Charge Partitioning at Gas−Solid Interfaces: Humidity Causes Electricity Buildup on Metals

Abstract

Isolated metals within Faraday cages spontaneously acquire charge at relative humidity above 50%: aluminum and chrome-plated brass become negative, stainless steel is rendered positive, and copper remains almost neutral. Isolated metal charging within shielded and grounded containers confirms that the atmosphere is an electric charge reservoir where OH(-) and H(+) ions transfer to gas-solid interfaces, producing net current. The electricity buildup dependence on humidity, or hygroelectricity, acts simultaneously but in opposition to the well-known charge dissipation due to the increase in surface conductance of solids under high humidity. Acknowledging this dual role of humidity improves the reproducibility of electrostatic experiments.

Adhesion Hysteresis from Interdependent Capillary and Electrostatic Forces

“…67 The standard deviation of the CPD values increased with RH, consistent with earlier reports of enhanced electrostatic charging and discharging of silica and metal surfaces. 23,28,68 Adhesion Hysteresis. The mechanistic differences in the adhesion forces upon approach and separation motivate a brief look at the extent of the resulting adhesion hysteresis.…”

Theoretical modeling of relative humidity on contact electrification of sand particles

“…In the experiment, the electric field intensity increases with moisture content in the region of 0.5% ~ 1.0%, but when it increases to 2%, electric field intensity decreases, which suggests that humidity can influent the charge transfer. Ducati et al17 found that the change of environment humidity can make the insulator surface charge easily. The wind tunnel experiment of Xie and Han18 showed that aeolian electrical field intensity linearly increases when the relative humidity is less than critical relative humidity, but exponentially decreases when the relative humidity is higher than the critical value.…”

Triboelectric charging in single-component particle systems

“…Evidence in favor of an ion transfer mechanism has been reported by a number of recent studies that show that changes in the adsorbed surface layers -either by changing relative humidity (Ducati et al, 2010;Gouveia and Galembeck, 2009), introducing vacuum (Hogue et al, 2004(Hogue et al, , 2005, or changing the hydrophobicity of the surface (Friedle and Thomas, 2010) -alter the charging behavior. When materials that do not inherently include mobile ions are involved, ions present in adsorbed water layers, such as hydroxide ions, may be the species transferred between surfaces (McCarty and Whitesides, 2008).…”