GB2111042A - Titanate based gel - Google Patents

Abstract

An aqueous binder for a basic refractory based on magnesia grains comprises a titanium alkoxide and an aminoalcohol.

Description

SPECIFICATION Titanate based gel This invention relates to the preparation of a gel based on titanium from titanium alkoxides and the use of this gel to bind basic refractory aggregates.

United States Patent No. 3,282,713 and British Patent 1,101,207 show that additions of titania and chrome ore as fine comminuted powders to magnesia give a basic refractory body having good thermal shock damage resistance and resistance to corrosion by slags. French Patent No. 1,365,206 and British Patent No.

1,014,083 describe the preparation of rigid coherent gels from tetraalkyl titanates Ti(OR)4, where R is an alkyl group, by treatment with an aminoalcohol and water.

According to the present invention there is provided a press for the preparation of a basic refractory having good thermal shock damage resistance comprising forming a slurry of magnesia grain, with a gel-forming mixture comprising water, an aminoalcohol and a titanium alkoxide which may be either a tetraalkyl titanate, an alkyl polytitanate or a mixture of a tetraalkyl titanate and an alkyl polytitanate, allowing the slurry to set and then firing the set slurry.

An example of a suitable basic magnesia grain is a Sardinian sea-water magnesia of typically 95.5 - 96.5% MgO and desirably with a lime to silica ratio of 2:1.

The gel-forming mixture may if desired include an alcohol such as ethanol or isopropanol. Refractory shapes can be prepared by pouring the slurry into a mould, allowing the slurry to set in the mould, removing the set slurry from the mould and then air-drying and firing the set slurry to obtain a refractory shape.

Examples of suitable titanium components include tetra-n-butyl titanate Ti(O-C4Hgn)4 and tetra-isopropyl titanate Ti(O-C3H7i)4. Another suitable titanium compound is the commercially available polybutyl titanate, which is a mixture of tetra-n-butyl titanate and butyl polytitanates containing the structural unit

sold under the registered Trade Mark TILCOM as TILCOM PBT. A suitable isopropyl titanate is sold under the registered Trade Mark TILCOM as TILCOM TIPT.

The magnesia grain used may also contain a fine fraction selected from at least one of the group comprising rutile titanium dioxide, chrome ore, chromic oxide Cr203 and alumina. Preferably the major portion of this fine fraction passes a 200 mesh B.S. 410 sieve and desirably all of this fine fraction passes a 200 mesh B.S. 410 sieve. The alumina can be fine calcined alpha-alumina, desirably ground to a particle size of one micron or less. Fine tabular alumina can also be used. Alternatively, a hydrous aluminium oxide, a hydrous chromium oxide or a hydrous titanium oxide may be dispersed in a mixture of the amino alcohol with either ethanol or isopropanol and this dispersion used in the gelation of the titanium alkoxide, as proposed in British Patent No. 1,574,210.

The process may be used to prepare nozzles for use in steel casting, also well blocks for use in steel casting. It can also be used to prepare well blocks of the type described in British Patent No. 1,451,548.

The microstructure of magnesia refractory shapes prepared using the gel derived from a titanium alkoxide resembles that found in refractory shapes made by the ethyl silicate bonding process. The microstructure shows the fine porosity and microcracks which are necessary to obtain good thermal shock damage resistance.

Preparation of rigid coherent gels for binding refractory grain using butyl polytitanate The Table gives conditions for the gelling of butyl polytitanate TILCOM PBT. To butyl polytitanate (TILCOM PBT-30ml) the required amount of triethanolamine is added to obtain Reaction Mixture A. Then the required volume of water, as given in the Table, is added to Reaction Mixture A. An exothermic reaction is observed on adding triethanolamine. At this stage, a viscous solution is obtained, which becomes a free-flowing liquid on stirring. An exothermic reaction is also observed on adding the water.

GELLING OF BUTYL POLYTITANATE (TILCOM PBT) Reaction Mixture A Volume of Water TILCOMPBT Triethanolamine Added Gel Time Observations More than 30 ml 30 ml 30 ml 24 Hours No coherent gel obtained 30 ml 20 ml 25 ml 24 hours Gel unsuitable as a binder 30ml 2.5 ml 16ml Instantaneous Gel contains water in matrix 30 ml 5.0 ml 16.5 ml Instantaneous Gel contains water in matrix 30 ml 7.0 ml 17 ml 15 minutes Weak but coherent gel Rigid coherent gel. Very Suit30 ml 10 ml 20 ml 12 minutes able for binding refractory grain Coherent gel, weaker, but suit30 ml 10 ml 30 ml 35 minutes able for binding refractory grain.

