DD297801A5 - METHOD FOR PRODUCING LOW TEMPERATURE QUARTZ GRANULATE FROM AMORPHIC SILICA - Google Patents

Abstract

The invention relates to a process for the production of cryogenic quartz granules from amorphous silicic acid. The aim of the invention is to make it possible to obtain a quartz starting material for the silica glass melt from an easily accessible SiO 2 raw material. The object of providing a process for producing high-purity, fusible quartz granules with inclusion-free microcrystals of suitable grain sizes of amorphous silica is achieved by dissolving a wet slurry of amorphous silicic acid with the addition of an activator and after setting a p H value range of 7-9 by means of ammonia water a 2-12taegigen hydrothermal isothermal treatment in an autoclave at 250-370C and a degree of filling of 80-85% to reach a pressure of 39.24 MPa to 147.15 MPa is subjected. Cryogenic quartz granules produced according to the invention can be used as starting material for the production of high-quality optical and silica glasses.

Description

Characteristic of the known technical solutions Silica glass is generally made by melting rock crystal granules. However, the rock crystal deposits are limited and sometimes already exhausted. Therefore, synthetic quartz crystals, according to the known hydrothermal synthesis by means of temperature difference

grown between nutrient and growth space and crushed to a specific grain, as a raw material for the

Silica glass melt used. The Hydrothermalsynthese of quartz crystals is a lengthy, complicated and for the Granule production ineffective process. As a nutrient are indeed fragments of processed, in nature far

However, for crystallization, in the growth space of the autoclave, germ plates or rods of rock crystal or pre-grown quartz crystals are to be introduced.

In the SU-copyright 285,908 a method for bulk crystallization and associated purification of Gangquarz using the well-known hydrothermal process described. How to nucleate,

is not stated. In addition, it should be very difficult, according to this method the same size crystal grain in the for dio

Silica glass melt required size, so that in turn a costly and impurities entraining Zerkleinerugnsvorgang must be followed. V. B Lazarev points out the possibility of obtaining finely crystalline quartz of grain size 0.1 to 0.5 mm from amorphous SiO ₂ containing industrial waste products by a 10 to 60 hours hot steam treatment in an autoclave in Presence of an activator.

(V. B. Lazarev, M.N. Danchevskaya, G.P. Panasyuk, V.M.Gavrilko, Soviet export 6 [141] 1982)

Details of this from the Kurnakov Institute of General Inorganic Chemistry of the Academy of Sciences of the USSR developed procedures are not specified. Object of the invention

The object of the invention is to enable the obtaining of a qualitatively suitable quartz starting material for the production of high quality optical and silica glasses from an easily accessible raw material.

Explanation of the essence of the invention The invention is based on the object, a method for producing high-purity, meltable Cryogenic quartz granules with poor gas-liquid inclusions, or free microcrystals of suitable particle size

to provide amorphous silica as SiO ₃ raw material. This object is achieved by a method of generating

Low-temperature quartz granules of amorphous silica according to the invention dissolved in that an aqueous slurry

from 350 to 500 g / l of amorphous silica containing from 2 to ₅ g / l of an activator, preferably nitrilotriacetic acid (C ₆ HgNOe),

Ethylenediaminetetraacetic acid (C, οΗ | _β Ν ₂ 0 ₈ ) or disodium dihydrogenated ethylenediaminetetraacetate dihydrate

(C ₁₀ Hi ₄ N ₂ Na ₂ O ₈ · 2HjO) and their pH is adjusted to pH 7-9 by addition of aqueous ammonia solution, a hydrothermal isothermal treatment in an autoclave at a temperature of SO ⁰ C to 37O ⁰ C and a degree of filling of 80 to 85% to reach a pressure of 39.24 MPa to 147.15 MPa for a period of 2 to 12 days.

Thermodynamically, the silica in the form of amorphous silica has a higher energy state than the SiO ₂ in Form of stable at low pressure in the temperature range up to 573 ⁰ C Tiefftemperaturqudrz modification. By the inventive method of hydrothermal isothermal treatment in the presence of a suitable activator

succeeds in converting the more energetic and therefore metastable state of the amorphous silica into the stable form of microcrystalline cryogenic quartz. The applied high pressure should change the modification of

support amorphous state of low-density SiO ₂ in the microcrystalline state with the higher density (=?, 65gcrrT ³ ).

Since the activator used: is an organic substance, no significant impurities are introduced in the form of foreign metal ions. An exception is the addition of disodium dihydrogenated ethylenediaminetetraacetate dihydrate. The small addition of Na "ions does not exert any analytically measurable influence on the self-purification process of the hydrothermal phase transformation.

Ausführungsbelsplele

The invention will be explained in more detail below with reference to two examples.

example 1

A suspension of 54 kg of amorphous silica and 64.41 of bidistilled water with the addition of 160 g of disodium dihydrogenated ethylenediaminetetraacetate dihydrate as activator is prepared, which is brought to pH 9 by adding ammonia water.

This slurry is spread on 12 teflon-coated containers (diameter 245 mm, height 200 mm), which are then placed one above the other in a Teflon-lined autoclave with a free volume of 120 l and a diameter / length ratio of the reactor chamber of 1:10. In order to achieve a filling level of 85%, 101 are distilled water. minus the amount already added for pH regulation (ammonia water). After the autoclave has been closed, it is heated isothermally to 27O ⁰ C and held isothermally for 8 days at this temperature. During this time, the microlocal, hydrothermal phase transformation of the amorphous silica takes place in low-temperature quartz granules.

Then, after switching off the heating and cooling down to 30 ⁰ C, the autoclave can be opened. To drain the granules, the containers are removed and placed in a dust-free drying room.

Example 2

440 g of amorphous silica are slurried with 521 ml of bidistilled water with the addition of 1.5 g of ethylenediaminetetraacetic acid and adjusted to pH 8 with ammonia water. The 5 containers made of silver filled with this slurry are placed one above the other in a silver-lined autoclave (50 mm diameter, 500 mm height) with a free volume of 910 ml. By adding 74 ml of bidistilled water, a filling level of 80% is achieved. At an isothermal reaction temperature of 350 ^° C. for 5 days, the hydrothermal treatment of the slurried silica is carried out. The removal and drying of the granules is carried out analogously to Example 1.

Claims (1)

A process for the production of low-temperature quartz granules of amorphous silica, characterized in that an aqueous slurry of 350 to 500g / l of amorphous silica with 2 to 5g / l of an activator, preferably nitrilotriacetic acid (CoH ₉ NOg), ethylenediaminetetraacetic acid (C ₁₀ H ₁₆ N ₂ O ₈ ) or disodium dihydrogenated ethylenediaminetetraacetate dihydrate (C ₁₀ H ₁₄ N ₂ Na ₂ O ₈ .2H ₂ O), and the pH thereof is adjusted to a pH range of 7-9 by addition of aqueous ammonia solution hydrothermal isothermal treatment in an autoclave at a temperature of 250 ⁰ C to 370 ⁰ C and a degree of filling of 80 to 85% to reach a pressure of 39,24MPa to 147,15MPa for a period of 2 to 12 days is subjected. Field of application of the invention The invention relates to a process for the production of low-temperature quartz granules of amorphous silica. Such low-temperature quartz granules obtained in particular can be used as starting material for the production of high-quality optical and silica glasses.