IL35662A - Articles of jewelry comprising refractory oxides - Google Patents

Description

WK nij'on tsiann o»V»aan ο·»»"»»3η »son Articles o Jewelry comprising refractory oxides E.I. DU PONT DE NEMOURS AND COMPANY C: 33840 Background of the Invention This invention relates to articles of jewelry vihich consist essentially of 10 to 0 volume percent refractory oxide, 1G to 90 volume percent refractory carbide, 0 to 10 volume percent auxiliary oxide and 0 to 10 volume percent metal.

Some such compositions are known in the art to Vie have discovered that the compositions of this invention when shaped as articles of Jewelry exhibit a number. of unusually desirable characteristics. Refractory carbides have been employed in the prior art in making watch cases as disclosed in U.S. Patent No. 3*242,664. However, refractory carbides have some drawbacks for use in malting articles of 'jewelry. Most, cemented r carbides have moderate electrical conductivity, a limited resistance to acid-corrosion such as that caused by perspiration, and very high density which makes the articles of jewelry quite heavy.

We have discovered that by incorporating oxides into articles of jewelry distinct advantages are obtained. The presence of oxides such as alumina reduce electrical conductivity, increase acid-corrosion resistance and decrease density resulting in jewelry which resists perspiration corrosion and is light weight. The oxides also impart a distinct and unusual color to the jewelry which is quite pleasing to the eye. In addition to a pleasing appearance, the articles of this invention are unusually scratch-resistant. They can thus be worn for extended periods without being marred or tarnished. The articles of this invention are also very strong and tough and are therefore very durable as compared to many natural and artificial s oner: and gems used in artic3.es of jewelry. Finally the articles of this invention are quite refractory and thus will not molt or decompose at high temperatures at which conventional metals or alloys, would collapse and diamonds would be destroyed.

Summary In summary this invention relates to articles of jewelry which comprise a hard polished composition consisting essentially of 10 to 90 volume percent alumina, zirconia, magnesium aluininate or their mixtures; 10 to 0 volume percent of a carbide of titanium, zirconium, niobium, tantalum, tungsten, molybdenum, hafnium or their mixtures; from 0 to volume percent chromium, molybdenum, tungsten, iron, cobalt, nickel, titanium, zirconium, . niobium, tantalum, hafnium or theirmixtures; and frpm 0 to 10 volume percent of silica, titania, magnesia, a rare earth oxide or their mixtures, said composition having a porosity of less than 5$, an average grain size of less than 10 microns, a resistance to perspiration by corrosion and a density of under 9 g./cc.

Such articles of jewelry are scratch and mar-resistant, strong, tough and very durable and possess a distinctive color.

Description of the Invention The articles of this invention comprise dense, fine-grained solids containing 10 to 90 volume percent of a refractory oxide or mixture of refractory oxides selected from among alumina, zirconia, magnesium alumlnate^ and, optionally, 0 to 10 volume percent of silica, titania, ma nesia or the rare earth oxides 10 to 0 volume percent of the carbides o titanium, zirconium, niobium, - tantalum, tungsten, molybdenum and hafnium; and 0 to 10 volume percent of a metal selected from the group chromium, molybdenum, tungsten, iron, cobalt, nickel, titanium, zirconium, niobium, tantalum or hafnium or the mixtures of these metals. These solids are characterized by low porosity, a small average grain size, a polished surface which is resistant to acid corrosion such as caused by" human perspiration and a density of less than 9 g./cc.

COMPONENTS The articles of this invention comprise dense solids which consist essentially of refractory oxides AI2O3, Zr02 or Al2O3»M 0 and, optionally, Si02, Ti02, MgO or rare earth oxides carbides of Ti, Zr, Nb, Ta, , Mo or Hf$ and, optionally, Cr, Mo, W, Pe, Co, Ni, Ti, Zr, Nb, Ta or HP metals or their mixtures . a) Oxides The refractory oxides which- can be used in the compositions of this invention are alumina, zirconia and magnesium aluminate (Al203*M O). These oxides are used in amounts ranging from 10 to 90 volume percent. Because corrosion resistance, lightness, electrical resistance and unusual color are increased with increased amounts of oxides, preferred, amounts of these oxides are 25 to 75 volume percent, more preferably 40 to 75 volume percent and most preferably 50 to 75 volume percent. Optionally other oxides, silica, titania, magnesia or the rare earth oxides can be used in amounts up to 10 volume percent.

Average particle size of the oxides should generally be less than about microns and preferably less than about 2 microns. The referred oxide s lum nd preferably its average particle size is less than 2. microns, most preferably less than 0.5 microns.

If the starting oxide material is appreciably larger than 5 microns in particle size, it can be pre-ground to reduce its size to that which is acceptable. Of course, the mix-milling of the components which is carried out to obtain a high degree of homogeneity, will result in some comminution of the components.

