Note: Descriptions are shown in the official language in which they were submitted.
206~60 ` I
PA~ENT
COATI~ ~oa C~A~TC CQ~PO~ITB~
FIEL~_P~ Llay~ ON
This invention relate~ to a ceramic coating ~ox
high-tempera~ure 6ilicon carbide ceramic composites
used in gae-~ired radiant burner tubes, gas burnex -~
nozzle liners, heat exchanger6, and other furnace
components. The ceramic coating of the present
10 invention ~ubstantially matches the thermal expansion
coefficient o~ the compositQ6, thus re~ulting in a
gas-impermeable composite that still maintains its
toughnes~. The invention also relates to using the
ceramic coating to bond ceramic composites together.
BACXa~O~N~ QF ~ INVENTION
Furnace components such as radiant burner tubes
must be able to withstand high temperatures and
corrosive environmentg in industrial heat-treating and
20 in aluminum melting furnace~. Commercially-availabla
burner tubes operate in the range from about 900COC to
about 1250C and are generally metal alloy tubes, - ~ -
ceramic monolith tubes, and ceramic composite tubes.
Of the first type, niakel-based superalloy metal tubes
25 are commonly used, but are limited to the lower
temperature range of ~00-1100aC. of the second type, -~
monolithic silicon carbida radiant burner tubes are
commonly used and generally have temperature
capabilities up to about 1250C but suffer from the
30l brittle failure problems typical of monolithic ceramic
shapes. Furnace components, used in very high
temperatureE and in corrosive environments, require a
special ~election of ~aterials to avoid chemical and
mechanical di~integratlon o~ the ceramic.
35 Ceramic-ceram~c compoeites, using ceramic fibers and
cloths as rein~orcements in a oeramic matrix, are the ~ --
third type o~ tube and are frequently the most ~
~0~6460
- 2 -
desirable choice ~or u8e in high temperature,
chemically-corroslv~ environments.
OnQ type of commerci~lly-available radiant burner
tube i~ produced under the trade de~ignation "SICONEX
5 FIBER-REINFORCED CERAMIC,~ and is commercially
available from the 3M Company of St. Paul, Minnesota.
"SICONEX FIBER-REINFORCED CERAMIC" radiant burner tube
i8 a ceramic-ceramic compo~ite comprising
aluminoborosilicate fiber~ in a silicon carbide matrix.
10 "SICONEX FIBER-REINFORCED CERAMIC" radiant burner tube
is prepared by first forming a tube or other shape of
alu~inoboro3ilicate ceramic fibers (e.g., a tube or
other shape made of alu~inoboro~ilicate fibers marketed
under the trad~ d~signation "NEXTEL CERAMIC FIBERS" by
15 the 3M Company) by braiding, weaving, or
filament-winding the ceramic fibers. The ceramie fiber
shape is treated with a phenolic resin to rigidize it,
and then coated via chemical vapor deposition at
temperatures ranging from 900 to 1200C to produce a
20 relatively impermeable, chemically-re~istant matrix of
a refractory material such a~ beta-silicon carbide.
The resultant rigid ceramic compo-~ite is then useful at
high temperature~ and in corro~ive environments.
However, the utility of these materials as furnace
25 compon~nts can, depending on the degree of thelr
permeabllity to gases, b~ ~omewhat limited.
Ceramic-ceramic composites ~uch as those marketed under
the trade designation "SICONEX" by the 3~ Company are
comprised o~ relatively open networks of ~ibers and can
30 remain permeable to gases, even after ex~en~ive
overcoating with a ceramic (e.g., silicon carbide)
layer.
Whlle there have been many approache~ to sealing
cera~ic comp~site sur~aces, the~s attempts have not
35 been coupled with ~ufficient matching o~ chemical,
thermal, and mechanical properties of the coatin~ to
achieve adequate thermal and chemical behavior at
2066 16~
~ 3
extreme temperatures and rQaction conditions. Thermal
expansion coefficient matching i8 e~pecially critical
due to th~ alevated temperature~ of use and repeated
thermal cycling in typical ~urnace application
Previou~ work in this field generally i8 direct~d
to coating, sealing, or adherin~ refractory materials. ~ ;
U.S. Patent No. 4,358,500 and related U.S. Patent No.
4,563,219 dQscribe a composition for bonding refractory
materials to a porous base fabric such as fiberglass,
10 using a ~oating compri~ed o~ colloidal silica,
monoaluminum phosphate, and aluminum chlorohydrate.
