Electrical charge distribution in ultrahigh vacuum fracture and etching of silicates for lunar simulation studie

Grossman, J. J.

Ryan, J. A.

Wegner, M. W.

English

NASA Technical Reports Server

-(
S	
AM5? q- 10322 
TAL	 ESTICTION OF ULTRAHIGH VACUUM ADHESION 
AS RELATED TO THE LUNAR SURFACE 
EIGHTEENTH OUARTERLY PROGRESS REPORT 
1 APRIL 1969 THROUGH 31 JUNE 1969 
CASE FILE
COPY 
J J Grossman 
Principal Investigator 
J. A Ryan 
Co-Principal Investigator 
M. W. Wegner 
Co-Principal Investigator 
R&D/Space Sciences Department 
•	 Prepared for: 
NASA Office of Advanced Research 
and Technology 
Washington, D.C. 
S	 Contract NAS7-307	 S 
	
•	 Date of Issue: 
	
•	 26 June 1964 
MCDONNELL DOUGLAS ASTRONAUTICS COANY 
WESTERN DIVISION 
MONICA, CALIFORNIA 90406 
https://ntrs.nasa.gov/search.jsp?R=19690021504 2020-03-12T03:38:22+00:00Z
ABSTRACT 
Non-polygonized dislocation arrays in naturally deformed 
olivine were observed for the first time on each of the 
rincipa1 crystallographic planes. Improved replication 
nd etching t&chniques have provided sharp etch figures 
which will be impptant for studying the Apollo lunar 
samples. 
•	
A synthetic CaF 7 crystal was cleaved on its close-packed 
: (111) plane in UHV and a charge distribution observed. 
Since the crystal is relatively pure and uniform (optical 
grade), the electrostatic charging is most probably strain 
induced.	 •
1
-	 TABLE OF CONTENTS 
A3STRACT 
110 INTRODUCTION 1 
11 General i 
1,2 Objectives i 
1.3 Approach 1 
1,4 Items of Interest 2 
2,0 EXPERIMENTAL RESULTS 3 
2.1 Defect Etching 3 
22 Electrostatic Charging 4 
30 DISCUSSION 6 
3.1 Defect Etching 6 
3.2 Electrostatic Charging 7 
40 FUTURE WORK 8 
REFERENCES 8
11 
100	 Introduction '• 
li	 Genera 
This report presents a summary of work accomplished during the period 1 
April 199 through 31 June l969 on the study of the ultrahigh vacuum 
adhesion of silicates as related to the lunar surface. This work is be-. 
ing conducted for the Office of Advanced Research and Technology, National 
Aeronautics and Space Administration, under Contract NAS7-307 
l2	 Objectives	
0 
T-ie gnaral urposes of this program are (a) to obtain quantitative ex-
data concerning the origin of the electrical charge distribu-
s produced by the ultrahigh vacuum fracture of various silicate minerals 
and model materials, (b) to achieve an understanding of the mechanisms 
responsible for the observed charge stability in relationship to the lunar 
environmnt, (c) to apply etching techniques to a variety of possible itinar 
1icatas including shock-loaded and/or radiation damaged materials, (d) 
apply the results to further, understanding the possible effects of environ-
ent on their structure in preparation for analyzing the lunar materials 
returnad by Apollo, and (e) attempt to obtain information concerning bond-
ing of crystal grains In polycrystalline rocks. 
Approach	
0 
'he approach used during--this report period has been (1) to cleave sili-
cates at ultrahigh vacuum and measure the.electrostatic charge distribution 
produced (2) to obtain microchemical and inicrophysical profiles on the 
1
cleaved ,urfaces and (3) to apply defect etching techniques to a variety 
of posibie lunar silicates 
Approach (1) serves to provide'rovid information on the origin and dynamics of 
the observed electrostatic charging and stability in dielectrics cleaved 
in u1rhigh vacuum. ' Approach (2) serves to provide direct evidence of 
the raltive roles played by composition gradients dislocations, and stress 
t^:arrs in electrostatic charging and the potential influence on stability 
lunar environment Approach (3) serves to provide information about 
ti s'cructure of dielectrics including those which are shock loaded and/or 
radiation daiiaged to aid' in recognizing shock and radiation effects in the 
inar samp le returned by Apollo. Approaches (2) and (3)' also serve 	 to pro-
vide information on intergranular bonding in polycrystalline rocks which 
will provide information concerning the basic adhesion and cohesion machan-
ismi and how these compare with previous observations. 
Items of 'Interest 
A review lecture on "Ultrahigh Vacuum Adhesion" was presented at the Carnegie- 
'l1on University, Pittsburgh, Pennsylvania, April 17, 1969, A paper "Elec-
trostatic Charge Distribution Measurements on Ultrahigh Vacuum Cleaved Di-
clectrics," was presented at the Southwest Regional Symposium of the American 
Vacuum . Society, May 7-9, 1969.'  
2
	2.0	 Enerimznta1 Results 
	
