Temperature Vulcanized Silicone Rubber Research Articles

Magneto‐piezoresistive characteristics of graphene/room temperature vulcanized silicon rubber‐silicon rubber magnetorheological elastomer

AbstractThe effect of graphene with different content on the magneto‐piezoresistive characteristics of graphene/room temperature vulcanized silicon rubber (GR/RTV) magnetorheological elastomer (MRE) was studied, and the relationship between the content of graphene and conductivity of GR/RTV‐MRE was described based on the general effective medium theory. A magneto‐piezoresistive model was established to describe the relationship among resistance, pressure, and magnetic field based on the magnetic dipole and tunneling theory. The samples of GR/RTV‐MRE with different content of graphene were prepared. The experimental platform with magneto‐piezoresistive characteristics controlled by magnetic field was built. The effect of graphene with different content on piezoresistive coefficient of GR/RTV‐MRE was obtained under different magnetic flux density. The experimental results showed that the piezoresistive coefficients of samples with different content of graphene decrease with the increase of magnetic flux density in the range of 0 ~ 80mT. For the same magnetic field, when the volume fraction of graphene is less than 12%, the piezoresistive coefficient is positively correlated with it, when the volume fraction of graphene is more than 12%; the increase of content has little effect on the piezoresistive characteristics. The experimental results are compared with theoretical calculations for correction and error analysis. The results showed that the modified model can well describe the variation of the resistance of GR/RTV‐MRE under magnetic field and pressure.

Germ-Reducing Titanium Dioxide - Silicone Rubber Composites

Germs are present in all areas of everyday life and can lead to dangerous infections. Surfaces with antimicrobial properties are used to reduce the risk of infection in sanitary facilities and hospitals. Apart from the addition of biocides or antibiotic agents to synthetic materials, research shows that it is possible to use the semiconductor titanium dioxide (TiO2) to generate antibacterial surfaces. Photocatalytically active TiO2 leads to the development of reactive oxygen species (ROS) that are able to kill germs. The aim of this research is to use TiO2 to generate antibacterial bulk material. Nanostructured TiO2 particles were incorporated into silicone rubber to obtain a photocatalytic active polymer surface. High temperature vulcanizing (HTV) silicone rubber was used as a matrix material, and samples with 10 wt% of TiO2 were produced. The distribution of TiO2 particles in the matrix was analyzed via light microscopy. The photocatalytic activity on the surface of the test samples was studied via microbial testing with E.coli bacteria. The samples showed different intensities of the photocatalytic effect depending on the type of additive. The effort to create a germ reducing silicone rubber surface by using TiO2 as an additive was successful.

Essential Investigation and Removal assets using Laser Induced Breakdown Spectroscopy in Silicone Rubber

With laserinduced breakdown spectroscopy (LIBS), the basic sytheses of the room temperaturevulcanized silicone rubber and the high temperature-vulcanized silicone rubber recently arranged examples were broke down in this paper. The LIBS spectra demonstrated that carbon (C), oxygen (O), aluminum (Al), silicon (Si), press (Fe), and zinc (Zn) were contained in the specimens; predictable with the energy dispersive X-ray spectroscopy (EDS) comes about. With scanning electron microscopy (SEM), the micromorphology and the profundity of the removal pits were watched. The pits ’sizes were just around 200?400 μm, and there was about no distinction between the hydrophobicity of the nonablated zone and the removed territory, and the static contact edge of the cavities was considerably bigger than that of the nonablated region, implying that the LIBS examination was practically nondestructive. The profundity of the removal pits indicated linearity association with the laser heartbeat number that would help a considerable measure in the in situ investigation. Expanding the laser energy of the shot, the force of spectra lines of unequivocal component and the electron number density would increment in the meantime. The review result demonstrated that the LIBS would be a promising component investigation method of silicone rubber particularly on line, and the piece of the composites could be plainly watched.

Mechanically durable superhydrophobic surfaces prepared by abrading

Superhydrophobic surfaces with both excellent mechanical durability and easy reparability based on polytetrafluoroethylene/room temperature vulcanized silicone rubber (PTFE/RTVSR) composites were prepared by a simple abrading method. The surface energy of RTVSR matrix decreased with the increasing volume fraction of PTFE particles, and the surface rough microstructures of the composites were created by abrading. A water droplet on the surface exhibited a contact angle of about 165° ± 3.4° and a sliding angle of about 7.3° ± 1.9°. Such superhydrophobic surfaces showed strong mechanical durability against sandpaper because the surfaces were prepared in the way of mechanical abrasion, and the fresh exposed surfaces were still superhydrophobic. In addition, the micro-structures on the elastic surface of the composite will be compressed by elastic deformation to avoid being broken during the friction cycles when cotton fabric was used as an abrasion surface. The deformation will rebound to renew the original surface structures when the load is withdrawn. Therefore, the elastic PTFE/RTVSR composites are of advantage to construct superhydrophobic surfaces with better abrasion resistance. More importantly, such superhydrophobicity can be repaired by a simple abrading regeneration process within a few minutes when the surface is damaged or polluted by organic contaminant.

