RTV Silicone Research Articles

Increasing the performances of various Types Outdoor Insulators by using RTV Silicone Rubber Coating

Insulator is one of the most important equipments in an electric power system. Since long time ago ceramic insulators are widely used in transmission as well as in distribution lines. As outdoor insulators, the insulators are subjected to outdoor environmental stresses such as humidity, temperature and pollution. Under polluted and wet condition, high leakage current may flow on the insulator surface. As the result a dry band arching may take place and in the long time it may degrade the insulator and initiate the insulator flash over leading to the failure of the lines. Several efforts may be taken to improve the insulator performance under polluted condition. They are increasing the number of insulator strings, modification of insulator design to increase the creep age distance and regular washing. This paper presents the investigation results on the silicone coating on ceramic insulators under laboratory and real environmental conditions. It was found that the coating was significantly suppressed the magnitude of leakage current and drastically eliminated the harmonic content. The coating also drastically suppressed the corona on the insulator and reduced the surface temperature. The coating also significantly increased the flash over voltage of the insulator. Leakage current analysis and simulation showed significant improvement of surface resistance of insulator after application of RTV coating under most environmental conditions compared to those of uncoated insulators. Overall investigation results indicated significant improvement of insulator performances by applying RTV silicone rubber coating.

Experiments on the Vibration Control of Flexible Rotor Using Shear Mode MR Elastomer Damper

A shear mode magnetorheological (MR) elastomer damper is designed and manufactured, in which the MR elastomer is made by mixing RTV silicone, carbonyl iron particles and silicone oil, and solidifying under magnetic field. A flexible cantilever rotor system with single disk is constructed, and the controllability, effectiveness and stability of vibration control for the imbalance response of the rotor system using the MR damper are experimentally studied. From the test, it is found that as the strength of applied magnetic field increases, the damping and stiffness of the damper are increased; the critical speeds of the rotor system supported on the MR damper is increased distinctly, and the vibration at two critical speeds are restrained; the on-off control method may be used to control the rotor vibration while passing through the two critical speeds. The study shows that the shear mode MR elastomer damper is suitable for active vibration control of flexible rotor.

Mechano-Chemical Preparation and Application of Mulberry-Like CaCo3/SiO2 Composite Particles in Superhydrophobic Films

This study focuses on preparation of mulberry-like CaCO3/SiO2 composite particles with a mechanochemical method and their application in superhydrophobic films. Silicon dioxide nanoparticles were adhered to calcium carbonate microparticles to form mulberry-like composite particles through vigorous stirring, which prevented agglomeration of silicon dioxide nanoparticles and maintained their nanocharacteristics. Then, hexamethyldisilazane was employed for hydrophobic modification of the mulberry-like CaCO3/SiO2 composite particles. The effect of CaCO3/SiO2 mass ratios, stirring speed, reaction temperature, and amount of modifying reagent on morphology and lipophilicity of composite particles was studied. Moreover, the superhydrophobic films with excellent film properties were obtained by through combination of mulberry-like CaCO3/SiO2 hydrophobic composite particles and RTV silicon rubber. The water contact angle and sliding angle of the superhydrophobic surface were measured to be 170 ± 2.5° and 4°, respectively. This approach proves to be ideal for substantial improvement of the self-cleaning property of RTV silicon rubber anti-pollution flashover coating.

Hydrophobicity Transfer Property of Silicone Rubber Material

In this paper, the influence of ambient temperature and relative air humidity on the hydrophobicity transfer property of HTV and RTV silicone rubber (SR) is investigated. The static contact angle on polluted HTV-SR samples and plates with RTV coating was measured while being stored at different temperature and relative humidity. It has been found that the transfer characteristics on HTV-SR exhibit a saltus between 50°C and 55°C. The results further show that the influence of relative humidity is related with the hygroscopicity of soluble and non-soluble substances in pollutants on the surface.

