Zhengjie An

To meet the demands of high-voltage power electronics, this study elucidates the role of ion flux in plasma-enhanced chemical vapor deposition in governing the sp3/sp2 ratio of diamond-like carbon (DLC) films on alumina particles, which is believed to have the potential to improve the interface between epoxy and filler particles. Independent control of ion flux revealed a non-monotonic trend in the sp3/sp2 ratio: it initially increases due to suppressed carbon relaxation at moderate flux, then decreases beyond a critical threshold due to thermal graphitization from excessive energy deposition. By integrating the subplantation model with energy analysis, this study clarifies the competition between kinetic stabilization and thermal degradation. This work provides a mechanistic understanding and a practical guideline for optimizing DLC-coated fillers in high-performance composites.

Non-intrusive measurement of the local electric-field direction in SF₆ gas-insulated equipment is important for insulation-condition assessment and electric-field distortion analysis. In this study, a three-projection electric-field direction measurement method based on electric field-induced second-harmonic generation is proposed. The feasibility of the method is validated using a known reference electric field, and the effects of electric-field strength, laser pulse energy, SF₆ pressure, and spatial electric-field non-uniformity on the direction-retrieval results are systematically investigated. The results show that increasing the electric-field strength or laser pulse energy enhances the second-harmonic modulation signal and thus reduces the direction-retrieval deviation. SF₆ pressure has a non-monotonic influence on the effective accumulation of the second-harmonic signal and the direction-retrieval accuracy through the competition between increased molecular number density and enhanced phase mismatch. Spatial electric-field non-uniformity weakens the ability of the three-projection retrieved direction to represent the local electric-field direction at the focus. Under the present experimental conditions, the maximum absolute angular deviations in the strongly non-uniform edge regions of the cylindrical and hemispherical electrodes are 6.68 ± 1.62° and 9.20 ± 1.84°, respectively.

Due to the outstanding thermal and electrical properties of diamond-like carbon (DLC), a strategy for fabricating high thermal conductivity epoxy composites through surface modification of filler particles via DLC deposition has been developed. However, a key challenge remains: the ion energy in the plasma-enhanced chemical vapor deposition used for particle modification exhibits a broad distribution, and the synergistic effects of ions with different energies on the sp ³ /sp ² ratio of DLC are still not well understood. In this study, the ion energy distributions under various voltage conditions were experimentally measured, and the evolution of the sp ³ /sp ² ratio in DLC films deposited on alumina particles was systematically characterised. The results indicate that the the sp ³ /sp ² ratio of DLC arises from the collective contribution of ions across multiple energy levels, though their individual influences vary significantly. Notably, ions within the 100 ∼ 200 eV energy range exhibit the greatest positive impact on enhancing the sp ³ /sp ² ratio. By integrating molecular dynamics simulations to capture the dynamic behavior of ions during the deposition process, a novel evaluation approach was proposed—assessing the influence of ion energy distribution on the sp ³ /sp ² ratio through the number density of ‘extra atoms’ introduced into the DLC network by ion implantation. This method enables direct prediction of the sp ³ /sp ² ratio trend based solely on ion energy distribution characteristics, offering a rational and efficient pathway for optimizing deposition parameters. It holds significant practical value for advancing the scalability and controllability of plasma-based surface modification technologies.

The incorporation of diamondlike carbon (DLC)-coated alumina particles as filler offers a viable approach to enhance the thermal conductivity and mechanical properties of epoxy composites. The bonding strength of alumina and DLC film is the key index to evaluate the modification effect. The deposition of diamondlike films onto the alumina surface was achieved through plasma-enhanced chemical vapor deposition. It has been observed that the DLC film exhibits a stratified structure, with a transition region containing carbon, oxygen, and aluminum at the interface between the DLC and alumina. The DLC and alumina can be combined due to the existence of the transition region. The process of DLC film deposition of hydrocarbon ions with different energies on the alumina surface was simulated by the molecular dynamics method. The formation of the transition region is contingent upon the introduction of energetic ions into the alumina. The transition region will have a larger geometric size in the deposition by high-energy ions, which explains the higher film-base bonding strength of DLC films formed by high-energy ions. The experimental measurement of the bonding strength between DLC and alumina under various conditions revealed that an increase in the number of ions with energy exceeding 200 eV enhances the bonding strength.