The coating provides heat and flama protection to the
fibergla~6 fabric.
U.S. Patent No. 4,507,355 describes an inorganic
15 bind~r prepared from colloidal silica, monoaluminum - -
phosphate, aluminum chlorohydrate and a catalyst of
alkyl tin halide. Thi~ mixture is applied to the
preferred substrate f~bergla6s to ~orm a heat-resistant
~abric. -~
U.S Patent 4,5g2,966 teaches a method of
strengthening a substrate (fiberglass or fiberglass
composites) by impregnating the substrate with, for
example, aluminum or magnesium phosphat~, magnesium ~ ~
oxide, or wollastonite, and a non-reactive phosphate. ~-
25 This i~ deRcribed as a cement which lends ~trength to
the fiber substrat0.
U.S. Patent 4,650,775 describe~ a thermally-bonded
fibrous product wherQin aluminosilicate fibers are
~onded together with silica powder and boron nitride
30 powder. These mixtures can bs formed into different
shapes and us~d as diesel 500t filters, kiln furniture,
combu~tor liners, and burner tube~.
U.S. Patent No. 4,711,666 and related U.S. Patent
No. 4,769,074 describe an oxidation prevention coating
35 ~or graphite. A bind~r/0usp~nsion of colloidal silica,
mono-aluminum phosphatQ and ethyl alcohol is applied to
a graphite surfac~ and prevente oxidation during heat
2066 160
-- 4 --
cycli~g.
U.~. Patent No. 4,861,410 de~cribes a mathod of
~oining a metal oxide ceramic body such a~ alumina with
a paste of a 501 of a metal oxide, aluminum nitrate,and
5 silicon carbide. This method is used to repair cracks
in ceramic materials and to permanently join ceramic
structure~ togeth~r.
Silicon carbide-cerAmic fiber composites would
benefit greatly from a aoating that would protect the
10 composite~ in high temp~rature and corrosivQ
environment~. To be most effective for high
temperature u3e3, the coating needs to match the
thermal expansion coe~ficient of the composite.
In US~8 which requir~ minimal trans~er of gases
15 through the walls, the coating needs to reduce the
permeability of the silicon carbide-ceramic fiber
composite. A further nead in this field is the ability
to ad~oin ceramic composite pieces together or to patch
holes in the composite article
To date, there has not been a coating composition
which matches th~ thermal expan6ion coefficient of an
aluminoborosilicate fiber-silicon carbide-coated
composlte under high temperature conditions, limits gas
permeability and can be u~ed to adjoin the
25 aforementioned composites together. The increased use
of ¢eramic compo~ite6 in high temperature and corrosive
environments creates a need for a coating composition
with the above attributes.
30 SUMMARY OF THE INV~NTION
The preBent invention provides a f ired ceramic
composite comprising: (a) a base fabric o~
aluminoboro~ilicate fibers; (b) a carbonaceous layer
coated on tha base fabr~c; (c) a silicon carbide layer
3S coated over the carbonaceous layex; and (d) a mixture
comprisinq ~ilicon carbide and aluminum phosphate
having a molar ratio o~ ~ilicon carbide to aluminum
.. ~,,, ..... ~ .. . ~ . .
206~l~a
- 5 -
pho~phata in the range o~ about 1:1 to 50:1 and
aluminoborosilicate partiole~ in the weight range o~ -
about 0.5 to 70 weight percent of the total mixture,
coated over the Bilicon carbide layer.
The ceramic composit~ iB formed by coating a
silicon carbide coated composite of aluminoborosilicate
fibers with a ceramic precursor coating comprised of an
aqueous su6pengion of an aluminum phosphate precursor,
flakes or chopped fibers of aluminoborosilicate and ~ -
10 silicon carbide powder, flakes, or fibers. Typically,
the composite article according to the present
invention i5 impermeabl~. The term "impermeable" is
meant to denote a coating which is substantially
impermeable to gases passing through the coating. The
15 coating can be applied by spraying, dipplng, or
brushing. ~he coating i~ dried in air and then fired
to form a hard and durable coating. -
By application of this coating, the strength of
the ceram~c composite, as ~easured by internal
20 pressurization to failure, i6 equal to or slightly
higher than that of an uncoated composite tube. Thi~ ;
behavior is an important 5 indicator of the composite ~-
character of the final coated structure. It is
particularly desirable to avoid ~iring or reacting
25 compo ite material~ to a point at which the compo~ite
actually takes on the characteristic~ of a monolithic
~tructurQ. In a practical enBe ~ the re~ult of
monolithic bQhavior i~ a dramatically increased
brittlene~s of the material; hence, monolithic
30 structures are dramatically less effective for uses
which sub~ect the material to mechanical stress. A
ceramic composite having th~ coating of the present
invention result~ in a tough ~tructure and not a ~- ;
monolithic ~tructure. The coating may also ~e used as
35 a bond coating which ~ecures two ceramic substrates,
particularly tubes, together.
