DE2145752A1 - Preparations containing silica and their use as binders - Google Patents

Description

DR. BERG DIPL.-IMG. STAPF

PATENT LAWYERS O 1 / C 7 C 1

8 MUNICH 2, HILBLESTRASSE 2O 4 I H W / V 4

Df. Berg Dipl-) ng. Stapf, 8 Munich 2. HllblesfraBe 20

Our sign date 1 S, ύ8Ρι la / 1

Attorney file 21 515
Be / Sch

Monsanto Chemicals Limited London / Great Britain

"Preparations containing silica and their use as binders"

This invention relates to silica-containing formulations and their use as binders in the manufacture of refractory materials.

Silica-containing preparations can be used as binders for the production of refractory forms instead of

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well known silica sol and alkyl silicate binders be used.

However, the silica gels rather quickly and the So far, the instability of the silica has been technical use as a binder excluded. It has now been found that the stability of silica solutions can be improved by certain water-soluble organic polymers.

It includes accordingly a preparation of the invention, an aqueous acid solution containing a water-soluble organic polymer having a molecular weight higher than 4400, wherein the silica content of the preparation ^ measured as S1O2, is at least 0.2 wt.%.

The silicic acid solutions stabilized according to the present invention are preferably obtained by contacting a dilute alkali metal silicate solution, usually a sodium silicate solution, with a cation exchange resin in the hydrogen form, as described for example in British patent application 645,703. A sufficiently high proportion of the alkali metal ions is removed so that the product has a pH value less than 7 and, preferably, the pH value is not higher than 6 at 15 ° C. Further verifications known to Paohmann

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can be used to produce silica solutions, for example the acidification of an alkali metal silicate solution with subsequent removal of the salt formed as a by-product, the electroosmosis of an alkali metal silicate solution or the hydrolysis of silicon tetrachloride. Because of their inherent instability, it is difficult to obtain silica solutions containing more than about 5 wt. # Si (^ include, although by means of special procedures concentrations up to 8 or even 12 wt.% Can be obtained. Preferably, the silicic acid solution, which is to of the invention is stabilized, freshly prepared, but silica that has already been stored for a certain time, for example 1, 2 or 3 or even up to 5 days at room temperature, can be used to form the solutions according to the invention.

For water-soluble organic polymers that can be used as stabilizers according to the invention, include the polymers of vinyl-substituted heterocyclic Nitrogen-containing compounds, for example N-vinylpyrrolidone, N-vinyl-O-alky! Pyrrolidone, Vinyl pyridine N-oxides, vinyl alkyl pyridine N-oxides and copolymers such compounds with each other or with other monomers, preferably polar monomers such as Vinyl acetate, alkyl acrylates and methacrylates and acrylonitrile. Specific examples of such water-soluble ones

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organic polymers are polyvinylpyrrolidone, vinylpyrrolidone-vinyl acetate copolymers, Polyvinyl-5-methylpyrrolidori, Vinyl-J-methylpyrrolidone-vinyl acetate copolymers, P.oly-2-vinylpyridine-N-oxide, poly-4-vinylpyridine-N-oxide, 4-vinylpyridine-N-oxide-Vinylac etatraischpolymerisate ,. Poly ~ 3-methyl-2-vinylpyridine-N-oxide, poly-ö-methyl ^ -vinylpyridine-N-oxide, poly-3-ethyl-6-vinylpyridine-N-oxide and poly-ol-methyl - ^ - vinylpyridine-N-oxide-methyl methacrylate copolymer.

Other water-soluble organic polymers that can be used are polyalkylene glycols, such as, for example Polyethylene glycols, polypropylene glycols and mixed polymeric glycols containing both ethylene and Contain propylene units; and water-soluble polyvinyl alcohols and water-soluble cellulose derivatives such as methyl cellulose.

The preferred water-soluble organic polymers are polyvinylpyrrolidone, poly-2-vinylpyridine-N-oxide and Polyethylene glycols.

The molecular weight of the water-soluble organic polymer is higher than 4400 and can, for example, in the ■ Range from 4500 to 1000 OQO. Preferably lies the molecular weight in the range from 5,000 to 200,000, and especially from 900CL to 80,000. Particularly useful

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Polyethylene glycols have a molecular weight in the range from 10,000 to 25,000 and particularly useful polymers and copolymers of vinyl heterocyclic Nitrogen containing compounds have molecular weights in the range of 35,000 to 50,000.

