JPS59141493A - Preparation of star corundum - Google Patents

Abstract

PURPOSE:To prepare star corundum having transparent and clear star inexpensively, by using a raw material rod obtained by molding and sintering mixed powder of TiO2-Al2O3 solid solution powder and Cr2O3 powder, synthesizing a crystal from it, annealing the crystal. CONSTITUTION:TiO2-Al2O2 Solid solution powder is blended with Cr2O3 powder as a colorant to give mixed powder, which is packed into a rubber tube, molded into a cylindrical rod by rubber press, and sintered in an electric furnace at 1,200-1,600 deg.C. The sintered rod is used as a raw material, corundum or a sintered rod of corundum is utilized as a seed crystal, a crystal is grown preferably in a reducing atmosphere by condensing floating zone method, it is annealed, to give red star corundum. The use of TiO2 and Fe2O3 as a colorant provides blue star corundum. The solid solution contains preferably 0.1-0.5wt% TiO2, the annealing is carried out at 1,100-1,600 deg.C and needle-like crystal of TiO2 is preferably precipitated.

Description

DETAILED DESCRIPTION OF THE INVENTION The color of corundum varies depending on the coloring agent added. For example, if chromium oxide is added, the color will be red, and if titanium oxide and ferric oxide are added, the color will be blue. When titanium oxide is added to these corundum raw materials and crystals are synthesized by the conventional B'Z method or Bernoulli method, raw star corundum is obtained.

By annealing this, when the cabochon is polished in the C-axis direction, lines appear radially at an angle of 60 degrees to each other around the C-axis, which looks like a star. However, star corundum synthesized by the conventional condensing F, Z method or the Bernoulli method is considerably inferior to natural corundum in terms of transparency and star clarity.

This is because titanium oxide is not uniformly dissolved in aluminum oxide. Therefore, in the present invention, an aluminum oxide-titanium oxide solid solution is prepared in advance, and the powder is mixed with a coloring agent such as chromium oxide to obtain a raw material powder. In addition, it was decided that the growth atmosphere would be a reducing atmosphere. With this K, titanium oxide could be uniformly dissolved in cicorundum. The synthesis method will be described in detail below.

The aluminum oxide-titanium oxide solid solution used as a raw material is obtained by placing desired aluminum oxide and titanium oxide in an iridium crucible, heating and melting the mixture at 2100° C. in a nitrogen or argon atmosphere, and rapidly cooling and solidifying. At this time, the amount of titanium oxide is -T: 0. IW% ~0.
If 5W% of 1° is less than 0.1W%, stars will not appear clearly when star corundum is synthesized. If it is more than 0.5 W%, it is unsuitable because it causes segregation during synthesis. Acid hichrome shells are added as a coloring agent to the aluminum oxide-titanium oxide solid solution powder obtained above. This is thoroughly mixed, packed into a rubber tube, and formed into a cylindrical rod using the rubber press method. This stick is 1
Sinter in an electric furnace at 200°C to 1600°C. At this time, sintering is insufficient below 1200°C, and there is no difference in the degree of sintering above 1600°C. Using this as a raw material and using a corundum crystal or sintered body as a seed crystal, a well-known light focusing F,
Synthesis is performed using the Z method. At this time, the growth atmosphere is an argon-hydrogen reducing atmosphere. Also, the hydrogen concentration is 1rili
tppM -11000pp. 1000pp
At M or higher, the colorant does not come out and the color does not trace, making it suitable for cinema.

](] The solid solution of titanium oxide is not promoted below ppM. Next, the synthesized corundum is heated at 1100°C to 160°C.
Anneal in an electric furnace at 0°C. At this time, temperatures as low as 1100°C or as high as 1600°C are unsuitable because needle-like crystals of titanium oxide (rutile) do not precipitate.

Further, after annealing, it is necessary to perform slow cooling at a rate of 5° C./min to H112/min to prevent cracks from occurring due to thermal distortion or the like.