2~6~ -~6~
-- 6 --
In accordancs with this invention, ~ilicon carbide
ceramic compo~ites are coated with an aqueous
Buspension of monoaluminum pho~phate (Al(H2PO4) 3 flakes
5 or chopped fibers of aluminoboro~ilicate, and silicon
carbide powder. The coating iB most easily applied by
brushing it onto the composite surface, although other
application method~l such as dip coating or spraying,
could be used. once the coating is applied to the
10 composite, it i8 allowed to air dry, and then fired to
about 1000C to form a hard and durable ceramic
coating.
There ar~ many sil~con carbide ceramic composites
which could be used in con~unction with the coating
15 compositions o~ the present invention. One brsnd of
composite i~ the afore-mentioned "SICONEX
FIBER-REINFORCED CERAMIC," commercially available from
the 3M Company, St. Paul, Minnesota. These composites
are formed by first braiding, weaving, or filament-
20 winding ~ibers of aluminoborosilicate (sold under thetrade designation "NEXTEL 312 CERAMIC FIBER," having an
alumina:boria mole ratio of from 9:2 to 3:1.5 and
containing up to 65 weight percent silica, as described
in U.S. Patent 3~795,524, assigned to the 3M Company)
25 to form a de~ired shape, such a& a tube. The tube is
coated with a phenolic resin in an organic solvent to
rigidiz~ ~t and thereaftsr coated with silicon carbide
via chemical vapor deposition.
The coating of the present invention is comprised
30 of silicon c~rbide, aluminum phosphate and :
aluminoborosilicate. An available source of silicon
carbide i8 available as fine abrasive powder,
commercially available from Fu~imi Kenzamaki Kogyo Co., ::
Inc., Nagoya, Japan. Other forms of silicon carbide
35 include flakes or fiber~. In the preferred embodiment,
1-50 micrometer diameter silicon carbide powder is
used.
, >~ :. ;
~ ; , . . : . ' ~
2066~6~
.
- 7 -
The precursor aluminum phosphate present in the
coating i~ prepared by discolving aluminu~ metal in
pho~phoric acid. A solution, 50 weight percent of
Al(H2P0~)3 in water, iB available from Stouffer Chemical
5 Company, Westport, Connecticut. A~ the coating is
fired, water and a portion of phosphate are released
from the aluminum phosphate solution. Thus, aluminum
phosphate is le~t after firi~g. The mole ratio of
silicon carbide to aluminum pho~phate (SiC:AlP04) in the
10 fired coating i8 preferably in the range of about 1:1
to 50:1. Most preferably, the mole ratio o~ SiC:AlP04
in a fired coating is in the range of about 5:1 to
30:1.
Aluminoborosilicat~ i~ al60 added to the coating
15 composition. This may be in ~he form of powder, flakes
or fibers. Preferably, aluminoborosilicate in the ~orm
of fibers iB used. Such ~ibers are commercially
available under the trade deeignation "NFXTEL CERAMIC
FIBER" from the 3M Company. The ceramic ~iber yarn
20 ranges in diam~ter from 11 to 15 micrometers and is
chopped by passing the yarn between two steel roller~
with knurled surfaces.- other methods of chopping
include ball milling or other methods known in the art.
The yarn i~ chopped to an average fiber length of about
.02 to .05 mm. The weight percent of the
aluminoborosilicate of the total coating composition is
in the range of about 0.5 to 70% and, preferably, in
the range o~ about 30 to 70%.
To fashion the ceramic composites for testing the ~ ~-
30 di~ferent coating compositions of the present
invention, caramic fiber braid (co~mercially available
under the trade deRignation "NEXTEL CERAMIC FIBER
BRAID" from the 3M Company) was fit onto a 5 cm
di~meter aluminum mandrel, and a solution of 10 ml of - ~-
35 phenolic reYin ~60-64% solids, commercially available --
under the trade designation "D~RITE SC-1008 PHENOLIC : .