30 ml 10 ml 10 ml Over 2 hours Gel unsuitable as a binder Binding of Sardamag magnesium oxide with isopropyl Titanate (i) Dissolve 75 grams diethanolamine in 225 ml titanium ester (tetraisopropyl titanate; isopropyl orthotitanate). This is exothermic. Allow to cool to ambient temperature before use. To 300 ml aqueous ethanol (specific gravity 0.85), add 10 ml water. This is the gelation agent.

Add the Sardamag grain to the titanium ester/diethanolamine mixture; then add the gelation agent. Mix thoroughly, cast under vibration. Allow to stand in mould for one hour before stripping.

The Sardamag magnesium oxide grain was as follows: B.S. 410 Sieve Mesh Number Weight per cent -5+7 40 - 7 + 25 20 - 25 27 Ball Milled Fines 13 Use 14 Ib of the above mix with the binding composition. The binding composition is the mixture of tetraisopropyl titanate, diethanolamine and gelation agent. A suitable isopropyl titanate is TILCOM TIPT.

Air-dry and then fire at 1600 C for three hours.

(ii) 168 ml of tetraisopropyl titanate (TILCOM TIPT) and 52 ml diethanolamine were mixed and the mixture added to 14 Ib Sardamag magnesia grain mix. 300 ml of an ethanol/water mixture, specific gravity 0.85 was also added, to give a slurry which was cast into a mould. The setting time of the slurry was about 20 minutes. The cast article was removed from the mould, then air-dried and fired at 1 600"C for th ree hours to give a refractory shape.

The Sardamag magnesia grain mix was as follows: B.S. 410 sieve number Percentage by Weight - 5+10 30 -10+25 20 -25+72 15 Ball-milled fines 35 (iii) 168 ml tetraisopropyl titanate (TILCOM TIPT) and 52 ml diethanolamine were mixed and the mixture added to 14 lb Sardamage magnesia grain mix containing 83.5 grams rutile TiO2 and 162.4 grams alpha-alumina, both passing 200 mesh B.S. 410 sieve. 300 ml of an ethanol/water mixture, specific gravity 0.85 was also added, to give a slurry which was cast into a mould. The setting time of the slurry was about 20 minutes. The cast article was removed from the mould, then air-dried and fired at 1600 C for three hours to give a refractory shape.

The Sardamag magnesia grain mix was as follows: B.S. 410 sieve Number Percentage by Weight - 5+10 30 -10+25 20 -25+72 15 Ball-milled fines 35 (iv) 168 ml tetraisopropyl titanate (TILCOM TIPT) and 52 ml diethanolamine were mixed and the mixture added to 14 lb Sardamag magnesia grain mix containing 162.4 grams alpha-alumina, passing 200 mesh B.S.

410 sieve. 300 ml of an ethanol/water mixture, specific gravity 0.85, was also added, to give a slurry which was cast into a mould. The setting time of the slurry was about twenty minutes. The cast article was removed from the mould, then air-dried and fired at 1 600"C for three hours to give a refractory shape.

The Sardamag magnesia grain mix was as follows: B.S. 410 Sieve number Percentage by weight - 5+10 30 -10+25 20 -25+72 15 Ball milled fines 35 Preparation of nozzle for casting of steel 600 ml butyl polytitanate and 205 ml triethylamine were mixed. When the mixture had cooled to ambient temperature 500 ml water was added to give the binding solution. Then 24 Ib Sardamag magnesia grain was added. The resulting mixture was cast under vibration into the mould. The cast nozzle was allowed to stand for 15 minutes in the mould before stripping. The nozzle was air-dried, heated to 200"C to remove volatiles, then fired to 1500"C in the course of 12 hours and held at 1 5000C for 6 hours.

The butyl polytitanate used was TILCOM PBT.

Preparation ofa Well Block of the type described in British Patent 1,451,548.

(a) 2700 ml butyl polytitanate and 962 ml triethanolamine were mixed. When the mixture had cooled to ambient temperature it was divided into three equal parts. To each part was added 640 ml water and 33 1/3 lb Sardamag grain, then each mixture was cast under vibration into the well block mould. The cast well block was allowed to stand for 15 minutes in the mould before stripping. The well block was air-dried, heated at 200"C to remove volatiles, then fired to 1550"C in the course of 12 hours and held at 1550"C for 6 hours.