The ability to manipulate ion energy is crucial for the practical implementation of pulsed hollow cathode discharge in plasma deposition. This paper presents a method for generating plasma through double pulse voltage superposition, which excites the hollow cathode discharge. By superimposing a high-amplitude pulse with a narrow width and a low-amplitude pulse with an extended width, gas ionization and ion acceleration can be stimulated respectively. With this approach, relative independent control over ion flux density and ion energy becomes possible. Increasing the amplitude of the narrow pulse enhances the ion flux density, while increasing the amplitude of the long pulse boosts average ion energy.

Depositing diamond-like carbon (DLC) film is considered to be more promising for surface modification of microparticles. The development of reliable and precise measurement techniques for DLC coatings on microparticles is crucial for advancing research in this field. This paper introduces a methodological approach for quantifying the thickness of the film on microparticles. The thickness of the film is obtained by establishing the quantitative relationship between the energy lost when electrons pass through the film and the thickness of the film. The proposed method allows for the estimation of film thickness by assessing solely the elemental abundance on the particle surfaces.

The high density and controllability of radio frequency (RF)-biased inductively coupled plasma offer significant potential for diamond-like carbon (DLC) deposition on alumina. However, the effects of power and atmospheric parameters on DLC deposition have been understudied due to multiple constraints, such as discharge conditions and carbon source requirements. In this study, considering the dual requirements of ion flux and ion kinetic energy for deposition, an RF-biased inductively coupled plasma-enhanced DLC deposition method was proposed. A total of 273 deposition experiments designed by response surface methodology were performed over wide parameter ranges to explore the influence of atmospheric parameters, such as gas pressure and Ar/H2 auxiliary gas fractions, on feasible power. The results showed that there was a power threshold for DLC deposition on alumina, which increased with gas pressure and slightly decreased with auxiliary gas addition. The effect of auxiliary gas on DLC deposition exhibited duality due to changes in the dominance of ion etching and methane dissociation. The feasible power region for DLC deposition in multicomponent atmosphere was jointly constrained by the power threshold and etching action. This research contributed to the DLC modification of alumina substrate in batches.

Diamond-like carbon (DLC)-modified alumina microparticles are expected to be an ideal filler that can greatly improve the thermal conductivity of epoxy-alumina composites with a high fill factor, while the composites can still maintain high dielectric properties. Plasma-enhanced chemical vapor deposition (PECVD) has been mostly used to prepare DLC film on bulk material, and the ion energy in the plasma shows a crucial influence on the properties of the DLC. However, the properties of the DLC on solid microparticles prepared through the PECVD method as well as the effect of the ion energy are still unclear. In this paper, DLC on alumina microparticles has been prepared through a highly efficient method of repeated pulsed hollow cathode discharge in methane gas, and the characteristics of the DLC on the alumina particles have been studied and analyzed. The morphology and bond composition of DLC on particles have been studied through electron microscopy, Raman spectrometer and x-ray photoelectron spectroscopy. The ion energy distribution in the discharge plasma was diagnosed and used to analyze its effect on the hybrid bond content of the DLC through correlation analysis. The correlation of the ion energies and the hybrid bond content of the DLC shows that hydrocarbon ions in the discharge plasma with an energy of 100–200 eV present the most benefit to the formation of the sp³ hybrid bond content of DLC film on alumina microparticles. In addition, hydrogen ions with an energy of 700–1000 eV are also beneficial to improve the sp³ hybrid bond content of the DLC film.

Conductive particles are one of the most important defects which can greatly degrade the performance of gas-insulated metal-enclosed switchgear (GIS). Many efforts have been made to clarify the influence on the withstand voltage, understand the flashover mechanism, and build a comprehensive model to describe the particle-initiated flashover. In this study, a partial discharge (PD) signal detected through a photomultiplier (PMT) and recorded by a high-speed data acquisition (DAQ) system was used to analyze the discharge development of a conductive particle-contaminated GIS insulator under constant high AC voltage. An additional PMT was used as a reference to eliminate the dark count of the PMT and the data collection method of a DAQ system was optimized to capture the pulse waveform of each PD to obtain detailed physical information. Spectra of the PD pulse amplitude over pulse width, PD counts within various amplitude ranges over time and phase resolved partial discharge (PRPD) patterns of the PDs in different stages are obtained through the captured PD waveforms. Characteristics of the PDs from the application of the high AC voltage up to the flashover of the insulator were then analyzed, and it was found that the features of the PDs in the near-flashover stage were significantly different to the previous stages.