High Temperature Amorphous Composition Based on Aluminum Phosphate

Abstract

A composition providing thermal, corrosion, and oxidation protection at high temperatures is based on a synthetic aluminum phosphate, in which the molar content of aluminum is greater than phosphorus. The composition is annealed and is metastable at temperatures up to 1400° C.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation of and claims priority benefit from application Ser. No. 10 / 362,869 filed Jul. 15, 2003, which in turn claims priority from U.S. national application filed under 35 U.S.C. § 371 of international application no. PCT / US01 / 41790 filed on Aug. 20, 2001, which is a continuation-in-part of and claims priority benefit from application Ser. No. 09 / 644,495 filed Aug. 23, 2000, now issued as U.S. Pat. No. 6,461,415, each of which is incorporated herein by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH[0002]The United States government has certain rights to this invention pursuant to Air Force Office of Scientific Research contract no. F49620-00-C-0022 and Department of Energy contract no. DOE DE-AC05-84OR21400-1DX-SY067V, both with Applied Thin Films, Inc.BACKGROUND OF THE INVENTION[0003]This invention relates to synthetic inorganic compositions which remain metastable and possess other...

AI Technical Summary

Benefits of technology

[0007]The present invention relates generally to substantially amorphous aluminum phosphate materials and / or compositions exhibiting metastability and various other related properties under high temperature conditions. In part, metastability can be evidenced by retention of amorphous characteristics under oxidizing conditions, such morphology and the extent thereof due at least in part to the aluminum content of such materials / compositions, with those having an overall stoichiometric excess of aluminum exhibiting enhanced amorphous character and associated stability as compared to their stoichiometric counterparts. Such properties and related high-temperature attributes can be effected in the preparation of such materials / compositions, primarily by admixture of the aluminum precursor to the corresponding phosphate precursor to initiate various structural and / or compositional modifications which manifest themselves in the high temperature performance of the resulting aluminum phosphate material / composition. In particular, and as illustrated more clearly in the following examples, aluminum can be identified upon addition to a phosphate precursor and shown as contributing to the amorphous character and associated metastability of the resulting aluminum phosphate material / composition. Addition of a stoichiometric excess of aluminum precursor enhances the resulting amorphous character and metastability.

[0016]A particular advantage of this approach is that the precursor solution provides a substrate coating of even and uniform thickness for substrate application. After initial heat treatment, subsequent coatings may be applied to increase coating thickness. This methodology is applicable to the formation of precursor phosphate solutions containing more than one metal ion. The ability to adjust the concentration of the composite solution over a wide range is another distinct advantage, allowing for precise or controlled amounts of metal phosphates to be formed.

[0017]Further and as directed more particularly to the present invention, the aforementioned admixture / precursor solution can be dried and then annealed, for example, at temperatures of up to 800° C. or greater, in air. The annealing step is believed to cause a transformation of the molecular structure, with the final product being more than 50% amorphous in content, and with the amorphous nature being sustained for long periods at temperatures up to 1400° C. or greater without oxidation. Depending on the synthetic procedure and presence of other components or additives, the composition may also contain small crystalline inclusions which can impact other desirable properties, such as toughness and optical activity. The composition exhibits other desirable properties, such as very low oxygen diffusivity, low thermal conductivity and high emissivity. Thus, a particularly suitable application is to use the composition as a coating on a substrate to minimize oxidation of the substrate at high temperatures.

Problems solved by technology

Up to the present time, however, there are no known synthetic oxides which can remain amorphous and metastable at temperatures up to 1400° C. or greater.

Aluminum phosphate, however, is unsuitable for use as a high temperature ceramic material because it undergoes polymorphic transformations (quartz-type, tridymite and cristobalite) with corresponding large molar volume changes.

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