2,1	 Da-fact Etching 
The chemical etching survey of crystalline structure defects in silicate 
air.era1s is being continued. New selective etchants for orthoclase and 
albita reveal in greater detail the dislocation structure of perthites 
in orthoclase. Etchants:which have been used are: Etchant I6 (see 17th 
Quart Report) and etches based on combinations of fluoroboric or hydro-
fluosilicic acids, respectively, with a complexing agent and an additive 
actin a's an etch inhibitor. The H 2SiF6 solutions etch the (10L) and 
(1OL ? ) planes at different rates 9 revealing more distinctly a difference 
WeCIi the two sides of the perthite-orthoclase interface. 
'Tetur1ly deformed single crystal olivine has been polished and select-

veiy etched, revealing deformation bands and dislocation etch pits on 
he (010) plane (Ref. 1 9 2). The orthorhombic crystal was X-ray oriented, 
cut, and polished on the three orthogonal crystal planes (010), (001), 
,and (100). The deformation bands ( see Figures 7 and 8a, 17th QuartQ 
Report) are mostly parallel to (lOG), with a few parallel to (001). 
non-destructive surface replication technique has been developed in 
which 'a carbon-Pt layer deposited on the crystal surface is covered with 
a numbur of thin layers 'of plastic, The dried composite is pulled off, 
1eavg the crystal surface undamaged. The plastic is subsequently dis-
solved 9 leaving the positive replica. When the surface is ordinarily re-
plicated by direct carbon-Pt deposition, a chemical etchant such as HF' 
3
is used to undercut the adhering film, thus' destroying the surface of the 
crystal being replicated. 
Non-destructive, positive replicas of olivine, etched with #6 etchánt (see 
P. 3) show that the etch pits on (010) are elongated in the (100) direction. 
When the crystal contains low-angle grain boundaries, the angle between ad-
jacent grains can be calculated by measuring the average spacing between 
dislocations in the boundary, This angle is equal to the tangent of the 
ratio of the cell constant (in the direction the dislocation spacing Is mea-
sured) to the average dislocation spacing. Angles up to one degree have been 
observed in single crystal olivines. 
Natural radiation fission damage has been observed in biotlte mica using 
theetch-pit method and employing the #6 etchant (see P. 3). Dislocation 
etci pits, local defect pits, and radiation damage tracks were revealed 
inultaneously. 
A ries of silicate minerals have been collected for etching studies, after 
being exposed to 100 keV protons. Darkening and refractive index changes 
• have been observed,
	 . 
2,2	 Electrostatic Charging 
242l	 Run No., E-11
0
 Calcium Fluoride (ill) 
A cylinder was ultrasonically cut perpendicular to a (111) face of a pure 
synthetic CaF2
 crystal (Harshaw Chemical Company, optical grade). Although 
CaY7
 cleaves easily and perfectly on (111) faces in air using a thin blade, 
4
the wide Wedge used previously with the very brittle silicates gave rela-
tively poor results with CaF 2 in ultrahigh vacuum. Figure 1 shows the 
surface topography after cleavage. The octahedral face marked (o) prob- 
ably chipped after cleavage due to an anvil pressure point. Four distinct 
cleavage planes are visible marked A through D. The step between A and B 
is shallow compared with B to C which, in turn, is larger than the C-D 
step . Fracture lines are visible on the. A and B faces and are sketched 
in on the left side. 
The electrical charge distribution at the-crystal periphery is shown in 
-10 
Figure 2 about 10 minutes after cleavage at 10 torr. A pressure burst 
was observed in the 10 range. The highest positive peak'corresponds to 
the plane D and the broad minimum is the notch region. The second post-
Ive peak is roughly at the A-B intersection, and the smaller negative 
eak corresponds to passage 'over the octahedral plane (o). 
The charge distribution became erratic after 15 minutes (shortly after 
Yure 2) and the peak at D split into a double peak. In retros pect, it 
appears that at this time the crystal fractured inside the collar, At first, 
electrostatic and mechanical forces held the crystal fixed. However, after 
24 hours it became apparent that the crystal was moving far enough up and 
down in the collar that the point D was periodically contacting the probe 
cn each revolution. This destroyed the gold guard-plane film on the glass, 
and the run was terminated.
5
3.0	 Discussion
 
