Varistors based on barium titanate-graphite-rubber composites

This paper describes the experimental and theoretical studies carried out on particulate composites consisting of BaTiO3, graphite, and rubber. It is shown that such composites exhibit a positive voltage coefficient of resistance beyond a certain voltage. A theoretical model developed to explain the observed V-R characteristics and their dependence on parameters of the composite like composition and grain size of the particles is also described. These composites seem to be useful as varistors with positive voltage coefficient of resistance and may find applications as voltage-regulating devices. Journal of Applied Physics is copyrighted by The American Institute of Physics.

Welfare outcomes for 3- and 6-month-old beef calves in a tropical environment castrated surgically or by applying rubber rings

Castration of cattle using rubber rings is becoming increasingly popular due to the perceived ease of the procedure and greater operator safety when compared with surgical castration. Few comparative studies have investigated the effects of different castration methods and calf age on welfare outcomes, particularly in a tropical environment. Thirty Belmont Red (a tropically adapted breed), 3-month-old (liveweight 71–119 kg) and 30, 6-month-old (liveweight 141–189 kg) calves were assigned to a two age × three castration (surgical, ring and sham) treatment factorial study (Surg3, Surg6, Ring3, Ring6, Sham3 and Sham6, n = 10 for each treatment group). Welfare outcomes were assessed post-castration using: behaviour for 2 weeks; blood parameters (cortisol and haptoglobin concentrations) to 4 weeks; wound healing to 5 weeks; and liveweights to 6 weeks. More Surg calves struggled during castration compared with Sham and Ring (P < 0.05, 90 ± 7% vs. 20 ± 9% and 24 ± 10%) and performed more struggles (1.9 ± 0.2, 1.1 ± 0.3 and 1.1 ± 0.3 for Surg, Sham and Ring, respectively), suggesting that surgical castration caused most pain during performance of the procedure. A significant (P < 0.05) time × castration method × age interaction for plasma cortisol revealed that concentrations decreased most rapidly in Sham; the Ring6 calves failed to show reduced cortisol concentrations at 2 h post-castration, unlike other treatment groups. By 7 h post-castration, all treatment groups had similar concentrations. A significant (P < 0.01) interaction between time and castration method showed that haptoglobin concentrations increased slightly to 0.89 and 0.84 mg/mL for Surg and Ring, respectively over the first 3 days post-castration. Concentrations for Surg then decreased to levels similar to Sham by day 21 and, although concentrations for Ring decreased on day 7 to 0.76 mg/mL, they increased significantly on day 14 to 0.97 mg/mL before reducing to concentrations similar to the other groups (0.66 mg/mL) by day 21. Significantly (P < 0.05) more of the wounds of the 3-month compared with the 6-month calves scored as ‘healed’ at day 7 (74% vs. 39%), while more (P = 0.062) of the Surg than Ring scored as ‘healed’ at day 21 (60% vs. 29%). At day 14 there were significantly (P < 0.05) fewer healed wounds in Ring6 compared with other treatment groups (13% vs. 40–60%). Liveweight gain was significantly (P < 0.05) greater in 3-month (0.53 kg/day) than in 6-month calves (0.44 kg/day) and in Sham calves (P < 0.001, 0.54 kg/day), than in Ring (0.44 kg/day) and Surg (0.48 kg/day) calves. Overall, welfare outcomes were slightly better for Surg than Ring calves due to reduced inflammation and faster wound healing, with little difference between age groups.

Welfare outcomes for 3- and 6-month-old beef calves in a tropical environment castrated surgically or by applying rubber rings

