Method of producing fullerene-dispersed ceramics

Details Method of producing fullerene-dispersed ceramics Method of producing fullerene-dispersed ceramics

1999-09-27

2001-07-03

Wood, Elizabeth D. (Department: 1755)

Compositions: ceramic

Ceramic compositions

Refractory

Reexamination Certificate

active

06255241

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing fullerene-dispersed ceramics in which fullerene is effectively compounded into ceramics.
2. Description of Related Art
As known in the art, fullerene-dispersed ceramics can be advantageously applied to various materials, such as self-lubricating abrasive materials, low-friction, abrasion-resistance materials, ferroelectric or piezoelectric materials having high permittivity due to interface-polarization effect, computer memory, materials micro-actuator materials and the like. Therefore, fullerene-dispersed ceramics can be used in a wide range of industrial fields such as automobiles, domestic electric appliances, computers and the like.
The inventors have already proposed a method for producing a composite material of ceramics and fullerene such as C
60
, as disclosed in Kunichi Miyazawa et al., “Characterization of C
60
-Doped Zirconia Prepared from Organic Solutions”, Processing and Fabrication of Advanced Materials VI, Volume I, The Institute of Materials, 1998, pp. 775-784. According to the method disclosed in this paper, the composite material is formed by preparing a solution of C
60
and metal alkoxide in which an organic solvent such as toluene is applied, and subjecting the solvent to drying and baking so as to make C
60
-ceramics composite powder, and sintering the composite powder while it is filled in a copper case.
FIG. 1
shows a flowchart of the production process of the fullerene-dispersed ceramics according to the above-mentioned proposal, in which toluene is filled in a glass beaker in an amount of 100 to 200 ml. Zirconium tetra n-propoxide (ZNP) is added into the beaker and dissolved while stirring the solution. Subsequently, C
60
powder is added into the beaker and dissolved while stirring the solution. The toluene solution with C
60
and ZNP dissolved therein is left standing for about 1 to 3 days to cause gelation of the solution. The precipitation resulting from the gelation is dried in a vacuum atmosphere at a temperature of about 100 to 110° C., so as to obtain a dry gel of C
60
comprised of ZNP. The dry gel is baked to form a zirconia composite powder comprised of C
60
, in an air atmosphere at, 400° C. for 30 minutes. In forming a sintered body, the powder is filled into a copper case in a nitrogen or an argon atmosphere, and then sintered at a temperature of 600° C. to 900° C., for 2 hours. The composition of the C
60
-doped zirconia is, for instance, ZrO
2
-3 to 30 mass% C
60
.
With the above-mentioned method, however, it was often difficult to obtain composite ceramics in which C
60
was uniformly dispersed.
FIG. 2
a
shows a scanning electron microscope image of the C
60
-dispersed zirconia ceramics sintered body produced by the method shown in FIG.
1
.
FIG. 2
b
shows a carbon X-ray image of the sami specimen at the same site as shown in
FIG. 2
a.
It is clear from the
FIG. 2
b
that carbon is segregated in a size of 10 &mgr;m, and is not uniformly dispersed in the ceramic matrix.
In order to improve the uniformity of C
60
dispersion in the ceramic matrix, the inventors developed a method of producing a composite material of ceramics and fullerene by utilizing a so-called micelle formation method. According to this method, C
60
-dispersed zirconiapowder is produced by forming C
60
micelle from a water solution of zirconyl nitrate (ZrO(NO
3
)
2
) wherein C
60
is added, by using C
16
TMA (CH
16
H
33
N(CH
3
)
3
Cl) as a surfactant, followed by formation of zircoma-gel corprising C
60
by controlling the acidity of the solution, and subsequent drying of the zirconia gel. The method is disclosed in Kunichi Miyazawa et al., “Production of C
60
-ZrO
2
composite material and structural evaluation thereof” Abstracts of the Japan Institute of Metals, 1998, pp. 208. In this paper, C
60
-dispersed zirconia powder is produced by dissolving C
16
TMA in a water solution of 100 cm
3
containing 0.1 mole ZrO(NO
3
)
2
, adding C
60
into the solution, stirring the solution for 12 hours, filtering the precipitate formed by dropping 2 mole NaOH in the solution, washing the precipitate by distilled water and then drying in the conditions of 150° C., 8 hours. According to this method, C
60
can be uniformly dispersed in the ceramics matrix, though it has been found that carbon other than C
60
still remains in the matrix. It would be highly desirable to realize C
60
-dispersed ceramics, having a further improved purity.
SUMMARY OF THE INVENTION
Therefore, it is a primary object of the present invention to provide a method of producing fullerene-dispersed ceramics in which fullerene such as C
60
can be uniformly dispersed in the ceramic matrix and carbon except C
60
can be effectively eliminated from the matrix.
The inventors conducted thorough investigations for the purpose of achieving the stated object, and arrived at a novel recognition that most of residual carbon except C
60
in the C
60
-ceramics composite powder is originated from the surfactant such as C
16
TMA, and that the organic matter originated in the surfactant is almost completely by carrying out the heat treatment to the powder under a relatively high temperature condition. Such recognition resulted in conception of the present invention, the features of which will be explained below.
The present invention provides a method of producing fullerene-dispersed ceramic pack which comprises the steps of:
forming a colloidal solution by dissolving a fullerene and a surfactant in a solution of metallic compound;
forming a gel from the colloidal solution by changing the hydrogen ion concentration thereof;
drying the gel; and
heat treating the gel so as to eliminate the remainder of the solvent and the surfactant.
The present invention further provides a method of producing fullerene-dispersed ceramics using the fullerene-dispersed ceramic powder described above, and then sintering the powder.
The preferable heat treatment conditions for carrying out the method according to the invention are described below.
atmosphere: air atmosphere, inert gas atmosphere or vacuum atmosphere
temperature: 250 to 500° C.
time: 0.5 to 4 hours
When sintering is carried out according to the invention, various types of sintering methods can be applied. However, the hot pressing method is particularly suitable as it is carried out under very high pressure so as to obtain a sintered body having an even higher density. Moreover, by applying the very high pressure hot pressing method, it is possible to produce a polymerized C
60
-dispersed ceramic or ceramic in which superfine diamond grains are dispersed as a result of enhanced polymerization or transformation of C
60
.
In the method according to the invention, it is preferred that the metallic compound comprises zirconyl nitrate, the fullerene is C
60
, and/or the surfactant is C
16
TMA. By using zirconyl nitrate as the metallic compound, C
60
as fullerene and C
16
TMA as the surfactant, C
60
-dispersed zirconia ceramics can be readily produced.
In addition, for carrying out the method according to the present invention, there may be used various types of metallic compound solutions provided that ceramic precursor is contained, therein as well as various types of surfactant provided that they are suitable for forming micelle in which fullerene is surrounded by surfactant. Moreover, the preferable amount of the surfactant per the amount of ceramic is within a range of about molar ratio 1:10 to 1:1.


REFERENCES:
patent: 5420081 (1995-05-01), Mattes et al.

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