Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1998-08-13
2001-01-30
Copenheaver, Blaine (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C156S322000, C427S181000, C427S244000, C427S295000, C427S443200, C428S338000, C428S312800
Reexamination Certificate
active
06180222
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to nanoporous aluminium oxide membranes, the nanopores of which contain ligand-stabilized gold clusters, a process for their production and their use for the production of red decorations.
Purple pigments based on colloidal gold or precursors thereof in and/or on a particulate carrier material, such as a glass frit or a metal oxide, and their use for the production of decorations on glass, porcelain and ceramic have been known for a long time, reference being made to DE-OS 44 11 104 and DE-OS 44 11 103 by way of example. The purple color can indeed be shifted somewhat further into the red region by co-using a small amount of a silver compound, but a pure red pigment based on colloidal gold or an intensely red decoration after application of a gold-containing pigment precursor onto a substrate which is stable to baking, with subsequent baking, has not been previously obtainable.
It has been possible to eliminate another disadvantage of gold-containing decoration preparations which are already known for the production of purple-colored decorations, that is to say an inadequate stability to baking at temperatures of about/above 1,000° C., by using ligand-stabilized gold clusters in decoration preparations—see DE Patent Application 197 04 479.4. However, the purple color of the decoration was not changed, in comparison with other gold compounds, by using the gold cluster.
Nanoporous aluminium oxide membranes with hollow or solid gold fibrils in the pores are known—see C. R. Martin, Chem. Mater., vol. 8, no. 8 (1996), 1739-1746 and J. Phys. Chem. (1994), 98, 2963-2971. The gold can be deposited without a current or electrochemically. While the nanoporous Al
2
O
3
itself is optically transparent, the membrane assumes a color in the range from red-purple to blue because of the gold deposit. The color shifts from red-purple to blue as the length to diameter ratio of the fibrils increases; as the diameter of the fibrils decreases (150 nm to 20 nm), there is a shift towards red (in FIG. 6 of this document, this has obviously been transposed from top to bottom).
Nanoporous Al
2
O
3
membranes with spheroidal gold particles having a diameter of about 3 to 9 nm can be obtained by electrochemical deposition of gold in the pores of a nanoporous AL
2
O
3
membrane obtained by anodic oxidation in phosphoric acid solution—see J. Preston et al., J. Phys. Chem. (1993), 97, 8495-8503. A cluster structure has been assigned to the gold particles of the size mentioned; the gold content was about 0.1 to 2 wt. %. There is no suggestion of using nanoporous Al
2
O
3
membranes containing gold compounds or elemental gold particles as agents for production of red decorations on substrates which are stable to baking in the documents acknowledged above.
SUMMARY OF THE INVENTION
The object of the invention is to provide gold-containing agents, with the aid of which intensely red decorations can be produced on substrates which are stable to baking, such as glass, porcelain, ceramic and metal.
Nanoporous aluminium oxide membranes have been found which are characterized in that the nanopores contain ligand-stabilized gold clusters. By thermolysis of the membranes loaded with a ligand-stabilized gold cluster, the color changes from yellow-brown to red, and not to purple, as a consequence of the ligand shell being split off and ligand-free gold clusters being formed in the nanopores. Only the gold clusters contained in each pore can agglomerate to larger Au particles. Since the number of ligand-stabilized Au clusters per pore can easily be controlled via the concentration, the pore width and the thickness of the Al
2
O
3
membrane and is limited, there is no impairment of the monodispersity of the Au particles during the thermolysis, and therefore also no further changes in color at higher temperatures.
DETAILED DESCRIPTION OF THE INVENTION
The ligand-stabilized gold clusters in the Al
2
O
3
membranes containing nanopores can be used directly to produce red decorations on substrates which can be baked, because the red color can be formed during baking, which also serves as fixing, after application of the membrane to the substrate. Alternatively, the membrane can first be subjected to thermolysis for the purpose of splitting off the ligand shell, and the red-coloured membrane can then be applied and baked for decorative purposes.
The nanoporous aluminium oxide membranes on which the membranes according to the invention are based have been known for a long time and in some cases are also commercially obtainable. They have nanopores in a regular arrangement with a pore width in the range from about 1 to 500 nm and a depth of up to 500 &mgr;m. The pore density is usually in the range from 10
9
to 10
12
pores/cm
2
. Overviews of the structure, production and properties of anodic oxide films in pore form are given by J. W. Diggle et al., Chem. Rev. 69, 365-405 (1969) and J. P. Gullivan et al., Proceeding of the Royal Society of London, 317 (1970), 51 et seq.; further references are to be found in C. A. Foss et al. J. Phys. Chem. (1994), 98, 2963-2971 and C. K. Preston et al., J. Phys. Chem. (1993), 97, 8495-8503. The nanoporous structures can be produced by anodic oxidation of aluminium surfaces in an aqueous solution containing a di- or triprotic acid. Sulphuric acid, oxalic acid, phosphoric acid and chromic acid, in particular, can be used as the acid. The anodic oxidation of aluminium for production of the membranes to be employed according to the invention is usually carried out at a low temperature, for example 0 to 5° C., and preferably using sulphuric acid or oxalic acid as the electrolyte, because thick, compact, and hard porous films are obtainable in this way. During production of the films, for example, a sheet of highly pure aluminium forms the anode in an electrochemical cell. The anodizing proceeds with precise monitoring of the potential and current. The pore diameter depends on the electrolyte, the temperature and the anodizing voltage, the diameter increasing as the voltage increases—a guideline value with sulphuric acid as the electrolyte being a pore width of 1.2 nm per volt of voltage applied. Thicker films can be produced using oxalic acid than using sulphuric acid. During the anodic oxidation, non-oxidized aluminium on the so-called barrier side can then be dissolved off or polished off in an acid bath in a known manner (see e.g. U.S. Pat. No. 4,687,551), nanoporous Al
2
O
3
membranes with a closed (barrier side) surface and an open (i.e. pore openings) surface being obtained. During polishing of the membrane down to the base region of the pores, membranes with an open and a half-open (i.e. very small pore openings) side are first obtained, and during further polishing membranes with approximately equally wide pore openings continuous to both side are obtainable. Alternatively to this, continuous pores can also be obtained by etching with, for example, KOH in glycol, the membrane being placed with the barrier side on the etching bath.
Nanoporous Al
2
O
3
membranes according to the invention containing ligand-stabilized gold clusters can contain ligand-stabilized gold clusters which differ in respect to the ligand and the number of Au atoms per cluster. There are known ligand stabilized clusters of gold and other precious metals with a magic number of 55, 309 and 561 metal atoms. The ligands may be monomeric or polymeric and contain one or more complexing atoms selected from the group of N, P, As and S. Useful monomeric ligands can be amines and N-heterocyclic compounds, like e.g. phenanthroline, phosphanes, sulfanes and triarylarsanes. Polymeric ligands can be selected from e.g. polyethylenimine, gelatine and polyvinylpyrrolidone. The gold clusters of nanoporous Al
2
O
3
structures according to the invention are preferably those of the general structure Au
55
L
12
X
6/m
, wherein L is the ligand and X is an anion of valency m. The ligand contains atoms responsible for the stabilizing, such as, for example, phosphorus, sulphur or nitrogen, p
Hornyak Gabor Louis
Sawitowski Thomas
Schmid G{umlaut over (u)}nter
Schulz Andreas
Cerdec Aktiengesellschaft Keramische Farben
Copenheaver Blaine
Wenderoth , Lind & Ponack, L.L.P.
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