Three-step thermal process quantitatively determines the hydroxyl content in samples of magnesium oxide. Analytical method can be adapted to large-scale production of hydroxyl-free magnesium oxide

Blosser, E. R.

Hall, E. H.

Iden, R. B.

English

NASA Technical Reports Server

NASA TECH BRIEF 
To Liquid N2 Trap 
& Mass Spectrometer 
Reaction Vessel
02 
April 1970
	 Brief 70-10017 
NASA Tech Briefs announce new technology derived from the U .S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Determination of Hydroxyl Content 
in Impure Magnesium Oxide 
Schematic of Laboratory Apparatus for OH Determination 
The problem: 
To devise an analytical method for the quantitative 
determination of tle hydroxyl (0!-!) content in sam-

ples of magnesium oxide (MgO). Most of the impuri-

ties present in MgO can readily be determined by 
standard chemical and instrumental methods. How-

ow-
ever,r, there has been no reliable method for determin-
ing the amount of OH present in samples of MgO con-
taining this impurity. Attempts to liberate OH (in the 
form of H20) from samples of MgO by raising the 
temperature to as high as 3300C failed to give repro-
ducible results. Reduction with carbon at elevated 
Alm	 (continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned-rights.
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temperatures was also unsuccessful. Mass spectro-
graphic methods are subject to inaccuracies, especially 
at high OH -content. Infrared methods are feasible only 
for transparent forms of MgO, and these methods do 
not enable the analyst to differentiate between the OH 
bound in the superficial H20 associated with the MgO 
and the OH chemically bonded to the magnesium (as 
in Mg(OH)2, for example). 
The solution: 
A three-step thermal process based on hypothesis 
and experimental work indicating that the OH may be 
associated with the MgO in three different ways: (1) in 
superficial H20 adsorbed on the MgO particles, (2) 
chemically bound OH in the form of Mg(OH) 2 , and 
(3) chemically bound OH that substitutes for an 0 
atom in the lattice and is present as Mg-OH. The OH 
in the latter chemical spcies is by far more tightly 
bound than the OH in Mg(OH)2 and cannot be lib-
erated (in the form of H 2 0) in a- reproducible manner 
by heating alone as in the case of Mg(OH)2. The key. 
(third) step in the process is the conversion of Mg-OH 
to Mg(OH)2 by heating the sample in an oxygen at-
mosphere. 
How it's done: 
The weighed sample to be analyzed is first heated at 
100°C in a vacuum (maintained in a degassed reaction 
vessel) for at least 30 minutes. During this step, surface 
water is liberated from the sample and the resultant ef-
fluent (water vapor plus other gases) is condensed in a 
liquid nitrogen trap. The trap is then isolated and 
warmed to expand the gases into a known volume at a 
measured pressure, and the amount of water in the gas 
is determined by mass spectrometry. In the second 
step, the sample is heated in the evacuated reaction 
vessel to 500°C, and the evolved water is analyzed as in 
the first step. The reaction in this step is represented by 
Mg(OH)2—.MgO+H20. In the final step, which is 
the new feature of the method, the sample is heated
at 500°C in an oxygen atmosphere to convert the 
tightly bond Mg-OH to water in accordance with the 
following equations: 
2Mg. OH + 1/202—. Mg(OH)2+ MgO
Mg(OH)2—.M90+H20 
The 02 pressure in this step can range from 1 to ap-
proximately 130 torr, and the water evolved is analyzed 
as in the preceding steps. The OH corresponding to 
the water released from the sample in each of the three 
steps is calculated from the stoichiometric relation, 
OH/H 20. The total OH, or the portion corresponding 
to the water released in each step, can then be expressed 
in weight percent of the sample analyzed. 
Notes: 
1. With suitable modification, this analytical method 
can be adapted to large-scale production of OH-
free MgO. 
2. The following documentation may be obtained from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: NASA-CR-96385 (N68-33378), 
Development of Chemical Analysis Tech-
niques for Advanced Materials 
Patent status: 
This invention is owned by NASA, and a patent ap-
plication has been filed. Royalty-free, nonexclusive 
licenses for its commercial use will be granted by NASA. 
Inquiries concerning license rights should be made 
to NASA, Code GP, Washington, D.C. 20546. 
Source: R. B. Iden, E. R. Blosser, and E. H. Hall of 
Caltech /J PL 
-	
-	 under contract to 
NASA Pasadena Office 
(NPO- 10774)
. 
is 
Brief 70-10017	 Category 04


Determination of hydroxyl content in impure magnesium oxide

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