DE2403561C3 - Method of making amethyst crystals - Google Patents

Description

The invention relates to a method of manufacturing> of amethyst crystals, d. H. of quartz crystals that are colored purple. Amethyst crystals are used as semi-precious stones in the jewelry industry.

Investigations on amethyst crystals according to the methods of optical spectroscopy, quantum mechanical paramagnetic resonance, chemical spectral analysis and neutron activation analysis have shown that the violet color of the quartz is related to the electron vacancies that result from the action of ionizing radiation on the colorless quartz crystal, which contains structural (isomorphic) foreign ions of the trivalent iron Fe ³⁺ , which are captured by the crystal during the growth. This electron vacancies are in the crystals at the above-mentioned foreign v> ion of trivalent iron localized. Thus, the presence of iron in a trivalent state in the solution from which the colorless quartz crystals are grown is the necessary condition for the formation of amethyst crystals. v->

From the essay »Synthetic quartz with amethyst color« by L). Z i η ο b e r and LG. Cencovain of the journal »Kristallografija« of the Academy of Sciences of the USSR, Volume 4, 1959, Delivery 4, Pages 633-635 is a method of making wi Amethyst crystals known, in which colorless quartz crystals are grown by the hydrothermal temperature gradient method in a high pressure autoclave on quartz seed crystal plates, which are parallel to the crystallographic faces of the positive {1011} - or μ of the negative (ITOI) rhombohedron, and although from aqueous solutions of potassium carbonate or Kaliumhydroxid, which contain iron, the dem Autoclave supplied in the form of metallic iron or in the form of its oxide or hydroxide compounds using crystalline quartz as a feedstock and then exposing the grown colorless quartz crystals to ionizing radiation.

The known method for producing amethyst crystals has the following disadvantages:

1. Poor reproducibility of the process of Growth of colorless quartz crystals due to the indeterminacy of the physico-chemical parameters this process (the concentrations of the solutions used, the amount of iron or its compounds fed to the autoclave, the crystallization temperature, the pressure in the autoclave and the Growth rate of the quartz crystals on the seed crystal plates with the above-mentioned crystallographic orientations).

2. Insufficiently high degree of purity of the violet (amethyst) color of the crystals obtained, which is im essentially on a relatively high content of aluminum admixtures in aqueous solutions of Potassium carbonate or potassium hydroxide based The main source of aluminum are inclusions of various aluminum-containing minerals in the natural crystalline quartz, which is used as an input material. It is well known that the aluminum additions form the During the cultivation by the colorless quartz crystals are captured, with the action of ionizing radiation on the mentioned crystals smoke-colored centers, which the purity of the coloration of the Amethyst crystals deteriorate significantly.

In addition, the low oxidation potential of the solutions mentioned means that the iron in them Solutions are present in both the bivalent and the trivalent state. The growing colorless Quartz crystal catches the iron from the solution not only in the "useful" trivalent form, but also in the "harmful" bivalent state. Due to the latter circumstance, the degree of purity also decreases the color of the amethyst crystals.

3. Excessive fissuring of the amethyst crystals obtained, especially in the case of growing the crystals Quartz seed crystal plates parallel to the crystallographic faces of the positive rhombohedron are oriented.

The object of the present invention is to provide a method for avoiding the disadvantages mentioned To create production of amethyst crystals, the physico-chemical process parameters of which are good Ensure reproducibility of the process and amethyst crystals of high purity color and high Allow transparency (i.e., without crevices) to be obtained.

Starting from a method of the type described above, this object proposed according to the invention that aqueous solutions of potassium carbonate or potassium hydroxide with a concentration of 4 to 7 weight percent can be used, metallic iron or a Iron compound can be added to the autoclave in an amount of 5 to 30 g / l solution, the solution I. lithium nitrite or lithium nitrate or manganese nitrate in an amount of 1 to 10 g / l potassium carbonate or Potassium hydroxide solution is added and the cultivation of the colorless quartz crystals at a crystallization temperature of 300 to 500 ° C and a pressure from 200 to 1700 kgf / cm · is performed.

Due to the breeding conditions mentioned, it becomes possible to obtain amethyst crystals of good quality and pure, intense color. The process of breeding is well reproducible in terms of the determinateness of its physico-chemical parameters. Further details- *> ten of the invention emerge from the following references and examples.

The use of seed crystal plates that run parallel oriented to the crystallographic surfaces of the negative rhombohedron brings the following advantages i < > in the cultivation of colorless quartz crystals in comparison to use seed crystal plates that are parallel to the crystallographic faces of the positive rhombohedron are oriented with them.