The oxides suitable for use in this invention can e in any form so long as they are finely divided. Thus, for example, alumina can be in the form of gamma, eta or alpha alumina or their mixtures. Alpha alumina is a preferred form of alumina because its specific surface area is lower than gamma or eta alumina and is likely to contain less adsorbed water.

The oxides can be prepared by any of the well-known conventional methods or they can be obtained commercially. A suitable commercial alumina is Alcoa Superground Alumina XA-16 with a specific surface area. of about 15 square meters per gram. Suitable commercial forms of the other oxides are powders graded -525 mesh such as those available from Metals for Industry Inc. b) Carbides The carbides which can be used in the compositions of this invention are the carbides of titanium, tungsten, molybdenum, tantalum,zirconium, hafnium and niobium. These carbides can be used in the compositions of this invention in amounts of 10 to 90 volume percent. Preferred amounts of these components are from 5 to 75 volume percent, more preferably 19 to" 57 volume percent and most-preferably 19 to 47 Volume percent. It is also preferred to use the carbides of .titanium, zirconium or tantalum and it is most preferred to use titanium carbide.

The carbides suitable for use in this invention should have an average particle size of less than 5 microns and preferably less than 2 microns. If the starting material has a particle size appreciably larger than 5 microns, it can be pre-ground to reduce its size to 5 microns or less prior to its use. Of course, the mix-milling of the components which is carried out to obtain a high degree of homogeneity, will result in some comminution' of the components.

Suitable carbides can be prepared by means well-known to the art or they can be obtained commercially.

Suitable commercial carbides are the powders graded -325 mesh such as those available from Materials for Industry Inc. or from Cerac Inc. Butler Wisconsin. c) Metals The metals which can be used in the compositions of this invention are molybdenum, tungsten, chromium, iron, nickel, cobalt, titanium, zirconium, niobium, tantalum, hafnium and their mixtures with each other.

These metals are used in the compositions of this invention in amounts ranging from 0 to 10 volume percent.

Preferred amounts of metal are from 3 to 6 volume percent metal because in this range there is an optimum balance in chip resistance when the pieces are cut and ground, ease of polishing and corrosion resistance.

Of the refractory metals, it is preferred to use Mo or VI and their alloys with the iron group metals. Of the iron group metals, Ni is preferred. It is most preferred to use Mo or \1 in combination with Ni.

As stated above, relatively high amounts of metals, up to 10 volume percent, can be used in the compositions of this invention. However, increases in the metal content of the composition should be coupled with corresponding increases in the carbide content to maintain the corrosion resistance of the compositions. It is believed that molybdenum metal diffuses into the lattice of carbides such as titanium carbide so that if there is sufficient carbide present, there will be little or no free molybdenum metal present, thereby maintaining the high resistance to corrosion.

The metals suitable for use in this invention should have an average particle size of less than 5 microns and preferably less than 2 microns. If the starting powder has a particle size appreciably larger than 5 microns, it can be pre-ground to reduce its size to 5 microns or less prior to its use. Of course, the mix-milling of the components, which is carried out to obtain a high degree of homogeneity, will result in some comminution of the components.

Metal powders with the required size and degree of purity can be obtained from commercial sources or they can be prepared by conventional means. A suitable method of preparation is low temperature hydrogen reduction of the corresponding metal oxide, or hydrogen reduction of iron, cobalt or nickel carbonate at a temperature between about 600°C. and 1200°C. Such preparations should be carried out at as low- a temperature as is practical to prevent excessive sintering and agglomeration of the metal being formed.

In the preparation of molybdenum and tungsten from their oxides, it is best to employ a two-stage reduction because of the relative volatility of these oxides. The first-stage reduction is carried out below the oxide melting point, such as at 600°C. Then the second-stage reduction is completed at say 900°C.

Metals prepared as described above can be milled in an inert medium to increase their surface area and can then be purified such as with hydrochloric acid. It is desirable to use grinding media, when milling the metal, which is made of the same metal as being ground, the components which are to be mixed with the metal, or very wear-resistant material to avoid introducing impurities by attrition of the media. ~» · ' Representative of suitable commercially available metals are fine tungsten powder from General Electric, Detroit, Michigan, with an oxygen content of 0.21$, a nitrogen specific surface area of 2 square meters per gram and a crystallite size of 17 millimicrons as measured by X'-ray line broadening,* and fine nickel powder available from International Nickel Co., with an oxygen content of 0.09$, a nitrogen specific surface area of 0.5 square meters per gram and a crystallite size of 150-170 millimicrons as measured by X-ray line broadening. d) Impurities The components to be used in the compositions of this invention are preferably quite pure. In particular, it is desired to exclude impurities such as oxygen which would tend to have deleterious effects on the dense compositions.

On the other hand, minor amounts of many impurities can be tolerated with no appreciable loss of properties .

Thus the metal can contain small amounts of other metals, although low melting metals like lead should be excluded.

