US3796584A - Colored rutile boules and method of making the same - Google Patents

Abstract

SINGLE CRYSTAL RUTILE BOULES MODIFIED WITH BOTH TUNGSTEN AND NICKEL ARE PRODUCED WHICH VARY IN COLOR FROM YELLOW TO REDDISH AMBER. THE BOULES ARE PORDUCED BY MIXING EQUIMOLAR QUANTITIES OF NICKEL AND TUNGSTEN OXIDES .006.03% MIO AND 0.02-0.8% WO3 BY WEIGHT OF TIO2, WITH RUTILE FEED POWDER FUSING SAID MIXTURE WITH A PLASMA OF FLAME HEAT SOURCE TO FORM A SINGLE CRYSTAL BOULE. THE BOULES PRODUCED HAVE POTENTIAL UTILITY AS A GEM MATERIAL OR IN MICROWAVE MASER APPILICATIONS.

Description

March 12, 1974 COLORED RUTILE BOULES AND METHOD OF MAKING THE SAME ABSORPT/O/V COEFF/C/ENT (/7' J. D. CHASE 3,796,584

Filed Aug. 14, 1972 ABSORPT/O/V COEFF/C/ENTS //v V/S/BLE PEG/0N FOR HUT/LE A/VD RU T/LE MOD/F/ED W/TH 0x/0E5 0F TU/VGSTE/V f NICKEL \\/RUT/LE m0 W03 RUT/LE l l l I l l 5500 4000 4500 5000 5500 5000 5500 WAVELENGTH (A0) INVENTOR.

JOH/V 00/vALO CHASE 7M QAEMZ D ATTORNEY United States Patent Oflice 3,796,584 Patented Mar. 12, 1974 3,796,584 COLORED RUTILE BOULES AND METHOD OF MAKING THE SAME John Donald Chase, Stamford, Conn., assignor to American Cyanamid Company, Stamford, Conn. Continuation-impart of abandoned application Ser. No. 118,748, Feb. 25, 1971. This application Aug. 14, 1972,

Ser. No. 280,695

Int. Cl. C04b 35/00, 35/46 US. Cl. 106-42 2 Claims ABSTRACT OF THE DISCLOSURE Single crystal rutile boules modified with both tungsten and nickel are produced which vary in color from yellow to reddish amber. The boules are produced by mixing equimolar quantities of nickel and tungsten oxides .006- 0.3% NiO and 0.020.8% W by weight of TiO with rutile feed powder and fusing said mixture with a plasma or flame heat source to form a single crystal boule. The boules produced have potential utility as a gem material or in microwave maser applications.

The present invention relates to rutile single crystal boules. More specifically it relates to colored rutile single crystal boules and to the production of such boules. This is a continuation-in-part application of US. patent application Ser. No. 118,748, filed Feb. 25, 1971, now abandoned.

BACKGROUND OF THE INVENTION Rutile is one of the three known crystal modifications of titanium dioxide. When substantially pure, a massive single crystal of rutile has gem-like properties; with a very light straw color; and, reflectance, refraction and brilliance greater than that of diamond.

Single crystals of rutile modified or doped with transition metal ions could also be useful in semi-conductor applications. For example, one of the best materials for microwave masers in rutile doped with nickel. (L. C. Morris and D. J. Miller IEEE J. Quantum Electronics QE-l, 164, 1965.)

The preparation of colored rutile crystal boules whereby a yellow to red coloration is caused by addition of either nickel oxide or cobalt oxide is described in US. Pat. No. 2,715,071 or blue coloration by the addition of tungsten oxide and mixtures thereof is described in US. Pat. 2,801,182. However, these boules are usually significantly more difiicult to grow than pure rutile due to the difficulty of incorporating the metal oxide into the rutile crystal lattice.

Although it is possible to incorporate various metal ions into a rutile crystal by the high temperature diffusion method, rather than adding the metal ions during growth, the former process involves an extra diffusion step which often requires more than 100 hours. Also, the maximum concentration of metal ion or ions added to the rutile by diffusion is less than that which can be incorporated during growth.

Rutile mixed with small quantities of two metal oxides is a commercial yellow pigment. An example of such a pigment is rutile mixed with oxides of nickel and antimony which is marketed by the Glidden Durkee Div. of S.C.M. Corporation.

OBJECTS 7 OF THE INVENTION The principal object of the present invention is the preparation of rutile single crystal boules, having colors ranging from yellow to amber, which may be used as gem material. A further object of this invention is the preparation of rutile single crystal boules modified with tungsten and nickel oxides. A further object is to produce rutile boules so modified with oxides of tungsten and nickel WhlCh may be used as a quantum electronic material.

