US2448511A - Glossing corundum and spinel - Google Patents

Description

Sept. 7, 1948. M. H. BARNES ETAL V ,GLQSSING CORUNDUM AND SYINEL INVENTORS MALCOLM H. BARNES EDWARD L. Mo CANDLESS ATTORNEY material.

Patented Sept. 7, 1948 UNITED" TA ES rATENT OFFICE Malcolm H. Barnes and Edward L. McCandless, Kenmore, N. ,Y. assignors to The-Linda Air ProductsCompany, a corporation of Ohio 7 Application October 1, 1943,"S erial No. 504,544

This invention is a process for: providing glossy scratch-free surface-s on crystalline incombustible precious and semiprecious stones, particularly crystalline bodies of synthetic corundum and spinel. The invention also relates to precious and semiprecious stones having glossy scratchfree surfaces.

surface composed of many microscopic sharp and angular crystal facets. Also, When stones are sawed or ground, their surfaces are covered with scratches caused by particles of abrasive Before a stone may be used as a jewel bearing, thread, guide, or other low-friction wear-resistant device, itmust be given a glossy surface. HeretoforaI-stones have been mechanically polished by rubbing them with successively smaller particles of diamond or like abrasive. While mechanically polished surfaces may appear to be smooth and uniform when viewed with the naked eye, a microscope reveals the existence of many small scratchesproduced by the small particles of abrasive. Furthermore, mechanical polishing is a slow, tedious, and expensive process.

The principal object of the present invention is the provision of a novel process for rapidly and inexpensively treating crystalline precious and semiprecious stones, such as, corundum and spinel, to give them glossy and scratch-free surfaces. Another object is the provision of such a process wherein glossing is accomplished by using both heat and addition agents. Another object is to provide a novel process for glossing stones whereby the character .of the surface finish may be accurately controlled. Other objects are the provision of crystalline precious and semiprecious stones having glossy and scratchfree surfaces; and rods, such as synthetic corundum and spinel, having substantiallyf even, glossy, and scratch-free surfaces {and 'rd d'shaving glossy but wavy surfaces. F

The'above and otherobjectsj and the-novel features of the invention,-will become; apparent from the following description, having reference to the accompanying drawing, wherein Figs. 1, 2, and 3 are highly magnified schematic longitudinal sectional views of, respectively, a synthetic stone rod in the as-grown condition, a similar rod partially glossed by the process of the invention, and a fully glossed similar rod.

The process of the invention is carried out by first applying to thesurfacejof the stone athin film of an addition agent, advantageously adding just enough to fill the pits and crevices in the surface. It is advantageous to use at least one oxide 14 Claims. (01, 117-421) Physics, vol. 14, page 26 (1943).

glossing the surface.

or oxide-forming compound fulfilling at least one of the following requirements: having a lower melting point than the stone, forming a eutectic .with the stone,.forming a solid solution with the stone, and forming a low melting peritectic with the stone. Then the film is bonded to the original surface by fusion with heat, as in a gas flame, an electric arc, or a furnace. Either a fully glossed, evensurface, as at c in Fig. 3, or a partially glossed, wavy surface, as at b in Fig. 2, can be obtained by properly controlling the heating. Oxides suitable for glossing stones, such as spinel and corundum, include calcium oxide, magnesia, sodium oxide, and silica (silicon dioxide). The oxides of calcium, magnesium, and sodium form eutectics with corundum and spinel. Silica and sodium oxide have lower melting points than corundum and spine]. Magnesia forms a solid solution with corundum prepared from beta alumina. Silica also forms a low melting peritectic with corundum and spinel.

One way to apply the oxide is to paint on the surface of the stone aslurry or solution in water or other liquid of the oxide, or a compound decomposable to form the oxide. By way of exam- ;ple, a synthetic clear sapphire (pure alumina) was glossed by wetting its surface with a lime solution, evaporating the lime solution to dryness, and heating at about 1500 C. for one minite ,in an oxy-hydrogen flame. Oxide also may .be applied in the molten condition. An alternative method for applying the thin which theoxide is vaporized by an electrically heated tungsten filament, as described by Heidenrich and Peck in Journal of Applied The coated stone then is placed within a furnace, or heated in a flame or are to form a glossy surface.

Sometimes it is desirable to shape the stone by mechanical cutting or grinding prior to heat For example, synthetic corundum and spine] rods sometimes are ground to uniform diameter in a centerless grinder, after which the ground surfaces are glossed by the novel process of the invention.

Synthetic unicrystalline corundum rods heat glossed by the process of the invention had an average tensile strength of 102,000 1b./sq. in.,

"compared with 67,000 1b./sq. in. for similar rod in the as-grown condition. traceable to the elimination This is believed of a notch effect existing in the uhglossed rod. Furthermore, the hardness of rod glossed by the process of the invention was about the same as the hardness of mechanically polished rod. For example, the

previously mentioned clear synthetic sapphire treated with a lime solution had a. Knoop hardness of 1780 after glossing by heating, which is comparable to the hardness of mechanically polished corundum, namely 1600 to 2100.

