Electro-erosion of metal surfaces
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the latter type of experiment are suspect since built up ridges form around the c r a t e r following a discharge and affect subsequent discharge events by reducing the effective distance between electrodes. I. E X P E R I M E N T A L
PROCEDURE
The electrical circuit used to produce the discharges (Fig. 1) and the discharge fixture have been discussed previouslyfl The metals studied in these experiments, their purities, and the methods used to refine them are shown in Fig. 2. The Mg, A1, and Ni electrodes were 1 cm in diam by 1.5 cm long. The remainder of the specimens were discs 1 cm in diam by 4 mm long brazed to an OFHC Cu base such that the overall dimensions of all samples were identical. Nb, Ti, and V electrodes required a Ag-Ti vacuum braze. A final polish with 0.03 ~m AlaOs was applied to all specimens with the exception of A1 and Mg for which the final polish was made with 0.3 ~m diamond paste. Precautions were taken to prevent contamination of the softest specimens (A1, Mg, and Cu) during the polishing steps. After polishing, the samples were rinsed in water followed by ethanol and finally cleaned ultrasonically in ether-petroleum. The samples were then kept in a desiccator until ready for testing. During a typical experiment the samples were placed in the discharge fixture which was i m m e r s e d in fresh kerosene. The kerosene used in these experiments was chemically analyzed by flame spectrophotometry and found to contain 85.88 pct C, 13.63 pct H, and 0.49 pct sulfur, nitrogen, oxygen, and impurities. The electrodes were slowly brought together by means by a differential screw drive until breakdown occurred in the dielectric and the fixed capacitor was discharged. The applied voltage was fixed and the gap spacing could be measured to within 1 ~m. o
~
N
1 Fig. 1--Eleetrieai circuit used to produce the discharges. R = 10 ka and C = 25~f. VOLUME 5, MARCH 1974-695
Mg
AI 99. 999~ HZR
99. 995~ HZR
Ti )9.975 EBM
Sc
V Cr } 9 99% 99, 996% EBZR VC
99.N9i95
]99.85%[ .....
IRIV~CO J_ - -
Cu Zn 99. 9990 99.999~ EBM HZR
EBM
I_. . . . . Zr
Nb
Pd
Mo
99. 9 9 % EBZM
L
L . . . .
Ta W 99. 996 { 99. 999' EBM EBZR
Hf
Fig. 2--A portion of the periodic table indicating the metals used in these experiments, their purity, and the method of refinement.
Ag
99.992~/c EBZR
Pt
!
! !
..... Au
! I I
t.--
I
E B Z R = E l e c t r o n B e a m Zone Refined HZR = H o r i z o n t a l Zone Refined E M Z M = E l e c t r o n B e a m Zone M e l t e d EBM = E l e c t r o n B e a m M e l t i n g VC = V a c u u m Cast
Present
Study
Tablel. Experimental Breakdown Electric Fieldsfor 180mJ Single Dischargesin Kerosene
d(#m)
e(lOsV/m)
Zn
Mg
Cr
V
Fe
Ni
Cu
AI
Mo
Ta
Nb
Ti
W
100 11
89 14
84 14
76 16
71 17
69 18
63 19
61 20
48 25
46 26
23 52
22 55
13 92
Table II. Experimental Breakdown Electric Fields as a Function of Applied Electrical Energy for Single Discharges in Kerosene Ni V (volts)
30 60 90 120 240
Mg
Cu
AI
d e d e d e d e (pm) (10SV/m) (,am) (10SV/m) (/.tin) (10SV/m) (pm)
Data Loading...