Castration of cattle using rubber rings is becoming increasingly popular due to the perceived ease of the procedure and greater operator safety when compared with surgical castration. Few comparative studies have investigated the effects of different castration methods and calf age on welfare outcomes, particularly in a tropical environment. Thirty Belmont Red (a tropically adapted breed), 3-month-old (liveweight 71–119 kg) and 30, 6-month-old (liveweight 141–189 kg) calves were assigned to a two age × three castration (surgical, ring and sham) treatment factorial study (Surg3, Surg6, Ring3, Ring6, Sham3 and Sham6, n = 10 for each treatment group). Welfare outcomes were assessed post-castration using: behaviour for 2 weeks; blood parameters (cortisol and haptoglobin concentrations) to 4 weeks; wound healing to 5 weeks; and liveweights to 6 weeks. More Surg calves struggled during castration compared with Sham and Ring (P < 0.05, 90 ± 7% vs. 20 ± 9% and 24 ± 10%) and performed more struggles (1.9 ± 0.2, 1.1 ± 0.3 and 1.1 ± 0.3 for Surg, Sham and Ring, respectively), suggesting that surgical castration caused most pain during performance of the procedure. A significant (P < 0.05) time × castration method × age interaction for plasma cortisol revealed that concentrations decreased most rapidly in Sham; the Ring6 calves failed to show reduced cortisol concentrations at 2 h post-castration, unlike other treatment groups. By 7 h post-castration, all treatment groups had similar concentrations. A significant (P < 0.01) interaction between time and castration method showed that haptoglobin concentrations increased slightly to 0.89 and 0.84 mg/mL for Surg and Ring, respectively over the first 3 days post-castration. Concentrations for Surg then decreased to levels similar to Sham by day 21 and, although concentrations for Ring decreased on day 7 to 0.76 mg/mL, they increased significantly on day 14 to 0.97 mg/mL before reducing to concentrations similar to the other groups (0.66 mg/mL) by day 21. Significantly (P < 0.05) more of the wounds of the 3-month compared with the 6-month calves scored as ‘healed’ at day 7 (74% vs. 39%), while more (P = 0.062) of the Surg than Ring scored as ‘healed’ at day 21 (60% vs. 29%). At day 14 there were significantly (P < 0.05) fewer healed wounds in Ring6 compared with other treatment groups (13% vs. 40–60%). Liveweight gain was significantly (P < 0.05) greater in 3-month (0.53 kg/day) than in 6-month calves (0.44 kg/day) and in Sham calves (P < 0.001, 0.54 kg/day), than in Ring (0.44 kg/day) and Surg (0.48 kg/day) calves. Overall, welfare outcomes were slightly better for Surg than Ring calves due to reduced inflammation and faster wound healing, with little difference between age groups.

Thermal decomposition studies on copolyurethanes based on hydroxyl terminated polybutadiene and poly(12-hydroxy stearic acid-co-TMP) ester polyol

Thermal degradation of copolyurethanes based on hydroxyl terminated polybutadiene (HTPB) and poly(12-hydroxy stearic acid-co-TMP) ester polyol (PEP) with varying compositions has been studied by thermo-gravimetric and pyrolysis-GC techniques. The copolyurethanes were found to decompose in multiple stages and the kinetic parameters were found to be dependent on the method of their evaluation. The activation energy for the initial stage of decomposition was found to increase, and for the main stage decreases with the increase in PEP content. The pyrolysis-GC studies on the ammonium perchlorate filled copolyurethanes (solid propellants) showed that the major products during the pyrolysis were C-2, C-3 hydrocarbons and butadiene. The amount of C-2 fraction in the pyrolyslate increased with solid loading, as well as with the HTPB content in the copolyurethanes. A linear relationship apparently exists between the amount of C-2 fraction and the burn rates of the solid propellants. (C) 2000 Elsevier Science Ltd. All rights reserved.

Super-plasticized natural rubber latex modified concretes

Polymeric admixtures to concrete ingredients modify the properties of the processed concrete. Ductility is one such property modification. This investigation deals with the development of a method of incorporating natural rubber latex into concrete ingredients with only marginal effects on the compressive strength of base plain concrete. This retention of the strength has been effected by reducing the water/cement ratio with the aid of a superplasticizer. The quantity of natural rubber latex is expressed as the dry rubber content by percentage of volume of concrete. The compressive and tensile strengths, as well as post peak ductile behaviour have been the basis for comparison with those of unmodified concrete.

Corona Aging Studies on Silicone Rubber Nanocomposites

In EHV and UHV power transmission lines, corona could occur even on well designed transmission line hardware and insulators especially under wet conditions. Corona if allowed to occur continuously can significantly damage the polymeric insulators used in such lines in the long run. This paper presents the experimental results of corona aging studies conducted on unfilled silicone rubber as well as filled silicone rubber nanocomposites. Corona aging studies were conducted on silicone rubber samples with filler concentrations of 0, 1, 2 and 3 % by wt of nanosilica for 25 h and 50 h. Needle-plane electrode geometry has been used to create the corona on the samples. Different characterization techniques such as Scanning Electron Microscopy, Energy Dispersive X-ray analysis, Hydrophobicity, Fourier Transform Infrared Spectroscopy, and Optical Profilometry have been used to assess the relative performance of the samples with respect to corona aging. Results indicate that at 3 wt %, the performance of the nanocomposite is much better than the unfilled silicon rubber which can be attributed to the modifications in the material caused by the size factor of the filler.

