Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F11/00—Compounds of calcium, strontium, or barium
  • C01F11/46—Sulfates
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B22/00—Use of inorganic materials as active ingredients for mortars, concrete or artificial stone, e.g. accelerators or shrinkage compensating agents
  • C04B22/08—Acids or salts thereof
  • C04B22/14—Acids or salts thereof containing sulfur in the anion, e.g. sulfides
  • C04B22/142—Sulfates
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B22/00—Use of inorganic materials as active ingredients for mortars, concrete or artificial stone, e.g. accelerators or shrinkage compensating agents
  • C04B22/08—Acids or salts thereof
  • C04B22/14—Acids or salts thereof containing sulfur in the anion, e.g. sulfides
  • C04B22/142—Sulfates
  • C04B22/143—Calcium-sulfate
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
  • C04B28/14—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing calcium sulfate cements
  • C04B28/145—Calcium sulfate hemi-hydrate with a specific crystal form
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
  • C04B40/0028—Aspects relating to the mixing step of the mortar preparation
  • C04B40/0039—Premixtures of ingredients
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/51—Particles with a specific particle size distribution
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2103/00—Function or property of ingredients for mortars, concrete or artificial stone
  • C04B2103/10—Accelerators; Activators
  • C04B2103/12—Set accelerators
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
  • C04B2111/00612—Uses not provided for elsewhere in C04B2111/00 as one or more layers of a layered structure
  • C04B2111/0062—Gypsum-paper board like materials

Definitions

• the present invention relates to a process for producing calcium sulphate dihydrate and to the use thereof for production of gypsum plasterboard.
• calcium sulphate dihydrate occurs naturally in large deposits which formed when oceans evaporated during the earth's history.
• calcium sulphate dihydrate is obtained as a product or byproduct in various industrial processes, for example flue gas desulphurization, in which sulphur dioxide is depleted from the combustion offgases of coal-fired power plants by means of a calcium carbonate or calcium hydroxide slurry.
• Calcium sulphate hemihydrate is an important building material for production of mortars, screeds, casting moulds and particularly gypsum plasterboard. Due to technical requirements, considerably varying properties are demanded of calcium sulphate binders. Particularly with regard to processing time and the time at which hardening occurs, the binders must be variably adjustable over the period from a few minutes to several hours. In order to satisfy these requirements, the use of setting- regulating additives is necessary.
• gypsum plasterboard Of crucial significance is the acceleration of setting in the production of gypsum slabs, especially gypsum plasterboard. At present, more than 8000 million m 2 of gypsum plasterboard per year are produced globally.
• the production of gypsum plasterboard has long been known. It is described, for example, in US Patent 4,009,062.
• the settable gypsum slurry composed of calcium sulphate hemihydrate and water used is typically produced in a flow mixer at high speed, applied continuously to a cardboard sheet and covered with a second piece of cardboard.
• the two cardboard sheets are referred to as the front and back boards.
• the line of boards then moves along what is called a setting belt, and almost complete conversion of the settable calcium sulphate phases to calcium sulphate dihydrate must have taken place at the end of the setting belt. After this hardening, the sheet is individualized into boards and the water still present in the boards is removed in heated multistage dryers.
• Such gypsum plasterboard is used on a large scale for interior roofs and walls.
• Modern plants for fabrication of gypsum slabs can reach manufacturing rates of up to 180 meters per minute.
• the greatest possible exploitation of the plant capacity is possible only through the use of high-efficiency accelerators.
• the setting time of the calcium sulphate hemihydrate here determines the time until the gypsum plasterboard can be cut and hence the length and the speed of the conveyor belt, and hence the production rate.
• the hydration has to be complete before the boards are exposed to high temperatures in the dryer. Otherwise, the strength potential of the binder is inadequately utilized and the risk of volume expansion arises as a result of post-hyd ration on ingress of moisture.
• the setting accelerator used nowadays in the industrial production of gypsum plasterboard is ground calcium sulphate dihydrate, a large portion of the particles used being in the region of 1 ⁇ .
• the production of a setting accelerator which is equally effective over a prolonged period still presents great technical problems.
• the ground calcium sulphate dihydrate can be used only in powder form since introduction into water leads immediately to the dissolution of the finest particles, which are crucial for the setting acceleration.