Curing behavior of silicone elastomer in the presence of two corticosteroid drugs

Silicone rubbers are widely used as carriers for delivery of drugs intended for parenteral administration as implantable devices. Drugs having different functional groups can significantly affect curing profile of silicone rubber, which in turn may negatively affect their biological applicability due to the loss in mechanical and drug retaining properties. To this end, the effects of two corticosteroid analogs (up to 2 %w/w of drug loading) that is, dexamethasone (DEX) and its sodium phosphate ester (DSP) on curing behavior of a non-restricted, two part RTV silicone rubber was studied using different characterization techniques including spectroscopic (FTIR), calorimetric (DSC), oscillating disk rheometry, and swelling studies. The results showed that curing time extends longer for DSP-loaded samples compared to the non-loaded silicone rubber. The presence of DSP in the formulation interferes in the curing of silicone elastomers, probably due to the thermal decomposition of DSP according to the spectral changes observed in FTIR spectra as confirmed by DSC analysis. Rheometric studies showed depreciated properties for silicone elastomers upon compounding with DSP. Swelling measurements indicated to lowered crosslink density for networks and increasing M(c) upon adding DSP to the formulations which can be attributed to disruption in crosslinking reaction by sodium phosphate moieties of DSP.

RTV Silicone Rubber Filled with Surface Modified Montmorillonite

The surface modification of pristine montmorillonite (MMT) with four kinds of coupling agents for reinforcement of the room temperature vulcanized vinyl-terminated polydimethylsiloxane (RTV PDMS) networks was investigated. The four coupling agents containing γ-glycidoxypropyltrimethoxysilane (KH-560), γ-methacryloxypropyltri methoxysilane (KH-570), isopropyl trioleic titanate (NDZ-105), and stearic acid (SA) without N, P, or S compounds were used because the coupling agents harmless to the platinum catalyst used normally in the curing of RTV vinyl-terminated PDMS. The interaction between MMT particles and coupling agents was confirmed by diffused reflectance infrared spectroscopy (DR-FTIR) tests. By scanning electron microscopy (SEM) characterization, surface modified MMT was dispersed heterogeneously in the PDMS matrix for all four coupling agents. By X-ray diffraction (XRD) characterization, the interlayer distances of the four surface modified MMT were not changed. Dielectric tests showed that the dielectric constant and dielectric loss of PDMS filled with KH-560, KH-570, and SA treated MMT were decreased comparing with those of PDMS filled with pristine MMT. With the increasing content of MMT treated with KH-570, the dielectric constant and dielectric loss value of PDMS composites increased.

Superhydrophobic RTV Silicone Rubber Coatings on Anodized Aluminium Surfaces

A superhydrophobic surface was elaborated using two inexpensive industrial processes: surface anodization in phosphoric acid and spin coating of the anodized surface by RTV silicone rubber. Scanning electron microscopy (SEM), atomic force microscopic (AFM) and water contact angle measurements have been performed to characterize the morphological features, and wettability of the surfaces. The water static contact angle of the elaborated surface reached 157 ° at room temperature. At supercool temperature (-10°C) the superhydrophobic coating showed an important delayed freezing time.

Improvement of Heat-resistance of RTV Silicone with Reduced Environmental Impact by Loading Selective Fillers Elastomers

本論文は高温・高湿下における室温硬化型シリコーンの耐久性に関するもので，機械的強度および接着強度についても論述する。著者らは，EU指令による有機スズ化合物使用規制に則ったスズフリー新規硬化触媒の開発に成功している。新規硬化触媒または従来型硬化触媒を用いて作成されたシリコーンの耐久性と機械的特性を比較すると，前者を用いて作成されたシリコーンは後者より作成されたそれより優れている。新規硬化触媒は，硬化剤としてのチタンアルコキシドと硬化助剤としてのカルボン酸エステルをそれぞれ等モル配合により作成される。新規硬化触媒を用いて作成されたシリコーン複合体は，それとほぼ同等組成である市販シリコーン複合体と同等以上の機械的性質と接着性を示し，チタンキレート硬化触媒で作成されたシリコーンより優れた機械的性質を示す。補強性フィラーであるアエロジルと増堂剤としての粉砕型炭酸カルシウムを選択的に組み合わせて作成したシリコーン複合体は，優れた高温・高湿特性を示す。

Superhydrophobic RTV silicone rubber insulator coatings

On wet days, environmental contamination of outdoor insulation surfaces can reduce the reliability of electrical transmission systems and lead to flashover and arcing over the entire insulator. The use of superhydrophobic coatings would resolve this problem due to their self-cleaning effect. Water droplets can pick up dirt particles and remove contamination from the surfaces of insulators. This paper reports on a study to make a superhydrophobic RTV silicone rubber coating that has contact angles of higher than 145° and good UV durability. The Inclined Plane Test, water durability test and adhesion test are presented to show the effectiveness of this coating and the best formulations. The results of tracking and erosion resistance test (Inclined Plane Test) showed that formulations with at least 35wt% ATH can be used for superhydrophobic RTV insulator coatings.