"Preferably the weight ratio is SiOp content water-soluble organic polymer content in a solution of the invention in the range from 150: 1 to 2a1, preferably from 30: 1 to 3: 1 and in particular from 15: 1 to 4/1. The ratio chosen will depend primarily on the shelf life desired because the stability of the solutions, i.e. the time required for gel formation during storage with the fraction of the polymer increased. It has been found that solutions of the invention, ratios from 30: 1 to 3: 1, are preferred from 20: 1 to 8: 1, for example 15: 1 to 10: 1, are particularly useful and have a sufficient one Have a degree of stabilization while avoiding the use of an unnecessarily large amount of polymer.

The upper limit of the concentration of silica in a solution of the invention as initially formed is determined by the above-noted difficulty in preparing concentrated silica solutions. A typical stabilized solution of the invention, as initially formed, comprises from 2 to 8 wt. # Silica or

less, usually from 2 to 10 $ silica. After stabilization, a certain concentration is possible, for example by evaporation under reduced pressure or by reverse osmosis, whereby contents of up to possibly 10 or 12% by weight or even higher are obtained. For practical purposes it is desirable to obtain as high a silica concentration as it is stable with reasonable storage stability, so that preferred solutions contain at least 3 wt.% Silica, for example 3 to 8, preferably at least 3-5 wt to 7 wt.% silica.

The pH of the solution should be less than 7jO, preferably less than 6, ο and in particular less than 4.0, for example from 1.5 to 3 _t 5 in.

The stability of the silica solutions is ensured by the Presence of anions adversely affected and a

Another object of the stabilized solutions of the invention is that the anion content be no higher than 25 ppm, although in some cases up to 50 ppm can be tolerated. The Entanionisierung can be accomplished by reacting the silica-exchange resin with an anion in the Hydroxylf orm either before or after the stabilization brings into contact · ⁺ b evorzugt he _n

i- f ^ß β 1 1/1 5 8 1

& ku β- 6 '<5 /! © β #

The solution of the invention can be prepared by adding the water-soluble organic polymer or a solution of the polymer in water or a water-miscible solvent to the aqueous solution of the silica, or vice versa, preferably under conditions such that rapid mixing takes place. When the water-soluble organic polymer is added as such, it is usually added as a finely divided powder. Suitable water-miscible solvents are lower alkenols, for example ethanol or methanol, or lower ketones, for example acetone, and ethers, for example tetrahydrofuran and ethoxyethanol.Solutions of the water-soluble organic polymer used to produce the preparations according to the invention can have weight concentrations of, for example, 0.5 to 50 have $. The polyalkylene glycols are preferably added suitably solid or as a solution, for example with a content of 5 to 50 wt.% Polymer and the nitrogen-containing water-soluble organic polymers as a solution containing from 0.5 to 8 wt. # Polymer.

The solutions of the invention can be used to make preparations that are good binders, such a preparation containing a mixture of (a) a stabilized silica solution of the invention and (b) a silicon-containing binder. The silicon

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-containing binder can for example be a Aquasol having a SiO ₂ content of 1 to 65 wt. ^, for example 30 to 50 wt. ^, or an organosol with a SiCl content of 1 to 50 wt.%. The silicon-containing binder can be prepared by partial or complete hydrolysis of an organic silicate such as an alkyl silicate or an alkyl polysilicate in which the alkyl group has from 1 to 4 carbon atoms and is, for example, ethyl or propyl, in an aqueous alcoholic medium in the presence of a strong acid such as Hydrochloric acid or sulfuric acid, according to British patents 926 9671 1 154, 376 and. British patent application -38527/69. The silica (silicon-containing) binder can also be a mixture of a silica aquasol and a hydrolyzed organic silicate. The silicon-containing binder preferably has an SiCU content of 5 to 55% by weight.

The preparations containing components (a) and (b) preferably have an SiOp content of 2 to 45 and in particular from 5 to 32, wt. #.

The preferred preparations have a weight ratio of components (a) and (b) from 20:80 to 80:20, preferably from 30:70 to 70:30 and in particular from 40:60 to 60:40.