Small amounts of other carbides can also be present. Even oxygen can be tolerated in small amounts such as occurs when titanium carbide has been exposed to air, resulting in a few percent of titanium oxy-carbide. However, after the o de components have been milled together and are in a highly reactive state, oxidation, particularly of the metals, occurs easily and should be avoided.

Preparation of the Articles of this Invention The preparation of interdispersions of the carbides with the oxides, and the metals if they are used, in The powder interdispersions of the carbides with the oxides, and the metal if they are used, are fabricated by sintering or hot-pressing in the form of a dense solid, referred to above.

The dense compositions consisting essentially of oxides, carbides and optionally metal can be shaped into articles of jewelry without the use of any other material.

Alternatively the dense compositions can be mounted on a backing such as metal, wood, plastic or cloth, or can be used as a mount for precious or semiprecious stones, gams and minerals. The resulting items of jewelry can be purely decorative, functional or combine function and decoration.

Items of jewelry are so well known and the. size, shapes, combinations of materials used and areas of use are so broad that it is impossible and should be unnecessary to list all possible types of jewelry for which the compositions of this invention are suitable. The following abbreviated list is merely representative of suitable uses. The compositions of this invention can be used alone or in combination with any structural materials or materials of apparel including metal, wood glass minerals lastics cloth paper, leather, precious stones, shells, or synthetic organic or inorganic materials. Combinations can be made for example by brazing, . soldering, gluing, cementing, insetting, pegging, and sewing, such jewelry items as the following: Watch cases Rings Cuff links Tie tacks Earrings Necklaces Pins Buttons Clips Pendants Lapel buttons Cigarette cases Bracelets Metal ornaments Monograms Trophies Medals Bottle openers Shoehorns Hairpins Hair ornaments Shoe buckles Belt buckles Pill boxes Compacts (cosmetic cases) Dress or shirt studs Charms for charm bracelets Identification tags Insignias. Paper weights Methods for fabricating such items of Jewelry as well as methods for cutting, shaping and polishing the dense compositions will be apparent to those skilled in the art and are more fully described in the examples.

Characterization Methods The compositions of this invention are characterized by their corrosion resistance to perspiration, high mechanical strength, outstanding toughness and hardness, low porosity, small grain size and homogeneity of the interdispersion between components. .

Determination of mechanical "strength and hardness are made by conventional transverse rupture and Rockwell A Methods for the doternr.l.nation of porosity, grain size and homogeneity of solid bodies are described in U.S.

Patent 3,'-1-0 , 16. The compositions of this invention are characterized by a porosity of less than and an average grain size of less than 10 microns. Preferably, compositions of this invention have a porosity less than Ij and an average grain size of less than 2 microns.

Toughness is determined only qualitatively by allowing a finished fabricated object of this invention to freely fall on a hard- wood floor from a height of seven feet. The compositions of this invention do not break or chip under the conditions of this test.

The actual density of the compositions can be determined by any recognized method, most simply by weighing in air, and immersed in water, a sample which has been previously measured. The water should be boiled before weighing the sample to remove dissolved air. The density is calculated from the formula weight in air x specific gravity of water density = weight in air - weight in water'* The theoretical density for the composition can be calculated on the basis that the volume for a given weight of the composition is equal to the sum of the volumes of the components calculated from the weight of each component divided by its density.

The solid bodies of this invention, as pointed out above, have a density of less than 9 grams per cubic centimeter and since their porosity is generally less than 1%, their actual density will ordinarily exceed 9 ^ of their theoretical density.

One of the characteristics that materials should and watch cases is resistance to corrosion by human skin-^^ excretions. It is known for example that in hot climates even stainless steel watch cases can be corroded completely through normal use on the wrist. To evaluate this characteristic, a corrosion test using a liquid with the average composition of human perspiration is employed. A solution is prepared with the composition stated to be the average composition of human perspiration in "Normal Values in Clinical Medicine" by F. W. Sunderman and F. Boerner, ¥. B. Saunders Co., Philadelphia and London, 19^9 at page 488. The composition is water sodium chloride lactic acid acetic acid propionic acid eapr lic and caproic acid citric acid ascorbic acid No urea or uric acid, included as "traces" in the average composition of human perspiration are added to the corrosion solution.

The corrosion solution is placed in a beaker in a constant temperature bath at 0°C. and glass stirrers are used to keep the solution stirring gently- Test specimens used as corrosion coupons are 0.810 inch x 0.500 inch x 0.100 inch in size. They are used as cut with resin-bonded diamond wheels without further grinding or polishing except as needed to conform the coupons to standard size.

Clean test specimens are accurately weighed and measured and then are immersed in boiling dimethylformamide removal from the dimethylformamide the coupons are water and acetone, are dried in a vacuum oven, and are transferred directly into the corrosion solution.

