WO1981002010A1 - Plaster products and a process for the production thereof - Google Patents

Plaster products and a process for the production thereof Download PDF

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Publication number
WO1981002010A1
WO1981002010A1 PCT/SE1980/000008 SE8000008W WO8102010A1 WO 1981002010 A1 WO1981002010 A1 WO 1981002010A1 SE 8000008 W SE8000008 W SE 8000008W WO 8102010 A1 WO8102010 A1 WO 8102010A1
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WO
WIPO (PCT)
Prior art keywords
potassium
sulfate
calcium sulfate
plaster
dihydrate
Prior art date
Application number
PCT/SE1980/000008
Other languages
French (fr)
Inventor
S Nordqvist
Original Assignee
Tenax Maskin Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Tenax Maskin Ab filed Critical Tenax Maskin Ab
Priority to BR8009013A priority Critical patent/BR8009013A/en
Priority to NL8020014A priority patent/NL8020014A/en
Priority to PCT/SE1980/000008 priority patent/WO1981002010A1/en
Priority to AT0913380A priority patent/AT380005B/en
Publication of WO1981002010A1 publication Critical patent/WO1981002010A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28B7/00—Moulds; Cores; Mandrels
    • B28B7/34—Moulds, cores, or mandrels of special material, e.g. destructible materials
    • B28B7/346—Manufacture of moulds
    • 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
    • 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
    • C04B28/141—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 containing dihydrated gypsum before the final hardening step, e.g. forming a dihydrated gypsum product followed by a de- and rehydration step
    • 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
    • C04B28/142—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 containing synthetic or waste calcium sulfate cements
    • C04B28/143—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 containing synthetic or waste calcium sulfate cements the synthetic calcium sulfate being phosphogypsum
    • 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
    • C04B2111/00939—Uses not provided for elsewhere in C04B2111/00 for the fabrication of moulds or cores

