Room Temperature Vulcanizing Silicone Research Articles

Hydrophobicity, surface charge and DC flashover characteristics of direct-fluorinated RTV silicone rubber

Silicone rubber (SiR), as a basic insulating material, is widely used in insulators for HVDC transmission lines. The prominent characteristics of the SiR coating are the hydrophobicity and the hydrophobicity recovery, which can suppress the development of leakage currents and dry-band discharges, and prevent the flashover incidents. Fluorination is a method to change the chemical component of the surface layer of polymers, which could induce the corresponding change in hydrophobicity and some electrical properties, thus influencing the dc surface flashover characteristics. Room temperature vulcanized (RTV) SiR samples were fluorinated in a stainless reaction vessel at about 298K (25°C) using a F2/N2 mixture with 12% F2 by volume and 0.05 MPa (500 mbar) for respectively 5, 10, 15 and 20 minutes. The hydrophobicity of samples with different fluorination time was measured by the static contact angle tests after corona aging. The variation of hydrophobicity with the lapse of time was recorded. DC flashover tests in different conditions were carried out between two plane electrodes on top of the material sample. The flashover voltage was found to be associated with the surface hydrophobicity status of samples. Obtained results showed the effects of the fluorination on the surface charge, hydrophobicity performance and dc flashover voltage. It is suggested that the appropriate fluorination can improve surface hydrophobicity and suppress surface charge accumulation, thus raising the dc flashover voltage.

COMPRESSIVE MECHANICAL BEHAVIORS OF HYBRID COMPOSITE MATERIALS BASED ON MICRO LATTICE STRUCTURE AND RUBBERLIKE MATERIALS

ABSTRACT This article investigates compressive and energy absorption characteristics for composites obtained by filling stainless steel micro lattice materials, manufactured via the selective laser melting method, with three different rubbers, including room temperature vulcanization silicone, natural rubber, and neoprene rubber. At the stage of building the composites with natural and neoprene rubbers, an experimental setup was designed for these two rubbers to be infiltrated into lattice spaces under vulcanization temperatures and high pressures. The results showed that the composites with silicone and neoprene matrix had a quite similar response as well as a seriously enhanced energy absorbing capacity and plateau stresses, in comparison with the corresponding lattice structures, for especially small sized lattice components. Also, the compression tests of the composite with natural rubber matrix clearly show that there should be no large differences between the individual mechanical properties of each component in the composite, and, in this way, the contribution of each component on the mechanical behavior of composite should be guaranteed to provide the satisfying performance.

Microstereolithography-Based Fabrication of Anatomically Shaped Beta-Tricalcium Phosphate Scaffolds for Bone Tissue Engineering.

Porous ceramic scaffolds with shapes matching the bone defects may result in more efficient grafting and healing than the ones with simple geometries. Using computer-assisted microstereolithography (MSTL), we have developed a novel gelcasting indirect MSTL technology and successfully fabricated two scaffolds according to CT images of rabbit femur. Negative resin molds with outer 3D dimensions conforming to the femur and an internal structure consisting of stacked meshes with uniform interconnecting struts, 0.5 mm in diameter, were fabricated by MSTL. The second mold type was designed for cortical bone formation. A ceramic slurry of beta-tricalcium phosphate (β-TCP) with room temperature vulcanization (RTV) silicone as binder was cast into the molds. After the RTV silicone was completely cured, the composite was sintered at 1500°C for 5 h. Both gross anatomical shape and the interpenetrating internal network were preserved after sintering. Even cortical structure could be introduced into the customized scaffolds, which resulted in enhanced strength. Biocompatibility was confirmed by vital staining of rabbit bone marrow mesenchymal stromal cells cultured on the customized scaffolds for 5 days. This fabrication method could be useful for constructing bone substitutes specifically designed according to local anatomical defects.

Surface charge accumulation and decay of direct-fluorinated RTV silicone rubber

Silicone rubber (SiR), as a basic insulating material, is widely used in insulators for HVDC transmission lines. In these lines, corona discharge even occurs on well-designed hardware and insulators, which can inject charge into the insulator surface. The existence of surface charge has a marked effect on insulation degradation and plays an important role during the development of the surface flashover. Direct-fluorination is a method to change the chemical component, which could induce the corresponding changes in electrical properties of the surface layer, thus influencing the charge injection. This paper tries to study the effect of fluorination time on surface charge accumulation and decay of room temperature vulcanized (RTV) SiR. The samples were fluorinated in a laboratory vessel at 298 K (25°C) using a F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixture with 12% F2 by volume at 0.05 MPa (500 mbar) for 5, 10, 15, and 20 minutes. The sample surface chemical composition was analyzed by means of ATR-IR. The behavior of surface potential under dc voltage was recorded at room temperature with a relative humidity of ~40%. Obtained results show a dependence of the surface potential and the dissipation time upon the fluorination time, varying with the charging time. It is suggested that the direct fluorination can significantly suppress the accumulation and accelerate the decay of the surface charge.