206G -~6a
- 8 -
RESINI' from Borden Chemical, Columbu~, Ohio~ in g0 ml
of methanol was prepared. A small amount of the resin
solution was poured over the ceramic fiber tube while
rotating tha mandrel, to a~ure uniform coverage by the
5 resin. The tube was then dried in air until ~olvent
odor could no longer be detected, and then cured in air
at 200OC for 20 minute3. Thi6 process resulted in a
rigid tu~e having a golden color due to the cured
polymer layer.
The rigid preform was placed in a chemical vapor
deposition chamber, as i8 well known in the art,
wherein vacuum is applied and the chamber is heated.
Hydrogen gas was bubbled through dimethyldichlorosilane
(DDS) and passed through the CVD furnace chamber,
15 thermally decomposing the DDS which thereby deposited a
layer of silicon carbide on the preform. By-product
and unreacted gase~ exited the opposite end of the tube
to the vacuu~ pumping and ~crubbing system. Typical
process conditions for the~e sample~ were pressure~ of
20 5 to 50 torr, flow rate~ of 0.15 liters per minute(lpm)
of DDS, and 1.0 lpm of hydrogen ga~ at temperatures of ~ -
900 to 1000C. Coating ti~e6 ranged from 4 to 8
hour Under these proceqs condition6 and times, the
samplea received fro~ about 100 to about 200 weight
25 percent increase due to silicon carbide deposition. In
this process, SiC coats and infiltrates the fibers and
the re~in coat i8 also decomposed to ~orm a
carbonaceous layer on the surface of the prefor~. It
is use~ul to examine the fractured surfaces of broken
3q composites made in the abov~ manner. The fractured
surfaces re~ulted in a "bru~hy" fracture surface which
~ndicates that the coated material has composite rather
than monolithic properties, and that heating and
proces~ing 8~ep8 have not destroyed the desired
35 composite prop~rti~s.
Coupons of a fib~r-rainforced ceramic
(commercially available under the trade designation
, . .
;
~ 2~66~160
g :. .
"SICONEX FIBER-REINFORCED CERAMIC" from the 3M company~
were prepared in a manner ~imilar to the tubes, using
woven ceramic fiber (commercially available under the
trade designation "NEX~EL 312 CERAMIC FI~ER'I ~rom the
5 3M Company) fabric. Coupons were convenient for
carrying out initial studias of coating fea~ibility and
were more convenient to u8e in order to examine the
adhesion and hardne~s of ths coating. Adhesion of the
coating on an exposed edge and the performance of the
10 coated edge are also importan~ indicators of the
coating performance.
Many sizes of tubes of the ceramic-ceramic
composite were coated and tested. Permeability of the
final fired tubes was te~ted by a differential flow . ~:
15 test using a flow meter.
Though not being bound by theory, it is believed
that the coating work~ to maintain the composite
characteri6tic6 o~ its composite substrate as well a~
to match the thermal expansion coefficient of the : -
20 substrate (which is important in furnace and high
temperature application~) because th~ coating itself is
a composite material, being compri6ed of flake or
~ibers and particles in a matrix. The flake~, fibers,
and particl2s act to fill the porous site~ in the
25 matrix, thereby blocking the ~low of gas through the
porous sit~s. Further, this discontinuous phase also
deflects cracks that may initiate in the coating ~rom
mechanical or thermal 6tress~s.
'
30 Ex~mpl~ 1
Aluminoborosllicate ceramic fiber (commercially
available under the trade designation "NEX~EL CERAMIC
FIBER" ~rom the 3~ Company, St. Paul, Minnesota)
ranging ln diameter from 11 to 15 micrometers was
35 chopped by passing the ~eramic fiber yarn between ~wo
ste~l rollers with knurled surface~. This resulted in
~hopped ~iber~ with an average length of about 50
.J~"'
2 ~ 6 ~
-- 10 --
micrometer3.
To a 50 percent by weight 801ut~0n 0~ monoaluminum
phosphate, (Al(H2POj)3 oommercially available from
Stauffer, We~tport, Connecticut) was added ~licon
5 carbide powder (#1500, 8 micron, commercially available
from Pu~imi Kenmazai Kogyo Co., ~td., Nagoya, Japan)
and chopped aluminoborosilicate ceramic fiber
(commercially available under the trade de~ignation
"NEXTEL 312 CERAMIC FIBER" from the 3M Company).
