Following abbreviations will be used throughout the text: US1 = US Patent 3,642,511 US2 = US Patent 4,956,321 US3 = US Patent 4,375,516 W1 = WO 97/19033 Invention = newly developed invention.

Background information US1 discloses a method to treat wollastonite by acid, say sulphuric acid and phosphoric acid, to a degree of pH <= 4.0. The aim of the treatment is to have a good opacity properties and low abrasiveness resistance, so that the final product, i. e., acid treated wollastonite, can be used as a pigment for paper industry (column 1, line 41-53).

US2 discloses a method to treat wollastonite by acid, say sulphuric acid, carbonate acid and acetate acid, to a degree that the treated wollastonite has a pH=9-10. The

treated wollastonite, called surface-pacified wollastonite in US2, may be used as an inert filler, or in the composition of US3. The aim of treating the wollastonite by the acid is to have a"reaction uniformity"of the wollastonite (column 1, line 19-27), so that the reaction, presumably the quick-setting process of the US3, will not be influenced by the different batches and grades of raw material. As a result, the treated wollastonite has a pH=9-10, which is not fundamentally different from that of the untreated wollastonite of pH=9-10.7 (column 2, line 34-39). This is an indication that US2 seeks to keep the reactivity of the US3 composition. As an evidence, Example 4 of US2 shows a setting time of 1 hour, which is considered as quick-setting in an industrial process. We have tested the Example 2 of US2 to examine its setting process, and the result shows that it has a setting time of less than 10 minutes at 20°C (Table 3).

W1, our previous invention, discloses a composition comprising an acid metal phosphate solution, a wollastonite compound and an oxy-boron compound as setting retarder. This composition discloses a technique to reduce reactivity of the composition by the setting retarder which results in a long pot life. The wollastonite used in the W1 is an untreated wollastonite

having a pH = 9-12. The W1 composition may provide a long pot life. However, its setting will take long time as well at 20°C because the reactivity of the composition is significantly reduced by the retarder. High temperature curing may be used to accelerate the setting, but there are times when high temperatures are not suitable.

There is a pressing need to develop a technique to accelerate setting reaction of a composition according to W1, using means other than increased curing temperature, so that a shaped body can be fully cured and obtained in a relatively short period.

It is an object of the present invention to provide a composition which fulfils the above need.

Description of the Invention The Invention disclosed herein relates to a phosphate cement composition, its method of preparation and resulting products formed therefrom.

Some particular objectives of the Invention are: (1) to reduce pH value of the wollastonite by a treatment so that reactivity of the said component A can be

fundamentally reduced, resulting in further extended pot life; and (2) to provide a technique so that setting of the composition become obtainable whenever it is required.

According to one aspect of the present invention there is provided a phosphate cement composition which comprises, in combination, a component A and a component B wherein the component A comprises an acid-treated wollastonite compound, an acid aqueous solution of metal phosphate, and a setting retarder; and component B comprises a setting accelerator.

Preferably the metal phosphate is selected from the group consisting of: aluminium phosphates, zirconium phosphates, magnesium phosphates, zinc phosphates, calcium phosphates, iron phosphates, including derivatives and mixtures thereof.

The setting retarder may be selected from the group consisting of boric acid, alkali metal and, alkaline-earth metal salts of boric acid, amine and ammonium salts of boric acid, including hydrates and mixtures thereof.

The setting retarder may be selected from the group

consisting of: boric acid, sodium borate, ammonium borate, calcium borate, including hydrates and mixtures thereof. Preferably said setting retarder is added as a powder or a liquid. Suitable accelerators are be known in the art; one is MgO.

The wollastonite of the said acid-treated wollastonite compound may be a natural or synthetic wollastonite, in calcined or non-calcined state, or a combination thereof.

The acid-treated wollastonite has preferably has a pH value of 6-8 a measured using a wollastonite 10 % water slurry.

The said acid used to treat the wollastonite may be an inorganic acid. For example, the acid used to treat the wollastonite may be sulphuric acid, phosphoric acid, carbonate acid, acetate acid, or a combination thereof.

According of another aspect of the invention there is provided a method of producing acid-treated wollastonite for a cement composition comprising: (1) mixing wollastonite with an inorganic acid aqueous solution in a concentration and quantity sufficient to form an acid/wollastonite mixture having a pH=6-8; and (2) drying

the mixture after its pH value becomes stable.

The said acid may be sulphuric acid, phosphoric acid, carbonate acid, acetate acid, boric acid, or a combination thereof. The said acid preferably has a normality of 0.03-0.05.

According to yet another aspect of the invention there is provided a shaped product formed from cement as hereinbefore described.

According to yet a further aspect of the invention there is provided a shaped product containing the acid treated wollastonite as hereinbefore described.

According to yet another aspect of the invention there is provided a method of making a solid shaped article comprising: providing composition A, forming the composition into a shape, and adding composition C to set the cement in the shape.

