RU2255792C1 - Method of production of filtering articles from silicon dioxide - Google Patents

Abstract

FIELD: production of filters from silicon dioxide.

SUBSTANCE: proposed method includes mixing fraction silicon dioxide with binder containing solution of polyvinyl alcohol in water, boron-containing additive is mixed with surfactant form series of organic fatty acids and silicon dioxide sol; mixture thus obtained is introduced discretely into fraction silicon dioxide at constant mixing, charge is granulated and molded by application of vibrating oscillations; blank thus obtained is dried for obtaining transportation strength, roasted in gas medium and subjected to mechanical treatment. Articles have strength of 30-40 Mpa at content of boron elements of 4-14x10^-5%; they are used for production of high-purity materials for fiber-optic light conduits.

EFFECT: enhanced efficiency.

8 cl, 1 tbl, 3 ex

Description

The invention relates to methods for the manufacture of filters of silicon dioxide used in the technique of producing high-purity materials for fiber optical fibers.

A known method of obtaining a filter material from silicon dioxide, including the creation of silicon particles of uniform size by introducing vapors of a volatile silicon compound into the flame of an oxygen-hydrogen burner with simultaneous deposition of the resulting particles on a substrate of coarse-porous refractory material, sintering at 900-1300 ° C, and the whole process receiving filter material is carried out for 5-100 min (RU 2038841, 07/09/95).

The disadvantage of this method is the use of toxic and explosive components, the formation of correlating compounds that lead to rapid deterioration of ventilation systems at the outlet of the reactor, and physicochemical processes are sensitive to changes in the volume and expiration of volatile compounds, which leads to the degradation of deposition modes in the manufacture of large-sized products various configuration.

The closest in technical solution and intended purpose - the prototype is a method for producing refractory filtering ceramic hard products, comprising mixing fractional refractory filler, a binder and a low-melting component containing technical calcium borate in an amount of 5-16% by weight, which is mixed with a refractory filler, after which the binder is introduced into the mixture and the resulting mass is mixed for 5-10 minutes with 3-7% of the mass. fine alumina, molding, drying and firing. Moreover, technical calcium borate with a particle size of 0.06-0.5 mm is used, and aluminum oxide with a particle size of 0.01-0.5 mm.

In addition, magnesium phosphate or aluminophosphate or soluble sodium or potassium silicate are used as a binder (SU 952811, 08.23.82).

The disadvantage of this method is the difficulty of obtaining a uniform distribution of boron-containing additives in the volume of fractionated filler by dry mixing, since the fine-grained particles of the additive are prone to coagulation and are not distributed over the surface of the filler particles, which leads to priority absorption of the introduced binder by porous coagulants and microlocal chemical compositional irregularities that determine significant residual stresses during sintering and a decrease in operational strength. In addition, various metal and halogen elements introduced with additives cannot be used in products for the production of materials for optical fibers, since they lead to degradation of the target properties.

The aim of the invention is to increase the mechanical strength of the products while maintaining the spectral purity of the material.

The goal is achieved in that in the method of manufacturing filter products from silicon dioxide, comprising mixing fractional silicon dioxide, additives that form the structure of the material of the binder, molding, drying and firing, according to the invention, fractional silicon dioxide is mixed with a binder containing a solution of polyvinyl alcohol (PVA ) in water, a boron-containing additive is mixed with a surfactant from a number of organic fatty acids, mixed with a ceramic binder consisting of silica sol I, the resulting mixture is discretely introduced into the fractional silicon oxide with constant stirring, the resulting mixture is granulated, molding is applied with a vibration load, the resulting preform is dried to obtain transport strength, calcined in a gaseous medium, the resulting semi-finished product is subjected to mechanical processing, and regeneration from mechanical products is carried out and the seating surfaces are blocked by sealing material.

The essence of the proposed technical solution consists in a set of operations and the sequence of their implementation, which allows to achieve the goal:

- mixing fractional silicon dioxide with PVA dissolved in water with vigorous stirring allows you to use the proppant effect of water and evenly distribute PVA on the surface of the filler particles. The content of 10-15% of the mass. PVA allows you to get a solution with a viscosity that determines the optimal mixing time of various volumes for 5-10 minutes;

- intervals of the number of temporary ligaments from 8 to 22% of the mass. over 100% affect the transport strength and drying processes of the workpieces and are justified by the fact that below 8% of the mass. the workpiece is deformed by its own weight, and above 22% of the mass. moisture removal processes are complicated;

- a boron-containing additive is introduced to exclude the cristobalization process associated with volume changes and a decrease in strength, and mixing with a surface-active substance (surfactant) from a number of organic fatty acids in an amount of 0.5-1% of the mass. by weight of the boron-containing additive excludes coagulation of finely dispersed particles due to surface energy and leads to the formation of mobile radical bonds that provide adsorption of a ceramic binder on their surface.