• a further accelerator also used in addition to ground calcium sulphate dihydrate is potassium sulphate.
• this has the disadvantage that it leads to a distinct decrease in the final compressive strength of the products produced.
• the encrustations have to be removed at regular time intervals in a highly laborious manner with shutdowns in production.
• WO 2005/021632 discloses a process for producing fine inorganic solids by
• the surface of the fine inorganic solids is coated here with at least one dispersant.
• the inorganic solids disclosed include precipitated calcium sulphate among many other compounds, while the dispersants used are, for example, acrylate or methacrylate copolymers and the salts, polyphosphates and modified fatty acid derivatives thereof.
• This object was achieved by a process for producing calcium sulphate dihydrate by reacting a water-soluble calcium compound with a water-soluble sulphate compound in the presence of water and a polymer containing acid groups, wherein the polymer containing acid groups comprises polyether groups of the structural unit (I)
• U represents a chemical bond or an alkylene group having 1 to 8 carbon atoms
• X is oxygen or an NR 1 group
• k O or l
• n is an integer with a mean, based on the polymer containing acid groups, in the range from 3 to 300,
• Alk is C2-C4-alkylene, where Alk may be the same or different within the (Alk-0) n group,
• W is a hydrogen, Ci-C6-alkyl or aryl radical or is the Y-F group
• Y is a linear or branched alkylene group which has 2 to 8 carbon atoms and may bear a phenyl ring,
• F is a nitrogen-bonded 5- to 10-membered nitrogen heterocycle which may have, as ring members, as well as the nitrogen atom and as well as carbon atoms, 1 , 2 or 3 additional heteroatoms selected from oxygen, nitrogen and sulphur, where the nitrogen ring members may have an R 2 group, and where 1 or 2 carbon ring members may be in the form of carbonyl groups,
• R 1 is hydrogen, Ci-C4-alkyl or benzyl
• R 2 is hydrogen, Ci-C4-alkyl or benzyl. It has been found here, surprisingly, that the calcium sulphate dihydrate produced by the process according to the invention has excellent efficacy as a setting accelerator for calcium sulphate hemihydrate and anhydrite. Particularly surprising in this context was the very good storage stability of the aqueous products obtained, which are preferably in the form of suspensions. Storage of the product over several months also does not lead to any change in the setting acceleration.
• the inventive polymer comprises an acid group.
• the term "acid group” in the present application is understood to mean both the free acid and the salts thereof.
• the acid may preferably be at least one from the group of carboxyl, phosphono, sulphino, sulpho, sulphamido, sulphoxy, sulphoalkyloxy, sulphinoalkyloxy and phosphonooxy group. Particular preference is given to carboxyl and phosphonooxy groups.
• Useful water-soluble calcium compounds and water-soluble sulphate compounds in each case are in principle also only comparatively sparingly water-soluble compounds, although preference is given to compounds which have good water solubility and dissolve completely or virtually completely in water in each case.
• the water-soluble calcium compound has a solubility of 0.01 to 8 mol/l, preferably 0.1 to 5 mol/l, especially 0.5 to 3 mol/l in water and the water-soluble sulphate compound has a solubility of 0.01 to 8 mol/l, preferably 0.1 to 5 mol/l, especially 0.5 to 3 mol/l in water.
• the water-soluble sulphate compound in a first step, is mixed with water and the polymer containing acid groups, such that a mixture preferably in the form of a solution is obtained, to which, in a subsequent second step, the water-soluble calcium compound is added, preferably as a solution. More particularly, the water-soluble calcium compound and the water-soluble sulphate compound can be used as aqueous solutions in the following concentrations:
• aqueous mixture may, as well as water, also comprise one or more further solvents.
• the reaction of the water-soluble calcium compound with the water-soluble sulphate compound is preferably conducted in the presence of water and a polymer containing acid groups at a temperature between 5 and 25°C. Higher temperatures lead to poorer efficacy of the setting accelerator.
• the water-soluble calcium compound is especially at least one from the group of calcium chloride, calcium nitrate, calcium formate, calcium acetate, calcium
• the water-soluble calcium compound is preferably at least one from the group of calcium chloride, calcium nitrate, calcium thiocyanate, calcium acetate and calcium formate.