Definitions

  • This invention relates to plaster (gypsum) products and process for the preparation thereof.
  • the plaster products are especially intended for wallboard (plaster board) and mould-s for use in the preparation of metal and ceramic articles.
  • plaster products by suspending gypsum (calcium sulfate semihydrate) in water, moulding the slurry to the desired product (desired shape) and solidifying (setting) this.
  • Varios additives can be added to the prepared slurry of calcium sulfate semihydrate in water, such as accelerators, retardants and resins. The solidification is apparently due to the fact that the semihydrate is hydrated forming dihydrate (calcium sulfate dihydrate).
  • the starting material of the gypsum product preparation i e calcium sulftate semihydrate (hemihydrate, half-hydrate)
  • calcium sulfate dihydrate here also called dihydrate gypsum
  • This burning requires large amounts of energy and, moreover, must be carefully controlled so that a correct content of water of crystallization is obtained.
  • plaster products with good strength properties and other mechanical properties which can be easily manufactured at a low price, comprise such that are built up of calcium sulfate dihydrate reinforced with potassium sulfate calcium sulfate dihydrate (syngenite) crystals and optionally potassium sulfate-magnesium sulfate-calcium sulfate dihydrate crystals.
  • the reinforcement can be substantially uniformly distributed in the whole plaster product or e.g. concentrated to certain layers or portions of the product, especially in the cases when the product consists of boards.
  • the minimum amount of double salt (potassium sulfate-calcium sulfate dihydrate) in such a reinforced plaster product or portion or layer of a plaster product is about 3-5 % by weight and is usually in the range of from 10 to 60 % by weight and prererably in the range of from 15 to 40 % by weight.
  • Plaster products with a reinforcement of potassium sulfate-calcium sulfate hydrate and optionally calcium sulfate-magnesium sulfate-calcium sulfate dihydrate can be prepared by adding a potassium salt, preferably potassium sulfate, to a water slurry of calcium sulfate dihydrate, optionally together with a magnesium salt, preferably magnesium sulfate, and optionally in combination with a carrier, after which the product is moulded (shaped) and further treated in known manner, the slurry being maintained below 70 C, preferably below 55°C, so that no calcining takes place.
  • a potassium salt preferably potassium sulfate
  • a magnesium salt preferably magnesium sulfate
  • the potassium salt consists preferably of potassium hydrogencarbonate or potassium tetraborate but, in the first place, potassium sulfate.
  • the potassium salts can be used as such or mixed with each other, e.g. a mixture of potassium sulfate and potassium hydrogencarbonate, and optionally dissolved in water or together with a carrier, e.g. sodium sulfate.
  • the magnesium salt possibly used can be added in the same way as the potassium salt, preferably together with the potassium salt.
  • the density of the resulting plaster product can be adjusted by addition of various additives and through the mixing procedure (air being added).
  • An addition of a wetting agent is suitable for this adjustment of the density.
  • potassium hydrogencarbonate a foam product is obtained and the expansion (the degree of blowing) can be adjusted by using potassium sulfate together with the potassium hydrogencarbonate, the proportions thereof being varied all according to the desired product.
  • the calcium sulfate dihydrate resulting as waste in the preparation of phosphate fertilizers is preferably used.
  • This starting material shows usually an analysis of
  • dihydrate gypsum which is obtained at purification of flue gas, and naturally occurring dihydrate gypsum. It is also possible to re-use as staring material the products obtained according to the present invention, which are then crushed and suspended in water.
  • the amount of potassium salt added can vary, the minimum amount being about 2 or 3 % by weight; the broad range is 5-40 % and a preferred range 6-20%, calculated on the amount of calcium sulfate dihydrate (CaSO 4 . 2 H 2 O). If magnesium sulfate is used minium amounts thereof are about 2-3 % by weight and a wide range 4-20 %, a suitable range being 6-10 % calculated on the amount of calcium sulfate dihydrate.
  • Such additives as create porosity e.g. of silicate type, are of special importance. These additives e.g. consist of perlite or vermiculite.
  • the resulting products e.g. boards or moulds, are heat insulating and have a good stiffness in flexing at a suitable thickness.
  • the potassium hydrogencarbonate is used according to the invention by itself for preparation of solidified, hard plaster foam products.
  • the potassium hydrogencarbonate is preferably used together with potassium sulfate and other of the indicated additives for the preparation of solidified plaster products.
  • potassium hydrogencarbonate other additives, such as sodium hydrogencarbonate, hydrogen peroxide, ammonium carbonate, aluminium bronze, which give off gas under the preparation conditions, can be used for the preparation of foam products.
  • these additives do not contribute to the solidifying effect. It is possible, and in many cases suitable, in preparation of the present plaster products to reinforce them by admixing e.g. steel fibres and/or glass fibres in the gypsum slurry.
  • Such reinforcing means as rods and nets can be embedded at discontinuous production of moulds or boards or be cast at continuous production of plaster boards.
  • the present plaster product, above all in the form of plaster board can in known manner also be cast on cardboard, plastic, foils and films of another type, rubber cloth, wood or metal, for instance, These agents also contribute to an increase of the strength.
