Analysis of conductance and interfacial polarisation behaviours of silicone rubber based on frequency domain spectroscopy

Silicone rubber(SR)is widely used for cable insulation and operates in multi-stress coupling conditions.Its dielectric properties and ageing performance are the essential factors affecting cable operation.In this study,the frequency domain spectroscopy of unaged SR and SR aged under various conditions is measured.The dielectric responses before and after ageing are analysed in depth by the conjoint analysis via multiple complex planes(permittivity,conductivity,and modulus).Typical conductivity and interfacial polarisation properties,as well as property changes resulting from thermal and tensile ageing,are examined.Experimental results show that tensile ageing promotes conductance and interfacial polarisation,while thermal ageing shows the opposite effects.Based on the multi-core model and charge carrier hopping transport model,thermal and tensile ageing mechanisms on the conductance and interfacial polarisation behaviours of SR are demonstrated.Both behaviours exhibit positively correlated changing characteristics,suggesting that the two behaviours may originate from a common process.The carrier transport process,promoted by the tensile effect and slightly suppressed by the thermal effect,is the primary factor and considered an important indicator to evaluate the dielectric properties of SR insulation.

Dielectric barrier discharge-based defect engineering method to assist flash sintering

Oxygen vacancy OV plays an important role in a flash sintering (FS) process. In defect engineering, the methods of creating oxygen vacancy defects include doping, heating, and etching, and all of them often have complex processes or equipment. In this study, we used dielectric barrier discharge (DBD) as a new defect engineering technology to increase oxygen vacancy concentrations of green billets with different ceramics (ZnO, TiO_(2), and 3 mol% yttria-stabilized zirconia (3YSZ)). With an alternating current (AC) power supply of 10 kHz, low-temperature plasma was generated, and a specimen could be treated in different atmospheres. The effect of the DBD treatment was influenced by atmosphere, treatment time, and voltage amplitude of the power supply. After the DBD treatment, the oxygen vacancy defect concentration in ZnO samples increased significantly, and a resistance test showed that conductivity of the samples increased by 2–3 orders of magnitude. Moreover, the onset electric field (E) of ZnO FS decreased from 5.17 to 0.86 kV/cm at room temperature (RT);while in the whole FS, the max power dissipation decreased from 563.17 to 27.94 W. The defect concentration and conductivity of the green billets for TiO_(2) and 3YSZ were also changed by the DBD, and then the FS process was modified. It is a new technology to treat the green billet of ceramics in very short time, applicable to other ceramics, and beneficial to regulate the FS process.

A fabrication method for adaptive dielectric gradient insulating components

Dielectric gradient components have advantages in electric field mitigation and insulation improvement.In this paper,we propose a fabrication method for adaptive dielectric gradient components using in situ AC electric field,including the mechanism and the corresponding operational procedures for industrial applications.Based on the electric polarisation and self-assembly effect of the filler particles in the liquid matrix,the chainlike structure in the high field strength region is constructed to enhance the local permittivity and mitigate the maximum of the spatial electric field.The dielectric gradient basin insulator is prepared by this method,and its flashover voltage is increased by 12.8%compared with that of a homogeneous dielectric basin insulator,and the improvement is 20.8%when metal particles are present on the surface.The more non-uniform the initial electric field is,the greater the improvement in flashover voltage.This method is expected to promote the industrial application of dielectric gradient insulating components.

Cold sintering process for fabrication of a superhydrophobic ZnO-polytetrafluoroethylene(PTFE)ceramic composite

Composite coatings or films with polytetrafluoroethylene(PTFE)are typically utilized to offer superhydrophobic surfaces.However,the superhydrophobic surfaces usually have limited durability and require complicated fabrication methods.Herein,we report the successful integration of PTFE with ZnO ceramics to achieve superhydrophobicity via a one-step sintering method,cold sintering process(CSP),at 300℃.(1–x)ZnO–x PTFE ceramic composites with x ranging from 0 to 70 vol%are densified with relative density of over 97%.Micro/nano-scale PTFE polymer is dispersed among ZnO grains forming polymer grain boundary phases,which modulate surface morphology and surface energy of the ZnO–PTFE ceramic composites.For the 60 vol%ZnO–40 vol%PTFE ceramic composite,superhydrophobic properties are optimized with static water contact angles(WCAs)and sliding angles(SAs)of 162°and 7°,respectively.After abrading into various thicknesses(2.52,2.26,and 1.99 mm)and contaminating with graphite powders on the surface,WCA and SA are still maintained with a high level of 157°–160°and 7°–9.3°,respectively.This work indicates that CSP provides a promising pathway to integrate polymers with ceramics to realize stable superhydrophobicity.

Flash sintering of high-purity alumina at room temperature

For the first time,the flash sintering(FS)of high-purity alumina at room temperature,which was previously considered unachievable due to its low electrical conductivity,was conducted herein.The electrical arc originating from surface flashover was harnessed to induce FS at room temperature and low air pressure.The successful FS of high-purity alumina was realized at 60 kPa under the arc constraint,resulting in a notable relative density of the alumina sample of 98.7%.The electric–thermal coupling between the arc and high-purity alumina sample during the arc-induced FS process was analyzed via the finite element simulation method.The results revealed the thermal and electrical effects of the arc on the sample,which ultimately enhance the electrical conductivity of the alumina sample.The formation of a conductive channel on the sample surface,a result of increased electrical conductivity,was the pivotal factor in achieving FS in high-purity alumina at room temperature.The arc constraint technique can be applied to numerous materials,such as ionic conductors,semiconductors,and even insulators,under room-temperature and low-air-pressure conditions.