• the water-soluble sulphate compound is especially at least one from the group of ammonium sulphate, magnesium sulphate, sodium sulphate, potassium sulphate, lithium sulphate, rubidium sulphate, caesium sulphate, sodium hydrogensulphate, potassium hydrogensulphate, lithium hydrogensulphate, rubidium hydrogensulphate, caesium hydrogensulphate and sulphuric acid.
• the water-soluble sulphate compound is preferably at least one from the group of ammonium sulphate, magnesium sulphate, sodium sulphate, potassium sulphate, lithium sulphate, rubidium sulphate and caesium sulphate.
• the polymer containing acid groups is a polycondensation product comprising
• (III) a phosphated structural unit having an aromatic or heteroaromatic system.
• the structural units (II) and (III) are preferably represented by the following general formulae
• A-U-(C(0))k-X-(AlkO) n -W where A is the same or different and is represented by a substituted or unsubstituted, aromatic or heteroaromatic compound having 5 to 10 carbon atoms in the aromatic system, where the further radicals are as defined for structural unit (I);
• D is the same or different and is represented by a substituted or unsubstituted, aromatic or heteroaromatic compound having 5 to 10 carbon atoms in the aromatic system.
• R 3 and R 4 are the same or different and are each independently represented by a branched or unbranched Ci- to Cio-alkyl radical, Cs- to Cs-cycloalkyl radical, aryl radical, heteroaryl radical or H, preferably by H, methyl, ethyl or phenyl, more preferably by H or methyl and especially preferably by H.
• the polycondensation product preferably contains a further structural unit (IV) which is represented by the following formula (IV)
• Y is the same or different and is independently represented by (II), (III) or further constituents of the polycondensation product.
• R 5 and R 6 are preferably the same or different and are represented by H, CH3, COOH or a substituted or unsubstituted, aromatic or heteroaromatic compound having 5 to 10 carbon atoms.
• R 5 and R 6 in structural unit (IV) are preferably each independently represented by H, COOH and/or methyl.
• R 5 and R 6 are each represented by H.
• the molar ratio of the structural units (II), (III) and (IV) of the inventive phosphated polycondensation product can be varied within wide ranges. It has been found to be appropriate that the molar ratio of the structural units [(II) + (III)] : (IV) is 1 : 0.8 to 3, preferably 1 : 0.9 to 2 and more preferably 1 : 0.95 to 1 .
• the molar ratio of the structural units (II) : (III) is normally 1 : 10 to 10 : 1 , preferably 1 : 7 to 5 : 1 and more preferably 1 : 5 to 3 : 1.2.
• the A and D groups in the structural units (II) and (III) of the polycondensation product are usually represented by phenyl, 2-hydroxyphenyl, 3-hydroxyphenyl,
• a and D may be selected independently of one another and may also each consist of a mixture of the compounds mentioned.
• the X and E groups are preferably each independently represented by O.
• n in structural unit (I) is represented by an integer from 5 to 280, especially 10 to 160 and more preferably 12 to 120, and b in structural unit (III) by an integer from 0 to 10, preferably 1 to 7 and more preferably 1 to 5.
• the respective radicals, the length of which is defined by n and b, may consist here of uniform component groups, but it may also be appropriate that they are a mixture of different component groups.
• the radicals of the structural units (II) and (III) may each independently have the same chain length, in which case n and b are each represented by a number. However, it will generally be appropriate that mixtures with different chain lengths are involved in each case, such that the radicals of the structural units in the
• polycondensation product have different numerical values for n and, independently, for b.
• the present invention further envisages that a sodium, potassium, ammonium and/or calcium salt and preferably a sodium and calcium salt of the phosphated polycondensation product is involved.
• the inventive phosphated polycondensation product has a weight-average molecular weight of 4000 g/mol to 150 000 g/mol, preferably 10 000 to 100 000 g/mol and more preferably 20 000 to 75 000 g/mol.
• the polymer containing acid groups is at least one copolymer obtainable by polymerizing a mixture of monomers comprising
• (V) at least one ethylenically unsaturated monomer comprising at least one radical from the group of carboxylic acid, carboxylic salt, carboxylic ester, carboxamide, carboxylic anhydride and carboximide
• the copolymers according to the present invention contain at least two monomer units. However, it may also be advantageous to use copolymers with three or more monomer units.
