Coating processes – Particles – flakes – or granules coated or encapsulated – Inorganic base
Reexamination Certificate
1998-11-27
2002-05-21
Jones, Deborah (Department: 1775)
Coating processes
Particles, flakes, or granules coated or encapsulated
Inorganic base
C427S218000, C427S279000, C427S372200, C427S377000, C427S397700, C427S421100, C428S404000, C428S406000, C428S428000, C428S446000, C428S325000, C428S336000, C501S032000, C106S287100, C106S287340
Reexamination Certificate
active
06391383
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to a high emittance glass coating which is provided on surfaces of various kinds of structures for the purpose of increasing an emissivity of the structures, and a method of producing the high emittance glass coating. Also, the present invention is concerned with an improvement in a high emittance glass coating material which is used for forming the high emittance glass coating.
BACKGROUND ART
A heat insulator system serving for an aerospace or ultra-supersonic aviation, for example, is required to have an excellent heat resistance and a high emittance. Thus, a structural body used for such a purpose is provided on its surface with a glass coating having high emittance, such as a light-weight inorganic fibrous refractory which constitutes an outer wall of a space shuttle of the National Aeronautics and Space Administration (NASA). An example of the glass coating is disclosed in U.S. Pat. No. 4,093,771. This glass coating is constituted, for example, by a glass structure composed of a reaction cured glass (RCG) of a high silica borosilicate, and a high emittance pigment consisting of molybdenum disilicide (MoSi
2
) or a boron silicide compound such as silicon tetraboride (SiB
4
) or silicon hexaboride (SiB
6
), such that the high emittance pigment is dispersed in the glass structure. Thus, the glass structure is constituted by the reaction cured glass of the high silica borosilicate which has a high degree of heat resistance, and the high emittance pigment is dispersed in the glass structure, thereby providing the glass coating with a high heat resistance and a high emittance.
The above-described glass coating is produced, for example, as follow. That is, a predetermined amount of boron oxide is first mixed with a glass powder including a high silica glass. The mixture is fired and ground, for thereby producing a reaction cured glass powder. Next, the high emittance pigment is added to the thus produced reaction cured glass powder, for preparing a glass paste. The glass paste is applied to the surface of the light-weight refractory or other structural body. The applied glass paste is dried and then fired so that the glass structure constituting the above-described glass coating is formed from the glass powder. It is known that restraining oxidation of the high emittance pigment in the firing step is essential in the above production process where a non-oxide such as the above-described boron silicide compound is used as the high emittance pigment, in view of a fact that the boron silicide compound is decomposed into silicon oxide and boron oxide when the boron silicide is oxidized, whereby the pigment no longer provides the required optical properties such as high emissivity.
According to the technique disclosed in the above-identified U.S. Pat. No. 4,093,771, the decomposition of the high emittance pigment is restrained by rapidly heating the glass paste in the firing step. That is, the rapid heating of the glass paste leads to a rapid melting of the glass powder, and accordingly the high emittance pigment is rapidly covered by the molten glass powder, thereby restraining the oxidation of the high emittance pigment. However, even where the glass paste is thus rapidly heated, the high emittance pigment is gradually decomposed in the process of the firing operation, as shown in the schematic chart of the reaction process described in the above-identified patent. That is, the decomposition of the high emittance pigment is not satisfactorily restrained in the disclosed technique.
DISCLOSURE OF INVENTION
A further study by the present inventors with the purpose of producing a glass coating having higher emittance revealed that the reduction in the emissivity is due not only to the oxidation of the high emittance pigment, but also to the fact that the high emittance pigment is melt into the glass structure constituting the glass coating in the firing step. That is, the study of the present inventors revealed that such a reaction between the high emittance pigment and the glass structure is a cause for the reduction of the emissivity. Further, the reaction causes a change in the composition of the glass structure, resulting in a reduction in the heat resistance of the glass coating. As described above, the glass coating is provided on the surface of the refractory or other structural body for the purpose of increasing the emissivity of the structural body which is used at a high temperature. Namely, the glass coating is repeatedly or always exposed to a high temperature while the structural body is used. Accordingly, the glass coating suffers from the problematic reduction in the emissivity and the deterioration of the heat resistance due to the interface reaction between the glass structure and the high emittance pigment not only while the glass coating is produced but also while it is used, and moreover, independently of whether the pigment is of a non-oxide or an oxide.
The present invention was developed under the above-described background situation and has a first object of providing a high emittance glass coating material which is capable of suitably restraining the interface reaction between the glass structure and the high emittance pigment that is dispersed in the glass structure while the high emittance glass coating material is produced or while the high emittance glass coating is used. The present invention further has a second object of providing a high emittance glass coating, and a third object of providing a method of manufacturing the high emittance glass coating.
The above first object may be achieved by a first feature of the present invention, which provides a high emittance glass coating material which is applied to a surface of a specific structural body and fired on the surface, for providing on the surface a glass coating having a glass structure in which pigment particles having a predetermined degree of emissivity are dispersed, the high emittance glass coating material being characterized by including: (a) a pigment covering film having a predetermined thickness, which is provided to cover each of the pigment particles, and which includes silicon dioxide such that a content of the silicon dioxide in the pigment covering film is higher than a content of the silicon dioxide in each portion of the glass structure which is adjacent to a corresponding one of the pigment particles.
According to the first feature of the present invention, the high emittance glass coating material includes the pigment covering film having the predetermined thickness, which is provided to cover each of the pigment particles, and which includes the silicon dioxide such that the content of the silicon dioxide in the pigment covering film is higher than the content of the silicon dioxide in each portion of the glass structure which is adjacent to the corresponding one of the pigment particles. Thus, the glass coating which is obtained by firing the glass coating material applied to the surface of the structural body, is provided, at its interface between each pigment particle and the glass structure, with the pigment covering film which has a comparatively low reactivity with the pigment particle owing to its higher content of the silicon dioxide than that in the glass structure. The provision of the pigment covering film at the interface permits effective restraint of an interface reaction between the pigment particles and the glass structure while the glass coating material is fired or while the glass coating is used. That is, the interface reaction can be suitably restrained by increasing, at the interface between the pigment particle and the glass structure, the purity of the silicon dioxide which is chemically stable.
The above-indicated second object may be achieved by a second feature of the present invention, which provides a high emittance glass coating which is provided on a surface of a specific structural body and which has a glass structure in that pigment particles having a predetermined degree of emissivity are d
Fukui Takamitsu
Hiyoshi Masakazu
Horimi Kazuhiro
Isogai Takamitsu
Iwata Misao
Boss Wendy
Jones Deborah
Noritake Co. Ltd.
Oliff & Berridg,e PLC
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