31	 Defect Etching 
The complex inorganic and organic etchants developed for feldspars show 
promise for application as selective etchants for other silicate mineral 
crystals including lunar samples. Factors found in the new etchants pro-
moting selectivity to dislocation etching in silicate mineral crystals 
are. the slight solubility of silicates in the complex fluorine acids, 
comolexing of the crystal cations with various organic acids, and the addi-
tion of inhibiting salts, whose cation radii are close to the size of the 
crystal cation radius. 
Voids in small grains and aggregates and
. the random orientation of crys-
tallites have caused problems in obtaining uniformly smooth, polished sur-
faces for etching. A new approach to encapsulation of small grains and 
aggregates by imoregnating them with a plastic or other material prior to 
embedding in an epoxy resin is being investigated. 
Tha artifact problem in preparing sheet plastic replicas (that is, elon-
gated streamers generated by plastic adhesion) hs been minimized b y
 limit-
log the amount of solvent used and thoroughly drying before stripping the
 
plastic replicas from the surface. 
A n on-destructive method of obtaining-Positive replicas has yielded even 
better electron photomicrographs from etched orthoclase and olivinecrys- 
ta! curfaces, Individual variations of replication methods are necessary, 
6
depending on the crystal surface structure and chemical compatibility 
with solvents used in replication. 
Etching of defect structures in olivine crystals presented new problems 
(which is true of each mineral class). Since polishing and etch rates 
differ on all three orientations due to hardness anisotropy and surface 
free energy respectively, difficulty has been observed in simultaneous 
etching of the three faces.. It seems that the (001) face is the fastest 
etching one using the #6 etchant. The observation of deformation bands 
in olivine shown in part in the 17th Quart. Report, Figures 17 'and 18, 
consisting of dislocation multiplication etch-pit arrays at the end ,of a 
low-angle grain boundary on the (001), (010), and (100) faces of olivine, 
have not been reported so far in the literature for naturally deformed 
crystals 
32	 Electrostatic Charging. 
Run E-ll''is the first run with a pure, synthetic model material. It thus 
seems reasonable to conclude that electrostatic charging is related main 
ly to crystal deformation 'in such a crystal. The peak charge distribu-
tions in Runs E-5 and E-6 with orthoclase suggest a pressure point at the 
anvi1. The octahedral,. face (o) seems to be the pressure point equivalent 
in this CaF7 cleavage. However, since a charge distribution map could nOt 
be made (due to the second spontaneous cleavage inside the crystal collar), 
the charge could be uniform on a given plane and the electric potential 
could ba varying only along the steps between the planes. If this is true, 
then deformation alone would not account for the charge. Experimental evi-
dence on this point should be an important key to determining the dominant 
charging mechanisms, unambiguously.
P:4
4.0	 Future Work 
Defect etching will be e:xtended to other silicate rock-forming minerals 
and to randomly oriented surfaces and crystalline aggregates. The etch-
p it ihod applied to naturally deformed minerals will be extended to 
shc loaded samples. Radiation effect studies will be continued. E1e- 
trical charge distribution measurements on cleaved model materials will. 
be continued and attempts niade to obtain more perfect CaF 2 cleavages. 
• . References	 . .	 . 
Ra1eigh C. B., Fabrics of Naturally and Experimentally Deformed 
•	 Olivine, 1963, Ph.D thesis, UCLA. 
2	 •	 Raleigh., C. B. Mechanisms of Plastic Deformation of Olivine, 
J.Geovs0RQs., 73, 5390-5406 (1968). 
8
n 
ii 	
.J• 
'; V 
.•	
// 
/
\	 / 
.1
ci 
Figure 1 Surface.
 topography of CaF crystal, Run R-11. 
A B C, and D are the four main (11) cleavage planes, 
and the plane (o) is another octahedral plane which in- 
tersects the (111) Diane.
100 mV Scale 
D 
Figure 2. Charge distribution on CaF 2
 crystal cleaved at 
l0	 torr, Run E-ll. The ordinate is charge in arbitrary. 
units and the Abscissa is crystal rotation angle.


Experimental investigation of ultrahigh vacuum adhesion as related to the lunar surface Quarterly progress report, 1 Apr. - 31 Jun. 1969

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