• the ethylenically unsaturated monomer (V) is represented by at least one of the following general formulae from groups (Va), (Vb) and (Vc):
• R 7 and R 8 are each independently hydrogen or an aliphatic hydrocarbyl radical having 1 to 20 carbon atoms, preferably a methyl group.
• B is H, -COOM a , -CO-0(C q H 2q O) r -R 9 , -CO-NH-(C q H 2q O) r -R 9 .
• the organic amine radicals used are preferably substituted ammonium groups which derive from primary, secondary or tertiary Ci-20-alkylamines, Ci-20-alkanolamines, Cs-s-cycloalkylamines and C6-i4-arylamines. Examples of the corresponding amines are methylamine,
• the aliphatic hydrocarbons here may be linear or branched and saturated or unsaturated.
• Preferred cycloalkyl radicals are considered to be cyclopentyl or cyclohexyl radicals, and preferred aryl radicals to be phenyl or naphthyl radicals, which may especially also be substituted by hydroxyl, carboxyl or sulpho groups.
• R 10 and R 11 are each independently hydrogen or an aliphatic hydrocarbyl radical having 1 to 20 carbon atoms, a cycloaliphatic hydrocarbyl radical having 5 to 8 carbon atoms, an optionally substituted aryl radical having 6 to 14 carbon atoms.
• Q may be the same or different and is represented by NH, NR 9 or O, where R 9 is as defined above.
• R 13 is H, -COOMa, -CO-0(C q H 2q O)r-R 9 , -CO-NH-(C q H 2q O) r -R 9 , where M a , R 9 , q and r are each as defined above.
• R 14 is hydrogen, an aliphatic hydrocarbyl radical having 1 to 10 carbon atoms, a cycloaliphatic hydrocarbyl radical having 5 to 8 carbon atoms, an optionally substituted aryl radical having 6 to 14 carbon atoms.
• the ethylenically unsaturated monomer (VI) is represented by the following general formula
• the process according to the invention based on the calcium sulphate dihydrate, preferably between 0.005 and 100% by weight, especially between 0.01 and 50% by weight, especially preferably between 0.02 and 30% by weight, more preferably between 0.03 and 15% by weight and most preferably between 0.05 and 10% by weight of the polymer containing acid groups is used.
• the present invention further provides calcium sulphate dihydrate producible by the process according to the invention.
• the present invention also provides for the use of calcium sulphate dihydrate, produced by reaction of a water-soluble calcium compound with a water-soluble sulphate compound in the presence of water and a polymer containing acid groups for production of gypsum plasterboard.
• the polymers containing acid groups may be the polymers which have polyether groups of structural unit (I) and are used in the process according to the invention. It is, however, additionally possible also to use at least one polymer containing acid groups from the group of polyacrylic acid, polymethacrylic acid, polyvinylphosphonic acid, and copolymers comprising acrylic acid, methacrylic acid, vinylsulphonic acid, 2-acrylamido-2-methylpropanesulphonic acid and vinylphosphonic acid. Especially preferred are polyacrylic acid, polymethacrylic acid and
• the calcium sulphate dihydrate obtained by reaction of a water-soluble calcium compound with a water-soluble sulphate compound in the presence of water and a polymer containing acid groups is used in the form of an aqueous suspension, particularly as obtainable directly from the process according to the invention, for production of gypsum plasterboard.
• the inventive calcium sulphate dihydrate suspension preferably contains between 0.1 and 3.0 mol/l, especially between 0.3 and 1.5 mol/l and more preferably between 0.6 and 1.0 mol/l of calcium sulphate dihydrate. It is particularly advantageous here that the gypsum slurry used for production of the gypsum plasterboard cannot be contacted with the inventive calcium sulphate dihydrate until after application to the cardboard sheet, the calcium sulphate dihydrate being used in the form of an aqueous suspension.
• the use of a calcium sulphate dihydrate suspension achieves easy applicability and a very good
• the compressive strength of the gypsum plasterboard is not affected or even improved by the use of the calcium sulphate dihydrate according to the invention.
• the calcium sulphate dihydrate obtained by reaction of a water-soluble calcium compound with a water-soluble sulphate compound in the presence of water and a polymer containing acid groups can be added at different stages of the production process.
• the calcium sulphate dihydrate according to the invention is applied at least on one of the surfaces of the cardboard sheets, in particular in the form of an aqueous suspension, to which the gypsum slurry is subsequently applied.