Long-term Accelerated Weathering of Outdoor Silicone Rubber Insulators

Multistress aging/weathering of outdoor composite polymeric insulators has been a topic of interest for power transmission research community in the last few decades. This paper deals with the long-term accelerated weathering of full-scale distribution class silicone rubber composite insulators. To evaluate the long-term synergistic effect of electric stress, temperature and UV radiation on insulators, they were subjected to accelerated weathering in a specially designed multistress-aging chamber for 30,000 h. All the insulators were subjected to the same level of electrical and thermal stresses but different UV radiation levels. Chemical, physical and electrical changes due to degradation have been assessed using various techniques. It was found that there was a monotonous reduction of the content of low molecular weight (LMW) molecules with the duration of the weathering. Further, due to oxidation and weathering there is an appreciable increase in surface roughness and atomic percentage of oxygen. There is no change in the leakage current of new and aged insulators under both wet and dry conditions at the end of the aging. The results also indicate that there is no influence of UV radiation on the silicone rubber for the durations and conditions under which the studies were made.

Tracking and erosion resistance of silicone rubber nanocomposites under positive and negative dc voltages

ASTM D2303 standard provides a method for evaluating the tracking and erosion resistance of polymeric insulators under ac voltages. In this paper, the above method has been extended for evaluating the performance of the insulators under dc stresses. Tests were conducted on polymeric silicone rubber (SR) insulators under positive and negative dc stresses. Micron sized Alumina trihydrate (uATH) and nano sized Alumina (nALU) were used as fillers in SR matrix to improve the resistance to tracking and erosion. Results suggest that SR composites perform better under negative dc than under positive dc voltages. Eroded mass and leakage current data support the above result. Samples with low concentration of nano alumina fillers performed on par with the samples with large loadings of uATH.

Compressive behavior and fracture features of rubber bearing glass-epoxy composites exposed to aqueous media

Epoxy systems containing HTBN rubber material and reinforced with E-glass fibres, exposed to a fixed time duration in three separate media were subjected to compressive mode of deformation. The yield stress and fractographic features noted on the compression failed samples are reported in this work. The experiment reveals that the seawater exposed sample exhibits a drop in strength compared to dry (unexposed) sample. This kind of drop is maintained if the media is changed from seawater to distilled water. When HCl is included in seawater. the experiment shows a small rise in strength value. These changes have been attributed to various factors like medium ingress into samples assisting interface failure, the larger-sized Cl- influencing the extent of diffusion of medium into system and finally their participation in the deformation phenomena. The fractographic features reveal interface separations that show either scattered debris or a cleaner surface or display a whitish-coated matrix region depending on whether the tests are done on unexposed samples or on ones following the immersion in the media.

Behavior of Sandwich Beams With Functionally Graded Rubber Core in Three Point Bending

The three-point bending behavior of sandwich beams made up of jute epoxy skins and piecewise linear functionally graded (FG) rubber core reinforced with fly ash filler is investigated. This work studies the influence of the parameters such as weight fraction of fly ash, core to thickness ratio, and orientation of jute on specific bending modulus and strength. The load displacement response of the sandwich is traced to evaluate the specific modulus and strength. FG core samples are prepared by using conventional casting technique and sandwich by hand layup. Presence of gradation is quantified experimentally. Results of bending test indicate that specific modulus and strength are primarily governed by filler content and core to sandwich thickness ratio. FG sandwiches with different gradation configurations (uniform, linear, and piecewise linear) are modeled using finite element analysis (ANSYS 5.4) to evaluate specific strength which is subsequently compared with the experimental results and the best gradation configuration is presented. POLYM. COMPOS., 32:1541-1551, 2011. (C) 2011 Society of Plastics Engineers

Tracking and Erosion of Silicone Rubber Nanocomposites under DC Voltages of both Polarities

In order to improve the tracking and erosion performance of outdoor polymeric silicone rubber (SR) insulators used in HV power transmission lines, micron sized inorganic fillers are usually added to the base SR matrix. In addition, insulators used in high voltage dc transmission lines are designed to have increased creepage distance to mitigate the tracking and erosion problems. ASTM D2303 standard gives a procedure for finding the tracking and erosion resistance of outdoor polymeric insulator weathershed material samples under laboratory conditions for ac voltages. In this paper, inclined plane (IP) tracking and erosion tests similar to ASTM D2303 were conducted under both positive and negative dc voltages for silicone rubber samples filled with micron and nano sized particles to understand the phenomena occurring during such tests. Micron sized Alumina Trihydrate (ATH) and nano sized alumina fillers were added to silicone rubber matrix to improve the resistance to tracking and erosion. The leakage current during the tests and the eroded mass at the end of the tests were monitored. Scanning Electron Microscopy (SEM) and Energy dispersive Xray (EDX) studies were conducted to understand the filler dispersion and the changes in surface morphology in both nanocomposite and microcomposite samples. The results suggest that nanocomposites performed better than microcomposites even for a small filler loading (4%) for both positive and negative dc stresses. It was also seen that the tracking and erosion performance of silicone rubber is better under negative dc as compared to positive dc voltage. EDX studies showed migration of different ions onto the surface of the sample during the IP test under positive dc which has led to an inferior performance as compared to the performance under negative dc.

