The difference between the two water plaster, the semi -water gypsum, and the water -free gypsum


The molecular formula of the two water gypsum is CASO4,2H2O. The chemical structurer has 2 calcium sulfate crystals with crystal water. In the heating treatment of different conditions, its structure water is easy to get rid of

Semi -water gypsum


Waterless plaster


When the temperature was heated at 65 ° C, the structure water began to release the two water plaster, but the dehydration speed was slow. At about 107 ° C and the water vapor voltage of 971mmHg, the dehydration speed quickly became faster. As the temperature continues to rise, the dehydration is faster. At L 70 -L90 ° C, the two water gypsum transforms into α -semi -water gypsum or β -semi -water gypsum at a fast speed. When the temperature continues to rise to 220 ° C and 320 to 360 ° C, the semi -water gypsum continues to dewater to become α -soluble water -free gypsum. However, the water -free non -water -free ointment generated in 220 ° C is more likely to absorb water into semi -water gypsum in the air. Water -free gypsum that becomes during 450 1,750 ° C is insoluble water -free gypsum. This kind of water -free gypsum is the “dead burning” gypsum; it is difficult to dissolve in water, almost no condensed, and does not have strength. At 800 ° C, the water -free gypsum began to decompose to CAO and SO2 plus O2. At this time, the condensation ability mainly relied on the condensation of CAO instead of plaster. This decomposition is more intense after 1050 ° C, and it does not end until 1350 ° C. In the restore atmosphere, it is conducive to the decomposition of Caso4.



After long -term placement, will its solubility in the water decreases after long -term placement? No, the solidified two water gypsum will be dehydrated and transformed into gypsum after long-term placement. In the data, the two water plaster is 2.08g/L, the alpha-semi-water gypsum is 6.20g/L, β-semi-water gypsum It is 8.15g/L, the soluble water -free gypsum is 6.30g/L, and the natural water -free plaster is 2.70g/L. So its solubility does not decrease but increases instead!



(1) After drilling and drying, it is used in the cement industry as a slowdown agent

(2) After drift drilling, it is used to produce ordinary β -type gypsum powder, and produces plaster blocks, large plates and other gypsum products;

(3) Directly used in agriculture and do land improvement agents;

(4) Directly used for road building materials.

Two water gypsum

Gypsum and two water gypsum

Theoretically, the amount of water required for chemical reactions when plaster and water are stirred by 18.6%; in the process of model production, the actual water increase is much greater than this value. The surface of smooth surface; excess water leaves a lot of capillary pores after drying, so that the gypsum model has water absorption.

The water absorption rate is an important parameter of the gypsum model, which directly affects the speed of the billet during grouting. The water absorption rate of ceramic gypsum molds is generally between 38 and 48%.

Plaster powder is placed in a dry place. Do not splash water or cut off plaster when used. The gypsum bag should be clean. Strictly prevent the used plaster residue or other debris mixed in the bag.


Usually white, colorless, colorless transparent crystals are called gypsum, and sometimes it is gray, light yellow, light brown and other colors due to impurities. Bar marks white. transparent. Glass luster, pearl luster, fiber -shaped collection of silk shiny. The ruling is extremely complete, and the medium, the diamond -shaped body with a cracking of the surface of the surface is 66 and 114. Crispy. Hardness is 1.5 ~ 2. Different directions have changed slightly. Relative density 2.3.

Under polarizing mirror:

colorless. Two -axis (+). 2V = 58. Ng = 1.530, nm = 1.523, np = 1.521. With the temperature increased by 2V, 2V is zero at about 90 ° C.

Crystalline water stage

There are 3 discharged crystalline water stages when heating: 105 ~ 180 ° C. First of all, 1 water molecule is discharged, and then half of the water molecules are discharged immediately to transform into plaster CA [SO4]? 0.5h2o, also known as cooked plaster or semi -water gypsum Essence 200 ~ 220 ° C, the remaining half of the water molecules were discharged, and it was transformed into type III hard plaster CA [SO4]? Εh2O (0.06


The microporous structure and heating and dehydration of gypsum and its products make it excellent sound insulation, insulation and fire resistance.

Gypsum belongs to a single oblique crystal system, which has a high degree of explanation and is easy to crack into thin slices. Heat the gypsum to 100 ~ 200 ° C, lose part of the crystalline water, and get semi -water gypsum. It is a hardened gel material, which has two forms of α and β, which are diamond -shaped crystals, but their physical properties are different. α -shaped semi -water gypsum crystals are good and solid; β -type semi -water gypsum is a sheet -like crystal, with a fine crystal, which is much larger than the surface area than alpha -type semi -water gypsum.

When producing plaster products, alpha -type semi -water gypsum requires less water than β type, and the product has high density and intensity. Generally, the steaming kettle is used in the steaming steaming medium. plaster. Chemical gypsum of industrial by -products has the same performance of natural plaster and does not require too much processing. The semi -water gypsum and water mixing the pulp to form two water gypsum, quickly condense and hardened during the drying process, and obtain strength, but it softened when it encounters water.

Two water gypsum formation:

Gypsum for building materials, including natural plaster and chemical gypsum. Natural gypsum includes natural Ershui Gypsum (CASO4? 2H2O) and natural waterless plaster (Caso4). The texture of the natural two water plaster is soft, and the texture of natural water -free gypsum is hard, so it is also called hard plaster. Natural two water gypsum is commonly used in industrial production. Generally, “gypsum” refers to natural Ershui gypsum in most cases.

Pure two water gypsum is transparent or colorless, with crystal shapes such as fiber, needle, and sheet shape. Natural Ershui plaster ore often contains more impurities. From the perspective of production, there are transparent gypsum, fiber plaster, snowflake gypsum, sliced ​​gypsum, mud plaster or soil plaster. The content of plaster plaster in the plaster is often referred to as taste, so as to classify gypsum. Level first plaster, more than 95%of two water plaster, 85%or more of two -level plaster, and more than 75%of the third level. Most of the production of plaster plates produced by three levels should be used.

Chemical gypsum generally refers to the by -products in various industrial production, which is industrial waste, which contains a certain amount of two water gypsum, and also contains more impurities. The name of the type, such as phospholly gypsum, fluorosol, smoke, desulfurization gypsum, gypsum, etc.

There are many forms of gypsum. After the gypsum is heated, it will be gradually transformed from the second water gypsum to another form. After moisture absorption, the opposite changes will occur. The production of plaster building products is based on the nature of gypsum.

Gypsum heating dehydration becomes semi -water gypsum (or other type of dehydrated gypsum), semi -water gypsum and water mix synthesize gypsum pulp, semi -water gypsum in gypsum plasma, and other dehydrated gypsum hydration and hardening. It has become a hardening gypsum product.

Semi-water gypsum condensation time is short, the building plaster is condensed at 4-8 minutes, and the end of 10-13 minutes is condensed; The short production cycle of the production of plaster building materials is to make full use of the characteristics of gypsum materials to condense hardly.