The main components of building gypsum and high-strength gypsum are β-type hemihydrate gypsum and α-type hemihydrate gypsum, which are mixed with water; semi-water gypsum will be rehydrated to form dihydrate gypsum, which will release heat and solidify into a certain strength. Hardened body.
The hemihydrate gypsum is first dissolved after adding water, and then hydrated to form dihydrate gypsum; since the solubility of dihydrate gypsum is lower than that of hemihydrate gypsum, dihydrate gypsum is precipitated from the supersaturated solution by colloidal particles. Due to the precipitation of dihydrate gypsum, the balance of the dissolution of hemihydrate gypsum is destroyed, and the hemihydrate gypsum continues to dissolve and hydrate. The dissolution of the hemihydrate gypsum and the precipitation of the dihydrate gypsum are continuously performed until the hemihydrate gypsum is completely consumed. In the above process, the free moisture in the gypsum slurry is gradually reduced by hydration and evaporation, and the slurry is gradually thickened. And lose plasticity, a process called condensation. Thereafter. The slurry continues to thicken, and the dihydrate gypsum gradually aggregates into crystals, which gradually grow, symbiosis and staggered to form a crystalline structure network. In this process, the slurry gradually hardens and the strength continues to increase, forming a hardened body with a certain strength, and the strength stops growing until it is completely dry. This process is called hardening.
The theoretical water demand meter for the hydration reaction of hemihydrate gypsum is 18.6% of its weight, in order to make the slurry have sufficient fluidity. The usual amount of water added is much larger than the theoretical water requirement: therefore, the hardened gypsum slurry contains a large amount of pores. The β-type hemihydrate gypsum in the building gypsum is mostly flaky, cracked crystal with fine grain and large specific surface area. When the gypsum slurry is mixed, the water requirement is 60%-80%, so the porosity after hardening is large. , the intensity is low. And in high-strength plaster. The type of hemihydrate gypsum has good crystallinity, coarse crystal grains and small specific surface area. When it is prepared into a plastic slurry, the water requirement is about 35% to 45%, and the porosity after hardening is small, so that it has high strength.
The hemihydrate gypsum is first dissolved after adding water, and then hydrated to form dihydrate gypsum; since the solubility of dihydrate gypsum is lower than that of hemihydrate gypsum, dihydrate gypsum is precipitated from the supersaturated solution by colloidal particles. Due to the precipitation of dihydrate gypsum, the balance of the dissolution of hemihydrate gypsum is destroyed, and the hemihydrate gypsum continues to dissolve and hydrate. The dissolution of the hemihydrate gypsum and the precipitation of the dihydrate gypsum are continuously performed until the hemihydrate gypsum is completely consumed. In the above process, the free moisture in the gypsum slurry is gradually reduced by hydration and evaporation, and the slurry is gradually thickened. And lose plasticity, a process called condensation. Thereafter. The slurry continues to thicken, and the dihydrate gypsum gradually aggregates into crystals, which gradually grow, symbiosis and staggered to form a crystalline structure network. In this process, the slurry gradually hardens and the strength continues to increase, forming a hardened body with a certain strength, and the strength stops growing until it is completely dry. This process is called hardening.
The theoretical water demand meter for the hydration reaction of hemihydrate gypsum is 18.6% of its weight, in order to make the slurry have sufficient fluidity. The usual amount of water added is much larger than the theoretical water requirement: therefore, the hardened gypsum slurry contains a large amount of pores. The β-type hemihydrate gypsum in the building gypsum is mostly flaky, cracked crystal with fine grain and large specific surface area. When the gypsum slurry is mixed, the water requirement is 60%-80%, so the porosity after hardening is large. , the intensity is low. And in high-strength plaster. The type of hemihydrate gypsum has good crystallinity, coarse crystal grains and small specific surface area. When it is prepared into a plastic slurry, the water requirement is about 35% to 45%, and the porosity after hardening is small, so that it has high strength.
Introduction to the classification of EVA foam board
EVA foam is a common foam material widely used in various fields, such as tool boxes, packaging box liners, and environmentally friendly toy craft products. The classification of EVA foam mainly includes the following aspects:
Foaming method: EVA foam is mainly divided into two types of foaming methods, namely closed cell foaming and open cell foaming. Closed cell foam is commonly used for EVA floor mats, while open cell foam has better breathability and elasticity.
Grade classification: EVA foam can be classified into C grade, B grade, A grade, 3A grade, CR material, high elasticity EVA material, rubberized EVA material, etc. The difference between these grades mainly lies in the density, hardness, elasticity, and other physical properties of the material.
Density classification: According to density, EVA foam can be classified into various densities such as 15 degrees, 20 degrees, 25 degrees, 30 degrees, 38 degrees, 45 degrees, 50 degrees, and 60 degrees. Different densities of EVA foam are suitable for different application scenarios. For example, high-density EVA foam is typically used in situations that require higher load-bearing capacity or stronger cushioning protection.
Functional classification: EVA foam can also be classified according to its functions, including high elasticity, anti-static, fireproof, impact resistant, and moisture-proof functions. These functional EVA foam are suitable for specific environments or application needs, such as packaging and transportation of electronic products.
Processing classification: According to the processing method, EVA foam can be divided into various forms such as sheet, roll, adhesive, backing, molding, and embossing. These processing methods enable EVA foam to adapt to various complex application scenarios and design requirements.
In summary, the classification of EVA foam is very diverse, and suitable types can be selected according to different application needs. From the perspective of foaming method, grade, density, function, and processing method, EVA foam has shown a wide range of application potential and diverse application scenarios.
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