SUMMARY OF THE INVENTION In its broadest aspects the present invention contemplates a rutile single crystal boule containing as a coloring agent the combined oxides of tungsten and nickel in substantially equimolar amounts. These colored boules are prepared according to the method of the present invention by progressively fusing a mixture of finely divided titanium dioxide and a small amount of said coloring agent mentioned above in a plasma or flame carrying an excess of an oxidizing gas to form said boule and thereafter oxidizing the boule so formed.

In this description of the present invention the word boule is used in its currently accepted meaning to denote a characteristic shape or form of an artificially prepared massive single crystal having a rounded end, or meniscus, a more or less rod-like body portion and a tapering end.

It has been found that rutile boules modified by additions of equal mole \quantities of tungsten and nickel are easier to grow than a boule grown using a feed powder which contained a similar amount of nickel oxide, but with no tungsten oxide. The reason for the greater ease in growing rutile crystals when both nickel and tungsten are present, is postulated to be due to charge balance which is possible in the lattice when metal ions of both higher and lower valences than titanium are present. By means of the present invention rutile single crystals may be produced in various colors. Further, these large single rutile crystals modified with more than one metal oxide additive can be used for making optical measurements to evaluate various mixed oxide systems as candidates for commercial colored inorganic pigments.

Many different oxides have been separately incorporated into a rutile host crystal such as Ga O C00, NiO, A1 0 which are described in US. Pats. 2,756,157, 2,715,071, 2,715,070 and Gd O Eu O Sm- O and Cr O which are reported elsewhere. In all cases the melting points of these oxides have been higher than 1820 C., the melting point of the rutile host. However, in the present invention where a rutile crystal has been modified with oxides of both tungsten and nickel, the tungsten oxide, W0 with a melting point of only 1473 C. was still retained in the boule. This was surprising, since it is normal during growth of crystals comprising several components by the Verneuil technique, for the most volatile components to distill off from the molten cap of the boule during the crystallization process. The reason for the surprising retention of W0 in the boule and thus the stability of this mixed oxide system is thought to result from the charge balance concept.

BRIEF DESCRIPTION OF THE DRAWING The drawing shows a comparison of the absorption coefficients for rutile and rutile modified in accordance with the invention. This modified rutile boule consists of 0.067 Weight percent of MO, 0.208 weight percent of WC, and balance is T102.

DESCRIPTION OF THE INVENTION for preparing a feed material especially adapted for the production of rutile single crystal boules is described.

The small amount of the coloring agent, i.e., the oxides of tungsten and nickel, may be mixed with the TiO starting material in any convenient manner, for instance, by

In progressively fusing the starting mixture of Ti and oxides of nickel and tungsten, there is employed a heat source which preferably contains oxygen. The heat source can be a plasma, preferred herein, or a flame. The fusion is carried out at a temperature of from 1825 C. to 1900 y blehdh'lg- A Particularly suitable feed material is one 5 C. The temperatureof the gas enveloping the boule should Where high P y z is mixed With reagent be carefully controlled during formation of the boule. grade thhgstic acid 4) and reagent g d nickel Rutile melts at about 1820 C. and therefore it is necesllitl'ate hexahydfate s)2 2 in such Proportions sary to operate so that the temperature at the top of the that the atomic ratios of TizWzNi are pre ent as 10 boule is somewhat above the melting point, e.g., 1825 C. 1'5:0.l:0.1. The mixture is then calcined above 700 C. If the temperature is in excess of 1900" C. an excessively and ground in a mortar to obtain a feed material of suitlarge portion of the boule melts at the top and the molten able consistency. Alternatively, the oxides may be made by material runs over the sides of the boule. For a plasma, Preparing the Phate double salt and argon or a similar inert gas is used as the carrier gas. In subsequently calcining this. order for the plasma to be suitably oxidizing it should con- The amount if coloring agent to be added to the TiO; min more than 2% oxygen.

feed material is' determined bythe color desired or more Excess oxygen in the boule enveloping gas is necessary precisely the location of the absorption edge within the because at elevated temperatures, titanium dioxide gives visible spectrum. For pleasing colors and good quality up oxygen and is converted to lower, or sub-oxides of tiboules the tungsten of the feed should not exceed 1% or 0 tanium, e.g., Ti O about 0.3% for nickel calculated as the element based on Even when operating with an excess of oxygen, the the weight of the TiO;;. The amounts of coloring agent boule as produced has generally a deep blue-black color will vary to produce the various depths of colors and the indicative of some deficiency in oxygen. Therefore, in orrange for each element will be subsequently described. der to produce a boule according to the instant invention The preferred lower limit of the feed is about 0.005% for in which the color ranges from yellow through reddish nickel and 0.0017% for tungsten at which the boules proamber, the blue-black boule has to be re-oxidized.

