improvement in the superhydrophobic activity of the treated cellulosic fabrics as the phosphor content was increased in the REANPs@RTV composite formula. Additionally, the stiffness and air permeability of the treated cellulosic fabrics were determined in terms of comfort characteristics.

Superhydrophobic coating to mitigate metal corrosion with electrically insulative and thermally conductive properties

• A superhydrophobic coating was developed for electronic circuit boards. • Surface modified silica and polystyrene nanoparticles were used. • Electrochemical methods and the salt spray method proved the corrosion inhibition. • High thermal conductivity and electrical insulating properties were incorporated. • The coating can be used for substrates that need multifunctional properties. A superhydrophobic coating with hydrophobic silica nanoparticles (SiO 2 ), polystyrene nanoparticles (PS), aluminium trihydrate (ATH), and room temperature vulcanized silicone rubber (RTV SiR) was developed. The nanoparticles and the nanostructure of the coating were investigated using Scanning Electron Microscopy (SEM). The anti-corrosion ability was studied using 100% pure iron plates. The coating was found to have high resistance against corrosion based on electrochemical analysis and the salt-spray test in addition to high electrical insulation and thermal conductivity.

RTV-SiR based composites aged in a multi-stressed environment under AC and bipolar DC voltages

Silicone rubber-based polymers are gradually replacing traditional insulators in outdoor applications due to their numerous advantages, in particular high hydrophobicity that is important for suppressing leakage current and hence surface flashover. However, the main problem with polymeric composites is their aging when exposed to environmental stresses causing loss of their desired properties and expected lifetime. In this work, aging behavior of three types of room temperature vulcanized silicon rubber (RTV-SiR) loaded with nano-silica and micro-ATH is studied. Samples of the materials with different specifications were fabricated and exposed to various environmental stresses in two specially designed weather chambers under both AC and bipolar DC voltages for a time period of 9000 hours. Thereafter, diagnosis was performed for identifying the degree of deterioration using several techniques. These include hydrophobicity classification, measurements of leakage current and mechanical properties, Fourier transform infrared spectroscopy, and Thermogravimetric analysis. Results of the conducted experiments indicated stronger degradation of the desired properties under positive DC stress as compared to the AC and negative DC voltages. Moreover, silicone rubber doped with nano-sized particles of silica filler demonstrated better anti-aging performance as compared to its micro-ATH filled counterpart.

Water-assistant ultrahigh fluorescence enhancement in perovskite polymer-encapsulated film for flexible X-ray scintillators

Methylammonium lead halide perovskites are well-known having a poor stability towards moisture. Water causes degradation of ionic perovskites and weaken the optical and electronic performance of perovskite-based devices. Main strategies to improve moisture stability are compositional engineering, surface engineering and matrix encapsulation. Herein, encapsulation strategy is implemented through screening a polymer matrix, a hydrophobic room-temperature vulcanized silicone rubber (RTV-2). Owing to the positive effect of moderate water on the performance of perovskites, the obtained MAPbBr3/RTV-2 composite film is processed with water post-treatment to undergo surface engineering. The composite film achieves a remarkable 8-fold fluorescence enhancement. Luminous efficiency of the film loaded on a 380 nm chip is improved from 51.4 lm/W to 135.37 lm/W. The flexible MAPbBr3/RTV-2 film responds sensitively under X-ray irradiation. Its detection limit is down to 12 nGyair s−1, 400 times lower than the regular dosage in X-ray diagnostics (5.5 μGy s−1). These results provide guidance to design perovskite-based devices with bright luminescence and excellent flexibility to qualify the wearable X-ray detectors for dose monitoring.

Antimicrobial properties of cotton fabrics coated with silicone rubber/ZnO nanocomposites under the effect of UV irradiation

In order to enhancement the antimicrobial properties and the thermal stability of the cotton fabrics for outdoor uses, they were coated with formulations of room-temperature vulcanizing silicone rubber (RTVSR)/synthesized zinc oxide nanoparticles (ZnO NPs). The coated fabrics were adjusted to different doses of ultraviolet (UV) irradiation, which act as a crosslinking factor to the silicone rubber, rather than as a photocatalytic agent for enhancing the antimicrobial activity of the ZnO NPs. The synthesized ZnO NPs were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM); meanwhile, its impurity was examined using energy dispersive X-ray (EDS) analysis. The thermal stability and surface morphology of the coated fabrics were characterized by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results showed that the mechanical strength (MPa) of the coated fabrics was enhanced by ∼11% after UV irradiation for 120 min, accompanied by decrease in its swelling and solubility by ∼10 and 20%, respectively, as a result of UV crosslinking effect upon RTVSR. Meanwhile, the antimicrobial activity of the coated fabrics was enhanced by ∼50%, as a result of the photocatalytic effect of UV irradiation (120 min), at the constant percentage of 3% (ZnO NPs) in the coating formulations.

Layered ultra-lightweight MXene based composite films for current conduction

Although aviation tools provide many conveniences to our lives, lightning has always been a significant factor affecting the safety of aviation activities. Nevertheless, designing a diverter strip with both favorable conduction current capability and remarkable environmental stability remains a great challenge. Here, a room temperature vulcanized silicone rubber (RTV) encapsulated Ti3C2Tx/Cu nanowire composite with a stacked structure is reported. Specifically, the assembly of nanowires and nanosheets behaves as an enhanced conductive network, and the encapsulation of RTV gives the film excellent environmental stability. The results show that Cu NWs loading at 10 % the composites can form effective discharge paths along the surface at output voltages of 96.48 and 201.6 kV. Furthermore, the composites exhibit excellent hydrophobicity (water contact angle of 108.09°) and lightweight properties (2.65 g/cm3). Overall, the composite material provides a promising design strategy for the preparation of new shunts that can be applied under realistic conditions.

Study on the Algae Contamination and Its Effects on the Properties of RTV-Coated Insulators

The surface of organic insulating materials such as room temperature vulcanized silicone rubber (RTV) coatings often has serious contamination deposition. In humid areas such as the Southwest region of China, algae contamination layers are present on the surface of the insulators. In this study, the geographical and creeping distribution of algae contamination on the surfaces of RTV insulators were studied by investigating and sampling various substations in the Southwest region. The main components of soluble salts in the contamination were studied by atomic absorption spectroscopy and ion chromatography. The algal genome was extracted by the cetyltrimethylammonium bromide method, and the species of algae and other microorganisms in the contamination layer were determined. The effects of algae or their secretions on the surface resistance and hydrophobicity were studied by quantitatively inoculating algae and smearing extracellular secretions on the RTV surface. The damage of the algae contamination layer to the microstructure of the silicone rubber was investigated by microscopic observation and thermogravimetric analysis. Results showed that the growth of algae was positively correlated with the surface contamination of RTV. The extracellular secretion of algae destroys the surface microstructure of RTV and causes the removal of alumina hydroxide, leading to the reduction of siloxane. Therefore, the resistance and hydrophobicity of the RTV surface were reduced. It is of great significance to study the characteristics and effects of the algae contamination layer for RTV maintenance.