GB2155915A

GB2155915A - Gel precursor for tin oxide material

Info

Publication number: GB2155915A
Application number: GB08506127A
Authority: GB
Inventors: Dr David Leslie Segal; Stephen Roberton Daish; J L Woodhead
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1984-03-16
Filing date: 1985-03-08
Publication date: 1985-10-02
Also published as: GB2155915B; GB8406883D0; GB8506127D0

Abstract

A process for the preparation of a tin oxide material includes gelling a dispersion containing finely divided tin oxide and a colloidal component (e.g. tin oxide or zirconia sol) thereby to form a gel. The gel may be treated further to give the tin oxide material (e.g. by heating). The tin oxide material may be tin oxide as such, or a mixed oxide material containing tin oxide and an oxide of another element.

Description

SPECIFICATION Improvements in or relating to materials The present invention relates to materials and more particularly to tin oxide materials and precursors therefor.

According to one aspect of the present invention there is provided a process for the preparation of a precursor for a tin oxide material which includes gelling a dispersion containing finely divided tin oxide and a colloidal component to form a gel precursor for a tin oxide material.

The gel precursor may be subsequently treated to give a tin oxide material. Thus, for example, the gel precursor may be heated to give a tin oxide material.

The process of the present invention may be used to prepare substantially spherical tin oxide material.

Thus in one embodiment of the present invention there is provided a process for the preparation of a precursor for a tin oxide material which includes forming a dispersion containing finely divided tin oxide and a colloidal component into droplets and gelling the droplets to give substantially spherical particles of gel precursor for a tin oxide material.

In this Specification "tin oxide material" embraces tin oxide as such and mixed oxide materials containing tin oxide and an oxide of another element (e.g. zirconia).

The tin oxide may be, for example, commercially available finely divided tin oxide powder obtained by the flaming of tin metal.

The colloidal component may be, for example, any convenient sol, anion deficient solution or colloidal dispersion capable of forming a gel carrying the finely divided tin oxide.

For example, the colloidal component may be a sol of tin oxide (or a sol of a precursor for tin oxide (e.g. hydrated tin oxide)) or a sol or colloidal dispersion of zirconia.

Other colloidal components for example indium oxide sol, may find application in accordance with the present invention.

A tin oxide sol suitable for use in accordance with the present invention may be, for example, prepared in accordance with the method described in UK Patent Application No. 8321666 (Publication No. 2 126 205A).

A zirconia sol suitable for use in accordance with the present invention may be one, for example, as described in the Specification relating to BP 1181794.

The ratio of tin oxide to colloidal component may be varied over a wide range. For example, when the- colloidal component is not a tin oxide sol or a sol of a precursor therefor the upper limit of colloidal component concentration is determined by how much material, other than tin oxide, is required or can be tolerated in the tin oxide material.

In accordance with the present invention free flowing powders of substantially spherical tin oxide material have been prepared by using a zirconia sol with tin oxide in a number of ratios. Thus powders have been prepared using a number of zirconia sol to tin oxide ratios such that a number of tin oxide materials have been prepared having Zoo,: SnO2 weight ratios in the range 1 : 4 to 1 2.

The lower limit of colloidal component concentration may be determined, for example, by the least amount of colloidal component which can give rise to satisfactory gelling and production of product of a desired form andlor properties. For example, substantially spherical particles of tin oxide material may be prepared in accordance with the present invention with 5 to 10 w/o of zirconia with the majority being Sun 02.

If desired more than one colloidal component can be used such that a mixed material containing tin oxide and more than one other element can be prepared. Also other materials can be present (e.g.

in the form of finely dispersed powder or introduced as a solution) to produce mixed materials of desired composition.

Substantially spherical particles in accordance with the present invention may be prepared at any desired size. For example, it is possible to produce particles ranging from a few microns to 1000 Fm depending upon the process of gelling used.

Gelling of the dispersion may be effected in any convenient manner. For example, the gelling may be effected by carrying out a sol-gel transformation to bring about the formation of a gel from colloidal component in the dispersion. A sol-gel transformation may be effected by any convenient manner.

Examples of processes for effecting a sol-gel transformation known in the art are dewatering to increase inorganic species concentration (e.g. by oven drying, organic dewatering, azeotropic distillation, or spray drying), treatment with a suitable gelling reagent (ammonia or ammonium hydroxide) or treatment with an anion extracting agent (e.g. Primene JMT) as disclosed in the Specification relating to BP 1266494.

By way of further example, gelling may be effected by use of a so-called internal gelation process (e.g. using hexamethylene tetramine).

The present invention also provides in another aspect a gel precursor for a tin oxide material prepared by gelling a dispersion containing finely divided tin oxide and a colloidal component.

The present invention also provides a precursor for a tin oxide material whenever prepared by a process in accordance with the present invention.