  • a plaster product according to the invention which is not being provided with a surface layer in said manner can be immersed in or treated with a solution of e.g. potassium sulfate or a borate, such as potassium or sodium tetraborate, which increases the hardness and the strength.
  • the hardness can also be increased by using as additive an agent, e.g. a salt, influencing the solubility of the gypsum, such as sodium thiosulfate, methaphosphate and hexamethaphosphate.
  • An additive which has been found to provide surprisingly good plaster products mainly plaster board
  • spent sulfite liquor as additive, the surface layer adhesion, especially of cardboard, to the plaster board is improved to a very large extent.
  • the strength is also improved.
  • Another agent also improving the surface layer adhesion is corn starch. However, this provides inferior results in comparison with spent sulfite liquor.
  • additives can also be used, e.g. agents retarding the setting rate, such as soda, glycerol, alginate.
  • agents retarding the setting rate such as soda, glycerol, alginate.
  • Other additives are sulfuric acid, hydrogen hexafluorosilicate, citric acid, ammonium carbonate
  • magnesium oxide in the form of a powder.
  • the magnesium oxide can comprise up to 50 I by weight of the calcium sulfate dihydrate. It is also suitable to admix perlite.
  • the water content can also be varied, i.e. you can dilute the calcium sulfate dih.yd ⁇ ate slurry with water, e.g. so that 70 % of the slurry consist of water, or admix various wetting agents.
  • the agents giving off gas and already described are used.
  • the process of the invention might also be considered to consist in a "solidification" of the calcium sulfate dihydrate, i.e. the included grains and the whole plaster product prepared will be harder.
  • the grain size of the potassium sulfate is of a certain importance, as the process is quicker the more fine granular the potassium sulfate is.
  • Potassium sulfate with a grain size of down to 70 um has been tested and this grain size will provide about the same rate of solidification as an aqueous solution of potassium sulfate.
  • solutions and salts and the like providing potassium sulfate when mixed are equivalent to potassium sulfate.
  • a solution of potassium chloride and a solution of magnesium sulfate can be used by adding them simultaneously, for instance.
  • the various indicated additives are usually used in an amount of 1-15 % by weight calculated on the included amount of calcium sulfate dihydrate.
  • the temperature of the water slurry shall be kept belottf 70o C all the time. In this way no substantial formation of calcium sulfate semihydrate is obtained even in the case where dehydrating agents as sulfuric acid," are present.
  • the temperature of the slurry should preferably be kept below 55o C, as e.g. below 45o C or 50o C, also during the drying and setting steps.
  • Exemple 1 50 kg K 2 SO4 were added to 1000 kg slurry of dihydrate gypsum containing 20 water. Addition was carried out under vigorous stirring at 1400 rpm. The slurry was immediately cast to a board and cubic test bodies (5 cm x 5 cm x 5 cm) were made. The board having ambient temperature about 20o C solidified in a very short time (some minutes). The test bodies showed a compression strength of 8 MPa after 24 h.
  • Example 2 300 kg of potassium sulfate in solid form were added to 3600 kg of a slurry of dihydrate gypsum under vigorous stirring, .such as in example 1. Board and test bodies were prepared as in example 1. The density of the resulting board was 1.1-1.3 g/cm 3 . The compression strength of the test bodies was 4.1 MPa as determined after 96 h at 20°C or 48 h at 40°C.
  • Example 5 1000 kg of dihydrate gypsum of 72 % were mixed with 35 kg of ammonium hydrogencarbonate and 60 kg of potassium sulfate. The mixture was cast in plane slabs. After a setting period of 15-20 minutes at 13o C a board with good strength properties was obtained.
  • Example 5 1000 kg of 72 % dihydrate gypsum in the form of a slurry were mixed with 55 kg of potassium sulfate having a grain size of 70 % less than 80 urn. Slabs were prepared on a plaster board machine, solidified and dried by microwave radiation for 2 seconds repeated six times in a 4 minutes' period. The temperature of the slurry was maximum about 44o C; locally it seemed as a slightly higher temperature temporarily was reached.
  • Example 6 A slurry of 72 % dihydrate gypsum containing 1.5 % spent sulfite liquor (dry substance) was continuously moulded to a thickness of about 13 mm on a running web of paper board on a plaster board machine.
  • Potassium sulfate (7 % by weight based on dry dihydrate gypsum) was added to the slurry during the moulding. It was in a fine granular form (80 % passing a 70 ⁇ m mesh sieve). The moulded slabs were solidified and dried in a conventional way, the slurry having a maximum temperature of about 41o C. Wall board of about 13 mm with good strength properties was obtained.
  • a plaster product having excellent properties is provided according to the invention and that this product can be prepared from a starting slurry having as major component calcium sulfate dihydrate.
  • the slurry contains mainly calcium sulfate dihydrate, say 80-100 %, preferably 90-100 % by weight of the solids including normal contaminants. It is not desirable that the slurry contains calcium sulfate semihydrate.
  • a potassium sulfate suitably in finely distributed, solid form, optionally together with a finely distributed, solid magnesium salt, as e.g. magnesium sulfate.
  • the potassium salt can also be added as solution, normally aqueous, and preferably as a concentrated solution, as e.g. substantially saturated solution.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Curing Cements, Concrete, And Artificial Stone (AREA)