First, the rate of growth is the crisis stand on the surfaces of the negative rhombohedron about 2 to 3 times higher, whereby the Yield increases and so does the cost of the colorless quartz crystal and thus also of the amethyst crystals sink. -> <>

On the other hand, the crystals grown on the surfaces of the negative rhombohedron contain practically no fissures, while the crystals in the Cultivation on the surfaces of the positive rhombohedron tends to intensify the formation of fissures. > ■>

In addition, colorless quartz crystals grown on quartz seed crystal plates oriented parallel to the crystallographic faces of the negative rhombohedron after exposure to the ionizing radiation receives amethyst crystals, which to show the effect of pleocroism of staining. This effect consists in a color shift of light purple to reddish purple with a change in the orientation of the crystal in relation to the light beam. The property of pleocroism of coloring, known for some varieties of natural amethyst, increases the value of the obtained crystals as a gemstone.

One zweckmä- w Big for producing Amethyst crystals with higher purity of the violet color used as a feedstock for the cultivation of the colorless QuarzkristaUe crystalline quartz having an aluminum content of impurities of not more than 5 ■ 10 ~ ³ weight percent

As such quartz, either natural quartz with the mentioned restriction with regard to the aluminum content or specially grown crystals of synthetic quartz can be used, the production process of which ^{ensures an aluminum additive content of not more than 5 · 10 -3} weight percent><>

To prepare such crystals of synthetic quartz according to the invention after the hydrothermal temperature gradient method in a high-pressure autoclave of quartz seed plates, the v, parallel to the crystallographic planes of the pinacoid (0001} are oriented, from aqueous solutions of sodium carbonate or sodium hydroxide with a concentration of 3 to 7 percent by weight using crystalline quartz as feed material at m> a crystallization temperature of 335 to 345 ° C and a pressure of 700 to 1500 kp / cm * crystals, with a growth rate of 0.15 to 0.5 mm / 24 Sets hours.

To avoid tension on the surface hi The seed crystal plates and thus the jagged amethyst crystals are best etched before the Cultivate the colorless quartz crystal using the quartz vaccine crystal plates at a temperature of 18 to 22 ° C for 2 to 3 hours with 40% hydrofluoric acid.

It is known that the aqueous solution of potassium carbonate or potassium hydroxide in metallic Form or in the form of its oxide or hydroxide compounds added iron under the conditions of Growth process in the solution in both the divalent and trivalent states present The addition of strong oxidizing agents belonging to the procedure according to the invention, such as Lithium nitrite or lithium nitrate or manganese nitrate to the solution, leads to the fact that the iron from the bivalent state largely changes into the trivalent state The predominance of the trivalent state Iron in the solution of potassium carbonate or potassium hydroxide favors the creation of amethyst crystals of extremely pure color. The lithium ions In addition, they »clean« the solution of potassium carbonate or potassium hydroxide from the undesired aluminum admixtures by making them too difficult to deal with convert soluble silicates of the type eucryptite LiAlSiO *, which also causes an increase in the degree of purity of the amethyst color

The method according to the invention for the production of amethyst crystals is carried out as follows:

Crystalline quartz charge is placed in the lower part of a high pressure autoclave (the dissolution chamber). Natural crystalline quartz, for example monomineral vein quartz or crystals made from synthetic quartz, can be used as the feedstock, which is particularly useful for the Production of amethyst crystals with a high degree of color purity is after the introduction of the A transverse plate with openings is used to insert the material to be used, which separates the dissolution chamber from the upper part of the autoclave, the growth chamber, separates Then one brings quartz seed crystal plates into the growth chamber, which lead to the crystallographic surfaces of the positive (10Ϊ1) or the negative (liOI) rhombohedron are oriented, either parallel to the crystallographic faces of the positive rhombohedron or parallel to the crystallographic faces Areas of the negative rhombohedron, or seed crystal plates of the two mentioned orientations are introduced

After the material and the seed crystal plates have been placed in the autoclave, a solution of potassium carbonate or potassium hydroxide (working solution) is poured into the autoclave. Additions of metallic iron or its oxide compounds (FeO, FezOj, Fe ₃ O ₄ ) or hydroxide compounds (Fe (OH) ₂ , Fe (OH) ₃ ) as well as additions of lithium nitrite or lithium nitrate or manganese nitrate are also added to the autoclave. The additives mentioned are either fed to the dissolving chamber when the material is loaded or to the growth chamber after the autoclave has been filled with the working solution

After loading, the autoclave is hermetically sealed and heated to the specified breeding conditions, d. H. a certain crystallization temperature and a certain pressure in the autoclave.

