Search

Silicone rubber housings crack under the combined internal and external factors and expose the core rod. The exposed core rod deteriorates or breaks under electric fields and electrical current. Based on the main characteristics and mechanism of the core rod corrosion, this paper performs an electrical erosion test in an acid-fog environment and analyzes the core rod's macroscopic results and physicochemical properties. The results indicate the following. First, the discharge on core rod during the electrical erosion process contains four consecutive stages. The electrical current, partial discharge, temperature increase, and macroscopic morphology show regular changes at different stages. The arc usually occurs in the carbonization channel, making the channel have the maximum heat. The area of the core rod heating constantly changes but mainly at the high-voltage side and presents as a regional temperature increase. Second, the fracture of glass fiber and ablation of epoxy resin matrix are related to the continuous action of nitric acid. The generation, expansion, and release of pyrolysis gas form bubbles and pores on the epoxy resin matrix. Erosion and pyrolysis cause the loss of the epoxy resin matrix. Third, the combined effect of electrical current, nitric acid, and heat damage the core rod axially and radially. The study provides support for the subsequent core rod deterioration and fracture mechanism.

Due to excellent anti-pollution performance, composite insulators have been widely used in transmission lines. However, composite insulators present various failures after long-term outdoor operation under environmental, mechanical, and electrical stress. This paper aims to investigate the mechanical deterioration of silicone rubber exposed to electrical stress in an acidic corrosive environment. This study examines the mechanical properties before and after experiments and uses physicochemical properties to analyze aging causes and mechanisms. The results are as follows: a) Subjected to electrical stress in acid mist, alumina tri-hydrate (ATH) decomposition and polydimethylsiloxane (PDMS) pyrolysis occur on the silicone rubber, and oxidative crosslinking reactions take place. The contents of highly oxidized silicon and oxygen increase, and carbon content decreases. The surface discharge aggravates the above progress. b) The electric field has no obvious effect on the penetration of nitric acid into silicone rubber. The surface discharge becomes intense with the increased energized voltage, resulting in decreased hydrophobicity and degraded surface properties. c) Mechanical properties of silicone rubber exposed to acid conditions continuously degrade. Physical crosslinking of the silicone rubber increases along with corrosion time and nitric acid concentration, increasing hardness, decreasing tensile strength, and elongation at break. This paper investigates the relationship between mechanical and physicochemical properties, and the results can provide references for studying the failure mechanism of silicone rubber in an acid corrosion environment.

For the benefit of knowing the method of insulator deicing using hot water, this paper investigated the physical aspects of propagation and the spatial temperature distribution of a hot water jet in the air. The numerical calculation model for the water jet flow field was established and validated, and the temperature spatial variation rule and influencing factors of the water jet were analyzed. The results indicate that the water column breaks as the distance increases. The numerical calculation results and the experimental results of the water jet flow field were approximated. As the distance increases, the mass entrainment rate of the water jet gradually increases, and the normalized axis velocity decreases approximately linearly. The jet temperature rises with the rise in the initial temperature of the hot water, and the rising rate decreases with the increase in distance. The temperature of the water jet falls as the jet distance increases. With the rise in the outlet pressure, the temperature of the water jet drops slightly. The influence of environmental wind speed on the water jet temperature is more significant than ambient temperature—the water jet temperature increases as the nozzle diameter increases. The thorough deicing efficiency is most outstanding when the hot water output temperature is around 86 °C and the jet pressure is ~3.5 MPa.

The changes in sap flow of Salix psammophila growing on a gentle slope (lower slope, P1), a middle slope (P2), and an upper slope (P3), and the response of sap flow to meteorological factors at the different slope positions were studied using the continuous and synchronized observations, the instrument were wrapped stem flowmeter EMS 62 sap-flow heat-balance-based system and the LSI-LASTEM automatic weather station. The results revealed that the soil moisture content was the highest and the growth conditions of Salix psammophila were the best at P1, followed by P2. At P3, however, although good apical dominance was observed, the proportion of dead branches was the highest. Furthermore, the daily variation patterns of sap flow on the three slopes presented as multi-peak bell-shaped curves. The daily accumulation changes in sap flow showed a trend of P1 > P3 > P2, and within the same diameter range, the sap flow at P1 was significantly different from that at P2 and P3, whereas the sap flow at P2 and P3 did not vary significantly. All the three slopes showed a significant and positive correlation with photosynthetically active radiation, atmospheric temperature, and vapor pressure difference, and a significant and negative correlation with relative humidity; however, the degrees of correlation varied slightly. The stepwise regression analysis showed that, at different slopes, different variables were selected for different branch diameters, but photosynthetically active radiation and atmospheric temperature played dominant roles on all slopes. This study reveals the sap flow pattern of Salix psammophila on different slopes and its response mechanism to meteorological factors, which was essential for understanding the restoration ability, physiological adaptability, and ecosystem stability of Salix psammophila communities.

This study was conducted to find an appropriate approach for the assessment of bioavailability of DDTs in soil to both earthworm and vegetables. Four chemical approaches—Soxhlet extraction with n-hexane, n-butanol agitation extraction, water agitation extraction, and matrix solid-phase microextraction (matrix-SPME)—were used to assess the relationships between the extractability of 1,1-dichloro-2,2-bis( p-chlorophenyl) ethylene ( p,p′-DDE), 1,1,1-trichloro-2-( p-chlorophenyl)-2-( o-chlorophenyl) ethane ( o,p′-DDT), 1,1-dichloro-2,2-bis( p-chlorophenyl) ethane ( p,p′-DDD), and 1,1,1-trichloro-2,2-bis( p-chlorophenyl) ethane ( p,p′-DDT) in soil and their amounts uptaken by the earthworm ( Eisenia foetida), Chinese cabbage ( Brassica campestris L. spp.), and cole ( Brassica napus L.). These results indicated that the extractability and bioavailability of DDTs in soil decreased with time of aging. Correlation analysis showed that n-butanol extraction or 12-h matrix-SPME could be used to assess the bioavailability of DDTs to the earthworm, and Soxhlet extraction, n-butanol extraction, or 12-h matrix-SPME could be used to predict the bioavailability of DDTs to both Chinese cabbage and cole. As a solventless, time-efficient, and negligible-depletion technique, it could be concluded that matrix-SPME is a better approach to predict the bioavailability of DDTs to both the earthworm and vegetables, compared with Soxhlet extraction, n-butanol extraction, and water extraction. [ABSTRACT FROM AUTHOR]