Forced triboelectrification of fine powders in particle wall collisions

Triboelectric separation as an inexpensive and environmentally friendly technique could contribute to material-specific sorting. However, the application as a widespread method is limited due to the complexity of the process. In particle wall collisions, various parameters like collision energy and angle, work function of the contact partners, humidity, surface roughness, etc. influence the particle charging in a hardly predictable way. This study investigates the possibilities of forced triboelectric particle charging by applying an electrical potential to the metal contact partner (copper/steel pipe). The variations included different pipe lengths (0.5 m–3 m), particle materials, and particle sizes for limestone. A distinction is made between the net charge of the particles and the positive, negative, and neutral mass fractions. The work functions of the investigated materials vary from about 3.2 eV to >8.5 eV for glass, limestone, artificial slag, and lithium aluminate particles. With the applied high-voltage potential, the particle net charge can be shifted linearly. For limestone, it is shown that the neutral fraction is highest at the Point of Zero Net Charge (PZNC). This observation may identify an approach for the material selective separation of one target component from a multi-material mixture

Moisture-controlled Triboelectrification during coffee grinding

Triboelectrification is the physical process where materials acquire surface charge from frictional interactions at their interfaces.The magnitude of charge depends on the interfacial material composition and can be harnessed in emergent technologies for energy generation. The mechanism of electrostatic accumulation is complex and is further obscured in granular materials where collisions are sufficiently energetic to cause fracturing. In this “fractoelectric” regime, crack initiation and propagation are thought to charge particles through transfer of electrons and/or ions at the hot crack interface. Whether a material’s charging is dominated by tribo- or fractoelectrification, fracture-generated granular flows often comprise particles whose surface charge density may exceed the theoretical maximum value of 27 μC per meter squared or charge-to-mass ratios in the range of 0.1–100 nC per gram. There remains fundamental interest in studying the mechanism and magnitude of charging and methods to control the process, in particular to mitigate spurious effects such as electrostatic discharges and agglomeration within industrial settings

Available Technologies and Commercial Devices to Harvest Energy by Human Trampling in Smart Flooring Systems: a Review

Technological innovation has increased the global demand for electrical power and energy. Accordingly, energy harvesting has become a research area of primary interest for the scientific community and companies because it constitutes a sustainable way to collect energy from various sources. In particular, kinetic energy generated from human walking or vehicle movements on smart energy floors represents a promising research topic. This paper aims to analyze the state-of-art of smart energy harvesting floors to determine the best solution to feed a lighting system and charging columns. In particular, the fundamentals of the main harvesting mechanisms applicable in this field (i.e., piezoelectric, electromagnetic, triboelectric, and relative hybrids) are discussed. Moreover, an overview of scientific works related to energy harvesting floors is presented, focusing on the architectures of the developed tiles, the transduction mechanism, and the output performances. Finally, a survey of the commercial energy harvesting floors proposed by companies and startups is reported. From the carried-out analysis, we concluded that the piezoelectric transduction mechanism represents the optimal solution for designing smart energy floors, given their compactness, high efficiency, and absence of moving parts

Multi-sensor electrometer

An array of triboelectric sensors is used for testing the electrostatic properties of a remote environment. The sensors may be mounted in the heel of a robot arm scoop. To determine the triboelectric properties of a planet surface, the robot arm scoop may be rubbed on the soil of the planet and the triboelectrically developed charge measured. By having an array of sensors, different insulating materials may be measured simultaneously. The insulating materials may be selected so their triboelectric properties cover a desired range. By mounting the sensor on a robot arm scoop, the measurements can be obtained during an unmanned mission

The Effect of Varying Environmental Conditions on the Performance of Triboelectric Generators

As data creation and collection continues to increase globally, the number of sensors needed to gather data also grows. One thing all types of sensors have in common is their need for power; however, current power sources, like batteries, are limited by their life, size, and weight. To reduce these power limitations, triboelectric energy generators (TENGs) can be used to generate power from the mechanical motion that is present throughout packaged product transport. Triboelectric generation is one such low power mechanism that due to its low cost, has potential in packaging applications. In the distribution environment, packaged products are exposed to a wide range of temperatures and relative humidities. It is important to know how the relative humidities and temperatures seen in packaging distribution environments affect the voltage output of triboelectric energy generators. In order to study relative humidity and temperature effect on TENGs, we mount an optimized triboelectric generator to an electrodynamic shaker located inside an environmental chamber and measure voltage output. This set up allows us to replicate sinusoidal vibration inputs over a wide range of environmental conditions. We found that as relative humidity increases, TENG’s root mean square (RMS) voltage output remains essentially the same, and as temperature increases, the TENG’s RMS voltage output also remains basically same. We also determined that charge build up is not affected by relative humidity and temperatures found within the packaging distribution environment and that steady state takes longer to establish than a few hundred seconds

Particulate Nanoinsecticides: A New Concept in Insect Pest Management

Nanostructured alumina (NSA) has insecticidal properties and has been demonstrated to be effective against stored product insect pests in laboratory bioassays. NSA is a nano-engineered material synthesized by oxidation of metals, and resulting particles show fixed electric charges. On the other hand, insects exhibit their own electric charges generated by triboelectrification. We propose that the mechanism of action of NSA involves two steps occurring in sequential order. First, a strong electrical binding between negatively charged NSA particles and positively charged insect. Next, dehydration of the insect occurs due to the strong sorbtive action of the NSA particles that remove the insect cuticular, leading to death by dehydration. As postulated for insecticidal inert powder in generals, particles attach to the insect cuticle surface disrupting water balance, and effectiveness decreases as ambient humidity increases, given that electrostatic bond forces are reduced by electrostatic discharge. The high insecticidal efficacy of NSA is a result of its intrinsic electric charge, small particle size and high sorptive potential due to its large specific surface area. NSA could provide an alternative to conventional synthetic organic insecticides due to its strong insecticidal properties with the advantage that its mechanism of action involves physical and electrostatic phenomena

Evaluation of a new dispersion technique for assessing triboelectric charging of powders

In a number of applications, especially in pharmaceutical drug development, there is often a very small powder quantity available for evaluating the manufacturability of new drugs. However, it is highly desirable to be able to quickly evaluate processing issues, and where possible using the smallest powder quantity. In the present work, a proprietary commercial powder dispersion device (the disperser of Malvern© Morphologi G3) is adapted to evaluate the triboelectric charging tendency. A very small powder quantity (as small as 0.1 mg) is dispersed by a pressure pulse of compressed gas such as air or nitrogen. This causes the particles to become air borne and collide with the containing walls, resulting in dispersion and leading to triboelectric charge transfer between the particles and the walls. In this work, the charging propensity of a number of materials is evaluated and the effect of particle surface functional groups on the tribo-electric charge transfer is analysed. Model materials with a well-defined shape (glass ballotini) but with different silane groups deposited on their surfaces as well as a number of organic crystalline particles (such as aspirin, α-lactose monohydrate and paracetamol) are tested. Following dispersion the particles move immediately to a Faraday cup placed directly underneath the disperser. Therefore, particle charge is measured with no decay. The method can differentiate charging of different polymorphs of the same material, different silane groups on the surfaces of glass ballotini and different crystal morphologies obtained from crystallisation from various solvents