Effects of low temperature and nanoparticles on electrical trees in RTV silicone rubber

The operating temperature of power cable system has a great influence on the electrical performance of room temperature vulcanizing (RTV) silicone rubber. This paper investigated the effects of low temperature and nanoparticles on electrical tree in RTV silicone rubber. Samples were prepared by mixing SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles into RTV silicone rubber, with the content of 0, 0.5, 1, 1.5 and 2 wt% respectively. The experiment temperature was ranged from - 30 to -90 °C. AC voltage with a frequency of 50 Hz was applied between a needle-plate electrode. The electrical tree patterns, growth rate, expansion coefficient, fractal dimension and proportion of accumulated damage were studied. The results reveal that both nanoparticles and low temperature environment have a significant impact on the electrical tree growth. The tree patterns are branch tree or bush tree when the temperature is higher than -60 °C; however, there is only pine tree when the temperature is lower than -90 °C. Compared with - 30 °C, some tree channels are easier to propagate at - 60 °C in silicone rubber. It is also suggested that the temperature affects the expansion coefficient of electrical tree. The fractal dimension of the electrical tree increases with the nanoparticle content, while the accumulated damage of treeing area shows the opposite tendency.

An Experimental Comparison on Dimensional Accuracy of Wax Patterns of Gas Turbine Blades Produced by Rapid Tooling

The primary objective of this research is to determine the accuracy of a typical turbine blade wax pattern that includes common areas (such as root, platform and airfoil) in all turbine blades, which are produced by soft tooling room temperature vulcanization (RTV) mold methods, epoxy molds and silicone rubber molds and also to compare them. It is necessary to use the optimum parameters of injection within the molding in order to obtain sufficient dimensional accuracy of wax patterns. Considering the current study, it can be concluded that the epoxy mold can produce more accurate models than the silicone rubber mold. In addition, the range of dimensional variations in different directions of the wax patterns was achieved. Average shrinkage percentage is equal to 0.6 and 3.5 % in the direction along the length and width of the root in output patterns from silicone rubber mold, respectively. It is equal to 0.6 % approximately perpendicular to the platform in the direction of the airfoil. However, the average shrinkage percentage is 1.1 and 0.6 % in the direction along the length and width of the root in output patterns from epoxy mold respectively, and is almost 0.6 % perpendicular to the platform in the direction of the airfoil. These studies will help those who use both rapid tooling and investment casting in the production of turbine blades to estimate the changes required for initial CAD drawings to produce a final casting with minimum dimensional inaccuracy.

Effects of thermal conductivity on dc resistance to erosion of silicone rubber/BN nanocomposites

Silicone rubber (SiR) is widely employed as an insulating material in transmission lines because of its excellent electrical properties and superior performance under wet and polluted conditions. However, the discharges that occur during operation can cause electrical erosion on the surface of silicone rubber insulators. The thermal conductivity of insulators has a correlation with the resistance to tracking and erosion. This study attempts to clarify whether the addition of boron nitride (BN) particles can improve the resistance to tracking and erosion of SiR by increasing its thermal conductivity. Before the tests, specimens were prepared by dispersing nano-BN particles into room temperature vulcanizing (RTV) silicone rubber at different loadings. In this paper, the dc test has been developed from the current IEC 60587 inclined plane tracking and erosion test to compare the phenomena occurring during the tests. Temperature distribution was observed by an infrared thermal imager. The experimental results indicate that the filled specimens have a lower degree of surface damage than the unfilled specimens. In addition, with the increase in content of fillers from 0 to 7 wt%, the thermal dissipation is improved and both the erosion depth and the weight loss show a decreasing trend, which proves the resistance of silicone rubber to tracking and erosion is improved.