Abstract

Plaster products comprising a mass of calcium sulfate dihydrate crystals intermingled with crystals of the double salt potassium sulfate-calcium sulfate hydrate and optionally the triple salt potassium sulfate-magnesium sulfate-calcium sulfate. Plaster products can be prepared from calcium sulfate dihydrate by adding to a water slum y of calcium sulfate dihydrate a potassium salt, especially potassium hydrogen-carbonate or potassium tetraborate but, in the first place, potassium sulfate, including a carrier, after which the water slurry is moulded and further worked in known manner to the desired plaster product, especially plaster board or moulds for the production of metal articles or ceramic articles.

Description

Plaster products and a processfor the production there of
This invention relates to plaster (gypsum) products and process for the preparation thereof. The plaster products are especially intended for wallboard (plaster board) and mould-s for use in the preparation of metal and ceramic articles.
It is known to prepare plaster products by suspending gypsum (calcium sulfate semihydrate) in water, moulding the slurry to the desired product (desired shape) and solidifying (setting) this. Varios additives can be added to the prepared slurry of calcium sulfate semihydrate in water, such as accelerators, retardants and resins. The solidification is apparently due to the fact that the semihydrate is hydrated forming dihydrate (calcium sulfate dihydrate). To obtain the starting material of the gypsum product preparation, i e calcium sulftate semihydrate (hemihydrate, half-hydrate), it is started from calcium sulfate dihydrate (here also called dihydrate gypsum), the content of water of crystallization being reduced by burning. This burning requires large amounts of energy and, moreover, must be carefully controlled so that a correct content of water of crystallization is obtained.
It is also known to prepare the calcium sulfate hemihydrate by eliminating water from calcium sulfate dihydrate by using the strong water absorbing agent sulfuric acid under hot conditions. Thus, the German laid open print (Auslegeschrift) 1 274 488 teaches the- preparation of calcium sulfate hemihydrate by treating calcium sulfate dihydrate with a hot (above 80°C) solution (about 12.7 to 37.2 % by weigth) of sulfuric acid, optionally together with modifyers of the crystal form and/or grafxing crystals.
Now it has been found that plaster products with good strength properties and other mechanical properties, which can be easily manufactured at a low price, comprise such that are built up of calcium sulfate dihydrate reinforced with potassium sulfate calcium sulfate dihydrate (syngenite) crystals and optionally potassium sulfate-magnesium sulfate-calcium sulfate dihydrate crystals. The reinforcement can be substantially uniformly distributed in the whole plaster product or e.g. concentrated to certain layers or portions of the product, especially in the cases when the product consists of boards. The minimum amount of double salt (potassium sulfate-calcium sulfate dihydrate) in such a reinforced plaster product or portion or layer of a plaster product is about 3-5 % by weight and is usually in the range of from 10 to 60 % by weight and prererably in the range of from 15 to 40 % by weight.
Plaster products with a reinforcement of potassium sulfate-calcium sulfate hydrate and optionally calcium sulfate-magnesium sulfate-calcium sulfate dihydrate can be prepared by adding a potassium salt, preferably potassium sulfate, to a water slurry of calcium sulfate dihydrate, optionally together with a magnesium salt, preferably magnesium sulfate, and optionally in combination with a carrier, after which the product is moulded (shaped) and further treated in known manner, the slurry being maintained below 70 C, preferably below 55°C, so that no calcining takes place. The potassium salt consists preferably of potassium hydrogencarbonate or potassium tetraborate but, in the first place, potassium sulfate. The potassium salts can be used as such or mixed with each other, e.g. a mixture of potassium sulfate and potassium hydrogencarbonate, and optionally dissolved in water or together with a carrier, e.g. sodium sulfate. The magnesium salt possibly used can be added in the same way as the potassium salt, preferably together with the potassium salt.
The density of the resulting plaster product can be adjusted by addition of various additives and through the mixing procedure (air being added). An addition of a wetting agent is suitable for this adjustment of the density. When using potassium hydrogencarbonate a foam product is obtained and the expansion (the degree of blowing) can be adjusted by using potassium sulfate together with the potassium hydrogencarbonate, the proportions thereof being varied all according to the desired product.
As starting material the calcium sulfate dihydrate resulting as waste in the preparation of phosphate fertilizers, such as different calcium phosphates and phosphoric acid, is preferably used. This starting material shows usually an analysis of
