GB1585490A - Microfibrous tricalcium silicate dihydrate - Google Patents

Description

(54) MICROFIBROUS TRICALCIUM SILICATE DIHYDRATE (71) We, TURNER & NEWELL LIMITED, a Company organised under the laws of Great Britain, of 20 St. Mary's Parsonage, Manchester M3 2NL, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statment: This invention relates to the preparation of tricalcium silicate dihydrate in microfibrous forum.

Tricalcium silicate dihydrate in microfibrous form can be prepared by heating at a temperature above 100 C and under elevated pressure an aqueous suspension of anhydrous tricalcium silicate or an aqueous suspension of a mixture of a less basic hydrated calcium silicate and calcium hydroxide.

The present invention makes use of a cheaper starting material, namely a hydraulic cement.

According to the invention, microfibrous tricalcium silicate dihydrate is prepared by heating an aqueous suspension of a hydraulic cement at a temperature above 1000C under elevated pressure. From the resulting aqueous suspension of microfibrous product, water can be separated in liquid form (as by filtration) and the product can then be dried. For some purposes, however, the aqueous suspension of product can, preferably after washing by decantation, be used direct.

The hydraulic cement, which is preferably Portland cement, can be kept in suspension by gentle stirring; too vigorous stirring reduces the yield of product in microfibrous form. The concentration of cement in the suspension is suitably in the range 1-15% by weight, and concentrations in the range 2-10% by weight are preferred.

The temperature employed is preferably at least 210 C, and temperatures in the range 240--270 C are particularly preferred.

The pressure employed is conveniently simply that of saturated steam at the temperature employed.

The aqueous suspension of cement preferably includes a dissolved material promoting fibre growth lengthwise ('habit modifier'), for example sodium or potassium hydroxide or calcium chloride. The habit modifier is suitably employed in an amount forming 1-15% by weight of the amount of cement used.

The microfibrous product obtained by the method of the invention is useful as reinforcement for thermoplastics (e.g. PVC, polypropylene, nylon) and thermosetting materials (e.g.

polyesters, epoxy resins, phenol-formaldehyde resins), as insulation, as catalyst support material, and as web-former in paper making processes and the Hatschek process for making cementitious sheet products.

The invention is further illustrated by the following Examples.

Example A suspension of Portland cement (15g, passing 7Sp aperture sieve) in aqueous sodium hydroxide solution (750 ml, containing 0.3g NaOH) was prepared and immediately poured into a l-litre autoclave fitted with a paddle stirrer of anchor shape. The autoclave cover was bolted on and the paddle was rotated (60 rpm) to give gentle agitation. During 1 hour, the temperature was raised to 240 C under saturated steam pressure (460 psi), and was kept at 240"C. for 4 hours. During 1 hour, with stirring continued at 60 rpm, the autoclave was cooled to room temperature by means of a cooling coil, and the product (in the form of a slurry) was washed with water until the washings were neutral. Removal of water by filtration gave the solid product, which was dried at 1100C for 12 hours. Samples of the product (a pale grey solid) were prepared for electron microscopy by gently crushing the solid under water, shaking and allowing drops of the resulting aqueous suspension to evaporate on conventional specimen grids. The tricalcium silicate dihydrate fibres present were up to 50y long, with diameters in the range 0.03-0.3u i.e. with aspect ratios considerably greater than 100:1.

Example 2 A suspension of Portland cement (75g) in aqueous sodium hydroxide solution (750ml, containing 1.5g NaOH) was treated following generally the procedure of Example 1 to give a product similar to that of Example 1.

Example 3 A suspension of Portland cement (375g) in aqueous sodium hydroxide solution (7,500ml, containing 7.5g NaOH) was poured into a 10litre autoclave of similar design to that used in Example 1. The suspension was heated under pressure as in Example 1 , but with temperature maintained at 2700C for 3 hours. The product (pale grey) had a high proportion of its fibres of length in the range 4O-SOp.

Example 4 A suspension of Portland cement (15g) in aqueous calcium chloride solution (750ml, containing 0.62g Cacti2) was heated under pressure following generally the procedure of Example 1.

WHAT WE CLAIM IS: 1. A method of preparing micro fib rous tricalcium silicate dihydrate, in which an aqueous suspension of a hydraulic cement is heated at a temperature above 100 C under elevated pressure.

2. A method according to Claim 1, in which the suspension is heated at a temperature above 210 C.

3. A method according to Claim 2, in which the suspension is heated at a temperature in the range 240-270 C.

4. A method according to Claim 1,2, or 3, in which the aqueous suspension contains 1-15% by weight of cement.

5. A method according to Claim 4, in which the aqueous suspension contains 2-10% by weight of cement.

6. A method according to any one of Claims 1 to 5, in which the aqueous suspension contains a habit modifier in the dissolved state.

7. A method according to Claim 6, in which the habit modifier is sodium or potassium hydroxide or calcium chloride.

8. A method according to any one of Claims 1 to 7, in which the hydraulic cement is Portland cement.

9. A method preparing microfibrous tricalcium silicate dihydrate, substantially as illustrated by the Examples.

10. Microfibrous tricalcium silicate dihydrate, whenever obtained by the process of any one of Claims 1 to 9.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. (pale grey) had a high proportion of its fibres of length in the range 4O-SOp. Example 4 A suspension of Portland cement (15g) in aqueous calcium chloride solution (750ml, containing 0.62g Cacti2) was heated under pressure following generally the procedure of Example 1. WHAT WE CLAIM IS:

1. A method of preparing micro fib rous tricalcium silicate dihydrate, in which an aqueous suspension of a hydraulic cement is heated at a temperature above 100 C under elevated pressure.

2. A method according to Claim 1, in which the suspension is heated at a temperature above 210 C.

3. A method according to Claim 2, in which the suspension is heated at a temperature in the range 240-270 C.

4. A method according to Claim 1,2, or 3, in which the aqueous suspension contains 1-15% by weight of cement.

5. A method according to Claim 4, in which the aqueous suspension contains 2-10% by weight of cement.

6. A method according to any one of Claims 1 to 5, in which the aqueous suspension contains a habit modifier in the dissolved state.

7. A method according to Claim 6, in which the habit modifier is sodium or potassium hydroxide or calcium chloride.

8. A method according to any one of Claims 1 to 7, in which the hydraulic cement is Portland cement.

9. A method preparing microfibrous tricalcium silicate dihydrate, substantially as illustrated by the Examples.

10. Microfibrous tricalcium silicate dihydrate, whenever obtained by the process of any one of Claims 1 to 9.