Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
1994-04-25
2001-12-18
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C427S162000
Reexamination Certificate
active
06331357
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to articles having surface coatings with selectively controllable absorptance and emittance, and particularly such articles suitable for use in a space environment.
Spacecraft are exposed to a wide range of external thermal conditions, while functioning in various ways. Care must be taken to maintain the interior of the spacecraft within acceptable limits for the passengers and apparatus occupying the spacecraft. For example, one side of a satellite in earth orbit receives the direct, unfiltered rays of the sun during a portion of the orbital path, and the other side faces a range of conditions that can include the void of space. In another portion of the orbit when in the shadow of the earth, both sides may be exposed to cold conditions. Some parts of the interior of the spacecraft may be occupied by human beings, while other parts may be occupied by electrical apparatus producing large amounts of heat energy that requires a substantial amount of heat dissipation.
A number of active and passive techniques are used to moderate the effects of the radiation and temperature extremes on the interior of the spacecraft. There are active heating and cooling systems, but these can be heavy, bulky, and use a large amount of power. The walls are provided with passive insulation, but desirably the amount of insulation is relatively low because of its weight and bulk. Some spacecraft may be rotated to prevent excessive heat buildup, but in many other cases the spacecraft must maintain a specific orientation in order to perform its mission.
The heat energy reaching and leaving the spacecraft is transferred almost exclusively by radiation, inasmuch as there is no medium for heat transfer by conduction or convection. Therefore, in yet another passive thermal control approach, the exterior surfaces of the spacecraft may be provided with a coating, somewhat similar in character to a specialized paint, that alters the radiative transfer of heat to and from the exterior surfaces. Any coating applied to the exterior surfaces of the spacecraft must adhere well to the surfaces. It must also be stable in the space environment. That is, the components of the coating cannot change their essential character or be lost to the space environment during exposure to the temperature extremes and radiation of space. The coating must not rapidly deteriorate when exposed to the space environment, including UV (ultraviolet) radiation, particle radiation, atomic oxygen, micrometeorites, and orbital debris.
One prior thermal control coating provides a degree of variability in the absorptance thermal control property by including varying amounts of white and black pigments in a ceramic binder. Different compositions of the coating can be used on different spacecraft, and even on different regions of a single spacecraft, to achieve a degree of control over the radiative transfer to and from the surface of the spacecraft. While operable, such a coating falls short of providing the desired broad range of radiative properties required for some applications.
There is a need for an improved approach for passive thermal control of spacecraft. Such an approach should be capable of providing a wide range of thermal control properties and also satisfy the other requirements for use in a space environment.
SUMMARY OF THE INVENTION
The present invention provides a coating, an article using the coating, and a method of preparing such an article. The coating has a controllable range of optical properties, including a controllably wide range of variation of both solar absorptance and infrared emittance. The spacecraft designer therefore has available a wide range of variation in thermal properties of the coating, from which particular formulations can be selected for specific applications. The coating is stable when exposed to the space environment.
In accordance with the invention, a coated article comprises an article having a surface, and a multicomponent coating on at least a portion of the surface of the article. The coating comprising a mixture of a high absorptance pigment, a low absorptance pigment, a low emittance material, and a binder. Preferably, the high absorptance pigment is a finely divided black powder, the low absorptance pigment is a finely divided white powder, the low emittance material is a finely divided metallic powder, and the binder is an inorganic or ceramic material having a high emittance and a low absorptance. Each of the components of the coating is stable when exposed to a space environment.
In one form, the coating comprises a mixture of from about 0 to about 99 parts by weight of a high absorptance pigment, rom about 1 to about 99 parts by weight of a low absorptance pigment, from about 1 to about 99 parts by weight of a low emittance material, balance binder and incidental impurities. The low absorptance pigment is preferably a white pigment such as zinc oxide. The high absorptance pigment is preferably a black pigment such as cupric oxide, cobalt oxide, or manganese dioxide. The low emittance material is preferably a metal such as aluminum. The binder is preferably an inorganic material or a ceramic such as potassium silicate, having a high emittance.
With these variations of high absorptance pigment, low absorptance pigment, and low emittance material, a wide range of physical thermal control properties can be achieved. The absorptance of the coating can be selectively varied from about 0.20 to about 0.90. The emittance of the coating can be selectively and independently varied from about 0.25 to about 0.90.
The ability to tailor the coating properties to control both absorptance and emittance, largely independently of each other, is an important advantage over prior coatings suitable for use in a space environment. In some applications, such as thermal radiators, it is desirable to have a low absorptance and a high emittance, so that the radiator can dissipate interior heat while absorbing little heat from the sun. On the other hand, in some other applications, such as a coating for a propulsion system, it is preferred to have both a high absorptance and a high emittance. The present approach permits the spacecraft designer to utilize a single coating system but to vary the proportions of the components of the coating system to realize the differing thermal properties required for different regions of the spacecraft.
The coating of the invention is readily prepared and applied. The components are mixed together in an aqueous slurry and applied to the surface of the article, preferably by spraying. The coating is dried, either by ambient temperature drying or at slightly elevated temperature. This permits the coating to be used with a wide range of article substrates, such as metals, ceramics, polymers, and composite materials.
REFERENCES:
patent: 3454410 (1969-07-01), Schutt et al.
patent: 3576656 (1971-04-01), Webb et al.
patent: 3620791 (1971-11-01), Krupnick
patent: 4008348 (1977-02-01), Slemp
patent: 4111851 (1978-09-01), Shai
patent: 4397716 (1983-08-01), Gilliland et al.
patent: 4741778 (1988-05-01), Horie et al.
patent: 4980206 (1990-12-01), Torre et al.
N. John Stevens, “Application of SERT II Thermal Control Coatings,” NASA-Langley publication E5859, pp. 1-33 (1971) no month given.
J. Cordaro et al., “Molecular Enginnering of Pigments for Degradation-Resistant Thermal Control Coatings,” AIAA Pub. AIAA-92-2167 (Apr. 1992).
Cheng Hsieh et al., “Conductive White Thermal Control Paint for Spacecraft,” 38th International SAMPE Symposium, pp. 609-622 (May 1993).
Babel Henry W.
Daneman Steven A.
DeJesus Ronaldo R.
Hasegawa Mark M.
Alston & Bird LLP
Dawson Robert
McDonnell Douglas Corporation
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