Coatings, consisting of zirconia powder bonded with orthophosphoric acid and a small amount of hydrofluoric acid, are hard, strong, and refractory, resist thermal shock, and provide good thermal protection. After the aqueous coating is applied to a metallic surface, only a 600 deg F cure is required before service

Accountius, O. E.

Carpenter, H. W.

Onoda, G. Y., Jr.

English

NASA Technical Reports Server

November 1970	 Brief 70-10580 
NASA TECH BRIEF 
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application. Tech Briefs are available on a subscription basis from the National Technical Information Service, Springfield, 
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nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Simple Bonding Technique for High-Temperature Ceramic Coatings 
Phosphate-bonded ceramic coatings such as zirconia 
(Zr0 2 ) have been used for many high-temperature 
applications. Such coatings, depending on formulation 
and environmental conditions, are refractory and 
reasonably chemically stable, and resist erosion. Phos-
phate-bonded zirconia is now made by mixing of zir-
conia powder, monofluorophosphoric acid, and am-
monium dihydrogen phosphate. These coatings, 
however, have proved to be unreliable at high temper-
atures because of excessive spalling or flaking. 
A recent investigation has found that the fluorine 
ion need only be present in very small concentrations 
for zirconia coatings to perform well at elevated 
temperatures. Thus the coating system can be simpli-
fied to zirconia powder bonded with orthophosphoric 
acid plus a small amount of hydrofluoric acid. 
Although a 20:1 ratio (by weight) of orthophos-
phoric acid to hydrofluoric acid produces a useful mix-
ture with good working and bonding properties, this 
ratio is not restrictive. Formulation of the coating 
depends also on the method of application: pour 
coating, dip coating, trowelling, or spray coating. 
After the aqueous slurry coating is applied to the 
metallic surface by one such method, only a 600°F 
cure is required before service. These simplified 
phosphate-bonded zirconia coatings are hard, strong, 
and refractory, resist thermal shock, and provide very 
good thermal protection. 
This coating system has survived multiple thermal 
shocks, between 70°F and temperatures above 4000°F, 
while protecting water-cooled metal substrates in 
tests with arc-plasma jets. Currently the coating sys-
tem is performing well under exposure to combustion
gases (temperature, about 5000°F) in tests with rocket 
motors; it does not appreciably erode, spall, or under-
go detrimental chemical reactions. 
This simplified bonding technique resulted from a 
continuing investigation of protective coating systems 
for regeneratively cooled rocket engines. Formula-
tion studies of phosphate-bonded thoria (ThO,) coat-
ings have produced strong, shock-resistant coatings; 
the thoria studies, however, are much less advanced 
than the zirconia developments. This bonding tech-
nique, which provides an insulating refractory coating 
that is easy to repair, should find many industrial 
uses where the substrate material is well cooled and 
the coating's surface operates at temperatures up to 
5000°F. A potential use may be in induction furnaces. 
Notes: 
1. The following documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: 
NASA-CR-72569 (N69-35125), Protective Coat-
ing System for a Regeneratively Cooled Thrust 
Chamber - Tasks I & II 
Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B70-10580
(continued overleaf) 
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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.
https://ntrs.nasa.gov/search.jsp?R=19700000562 2020-03-17T00:39:02+00:00Z
Patent status: 
No patent action is contemplated by NASA. 
Source: H.W. Carpenter, G.Y. Onoda, Jr., 
and O.E. Accountius of 
North American Rockwell Corp. 
under contract to 
Lewis Research Center 
(LEW. l 1085)
fl 
S 
Brief 70-10580	 Category 08


Simple bonding technique for high-temperature ceramic coatings

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