When a stabilized silica solution of ^{the invention 209813/1583 ~ 9} -

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or a preparation containing components (a) and (b), as described above, is used as a binder for the production of a ceramic material or object, for example a ceramic shell mold for the metal cast, the manner of use corresponds essentially to that of the conventional one silicon-containing binders, which were given above under (b). For example, making a ceramic shell mold involves applying alternating mud and stucco coatings to an available model, the slurry being a slurry of particulate refractory material in a binder, suitably a silicon-containing binder, such as a silica sol or hydrolyzed alkyl silicate, and according to the Invention is a stabilized silica solution or the mixed binder preparation described above. The strength of the ceramic product after drying and firing depends on the ratio of binder (as SiOo) to refractory material in the slurry and while the optimal ratio depends on the type and nature of the refractory material and whether the slurry intended for use is primary or secondary Coating is used changes, the ratio will normally be in the range of 1; 7 to. 1:55 » based on the weight, lie · When making a ceramic bowl mold, each slurry and stucco layer is allowed to gel and usually partially dry before the

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next applies and, if desired, gelling can be accelerated by adding a binder exposing coating containing the invention to an alkaline atmosphere such as ammonia.

Slurries of particulate refractories in a stabilized silica or mixed binder formulation of the invention can also be used for cast team coating for making metal ingots. Metal ingots are poured into shapes that are retained in their bases, commonly known as spans, which are flat shells made of metal, usually cast iron. If the surface of the combination is not protected in some way, it suffers from rapid aerosion, while the aerosion in turn causes the ingot to stick to the combination because of the irregular surfaces formed thereby. It is accordingly customary to provide the team with a protective covering and, as indicated above, the previously indicated slurries are very suitable for this purpose.

It has also been found that paper treated with a stabilized silica solution of the invention has better grip (anti-slip properties) compared to untreated paper.

It was further established that carpets “made with a

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stabilized silica solution of the invention, optionally treated with the content of a surface-active agent, improved soil-repellent properties compared to untreated carpets.

The invention is illustrated by the following examples.

example 1

This example describes the production of preparations according to the invention.

Aqueous sodium silicate solution (specific weight 15 _t 5 ^O 0 / 15.5 ° C 1.042, SiO ₂ : Na ₂ O, = 3.3: _{1.4 t} 0 # SiQ ₂ GeWo / wt «, 4 1.) was by a column of Zeokarb 225 (i * ¹ Clei * H ⁺ form) and the silica obtained (3 »6 # SiQ ₂ weight _o / w., 4 1) under pressure from a Watson-Marlow flow controller through a column of Deacidite e (in the OH * ~ form) percolated, whereby chloride-free silica was obtained. The pH of the silica was 3 * 0.

Solutions of polyvinylpyrrolidone (molecular weight approximately 44,000.) In water, "which have a pH of 3» 0 to 4.0 were mixed with separate (100 ml) portions of the chloride-free silica at room temperature. The reac-. tion mixtures were vigorous with a magnetic stirrer touched. The pH of the silica changed

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not when mixed with the polyvinylpyrrolidone solutions became. Turbidity occurred immediately upon mixing.

In some classes the silica was first used with Treated with hydrochloric acid.

Except for the three tests (tests _19? 20 and 21), the polyvinylpyrrolidone was added to the silica. In experiments 19 to 21 the silica was added to the polyvinylpyrrolidone solution.

Further details of the experiments can be found in Table I.

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13 - water
(ml) mixed Gel time
of the product Table I. 2.0 other at 25 O
(Weeks) 1.5 O 5 Ver
suctis- 1.5 O 4- number With 100 ml of silica
t material 1.0 O 4- Λ PolyvinylT
pyrrolidone
(G) 0.5 O 4- 2 0.03 4 ·, 0 O M- 3 0.03 4-, O O 7th 4- . 0.03 3.0 2 ml N /
10 HOl. -λ 2 5 0.03 2.5 O 6th 6th 0.03 2.0 O 5 7th 0.06 6.0 O 5 8th 0.06 ^ t 5 Q 10 9 0.06 4.5 O 9 10 0.06 4.5 O 9 11 0.06 3.0. 2 ml N /
10 HOl. 2 12th 0.09 2.5 α 8th 13th 0.09 9.0 O 8th 14- 0.09 6.0 O 23 15th 0.09 6.0. O 21st 16 0.09 6.0 Q 20th 17th 0.0.9 8.8 O 28 18th a, 18 6.0 O 32 19th 0.18 O > 35 20th 0.18 21st 0.24 22nd 0.26 Q, 30

Except for experiments 3 and. 13 became silica within use 8 hours after manufacture from sodium silicate

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det. Experiments 3 and 13 were carried out using Silica carried out from I sodium silicate for 2 days was made earlier.