Construction of 2D transparent micromodels in polyester resin with porosity similar to carrots

Microscopic visualization, especially in transparent micromodels, can provide valuable information to understand the transport phenomena at pore scale in different process occurring in porous materials (food, timber, soils, etc.). Micromodels studies focus mainly on the observation of multi-phase flow, which presents a greater proximity to reality. The aim of this study was to study the process of flexography and its application in the manufacture of polyester resin transparent micromodels and its application to carrots. Materials used to implement a flexo station for micromodels construction were thermoregulated water bath, exposure chamber to UV light, photosensitive substance (photopolymer), RTV silicone polyester resin, and glass plates. In this paper, data on size distribution of a particular kind of carrot we used, and a transparent micromodel with square cross-section as well as a Log-normal pore size distribution with pore radii ranging from 10 to 110 µm (average of 22 µm and micromodel size of 10 × 10 cm) were built. Finally, it stresses that it has successfully implemented the protocol processing 2D polyester resin transparent micromodels.

A biomimetic robotic jellyfish (Robojelly) actuated by shape memory alloy composite actuators

An analysis is conducted on the design, fabrication and performance of an underwater vehicle mimicking the propulsion mechanism and physical appearance of a medusa (jellyfish). The robotic jellyfish called Robojelly mimics the morphology and kinematics of the Aurelia aurita species. Robojelly actuates using bio-inspired shape memory alloy composite actuators. A systematic fabrication technique was developed to replicate the essential structural features of A. aurita. Robojelly's body was fabricated from RTV silicone having a total mass of 242 g and bell diameter of 164 mm. Robojelly was able to generate enough thrust in static water conditions to propel itself and achieve a proficiency of 0.19 s−1 while the A. aurita achieves a proficiency of around 0.25 s−1. A thrust analysis based on empirical measurements for a natural jellyfish was used to compare the performance of the different robotic configurations. The configuration with best performance was a Robojelly with segmented bell and a passive flap structure. Robojelly was found to consume an average power on the order of 17 W with the actuators not having fully reached a thermal steady state.

Shrinkage of Renal Tissue after Impregnation via the Cold Biodur Plastination Technique

Thorough dehydration is a key for good plastination and invariably it leads to shrinkage. Shrinkage during plastination has been studied to lesser extent. Shrinkage was studied in 10 pig kidneys including regional shrinkage (cortex, medulla, sinus) and at which stages of the process (dehydration, impregnation, curing) shrinkage occurred. Kidneys were fixation by perfusion of 10% neutral buffered formalin solution via the renal artery. The vessels and ureter were filled with colored silicone (Dow Corning, Silastic E RTV Silicone Rubber) and the kidneys were cut into one centimeter transverse slices. Two slices of each kidney were plastinated via the classic von Hagens' method. Slices were photographed at the same focal length after preparation and at the end of each stage of plastination. Slice surface area was determined by a point-counting planimetry method. Post dehydration shrinkage of the kidney was 10.21% while post impregnation 10.11%. After completion of plastination, total area of kidney slice shrinkage was 19.72%. Cortical area shrunk 12.81% after dehydration and 13.16% after impregnation. After plastination, cortical area had shrunk 24.28%. No significant shrinkage occurred in the medulla and sinus. Results demonstrate that kidney shrinkage during impregnation is as intense as during dehydration. Significant shrinkage occurred in the renal cortex but not in the medulla and sinus. This demonstrates that different tissue types, even in the same specimen, have different rates of shrinkage during dehydration and impregnation. Therefore, plastinated specimens should be used carefully in research where obtaining measures is important.

Experimental study of silicone‐epoxy dual adhesive joints for high temperature aerospace applications

AbstractAdhesive bonding is extensively used in aerospace applications. Some of the most important aerospace applications are in heat shields intended to protect metallic structures from extreme heat. Many heat shields are bonded with RTV silicone based adhesives, which have excellent resistance to high temperature but very low strength. This work proposes and studies three alternative configurations to these adhesive layers. One configuration with RTV silicone only (RTV106), one with only a high temperature epoxy (XN1244) and finally another configuration introducing both adhesives in the same joint (mixed joint). Experimental specimens and a testing device intended to simulate the loads on an actual heat shield were manufactured. These specimens were subjected to loading and tested until failure at both low and high temperatures. It was demonstrated that while the RTV silicone joints lose strength at 100°C, the epoxy and mixed joints are able to retain most of their strength. The mixed joint is also able to withstand large values of displacement at relatively high forces, indicating excellent capabilities at absorbing directed energy. The improvements and advantages deriving from the use of these alternative configurations are described and compared.