Small element array algorithm for correcting phase aberrations using near-field signal redundancy. Part II: Experimental results

For part I see ibid., vol.47, p.29 (2000). A small element array algorithm for phase-aberration correction using near-field signal redundancy was proposed in part I. Using this algorithm, subarrays are formed to narrow the transmitted and received beams when collecting common midpoint signals, so that angle-dependent aberration profiles across the array can be measured. In this paper, this algorithm is tested on data collected from a phantom with a non-isoplanatic aberrator attached to the front surface of a phased array. The aberrator is made from cast room temperature vulcanizing (RTV) silicone rubber, which has a sound velocity of about 1.02 mm.micros(-1). Results show that the subarray technique can be used to measure and correct angle-dependent, phase-aberration profiles. The theoretical results regarding the performance of several implementation methods for dynamic near-field delay correction on subarrays are also experimentally tested using data from a phantom.

Modified gas-permeable silicone rubber membranes for covalent immobilisation of enzymes and their use in biosensor development.

Novel enzyme membranes are introduced. Modified polymeric gas-permeable layers were developed enabling biological components which have available reactive groups (-NH2, -OH, -SH, -COOH) to couple covalently on to their surfaces. Therefore, gas-permeable two component room temperature vulcanizing (2K-RTV) silicone rubber was modified using additional cross-linking agents. Triethoxysilanes with functional groups on their side chains such as epoxy or amino groups were used. A special attribute of the resulting gas-permeable membranes is that their formation and modification occur simultaneously during one reaction step. IR spectroscopy was used to observe the changes in the polymeric structure due to the reaction with the additional cross-linking agents. Sensors equipped with these layers are suitable to measure dissolved gases such as O2, CO2 and NH3 consumed or produced by enzymes converting their substrates. Determination of glucose, a well investigated enzymatic detection process, was chosen to demonstrate the applicability of the enzyme immobilisation. Glucose oxidase was immobilised on the membranes and glucose was detected by amperometric measurement of oxygen consumption. It is expected that this immobilisation method will also be useful for miniaturised planar biosensors.

Influence of thickness, substrate type, amount of silicone fluid and solvent type on the electrical performance of RTV silicone rubber coatings

Room temperature vulcanizing (RTV) silicone rubber coating is increasingly being used by power utilities to overcome the contamination problems encountered in ceramic and glass insulators under wet conditions. The formulation of the RTV coating system is currently undergoing an intensive development in an effort to optimize its performance and in particular to extend its lifetime. While there are many forms of RTV, those used for insulator coating purposes invariably use a base of polydimethylsiloxane. The amount of RTV used in the service application is also important as it impacts on both the cost of the protection offered and on the electrical performance. This paper reports on a study of the influence of the coating thickness, different substrates, addition of silicone fluid to the coating formulation and different carrier solvents on the leakage current, pulse current count rates and the lifetime of the RTV coatings. It has been found that all these parameters affect the electrical performance under wet and contamination condition in a salt-fog. The optimum coating thickness has been determined for a fixed substrate. Mechanisms by which these four parameters affect the performance are suggested and discussed.

AC clean fog tests on nonceramic insulating materials and a comparison with porcelain

AC clean fog tests were performed on nonceramic materials used for outdoor high voltage insulators, namely, room and high temperature vulcanizing (RTV and HTV) silicone rubber, and ethylene propylene rubber (EPR), with porcelain used as the reference. The steam input rate was varied upwards from the value standardized for porcelain insulators. Results indicate that higher steam input rates produce a significant reduction in the flashover voltage of silicone rubber family materials, although it is always higher than that obtained for EPR and porcelain. For EPR, the reduction is less and is similar to that established for porcelain. The mechanisms involved have been examined. The trend in the results is found to be consistent for different formulations and insulator geometries of the generic polymer (e.g. silicone rubber, EPR) evaluated. A new, simple method for consistently applying uniform contamination on silicone rubber (both RTV and HTV) is described, without the use of extensive physical or chemical treatments, or prior conditioning by dry band arcing. >

Face-Down TAB for Hybrids

Bell Laboratories has for some time been developing tape automated bonding (TAB) techniques for hybrid applications involving medium- and large-scale integrated (MSI/LSI) chips. The present paper describes a face-down TAB approach which results in a structure that resembles a beam lead structure. Process steps required for the fabrication of the face-down TAB structures and physical design requirements to control mechanical failure modes are presented. Detailed information is given in the fabrication of a test structure designed to these requirements. The structure uses gold plated copper tape leads to attach an MSI chip to a thin-film metalized ceramic substrate. The structure is environmentally protected with an room temperature vulcanizing (RTV) silicone rubber encapsulant using the same techniques that are employed for the encapsulation of Bell System hybrids with beam leaded chips. Accelerated temperature cycling tests were carried out using this structure over a range of temperature differentials. The results are encouraging from the standpoint of mechanical reliability for communication applications. The face-down TAB approach is compared to the conventional face-up TAB approach where the back side of the chip is bonded to ceramic substrate on the bases of 1) process steps (with implications for assembly cost), 2) hybrid substrate area requirements, and 3) junction-to-substrate thermal resistance. It was found that the facedown structure appears preferable for hybrid applications where cost and/or area considerations dominate. The face-up structure appears preferable when higher thermal conductivity and/or backside electrical contact are required. It is concluded that for many communication applications the face-down TAB approach can be used to attach MSI/LSI chips to multichip hybrids with size, cost, and reliability benefits analogous to those presently associated with beam leaded chips.