(b) 2970 ml butyl polytitanate and 990 ml triethanolamine were mixed. When the mixture had cooled to ambient temperature it was divided into three equal parts. To each part was added 660 ml water and 34 lb Sardamag grain, then each mixture was cast under vibration into the well block mould. The cast well block was allowed to stand for 20 minutes in the mould before stripping. The well block was air-dried, heated at 2000C to remove volatiles then fired to 1550 C in the course of 12 hours and held at 15500C for 6 hours.

The Sardamag grain mix used in (aJ and (b) was as follows: B.S. 410 Sieve mesh number Weight Percentage - 5+7 10 - 7 + 25 30 - 25 40 Ball-milled fines 20 The butyl polytitanate used in (a) and (b) was TILCOM PBT.

For the above Sardamag grain mix, preferred quantities per pound of Mix are TILCOM PBT - 27 ml/lb Triethanolamine - 9.6 ml/lb Water - 19.2 mb/lb Giving a setting time of about 15 minutes.

Other preferred quantities per pound of the above Sardamag grain mix are TILCOM PBT - 25 ml/lb Triethanolamine - 8.3 ml/lb Water - 16.7 ml/lb Giving a setting time of about 12 minutes.

Properties of butyl-titanate-bonded Sardamag bodies The Sardamag grain used had the particle size distribution which was used for the preparation of well-blocks. The test specimens were made following the procedure used to prepare nozzles for the casting of steel. The firing schedule was to fire slowly to 1500"C, hold overnight at 1500"C, fire to 1 6000C and hold at 1 6000C for two hours, then cool slowly to ambient temperature. The following properties were determined, at ambient temperature.

% shrinkage - 1.55 Modulus of rupture - 13.9mPA Young's Modulus - 8.22 x 1010 PA Work of Fracture - 82 J/m2 Fracture Initiation Energy - 4.13 J/m2 Density - 2574 Kg/m2 Hasselman Thermal Shock Damage Resistance Parameter R - 4.1 Work of Fracture Ratio ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -19.85 Fracture Initiation Energy The values for R"" and the ratio Work of Fracture show that the Fracture Initiation Energy butyl-titanate-bonded Sardamag material has a very good resistance to damage by thermal shock. For similar figures for some ethyl-silicate-bonded systems and a discussion of the significance of the figures, see A.J. Rigby, H.G. Emblem and E.W. Roberts, Tran. J. Brit. Ceram. Soc., 1979, Volume 78 page 10.

Properties of tetraisopropyl-titanate-bonded Sardamag bodies The test specimens were made by the procedure given in "Binding of Sardamag magnesium oxide with isopropyl titanate" Method (ii). The firing schedule was to fire slowly to 1500 C., hold overnight at 1500 C, fire to 1 6000C and hold at 1600"C for two hours, then cool slowly to ambient temperature. The following figures were obtained for the modulus of rupture at various temperatures.

Temperature "C Modulus of rupture mPA Standard Deviation 800 18.2 2.6 900 16.0 3.5 1000 13.0 4.0 1100 12.9 2.1 1200 12.6 2.0 1300 9.0 1.4 The density was 2850 Kg/m3 Materials The Sardamag grain used was Sardamag 251 SP grade.

The ball-milled fines had the following properties: Al203 - 0.25% by weight Fe2O3 - 0.22% by weight CaO - 1.62%byweight SiO2 - 0.78% by weight Residue MgO BET surface area 2m2/g (approx.) Surface area by Rigden method 0.25 - 0.30m2/g.

Sardamag 251 SP grain has the following typical analysis: Mineral Weight Percent SiO2 0.7- 0.9 Al203 0.2- 0.4 Fe2O3 0.15-0.3 B203 0.02-0.04 CaO 1.8-2.3 MgO 95.5-96.5 The alpha-alumina was BACO MA 95 Calcined alumina. The titanium dioxide was BDH Chemicals Limited Catalogue No. 30466 material.

Claims (2)

1. A process for the preparation of a basic refractory having good thermal shock damage resistance comprising forming a slurry of magnesia grain with a gel-forming mixture comprising water, an aminoalcohol and a titanium alkoxide which may be either a tetraalkyl titanate, an alkyl polytitanate or a mixture of a tetraalkyl titanate and an alkyl polytitnate, allowing the slurry to set and then firing the set slurry.

2. A process as claimed in Claim 1 wherein the gel-forming mixture additionally includes an alcohol such as ethanol or isopropanol.