Restraining Surface Charge Accumulation and Enhancing Surface Flashover Voltage through Dielectric Coating

A conductive metallic particle in a gas-insulated metal-enclosed system can charge through conduction or induction and move between electrodes or on insulating surfaces, which may lead to breakdown and flashover. The charge on the metallic particle and the charging time vary depending on the spatial electric field intensity, the particle shape, and the electrode surface coating. The charged metallic particle can move between the electrodes under the influence of the spatial electric field, and it can discharge and become electrically conductive when colliding with the electrodes, thus changing its charge. This process and its factors are mainly affected by the coating condition of the colliding electrode. In addition, the interface characteristics affect the particle when it is near the insulator. The charge transition process also changes due to the electric field strength and the particle charging state. This paper explores the impact of the coating material on particle charging characteristics, movement, and discharge. Particle charging, movement, and charge transfer in DC, AC, and superimposed electric fields are summarized. Furthermore, the effects of conductive particles on discharge characteristics are compared between coated and bare electrodes. The reviewed studies demonstrate that the coating can effectively reduce particle charge and thus the probability of discharge. The presented research results can provide theoretical support and data for studying charge transfer theory and design optimization in a gas-insulated system.

Rf-Sputtered Teflon®-Modified Superhydrophobic Nanostructured Titanium Dioxide Coating on Aluminum Alloy for Icephobic Applications

Icing on surfaces such as cables or high-voltage insulators may often lead to severe safety issues such as power outages in cold winter conditions. Conventional methods used to tackle such icing problems include mechanical deicing, where the ice is scraped or broken, and chemical deicing, where deicers such as ethylene glycol are used. However, the best approach to addressing these issues is to prevent ice formation in the first place. Research in the past few decades have shown hydrophobic and superhydrophobic surfaces to be effective in reducing ice adhesion. We used the concept of water repellency to turn an aluminum surface superhydrophobic to minimize ice adhesion on these surfaces. However, to render these surfaces also applicable to insulating surfaces, we also demonstrated the adaptability of the concept on a low dielectric oxide, TiO2, to an aluminum surface with icephobic properties. This work demonstrates the importance of the coexistence of rough nanostructures as well as low-surface-energy compositions on a surface to make it superhydrophobic and icephobic and is applicable on metals and insulating surfaces.

Improvement of the Corrosion Resistance of Biomedical Zr-Ti Alloys Using a Thermal Oxidation Treatment

Binary Zr-Ti alloys spontaneously develop a tenacious and compact oxide layer when their fresh surface is exposed either to air or to aqueous environments. Electrochemical impedance spectroscopy (EIS) analysis of Zr-45Ti, Zr-25Ti, and Zr-5Ti exposed to simulated physiological solutions at 37 °C evidences the formation of a non-sealing bilayer oxide film that accounts for the corrosion resistance of the materials. Unfortunately, these oxide layers may undergo breakdown and stable pitting corrosion regimes at anodic potentials within the range of those experienced in the human body under stress and surgical conditions. Improved corrosion resistance has been achieved by prior treatment of these alloys using thermal oxidation in air. EIS was employed to measure the corrosion resistance of the Zr-Ti alloys in simulated physiological solutions of a wide pH range (namely 3 ≤ pH ≤ 8) at 37 °C, and the best results were obtained for the alloys pre-treated at 500 °C. The formation of the passivating oxide layers in simulated physiological solution was monitored in situ using scanning electrochemical microscopy (SECM), finding a transition from an electrochemically active surface, characteristic of the bare metal, to the heterogeneous formation of oxide layers behaving as insulating surfaces towards electron transfer reactions.

Deterministic control of surface mounted metal–organic framework growth orientation on metallic and insulating surfaces

Surface-Mounted Metal–Organic Frameworks (SURMOFs) growth orientation in [100] or [111] can be deterministically controlled by the SAM chain length, regardless of the surface nature (metallic or insulating).

Limitations Regarding Use of the ABC-Model for Interpretation of Partial Discharge Measurements

The main purpose of the work presented here is to facilitate use of partial discharge (PD) measurements as a diagnostic tool for condition assessment of hydropower generator bars. The main aim of the work is to clarify how measured inception and extinction voltage, detected number and magnitude of PDs relate to the void size and the physical discharge mechanisms in the voids. The laboratory tests were performed on 3 mm thick samples, consisting of three 1 mm thick layers containing a cylindrical disc shaped void in the center of the middle layer. The void diameters varied from 3 to 20 mm. Insulation discs of polycarbonate and generator insulation based on mica and glass fiber reinforced epoxy tape were examined. In case of the polycarbonate samples comparable tests were performed on objects with either conductive or insulting void surfaces. During application of a stepwise increasing/decreasing 50 Hz AC voltage, the partial discharge activity was detected using a conventional PRPDA detection system.The inception voltage was found to decrease with increasing void diameter, in accordance with results from electric field calculations showing increased field enhancement in the larger voids. In all cases the apparent discharge magnitude increased with increasing diameter. In case of conducting void surfaces this discharge magnitude and number of PDs per period were, in accordance with the theory, found to be proportional to the total surface area of the void. In case of voids with insulating surfaces, this proportionality was valid up to a void diameter of 10 mm. Larger voids resulted in higher number of PD each at lower apparent charge magnitude than expected, indicating several parallel discharges, during which a section of the void surface is discharged only. In contradiction to the assumptions of the abc-model nearly no difference was observed between the PD inception and extinction voltage, indicating a high and rapidly decaying remanent charge.Thus, the abc-model assumption of each PD causing a complete void discharging is only fulfilled if the surfaces are conducting, or the voids are small. The results indicate that changes of internal conditions of the void during the period of PD measurements

Quantifying plasma immersion ion implantation of insulating surfaces in a dielectric barrier discharge: how to control the dose

The plasma physics of dielectric barrier discharges (DBD) for carrying out ion implantation in insulators is investigated. A hollow cathode DBD excited by high-voltage pulses is suitable for ion bombardment of the surfaces of insulating tubing, porous material, particles and sheets. Plasma immersion ion implantation of insulating surfaces is useful for many applications in medicine and engineering. The ion bombardment of glass is useful for cleaning and surface modification. The ion implantation of polymers creates radicals that are able to bind molecules to their surfaces for applications in medical procedures and diagnostics. A wire diagnostic probe and optical emission spectroscopy are used for experimental work. A theory based on mutual capacitance is developed to convert data from the probe to give implanted charge as a function of pressure, voltage and pulse duration. We find the operating conditions that allow for charge to be implanted and those that achieve the highest implanted charge.