Formation of Super-Hydrophobic Surface by Accumulating Pollution on RTV Silicone Rubber Coating Surface

The Super-hydrophobic surface can be obtained easily by pollution accumulation on room temperature vulcanized (RTV) silicone rubber coating surface. The photos taken by digital camera show that the amount of pollution on the RTV coating surface was increased with time, and after one year, the RTV coating surface nearly could hardly be seen. The water state contact angle (CA) measurement, which was investigated by the static contact angle instrument, reveals that the CA value of RTV coating surface is increased with increasing the pollution accumulation, and in suitable amount of pollution accumulation, the super-hydrophobic surface (water contact angle of 152o and roll-off angle smaller than 5 o) was obtained. The scanning electric microscope (SEM) of RTV coating with different pollution accumulation was investigated. It shows that the continuous micro-nanobinary structure can be formed with enough dust particles on the RTV surface. The mechanism of the effect of pollution accumulation on the wetting property was analyzed, the migration of hydrophobic molecular in RTV coating onto the pollution surface and the formation of micro-nanobinary structure on the RTV coating surface have synergistic effect on the super-hydrophobic surface formation caused by the pollution accumulation.

A Study of Performance on Anti-Pollution Flashover Coating Based on Composite Room Temperature Vulcanized Silicone Rubber

The article totally discusses the influence of polytetrafluoroethylene (PTFE) to the property of room temperature vulcanization silicone rubber (RTV) pollution flashover coating, inclduding hydrophobic, corrosion resistance and heat resistance. It is turned out that the PTFE can effectively improve the corrosion resistance of the coating only if the contents of PTFE has no impact on the mechanical property, flame retaradant and heat resisting property of the coating and highly enhances the hydrophobicity property.

Preparation and thermal degradation behavior of room temperature vulcanized silicone rubber-g-polyhedral oligomeric silsesquioxanes

Room temperature vulcanized (RTV) silicone rubber-g-polyhedral oligomeric silsesquioxanes (POSS) was prepared and its thermal degradation behavior and thermo-oxidative stability were investigated by thermogravimetric analysis (TGA). The results demonstrated that the chemical incorporation of POSS into polydimethylsiloxane (PDMS) chains significantly enhanced thermal stability of RTV silicon rubber in both nitrogen and air atmosphere. The degradation behavior was further monitored by TGA coupled with real time Fourier transform infrared spectra (FTIR), and the residues were characterized by FTIR and X-ray photoelectron spectroscopy (XPS). It was found that the remarkable improvement in thermal stability could be attributed to the following reasons: (1) the branched structure of RTV silicone rubber-g-POSS and interaction between POSS molecules and PDMS chains; (2) POSS traps generated and grafted or cross-linked structure formed; (3) intumescent ceramic protective barrier formed; (4) the perfect distribution of POSS in RTV silicone rubber-g-POSS.

Measuring the solidification time of silicone rubber using optical inspection technology

A room temperature vulcanization silicone rubber was widely used as the mold making material due to its high elasticity, good heat-resistance and low surface energy. To enhance the efficiency of making the silicone rubber mold, accurately measuring the solidification time is an important issue. This study demonstrated a non-invasive measurement system to measure the solidification time of silicone rubber. The solidification time can be determined rapidly from the thickness of silicone rubber according to the predicted equation. The maximum relative error of the predicted equation is about 8.26%. The temperature rise of the silicone during the solidification process is an important phenomenon to determine the solidification behavior of silicone rubber. The solidification mechanism of silicone rubber mold is demonstrated.

Effect of UV Radiation and Leakage Current on Hydrophobicity of RTV Silicone Rubber

The effect of UV radiation and surface leakage current on the hydrophobic behavior of the RTV(room temperature vulcanized silicone rubber )silicone rubber was investigated. It's found that the ultraviolet radiation and surface leakage current both could weaken the hydrophobicity of the RTV surface in different degree.

All-silicone prestrain-locked interpenetrating polymer network elastomers: free-standing silicone artificial muscles with improved performance and robustness

We present a novel all-silicone prestrain-locked interpenetrating polymer network (all-S-IPN) elastomer for use as a muscle-like actuator. The elastomer is fabricated using a combination of two silicones: a soft room temperature vulcanizing (RTV) silicone that serves as the host elastomer matrix, and a more rigid high temperature vulcanizing (HTV) silicone that acts to preserve the prestrain in the host network. In our novel S-IPN fabrication procedure we co-dissolve the RTV and HTV silicones in a common solvent, cast thin films, and allow the RTV silicone to cure before applying prestrain and finally curing the HTV silicone to lock in the prestrain. The free-standing prestrain-locked silicones show a performance improvement over standard free-standing silicone films, with a linear strain of 25% and an area strain of 45% when tested in a diaphragm configuration. We show that the process can also be used to improve electrode adhesion and stability as well as improve the interlayer adhesion in multilayer actuators. We demonstrate that, when coupled with carbon nanotube electrodes, fault-tolerance through self-clearing can be observed. We use the fault-tolerance and improved interlayer adhesion to demonstrate stable long-life (>30 000 cycles at >20% strain) actuation and repeated high-performance actuation (>500 cycles at ∼40% strain) of prestrained free-standing multilayer actuators driving a load.