In general, the component A has a sufficiently long pot life, while the component B can be added to component at any moment during the pot life to form the cement which sets in relative short period so that a shaped body can be fully cured and produced at circa 20°C by the

Invention.

In general, reducing reactivity of the composition A of the Invention is achieved by treating the wollastonite with acid, to a degree that the treated wollastonite has a pH = 6-8 in wollastonite 10 % water slurry (this method of pH measurement will be used hereafter). When this treated wollastonite of pH = 6-8 meets acid metal phosphate solution, it reacts much slower than that of untreated wollastonite having a pH = 9-12. This results in a more extended pot life for the component A, even compared to that of W1.

On the other hand, controlling the setting time is realised using a setting accelerator. When this setting accelerator is added to the Invention composition A at any moment during the pot life, a setting mechanism is induced immediately which causes setting and full curing of the Invention composition at ambient temperature condition in a relatively short period.

These techniques have never been developed prior to this Invention, specially for the accelerator. This is because the phosphate cement using wollastonite as primary material has always been known as a quick-setting cement (with the exception of that disclosed in W1) so no

setting accelerator has ever been considered necessary.

Following is a description of some comparative tests illustrating the effectiveness of the compositions of the present invention.

Composition With respect to composition, the Invention is fundamentally different frown the W1 (Table 1) in the particular wollastonite employed and presence of the setting accelerator. This significantly improves industrial applicability of the technology.

Compared to US2, the composition of the Invention is evidently different not only in the presence of setting retarder and a setting accelerator, but also in the particular wollastonite employed. The Invention wollastonite is a mixture of a calcium salt of the particular acid used in the treatment (calcium sulphate, for instance), a silica gel and an un-reacted wollastonite, characterised by pH = 6-8. The presence of silica gel indicates that wollastonite structure is attacked during the treatment. While the US2 wollastonite is only surface-pacified with a surface-displaceable anion without altering crystal structure, and having a

pH = 9-10 (column 3, line 30-38). These therefore are two different materials, to be used for different applications.

Table 1 Composition difference Invention W1 US2 as material as material 1. as method to composition composition treat wollastonite 2. to be used in US3 or as inert filler acid treated wollastonite acid treated wollastonite pH = 6 compound pH = 9 to wollastonite pH = 9 to 8 12 to 10 metal phosphate metal phosphate metal phosphate oxy-boron compound oxy-boron compound setting accelerator Setting process Because of the difference in material composition, setting process of the Invention, US2 and Wl are consequently different, as summarised in the Table 2.

Table 2 Difference in the setting process

quick-setting controlled controlled pot-life setting time US2 uncontrollable quick setting W1 No Yes-- Invention controllable Yes Yes quick-setting* *Controllable quick setting in the sense that the setting can be realised by adding setting accelerator.

Comparative tests Comparative tests has been made, using compositions of the Invention, Wl and US2 to verify their setting process (Table 3). The wollastonite used in the test is very reactive and has a pH=12. The surface-pacified wollastonite used for US2 is obtained by treating it with sulphuric acid having a normality of 0.01, rinsed with de-ionised water and then dried, as required by the Example 2, US2 (column 3, Example 2). The acid treated wollastonite used in the Invention is a mixture comprising calcium sulphate, silica gel and un-reacted wollastonite obtained by treating it with sulphuric acid having a normality of 0.04 and then dried at 60°C.

Table 3 Pot life at 20°C

W1 US2 Invention wollastonite wollastonite wollastonite as suppliedsurface-acid treated pH=12 pacified pH=9 pH=7 min. min. min. phosphate W1 pot life =30,--pot life = 180 ratio = 1.4 (1) set=45 (2), set=24 hours phosphate (3) foaming foaming, foaming, ratio = 1.4 setting < 10 setting < 10 setting < 10 min. min. min.

(1) phosphate to wollastonite ratio (2) maximum pot life, no setting accelerator is used (3) aluminium phosphate from US2 Example 2, columns 3-4.

The test results show that when the US2 composition is used, it is always quick-setting together with foaming, independent of the pH value of the wollastonite. It demonstrates that the surface-pacified wollastonite cannot provide long pot life. On the other hand, when the

Invention composition is employed, the wollastonite of pH = 7 does reduce reactivity of the component A compared to Wl and the US2, indicated by the dramatic increase of pot life.

Field of Application The field of application and industrial applicability is summarised in the table 4.

Table 4 properties and field of application

Field of application Industrial suitability Invention 1. fibre reinforced much improved over composites W1 3. cement 4. adhesive 5. foams Wl 1. fibre reinforced Yes composites 3. cement 4. adhesive 5. foams US2 1. foams difficult 2. quick-setting applications

In view of the difference in composition, setting process and industrial applicability, the Invention has novelty. inventive step and industrial applicability with regard to its composition, method of treating the wollastonite and the resulting products formed from the cement.