duced possesses a light yellow color. Concentrations of The reoxidation of the boule is preferably carried out by coloring agents below the above lower limits result in heating the blue-black boule in an oxidizing atmosphere, boules substantially similar in color to plain rutile boules. for instance, air or oxygen. The temperature of the treat- The single crystal rultile boules thereby produced have ment should be within the range from about 650 C. to pleasing colors varying from yellow to reddish amber. about 1500 C. It has been found that at temperatures to This is achieved by the presence of substantially equiy eXteHt below OXYgeH Will not he appreciably molar amounts of nickel oxide and tungsten oxide with the incorporated into the rutile Single y There is a nickel oxide ranging from 0.006 to 0.3 weight percent cided loss in brilliance, lustre and fire when the treatment based on the total weight of the boule. This range in turn s Carried out b ve 1 and at that temperature the defines the range of tungsten id hi h i from 0.02 t rate of oxygen incorporated into the rutile crystal is ex- 0.8 weight percent. A preferred concentration of i k l cessively rapid and difiicult to control. Preferably the oxioxide ranges from 0,06 t6 ()7 weight percent which in dation should be carried out at about 1100 C. to 14-75 turn establishes that the equimolar range of tungsten ox- P p y anneal the boule- The heating should be ide is 0.19 to 0.23 weight percent for this provides a transchhhhhed until the boule Obtains the desired o parent, uniquely amber rutile crystal. at least hours at 1450 Another requirement of the amounts of coloring agents, Accorfhhg to the Prhsent invention it is necessary to i.e., nickel oxide and tungsten oxide, is that they be pres- X oxldlze the hhle'hlack single 'y boule When ent in substantially equal mole quantities in the feed mah the colonhg agent in Order to revehl the charterial in order for them to be present in the boule in this actehshc h 9 of Such agent when the boule is only ratio. The following model is suggested to explain the in- Parhahy oxldlzeq the true @0101 is masked by the blue of creased stability of the solid solution system consisting of the,Xygeh h hohle thus Producing Colors having rutile modified with nickel and tungsten. bluish or green sh tone. The elements when added to It is known that metal ions incorporated into a rutile 5O T10 feed material produce boules having various colors. crystal lattice are usually in substitutional sites. That is, The color of the homes vanes depth and tone When they occupy the position normally occupied by titanium the elements are present in diflierent amounts. When any i n+4) In prior art when a single metal oxide is of these elements are present in the boule in very small added to a rutile boule, ch.rlrge balance will not Occur quantities the color of the boule is yellow, varying from a without defects or dislocations because the single cations paleyellqw to a Yellow W1th a hrWhish t When P ha,e valghces other than For example, if charge bah ent in slightly larger quantities the rutile single crystal ance was to obtain with two +2 valence metal ions then boule posseshhs hh amber color when hreseht ih Shh either these two ions would both have to occupy a Single larger quantities the color changes from a reddish amber titanium'ion substitutional site, or a defect or dislocation to ahhhst i colormust occur in the lattice. Of these two possibilities, the "i lhustrahohof the quahty of h obhhhed from former is-unlikely since the relevant metal ion additives vanohs composlhohs of h Powder 1s gweh Table are quite Similar in Size to titanium According to this The improved boule quality resulting from the addition vgmjoh, however, since two metal ions are added to the of both tungsten and nickel compared to that of nickel rutile lattice, one f which has a valence higher than alone is shown, as is also the effect of concentration of +4 he, w+6 and the other hi has a valence lower the tungsten and nickel additives on boule color. than Ti, i.e., Ni+ then charge compensation can occur In order to more fully illustrate this invention the when two titanium ions are replaced by one tungsten and method of preparing the boule f the invention is hereone nickel ion. after described in the example.

TABLE 1 Amount addition agent (calculated as atomic Addition agent i il v thi e g ion m Condition of boule 5,3152%" furnace Nickel oxide rthstilt hiphmstahh sfhfiihltrltafisstiths.

Nickel oxide and tungsten oxide 0.1: D Ti:W:Ni=l5:0.5:

Good quality do Amber (tnansparent).