The number of surfactants introduced is determined experimentally. In addition, boron nitride with a specific surface area (S) = 15000-1600 cm ² / g can be used as a boron-containing additive, and oleic, stearic acid or mixtures thereof as a surfactant.

- mixing a boron-containing additive treated with a surfactant with a ceramic binder provides for its uniform distribution, and the experimentally determined amount is 0.5-1.5% by weight of silicon dioxide formed from sol;

- ash-like ceramic binder during firing gives a material of spectral purity identical in chemical composition to fractional silicon oxide, and excludes the introduction of impurities that affect the target properties of the product;

- the process of mixing fractional silicon dioxide and a mixture of sols with a boron-containing additive is intended to obtain a molding mixture with a uniform distribution of components, and the discrete introduction of the mixture, for example 15-20% of the mass. from its total content, at time intervals of 5-10 minutes intensifies the process of homogenization;

- the quantitative content of the mixture in fractional silica from 4 to 9% of the mass. determines the optimal properties of products;

- granulation of the charge provides additional homogenization of the mixture, and the receipt of spherical particles of different fractions promotes fluidity when filling the mold and denser packaging of the material;

- the application of vibration makes it possible to obtain the maximum possible bulk density of the backfill for this conglomerated system and to carry out the pressing process at specific pressures not exceeding the tensile strength of the filler particles, which eliminates the unregulated pore size and ensures the preservation of the calculated average hydraulic pore size over the entire volume of the product;

- the achievement of transport strength during drying is necessary to exclude marriage of products in the form of various kinds of deformations and destruction when moving workpieces for firing and organizing cages;

- firing in a gaseous medium is intended to obtain the specified physical, mechanical, structural characteristics and chemical composition of the product material;

- machining allows you to remove technological allowances and obtain the geometric dimensions of the products in the tolerances determined by the requirements of the drawing documentation;

- as a result of mechanical treatment, in particular large front surfaces with the use of cooling emulsions, a significant amount of contaminants enter the pores, which are removed by regenerating components under pressure not exceeding the structural strength of the porous product, as a result of which all physical and mechanical chemical characteristics of the starting material are preserved and a given permeable porosity of the products;

- in quartz reactors, where feedstock is prepared for fiber optic fibers using a mixture of nitric and hydrofluoric acid, silicon dioxide filters are mounted in contact with metal structures, and to prevent metal corrosion, contact seating surfaces are blocked by acid-resistant sealing materials, for example, paste containing fluoroplastic , which increases the serviceability of the supporting structures.

Examples of implementation.

Example 1

1. The proposed method was used to manufacture a filter product with geometric dimensions: h = 40 mm, D = 500 mm.

2. The fractional filler, silicon dioxide with a particle size of 1.6 + 0.63 mm, with an impurity content of ≤5 × 10 ^-3 % is mixed with a 12.5% solution of PVA in water at a content of 15% in excess of 100% and 115 gr mixture with the content of components,% mass .: SiO ₂ - 100; PVA - 1.875; water - 13.125.

3. A boron-containing additive in the form of boron nitride with a specific surface area (S) of 15,000-16,000 cm ² / g is moistened with oleic acid (surfactant) in an amount of 0.7% by weight. and produce mixing in a planetary centrifugal mill lined with agate for 1-2 minutes.

A ceramic binder is added to the moistened surfactant boron nitride at a content of components,% wt. on dry weight:

SiO ₂ - 99,465

BN - 0.5

Surfactant - 0.035 and the components are mixed for 3-5 minutes.

4. The resulting mixture in an amount of 6% of the mass. added to fractional silicon dioxide with PVA at 20% of the mass. after 5 minutes with constant stirring.

5. The resulting mixture containing components,% mass:

fractional silicon dioxide

(SiO ₂ ) 92.6

Ceramic binder

(SiO ₂ ) 5.53

Boron Nitride (BN) 0.0278

Polyvinyl (PVA)

alcohol 1,738

oleic acid

(Surfactant) 2 × 10 ^-3

water, in excess of 100% 12.2

wiped through a sieve with a mesh size of 4-5 mm

6. The mixture was weighed on a platform scale in order to obtain the product h = 40 mm, D = 500 mm, taking into account the porosity of the finished product.

7. After filling the mold, a vibration load was applied for 3-5 seconds, then the upper punch was pressed with a specific pressure of 100-150 MPa / cm ² _, and with constant vibration, the process was carried out until the punch was set to a predetermined level.