At measured intervals the specimens are removed from the corrosion liquid, are rinsed with distilled water and acetone, are dried in a vacuum oven and are then weighed. They are then recleaned in boiling dimethylformamide, water and acetone and are dried and returned to the corrosion liquid. Weight loss is calculated per unit of surface area of the specimen for the given intervals of time. The surface.,<5f some specimens are examined by optical micrograph before starting the test and at fixedixttervals during the test to observe the extent of etching.

The dense compositions of this invention are characterized by a weight loss of less than 0.2 milligrams per square centimeter afterimmersion in the above described synthetic perspiration at 0°C. for ten days. This resistance to perspiration corrosion is greater than that of >oK stainless steel, a. metal similar to those used commercially to make watch cases and is much greater than cobalt-bonded tungsten carbide compositions which are currently being used to make scratch resistant watch cases.

UTILITY The jewelry articles comprising compositions of this invention can be used in whatever areas items of jewelry are used, either in a purely decorative sense, or to combine practical utility with decorative advantages. These jewelry compositions have an unusually pleasing metallic luster which because of the presence of the oxides is somehow softened and made less harsh than either conventional polished metals or polished tungsten carbide. While the unusual appear can be observed with the human eye but is difficult to define, to measure or to quantify. Also, as mentioned above, in contrast to conventional metals, including stainless steels, silver or gold, articles of jewelry comprising the compositions of this invention are unusually scratch-resistant.

By virtue of their fine. rain size and lack of porosity, compositions of this invention can be polished to an unusually high degree and this polish is not scratched, marred, or dulled in even the roughest conventional use when contacted with any conventional materials of construction or items of apparel including metals, glass, concrete, bricks, wood, plastics etc. Also, because of the unusual corrosion resistance, the compositions of this invention are not tarnished when worn for long periods in contact with human skin and perspiration.

The compositions of this invention are stronger and tougher than many materials such as natural or artificial stones or gems or insets used in jewelry, and so they are more durable. Since the materials of this invention are extremely refractory they will not melt or decompose at high temperatures at which conventional metals or alloys would collapse and diamonds would be destroyed. This unusual combination of properties makes these materials unexpectedly valuable for use in articles of jewelry.

The following examples illustrate the invention.

Parts and percentages referred to in the examples are ky weight unless otherwise indicated.

Example 1 This is an example of a composition containing 50 volume percent of aluminum oxide, 45 volume percent of titanium carbide and 5 volume percent of metal consisting of about equal The alumina, in the form of very finely divided alpha alumina obtained commercially as Alcoa Superground Alumina XA-16 and characterized by X-ray examination as pure alpha alumina, having a specific surface area of about 13 square meters per gram. This surface area is equivalent to a spherical particle size of about 115 millimicrons.

Under an electron microscope this alpha alumina powder appears as aggregates of alumina crystals in the range of 100 to 150 millimicrons in diameter.

The titanium carbide powder has a nominal average particle size of 0.6 microns as measured by the Fisher Sub-Sieve Sizer and a specific surface area of about 10 square meters per gram as determined by nitrogen adsorption. This titanium carbide powder "milled to 0.6 microns" grade is commercially available from the Adamas Carbide Corp., Kennilworth, New Jersey. An electron micrograph of a dry mount preparation shows that the titanium carbide grains are between 0.2 and 3 microns in diameter and sometimes are clustered in the form of loose aggregates. The titanium content is about 77.8$, the total carbon content is about 18.8$, the free carbon is around 0.07$, and the oxygen analyses indicate the oxygen content may vary between about 0.8 to 1.6$ . Analysis by emission spectroscopy shows that Ti is the major component and also gives 0.5 to 2$ Mo, 0.5 to $ W, 0.5 to 2$ Ni, 00 to 2500 ppm of Al, 200 to 1000 ppm of Co, 300 to 1 00 ppm of Fe, 300 to 1500 ppm of Nb, 200 to 1000 ppm of Cr, 200 to 1000 ppm Si, 100 to 500 ppm of Zr, 0 to 250 ppm of Ca, 50 to 250 ppm of Mn, and 5 to 25 ppm of Mg.

The molybdenum powder is the current standard grade available from Sylvania Electric Products, Inc., Philadelphia, surface area as determined by nitrogen adsorption of Ο.29 square meters per gram and an average crystallite size of millimicrons as determined by X-ray diffraction line broadening. An electron micrograph shows the molybdenum powder consists of grains 1/2 to microns in diameter clustered together in open aggregates. Chemical analysis of the powder reveals 0.2?o oxygen and no other impurities over 500 ppm.

The nickel povjder is Mond. current standard grade, available from International Nickel Co., New York City, N.Y. The fine nickel powder contains 0.15$ carbon, 0 , 07^ oxygen, and less than 300 ppm iron. The specific surface area of the nickel powder is 0.48 square meters per gram, its X-ray diffraction pattern shows only nickel, which from the line broadening has a crystallite size of 150 millimicrons. Under electron microscope, the powder appears as polycrystalline grains 1 to 5 microns in diameter.