H3PO4 about 0.1 % by weight (calculated as P)
H3PO4 non-dissolved about.0.3 % by weight (calculated as P)
F about 1.0 % by weight
Silicate about 2 % by weight
Heavy metals 10 g/ton
Leaching water pH 2-3 Water about 25 % by weight
Grain size 70 % < 74 μm
Other starting materials can be used, e.g. dihydrate gypsum, which is obtained at purification of flue gas, and naturally occurring dihydrate gypsum. It is also possible to re-use as staring material the products obtained according to the present invention, which are then crushed and suspended in water.
The amount of potassium salt added can vary, the minimum amount being about 2 or 3 % by weight; the broad range is 5-40 % and a preferred range 6-20%, calculated on the amount of calcium sulfate dihydrate (CaSO4. 2 H2O). If magnesium sulfate is used minium amounts thereof are about 2-3 % by weight and a wide range 4-20 %, a suitable range being 6-10 % calculated on the amount of calcium sulfate dihydrate.
It has also been found that different agents can be admixed in the present starting slurry, plaster products being obtained with different modifications of the properties. It is possible to add semihydrate gypsum. Addition of water glass, such as silicate of soda, increases the hardness. Plastics, such as polyacrylates and melamine-resins, or plastic starting materials hardening simultaneously with the solidifaction of the plaster products can be added for increasing the strength or the water resistance. Other additives are calcium silicate, carboxymethyl cellulose, bentonite and cement.
Such additives as create porosity, e.g. of silicate type, are of special importance. These additives e.g. consist of perlite or vermiculite. The resulting products, e.g. boards or moulds, are heat insulating and have a good stiffness in flexing at a suitable thickness.
The potassium hydrogencarbonate is used according to the invention by itself for preparation of solidified, hard plaster foam products. However, the potassium hydrogencarbonate is preferably used together with potassium sulfate and other of the indicated additives for the preparation of solidified plaster products. Instead of potassium hydrogencarbonate other additives, such as sodium hydrogencarbonate, hydrogen peroxide, ammonium carbonate, aluminium bronze, which give off gas under the preparation conditions, can be used for the preparation of foam products. However, these additives do not contribute to the solidifying effect. It is possible, and in many cases suitable, in preparation of the present plaster products to reinforce them by admixing e.g. steel fibres and/or glass fibres in the gypsum slurry. Such reinforcing means as rods and nets can be embedded at discontinuous production of moulds or boards or be cast at continuous production of plaster boards. The present plaster product, above all in the form of plaster board, can in known manner also be cast on cardboard, plastic, foils and films of another type, rubber cloth, wood or metal, for instance, These agents also contribute to an increase of the strength. A plaster product according to the invention which is not being provided with a surface layer in said manner can be immersed in or treated with a solution of e.g. potassium sulfate or a borate, such as potassium or sodium tetraborate, which increases the hardness and the strength. The hardness can also be increased by using as additive an agent, e.g. a salt, influencing the solubility of the gypsum, such as sodium thiosulfate, methaphosphate and hexamethaphosphate.
An additive which has been found to provide surprisingly good plaster products, mainly plaster board, is concentrated spent sulfite liquor, especially on sodium base. Using spent sulfite liquor as additive, the surface layer adhesion, especially of cardboard, to the plaster board is improved to a very large extent.
The strength is also improved. Another agent also improving the surface layer adhesion is corn starch. However, this provides inferior results in comparison with spent sulfite liquor.
Other additives can also be used, e.g. agents retarding the setting rate, such as soda, glycerol, alginate. Other additives are sulfuric acid, hydrogen hexafluorosilicate, citric acid, ammonium carbonate
(hartshorn), urea phosphate, ammonia. These agents are i.a. used for adjustment of pH.
If plaster products very resistant to high temperatures are desired, it is suitable to admix magnesium oxide in the form of a powder. The magnesium oxide can comprise up to 50 I by weight of the calcium sulfate dihydrate. It is also suitable to admix perlite.
For variation of the density of the plaster products the water content can also be varied, i.e. you can dilute the calcium sulfate dih.ydτate slurry with water, e.g. so that 70 % of the slurry consist of water, or admix various wetting agents. To obtain plaster products with an especially low density the agents giving off gas and already described are used.
