Standard compositions suitable for electron probe microanalysis of various silicates are prepared by coprecipitation of specified salts with colloidal silica to form a gel which is decomposed into a powdered oxide mixture and compressed into thin pellets. These pellets of predetermined standard are compared with a silicate sample to determine its composition

Walter, L. S.

English

NASA Technical Reports Server

June 1966	 Brief 66-10234 
.	 NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Standards for Electron Probe Microanalysis of Silicates

Prepared by Convenient Method 
The problem: 
The effective use of the electron probe for micro-
analyis of various silicates is often made difficult or 
impossible by the lack of adequate standards approxi-
mating the composition of the silicate samples to be 
analyzed. 
The solution: 
Standard compositions, suitable for electron probe 
microanalysis, prepared by a method involving co-
precipitation of specified salts with colloidal silica 
to form a gel, which is then decomposed by heating 
into a mixture of powdered oxides that is compressed 
into thin pellets. 
How it's done: 
Standardized aqueous solutions of the desired salts 
(e.g., aluminum nitrate and ferric nitrate) are mixed 
with dilute nitric acid and a commercial mildly 
alkaline aqueous sol of silica to form a gel. This gel, 
which is an aggregate of the salts and silica particles, 
is rapidly desiccated by spraying it onto platinum 
foil whose undersurface is heated with a gas burner. 
The desiccated powder on the platinum foil is then 
converted into an intimate mixture of oxides by heat-
ing it in a furnace at approximately 900°C for two 
hours. The resulting powdçred oxide mixture is 
scraped from the platinum foil and formed into a 
dense, smooth surfaced, translucent pellet using a pair 
of tungsten carbide anvils with 0.25-inch-diameter 
polished faces under a pressure in the range of 30 to 
50 kilobars. The pellet is then coated with carbon and 
mounted on a microprobe specimen holder for use as 
a standard. 
Notes: 
I. The pellets are not perfectly homogeneous to the
microprobe and thus require special analytical 
techniques for their use. A suitable technique is to 
integrate X-ray counts from the pellet while it is 
slowly moved under the electron beam to average 
out local variations in composition. 
2. Only portions of the prepared solutions need be 
converted to gels and desiccated at one time. The 
remaining solutions can be stored and later modi-
fied in composition as required. 
3. The pellets can be used as standards -for micro-
probe analysis of multicomponent silicate systems 
by successive approximations. In this method a 
rough approximation of the silicate sample com-
position is made and a suitable standard prepared. 
Comparison of the sample with this standard will 
indicate the composition of a second standard that 
more closely approximates the sample composi-
tion. This process is repeated until the desired 
precision is obtained. 
4. These easily prepared standards are useful when 
more homogeneous, stable crystalline or glassy 
standards are not available. 
5. Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland 20771 
Reference: B66-10234 
Patent status: 
No patent action is contemplated by NASA. 
Source: Louis S. Walter 
(GSFC-469) 
Category 03 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person 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 such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19660000233 2020-03-11T17:32:18+00:00Z


Standards for electron probe microanalysis of silicates prepared by convenient method

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