Crystalline precious and semiprecious stones treated by the process of the invention have glossy, clear, and scratch-free surfaces which render them useful for many purposes. For example; fully heat glossed stones, such as unicrystalline synthetic corundum and spinel, are useful asjewel bearings. Heat glossed synthetic spinel and corundum rods also may be used as thread guides and tension posts in textile mills. Partially glossed synthetic corundum and spinel rods, having a wavy surface, are particularly useful as thread guides and tension posts because the slightly wavy surfaces provide a series of grooves within which the thread may run.

The process of the invention has been described specifically by way of illustration only. It is apparent, however, that'variations in procedure may be made within the spirit and scope of the invention, as defined in the. claims.

What is claimed is:

1. A process for glossing a unicrystalline body of material selected from the group consisting of corundum and spinel comprising applying to a rough surface of such a body in thin film of at least one substance selected from the group consisting of metal oxides and substances forming metal oxides fulfilling at least one of the following requirements: having a. melting point lower than such material fonmng a eutectic with such material, forming a low melting peritectlc with such material, and forming a solid solution with such material; and subsequently heat bonding such film to said surface.

2. A process for glossing a unicrystalline body of material selected from the group consisting of corundum and spinel comprising applying to a rough surface of such a body a thin film of a slurry including at least one substance selected from the group consisting of metal oxides and substances forming metal oxides fulfilling at least one of the following requirements: having a melting point lower than such material, forming a eutectic with such material, forming a solid solution with such material, and forming a low melting peritectic with such material; and fusing such film to said surface.

3. A process for glossing crystalline precious and semiprecious stones selected from the group consisting of unicrystalline corundum and spinel comprising vaporizing at least one metal oxide fulfilling at least one of the following requirements: having a melting point lower than such a stone, forming a eutectic with such a stone, forming a low melting peritectic with such a stone,

and forming a solid solution with such a stone;

condensing a thin film of the oxide vapor on a rough surface of such a stone; and fusing such film to said surface.

4. A unicrystalline corundum body having a glossy scratch-free surface, said body having small surface pits and crevices, said body having bonded thereto over a substantial surface area a film of fused oxide selected. from those of calcium, silicon, magnesium, and sodium, said pits and crevices being filled with such fused oxide, said surface having a Knoop hardness of at least 1600.

5. A unicrystalline spinel body having a glossy scratch-free surface, said body having small surface pits and crevices, said body having bonded thereto over a substantial surface area a film of fused oxide selected from those of calcium, silicon, magnesium, and sodium, said pits and crevices being, filled with such fused oxide.

6. A unicrystalline body of material selected from the group consisting of corundum and spinel having bonded thereto over a substantial surface area a film of metal oxide fulfilling at least one of the following requirements: having a melting point lower than such material, forming a eutectic with such material, forming a solid solution with such material, and forming a low melting peritectic with such material, said body having a glossy scratch-free surface.

7. A body as claimed in claim 6, wherein such oxide comprises calcium oxide.

8. A body as claimed in claim 6, wherein such oxide comprises silicon dioxide.

9. A unicrystalline body of material selected from the group consisting of corundum and spinel having bonded thereto over a substantial surface area a film of metal oxide fulfilling at least one of the following requirements; having a melting point lower-than such material, forming a eutectic with such material, forming a solid solution with such material, and forming a low melting peritectic with such material.

10. A unicrystalline corundum body having small surface pits and crevices, said body having bonded thereto over a substantial surface area thereof a film of fused oxide selected from those of calcium, silicon, magnesium, and sodium, said pits and crevices being filled with such fused oxide, said oxide-filmed surface area having a Knoop hardness of at least 1600.

11. A process in accordance with claim 1 wherein said metal is calcium.

12. A process in accordance with claim 1 wherein said metal is silicon.

13. A process in accordance with claim 1 wherein said metal is magnesium.

14. A body as claimed in claim 6, wherein such oxide com-prises magnesia.

MALCOLM H. BARNES. EDWARD L. MCCANDLESS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date:

270,018 Chevassus Jan. 2, 1883 1,178,256 Miller Apr. 4,1916 1,422,216 McDougal July 11, 1922 1,653,918 Martin Dec. 27,1927 1,680,681 Herzog Aug, 14, 1928 1,775,868 Sandmeier Sept. 16, 1930 1,806,589 Espig May 26, 1931 1,814,219 Jaeger July 14, 1931 1,852,840 Fuwa Apr. 5, 1932 1,949,884 Slayter Mar. 6, 1934 2,018,056 Delpech Oct. 22, 1935 2,043,867 Rava June 9, 1936 2,085,757 Kazaniian July, 6, 1937 2,145,732 Nickle Jan. 31, 1939 2,152,754 Wagner Apr. 4, 1939 2,332,424 Zwermann Oct. 19, 1943 2,371,486 Walker Mar. 13, 1945 FOREIGN PATENTS Number Country Date 243,251 Great Britain Nov. 26, 1925 502,978

Great Britain Mar. 29, 1939

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