At the description of the present invention it has been indicated that the slurry of calcium sulfate dihydrate "solidifies" or "is set". However, the process of the invention might also be considered to consist in a "solidification" of the calcium sulfate dihydrate, i.e. the included grains and the whole plaster product prepared will be harder. When carrying out the process the grain size of the potassium sulfate is of a certain importance, as the process is quicker the more fine granular the potassium sulfate is. Potassium sulfate with a grain size of down to 70 um has been tested and this grain size will provide about the same rate of solidification as an aqueous solution of potassium sulfate. Of course, solutions and salts and the like providing potassium sulfate when mixed are equivalent to potassium sulfate. Thus, a solution of potassium chloride and a solution of magnesium sulfate can be used by adding them simultaneously, for instance. The various indicated additives are usually used in an amount of 1-15 % by weight calculated on the included amount of calcium sulfate dihydrate. The temperature of the water slurry shall be kept belottf 70º C all the time. In this way no substantial formation of calcium sulfate semihydrate is obtained even in the case where dehydrating agents as sulfuric acid," are present. The temperature of the slurry should preferably be kept below 55º C, as e.g. below 45º C or 50º C, also during the drying and setting steps.
It has also been found that the use of microwave radiation, particularly in the wave length range of 1-10 cm, gives plaster products having a higher degree of crystallization in the centre and also better strength properties. This embodiment is preferred for the preparation of plaster board.
In order to obtain a fast reinforcement it has been found to be desirable to provide in the water solution of the slurry a potassium salt concentration of at least 3 % at about 20º C. The required concentration potassium salt increases with temperature. following examples.
Exemple 1. 50 kg K2SO4 were added to 1000 kg slurry of dihydrate gypsum containing 20 water. Addition was carried out under vigorous stirring at 1400 rpm. The slurry was immediately cast to a board and cubic test bodies (5 cm x 5 cm x 5 cm) were made. The board having ambient temperature about 20º C solidified in a very short time (some minutes). The test bodies showed a compression strength of 8 MPa after 24 h.
Example 2. 300 kg of potassium sulfate in solid form were added to 3600 kg of a slurry of dihydrate gypsum under vigorous stirring, .such as in example 1. Board and test bodies were prepared as in example 1. The density of the resulting board was 1.1-1.3 g/cm3. The compression strength of the test bodies was 4.1 MPa as determined after 96 h at 20°C or 48 h at 40°C.
Example 5. 1000 kg of dihydrate gypsum of 72 % were mixed with 35 kg of ammonium hydrogencarbonate and 60 kg of potassium sulfate. The mixture was cast in plane slabs. After a setting period of 15-20 minutes at 13º C a board with good strength properties was obtained. Example 4. 100 kg of semihydrate gypsum, 1000 kg of dihydrate gypsum of 72-73 % , 35 kg of ammonium carbonate and 60 kg of potassium sulfate were mixed. After a setting period of 15-20 minutes at 13°C after casting to board, board of somewhat inferior properties than those according to example 1 were obtained.
Example 5. 1000 kg of 72 % dihydrate gypsum in the form of a slurry were mixed with 55 kg of potassium sulfate having a grain size of 70 % less than 80 urn. Slabs were prepared on a plaster board machine, solidified and dried by microwave radiation for 2 seconds repeated six times in a 4 minutes' period. The temperature of the slurry was maximum about 44º C; locally it seemed as a slightly higher temperature temporarily was reached. Example 6. A slurry of 72 % dihydrate gypsum containing 1.5 % spent sulfite liquor (dry substance) was continuously moulded to a thickness of about 13 mm on a running web of paper board on a plaster board machine. Potassium sulfate (7 % by weight based on dry dihydrate gypsum) was added to the slurry during the moulding. It was in a fine granular form (80 % passing a 70 μm mesh sieve). The moulded slabs were solidified and dried in a conventional way, the slurry having a maximum temperature of about 41º C. Wall board of about 13 mm with good strength properties was obtained.
Thus, it is clear that a plaster product having excellent properties is provided according to the invention and that this product can be prepared from a starting slurry having as major component calcium sulfate dihydrate. Thus, in addition to water the slurry contains mainly calcium sulfate dihydrate, say 80-100 %, preferably 90-100 % by weight of the solids including normal contaminants. It is not desirable that the slurry contains calcium sulfate semihydrate. To this slurry isadded a potassium sulfate, suitably in finely distributed, solid form, optionally together with a finely distributed, solid magnesium salt, as e.g. magnesium sulfate. The potassium salt can also be added as solution, normally aqueous, and preferably as a concentrated solution, as e.g. substantially saturated solution.