According to a further aspect of the present invention there is provided a process for the preparation of a tin oxide material which comprises gelling a colloidal dispersion containing finely divided tin oxide and a colloidal component to form a gel precursor and heating the gel precursor to form a tin oxide material.

The invention further provides a tin oxide material whenever prepared by a process which includes gelling a colloidal dispersion containing finely divided tin oxide and a colloidal component to form a gel precursor and heating the gel precursor.

Further the invention provides a tin oxide material whenever prepared by a process in accordance with the present invention.

The invention will now be further described, by way of example only, as follows: Example 1 A thick slurry was prepared by adding 200 ml water to 250 g of finely divided tin oxide powder ("Superlite" ex Keeling % Walker; 88.7 w/o SnO2).

This slurry was mixed with 147 ml of a zirconia sol (502 g per litre zirconia, pH 0.65 density 1.59 cm-3 viscosity 30 cps, and NO3 : ZrO2 mole ratio 0.9 1) by stirring about one quarter of the slurry into the sol and then adding the resulting mixture to the remainder of the slurry together with 80 ml of water. The volume of the resulting dispersion was about 0.54 1 and it had an oxide concentration of about 540 g per litre of composition 75 w/o SnO21 25 w/o ZrO2.

The dispersion was dispersed as droplets with stirring into Genklene containing 1 w/o Span 80 using a 4 : 1 volume ratio of organic to aqueous phases.

Gelling was effected by adding ammonia gas to the dispersed phases and the resulting gel collected by filtration, washed with Genklene and left in air at room temperature (30 C) for about 20 hours. The gel was passed through a 63 micron sieve and the resulting powder had a tap density of 1.50 g cm-3 and a sphere diameter of about 25 microns. (Thermogravimetric analysis of the gel showed that gel decomposition had occurred by 500do).

Example 2 The gel powder prepared as in Example 1 was calcined in air at a rate of about 300 C per hour up to a temperature between 600 - 700 C and held at that temperature for 1 hour. The resulting material was a free-flowing tin oxide material powder having a tap density of 1.57 g cm-3 and a sphere diameter of about 25 microns.

Claims

1. A process for the preparation of a precursor for a tin oxide material which includes gelling a dispersion containing finely divided tin oxide and a colloidal component to form a gel precursor for a tin oxide material.

2. A process as claimed in claim 1 for the preparation of a precursor for a tin oxide material which includes forming a dispersion containing finely divided tin oxide and a colloidal component into droplets and gelling the droplets to give substantially spherical particles of gel precursor for a tin oxide material.

3. A process as claimed in claim 1 or claim 2 wherein the colloidal component is a sol, an anion deficient solution or a colloidal dispersion.

4. A process as claimed in claim 3 wherein the colloidal component is a sol of tin oxide, a sol of a precursor for tin oxide, a sol or colloidal dispersion of zirconia.

5. A process as claimed in any one of the preceding claims wherein tin oxide and a zirconia sol are used such that a tin oxide material is produced with a Zoo2: SnO3 weight ratio in the range 1: 4 to 1: 2.

6. A process as claimed in any one of claims 1 to 4 wherein tin oxide and a zirconia sol are used such that a tin oxide material is produced with 5 to 10 weight per cent of zirconia.

7. A process as claimed in any one of the preceding claims wherein more than one colloidal component is used such that a tin oxide material is produced containing tin oxide and more than one other element.

8. A process as claimed in any one of claims 1 to 6 wherein another material is present in finely dispersed powder form or as a solution such that a mixed tin oxide material is produced.

9. A process as claimed in any one of the preceding claims wherein substantially spherical particles of gel precursor for a tin oxide material are produced.

10. A process as claimed in any one of the preceding claims wherein the gelling is effected by a sol-gel transformation or by an internal gelation process.

11. A process as claimed in any one of the preceding claims including the further step of treating the gel precurson to form a tin oxide material.

12. A process as claimed in claim 11 wherein the gel precursor is treated to give a tin oxide material by heating.

13. A process as claimed in claim 11 or 12 wherein substantially spherical particles of tin oxide material are prepared.

14. A gel precursor for a tin oxide material prepared by gelling a dispersion containing finely divided tin oxide and a colloidal component.

15. A process for the preparation of a gel precursor substantially as hereinbefore described with reference to Example 1.

16. A process for the preparation of a tin oxide material substantially as hereinbefore described with reference to Example 2.

17. A precursor for a tin oxide material whenever prepared by a process as claimed in any one of claims 1 to 10 or claim 15.

18. A tin oxide material whenever prepared by a process which includes gelling a colloidal dispersion containing finely divided tin oxide and a colloidal component to form a gel precursor and heating the gel precursor.

19. A tin oxide material when prepared by a process as claimed in any one of claims 11, 12, 13 or 16.

20. A gel precursor for a tin oxide material substantially as hereinbefore described with reference to Example 1.

21. A tin oxide material substantially as hereinbefore described with reference to Example 2.