The powders are milled by loading 6000 parts of preconditioned cylindrical cobalt-bonded tungsten carbide inserts, 1/4 inch long and 1/4 inch in diameter, into a 1.3 liter steel rolling mill about 6 inches in diameter, also charged with 28.7 parts of "Soltrol" 130 saturated paraffinic hydrocarbon, boiling range 165-210°C. centigrade.

The mill is then charged with 83 .6 parts of the alpha alumina, 47.Ο parts of the titanium carbide powder, 7.65 parts of the molybdenum powder, and 6.68 parts of the nickel powder, all as above described.

The mill is then sealed and rotated at 90 revolutions per minute for 5 days. The mill is then opened and the contents emptied while keeping the milling inserts inside. The mill of the milled solids are removed.

The milled powder is transferred to a vacuum evaporator, and the excess hydrocarbon is decanted off after the suspended material has settled. The wet residual cake is then dried under vacuum with the application of heat until the temperature within the evaporator is between 200° and 300° C and the pressure is less than about 0.1 millimeters of mercury. Thereafter the powder is handled entirely in the absence of air.

The dry powder is passed through a 70 mesh screen in a nitrogen atmosphere, and then stored under nitrogen in sealed plastic containers.

A consolidated billet is prepared from this powder by hot pressing the powder in a cylindrical graphite mold having a cylindrical cavity 1 inch in diameter and fitted with opposing close-fitting pistons. One piston is held in place in one end of the mold cavity while 17.5 parts of the powder is dropped into the cavity under a nitrogen atmosphere and evenly distributed by rotating the mold and tapping it lightly on the side. The upper piston is then put in place under hand pressure. The assembled mold and contents are then placed in a vacuum chamber of a vacuum hot press, the mold is held in a vertical position, and the pistons extending above and below are engaged between opposing graphite rams of the press under pressure of about 100 to 200 pounds per square inch. Within a period of a minute the mold is raised into the hot zone of the furnace at 1000°C. and at once the furnace temperature is increased while the positions of the rams are locked so as to prevent further movement durin the heatup period. The temperature is raised from 1000 to l800°C. in 10 minutes, and the temperature of the mold is held at l800°C. for another 2 minutes to ensure uniform heating of the sample. Λ pressure of pounds per square inch is then applied through the pistons for four minutes. Immediately after pressing, the mold and contents, still being held between the opposing reins, 'is moved out of the furnace into a cool zone where the mold and contents are cooled to dull red heat in about 5 minutes.

The mold and contents are then removed from the vacuum furnace and the billet is removed from the mold and sand blasted to remove any adhering carbon.

Density of the finished piece as determined by accurate weighing and measurement of the dimensions is only 4.82 grams per cubic centimeter.

The hot pressed composition is essentially nonporous when examined under 1000 X magnification. This characteristic is important since nonporous materials are more corrosion resistant than porous materials of the same chemical composition. Structurally, the composition consists of an extremely fine co-continuous interpenetrating network of polycrystalline alpha alumina and of metal bonded titanium carbide.

The specimen is so tough that it does not break or chip when dropped freely to a hard wood floor from a height of 7 feet.

The composition has a specific resistivity of about 2000 micro-ohm cm. This degree of conductivity indicates continuity of the conducting components of the structure, namely, the metal and titanium carbide. Electron micrographs indicate a very fine grain structure, few grains exceeding 1 or 2 microns in size. The alumina is generally the coarsest phase.

The continuity of the alumina phase is indicated by removing the titanium carbide and metal from the composition by anodic attack for 2h hours in .ammonium biiluoride solution . This leaves em electrically non-conducting porous layer on the surface, which to the eye appears to be unchanged, but under electron microscope is shown to be porous due to the removal of the electrically conducting components.

The sample is polished by pressing its faces firmly against rotating diamond impregnated cloth discs. A Beuhler, Ltd. polishing machine is employed for this operation.

A 400 grit diamond wheel is used at 1175 revolutions per minute in the first polishing step and a 1000 grit diamond at 550 revolutions per minute is used in a second, finishing step.

The sample polished in this manner has an attractive ornamental appearance with dark, hazy, silver color and metallic luster, and is cemented as an inset on a metal tie bar Chemical analysis shows, in addition to the alumina. titanium carbide, molybdenum and nickel, the presence of about 2$> of iron, presumably attrition from the mill, and ho by weight of tungsten presumably present as tungsten carbide and about 0. ^ o cobalt, both probably picked up from piece. Strips O.080 inch in thickness are cut from the ^material remaining to each side of this center piece and are X further cut in O TO inch =0 O inch square bars for testing transverse rupture strength. Other portions of the billet are used for indentation hardness tests and for other product characterization. The transverse ru ture stren th as . - 20 - a 9/16 inch span is' about 150,000 pounds per square inch.

