A method of preventing oxidation of graphite fireproof material is given. A blend of 1 to 33 weight parts alumina and 3 to 19 parts of K2O + Na2O in 100 parts of SiO2 is pulverized followed by addition of 5 to 160 parts of silicon carbide powder in 100 parts of the mixture. This is thoroughly blended and coated on the surface of graphite fireproof material

Suzuki, H.

Yamauchi, S.

English

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NASA TECHNICAL TRANSLATION
	 NASA TM-76786
METHOD OF PREVENTING OXIDATION OF GRAPHITE FIREPROOF MATERIAL
S.YAMAUCHI, H. SUZUKI
(11A5A-T11-76786)	 HETHCD OF FAETENTING	 N82-1618J
OXIDATION OF GHALHiZE FIEEFECCF MATERIAL
(National Aeronautics and space
Adainistration) 10 p HC A02/8F A01 CSCL 11D	 UnclasG3/24 07984
Translation of Japanese Patent Disclosure Number 29-3485 (1954)
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546	 DECEMBER, 1981
https://ntrs.nasa.gov/search.jsp?R=19820008307 2020-03-21T10:43:56+00:00Z
NASA TM-76786NASA TECHNICAL TRANSLATION
METHOD OF PREVENTING OXIDATION OF GRAPHITE FIREPROOF MATERIAL
S. YAMAUC :II, H. SUZUKI
(NASA-TM-76766) METdCD OF PEEVENTING 	 N82-1618)
OXIDATION OF GRAkhLIE FIFtEFSCCF MATERIAL
(Natioual Aeronautics and Space
Administration)	 10 p HC A02/9F A01 CSCI 11D	 Unclas
G3/24 07984
Translation of Japanese Patent Disclosure Number 29-3485 (1954)
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHIIGTON, D.C. 20546	 DECEMBER, 1981
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STANDARD TITLE PAGE
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76786NA
11^^ 
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RO 2. Owernmono Accession Ne. ?	 Rocipient's Cetelog NO,
d. Title and Su ►tiNa	 METHOD OF PREVENTING S.	 Report Dots
naromhar 1 281OXIDATION OF GRAPHITE FIREPROOF MATERIAL
•.	 Perterming Orgomsehon Cod. ^l
7.	 Awthorls) 1.	 Performing Organisation Report No.
S. Yamauchi and H. Suzuki
10.	 work Unit No.
0,	 Ptrtorming Organisation Name and Address 11.	 Contract or Grant No,
Leo-Kanner Associates NASW-3541
17.	 T ype of Report and Period Co•ot* riRedwood City, California 94063
Translation--
12. Sponsoring Agency Name end Address
National Aeronautics and Space Adminis-
tration, Washington, D.C. 20546 14.	 Sponsoring Agency Coda
13.	 Supplementary Notes
Translation of Japanese Patent Disclosure Number 29-3485(1954) .
16.
	 Abstract
A method of preventing oxidation of graphite fireproof materia l
is given, characterized by fine pulverization of a blend of
1 to 33 weight parts alumina and 3 to 19 parts of X20 + Na20
in 100 parts of S102, *followed by addition of 5 to 160 parts
of silicon carbide powder in 100 parts if the mixture. 	 Vais
is thoroughly blended and coated on the surface of graphite
fireproof material.
17.	 Kay words (Selected by Author(s))	 11.	 Distribution Statement
Unclassified - Unlimited
T 21•19.	 Socu111y ClesNl. (oI this #*port)	 20.	 Security Closnl. lei th ' s page)	 No. of Pages	 22.
Unclassified	 Unclassified
.,.cA sin
THE PATENT AGENCY OF JAPAN
PUBLIC DISCLOSURE OF A PATENT NOTICE
Disclosure Number	 29-3485 (1954)
Int. C1. 2	 0 B 262
(20 B 5)
Date of Disclosure
Application Number
Date of Application
Applicant, Inventor
June 15, 1954
(total 3 pages)
25-10324
August 9, 1950
S. Yamauchi
Tokyo-to, Meguro-ku,
Rokugaoka 2340
H. Suzuki
Tokyo-to, Ota-ku,
Kitasensoku-cho 603
* Numbers in the margin indicate pagination in the Japanese text.
1
Method of Preventing Oxidation of Graphite Fireproof Material
Detailed Description of the Invention
Graphite fireproof material has many superior properties,
but its major defect is that it readily undergoes oxidation at
high temperatures. Consequently, graphite fireproof material is
the cause of various disturbances since it is incapable of flame
calcination and its life is drastically shortened in use.
This invention pertains to a mixture of 100 weight parts of
silicic aid (Si0 2 ), 1 t o 33 parts of alumina (Al 203) and 3 to 19
parts of alkalil metal oxide (R 20 + Na 20) which is finely
pulverized, followed by the addition of 5 to 160 parts of silicon
carbide powder. This is then coated on the surface of graphite
fireproof material and heated, readily forming a film which
prevents oxidation.
Specifically, silicon carbide would be ideal as a
constituent element of a film to prevent oxidation of graphite
fireproof material since it has intense corrosion resistance even
in relation to ash of fuel because of its great thermal
conductivity rate and radiant density. However, it must be used
in an appropriate blend since it alone does not adhere tightly to
the surface of graphite fireproof material. Such a mixture must
form a dense film at low temperatures below 900°C at which
oxidation of graphite readily occur3, and it must stably maintain
silicon carbide even to high temperatures abo ve 1400°C without
becoming fluid or bubbling.
Thus, the objective of this invention is to produce a
mixture with such properties.
The inventors have considered types of alkali (R20) (K 20 and
Na 20 separately) and have conducted detailed studies of the
reactivity of S102-Al2O 3-R20 systems with silicon carbide at high
temperatures. They discovered a mixture with the properties
suitable for the aforementioned objectives in that system.
2
Specifically, many experiments revealed that silicon carbide
usually decomposes when the temperature exceeds 1250°C when more
than 20 parts of P,O are blended in 100 parts of 510 2 , while a
sufficiently air-tight film cannot be produced below 1400°C if
the R2O content is below two parts.
Consequently, the effects resulting from changes in Al2O3
were examined in a range of 3 to 19 Farts of R 2O in 100 parts of
S1O2 . The result was that film did not tightly adhere to
fireproof material when the content of Al 2O3 was below one part,