These predetermined cultivation conditions are maintained in the autoclave for the entire duration of the process. The duration of the process (in hours) is calculated using the formula r = d / V. where d (in mm) is the specified thickness of the

Seed plate grown layer of the crystalline Quartz, V (in mm / 24 hours) the rate of growth that occurs as a function of the conditions the grown layer of crystalline quartz on the seed plate of the chosen Orientation means After the cultivation process is finished, the autoclave is heated interrupted and this cooled to room temperature, after which the grown colorless quartz crystals be discharged from the autoclave.

The colored quartz crystals are exposed to ionizing radiation (y-rays, hard X-rays, fast electrons) with a dose of 1 · 10 ³ Ws 1 · 10 ⁷ X-rays, preferably 5 · 10 ⁵ DiS 1 - 10 * X-rays, whereby the crystals take on the purple amethyst color.

For further explanation, some concrete examples for the production of amethyst crystals are given below cited

example 1

In a high-pressure autoclave, natural crystalline quartz is used as input, parallel to the crystallographic faces of positive {1011} and negative {1101} rhombohedron oriented quartz seed crystal plates and an aqueous potassium carbonate solution having a concentration of 5 percent by weight. In addition, iron is introduced in the form of iron (II) oxide (FezCh) in an amount of 20 g / l solution and lithium nitrate (LiNCh) added in an amount of 7 g / l potassium carbonate solution

Before being placed in the autoclave, the seed crystal plates had been subjected to etching with 40% hydrofluoric acid ^{at a temperature of 20 ° C. for 2.5 hours.}

To grow the colorless quartz crystals, a crystallization temperature of 360 ° C. and a pressure of 1500 kgf / cm ^{2 are} set, resulting in a growth rate of 0.15 and 03 mm / 24 hours on the areas of the positive and negative rhombohedra, respectively.

The crystals obtained are transparent and do not contain any fissures.

After exposure to y-radiation with a dose from 1 -10 * X-ray the crystals take on a very pure, dark purple color. The on the surfaces of the Crystals grown in negative rhombohedra show a strongly pronounced appearance after irradiation Pleocroism of color.

Example 2

In a high pressure autoclave, natural crystalline quartz and parallel to the crystallographic faces of the negative {1101} rhombohedron oriented quartz seed crystal plates, an aqueous potassium carbonate solution with a concentration of 5 percent by weight, iron HI, III) oxide (FesOO in an amount of 30 g / l solution and Lithium nitrate (L1NO3) in an amount of 5 g / l solution a.

The growth of the colorless quartz crystals was carried out under conditions as in Example 1 are named. The crystals grown are transparent and do not contain any crevices.

After exposure to y-radiation with a dose from 1 · 10 * X-rays the quartz crystals take on the violet color with pronounced pleocroism slide>. regular distribution of the color over the volume the Ulistalle.

Example 3

ί Natural crystalline quartz, which contains aluminum in an amount of 5 · ΙΟ- ³ percent by weight, and quartz seed crystal plates, oriented parallel to the crystallographic surfaces of the positive, are placed in a high-pressure autoclave

in {1011} and the negative {1101} rhombohedron, one aqueous potassium carbonate solution with a concentration of 5 percent by weight, iron (III) oxide (Fe2Oj) in in an amount of 20 g / l solution and lithium nitrite (L1NO2) in an amount of 1 g / l solution.

π Prior to introduction into the autoclave, the lmpfkristallplatten at a temperature of 20 ⁰ C for 2.5 hours to etching with 40% hydrofluoric acid exposed

The cultivation of the colorless quartz crystals is carried out at

2n a crystallization temperature of 360 ⁰ C and a pressure of 1500kp / cm ^{2 was} carried out to give a growth rate of 0.2 and 0.4 mm / 24 hours on the surfaces of the positive or negative setting of the rhombohedron.

2 ^r > The grown crystals are transparent and have no crevices. After exposure to X-rays with a dose of 5 · ΙΟ ⁵ X-rays, the quartz crystals take on a highly pure, violet color. Those on the faces of the negative

) '> Crystals grown in the rhombohedron show a pronounced pleocroism of color.

Example 4

First, the input material is prepared from the

η crystals made of synthetic quartz with a content of aluminum admixtures of 1 ± ³ percent by weight. For this purpose, natural crystalline quartz and quartz seed crystal plates, oriented par-

4 (i all! To the crystallographic faces of pinacoid {0001}, and an aqueous sodium hydroxide solution at a concentration of 3 percent by weight.