Claims

1. A method of preparing plaster products, especially plaster board and moulds for the production of metallic and ceramic articles, characterized in that a: potassium salt in an amount of at least about 3 % by weight and optionally a magnesium salt in a minor amont is added to a water slurry of calcium sulfate dihydrate and that the product is then moulded and further worked in a way known per se, the slurry being kept below 70°C.'
2. The method as claimed in claim 1, wherein the slurry is kept below 55°C.
3. The method as claimed in claim 1 , characterized in that the potassium salt is in solid form or in the form of a solution, such as water solution.
4. The method as claimed in claim 1 or 3, characterized in that the potassium salt consists of potassium sulfate.
5. The method as claimed in claim 1 or 3, characterized in that the potassium salt consists of potassium hydrogencarbonate.
6. The method as claimed in claim 1 or 3, characterized in that the potassium salt consists of potassium tetraborate.
7. The method as claimed in any one of claims 1-6, characterized in that setting of the gypsum is accomplished by means of microwave radiation.
8. The use of potassium salt to bring a calcium sulfate dihydrate slurry to set forming a solidified calcium sulfate dihydrate.
9. Plaster products, particularly wall board and moulds for metallic and ceramic articles, characterized in that it at least partially is a mass of calcium sulfate-dihydrate crystals intermingled with crystals of potassium sulfate-calcium sulfate-hydrate and optionally of potassium sulfate-magnesium sulfate-calcium εulfate- -hydrate.
PCT/SE1980/000008 1980-01-09 1980-01-09 Plaster products and a process for the production thereof WO1981002010A1 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BR8009013A BR8009013A (en) 1980-01-09 1980-01-09 PLASTER PRODUCTS AND PROCESS FOR ITS PRODUCTION
NL8020014A NL8020014A (en) 1980-01-09 1980-01-09 PLASTER PRODUCTS AND A METHOD FOR THE PRODUCTION THEREOF.
PCT/SE1980/000008 WO1981002010A1 (en) 1980-01-09 1980-01-09 Plaster products and a process for the production thereof
AT0913380A AT380005B (en) 1980-01-09 1980-01-09 METHOD FOR PRODUCING PLASTER PRODUCTS

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
PCT/SE1980/000008 WO1981002010A1 (en) 1980-01-09 1980-01-09 Plaster products and a process for the production thereof
WOSE80/00008 1980-01-09

Publications (1)

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AT (1) AT380005B (en)
BR (1) BR8009013A (en)
NL (1) NL8020014A (en)
WO (1) WO1981002010A1 (en)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3523115A1 (en) * 1985-06-28 1987-01-08 Friedrich Priehs Process for producing plaster-bonded board materials
EP0210027A2 (en) * 1985-07-12 1987-01-28 Hitachi, Ltd. Method for forming cast article by slip casting
EP0312027A2 (en) * 1987-10-13 1989-04-19 Toto Ltd. Method for hydrating hemihydrate gypsum
EP3398919A1 (en) * 2017-05-05 2018-11-07 Saint-Gobain Placo Tile mould and plaster composition for mould
WO2021217200A1 (en) * 2020-04-27 2021-11-04 Pact Renewables Pty Ltd Mineral-based composites
WO2021258139A1 (en) * 2020-06-25 2021-12-30 Pact Renewables Pty Ltd Degradable materials containing waste paper products

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE432542C (en) * 1924-04-15 1926-08-09 Morduch E Lewin Process for the production of a cement-like mass
GB324320A (en) * 1928-10-18 1930-01-20 Bindphast Products Ltd Improvements in and relating to the manufacture of solid bodies from disintegrated alabaster, gypsum, marl and the like
GB348766A (en) * 1930-03-12 1931-05-21 Peter Petrowitch Budnikoff Improvements in or relating to anhydrite or gypsum cementing compositions
DE821921C (en) * 1948-10-02 1951-11-22 Metallgesellschaft Ag Process for the production of lightweight construction elements
FR2086620A5 (en) * 1970-04-03 1971-12-31 Cochery Albert Entr Road surfacing material - contg calcium and other sulphates
DE2324312A1 (en) * 1972-05-15 1973-11-29 Raytheon Co PROCESS FOR THE PRODUCTION OF CASTING MOLDS OR PARTS THEREOF FROM PLASTER MOLDING
GB1430309A (en) * 1972-04-13 1976-03-31 Motus Chemical Inc Refractory cement incorporating fluxing and grog components
US4146402A (en) * 1977-03-23 1979-03-27 Mitsubishi Mining & Cement Company, Ltd. Process of producing fiber-reinforced hardened body of gypsum system
WO1980000248A1 (en) * 1978-07-13 1980-02-21 Tenax Maskin Ab A method of preparing gypsum articles
DE2739275B2 (en) * 1976-08-31 1980-04-24 Denki Kagaku Kogyo K.K., Tokio Calcium sulphate material for the production of hardened moldings

