TW202432500A - Synthetic gypsum and gypsum boards produced therefrom. - Google Patents

Abstract

This invention discloses a synthetic gypsum and gypsum boards produced therefrom. Limestone (calcium carbonate), slaked lime (calcium hydroxide), water, and sulfuric acid are mixed, and [alpha] hemihydrate gypsum is optionally added as crystal seed to produce synthetic gypsum. The synthetic gypsum is then used to make gypsum boards. The gypsum boards produced according to this invention contains at least 10% [alpha] hemihydrate gypsum.

Description

Synthetic gypsum and gypsum board made of the same

The present invention relates to a synthetic gypsum and a gypsum board made from the synthetic gypsum, in particular to a gypsum board containing alpha hemihydrate gypsum.

Traditional gypsum boards do not contain α-hemihydrate gypsum, and their gypsum board strength is relatively low. In order to meet the current construction requirements, the development of a new generation of high-strength gypsum boards has always been the direction of gypsum board manufacturers.

If limestone (CaCO ₃ ) and sulfuric acid (H ₂ SO ₄ ) are simply reacted to produce gypsum (CaSO ₄ •2H ₂ O), when gypsum is produced, it is easy to recrystallize on the surface of the original limestone to form a layer of gypsum with low solubility. When the gypsum completely covers the original limestone core, the temperature is about 45 degrees Celsius, and the reaction will gradually stop. In order to make the core limestone and sulfuric acid continue to react, an external heat source must be added to a higher temperature and stirred to destroy the covering gypsum layer and continue the reaction to completion.

Take room temperature at 25 degrees Celsius as an example to illustrate: the higher the ratio of slaked lime added, the higher the process temperature will be. That is, when limestone and slaked lime are mixed in a ratio of (2:1), the process temperature can be raised to above 45 degrees Celsius; when limestone and slaked lime are mixed in a ratio of (2:8), the process temperature can reach around 80 degrees Celsius; therefore, the present invention uses limestone and slaked lime mixed raw materials to make synthetic gypsum under normal pressure hydrothermal, without the need for pressure or external heat source, and can achieve the effect of energy saving and carbon reduction.

The present invention further uses synthetic gypsum to manufacture high-strength gypsum board containing α-hemihydrate gypsum. The gypsum board manufactured by the present invention contains more than 10% α-hemihydrate calcium sulfate.

The chemical reactions related to the present invention are described as follows:

Calcium sulfate dihydrate (CaSO ₄ •2H ₂ O) is commonly known as gypsum, or dihydrate gypsum. When dihydrate gypsum is heated, it loses 1.5 crystal waters and forms hemihydrate gypsum (CaSO ₄ ‧1/2H ₂ O): CaSO4‧2H2O→ CaSO4‧1/2H2O+3/2H2O Hemihydrate gypsum is further divided into α hemihydrate gypsum and β hemihydrate gypsum:

When dihydrate gypsum is heated to around 97°C, it loses 1.5 crystal waters and forms α-hemihydrate gypsum. When dihydrate gypsum is heated to around 45°C, it loses 1.5 crystal waters and forms β-hemihydrate gypsum. Both α-hemihydrate gypsum and β-hemihydrate gypsum are rhombic crystals, but they have different physical properties. Under a microscope, α-hemihydrate gypsum is a short columnar crystal with regular shape; β-hemihydrate gypsum is a loosely aggregated microporous solid.

Limestone (CaCO3) plus sulfuric acid and water produces dihydrate gypsum and carbon dioxide:

Slaked lime (Ca(OH) ₂ ) plus sulfuric acid produces dihydrate gypsum: CaCO3(aq) +H2SO4(aq) + H2O(l)→ CaSO4‧2H2O↓ +CO2(g)↑ΔH=-306.98 kj/mol

The present invention first discovered that the gypsum board containing α-hemihydrate gypsum has significantly increased physical strength compared to the conventional gypsum board without α-hemihydrate gypsum. Please refer to Table 1: Physical Properties Comparison Table. Table 1: Physical Properties Comparison Table Project The gypsum board of the present invention ( containing more than 10% of α-hemihydrate gypsum) Traditional gypsum board ( not containing α-hemihydrate gypsum) thickness 15 mm 15 mm Bending in the length direction will damage the cutting weight 970 N 910 N Bending in the width direction destroys the cutting weight 580 N 310 N Impact resistance When the weight hammer height is 800 mm, the diameter of the depression is less than 20 mm, and there is no crack that penetrates the back side. When the weight hammer is 800 mm high, the diameter of the depression is less than 25 mm, and there is no crack that goes through the back. Lateral nailing force 825 N 750 N