Wettability behaviour of RTV silicone rubber coated on nanostructured aluminium surface

A nanostructutered superhydrophobic surface was elaborated by applying an RTV silicone rubber coating on electrochemically processed aluminium substrates. Study of anodisation voltage on surface morphology showed that higher anodising voltage led to larger pore sizes. Scanning electron microscopy image analysis showed bird's nest and beehive structures formed on anodised surfaces at 50 V and 80 V. Water static contact angle on the treated surfaces reached up to 160° at room temperature. Study of superhydrophobic surfaces at super cooled temperature showed important delayed freezing time for RTV hydrophobic surfaces when compared to non-treated aluminium. However, lower wettability was observed when surface temperature went down from 20 °C to −10 °C. Also, it was found that the capacitance of superhydrophobic surfaces decreased with increasing anodising voltage.

Epoxy Specimen Fabricated by Rapid Prototyping Method for Photo-Elastic Technique

Stress concentration due to the circular hole within the mechanical part is concerned during design phase. The stress concentration of the circular hole within the mechanical mart can easily derived by the photo-elastic technique if the testing specimen is sufficiently developed. The testing specimen using the characteristic of the photo-elastic coefficient, with actual form like the mechanical part by rapid prototyping forming is thus used in this paper. The rapid mold for prototype is made by the RTV-2 silicone gel associated with the vacuum chamber to remove the air within it. Totally twelve specimens divided into two sets, the first set with the machined holes by milling at the centroid of the specimens with diameters of 5, 8, 10, and 12 mm. The second set with the formed holes by molding with the previous diameters. The testing scheme is by way of the simply supported beam where the load is imposed on the middle of the specimen. Results show that the smaller diameter of hole on specimen provides a larger stress concentration effect. When the diameter of the hole is small, the stress concentration effects caused by the machined hole and the forming hole have almost no difference. However, the stress concentration effects of the larger diameter of the machined hole and of the formed hole give significant difference, the stress concentration caused by the machined hole is much greater than one of the formed hole. In this paper, the actual shape of the specimen which is as same as the original mechanical components can be quickly obtained by the rapid prototyping technology for the photoelastic technique to reveal the experimental mechanics of real applications.

The role of interfacial compatibilizer in controlling the electrical conductivity and piezoresistive behavior of the nanocomposites based on RTV silicone rubber/graphite nanosheets

New pressure sensitive nanocomposites with high reversible piezoresistive behavior based on room temperature vulcanizing silicone rubber (RTVSR), graphite nanosheets (GN) and an alkylammonium salt as interfacial compatibilizer were fabricated employing reactive solution mixing process. The role of the compatibilizer in controlling the graphite dispersion state and hence electrical and piezoresistive behavior was investigated. The microstructure of the nanocomposite in liquid state was correlated with dynamic rheological behavior. The scanning electron microscopy and X-ray diffractometry were used to analyze the obtained nanocomposites. Uncompatibilized SR/GN vulcanizates with a GN content close to the percolation threshold (3 wt.%) showed a sharp negative pressure coefficient of resistance at the pressure range of 0.7–10 MPa. The unvulcanized nanocomposite containing 30 wt.% of compatibilizer exhibited higher viscosity and enhanced storage modulus within low frequency region indicating the presence of the interconnected conductive networks throughout the SR matrix leading to the reduction of conductivity threshold from 3 to 1 wt.% and less negative piezoresistivity.

