Chemistry of inorganic compounds – Carbon or compound thereof – Oxygen containing
Reexamination Certificate
1998-06-03
2002-11-12
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Oxygen containing
C423S165000
Reexamination Certificate
active
06479029
ABSTRACT:
The invention relates to an alkaline earth metal carbonate in particle form, and to its production and its use.
Calcium carbonate, barium carbonate and strontium carbonate are used for many technical purposes, for example as starting material for the synthesis of other calcium, strontium and barium compounds. The carbonates are suitable also for use in solid reactions, such as the preparation of oxide-contain ceramic materials for electrical and magnetic applications, e.g., for the manufacture of thermistors and condensers; they are used for the production of glass and for the manufacture of high-temperature superconducting material. Calcium carbonate is also used in paper manufacture.
Japanese patent application 7/025611 discloses a micronized barium carbonate which has a surface area of 5 to 25 m
2
/g. For its production an aqueous solution of barium hydroxide, to which carbon dioxide is added, is passed through three pumps in tandem and adds to the reaction product leaving the third pump a carboxylic acid or carboxylic acid derivative such as carboxymethylcellulose, which is intended to prevent crystal growth.
The present invention is addressed to the problem of devising an effective method for the preparation of micronized calcium carbonates, barium carbonates and strontium carbonates in the form. of particles with a narrow grain distribution. This problem is solved by the method of the invention.
The method of die invention for the preparation of particulate alkaline earth carbonate MCO
3
, wherein M represents Ca, Sr or Ba, provides for adding carbon dioxide to an M(OH)
2
solution with a concentration of 0.1 to 0.75 mol/l of M(OH), with the formation of a reaction mixture, using about 2 to 30 l of carbon dioxide gas per liter of solution, passing the reaction mixture through a continuously running mixing reactor in which shearing, thrusting and friction forces of interacting tools with a high relative velocity act upon the reaction mixture according to the rotor-stator principle, and separating and drying the alkaline earth carbonate formed from the reaction mixture after it passes through the reactor. The shearing, thrusting and friction forces in the reactor bring it about that the carbon dioxide enters in extremely finely divided form into the alkaline earth metal hydroxide solution. The liters of the carbon dioxide gas referred to are liters under standard conditions.
In the practice of the method of the invention micronized alkaline earth metal carbonate is obtained in which at least 90% of the particles have a diameter ranging from 0.1 to 1.0 &mgr;m, preferably ranging from 0.2 to 1.0 &mgr;m in the case of barium carbonate or strontium carbonate. In the case of calcium carbonate, at least 90% of the particles have a diameter ranging from 0.2 to 1.0 &mgr;m. In barium carbonate the BET surface area ranges from 3 to 30 m
2
/g, preferably 3 to 20 m
2
/g, especially 8 to 15 m
2
/g. In calcium carbonate and strontium carbonate the surface area ranges from 3 to 50 m
2
/g.
The method of the invention is very efective. Only one reactor is needed in order to achieve a virtually quantitative reaction. In the method of the state of the art, three pumps are used in tandem.
Very suitable are apparatus in which the rotor revolves at a high speed. The rotor speed amounts preferably to 2,000 to 8,000 revolutions per second. The time of stay of the reaction mixture in the mixing and homogenizing apparatus amounts preferably up to 5 sec.
In this manner, BaCO
3
for example, can be produced, wherein 90% and more of the particles have a diameter ranging from 0.2 to 0.7 &mgr;m.
Measurement of the BET surface area was performed with an apparatus able to measure micropores, of the firm, Micro Meritics. Adsorption gas was nitrogen, and the measurement was made at the temperature of liquid nitrogen in the range of 0.01-0.1 P
rel
using the BET equation.
In one embodiment of the invention the method is practiced without the addition of a crystal growth inhibitor This embodiment will be further explained in connection with the preferred production of BaCO
3
.
Before the drying operation, which is best performed in the range of 100 to 120° C., the barium carbonate separated immediately after passing through the reactor, can be washed one or more times with water.
The precipitation of barium carbonate in the barium hydroxide solution treated with carbon dioxide is best performed at a temperature in the range from 40 to 130° C.
The addition of agents intended to prevent crystal growth in the reaction mixture leaving the homogenizer is not performed; the carbonate is separated immediately after leaving the reactor.
Additional subject matter of the invention is the particulate barium carbonate, which is obtainable by the method of the invention and has a BET surface in the range of 3 to 30 m
2
/g, preferably 3 to 20 m
2
/g, especially 8 to 15 m
2
/g, in which at least 90% of the particle has a diameter ranging from 0.2 to 1.0 &mgr;m, and which is free of agents preventing crystal growth.
Additional subject matter of the invention is particulate calcium carbonate with a BET surface ranging from 3 to 50 m
2
/g, wherein at least 90% of the particles has a diameter ranging from 0.1 to 1.0 &mgr;m, preferably 0.2 to 1.0 &mgr;m, obtained by the method of the invention, which is free of agents preventing crystal growth.
Subject matter of the invention is also particulate strontium carbonate with a BET surface ranging from 3 to 50 m
2
/g, wherein at least 90% of the particles has a diameter ranging from 0.1 to 1.0 &mgr;m, obtained by the method of the invention, which is free of agents preventing crystal growth.
Another embodiment of the invention provides that an agent preventing crystal growth is added to the reaction mixture before, during and/or after the reaction in the reactor. In this embodiment also, calcium, strontium and barium carbonates can be made with the above-mentioned characteristic of particle diameter and specific BET surface area. It is preferentially suited for the preparation of barium carbonate and strontium carbonate. This preferred embodiment will he further explained; special crystal growth inhibiting agents are used which are given preference. Also usable would be the acids themselves or the alkali metal salts, for example.
The particles occur in rod shapes. The statement of the diameter of the particles relates to the length of the rods.
The preferred method of the invention for the preparation of particulate barium carbonate with a BET surface area ranging from 3 to 30 m
2
/g, preferably 3 to 20 m
2
/g and strontium carbonate with a BET surface ranging from 3 to 50 m
2
/g, wherein at least 95%, preferably at least 90%, and especially 100% of the particles have a diameter ≦1.0 &mgr;m, provides that, with the use of an agent preventing crystal growth selected from the group of the ammonium salts and alkyl ammonium salts of carboxylic acid having a total of 3 to 12 carbon atoms as well as at least 2 COOH groups, or at least 2 OH groups, a barium hydroxide solution or strontium hydroxide solution with a concentration of 0.1 to 0.75 mol/l of Ba(OH)
2
or Sr(OH)
2
, respectively, is treated with carbon dioxide with the formation of a reaction mixture, using about 2 to 30 l of carbon dioxide gas per liter of solution, the reaction mixture is passed through a mixing reactor in which shear and friction forces act upon the reaction mixture. The shear and friction force in the reactor cause the carbon dioxide to enter in extremely finely divided form into the barium or strontium hydroxide solution. The liter specification (mainly 10 to 20 l in the processes) of the carbon dioxide gas refers to standard conditions. If 100% of all particles have a diameter ≦1 &mgr;m, this means that no more than very minor undesired amounts, e.g., less than 0.1% of the particles, have a diameter greater than 1 &mgr;m.
The agent preventing crystal growth is used at least in the amount that limits the crystal growth of the barium carbonate and strontium carbonate such it at least 99% of the particles
Gabel Hans
Koehler Karl
Mingels Norbert
Park Jai Won
Crowell & Moring LLP
Hendrickson Stuart L.
Nave Eileen E.
Solvay Barium Strontium GmbH
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