The specific surface areas of the fresh silica and the products obtained from experiments 18 and 19 were using one of Sears, Anal. Chem. 1956 » 28, 1081 described titration method determined » The following results were obtained:

Specific surface (m / gSiO ₂ )

Silica 1312

Product from experiment 18 1291

Product from experiment 19 1271

Example 2

This example describes the production of a further preparation according to the invention.

Experiment 18 of Example 1 was on an industrial scale repeated to form 3 l of preparation. The product had the following properties:

Appearance: cloudy

% SiO ₂ w / w : 3.4

.V.E; W / W ratio: 20/1

pH at 20 ⁰ O: 3.0

Specific surface (titration): 1271 Di ₂

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Specific surface after 8 weeks

for room heating : 1271 m

Gel time (storage at

Room temperature): 20 weeks

Particle size determination using the scattered light method

Weight average diameter

(90 scatter): 47 nanometers (nm)

Weight average diameter

(by dissymmetry). : 130 nm

Weight average diameter

(according to the Zimm plot method): 184 nm

These results indicate that the particles are not spherical are.

Example 3

This example describes the manufacture of a ceramic bowl mold using the preparation of Example 2,

A ceramic bowl was made using a Sludge prepared from the preparation of Example 2 (800 ml), Lissapol NX (4 ml), n-octanol (8 ml) and Zircosil 200 (2575 g) was made. A wax model (11.43 cm by 2.54 cm by 0.32 cm) was immersed in the slurry and coated with fine stucco (Molochite -30 / + 80) and let the coating dry in air for 1 hour. Four more coats of coarse Pieces (Molochite -16 / + 30) were then placed one after the other

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using the same procedure. The 5-layer casing was then left to dry in air for 24 hours and then ^{fired at 1000 °} C. for 1 hour.

Example 4

The preparation described in Example 2 (150 ml) was with silica aquasol (150 ml), which has an SiO ^ content of 30 wt. ^, A density of 1.204 and a specific -

Surface area of 25O m / gSiO ₂ , mixed to form a preparation which had an SiO ₂ gel of 17.7% by weight.

Example 5

This example describes the manufacture of a ceramic bowl mold using the preparation of Example 4.

The formulation of Example 4 (hereinafter referred to as A) was used to form primary and secondary slurries for making a ceramic bowl mold (as indicated in Table II). For comparative purposes, a further amount of the same Silikaaquasols, as was used in Example 4, diluted with water to form a Silikaaquasols (hereinafter called B), the 'a SiO ₂ had _Gehalt of 17.7 wt.%. This silica aquasol-B was used for the production of primary and secondary slurries for the production of a ceramic bowl mold,

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as indicated in Table II was used.

table II

Erimeric sludges Secondary sludges

Composition slurry composition slurry

viscosity viscosity

(Cup 4B) (Cup 4B)

A (500 ml) A (500 ml)

Lissapol NX. (4ml) 118 sec. Lissapol NX (2 ml) 115 sec.

n-octanol (8 ml) n-octanol (4 ml)

Zircosil 200 (2.5kg) Malochite No.6 (80Og)

B (500 ml) B (500 ml)

Lissapol NX (4 ml) Lissapol NX (2 ml)

n-octanol (8 ml) 31 sec _e n-octanol (4 ml) 30 sec.

Zircosil 200 Molochite No.6

(800 g) (800 g) ^

The slurries made from A had a shelf life of approximately two weeks.

Coatings were made on a wax model (11.43 cm χ 2.54 cm χ 0.32 cm), for which the model is dipped in the appropriate slurry and either a fine Stucco (Molochite -30 / + 80) or coarse stucco (Molochite -16 / + 30). The coating was left in the air Allow 2 hours to dry before applying the next coat. The five-layer trays were made afterwards let air dry for 24 hours.

The wax was removed from the bowls and the flexural strength of ceramic strips was determined by a method in which increasing pressure was applied to the center

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a 7162 cm field of the ceramic strip 2.54 cm wide was applied until the strip breaks; The flexural strength of the ceramic strips which have been gebrannt- 1 hour at ⁰ 100Q O were also determined. The ceramic strips were 0.5 to 0.75 cm thick.

Details of the casings tested and the flexural strength obtained are given in Table III. Any number the flexural strength is the average of the values obtained from six test strips.