The cultivation of the crystals of synthetic quartz with the above-mentioned aluminum content is carried out at

■ »■> carried out at a crystallization temperature of 345 ° C. and a pressure of 1500 kp / cm ² , a growth rate of 0.5 mm / 24 hours being established.

Then you put in another high-pressure car

V) klav the feedstock prepared in the manner described above (crystals of synthetic quartz), quartz seed crystal plates, oriented parallel to the crystallographic surfaces of the positive {1011J and the negative {1101} rhombohedron, an aqueous potassium carbonate solution with a concentration of 5 Percentage by weight, iron (III) oxide (Fe ^) in an amount of 15 g / l solution and lithium nitrate (LiNOs) in an amount of 5 g / l solution.
Before being placed in the autoclave, the

with seed crystal plates etched with 40% hydrofluoric acid subjected at a temperature of 22 ° C for 2 hours.

The cultivation of the colorless quartz crystals takes place at a crystallization temperature of 35O ⁰ C and

h ^r > a pressure of 1300 kp / cm ² , with a growth rate of 0.1 and 0.2 mm / 24 hours on the surfaces of the positive and the negative rhombohedron, respectively.

IO

The crystals grown are transparent and have no crevices. Under the action of y-radiation with a dose of 1 · 10 * X-rays the quartz crystals take on a very pure purple color. Those at the parallel to the crystallographic Crystals grown on surfaces of the negative rhombohedron oriented seed crystal plates demonstrate the irradiation has a very pronounced pleochroism Color on.

Example 5

First one prepares the feedstock composed of crystals of synthetic quartz having a content of aluminum admixtures of 8 x 10- ⁴ percent by weight. To do this, natural quartz and quartz seed crystal plates, oriented parallel to the crystallographic surfaces of pinacoid {0001}, and an aqueous sodium carbonate solution with a concentration of 7 percent by weight are brought into a high-pressure autoclave as starting material. The crystals of synthetic quartz with the above-mentioned aluminum content are grown at a crystallization temperature of 335 ° C. and a pressure of 700 kgf / cm ² , resulting in a growth rate of 0.15 mm / 24 hours.

The prepared in the manner described is then placed in another high-pressure autoclave

Charge (synthetic quartz crystals), quartz seed crystal plates, oriented parallel to the crystallographic surfaces of the positive | 10Tl (- and des negative (1101 | rhombohedron, an aqueous solution of potassium carbonate at a concentration of 5 percent by weight, metallic iron in an amount of 20 g / l solution and manganese nitrate (Mn (NO3> 2) in one Amount of 10 g / l solution.

Before being placed in the autoclave, the seed crystal plates are subjected to etching with 40% strength hydrofluoric acid at a temperature of 18 ^° C. for 3 hours.

The colorless quartz crystals are grown at a crystallization temperature of 360 ° C. and a pressure of 1500 kp / cm ² , with growth rates of 0.15 and 0.3 mm / 24 hours on the surfaces of the positive and negative rhombohedra, respectively adjusts.

The crystals grown are transparent and have no crevices. When exposed to y-radiation with a dose of 1 - 10 ⁶ X-rays, the quartz crystals take on a very pure violet color. The crystals which were grown on the seed crystal plates, which were oriented parallel to the crystallographic surfaces of the negative rhombohedron, show a very pronounced pleochroism of color after irradiation.

809 635/273

Claims (1)

Claim: A process for preparing Amethyst crystals by growing colorless quartz crystals after ^r> the hydrothermal temperature gradient method in a high-pressure autoclave of quartz seed plates which are parallel to the crystallographic Avenge the positive {1011} - or the negative | 1101} -Rhomboeders are oriented from aqueous "> Solutions of potassium carbonate or potassium hydroxide, which contain iron, which has been added to the autoclave in the form of metallic iron or in the form of its oxide or hydroxide compounds, using crystalline quartz 'ϊ as feed and subsequent exposure to ionizing radiation on the grown colorless quartz crystals, characterized in that aqueous solutions of potassium carbonate or potassium hydroxide are used with a concentration of 4 to 7 μ weight percent, metallic iron or an iron compound are fed to the autoclave in an amount of 5 to 30 g / l solution, the solution lithium nitrite or lithium Mnitrate or manganese nitrate in an amount of 1 to 10 g / l - "> potassium carbonate or potassium hydroxide solution is added and the cultivation of the colorless quartz crystals at a crystallization ^{temperature of 300 to 500 0} C and a pressure of 200 to 1700 kp / cm ² is carried out. ι «