Peterson 
face irregularities and corrosion, Second, an attempt was made to 
increase the wettability of the solid in order to promote wetting of 
microscopic crevices by the water. 
Electron probe microanalysis of the gold plated copper head- 
forms was carried out. In the secondary electron mode of operation 
no copper x-rays were found that would have indicated a pore in the 
plating. Although resolution was limited to lum, experience with 
gold plated materials of this type leads us to suspect that no pores of 
smaller size were present, 
A scanning electron microscope was used to study the surface 
features of both the plastic (DELRIN) and metallic (gold plated) bo- 
dies. The most significant surface feature on the gold surface was 
the scratch shown in Figure 15, All surface scratches were less than 
0.5 wm across and shallow. All protuberances appeared to be less 
than 0.2 yum. The plastic surface shown in Figure 16 can best be 
characterized as consisting of a series of shallow scratches, the width 
of which are larger than the typical surface roughness element. 
High speed photography gave no macroscopic indication that cavities 
repetitively occurred from any single location. 
The gold plated bodies were coated with 1% colloidal silica and 
the plastic headform surface coated with a positive sol also of 1% 
concentration. This procedure is described in detail in Appendix B. 
The results of studies on various surface treatments can be 
summarized as follows : 
a. Gold plating a copper headform to give a smoother surface 
did not change a, , 
b. Colloidal silica coating on the gold plated surface did not 
change gs 
c. Use of a positive sol on the plastic headform did not 
change og 
It is concluded from these studies that cavity nucleation was 
not significantly affected by roughness elements or from gas trapped 
in hydrophobic crevices on the solid surface of the headforms. 
D. Boundary Layer Separation 
Separation of the boundary layer could have a strong influence 
on the local velocity and pressure distribution of the headform. As is 
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