Table 1 shows the comparison of the physical properties of the gypsum board of the present invention and the traditional gypsum board, which at least includes the following advantages: (1) The bending breaking weight of the gypsum board of the present invention in the length direction is 970 N, which is better than the 910 N of the traditional gypsum board. (2) The bending breaking weight of the gypsum board of the present invention in the width direction is 580 N, which is better than the 310 N of the traditional gypsum board. (3) The gypsum board of the present invention has an impact resistance, with a dent diameter of less than 20 mm, which is better than the dent diameter of less than 25 mm of the traditional gypsum board. (4) The lateral nailing force of the gypsum board of the present invention is 825 N, which is better than the 750 N of the traditional gypsum board. The present invention mixes limestone (calcium carbonate) and slaked lime (calcium hydroxide) in a specific ratio, adds a certain amount of α-hemihydrate gypsum to the suspension as a calcium sulfate dihydrate seed, and reacts with sulfuric acid under normal pressure hydrothermal conditions to produce dihydrate gypsum while controlling the concentration, pH, drying and reaction time of the reactants. The entire process is carried out under normal pressure hydrothermal conditions without the need for additional heating.

The composition of the dihydrate gypsum produced by the present invention is analyzed by the following method:

Synthetic gypsum analysis 1. Free water % content analysis: Weigh about 50 g of gypsum sample into a weighing pan, dry the sample at 45°C until the weight is constant, and calculate the free water % content;

Synthetic gypsum analysis 2, crystallization water content% and converted purity: Continuing from analysis 1, weigh 1g of gypsum, put it into an oven at 220 °C to dry the sample until constant weight, calculate the crystallization water content% and converted purity.

Synthetic gypsum analysis 3, calculate the α hemihydrate gypsum content%, β hemihydrate gypsum content%, dihydrate gypsum content%, and impurity content%: Continuing from synthetic gypsum analysis 1, weigh 5 g of the gypsum sample, add water for rehydration reaction, and all samples need to be immersed in water. After standing indoors for about 48 hours, put the sample in an oven at 45 °C to dry it to constant weight, and calculate the β hemihydrate gypsum content%; put the sample in an oven at 97 °C to dry it to constant weight, calculate the α hemihydrate gypsum content%; and then calculate the dihydrate gypsum content%, and impurity content% respectively. Among them, synthetic gypsum analysis 1 and synthetic gypsum analysis 2 are performed according to ASTM C471M analysis method. Synthetic gypsum analysis 3 is analyzed using a gypsum phase composition analyzer. ASTM-C471M standard refers to: ASTM-C471M Standard Test Methods for Chemical Analysis of Gypsum and Gypsum Products (Metric)

The gypsum board of the present invention and its manufacturing method include:

Step 1: Mix limestone (calcium carbonate) and slaked lime (calcium hydroxide) in a ratio of (2:1-8), add water to form a suspension with a solid concentration of 20%-40%; add (0.3-5%) α-hemihydrate gypsum to the suspension as calcium sulfate dihydrate seed crystals;

Step 2: Slowly add 20%~60% sulfuric acid solution at atmospheric pressure, the volume of which is about 1~1.5 times the molar number of the same calcium material, and stir at a speed of 150~500 rpm. At this time, the water temperature will continue to rise by 25~50 degrees Celsius and gas will be generated. Wait until the gas generation stops;

Step 3: Centrifuge and dehydrate, add 1 to 3 times the amount of water to mix, add 20% to 35% dilute sulfuric acid solution, stir at 150 to 500 rpm until the pH value is 3 to 5, let it stand to precipitate, centrifuge and dehydrate, wash with water 3 times; dry at 105 degrees for about 2 to 3 hours; produce synthetic gypsum.

The composition of the synthetic gypsum produced by the present invention is analyzed as follows: free water content less than 10%; pure CaSO ₄ •2H ₂ O content more than 95%; particle size more than 150 µm; pH value 5-8. α hemihydrate gypsum is about 20-80%, and the rest is β hemihydrate gypsum and impurities. The pH is obtained by the following method: Take 10g of gypsum sample and add water to 100g, stir with a magnet and measure the pH value until it is stable and record it.

