A family of tantalum-based ceramics has been invented as ingredients of high-temperature composite insulating tiles. These materials are suitable for coating and/or permeating the outer layers of rigid porous (foam-like or fibrous) ceramic substrates to (1) render the resulting composite ceramic tiles impervious to hot gases and (2) enable the tiles to survive high heat fluxes at temperatures that can exceed 3,000 F ( 1,600 C)

DiFiore, Robert

Kalvala, Victor

Leiser, Daniel

Stewart, David A.

NASA Technical Reports Server

18 NASA Tech Briefs, June 2006
that most of the interior of the material
is accessible for intercalation of lithium.
Moreover, the greater accessibility of
SWCNT structures can be expected to
translate to greater mobilities for ion-ex-
change processes and, hence, an ability
to sustain greater charge and discharge
current densities. 
For the experiments, soot containing
carbon nanotubes was produced by laser
vaporization of a graphite target con-
taining 1.2 atomic percent Ni/Co in an
argon atmosphere at a pressure of 500
torr (≈ 67 kPa) at a temperature of 1,200
°C. The soot was purified by refluxing in
nitric acid at a temperature of 125 °C fol-
lowed by annealing in oxygen at 550 °C
for 30 minutes. By means of scanning
electron microscopy, transmission elec-
tron microscopy, ultraviolet-visible spec-
trophotometry, and thermogravimetric
analysis, 99 weight percent of the puri-
fied soot was found to consist of SWC-
NTs. The specific surface area of the pu-
rified material, as measured by use of
the Brunauer, Emmett, and Teller
(BET) technique based on adsorption of
nitrogen, was found to be 1,200 m2/g —
much greater than the specific surface
areas of several other carbonaceous
anode materials that were also subjected
to the BET test. 
Anodes were fabricated by casting,
onto copper foils, thin films of the puri-
fied SWCNT material dispersed at a con-
centration of 5 weight percent in
poly(vinylidiene fluoride). The anodes
were incorporated into standard three-
electrode test cells along with lithium-foil
counter and reference electrodes and an
electrolyte comprising 1.0 M LiPF6 in a
solution of ethylene carbonate (2 parts by
volume) and dimethyl carbonate (1 part
by volume). Over-potentials for interac-
tion of the anodes with lithium and
lithium capacities of the anodes were
measured by use of cyclic voltammetry
and galvanostatic cycling, respectively. 
The figure shows representative
charge and discharge capacities deter-
mined from the measurements. The
plotted values show a high degree of re-
versibility after the initial cycle. The
specific capacity after 30 cycles was
found to be about 1.33 Ah/g — almost
3 times the generally accepted value
(0.45 Ah/g) for graphite. 
This work was done by Aloysius F. Hepp
of Glenn Research Center; Ryne Raf-
faelle and Tom Gennett of Rochester Insti-
tute of Technology; Prashant Kumta and
Jeff Maranchi of Carnegie-Mellon Univer-
sity; and Mike Heben of National Renewable
Energy Laboratory. Further information is
contained in a TSP (see page 1).
Inquiries concerning rights for the com-
mercial use of this invention should be ad-
dressed to NASA Glenn Research Center,
Commercial Technology Office, Attn: Steve
Fedor, Mail Stop 4–8, 21000 Brookpark
Road, Cleveland, Ohio 44135. Refer to
LEW-17356-1 
Tantalum-Based Ceramics for Refractory Composites
Compositions can be graded from porous substrates to impervious outer layers.
Ames Research Center, Moffett Field, California
A family of tantalum-based ceramics
has been invented as ingredients of
high-temperature composite insulating
tiles. These materials are suitable for
coating and/or permeating the outer
layers of rigid porous (foamlike or fi-
brous) ceramic substrates to (1) render
the resulting composite ceramic tiles
impervious to hot gases and (2) enable
the tiles to survive high heat fluxes at
temperatures that can exceed 3,000 °F
(≈1,600 °C). Originally intended for use
