Synthesis of and Uses of Alkaline Earth Metal Stannates

Abstract

The present invention provides a particularly advantageous form of alkaline earth metal hydroxystannate and alkaline earth metal stannate exhibiting a BET specific surface area of from 20 to 200 m2/g. A method of producing such particulate material and evidence of its benefits in use such as in at a reduction in a polymer sample at elevated temperature is also disclosed.

Claims

1. An alkaline earth metal stannate, where the alkaline earth metal is Mg or Ca, or an alkaline earth metal hydroxystannate where the alkaline earth metal is one of Mg, Ca or Ba; having a surface area using the B.E.T. method of from 20 to 200 m.sup.2/g.

2. The metal stannate or hydroxystannate of claim 1 in which the surface area is from 50 to 90 m.sup.2/g.

3. The metal stannate or hydroxystannate of claim 1 in which the alkaline earth metal is Ca.

4. A method of producing a high surface area alkaline earth metal hydroxystannate by precipitation, the method comprising the steps: providing an agitated aqueous solution of an alkaline earth metal salt in the range 20% to 50% by weight at a specified temperature between 25 C. and 40 C.; introducing with mixing into said solution approximately a molar equivalent of alkali metal stannate at a temperature in the range 35 C. to 45 C.; completing the introduction with agitation for a time period in the region of 1 to 5 hours; subsequently adjusting pH of the composition to between 6.0 and 7.0 using the acid equivalent of the alkaline earth metal salt said acid being in the concentration range of 10% to 30% by weight acid; to precipitate alkaline earth metal hydroxystannate.

5. The method of claim 4 in which the adjusting of pH is in the range 6.5 to 6.7.

6. The method of claim 4 in which the alkali metal stannate is at a temperature of 40 C.+/3 C.

7. The method of claim 4 in which the specified temperature is 30 C.+/5 C.

8. The method of claim 4 in which the metal of the alkali metal stannate is calcium stannate.

9. (canceled)

10. A polymer comprising a component that involves acid at elevated temperature in combination with the alkaline earth metal stannate or alkaline earth metal hydroxystannate of claim 1.

11. The polymer of claim 10 in which the polymer is PVC.

12. A materbatch comprising 20% or more of the alkaline earth metal stannate or alkaline earth metal hydroxystannate of claim 1.

13. The masterbatch of claim 11 in which the masterbatch comprises one of polyvinyl chloride, a polyolefin or a polyamide.

14. (canceled)

15. (canceled)

16. The metal stannate or hydroxystannate of claim 1 in which the surface weighted mean D(3,2) particle size as determined by light scattering is 1 to 4 microns.

17. The metal stannate or hydroxystannate of claim 16 in which the surface weighted mean D(3,2) particle size as determined by light scattering is 1.5 to 3.0 microns.

18. A method of lubricating a polymer extrusion process in injection molding, the method comprising using an alkaline earth metal stannate or alkaline earth metal hydroxystannate according to claim 1 as a lubricant.

Description

[0044] The present invention is illustrated by the figures in which:

[0045] FIG. 1 shows a two thousand times magnification of Calcium Hydroxystannate produced by the present invention;

[0046] FIG. 2 shows a two thousand times magnification of calcium stannate produced by the present invention;

[0047] FIG. 3 shows a four thousand times magnification of Calcium Hydroxystannate produced by the present invention;

[0048] FIG. 4 shows a four thousand times magnification of calcium stannate produced by the present invention;

[0049] FIG. 5 shows a two thousand times magnification of stannate produced by a comparative method;

[0050] FIG. 6 shows a two thousand times magnification of stannate produced by a comparative method;

[0051] the comparative method and micrographs are as disclosed in T. Iveti1, M. V. Nikoli, P. M. Nikoli, V. Blagojevi, S. udi, T. Srekovi and M. M. Risti, Science of Sintering, 39 (2007) 153-160, Investigation of Zinc Stannate Synthesis Using Photoacoustic Spectroscopy. This article is particularly relevant as its objective is to provide a high surface area stannate. The figures clearly show the contrast between the very high surface area of the present method which comprises a combination of large cubic crystals which cement together a matrix of finer particulate material having high porosity.

[0052] It has also been found that when polymer, such as PVC, polyethylene, polypropylene and PTFE is extruded under pressure and temperature in an injection moulding apparatus that the backpressure can increase over time. However, a composition in which a zinc stannate is replaced by a calcium stannate (composition as tables 1 and 2) show that backpressure increase over time is reduced. This is attributed to a lubricating effect from the calcium stannate. This is particularly marked for PVC where HCl gas evolution may also contribute to backpressure. A preliminary comparison of

[0053] Temperatures herein are 20 C. unless specified otherwise, pressure is atmospheric pressure. Test methods are those methods current at the date of application.