Gypsum powder (hereinafter referred to as semi-hydrated gypsum powder CaSO4.1/2H20, the same below) is widely used in ceramics forming consumption for its high quality, low cost, good activity after mixing with water, incomparable condensation, water absorption and easy processing properties, and is used to manufacture models of grouting, rolling and cold-forming.

　　石膏粉是由自然石膏礦物炒制加工而成。自然石膏是含有兩個結晶水的硫酸鈣礦物CaSO4·2H20。依據差熱剖析，二水石膏在低溫階段有兩個吸熱反響。當溫度為140℃左右時，其結晶水開端排出。在150℃～170℃時，很快合成為半水石膏(CaSO4·1/2H20)，當溫度繼續升高到225℃時，則失去全部結晶水，變成無水石膏(CaSO4)。

　　Gypsum powder is prepared by stirring natural gypsum minerals. Natural gypsum is a calcium sulfate mineral CaSO4.2H20 containing two crystalline water. According to differential thermal analysis, there are two endothermic reactions in dihydrate gypsum at low temperature. When the temperature is about 140 C, the crystal water is discharged at the beginning. When the temperature ranges from 150 to 170 C, it is quickly synthesized into hemihydrate gypsum (CaSO4.1/2H20). When the temperature continues to rise to 225 C, all crystalline water will be lost and anhydrous gypsum (CaSO4) will be formed.

　　石膏粉依據加工炒制工藝和產品晶型構造的不同可分為兩種，即普通石膏粉（也叫β石膏粉）和高強石膏粉（也叫α石膏粉）。β石膏粉是在常壓下凸底鐵鍋內160℃～170℃煅燒自然石膏粉料炒制而得；α石膏粉是將自然石膏塊狀料放在蒸壓釜內，在130℃及1.5～3個大氣壓下蒸壓3～5h加熱加壓脫水，然后150℃～170℃枯燥室內烘干，將其粉碎而得。 由于兩種石膏粉的制造工藝不同，形成它們的晶型構造和產品性質不同。β石膏粉晶型構造是規則的片狀晶體，晶粒的孔隙和裂紋較多

　　Gypsum powder can be divided into two kinds according to the different processing technology and product crystal structure, namely ordinary gypsum powder (also known as beta gypsum powder) and high strength gypsum powder (also known as alpha gypsum powder). Beta gypsum powder is prepared by calcining natural gypsum powder in a convex bottom iron pot at 160 ~170 C under atmospheric pressure; alpha gypsum powder is prepared by placing natural gypsum block material in autoclave, heating and dewatering under autoclave pressure for 3~5 hours at 130 ~1.5~3 atmospheric pressure, then drying in a drying chamber at 150 ~170 ~C and crushing it. The crystalline structure and product properties of the two gypsum powders are different due to their different manufacturing processes. The crystalline structure of beta gypsum powder is regular flake crystal, and there are many holes and cracks in the grain.

　　比外表積大，規范稠度需水量大，石膏粉與水混合后水化反響才能強，初凝時間短，模型的氣孔率、吸水率高，但模型的強度低；而α石膏粉晶型構造是齊整的針狀晶體，比外表積小，規范稠度需水量小，模型的氣孔率、吸水率小，石膏粉與水混合后反響才能差，石膏漿體的活動性好，初凝時間長，模型強度高。依據這兩種晶型石膏的特性，普通β石膏粉制造注漿成形模型，而α石膏粉制造滾壓成形模型和塑壓成形模型。

　　The water requirement of the standard consistency is larger than the surface area, the hydration reaction of the model is stronger after mixing gypsum powder with water, the initial setting time is shorter, the porosity and water absorption of the model are higher, but the strength of the model is lower; while the crystal structure of the alpha gypsum powder is a neat needle crystal, smaller than the surface area, the water requirement of the standard consistency is smaller, the porosity and water absorption of the model are smaller, and the reaction of the model after mixing gypsum powder with water is worse. The gypsum paste has good activity, long initial setting time and high model strength. According to the characteristics of these two crystalline gypsum, the grouting forming model is made of ordinary beta gypsum powder, while the rolling forming model and plastic forming model are made of alpha gypsum powder.

　　除了以上兩種石膏粉外，消費中還運用由以上兩種石膏粉按不同比例（普通是70%～80%的β石膏粉與30%～20%的α石膏粉）混勻構成的混合石膏粉。這種石膏粉是應用β石膏的吸水性能好和α石膏強度高的特性，用于陶瓷消費中注漿成形模型的制造（例如衛生陶瓷模型）。近些年來，隨著陶瓷行業開展之需，在高強α石膏粉的根底上經過改良加工工藝和添加一些特殊外加劑又衍生出許多有特殊用處的超高強石膏粉，如母模石膏粉、K型粉、樹脂石膏粉等等。

　　In addition to the above two kinds of gypsum powder, mixed gypsum powder composed of the above two kinds of gypsum powder in different proportions (usually 70%-80% of beta gypsum powder and 30%-20% of alpha gypsum powder) is also used in consumption. This kind of gypsum powder is applied to the manufacture of grouting forming models (e.g. sanitary ceramics models) in ceramic consumption because of its good water absorption performance of beta gypsum and high strength of alpha gypsum. In recent years, with the development of the ceramic industry, many super-high strength gypsum powders, such as mother mould gypsum powder, K-type powder, resin gypsum powder and so on, have been derived from high strength alpha gypsum powder by improving processing technology and adding some special additives.