In summary, the present invention has made it possible to provide star corundum, which is comparable to natural star corundum, to the general public at a low cost. In order to make the effects of the present invention clearer, <Examples> are shown below.

<Example 1> - Raw material rod production method Aluminum oxide 99', 9F and titanium oxide 0.12 are placed in an alumina chute and mixed thoroughly. The mixture was placed in an iridium crucible, melted by high-frequency heating in a nitrogen atmosphere, and rapidly solidified. This was crushed into powder. This powder is thoroughly mixed with 201 and 0.62 of chromium oxide using an alumina pestle. Pack this into a rubber tube and remove the air inside the tube.

Next, by a rubber press method, a rod of 12 ms [φl×100 ma-] was obtained using a pressure of 3000 mm. This was sintered in an electric furnace at 1600° C. for 4 hours to obtain a raw material rod.

Method for growing crystals Using an infrared concentrated heating wheel crystal manufacturing device manufactured by Nichiden Machinery Co., Ltd., the crystals were grown under the following conditions.

Seed Crystal White Zaphire Growth Direction (001) Shaft rotation speed Upper and lower rotations are 3 orpm and reverse rotation atmosphere Hg, ArH2 concentration (iooo
ppM) Growth rate: 2 hours/H Growth time: 40 hours・Annealing condition temperature: 1600°C Time: 12 hours Slow cooling rate: 5°C/min・Results were cloudy red crystals. When this was cut into a cabochon with the zero side facing up, a clear star appeared.

<Example 2> - Preparation of raw material rod Aluminum oxide 99°52 and titanium oxide O,52 are taken into an alumina milk and thoroughly mixed. Hereinafter, the same operations as in <Example 1> are performed.

・Cultivation method The cumulative concentration of water in the growth atmosphere gas is set to 10 p7yM.

The rest follows <Example 1>.

・Annealing condition temperature: 1100°C Time: 30 hours Annealing rate: HJ°C per minute ・Result: cloudy red crystals were obtained. When this was cut into a cabochon with the 0 side facing up, a clear star appeared.

<Example 3> - Preparation of raw material rod Aluminum oxide 99.51 and titanium oxide 0.57 are taken into an alumina milk and thoroughly mixed. This was placed in an iridium crucible, melted by high frequency heating in an argon atmosphere, and rapidly solidified. This was crushed into powder. This powder 2Or, titanium oxide 27, and ferric oxide 62 are placed in an alumina mortar and mixed thoroughly. The following operations follow <Example 1>.

・Cultivation method According to <Example 1>.

・Annealing conditions According to <Example 1>.

・As a result, cloudy blue crystals were synthesized. When this was cut with the zero side facing up, a clear star appeared.

that's all Applicant: Shikiwa Seikosha Co., Ltd.

Claims (1)

[Claims] [11 Titanium oxide-aluminum oxide solid solution powder, chromium oxide powder or titanium oxide as a coloring agent,
Add iron powder. This powder is mixed, the core is packed into a rubber tube, and it is formed into a cylindrical rod by a rubber press method. The kernel bar is sintered in an electric furnace at 1200°C to 1600°C. Using this sintered rod as a raw material, using corundum or a sintered corundum rod as a seed crystal, it is characterized by being synthesized and annealed by the known condensing flow buifugu zone method (hereinafter referred to as condensing F, Z method). How to make star corundum. (2) The star powder according to claim 1, wherein the titanium oxide in the titanium oxide-aluminum oxide solid solution is 0.1 W% to 0.5 W% with respect to the total amount. manufacturing method. (3) A method for producing star corundum according to claim 1, characterized in that the growth atmosphere is a reducing atmosphere. (4) In claim 1, for precipitating needle-like crystals of titanium oxide (rutile) in the grown crystals, 1
The method for producing star corundum according to the above item, characterized in that annealing is performed at 100°C to 1600°C.