Experimental characterization of particle wall-loss behaviors in UCR dual-90m3 Teflon chambers.

Particle size dependent wall-loss rates vary widely between Teflon environmental chambers. For instance, the UCR/CE-CERT dual-90 m3 collapsible Teflon chambers (UCR collapsible chamber) measured particle wall-loss rates are relatively insensitive to particle size, while other chambers (e.g., Caltech, GaTech, UC Davis) exhibit a strong dependence of wall loss rates on particle size. Particle wall loss rates in the larger UCR collapsible chambers exceed those reported for some smaller volume chambers. The size-dependent particle wall-loss patterns in the absence of coagulation within the UCR collapsible chambers were experimentally characterized in this work using a monodisperse particle injection method. Electrostatic charges on chamber surfaces were found to dominate the particle deposition in the UCR collapsible chamber. Charged particles ∼50 nm in diameter decay much faster than charged 200 nm particles, but the overall decay enhancement by electrostatics was determined to be smaller for 50 nm particles due to kinetic charging limitations. Particles in the chamber, regardless of initial charge state, approached a chamber-specific charge steady-state, where the charge steady-state for smaller particles was driven by preferential loss of charged particles while the charge steady-state for larger particles was driven by bidirectional diffusion charging. Coagulation was found to be significant when high particle number loadings are present (e.g., 5 × 104 cm−3). Mitigation strategies are needed for environmental chambers susceptible to surface charging (e.g., UCR collapsible chambers) in order to lower the influence from electrostatics. The shape of the particle wall-loss pattern can be used to identify chambers driven by significant electrostatic particle wall-loss. [ABSTRACT FROM AUTHOR]