The hardness is 9 ?0 on the Rockwell, A scale. " Corrosion tests in a liquid with the composition of human' perspiration were made at 40°C. using 0.810 inch x 0.500 inch x 0.100, inch coupons.

A liquid with the composition of human perspiration (cf. page 12) is prepared and the accurately measured and weighed, and carefully cleaned corrosioh coupons are immersed in liquid. Cleaning of the coupons is done by immersion in boiling dimethylformamide for 5 minutes, followed by rinsing in water and in acetone.

The test is carried out by allowing the specimens to stay in the corrosion liquid for a measured length of time, then removing, rinsing with water and acetone, drying in a vacuum oven, and weighing. After . weighing, the specimens are again cleaned in boiling dimethylformamide, rinsed in H20 and acetone, and when dried, replaced in the corrosion liquid.

The above mentioned procedure is repeated for various lengths of time . ' The corrosion liquid is gently stirred during ifor"'' test and the temperature of the liquid is kept at 0°C. in a controlled constant temperature bath. Specimens of commercial stainless steel 30 and "Carboloy" grade 90 of the some size and cut and cleaned in the same way as the compositions of this invention are also tested, for comparison.

After 10 days, the average weight loss of the composition prepared above is 0,l milligrams per square centimeter. Under the same test conditions, commercial cemented tungsten carbide, "Carboloy" 0, shows an average weight loss of 25 milligrams per square centimeter and stainless steel >0 , a metal similar to that used in commercially available watch cases, shows an average weight loss of 0.5 milligrams per square centimeter.

The tests show that the composition prepared above is more resistant to corrosion by human perspiration than stainless steel j50 , and far more resistant than commercial. "Carboloy" 90.

Optical microscope observations of "Carboloy" 90 samples at 7-0 X magnification after 10 hours of immersion in the corrosion test solution show that the surface has been extensively etched by the perspiration solution under the conditions of our experiments. On the other hand, the composition of this example, when observed under the optical microscope after 10 hours in the corrosion test solution, shows only slight surface etching.

Example 2 This is an example of a watch case made with the composition of Example 1.

The procedure of Example 1 is repeated to obtain a dry powder ready to be hot pressed.

A watch case · is prepared from this powder by hot pressing the powder in a graphite mold assembly designed in such a way as to permit hot , pressing the -powder in the shape of a ring with a round hole of a size into which the encased operating works of a watch can later be press-fitted,, the ring serving as a protective and decorative case. The graphite mold consists of a 4 inch long hollow cylinder of graphite with an outside diameter of 2-1/2 inches, the cross-section of the ca\rity being in the shape of a square with rounded sides.

The maximum inside diameter of the cylinder is 2 inches.

A hollow piston is placed into the bottom end of the cylindrical mold, the outside diameter of the piston fitting snugly into the inside diameter shape of the mold. The piston has a cylindrical cavity with a 1-5/8 inch, round cross-section. The end of the piston in the mold is tapered or dished so that the bottom of the ring to be formed from the powder will have a somewhat decorative rounded surface rather than a flat surface. A third hollow cylinder with an outside diameter of about 1-5/8 inch and a wall thickness of 1/ΐβ inch fits snugly into the hollow piston and extends up beyond the piston into the mold. Finally, a solid rod fits into the thin-walled inner cylinder to keep it from collapsing during the pressing operation. A weighed amount of powder calculated to result in •' a completely dense pressed piece with the proper thickness is poured into the mold and the mold is tapped so that the powder packs in the cavity formed by the inner wall of the mold, the outer surface of the ' thin-walled cylindrical spacer and the upper hollowed end of the bottom piston. A second hollow piston is then fitted into the assembly from the top to provide the upper surface for the powder cavity. The entire assembly is placed into a hot press and is heated and ressed under the conditions described in Example 1. The pressure is applied through top and bottom solid graphite rams acting on the outer ends of the hollow pistons which protrude from the top and bottom of the mold. When the pressing has been completed, the mold is removed from the hot zone and the solid rod spacer is permitted to slide out of the center of the assembly. As the mold cools, the pressed watch case ring contracts more than the graphite. If the solid rod had been left in place, the ring would fracture from strains set up. Instead, the shrinking ring compresses the thin-walled graphite cylinder which remains in the hole, and the cylinder crafcks instead of the ring. The thin-walled cylinder is used simply to permit initial easy withdrawal of the solid rod which otherwise would be held up by sticking to the ring. After the mold has cooled, the pistons and the ring are removed, by pressure if needed. The ring is then polished as described in Example 1, and fitted around the encased watch works.

Example 5 This is an example of the use of a composition of Example 1 as fin inset for tie clips.

The procedure of Example 1 is repeated to obtain a dense hot pressed billet.