Surface Degradation of Silicone Rubber Nanocomposites Due to DC Corona Discharge

Corona discharge is recognized as one of the mechanisms that can influence the surface hydrophobicity of Silicone Rubber (SR) because of the chemical changes that occur on its surface. In this study SR samples were exposed to positive and negative DC corona for 25 and 50 hours using a needle-plane electrode system. Hydrophobicity changes were monitored using a sessile drop contact angle measurement facility. The physical changes on the surface were studied using Scanning Electron Microscopy (SEM) and surface roughness measurements. The effect of positive dc corona was found to be different from that of negative dc corona. Significant surface degradation and loss of hydrophobicity was found in the case of negative dc corona exposed samples. Significant improvement in the above mentioned properties were obtained by adding small quantities of nSIL into the SR matrix.

Azide and Alkyne Terminated Polybutadiene Binders: Synthesis, Cross-linking, and Propellant Studies

In composite solid propellants, the fuel and oxidizer are held together by a polymer binder. Among the different types of polymeric binders used in solid propellants, hydroxyl terminated polybutadiene (HTPB) is considered as the most versatile. HTPB is conventionally cured using isocyanates to form polyurethanes. However, the incompatibility of isocyanates with energetic oxidizers such as ammonium dinitramide and hydrazinium nitroformate, the short pot life of the propellant slurry, and undesirable side reactions with moisture are limiting factors which adversely affect the mechanical properties of HTPB based propellant. With an aim of resolving these problems, HTPB was chemically transformed to azidoethoxy carbonyl amine terminated polybutadiene and propargyloxy carbonyl amine terminated polybutadiene by adopting appropriate synthesis strategies and characterizing them by spectroscopic and chromatographic techniques. This is the first report on 1,3-dipolar addition reaction involving azide and alkyne end groups for cross-linking HTPB. The blend of these two polymers underwent curing under mild temperature (60 degrees C) conditions through 1,3-dipolar cycloaddition reaction resulting in triazoletriazoline networks. The curing parameters were studied using differential scanning calorimetry. The kinetic parameter, viz., activation energy, was computed to be 107.6 kJ/mol, the preexponential factor was 2.79 x 10(12) s-(1), and the rate constant at 60 degrees C was computed to be 3.64 x 10-(5) s-(1). The cure profile at a given temperature was predicted using the kinetic parameters. Rheological studies revealed that the gel time for curing through the 1,3-dipolar addition is 280 min compared to 120 min for curing through the urethane route. The mechanical properties of the resultant cured polybutadiene network were superior to those of polyurethanes. The cured triazolinetriazole polymer network exhibited biphasic morphology with two glass transitions (T-g) at -56 and 42 degrees C in contrast to the polyurethane which exhibited a single transition at -60 degrees C. This was corroborated by associated morphological changes observed by scanning probe microscopy. The propellant processed using this binder has the advantages of improved pot life as indicated by the end of the mix viscosity which is 165 Pas as compared with 352 Pas for the polyurethane system along with a slow build- up rate. The mechanical properties of the propellant are superior to polyurethane with an improvement of 14% in tensile strength, 22% enhancement in elongation at break, and 12% in modulus.

Effect of Coldfog on the Corona Induced Degradation of Silicone Rubber Samples

Corona is an unavoidable phenomena in high voltage power transmission system, in spite of suitably designed insulator accessories and transmission line hardware. It is a proven fact that the continuous occurrence of corona can subject the polymeric insulator to a severe degradation. Further, moisture in the air has a positive influence on the corona activity. This paper presents the methodology to evaluate the corona performance of the silicone rubber housing material with simultaneous application of cold fog. Analysis conducted after corona treatment by the Fourier Transform Infrared Spectroscopy (FTIR) present an interesting results showing a higher hydroxylation of sample surface under the moisture application than in the normal condition for both AC and DC excitation. FTIR spectrum also indicates the presence of nitric acid on the treated surface with coldfog application. Results obtained from SEM analysis are also presented.