but that abnormal erppnis on due to free silicic acid resulting
primarily from film p,-_Ling dec-eased, and that the adhesion was
good (the refractoriness declined somewhat with increase of Al2O3
up to a range of 3 to 17 parts, but it posed no practical
difficulties). In addition, the silicon carbide dial not
decompose.
However, the acidity of the mixture gradually decreases with
increase in Al 2O3 , and silicon carbide can no longer be stably
maintained at high temperatures when the content of Al 2O3 exceeds
34 parts. The material decomposes, readily producing bubbles.
Thus, it was determined that the blend of Si0 2 , Al 2O3 and
R2O should be in the range of 1 to 3; parts of Al 2O3 and 3 to 19
parts of R20 (K 20 + Na 2O) in relation to 100 parts of S1O2.
Silicon carbide is believed to readily decompose at high
temperatures in molten liquid containing alkali. Actually, in
experiments producing film by preparing a blend of clay with
feldspar, water glass or borax, either alone or blended together,
followed by adding silicon carbide to this, molten liquid
containing alkalli formed at high temperatures, decomposing the
silicon carbide, forming bubbles and destroying the film when the
composition was adjusted to prevent oxidation at low temperatures.
That indicated that this explanation is correct. However, the
results were because the compositions of these mixtures were
:side of the aforementioned constituent ranges. In particular,
3
the results were due to the fact that there were often more than
34 pt s of Al 203 in relation to 100 parts of 5102-
A more stable product at high temperatures is produced when
there is more K20 than Na20, but a fairly effective film can be
formed even if there is a large Na 20 content.
Suitable raw materials which are readily available a:.e used 	 /2
in producing the aforementioned mixture, and the content% may be
calculated and blended by the method described below. Fe203P 1490
and Ca0 are usually present to some extent in these raw
materials, but that is permissible so long as their total content
is below 7% of total S102
 in the mixture.
In calculating the blending ranges of the raw materials for
producing mixtures, the constituents of the mixture must first be
selected within the aforementioned ranges, considering the type
and use of fireproof material in which oxidation is to be
prevented. Thus, there are various raw materials such as glass
or minerals which can be the principal ingredients in S102-
alkali-, Si02-Al 2O3- or Si02-Al 203-alkali- systems, and they are
divided into those with low melting properties and those which
ars flavieproof. Since raw materials with low melting properties
generally contain considerable amounts of alkali, virtually all
of the permissible amount of alkali in the mixtures is calculated
to be supplied in these, and that amount is determined first.
Here, natural glass (obsidian, perlite or pitchatone), soda-lime
glass fragments, alkaline silicate, feldspar and other available
materials are considered to be the raw materials with low melting
properties, but there are considerable differences among these in
terms of their chemical constituents, melting points, softening
points and viscosities of molten liquids. Suitable materials
would be used alone or in various blends, depending on the
fireproof material whose oxidation is to be prevented, since they
have individual chrateristics. Next, the remaining S102 or Al203
ingredients are alloted to the fireproof raw materials. Since
4
there are many 5102-Al2O3 raw materials in the natural world, the
most appropriate of them would he selected and used as fireproof
raw materials. At this time, chamotte would be used in the raw
state as material with great calcination contraction. in
addition, adequate caution :s required regarding the use of
silica since it expands abnormally. The principles in
calculation are to allot Al 2O3 in the 5102-Al2O3 raw materials,
followed by supply of insufficient S1O2 through silica.
Slight amounts of cordierite or clay may be added in
practice to regulate the thermal expansion coefficient and to
facilitate application, but these would be treated in proportion
to the fireproof raw material, as illustrated in the example.
The fireproof degree of the film increases, but the
capability of preventing oxidation declines when an excessive
amount of silicon carbide is added to the aforementioned mixture,
while the fireproof degree declines, contraction cracks form or
the expansion coefficient increases, resulting in peeling when
the amount is insufficient. Consequently, a suitable amount in
the range of 5 to if n parts per 100 parts of said mixture would
be used depending on the uses and the type of fireproof whose
oxidation is to be prevented.
The various raw materials of the mixture are subjected to
wet pulverization and thoroughly blended, followed by the
addition of silicon carbide powder and water, forming a paste
which may be applied to the surface of graphite fireproof
material.
A method of implementation of this invention and its effects
are described in further detail in the case of a iraphite
crucible for molten metal as one type of graphite fireproof
material.
First, the ingredients of the mixture would form a
satisfactory oxidation preventive film if they are in the
aforementioned ranges, but since 19.5 parts of Al 2O3 and 8 parts
5
F	 r^ ^QANAL 'PA"It', 4^
3
^PoQR QUALITY
1
of K20 + Na 20 in 100 parts of 310 2 was discovered to be an
outstanding composition especially in a graphite crucible, they
were specified to be the constituent ingredients, and the
blending rates of the raw materials were calculated as
illustrated below.
3
1co. o ?	 ^... , >. c < r
6 fi'	 x
i^
12.3 8. CS 0.	 .ii _ 7^ 1.41
8 :. 1. i9
7	 :.• 1.67
11 15 0.05
12 da 5 2. G' 1. , --- 0.69
1 name of blended raw =terial
	