8. The products were dried in an electric dryer with a vertical arrangement of the product in a wooden cassette at a temperature of 70-100 ° C, for the time required to achieve a moisture content of 0.1-0.2%.

9. Products were fired in a gas-flame furnace with flame isolation at a temperature of 1200–1350 ° С.

Sintered products were controlled by weight and size to determine density. Samples (10-12 samples) were cut from one product to determine the composition, physico-mechanical properties by standard methods. Characteristics of the materials are presented in the table.

10. The blanks sintering were treated by the seating surfaces on the round-the-surface grinding machine and using diamond wheels on the copper bonded brand AU ^12,400 / 312 particle size M ₂ - 01-150, using a waterborne cooling agent.

Finished products were placed in a sealing cassette and rinsed with discarded water at a pressure of 0.8-0.85 Top for 15-20 minutes.

12. After regeneration from the processed products, the products were dried, a cardboard stencil was placed on the front surface, and the side surface and the unprotected part of the front surface were blocked with a soluble fluoroplastic paste. After drying, the products were used in a quartz reactor to obtain spectrally pure silicon dioxide by washing it from impurities in mixtures of nitric and fluoric acids.

Example 2

1. When implementing example 2, all operations of example 1 were carried out using a mixture containing components,% of the mass:

Factional

silicon dioxide (SiO ₂ ) 87.3

Ceramic

binder (SiO ₂ ) 9.0

Boron Nitride (BN) 0.09

Polyvinyl alcohol

(PVA) 3.64

Oleic acid 4.35 × 10 ^-3

(Surfactant)

Water, in excess of 100% 17.6

Example 3

1. When implementing example 3, the entire sequence and parameters of the technological process operations were duplicated according to the example with the changed content of components in the charge,% of the mass.

Fractional dioxide

silicon (SiO ₂ ) 94.74

Ceramic

binder (SiO ₂ ) 4.0

Boron Nitride (BN) 0.06

Polyvinyl alcohol (PVA) 1.2

Oleic acid 6 × 10 ^-3

Water, in excess of 100% 6.8

These tables show that the proposed method for producing products from silicon dioxide allows to obtain products with enhanced performance characteristics, which ensures the serviceability of the product in the apparatus for obtaining the initial product for the production of fiber optics.

The inventive method is carried out on standard industrial equipment, objectively controlled in the manufacture of industrial batches of products of a given composition.

No. p / p Examples of implementation The composition of the material,% of the mass. Open Porosity,% Tensile Strength, σcf, MPa Breathability, m ³ cm / m ² h × mm aq. Art. SiO ₂ Admixture of boron,% 1 Example 1 100 4.7 × 10 ^-5 32 thirty 60 2 Example 2 100 9 × 10 ^-5 thirty 37 53 3 Example 3 100 14 × 10 ^-5 26 40 47 4 Famous silicate 1,07 ÷ 2,14 26-32 10-20 20-50

Claims (8)

1. A method of manufacturing filter products from silicon dioxide, comprising mixing a fractional silica-containing component, a boron-containing additive, a binder, molding, drying and firing, characterized in that the fractional silicon dioxide is mixed with a solution of polyvinyl alcohol in water, the boron-containing additive is mixed with a surfactant from a number of organic fatty acids and a silica sol and the resulting mixture is discretely introduced into the prepared fractional silica with constant stirring, floor chennuyu granulated batch, molding is carried out with imposition of vibrations, the preform is dried to obtain a transport strength, is calcined in a gas atmosphere, is subjected to machining, regeneration is carried out by machining products and sealing surfaces block the sealing material. 2. The method according to claim 1, characterized in that the solution of polyvinyl alcohol (PVA) in water contains, wt.%: PVA 10-15 Water 90-85 and is taken in the amount of 8-22% in excess of the total content of the mixed components. 3. The method according to claim 1, characterized in that the boron-containing additive is introduced in the form of boron nitride with a specific surface area (S) = 15000-16000 cm ² / g 4. The method according to claim 1, characterized in that as the surface-active substances (surfactants) use oleic and stearic acid or a mixture thereof. 5. The method according to claim 1, characterized in that the total amount of surfactants is introduced from 0.5 to 1% by weight of boron-containing additives. 6. The method according to claim 1, characterized in that the silica sol is mixed with a boron-containing additive taken in an amount of 0.5-1.5 wt.% By weight of the silica sol. 7. The method according to claim 1, characterized in that the mixture of boron-containing additives with a surfactant and a silica sol is introduced into the prepared fractional silicon dioxide by adding it in an amount of 15-20 wt.% Of the total content over time periods of 5-10 minutes. 8. The method according to claim 7, characterized in that the mixture is introduced into fractional silicon dioxide in an amount of from 4 to 9 wt.%.