Further experiments on collisional tribocharging of cosmic grains

Abstract

Abstract. We experimentally investigated tribocharging in bouncing dust grain collisions under conditions which are relevant for the early solar nebula. We used silica, diamond, graphite, and silicon carbide grains and cm-sized targets of aluminum, iron, and graphite. We varied particle size around 1 µm, collision velocity between 38 to 106 m s −1 , and target temperature between 240 K and 360 K. Generally, the grains acquire something in the order of hundreds or thousands of negative elementary charges, which is at the upper end of the range previously discussed in astrophysical research. Mainly, a temperature difference caused by the dissipation of collisional energy or by initial temperatures determines the amount of charge transfer. It suggests a thermally diffusive charge transfer process of negative charge carriers. Nevertheless, also other processes of secondary importance were effective. Material-dependent contact charging is ruled out as the dominant charge transfer process in our experiments. For most particle-target combinations, the charge transfer can be described by an empirical function of collision energy which we propose for future astrophysical applications, especially for applications on the sticking efficiency in the preplanetary dust aggregation process, on the particle motion in the solar nebula, and on the possibility of nebular lightning.

The Physics of Protoplanetesimal Dust Agglomerates. I. Mechanical Properties and Relations to Primitive Bodies in the Solar System

“…These processes altered the original packing densities of the constituent particles within these porous objects, as we discuss in more detail in x 6.2. proposed another mechanism for the growth beyond the fragmentation limit, based on electrostatic charging in mutual collisions. Poppe et al (2000b) and Poppe & Schräpler (2005) showed that mutual collisions among dust grains lead to an electrostatic charging of the collision partners. A succession of nonsticking collisions between a macroscopic dust agglomerate and smaller bodies in the solar nebula can cause an accumulation of charges on the larger body, whose electrical field close to the surface, as a consequence, grows in strength.…”

“…At some critical value for the field strength, the escaping fragments, on average oppositely charged to the protoplanetesimal, are no longer able to escape the attractive Coulomb potential and are therefore reattracted to the surface of the larger body. As the mean size of the protoplanetesimals grows, the mean collision velocity, and hence the number of electrostatic charges per unit projectile mass separated in a collision, also increases ( Poppe et al 2000b;Poppe & Schräpler 2005), so that the timescales for reaching the critical electrical field strength decreases. In contrast to the abovementioned ''aerodynamic'' accretion, we call this phenomenon ''electrostatic'' accretion.…”

Quasi‐electrostatic field analysis and simulation of Martian and terrestrial dust devils

“…Upon collision, a significant amount of charge is placed on each particle. More recent studies show that the charge of dust grains after collision depend on humidity, temperature, and its velocity [Poppe and Schrapler, 2005]. On the basis of the two tribocharging scenarios and the vertical charge transport similar to the thunderstorm precipitation electrification mechanism [Mathpal et al, 1980], Farrell et al [2003] developed a fully analytical electrodynamic model of a dust devil with simplified assumptions of dust devil structures, time rate of charging, etc.…”

Electrical Activity and Dust Lifting on Earth, Mars, and Beyond

“…The simple model described by equations (1) and (2) has a functional form consistent with observations -smaller particles acquire net negative charge during collisions with larger particles, and the charge transfer increases with the relative difference in particle size. However, this model does not account explicitly for other variables that likely affect the charge transfer such as temperature, humidity (Guardiola et al, 1996) and particle speed (Poppe and Schrapler, 2005). Moreover, it assumes that particles get fully charged after a single collision.…”