Control of pore fluid pressure on depth of emplacement of magmatic sills: An experimental approach

In sedimentary basins, the emplacement of magmatic sills tends to occur within rock of low mechanical competence and permeability, such as shale. This often contains pore fluids at abnormally high pressure. We first theoretically show that, in anisotropic media, the higher the pore fluid pressure, the deeper the sill emplacement. Then we introduce a new technique for analogue modelling of such intrusive bodies under conditions of fluid overpressure (greater than hydrostatic), which corroborate the theoretical analysis. As an analogue of brittle sediment, we use a diatomite powder. This material is a dry, fine-grained, frictional, cohesive and permeable material. As an analogue for magma, we take a silicone putty (RTV silicone), which is at first Newtonian, but then solidifies at room temperature. We use compressed air as a pore fluid. Under these experimental conditions, we investigate the intrusion of magma into the host powder under various fluid overpressures. In homogeneous diatomite powder, having uniform cohesion, intrusive bodies are segmented dykes. These become feeders to sills, if the fluid overpressure exceeds the weight of overburden. Where the sedimentary column has a horizontal discontinuity in strength, the transition from dyke to sill occurs at a smaller overpressure (hydrostatic < λ ex < 1). As a possible illustration of these results, we consider sills within source rocks of the Neuquén Basin and of the Parana Basin, both in South America, where overpressure may have resulted from maturation of organic material.

Design and Development of a Novel Biostretch Apparatus for Tissue Engineering

A uniaxial cyclic stretch apparatus is designed and developed for tissue engineering research. The biostretch apparatus employs noncontact electromagnetic force to uniaxially stretch a rectangular Gelfoam or RTV silicon scaffold. A reliable controller is implemented to control four stretch parameters independently: extent, frequency, pattern, and duration of the stretch. The noncontact driving force together with the specially designed mount allow researchers to use standard Petri dishes and commercially available CO(2) incubators to culture an engineered tissue patch under well-defined mechanical conditions. The culture process is greatly simplified over existing processes. Further, beyond traditional uniaxial stretch apparatuses, which provide stretch by fixing one side of the scaffolds and stretching the other side, the new apparatus can also apply uniaxial stretch from both ends simultaneously. Using the biostretch apparatus, the distributions of the strain on the Gelfoam and GE RTV 6166 silicon scaffolds are quantitatively analyzed.

Measurement method of complex viscoelastic material properties

A measurement technique of viscoelastic properties of polymers is proposed to investigate complex Poisson’s ratio as a function of frequency. The forced vibration responses for the samples under normal and shear deformation are measured with varying load masses. To obtain modulus of elasticity and shear modulus, the present method requires only knowledge of the load mass, geometrical characteristics of a sample, as well as both the amplitude ratio and phase lag of the forcing and response oscillations. The measured data were used to obtain the viscoelastic properties of the material based on a 2D numerical deformation model of the sample. The 2D model enabled us to exclude data correction by the empirical form factor used in 1D model. Standard composition (90% PDMS polymer + 10% catalyst) of silicone RTV rubber (Silastic ® S2) were used for preparing three samples for axial stress deformation and three samples for shear deformation. Comprehensive measurements of modulus of elasticity, shear modulus, loss factor, and both real and imaginary parts of Poisson’s ratio were determined for frequencies from 50 to 320 Hz in the linear deformation regime (at relative deformations 10 −6 to 10 −4) at temperature 25 °C. In order to improve measurement accuracy, an extrapolation of the obtained results to zero load mass was suggested. For this purpose measurements with several masses need to be done. An empirical requirement for the sample height-to-radius ratio to be more than 4 was found for stress measurements. Different combinations of the samples with different sizes for the shear and stress measurements exhibited similar results. The proposed method allows one to measure imaginary part of the Poisson’s ratio, which appeared to be about 0.04–0.06 for the material of the present study.

점탄성 재료의 복소수 동특성 측정방법

A novel technique to measuret of viscoelastic properties of polymers is proposed to investigate complex Poisson’s ratio as a function of frequency. The forced vibration responses for the samples under the normal and the shear deformation are to be measured with varying load masses. The measured data were used to obtain the viscoelastic properties of the material based on an accurate 2D numerical deformation model of the sample. The 2D model enabled us to exclude data correction by the empirical form factor used in 1D model. Comprehensive measurements of viscoelastic properties of two slightly varied silicone RTV rubber (Silastic<SUP>®</SUP> S2) compositions were performed. Standard composition (90% PDMS polymer + 10% catalyst) and modified composition (92.5% polymer + 7.5% catalyst) were tested in temperature range from 30℃ to 70℃. Shear modulus, modulus of elasticity, loss factor, and both the real and the imaginary parts of the Poisson’s ratio were determined for frequencies from 50 to 400Hz in the linear deformation regime (at relative deformations 10<SUP>-4</SUP> ~10<SUP>-3</SUP>).