Table III

Preparations,
the for
Manufacture d.
Sludge
used
became

Used to make the cover Coatings

Flexural strength of the envelope before burning after ^^ burning b / DGu

(lb./in*)
kg / cm ⁴ = ¹

(lb / in?) kg / cm ^

1 coating of primary slurry / fine stucco + 4 layers of secondary slurry / fine stucco

1 coating of primary slurry / fine stucco + 4 layers of secondary Sludge / coarse stuok

3 »
(47

1 coating primary

Sole ridges / f of a Stuok + -ip 1

4 layers secondary (λο \\

Sole ridges / fine stucco ^{k t0)}

1 coating of primary slurry / fine stucco + 4 layers of secondary sludge / coarse stuok

(110

24.5 (349)

12.6 (179)

(529)

(4075

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These results show that Preparation A is the same as Preparation B is superior in the manufacture of ceramic shell molds.

Example 6

This example describes the manufacture of a ceramic Shell shape using the primary and secondary slurries of Example 5i which contain the 'binder preparation A and the production of a metal casting using the form..

A total of 6 coatings were applied to a wax model, a first coat of primary slurry / fine stucco and five subsequent coats of secondary sludge / coarse stucco. Each coating was allowed to dry for 2 hours before the next coating was applied. The 5-layer cover was last used in dried in a wind tunnel for 4 days.

The wax was taken from the mold in a steam autoclave removed and the form fired at 1000 ° C for 1 hour.

A casting of stainless steel was carried out using a mold temperature of 1000 ⁰ C and a liquid metal temperature of 1600 ⁰ C. The casting was satisfactory and free from mold deposits, cracks and deformations.

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Example 7

This example describes the production of a preparation according to the invention.

An aqueous sodium silicate solution (specific weight 15 »5 / 15.5 ° 0 1.073, SiQ ₂ ilia Ο" = 3.3: 1, 6.6 $ SiO ₂ w / w) was passed through a column of Zeokarb 225 ( in the H form) and the silica obtained (specific weight 1.038) was percolated under pressure through a column of Deacidite E (in the OH "form) to form chloride-free silica. The pH of the silica was 3.1 and the specific gravity of the silica was 1.037.An aqueous solution of polyethylene glycol (10% w / w, molecular weight 20%, 1 1/3 l) was added to the chloride-free silica (6%) / 3 1) added at room temperature with vigorous stirring. The stabilized silica obtained had a SiO ₂ content of 5.9 wt.%, And a storage period of over a year.

Example 8

This example describes the production of paper with improved hand.

An aqueous solution of silica stabilized by polyethylene glycol (molecular weight 20,000) in a weight ratio of SiO ₂ to polyethylene glycol of 20: 1 and with a content of 4% by weight SiQ ₂ was prepared. This solution (0.5 ml)

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was mixed with water (1 ml) and the mixture concentrated Piece of Kraft paper (22.8 χ 7 »6 cm) sprayed. The application

ratio was 0.012 g mixture / dm. The slide angle for the treated paper was 31 °, while the angle for the untreated paper averaged 19 °.

Example 9

This example describes the production of carpets with improved soil release properties.

An aqueous solution of silica, stabilized by polyethylene glycol (molecular weight 20 OQQ), weight ratio SiO ₂ to polyethylene glycol 20: 1 and SiO ₂ content 4 wt. ^, Was prepared. This solution (33 g) was mixed with 10 # Teepol (0.2 ml) and the mixture sprayed onto carpet samples. A mixture of sieved vacuum cleaner dirt (350 g) and carbon black (50 g) was mixed and the mixture was rubbed into the carpet samples, the surface

bring ratio was 0.27 g / dm. When the carpet samples shaken and cleaned, the treated parts of the * carpet were much cleaner than the untreated Parts.

-Patent claims-

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Claims (2)

2U5752 - 22 claims: 1. Aqueous silica solution, which is a water-soluble contains organic polymer and has a silicon content, measured as SiCU, of at least 0.2 wt <> #, characterized in that the water-soluble organic polymer has a molecular weight greater than 4400. 2. Preparation according to claim 1, characterized that the water-soluble organic polymer is a polyethylene glycol with a molecular weight is in the range of 10,000 to 25,000. J. Preparation according to claim 1, characterized that the water-soluble organic polymer is a polymer or copolymer a vinyl substituted heterocyclic nitrogen containing one Compound, the polymer or copolymer having a molecular weight in the range of 35,000 to 50,000. Has. 20981371583