The billet is cut so that a 9/l6 inch x 5/l6 inch rectangular piece is removed from the center. The rectangular piece is polished by pressing its faces firmly against rotating diamond impregnated cloth discs. The same Buehler, Ltd. machine employed in Example 1 for polishing the sample is used in this operation. A 400 grit diamond wheel is used at 1175 revolutions per minute in the first polishing step and a 1000 grit diamond at 550 revolutions per The rcctn.iii5ii.lar piece poli hed in this manner J&s a metallic silver appearance, and is used as an . ornamental inSe by cementing it with epoxy resin to the surface of a metal tie clip* The article of jewelry of this example shows an excellent resistance to perspiration corrosion.

Example The procedure of Example 1 is repeated except that only alumina, and titanium carbide are used as components, to give a composition containing *!0 volume, percent alumina and 60 volume percent titanium carbide.

The amounts of components loaded in the 1. liter steel mill are !·7 ·7 parts of alumina and 88.9 parts of titanium carbide.

A 'billet is prepared as in Example 1, except that the maximum temperature used in the hot pressing operation is l850°C. The product has a density of .85 grams per cubic centimeter, a hardness higher than ^ · 5 on the Rockwell A scale, and a transverse rupture strength of about 120, 000.

The billet is dropped on a hard wood floor from a height of feet without breaking or chipping.

The billet is essentially nonporous, when examined under 1000 X magnification. The structure of the composition consists of two very fine continuous interpenetrating networks, one of polycrystalline alpha alumina and one of titanium carbide.

The composition has a specific resistivity of, 1000 micro-ohm.cm. , indicating continuity of titanium carbide, the conducting component of the structure.

Electron micrographs indicate a very fine grain structure, few grains exceeding > or microns in size.

Chemical analysis shows, in addition to the alumina and titanium carbide, the presence of about 0.5 weight percent of iron, presumably attrition from the steel mill, and about 1.1$ by weight of tungsten, presumably present as tungsten carbide, and about 0.1$ of cobalt, both of the latter two probably picked up from attrition of the milling inserts.

Corrosion tests in a liquid with the average composition of human perspiration at 4q°C. show that this sample is more resistant to corrosion than stainless steel >0h and far more resistant than commercial "Carboloy" 90 tungsten carbide.

The billet of this composition is cut and polished as in Example 3, to obtain a piece one-half inch square.

The square piece is used as an ornamental insert by cementing it with epoxy resin on a medallion.

Example 5 The procedure of Example 1 is repeated, except that the components are used in amounts to give a composition containing 25 volume percent alumina, 25 volume percent zirconia, volume percent titanium carbide, and 5 volume percent of metal consisting of 5 volume percent nickel and 50 volume percent molybdenum.

The zirconium oxide powder used is obtained commercially under the trade name of "Zircoa" AHC. This powder has an average particle size of 1.3 microns as measured with the Fisher Sub-Sieve Sizer, and has a nitrogen specific surface area of 1 square meter per gram. Chemical analysis of this zirconium oxide shows that it contains 0.1$ of calcium oxide.

The actual amounts of components loaded in the 1.3 liter steel mill are 2 .8 arts of alumina 42 arts of molybdenum and 6.68 parts of nickel. ' A watch case prepared with this composition as in Example 2 has an attractive, hazy, dark, silver-gray appearance and does not break or chip when allowed to fall freely on a hard wood floor from a height of 7 feet. Density of this watch case is practically equal to theoretical density.

This watch case is tested and shown to be more resistant to corrosion by human perspiration than stainless steel 304 and "Carboloy" 90.

Example 6 The procedure of Example 1 is repeated except that the components are used in amounts to give a composition containing 40 volume percent alumina, 10 volume percent titanium dioxide, 45 volume percent titanium carbide, and 5 volume percent of metal consisting of 50 weight percent nickel and 50 weight percent tungsten.

The titanium dioxide powder is obtained commercially from Materials for Industry, Inc., and has a nitrogen specific surface area of 8.8 square meters per gram. Electron micrographs show it to be composed of aggregates in turn composed of fine particles about 1/4 of a micron in diameter.

The amounts of components loaded in the 1.3 liter steel mill are 53.8 parts of alumina, 6.4 parts of titanium oxide, 66.6 parts of titanium carbide, 7.65 parts of molybdenum and 6.67 parts of nickel.

A billet prepared as in Example 1 from this hot pressed composition has a hardness of 93.5 on the Rockwell* A scale and a transverse rupture strength of about 140,000 pounds per square inch. The billet is very tough. and is dropped from a height of 7 feet on a hard wood floor without breaking or chipping.

The billot is essenti lly nonp ous , v/ cn exar.o.tifMJ under 1000 X Magnification and having a density equal to its theoretical density. Electron micrographs indicate a very fine grain structure, few grains exceeding 1 or 2 microns in size.

After polishing, this sample shows an attractive ornamental appearance. The sample has a smokey or hazy, dark, silver-gray color. The sa.mple is cut to give a hexagonal piece, which is set in a platinum ring as an ornament.