Erosion resistance of electrospun silicone rubber nanocomposites

This paper presents the results of an examination of the erosion resistance of two-part room temperature vulcanizing (RTV) silicone rubber (SiR) nanocomposites. The SiR composites were filled with 7 nm size fumed silica and 1.5 μm size micro-silica. Separate samples were prepared using conventional mechanical mixing and an electrospinning technique, and their erosion resistances were compared. The electrospinning technique allows for a higher volume fraction of nanofiller and micro-filler in the composites as compared to the conventional samples. The erosion resistances were tested using both an infrared-laser-based source and the ASTM D2303 standard inclined plane tracking and erosion method (IPT). The experimental results for the eroded mass, tracking voltage, and tracking time show that the erosion resistances of electrospun samples are much greater than those of conventional samples. Scanning electron microscope (SEM) images and variable tracking patterns of the conventional samples after the IPT tests suggest an improvement in the dispersion of the fillers within the electrospun samples compared to the conventional samples. Power analysis during the IPT tests also shows that more power is required to track and erode electrospun samples before sample failure occurs than is needed for conventional samples, which suggests improved bonding between the fillers and the silicone rubber matrix. These findings also are supported by the results of thermo-gravimetric analysis.

Properties of functionalized graphene/room temperature vulcanized silicone rubber composites prepared by an In-situ reduction method

Functionalized graphene oxide (FGO) was prepared by treating graphene oxide with γ-aminopropyl triethoxysilane (KH-550) before the mixture was dispersed into α, ω-dihydroxy polydimethylsiloxane to get room temperature vulcanized (RTV) silicone rubber composites by solution casting. The cured composites were then reduced with hydrazine hydrate to obtain functionalized graphene (FG)/RTV silicone rubber composites. The structures of FGO and the resultant composites were characterized by atomic force microscopy, FT-IR spectra and X-ray diffraction. KH-550 was found to be grafted onto graphene sheets, leading to an increased interlayer spacing. Significant improvements in thermal and mechanical properties were obtained. Both the FGO/RTV silicone rubber composite contain 1.0 wt% of FGO, and its reduced product showed an increase of one-step weight loss temperature with 61 °C and 133 °C higher than that of pure silicone rubber. Tensile strength and elongation at break of FG/RTV silicone rubber composite (with 0.5 wt% FGO content) increased by 175% and 67%, respectively, compared with those of pure silicone rubber.

Application of Silicone TQ Resin Reinforced RTV Silicone Rubber in Architecture

A kind of silicone TQ resin was first synthesized with Dodecyltrimethoxysilane (WD10) and tetraethoxysilane (TEOS) by sol-gel method. And the RTV (Room Temperature Vulcanized) silicone rubbers using as-synthesized TQ silicone resins as filler were prepared. Thermal degradation and mechanical properties of these RTV silicone rubbers were studied by means of thermogravimetric analysis and tensile testing. The experimental results showed that both mechanical properties and thermal stabilities of RTV silicone rubbers were significantly improved by using the as-synthesized TQ silicone resins as filler. The RTV silicone rubber can be used to make the molds of architectural components ornamentation. The aim is not only to repair architectural components with decoration, but also for further study and research of ancient architectural conservation.

Anti-icing Performance of a Superhydrophobic PDMS/Modified Nano-silica Hybrid Coating for Insulators

This paper presents a new type of poly(dimethylsiloxane)/modified nano-silica (PDMS/modified nanosilica) hybrid superhydrophobic coating to reduce ice accumulation on insulators. The PDMS/modified nano-silica hybrid coating and a room temperature vulcanized (RTV) silicone rubber coating were formed on glass insulators for ice accumulation experiments in the laboratory. The hydrophobicity of the two coatings was measured and compared. Average water contact angle on the PDMS/modified nano-silica hybrid coating reached 161°. The microstructures and functional groups on the surfaces of both coatings were investigated using field-emission scanning electron microscopy (FE–SEM) and attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectroscopy, respectively. Analysis results show that both multiscale microstructure and low surface energy contributed to the superhydrophobicity of the PDMS/modified nano-silica hybrid coating. Finally, experiments on ice accumulation on insulators were carried out to investigate the anti-icing properties of the PDMS/modified nano-silica hybrid coating on insulators. Significantly smaller rate of ice accumulation was observed for the insulators treated with the PDMS/modified nano-silica hybrid coating, relative to that treated with the RTV silicone rubber coating.

