Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1999-08-26
2001-11-20
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C428S632000, C428S633000, C428S678000, C428S680000, C428S472000, C428S937000
Reexamination Certificate
active
06319615
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a thermal spray method for the manufacture of a heat insulating coat and to machine components with a heat insulating coat of this kind; it furthermore relates to uses of machine components of this kind.
2. Description of the Prior Art
A method for the manufacture of a plasma spray coat is known from DE-C 23 28 395 in which zirconium silicate ZrSiO
4
(or ZrO
2
.SiO
2
) is sprayed on. This material, which is very heat resistant (“fireproof”) occurs naturally as a raw material, namely as sand from the mineral zircon. In the disclosed method a spray coat arises which is substantially composed of a mixture of tetragonal stable zirconium oxide ZrO
2
and amorphous silicon dioxide SiO
2
. The tetragonal modification of the zirconium oxide is well suited for the development of protective coatings in contrast to the monoclinic modification, which is normally present at ambient temperature. These coatings form a protection against corrosion and wear at high temperatures.
Furthermore, it is known to use ZrO
2
for the manufacture of heat insulating coats, for example as a coating of guide blades in gas turbines. The object of the present invention is to use a thermal spray method in such a manner that a heat insulating coat of zircon which is more economical than ZrO
2
, can be produced. In this it is to be achieved by suitable measures that the heat conductivity of a heat insulating coat of this kind is better up to 900° C. than that of the known coatings of ZrO
2
(heat conductivity index about 0.6-1.0 W/m.K at atmospheric pressure and room temperature).
SUMMARY OF THE INVENTION
The use in accordance with the invention of a thermal spray method relates to the manufacture of a layer for a heat insulating coat from a material in powder form. This material consists of zirconium silicate ZrSiO
4
at least to 80 mol %, in particular of the mineral zircon, and the majority of its powder particles have diameters in the region between 10 and 100 &mgr;m. During the spraying on the particles are at least partially melted through in a gas flow under reducing conditions and at a temperature greater than 2000° C. Method parameters, among others the dwell time of the particles in a heat imparting medium, in particular in a plasma or a flame, the temperature of the heat imparting medium and the momentum transferred to the particles are chosen in such a manner that the layer which is formed from the particles has a structure with laminar elements. Suitable gases or gas mixtures, preferably hydrogen, are used as reducing means for the liberation of gases containing silicon, in particular silicon monoxide SiO, and/or a thermal liberation of gases containing silicon takes place as a result of a higher temperature of the heat imparting medium.
Measurements at heat insulating coats which have been manufactured using the measures in accordance with the invention have yielded the following for the heat conductivity index at a pressure of 0.02 mbar: for a starting material ZrSiO
4
-4.5 mol % Nd
2
O
3
containing lanthanum dioxide, about 0.22 W/m.K at room temperature and about 0.31 W/m.K at 800° C. (at atmospheric pressure and room temperature the heat conductivity index is 0.6 W/m.K); for a starting material ZrSiO
4
-4.5 mol % Dy
2
O
3
, about 0.18 W/m.K at room temperature and about 0.24 W/m.K at 800° C.
REFERENCES:
patent: 4487841 (1984-12-01), Bartuska et al.
patent: 5350599 (1994-09-01), Rigney
patent: 5384200 (1995-01-01), Giles
patent: 5418015 (1995-05-01), Jackson et al.
patent: 2356957 (1975-05-01), None
patent: 0705911A1 (1996-04-01), None
patent: 0712940A1 (1996-05-01), None
Jones Deborah
McNeil Jennifer
Sulzer Innotec AG
Townsend and Townsend / and Crew LLP
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