10 Deio~ized water wa6 added to some mixtures to adjust
the consistency for coatability. Table I shows
compositions representing approximately 40-70% fired
solids and mole ratios of SiC to AlPO4 in the fired
product o~ from about 5 to about 20
TAB~ I COATING ~OMPOSITIONS
c~mponent ma~s.g moles SiC:AlPO1 ~ fired solids
a. Al(H2PO4)32.9 6 40 :
SiC powder1.1
alumino-
boro~ilicate
fibar
("N~XTEL
CERANIC :
FIBER") 1.3
deionized
water 2.0
b. Al(H2PO4)345.0 6 50
SiC powder 16.3
alumino-
boro~ilicat~
~iber
("NEXTE~
CERAMIC
FIBER") 11.4
deionized
water ---
2~f~6~
.
c. Al(H2PO4~3 50-0 6 55
SiC powder 1~.
alumino-
boro~ilicate
fi~er
("NEXTEL
CERAMIC
FIBER") 21.7
deion~zed
water
15 d. Al(HlPO4)3 5.0 16 69
SiC powder 5.Q
alumino-
borosilicate
fiber
("NEXTEL
CERAMIC
FIBER") 5.0
deionized
watQr 1.0 :
e. Al(H2PO4)3 1.5 20 47
:
SiC powder 1.9
alumino-
boro~ilic~te
fiber
(~NEXTEL ~ :
CERAMIC
FIBER") 1.9
deionized
water 4.0
Tube-shaped ~iber-reinforced ceramic (co~mercially
available under the trade de~ignation "SICONEX FIBER-
45 REINFORCED CERAMIC" from the 3M Company) samples weredipped in, or painted with, each coating formulation,
typically ~n only one pa~s. Coated parts typically ::
weighed 10 to 20% more than the weight of the original -~
part and had a coating thickne3s of about I mm. The
50 coated parts were allowed to dry at ambient temperature -~
2~6~6a
,,~ . .
- 12 -
and humidity for 24 hours and then were gired in air by
ramping th~ temperature at 250C per hour to 1000C,
and holding for 1 hour. Th~ coatings were hard and
durable as indicated by attempting to remove or crack
5 the coating by scratching the surface with a steel
needle. Intact ceramic fibers and particIes o~ SiC
could be seen by examination under a microscope at 50X
magnification. X-ray diffraction powder patterns of
the fired coatings showed beta-SiC, mullite, and ALP0 4
10 as crystalline phases.
Bxa~ple 2
In order to test the per~eability of a sample
before and a~ter coating, tube-shaped samples were
15 used. Through-wall permeability of two tubes (5.0 cm
outer diameter x 20.0 cm long) was measured by closing
each end o~ the tube with a one-hole stopper, and
flowing air through the tube. Air at a regulated
pre~sure of 1 atmosphere (1.03 Kg/cm2) was admitted
20 through a needle valve and monitored by a flow meter at
the inlet end of the tube. A ma~ometer at the exit end
of the tube measured the difference in pressure between
the inside of the tube (pressurized air flowing through
it) and the outside of the tube (room pressure). For a
25 particular pre6sure drop, the air flow in cm3/min is
read from the ~low meter. This flow rate, divided by
the sur~ace area of the tub~, is permeability (cubic
centimeters per minute per ~quare centimeter).
A coating of 55 weight percent fired solids and a
30 6:1 SiC:AlP04 mole rat~o (as per Example lc) was applied
to the outside surface of the tubes. The wet coating
wa6 12 to 15% of the original part weight. After air
drying, the tubes wera fired to 1000C. ~he tubes were
weighed and perme~bility checked again. Table II shows ~ -
35 weight and permeability changes: ~
20~6 ~
,~ ~
- 13 -
TABLE II PERMEABILITY DATA
. permeabil~ty
tubewei~ht(om~ %wt.aain(cm3minlcm-
coat~d coated
uncoated & fired uncoated ~_~iEÇ~
177.62 85.19 9.8%132.0 1.2
295.80 103.86 8.610.2 ~.02 ~ .
10 Gas permea~ility wa5 reduced by a factor of
approximately 100 for tube 1 and a factor o~ 500 ~or
tube 2.