Synergistic effect between POSS and fumed silica on thermal stabilities and mechanical properties of room temperature vulcanized (RTV) silicone rubbers

In this paper, both divinyl-hexa[(trimethoxysilyl)ethyl]-POSS (DVPS) and fumed silica were firstly introduced into polydimethylsiloxane (PDMS) system using as the cross-linker and the reinforcing filler respectively. And a series of novel RTV silicone rubbers synergistically enhanced by DVPS and fumed silica were prepared. The cross-linked networks in the novel RTV silicone rubbers have been studied by attenuated total reflection infrared spectroscopy, and the dispersions of POSS and fumed silica in these novel RTV silicone rubbers have been observed by means of scanning electron microscope (SEM). And thermal stabilities, thermo-oxidative stabilities and mechanical properties of these novel RTV silicone rubbers were studied by means of thermal gravimetric analysis and universal tensile testing machine, respectively. From the obtained results, it was found that synergistic effect between POSS-rich areas and fumed silica on thermal stability and mechanical property of RTV silicone rubber indeed existed. And the experimental results also exhibited that the thermal stabilities and mechanical properties of the novel RTV silicone rubbers were far better than those of the reference materials (DVPR and MTFR). The striking enhancements in thermal properties and improvements on mechanical properties of novel RTV silicone rubbers were likely attributed to the synergistic effect between POSS-rich domains and fumed silica. Meanwhile, it was found that the mechanical properties of RTV silicone rubbers prepared with a given amount of POSS cross-linker were enhanced with the increment of the loading amount of fumed silica.

Preparation and characterization of foamed polyurethane/silicone rubber/graphite nanocomposite as radio frequency wave absorbing material: The role of interfacial compatibilization

A novel method for the preparation of radio frequency (RF) wave absorber polyurethane foam (PU) has been developed by impregnation of PU foam in n-hexane solution of room temperature vulcanizing (RTV) silicone rubber (SR) hybridized with graphite nanosheets (GNs) called doping solution. Extent of the GNs dispersion was optimized by the incorporation of a specific type of bifunctional compatibilizer. Insulator to conductive transition threshold as well as electromagnetic wave absorption characteristics of the fabricated nanocomposites was shown to be dependent upon the compatibilizer functionality. All PU/SR/GN nanocomposites generated from bifunctional compatibilizer exhibited higher electrical conductivity with enhanced permittivity implying enhanced formation of conductive networks by GN platelets. Permittivity of the PU/SR/GN nanocomposite based on bifunctional compatibilizer showed to be higher than uncompatibilized counterpart. Electromagnetic reflection loss behavior of the PU/SR/GN nanocomposites exhibited a non-linear correlation with the electrical conductivity. Although all PU/SR/GN prepared nanocomposites exhibited electromagnetic wave reflection loss behavior, but this revealed to be affected by the GN level as well as the size and dispersion state of the graphite nanosheets.

Preparation and Performance of RTV Coating for Anti-Pollution Flashover with Superhydrophobicity by Filling CaCO&lt;sub&gt;3&lt;/sub&gt;/SiO&lt;sub&gt;2&lt;/sub&gt; Composite Particles into Silicone Rubber

Room temperature vulcanizing (RTV) silicone rubber coating with superhydrophobicity for anti-pollution flashover is prepared by filling silica-encapsulated calcium carbonate particles (CaCO3/SiO2 composite particles) into polydimethylsiloxane (PDMS) rubber. Two-step spraying technology is applied for fabricating the superhydrophobic RTV coating film on outdoor insulators. The primary spray coating provides basically the strong adhesion and certain hydrophobicity, and the second one produces the appropriate roughness structure and further enhances the superhydrophobicity. The water contact angle on the prepared RTV coating film is 165°and the sliding (rolling) angle of water droplet is about 5°, allowing water droplets to move easily on the coating surface and give self-cleaning function of the RTV coated insulator surface. The flashover voltage of insulators with superhydrophobic RTV coating is 29.95 kV, quite higher than that of insulators with common RTV coating (23.29) and that without RTV coating (11.34 kV).