The article of jewelry fabricated in this manner shows an excellent resistance to human perspiration corrosion.

E a ple 7 The procedure of Example 1 is repeated except that zirconium carbide is used instead of titanium carbide to give a composition containing βθ volume percent alumina, volume percent zirconium carbide, and 5 volume percent of metal consisting of 50 weight percent nickel and 50 weight percent, molybdenum.

The zirconium carbide powder is obtained commercially from Materials for Industry, Inc., and has a nitrogen specific surface area of 0.5 square meters per grau. and an oxygen content of 0.l8 S.

The amounts of components loaded in the 1.3 liter steel mill are 71.6 parts of alumina, 70.5 parts of zirconium carbide, 7.6 parts of molybdenum, and 6.66 parts of nickel.

• A billet prepared as in Example 1 has a density of 4.7 grams per cubic centimeter, a hardness of about 93 .1 o the Rockwell A scale, and transverse rupture strength of about 125, 000 pounds per square inch.

Under 1000 X magnification the billet shows an The billet Is cut with a resin bonded diamond wheel and polished to give two ornamental pieces of attractive hazy, dark, silver-gray appearance. These two pieces are cemented with epoxy resin to two metal cuff links. The articles of jewelry obtained in this manner show an excellent resistance to human perspiration corrosion.

Example 8 The procedure of Example 1 is repeated except that niobium metal is used instead of molybdenum metal to give a composition containing 50 volume percent alumina, 45 volume percent titanium carbide, 4 volume percent niobium metal, and 1 volume percent nickel.

The niobium metal used in this composition is obtained commercially from Cerac, Inc., as a -225 mesh powder. This powder has a nitrogen specific surface area of 0.2 square meters per gram and electron micrographs reveal that it is composed of dense particles between 2 and 12 microns in diameter, with most particles between 4 and 8 microns in diameter.

The amounts loaded in the 1.3 liter steel mill are 58.5 parts of alumina, 66.5 parts of titanium carbide, 10.28 parts of niobium metal, and 2.66 parts of nickel metal.

A billet prepared as in Example 1 has a density of 5.02 grams per cubic centimeter, a hardness of about 94.0 on the Rockwell A scale and transverse rupture strength of about 155, 000 pounds per square inch.

The billet shows an excellent resistance to human perspiration corrosion.

Claims (1)

1. An article of comprising a hard composition consisting essentially of 10 to 90 volume percent of aluminate or their 10 to volume percent of a of molybdenum or their mixtures 0 to 10 volume percent of hafnium or their 0 to 10 volume percent of a rare earth oxide or their said composition havin a porosity of less than an average grain size of less than 10 a resistance to perspiration corrosion and a density of less than 9 grams per cubic An article of Claim 1 in the composition consists of 25 to 75 volume percent aluminate or their to 75 volume percent of a carbide o molybdenum or their and to 6 volume percent of hafnium or their An article of Claim 1 in which the composition has a porosity of less than and an average grain size of less than 2 An article of Claim 1 in which the composition consists essentially of 0 to 75 volume percent to 57 volume percent titanium zirconium tantalum carbide or their mixtures and to volume percent article of Claim in which carbide titanium carbide mid the of 10 to 95 percent and 5 to 0 weight percent An article of Claim in which the composition consists of 50 to 75 volume percent 19 to volume percent carbide and to 6 volume percent 7 An article of Claim 6 in which the carbide is titanium carbide and the metal is mixture of 10 to weight percent molybdenum and 5 weight percent A watch case having an exposed outer area comprising a hard polished composition consisting essentially of to 90 volume percent of aluminate or their 10 to 90 volume percent of a carbide of molybdenum or their 0 to 10 volume cent of hafnium or their and 0 to 10 volume percent of a rare earth oxide or their said composition having a porosity of less than average grain size of less than 10 a resistance to perspiration corrosion and a density of less than 9 grams per cubic A watch case of Claim 8 in which the composition consists essentially of 5 to 75 volume percent magnesium aluminate or their 25 to 75 volume percent of a carbide of molybdenum or their to 6 volume percent of Λ watch of which the has a porosity of than an average grain of less than 2 A watch case of Claim 0 in which the composition consists essentially of 40 to 75 volume percent 19 to 57 volume percent titanium zirconium carbide or their mixtures and to 6 volume percent of metal selected among tungsten and their cobalt or A watch case of Claim 11 in which the carbide is titanium carbide and the metal is mixture of to 95 weight percent molybdenum and 5 to 0 weight percent A watch case of Claim 11 in which the composition consists essentially of to 75 volume percent 19 to 47 volume percent carbide and to 6 volume percent A watch case of Claim in which the carbide is titanium carbide and the metal is a mixture of 10 to 95 weight percent molybdenum and 5 to 90 weight percent insufficientOCRQuality