Step 4: Dry, grind and calcine the synthetic gypsum into gypsum powder containing 10-50% α calcium sulfate hemihydrate, then crush and store it.

Step 5: Add gypsum powder, mixed water, and auxiliary materials such as hardener, foaming agent, water reducer, starch, retarder, etc. to form gypsum slurry.

Step 6: A surface paper and a bottom paper are provided on the upper and lower sides, and gypsum slurry is injected, and the finished gypsum board is made through continuous forming, hardening, cutting into wet boards, oven drying, cutting and trimming. According to the ASTM-C471M standard, the composition of the gypsum board produced by the present invention contains more than 10% of α-calcium sulfate hemihydrate.

The limestone (calcium carbonate) used in the present invention can be replaced by calcium carbonate-containing materials. The calcium carbonate-containing products include minerals such as limestone, marble, Iceland spar, or biological calcium oyster shell powder.

The slaked lime (Ca(OH) ₂ ) used in the present invention can be replaced by quicklime CaO(s), because quicklime plus water produces slaked lime (calcium hydroxide): CaO(s) + H ₂ O (l) → Ca(OH) ₂ (s).

The above description discloses the preferred embodiments and design drawings of the present invention. However, the preferred embodiments and design drawings are merely illustrative and are not intended to limit the scope of the present invention. Any rights covered by the following patent application or any equivalent technical means for implementing the present invention shall not deviate from the spirit of the present invention and shall be the applicant's rights.

Claims (20)