Gas-discharge induced flash sintering of YSZ ceramics at room temperature

This is the first study to conduct the flash sintering of 3 mol%yttria-stabilized zirconia(3YSZ)ceramics at room temperature(25℃)under a strong electric field,larger than 1 kV/cm.At the standard atmospheric pressure(101 kPa),the probability of successful sintering is approximately half of that at low atmospheric pressure,lower than 80 kPa.The success of the proposed flash sintering process was determined based on the high electric arc performance at different atmospheric pressures ranging from 20 to 100 kPa.The 3YSZ samples achieved a maximum relative density of 99.5%with a grain size of~200 nm.The results showed that as the atmospheric pressure decreases,the onset electric field of flash sintering decreases,corresponding to the empirical formula of the flashover voltage.Moreover,flash sintering was found to be triggered by the surface flashover of ceramic samples,and the electric arc on the sample surfaces floated upward before complete flash sintering at overly high pressures,resulting in the failure of flash sintering.This study reveals a new method for the facile preparation of flash-sintered ceramics at room temperature,which will promote the application of flash sintering in the ceramic industry.

High‐performance ZnO varistor ceramics prepared by arc‐induced flash sintering with low energy consumption at room temperature

The development of ultra‐high voltage transmission lines requires a ZnO arrester with excellent electrical response and high voltage gradient.Compared with conventional preparation methods,flash sintering allows fast production of novel high‐performance ZnO varistor ceramics with low energy consumption and controlled grain growth.Herein,ZnO varistor ceramics were prepared using the flash sintering method at an air pressure of 21 kPa for 60 s at 25℃.The results showed that the flash‐sintered samples had fine grains and reduced loss of volatile elements.Moreover,the voltage gradient,leakage current density,and non‐linear coefficient of the flash‐sintered varistor ceramics were significantly improved compared with those of conventionally sintered samples.Owing to the short preparation time and absence of a heating process,the energy consumption of the proposed flash sintering method was significantly reduced to 10%of that by conventional sintering.The proposed method is a promising approach for the preparation of ZnO arresters with excellent electrical properties and serves as an effective method that realises energy saving and emission reduction.

Review of flash sintering with strong electric field

Flash sintering is a novel field‐assisted sintering technology for ceramics that allows a dramatic reduction in processing time and temperature.Since 2010,when flash sintering was first reported,it has been a focus of research interest in the field of materials science.Recent study results have confirmed that the sintering temperature decreases with the strength of the applied electric field;for some ceramics,the sintering temperature can be lowered even to room temperature.This represents an innovative breakthrough for ceramic sintering at ultra‐low temperatures.However,once the electric field strength in flash sintering is increased,new questions and challenges arise,such as whether or not partial discharge occurs in the green body if under electro‐thermal coupling stress,how to quantitatively analyse the impact of discharge on sintering,and,moreover,whether the sintering mechanism under a strong electric field is consistent with that under a weak electric field.These research questions require knowledge of partial discharge detection,dielectric theory,and other topics that are beyond the scope of materials science.To address this need,this review summarises the work carried out in flash sintering with a strong electric field from the perspective of high voltage and insulation technology.First,the flash sintering process and mechanism are briefly introduced.Then,the published literature on flash sintering with a strong electric field for various ceramic materials is summarised in depth.In addition,experimental phenomena that are observed in flash sintering with a strong electric field,such as flash and blackening,are discussed.Finally,some suggestions for future work are presented.It is anticipated that the knowledge gap between different areas of study can be filled by this review.

A versatile defect engineering strategy for room-temperature flash sintering

In this study,we reported that flash sintering(FS)could be efficiently triggered at room temperature(25℃)by manipulating the oxygen concentration within ZnO powders via a versatile defect engineering strategy,fully demonstrating a promising method for the repaid prototyping of ceramics.With a low concentration of oxygen defects,FS was only activated at a high onset electric field of~2.7 kV/cm,while arcs appearing on the surfaces of samples.Strikingly,the onset electric field was decreased to<0.51 kV/cm for the activation of FS initiated,which was associated with increased oxygen concentrations coupled with increased electrical conductivity.Thereby,a general room-temperature FS strategy by introducing intrinsic structural defect is suggested for a broad range of ceramics that are prone to form high concentration of point defects.

Analytical model for the transient permittivity of uncured TiO_(2) whisker/liquid silicone rubber composites under an AC electric field

The electric field grading of dielectric permittivity gradient devices is an effective way of enhancing their insulation properties.The in situ electric field‐driven as-sembly is an advanced method for the fabrication of insulation devices with adaptive permittivity gradients;however,there is no theoretical guidance for design.In this study,an analytical model with a time constant is developed to determine the transient permittivity of uncured composites under an applied AC electric field.This model is based on optical image and dielectric permittivity monitoring,which avoids the direct processing of complex electrodynamics.For a composite with given components,the increased filler content and electric field strength can accelerate the transient process.Compared with the finite element method based on differential equations,this statistical model is simple but efficient,and can be applied to any low‐viscosity uncured composites,which may contain multiple fillers.More importantly,when a voltage is applied to an uncured composite insulating device,the proposed model can be used to analyse the spatiotemporal permittivity characteristics of this device and optimise its permittivity gradient for electric field grading.