Two analytical techniques, a gold nucleation and an etch-decoration technique have been developed for determining the presence and mobility of boron in graphite

Hennig, G. R.

Montet, G. L.

English

NASA Technical Reports Server

April 1968
	
Brief 68-10102 
•1I:	 AEC-NASA TECH BRIEF 
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
.of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
AnalyticalTechniques for Determining Boron in Graphite 
fl
The problem: 
To develop rapid and straightforward analytical 
techniques for. determining the presence and mobility 
of boron in graphite. Because of the influence of 
boron on the physical and chemical properties of 
graphite, a highly sensitive analytical test for boron is 
required. The determination by spectroscopic or spec-
trophotometric methods is too insensitive and unrelia-
ble. These techniques are particularly unsuited for the 
analysis of sizable single crystals because they cannot 
be adequately powdered for introduction into spectro-
scopic electrodes. 
The solution: 
Two analytical techniques have been developed and 
tested for the determination of boron in graphite, a 
gold nucleation and an etch-decoration technique. The 
gold nucleation technique is faster, requires smaller 
samples, and is more precise at high' concentrations 
than spectrographic or spectrophotometric tech-
niques. The etch procedure, which makes it possible 
to locate individual boron atoms by electron micros-
copy, is precise at low concentrations of boron where 
spectroscopic techniques are unreliable. This etch 
technique is probably more precise than that of any 
chemical or radiochemical method used previously in 
diffusion analysis. 
How it's done: 
The gold nucleation method is based on the obser-
vation that lattice defects such as vacancies, or boron 
atoms in the cleaved surfaces of graphite crystals, 
under appropriate conditions will act as nucleation 
centers when minute amounts of gold are evaporated 
onto the cleavage surfaces.
The method was calibrated against a series of 
boronated crystals. The boronation was accomplished 
by induction heating at 2600°C for 3 hours in a 
thick'-walled graphite crucible, previously impregnated 
several times with saturated solutions of boric acid. 
The boronated crystals were mixed during impregna-
tion with powdered spectroscopic graphite, which was 
subsequently analyzed. It was assumed that the boron 
content of the crystals equaled the analyzed content of 
the powder. Comparison of the spectrographic anal-
ysis of the powder with the nucleation density on 
the, crystal indicated that the nucleation efficiency 
of boron is only about l%, but the technique is rapid 
and applicable at high concentrations where the etch-
decoration technique fails. 
The etch-decoration method is based on the obser-
vation that the carbon atoms surrounding a boron 
atom in the surface are as reactive chemically as the 
atoms surrounding a lattice vacancy in graphite. If 
cleaved crystals are gently oxidized, the enhanced 
reactivity at vacancies and at boron atoms causes these 
defects to expand into monolayer depressions in the 
cleavage surface. These monolayer depressions, desig-
nated as loops, can then be enhanced by gold decora-
tion and measured in an electron microscope. This 
method exhibits a high degree of reproducibility and 
reliability, particularly at low concentrations of boron. 
The etch decoration method can be used for meas-
uring the diffusion of boron parallel to and perpen-
dicular to the layer planes of graphite. 
For measurement of parallel diffusion, batch and 
constant-source diffusion methods were used. In the 
batch method, a number of crystals were contami-
nated simultaneously with boron and then heated 
(continued overleaf) 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000102 2020-03-12T05:26:41+00:00Z
individually with an electron beam gun to cause dif-
fusion of the "batch" boron. The initial impregnation 
was carried out at 1900 1 C in boronated graphite 
powder containing 20 ppm of boron. After impregna-
tion, the crystals were separated from the boron 
source by washing in acetone or by cleaving off the 
outermost layer planes. 
In the constant-source diffusion experiments, the 
boron source was a crucible machined from spectro-
scopic graphite filled with SPIL powder or boronated 
lampblack. The crucible and its charge were heated in 
a "dirty" tube furnace long enough to give diffusion 
lengths of lOi to lOOt, so that the etched loops could 
be clearly resolved. 
The diffusion of boron perpendicular to the graph-
ite layers was also determined by the constant-source 
method. 
Results indicate that the mobility of boron is not 
very sensitive to the boron concentration for B/C 
values between 10- 2 and 10-8. The diffusion con-
stants measured between 1700° and 2400°C are 6320 
exp (-157,000/RT) for motion parallel to the layer 
planes and 7.1 exp (-153,000/RT) for motion per-
pendicular to the layers.
Notes: 
1. The etch-decoration technique for determining 
reaction rates of ozone with graphite is presented 
in Tech Brief 68-10101. 
2. Additional details are contained in Journal of 
Chemical Physics, vol. 42, no. 4, p 1167-1172, 15 
February 1965. 
3. Inquiries concerning this innovation may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B68-10102 
Source: G. L. Montet and G. Hennig

Solid State Sciences Division

(ARG- 10087) 
Patent status: 
Inquiries about obtaining rights for commercial use 
of this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
Brief 68-10102	 Category 03


Analytical techniques for determining boron in graphite

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server