A synthetic gypsum is produced according to the following process, which includes: step 1: mixing calcium carbonate (CaCO ₃ ) and calcium hydroxide (Ca(OH) ₂ ) or calcium oxide (CaO) in a certain proportion, and adding water until the solid concentration reaches a certain concentration of suspension; and step 2: adding excess sulfuric acid under normal pressure and stirring it, at which time the water temperature will continue to rise and gas will be generated, and gypsum precipitate will be produced at the same time, and after drying, synthetic gypsum will be produced. The synthetic gypsum as described in claim 1, wherein a certain amount of α-hemihydrate gypsum is further added to the suspension in step 1 as calcium sulfate dihydrate seed crystals. The synthetic gypsum as claimed in claim 1, wherein the step 1 of mixing calcium carbonate (CaCO ₃ ) and calcium hydroxide (Ca(OH) ₂ ) or calcium oxide (CaO) in a certain ratio refers to mixing in a ratio of (2:1-8). The synthetic gypsum as described in claim 1, wherein the amount of water added in step 1 to obtain a suspension having a certain solid concentration refers to a suspension having a solid concentration of 20% to 40%. The synthetic gypsum as described in claim 2, wherein the adding of a certain amount of α-hemihydrate gypsum refers to adding (0.3~5%) α-hemihydrate gypsum. The synthetic gypsum as described in claim 1, wherein the adding of excess sulfuric acid in step 2 refers to adding a 20% to 60% sulfuric acid solution, and the volume added is about 1 to 1.5 times the molar number of the same calcium material. The synthetic gypsum as described in claim 1, wherein in step 2, excess sulfuric acid is added and the pH is adjusted to pH 3-5 with dilute sulfuric acid. The synthetic gypsum as described in claim 2, according to the ASTM-C471M standard, is analyzed for its composition, including: free moisture less than 10%, pure CaSO ₄ •2H ₂ O content more than 95%, particle size more than 150 µm, pH 5-8, and alpha hemihydrate gypsum about 20-80%. The synthetic gypsum as described in claim 1, wherein the entire process is carried out by normal pressure hydrothermal method without the need for additional heating. A synthetic gypsum is prepared according to the following process, which comprises: Step 1: Mix calcium carbonate (CaCO ₃ ) and calcium hydroxide (Ca(OH) ₂ ) or calcium oxide (CaO) in a ratio of (2:1-8), and add water to a solid concentration of 20%-40% suspension; Step 2: Slowly add 20%-60% sulfuric acid solution at normal pressure, the volume is about 1-1.5 times the molar number of the same calcium material, stir and mix, at this time the water temperature will continue to rise and gas will be generated, and the gas generation will stop; Step 3: Centrifugal dehydration, add water to mix, add dilute sulfuric acid solution, stir and mix, adjust the pH to pH 3-5, static sedimentation, centrifugal dehydration, water washing, and drying; synthetic gypsum is produced. The synthetic gypsum as described in claim 10, wherein (0.3-5%) α-hemihydrate gypsum is further added to the suspension in step 1 as calcium sulfate dihydrate seed crystals. The synthetic gypsum as described in claim 11, according to analysis based on ASTM-C471M standard, has the following components: free water content of less than 10%; pure CaSO ₄ •2H ₂ O content of more than 95%; particle size of more than 150 µm; pH 5-8; and α-hemihydrate gypsum of approximately 20-80%. A synthetic gypsum, according to ASTM-C471M standard, its composition is analyzed, including: Free moisture less than 10%; pure CaSO4•2H2O content more than 95%; particle size more than 150 µm; pH 5~8; α hemihydrate gypsum is about 20~80%, and the rest is β hemihydrate gypsum and impurities. A gypsum board is made by the following process, which includes: Step 1: Mixing calcium carbonate (CaCO ₃ ) and calcium hydroxide (Ca(OH) ₂ ) or calcium oxide (CaO) in a certain proportion, and adding water until the solid concentration reaches a certain concentration of suspension; Step 2: Slowly adding a sulfuric acid solution of a certain concentration under normal pressure, the volume is a certain multiple of the calcium material, and stirring it, at this time the water temperature will continue to rise and gas will be generated, and the gas generation will stop; Step 3: Centrifugal dehydration, adding water to mix, adding a dilute sulfuric acid solution, stirring to mix, adjusting the pH to 3-5, static precipitation, centrifugal dehydration, water washing, drying, and producing synthetic gypsum; Step 4: drying, grinding and calcining the synthetic gypsum into gypsum powder containing 10-50% α calcium sulfate hemihydrate, and then crushing and storing; Step 5: forming gypsum slurry with the gypsum powder, mixed water and auxiliary materials; and Step 6: providing a surface paper and a bottom paper on the upper and lower sides, and injecting gypsum slurry, and manufacturing the gypsum board product through continuous forming, hardening, cutting into wet boards, drying, cutting and trimming. The gypsum board as described in claim 14, wherein a certain amount of α-hemihydrate gypsum is added to the suspension in step 1 as calcium sulfate dihydrate seed crystals. The gypsum board as described in claim 15, wherein a certain amount of α-hemihydrate gypsum is further added to the suspension in step 1, which refers to adding (0.3~5%) α-hemihydrate gypsum. The gypsum board as described in claim 15, wherein the composition thereof is analyzed in accordance with ASTM-C471M standard and contains at least 10% alpha calcium sulfate hemihydrate. A gypsum board is made by the following process, which includes: Step 1: Mix calcium carbonate (CaCO ₃ ) and calcium hydroxide (Ca(OH) ₂ ) or calcium oxide (CaO) in a ratio of (2:1-8), and add water to a solid concentration of 20%-40% suspension; Step 2: Slowly add 20%-60% sulfuric acid solution at normal pressure, the volume is about 1-1.5 times the molar number of the same calcium material, stir and mix, at this time the water temperature will continue to rise and gas will be generated, and the gas generation will stop; Step 3: Centrifugal dehydration, add water to mix, add dilute sulfuric acid solution, stir and mix, adjust the pH to pH 3-5, static sedimentation, centrifugal dehydration, water washing, drying; producing synthetic gypsum; step 4: drying, grinding, and calcining the synthetic gypsum into gypsum powder containing 10-50% α calcium sulfate hemihydrate, and then crushing and storing; step 5: forming gypsum slurry with the gypsum powder, mixed water and auxiliary materials; and step 6: providing a surface paper and a bottom paper on the upper and lower sides, and injecting gypsum slurry, and making the gypsum board product through continuous forming, hardening, cutting into wet boards, drying, cutting and trimming. The gypsum board described in claim 18, wherein (0.3-5%) α-hemihydrate gypsum is further added to the suspension in step 1 as calcium sulfate dihydrate seed crystals. A gypsum board, wherein the composition thereof is analyzed according to ASTM-C471M standard and contains at least 10% alpha calcium sulfate hemihydrate.