EXAMPLE To prepare the feed material for' atomic ratios of Ti:W:Ni=l5:0.1:0.1, 8.56 grams of 99.95+% TiO ('Gallard Schlesinger Co.) were mixed with 0.18 gram reagent grade H WO and 0.21 gram of reagent grade Ni(NO '6H O. This mixture was slurried in water before grinding in an electric mortar. Then the mixture was calcined for 4 hours in a furnace at 1000 C. After grinding again in the mortar the powder was screened and that which passed through a No. 70 mesh screen was used as the feed powder.

The feed powder, having an average particle size of 0.3 4 and composed of mainly TiO along with smaller quantities of W0 and NiO, was fed at a constant rate of 0.05 gram/minute; suspended in an argon flow of 1 liter/ minute; and passed by means of a cooled-probe through an induction plasma. The plasma gas was a mixture of 97% argon and 3% oxygen; and, was admitted at the rate of 18 l./m. to a plasma torch consisting primarily of a 28 mm. I.D. quartz tube in which power is inductively coupled to the gas, thereby cold gas and feed material entered at the back and the hot gases and feed material were expelled at the front into a 2 in. I.D., zirconia mufile. Positioned in the muflie just below the torch and enveloped by the tail fi'ame from the plasma, the boule was located on the top of an alumina rod which was rotated and withdrawn at the boule growth rate. A sight port in the muffle allowed constant observation of the boule growth and measurement of temperature by an optical pyrometer. A in. long boule, of diameter which varied from V8 in. at the bottom to /2 in. at the top, was grown over a period of 4 hours. The as-grown boule was black in color. After growing the boule it was oxidized for 65 hours at 1425 C. in a tube furnace. The oxidized boule was a yellow-amber color. A 1 millimeter thick slab, cut from the boule and polished, was transparent and consisted of 0.067 weight percent of NiO, 0.208 weight percent of W0 and balance of TiO In order to show the effect of the addition of nickel and tungsten oxide to rutile, the measured absorption coeflicient of the boule of the example is plotted in the drawing for the visible region of the spectrum and compared with a pure rutile crystal. The absorption edge is seen to be shifted about 500 A. to longer wavelengths and toward the red end of the visible spectrum, and a residual absorption about 100 times greater than that of rutile was imparted to the boule by the nickel and tungsten oxides.

From the above description it has been shown that pleasant appearing colored rutile boules may be formed by the present invention. The coloring agents produce products which range in color from yellow through amber to reddish-black tones when added in varying quantities. The precise depth of tone and nature of the color obtained is readily controlled as hereinbefore described by employment of the appropriate mixture. These colored boules may be cut into gems which possess the required characteristics, particularly that of hardness and a pleasing appearance, which are necessary for the gem trade. They may also have application as a quantum electronic material, for example, a microwave maser.

While this invention has been described and illustrated by the example shown, it is not intended to be strictly limited thereto and other modifications and variations maiy lie employed within the scope of the following claims.

c aim: 1. A colored rutile single crystal boule containing oxides of tungsten and nickel in substantially equimolar amounts wherein said W0 content ranges from 0.02 to 0.8 percent and said NiO content ranges from 0.006 to 0.3 percent by weight based on said boule.

2. The boule of claim 1 wherein said W0 content ranges from 0.19 to 0.23 percent and said NiO content ranges from 0.06 to 0.07 percent.

References Cited UNITED STATES PATENTS 2,715,071 8/ 1955 -Merker 10642 2,801,182 7/1957 Merker 10642 2,715,070 8/1955 Moore 10642 3,558,333 1/1971 Beals 10642 FOREIGN PATENTS 686,490 1/ 1953 Great Britain 10642 OTHER REFERENCES Johnson, G., et al.: Influence of Minor Additions on Color and Electrical Properties of Rutile, J. Am. Cer Soc. 32 (1949), pp. 398-401.

HEL'EN M. MCCARTHY, Primary Examiner US. Cl. X.R. 2330l UNITED STATES PATENT OFFICE A CERTIFICATE OF CORRECTION Patent No. 3796"58)+ Dated March 20, 197" Inventor(s) CHASE, JOHN DONALD It is certified that error appears in the above-identified patent and that said'Letters Patent are hereby corrected as shown below:

Column 1, line 39, after the word masers, change "in" to is Column 3, line 16, after the word amount, change "ii" to of Signed and sealed this 23rd day of July 1971 (SEAL) Attest:

c. MARSHALL DANN MCCOY GIBSON JR Commissioner of Patents Attesting Officer P F RM P040550 (10-69) uscoMM-Dc 60376-P69 1 9 US. GOVIRNMINT PRINTING OFFICE z I!" 0-366-334

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