• the calcium sulphate dihydrate according to the invention in the production process of the cardboard sheets.
• the calcium sulphate dihydrate according to the invention can also be added to the flow mixer, directly after the flow mixer, to the batching water, to the foam and/or to the stucco preparation before it is added to the flow mixer.
• the calcium sulphate dihydrate according to the invention is used in combination with calcium sulfate dihydrate powder, preferably in a finely ground form, for the production of gypsum plasterboard.
• the present invention further provides a process for producing a gypsum plasterboard, wherein 0.0001 to 1 % by weight of the calcium sulphate dihydrate as obtainable directly from the process according to the invention, based on the calcium sulphate hemihydrate used in the production of the gypsum plasterboard, is used.
• the gypsum slurry used for production of the gypsum plasterboard is not contacted with the calcium sulphate dihydrate until after application to the cardboard sheet, the calcium sulphate dihydrate being used in the form of an aqueous suspension.
• a glass reactor equipped with a stirrer, thermometer, pH electrode and several feed devices is initially charged with 180 g of deionized water and heated to a
• polymerization start temperature 80°C (initial charge).
• a separate feed vessel 4669 g of a 25.7% purified aqueous methyl polyethylene glycol (5000) methacrylate (MPEG5000 methacrylate) solution are mixed with 297.6 g of hydroxyethyl
• a heatable reactor equipped with a stirrer is charged with 17.8 parts of polyphosphoric acid and heated to 90°C. Within 15 min, 30.7 parts of phenoxyethanol are metered in while stirring. After 60 min, 445 parts of poly(ethylene oxide) monophenyl ether (mean molecular weight 5000 g/mol), 34.8 parts of concentrated methanesulphonic acid, 14.16 parts of paraformaldehyde and 23.2 parts of water are added. The reaction mixture is heated to 105°C while stirring for a further 6 hours. It is then allowed to cool and neutralized to pH 7 with 50% sodium hydroxide solution. The condensation product has a mean molecular weight M w of approx. 22 000 g/mol (determined by GPC).
• the comb polymer Melflux 2650 L is a commercially available polycarboxylate ether from BASF Construction Polymers GmbH.
• the polymer is based on the monomers maleic acid, acrylic acid, vinyloxybutyl polyethylene glycol - 5800.
• M w 36 000 g/mol, determined by GPC; the solids content of the solution is 33%.
• the resulting suspension is stirred with an axial stirrer at 800 revolutions per minute for 1 hour.
• a solution of 44.4 g of calcium chloride (anhydrous, 0.4 mol) in 75 g of water is added to a solution of 98.6 g of magnesium sulphate heptahydrate (0.4 mol) and 0.46 g (based on active content of polymer) of the above-described comb polymer containing phosphoric ester in 282 g of water.
• the resulting suspension is stirred with an axial stirrer at 800 revolutions per minute for 1 hour.
• a solution of 44.4 g of calcium chloride (anhydrous, 0.4 mol) in 75 g of water is added to a solution of 57.6 g of ammonium sulphate (0.42 mol) and 0.93 g of the above- described phosphated polycondensation product (based on active content of polymer) in 282 g of water.
• the resulting suspension is stirred with an axial stirrer at 800 revolutions per minute for 1 hour.
• the resulting suspension is stirred with an axial stirrer at 800 revolutions per minute for 1 hour.
• sample 1 Also used as comparative examples were two samples of ground calcium sulphate dihydrate which are used commercially in the production of gypsum plasterboard. These are referred to hereinafter as sample 1 and sample 2.
• Table 1 Particle size distributions for samples 1 and 2 (ground calcium sulphate dihydrate) and of the samples described in Examples 1 to 6.
• inventions exhibit a very stable particle size distribution over a long period.
• Figure 5 shows the characteristic data for the particle size distribution (measured by means of static light scattering with a Malvern
• Mastersizer 2000 of a calcium sulphate dihydrate suspension produced in accordance with the invention. It can be seen that the particle sizes are virtually unchanged over a period of at least 160 days. This behaviour is also reflected in the use test: the performance remains constant over the period examined.
• Example 1 For comparison, a dosage curve for a suspension produced in accordance with the invention (Example 1 ) is shown. A much higher dosage efficiency and a significantly higher maximum performance are evident.

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• Curing Cements, Concrete, And Artificial Stone (AREA)
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• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

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