Calcium sulfate crystals and methods for making the same

Patent metadata

Field	Value
Publication number	US-10280288-B2
Application number	US-201414561239-A
Country	US
Kind code	B2
Filing date	Dec 5, 2014
Priority date	Dec 6, 2013
Publication date	May 7, 2019
Grant date	May 7, 2019

Abstract

A composition of matter is provided, including anhydrite calcium sulfate whiskers having a mean aspect ratio of at least 30. Another composition of matter is provided, including alpha-derived anhydrite calcium sulfate whiskers. Yet another composition of matter is provided, including fine alpha particle-derived anhydrite calcium sulfate whiskers.

First claim

What is claimed is:

1. A composition of matter, comprising anhydrite form calcium sulfate whiskers derived from alpha calcium sulfate hemihydrate particles,
wherein the anhydrite form calcium sulfate whiskers have been formed through a method comprising:
subjecting dihydrate calcium sulfate to a pressurized calcination process to produce particulate alpha calcium sulfate hemihydrate;
sizing the alpha calcium sulfate hemihydrate to have a median particle size of from about 1 μm to about 5 μm;
combining water and the particulate alpha calcium sulfate hemihydrate to form a slurry;
autoclaving the slurry to form alpha calcium sulfate hemihydrate whiskers in water;
dewatering the alpha calcium sulfate hemihydrate whiskers; and
heating the alpha calcium sulfate hemihydrate whiskers to form the anhydrite form calcium sulfate whiskers.

2. The composition of claim 1 , wherein the anhydrite form calcium sulfate whiskers have a mean aspect ratio from about 30 to about 140.

3. The composition of claim 1 , wherein the anhydrite form calcium sulfate whiskers have a mean diameter from about 0.3 μm to about 1.5 μm.

4. The composition of claim 1 , wherein the anhydrite form calcium sulfate whiskers have a mean length from about 20 μm to about 100 μm.

5. The composition of claim 1 , wherein the anhydrite form calcium sulfate whiskers have a mean length from about 60 μm to about 75 μm, a mean diameter from about 1.0 μm to about 1.5 μm, and a mean aspect ratio from about 40 to about 75.

6. The composition of claim 1 , wherein the anhydrite form calcium sulfate whiskers comprise fine alpha particle-derived anhydrite calcium sulfate whiskers.

7. The composition of claim 6 , wherein the anhydrite form calcium sulfate whiskers have a mean length from about 45 μm to about 55 μm, a mean diameter from about 0.4 μm to about 0.8 μm, and a mean aspect ratio from about 55 to about 140.

8. The composition of claim 1 , wherein the anhydrite form calcium sulfate whiskers have a Mohs hardness from about 3 to about 3.5.

9. The composition of claim 1 , wherein the anhydrite form calcium sulfate whiskers are thermally stable up to at least 1400° C.

10. The composition of claim 1 , wherein the anhydrite form calcium sulfate whiskers have a mean true density of greater than 2.91 g/cm 3 .

11. The composition of claim 1 , wherein the anhydrite form calcium sulfate whiskers have a mean true density from about 2.913 g/cm 3 to about 2.918 g/cm 3 .

12. The composition of claim 1 , wherein the anhydrite form calcium sulfate whiskers have a mean specific surface area from about 2.283 m 2 /g to about 2.304 m 2 /g.

13. A composition of matter, comprising insoluble anhydrite form calcium sulfate whiskers derived from alpha calcium sulfate hemihydrate particles, the insoluble anhydrite form calcium sulfate whiskers having a mean aspect ratio of at least 30,
wherein the insoluble anhydrite form calcium sulfate whiskers have been formed through a method comprising:
subjecting dihydrate calcium sulfate to a pressurized calcination process to produce particulate alpha calcium sulfate hemihydrate;
sizing the alpha calcium sulfate hemihydrate to have a median particle size of from about 1 pm to about 5 pm:
combining water and the particulate alpha calcium sulfate hemihydrate to form a slurry;
autoclaving the slurry to form alpha calcium sulfate hemihydrate whiskers in water;
dewatering the alpha calcium sulfate hemihydrate whiskers;
heating the alpha calcium sulfate hemihydrate whiskers to form the insoluble anhydrite form calcium sulfate whiskers.

14. The composition of claim 13 , wherein the insoluble anhydrite form calcium sulfate whiskers have a mean diameter from about 0.3 μm to about 1.5 μm.

15. The composition of claim 13 , wherein the insoluble anhydrite form calcium sulfate whiskers have a mean length from about 20 μm to about 100 μm.

16. The composition of claim 13 , wherein the insoluble anhydrite form calcium sulfate whiskers have a mean length from about 60 μm to about 75 μm, a mean diameter from about 1.0 μm to about 1.5 μm, and a mean aspect ratio from about 40 to about 75.

17. The composition of claim 13 , wherein the insoluble anhydrite form calcium sulfate whiskers have a Mohs hardness from about 3 to about 3.5.

18. The composition of claim 13 , wherein the insoluble anhydrite form calcium sulfate whiskers are thermally stable up to at least 1400° C.

19. The composition of claim 13 , wherein the insoluble anhydrite form calcium sulfate whiskers have a mean true density from about 2.913 g/cm 3 to about 2.918 g/cm 3 .

20. The composition of claim 13 , wherein the insoluble anhydrite form calcium sulfate whiskers have a mean specific surface area from about 2.283 m 2 /g to about 2.304 m 2 /g.

21. The composition of claim 13 , wherein the particulate alpha calcium sulfate hemihydrate has a median particle size of from about 2 μm to about 5 μm.

22. The composition of claim 13 , wherein the heating the alpha calcium sulfate hemihydrate whiskers to form the insoluble anhydrite form calcium sulfate whiskers is at a temperature from about 500° C. to about 900° C. for a duration from about 20 minutes to about 24 hours.

23. The composition of claim 1 , wherein the sized alpha calcium sulfate hemihydrate has a median particle size of from about 2 μm to about 5 μm.

24. The composition of claim 1 , wherein the heating the alpha calcium sulfate hemihydrate whiskers to form the anhydrite form calcium sulfate whiskers is at a temperature from about 500° C. to about 900° C. for a duration from about 20 minutes to about 24 hours.

Assignees

• Georgia Pacific Gypsum Llc

Inventors

• Wu Mianxue
• Fields Jeffrey T

Classifications

• C30B7/10

  by application of pressure, e.g. hydrothermal processes · CPC title

• C30B29/10

  Inorganic compounds or compositions · CPC title

• C01F11/466

  Conversion of one form of calcium sulfate to another · CPC title

• C08K2201/004

  Additives being defined by their length · CPC title

• C08K2201/003

  Additives being defined by their diameter · CPC title