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE432542C (en) * 1924-04-15 1926-08-09 Morduch E Lewin Process for the production of a cement-like mass
GB324320A (en) * 1928-10-18 1930-01-20 Bindphast Products Ltd Improvements in and relating to the manufacture of solid bodies from disintegrated alabaster, gypsum, marl and the like
GB348766A (en) * 1930-03-12 1931-05-21 Peter Petrowitch Budnikoff Improvements in or relating to anhydrite or gypsum cementing compositions
DE821921C (en) * 1948-10-02 1951-11-22 Metallgesellschaft Ag Process for the production of lightweight construction elements
FR2086620A5 (en) * 1970-04-03 1971-12-31 Cochery Albert Entr Road surfacing material - contg calcium and other sulphates
GB1430309A (en) * 1972-04-13 1976-03-31 Motus Chemical Inc Refractory cement incorporating fluxing and grog components
DE2324312A1 (en) * 1972-05-15 1973-11-29 Raytheon Co PROCESS FOR THE PRODUCTION OF CASTING MOLDS OR PARTS THEREOF FROM PLASTER MOLDING
DE2739275B2 (en) * 1976-08-31 1980-04-24 Denki Kagaku Kogyo K.K., Tokio Calcium sulphate material for the production of hardened moldings
US4146402A (en) * 1977-03-23 1979-03-27 Mitsubishi Mining & Cement Company, Ltd. Process of producing fiber-reinforced hardened body of gypsum system
WO1980000248A1 (en) * 1978-07-13 1980-02-21 Tenax Maskin Ab A method of preparing gypsum articles

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Ullmanns Encyklop{die der technischen Chemie, fourth edition, volume 12, p.294 *

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3523115A1 (en) * 1985-06-28 1987-01-08 Friedrich Priehs Process for producing plaster-bonded board materials
EP0210027A2 (en) * 1985-07-12 1987-01-28 Hitachi, Ltd. Method for forming cast article by slip casting
EP0210027A3 (en) * 1985-07-12 1988-01-27 Hitachi, Ltd. Method for forming cast article by slip casting
US4883621A (en) * 1985-07-12 1989-11-28 Hitachi, Ltd. Method for forming cast article by slip casting
EP0312027A2 (en) * 1987-10-13 1989-04-19 Toto Ltd. Method for hydrating hemihydrate gypsum
EP0312027A3 (en) * 1987-10-13 1991-01-30 Toto Ltd. Method for hydrating hemihydrate gypsum
EP3398919A1 (en) * 2017-05-05 2018-11-07 Saint-Gobain Placo Tile mould and plaster composition for mould
FR3065899A1 (en) * 2017-05-05 2018-11-09 Saint-Gobain Placo TUILERIE MOLD AND PLASTER COMPOSITION FOR MOLD
WO2021217200A1 (en) * 2020-04-27 2021-11-04 Pact Renewables Pty Ltd Mineral-based composites
GB2610096A (en) * 2020-04-27 2023-02-22 Pact Renewables Pty Ltd Mineral-based composites
WO2021258139A1 (en) * 2020-06-25 2021-12-30 Pact Renewables Pty Ltd Degradable materials containing waste paper products
GB2611904A (en) * 2020-06-25 2023-04-19 Pact Renewables Pty Ltd Degradable materials containing waste paper products

Also Published As

Publication number Publication date
BR8009013A (en) 1981-11-24
AT380005B (en) 1986-03-25
ATA913380A (en) 1985-08-15
NL8020014A (en) 1981-12-01

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