~x~mple 3
15Two 5.0 x 20.3 cm fiber-rein~orced ceramic . :
compo~lte tube~ ("SICONEX FIBER-REINFORCED CERAMIC'I) ~-:
were coated as described in Example 1 with the coating
formulation of Example lc (designated A in Ta~le III,
below), and two tube~ with no coating (designated B in
20 Tabl~ III) wer~ ~ired together to 1000C for 1 hour.
All tubes were cut into 2.5 c~ long ring~ in order to
do strength te~ting.
Additional &le~ were prepared to evaluate-the ~:
coating a~ an edge protector for the fiber-reinforced
25 ceramic. Three 15.2 cm (6'l) #amples were cut from one
5.1 by 45.7 cm (2"x18") tube and treated a~ follows~
Sample C (end~ of 15.2 cm piece coated, heat treated to
1250C for 10 hour~), Sample D (cut into 2.5 (1 inch)
samples, cut edge coated, heat treated at 1250C for 10 :~
30 hour~), and Sample E (cut into 2.5 cm (1 inch) samples, .
heat treated at 1250C for 10 hours).
Burst ~trength was ~easured on 2.5 cm (1 inch) : :
rings from all tubes by internal pres6urization to
~ailure (burst test); average 5 re6ults of the samples
35 are shown in Table III.
,: .
: ,~. :,
: , . . .
2066~6~
- 14 -
TA~LE III
STRENGTH DATA
bur~t str~n~th
trea~ t aver~ge. MPa (p~ t. dev.
5 1000C, 1 hr.
A coated 65.9 (9420) 3.8 ~540)
B uncoated 64.6 (9230) 10.3 (1470)
1250C, 10 hr.
C HT. as pi~c~, cut 56 ~8000) 6.4 (920~
10 D cut, edge coated, HT. 47.9 (6840) 7.6 (1080)
E cut, no coating, HT. 37.9 (5420) 4.7 (670)
In comparing ~ample~ A and B, the burst strength
of the samples ~hows some improvement after coating.
In the data ~or Sample C (15 cm-long sample,
heated, sectioned, and tested) and E (8iX 2.5 cm ring
samples, heated, and teated), it appeared that cutting
samples before heat treating resulted in a loss of
strength o~ about 33% with uncut sample~. Cut ~ampls~
20 which were al~o edge-coated (Sample D) suffered only
about a 15% strength loss. Fracture surface of
Sample~ C and D are "brushy" (meaning individual fibers
are visible and have not fused to~ether during heat
treatment) and composite-l$ke, while fractured samples
25 of E were quite brittle with le6s evidence of fiber
pull-out. Although not intending to be held to any
theory, it is speculated that unprotected edges allow
oxygen to penetrata into the interface between fibers
and the matrix. oxidation within the matrix is
30 suspected to result in bonding between the fibers and ~
the matrix and; thus, brittle fracture behavior -
results. ~-
: ~ '
Ex~pl~ 4 -
Thrse coating formulation~ were prepared a~ ~ -
de~cribed in Example 1 with the formulation of Example
ld, except that the particle size of the SiC wa~
' ''
~ - ; , . ... , .... - .. ~ . .. .. . . . .
2066ll6~ ' :
- 15 -
varied. Th~ particle size~ were one micron, 8 mlcron,
and 50 ~icron SiC powd~rs, commercially available ~rom
Fujimi Kenmazai Kogyo Co. Ltd., Nagoya, Japan. Small
fiber-reinforced ceramic (I~SICONEX FIBER-REINFORCED
5 CERAMICI~) composit~ samples werQ painted with the
coatings and fired first to 1onooc for a period of one
hour at a heat-up rate of 250C/hour and then to 1200C
for a period of one hour. Each 6ample was hard and
durable as indica~ed by visual inspection after
10 attempting to remove or crack the coating by scratching
the surface with a ~teel needle. Thus, a wide range of
silicon carbide particle ~ize~ and a wide firing
temperature range produce acceptable coatings.
15 Ex~ple 5
This Qxample shows how the coating compo~ition3
can be used as adhesive~ to join two samples together.
To te~t for shear strength of the coating when used as
a bonding agent, 2.5 cm-long fiber-reinforced ceramic
20 tubes ("SICONEX FIBER-REINFORCED CERAMIC") of two
different diameters were used t5 cm and 4.4 cm in outer
d~ameter).