on the future space exploration vehi-
cles, insulating tiles made with these ma-
terials may also be useful in terrestrial
applications (e.g., some industrial
processes) in which there are require-
ments to protect against flows of hot, ox-
idizing gases.
The starting ingredients of a ceramic
of this invention are the following:
• Tantalum disilicide (TaSi2), which can
act as either an emittance agent or a
matrix material, depending upon the
overall composition;
• Molybdenum disilicide (MoSi2), which,
depending on the overall composition,
acts as a secondary emittance agent or
as an oxygen getter (to inhibit the oxi-
dation of tantalum within the finished
composite);
• A borosilicate glass (B2O3·SiO2), which
acts as a source of boron and may, de-
pending on the overall composition,
act as an alternative matrix; and
• Silicon hexaboride (SiB6), which acts as
a processing aid by facilitating sintering
of the aforementioned ingredients.
These ingredients are milled together
in ethanol, and the resulting slurry is
sprayed or painted onto a porous ce-
ramic substrate. The underlying layers
(sub-layers) of different compositions
are used to integrate the outer layer
(coating) with a wide variety of porous
substrate materials.  For this purpose, in-
filtration of these compositions into the
substrate results in a functional gradient
system that accounts for the difference
in the coefficient of thermal expansion
(CTE) between coating and substrate.
The preferred composition for such un-
derlying layers are in the approximate
range of 20 to 60 weight percent of
MoSi2, 0 to 60 weight percent of TaSi2,
40 to 80 weight percent of borosilicate
glass, and 1 to 5 percent of SiB6. The in-
gredients are then sintered by heating
the treated substrate at atmospheric
pressure at either a temperature of 2,225 °F
(≈1,218 °C) for 90 minutes or a temper-
ature of 2,400 °F (≈1,316 °C) for 10 min-
utes. The milling, coating, and sintering
process conditions are chosen to mini-
mize the undesired oxidation of tanta-
lum compounds.
For an outer coating layer, the preferred
composition is between 20 and 45 weight
percent of borosilicate glass, between 10
and 65 weight percent of TaSi2, between 5
and 30 weight percent of MoSi2, and be-
tween 1 and 5 weight percent of SiB6. An
underlying layer or sublayer of different
composition can be used to integrate the
outer layer with the substrate and, for this
purpose, may be allowed to infiltrate to
some small depth below the surface of the
substrate. The preferred composition for
such an underlying layer lies in the approx-
imate range of 20 to 60 weight percent of
A Porous Ceramic Substrate Is Coated with one
or more ceramic layers to render it impervious to
hot gas and increase its ability to withstand high
heat flux.
Porous Ceramic Substrate
High-Emittance, Impervious
Outer Ceramic Coating Layer Ceramic Intermediate
Layer (Optional)
ARC14743-1
ABPI
3-8-04 bs
https://ntrs.nasa.gov/search.jsp?R=20100021278 2019-08-30T09:38:43+00:00Z
NASA Tech Briefs, June 2006 19
MoSi2, 40 to 80 weight percent of
B2O3·SiO2, and 1 to 5 percent of SiB6. One
or more intervening layer(s) of intermedi-
ate composition(s) could also be included
(see figure). The precise composition of
the sublayer should be chosen to match the
CTE of the substrate, while the composi-
tions of intermediate layers should be cho-
sen to grade the transition from the CTE
and porosity of the substrate to the CTE
and full density of the outer coating layer.
This work was done by David A. Stewart,
Daniel Leiser, Robert DiFiore, and Victor
Katvala of Ames Research Center.
This invention is owned by NASA, and a
patent application has been filed. Inquiries
concerning rights for the commercial use of
this invention should be addressed to the
Ames Technology Partnerships Division at
(650) 604-2954. Refer to ARC-14743-1.


Tantalum-Based Ceramics for Refractory Composites

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