2 blending amount (weight ratio)
3 specified constituent ingredients of mixture (weight ratio)
4 etc.	 5 potassium silicate
6 natural glass 04ikawa cordierite) 	 7 soda-lime glass fragments
8 Kawabo feldspar
9 total of above raw materials with low melting properties
10 residual amounts of specified composition
11 Motoyaema clay	 12 cordierite	 L
13 petroleum wax-chamotte 	 14 Pukushima white silica
15 total of aforementioned side ingredients and fireproof raw materials
Here, the total amount of Fe 2031 MgO and Ca0 is three, which
is permissible. Each raw material of the mixture was coarsely
ground in advance and weighed out following the calculation
results, and all materials were then combined, subjected to wet
pulverization using a crucible, and 20 parts of silicon carbide
6
powder as well as appropriate amounts of water were then added to
100 parts of the mixture which was then thoroughly blended for
numerous hours, forming a suitable paste which was applied in an
even, thin coating on the surface of a crucible. After drying,
this was subjected to calcination at 1250°C. A thin film with
good oxidation prevention was formed without any oxidation on the
surface of a crucible using a down-draught kiln in calcination
without calcination by a reduction flame.
The metal of number 80 and 100 graphite crucibles
implemented by this method was melted and the durability was
compared with cases in which the preventive method was not
implemented. The results are illustrated below.
durability frequency
material with film based on this method	 30-45
material without the film 	 12-18
However, these results involve dissolution of copper at a
surface temperature of the crucible of approximately 1500°C using
a fuel oil furnace.
Oxidation of graphite is extreme when the oxidation
preventive method is not implemented when a crucible in an
oxidative atmosphere such as a fuel oil furnace is used in this
fashion. Consequently, the durability frequency is very slight,
but when this method is implemented, the durability is 2 to 3.7
times greater since the oxidation action is effectively prevented
for prolonged periods of time.
In past implementation of the invention as mentioned above,
the material was placed in a conventional reduction flame
crucible, coke or graphite powder was plugged in the spaces and
calcination was carried out, but high temperature calcination is
possible without resorting to such complicated methods and the
durability frequency can be markedly increased when the product
is used.
7
Scope of Patent Claim
A method of preventing oxidation of graphite fireprmf
material characterised by fine pulverisation of a blend of 1 to
33 weight parts alumina and 3 to 19 parts of K20 + Na 20 in 100
parts of Si02# followed by the addition of 5 to 160 parts of
silicon carbide powder in 100 parts of the mixture. This is
thoroughly blended and coated on the surface of graphite
fireproof material.
8


Method of preventing oxidation of graphite fireproof material

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