The tubes were ~oined together by fitting the
smaller diameter tub~ part-way into the larger tube,
25 6uch that th~ smaller diameter tube pro~ected 1.25 cm
out of the larger diameter tube. A 1.25 cm band of
coating (70 weight% solids) was placed on the outer
surface o~ the æmaller tube, and then a 1.25 cm wide
piece of aluminoborosilicate ceramic fiber tape
30 (commercially available under the trade designation -
"NEXTEL 312 CERAMIC FIBER TAPE" from the 3~ Company)
was placed on the coating. Additional coating was
added to the tape, and then the tube with the coating
and the ceramic fiber tape was fitted into the larger
35 tube.
Addi~ional coatlng was added to ~ill the gap
between the two tubes. ~his bonded piece was dried for
: i .. ,, ~ ~ .- ,
: : : . : ~ :.;; -
.~ . ~ - ~ : - -
.,, , ~ . . ~ ~
, ~ , ,
2066~60
- 16 -
24 hours at ambient temperature and humidity, heated
for lo hours at 110C, and ~ired for 2 hours at 1000C.
An axial co~pression te~t of the joined tubes was
carried out. In thi~ test, pressure was applied to the
5 long axis of the ~oinad tubes to try to break the
adhesive bond formed by the dried and fired coatlng
betweQn the two tube6. Axial compression tests of
fired tubes were carried out at .051 cm/min (.02"/min)
crosshead speed with an In~tron Model 1125 load frame.
10 Joints tested in this way did not fail under a 1000 lb.
(455 Kg) load at room temperature. This indicates that
the coating can be usQd e~fectively to join -
fiber-reinforced ceramic composite tubes ("SICONEX
FIBER-REINFORCED CERAMIC COMPOSITE TUBES") together.
15 This is u~eful for making T- or U-shaped ~ubes, or for
cases in which the tube diameter must change in order
to fit another piece.
A further test of the bonding ~trength o~ the
coat~ng was to rapidly cycle ~oined piece~ through a
20 heating and cooling sequenc~. Two 5-cm long by 4.4 cm ~ ~-
diameter ~ib~r-rein~orced ceramic composite tubes
~"SICON~X FIBER-REINFORCED CERAMIC COMPOSI~E TUBES")
were butt-~oined u~ing the coating composition prepared
as de~cribed above. An outer sleeve of 5 cm diameter
25 and 2.5 cm long was addQd at the joint to further
reinforce the butt-~oint. The assembled tube was dried
and fired as described abova. The ~oined tubes were
flame-cycle te~ted by heating the in~ide of the ~oined ;-
tubes with the gas fla~e of a Meeker burner to a
30 temperature of approxi~ately 800C while cooling the -~
outside of the tube with a flow of compressed air.
ThQse heat cycle~ did not cause failure of the bonds.
Further heating of thi~ heat-cycled joint for 100 hours
at 1000C in a~r caused no detectable strength change. --
~` 2066`~6~
- 17 -
æxampl~ C
In order to show utility of ths coating
~ormulations as an adhe~$ve ~or patch~ng ~iber-
rein~orced ceramic compo~it~ tubes (IlSICONEX FIBER- :
5 REINFORCED CERAMIC COMPOSI~E") composite part~
together, a coating with 70 waight% 601ids wa~ applied
by brushing ~t onto a ~iber-reinforced ceramic
composite tube ("SICONEX FIBER-REINFORCED CERAMIC
COMPOSITEII), drying in air ~or several hours, and
10 firing with a ga~-air torch of the kind typically uæed ~ ~:
for gla88 wor~ing. co~pon~ntB of the coating melted
slightly, lightened in color, and then hardened.
Th~ coating i~, thu~, effective in attaching a :~
patch ts another fibQr-rein~orced ceramic composite ~ :
15 tube ("SICONEX FIBER-REINFORCED C~SRAMIC COMPOSITE" )
with a hole in it or in bridging small gaps or crack~
in fiber-reinforced ceramic compo~ite tubes (~SICONEX
FI8E~-REINFORCED CERAMIC COMPoSITE'I) in situations
where the tubos are in need of repair and require spot
20 heat-treating. :
As will be apparent to those killed in the art, : :
variou~ other ~odif~c~tion~ can be carried out ~or the
abov~ di~closure without departing from the spirit and
25 scope o~ the lnv~ntion.
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