Biomedical Engineering Reference
In-Depth Information
surface coating, and also alleviates the problem of oxidation inherent to the
thermal spray process (Fukanuma et al., 2006). This discovery led to many
subsequent future studies investigating the potential of depositing a wide range
of materials onto various substrate types. Research such as that completed by
Klinkov, Kosarev, and Rein (2005) attempts to quantify the effects of particle
size and velocity on the potential for particles to bond to substrates. While
some studies of this nature have been completed, the study of bonding solid
phase particles to substrates through impacts remains very young, with many
effects of variables unexplored.
Klinkov (2005) theorizes bonding mechanisms in particle impacts are
thought to be mechanical interlocking, repeated impacts, sticking, and
topochemical reactions. Grujicic (2003) additionally suggests atomic diffusion
and surface adhesion, while Assadi (2003) refer to the adiabatic shear
instability mechanism, similar to the mechanical interlocking idea referred to
by Klinkov (2003). Methods employed to measure speeds of particles in the
cold gas process include an imaging technique with a pulsed laser (Raletz et
al., 1998), and a method utilizing slits in a mask, paced in front of a detector,
to measure the velocity (Fukanuma et al., 2006). The accuracy of the imaging
technique is claimed to be 2%, while the authors do not provide the accuracy
of the technique employing the mask with slits in front of the sensor. Existing
devices for pneumatic firing of particles include cold gas dynamic spray
devices (Hermanek 2002), pneumatic capillary guns (Rinberg et al., 2005),
pneumatic pipe guns for plasma fueling (Viniar and Sudo, 1996; Frattolio et
al., 1999), and gas guns of various sizes developed by NASA to study debris
impacts. Combs, Foust, and Gouge (2004) present a fast-acting valve,
electromagnetically operated, with a claimed opening time of 2 ms. A similar
type of valve is presented by Shen et al. (1994) with a claimed opening time of
20-800 µs. Baksht and Fedyunin (1989) measured opening times for Mylar
diaphragm valves, also knows as burst discs, to be 60 µs.
3.
D
EVELOPMENT OF
E
XPERIMENTAL
A
PPARATUS
3.1. Vacuum-Powered Projecting Gun
A vacuum-powered particle-projecting gun has been used as a
demonstration device. It fires balls with a muzzle velocity that can exceed 700
feet/sec. The gun is simply a long tube with sealed ends, from which air has
been removed. The gun is fired by puncturing the seal on one end of the gun
