Calcium sulfate whiskers

Calcium sulfate whiskers, also known as gypsum whiskers, are fibrous single crystals of anhydrous calcium sulfate and are classified into anhydrite (CaS04), hemihydrate (CaSO4-0.5H2O), and dihydrate (CaS04-2H20) calcium sulfate whiskers. 

Hemihydrate calcium sulfate whiskers (CaSO4-0.5H2O molecular weight, 145.15) are white fluffy solids in appearance and fibrous or acicular monocrystals under a microscope, with diameter, length, hardness, heat resistance, and intensity 

Dihydrate calcium sulfate whiskers (CaS04-2H20 molecular weight, 172.18) are white fluffy solids in appearance and fibrous or acicular crystals long fibers under a microscope. Their diameters are 10-50 pm, lengths are 500 pm, and L/D ratios are 20-100. They have relatively poor hardness, heat resistance, and intensity. These whiskers will dehydrate at room temperature and transform to amorphous calcium sulfate particles at about 110°C. Thus, applications of dehydrate calcium sulfate whiskers in composites are limited.  

Appearance White fluffy solid, needle-like under a microscope White fluffy solid, needle-like under a microscope 

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Typical fillers barium sulfate, calcium carbonate, carbon black, calcium sulfate whiskers, diatomaceous earth, glass fiber, glass spheres, hollow silicates, kaolin, mica, talc, wollastonite, silica, magnesium hydroxide, hydrotalcite, red mud, ground tire rubber, ferromagnetic powder, nickel fibers, wood flour, zirconium silicate, starch, soot, marble, aluminum, lignin, sand... 

Franklin Fiber Filler. P.S. Gypsum] Calcium sulfate whisker fiber fiUer. 

Table 3.9 Enterprise Standard of Calcium Sulfate Whiskers...

The treatment process of calcium carbonate whiskers using the dry method is as follows. Measured materials are mixed in a high-speed mixer at slow speed for 1 minute and at high speed for 1 minute. Wang et al. added calcium sulfate whiskers into a high-speed mixer, then heated and stirred. They then added surface treatment agent diluted with liquid paraffin at 100°C, stirred for 6 minutes, and obtained modified calcium sulfate whiskers. 

As is shown in Figure 3.14, KH-550 has the best modification effect on calcium sulfate whiskers with an activation index (99.6%) higher than that of other coupling agents. The sample modified with KH-550 cannot be wetted by water. Figure 3.15 shows the modification results of calcium sulfate whiskers affected by KH-550 concentration. Modification results become much better with an increase of KH-550 concentration. But the rising trend of activation index is no longer obvious when the concentration of KH-550 is more than 8 wt%. 

Consider, for example, the preparation of polypropylene composite material filled with calcium sulfate whiskers... 

Although the price of inorganic whiskers is lower than in the past, it is still higher than that of other inorganic mineral packing. The price of relatively cheap calcium sulfate whiskers and calcium carbonate whiskers is hundreds of US dollars per tonne, but the price of calcium carbonate is tens of US dollars per tonne. Thus it can be seen that high cost hampers the... 

Shi et al. 5 also discovered that the wear resistance of PTFE improved about 300 times that of the pure PTFE after adding potassium titanate whiskers. Hu and Liang added aluminum borate whiskers and calcium sulfate whiskers respectively to bismaleimide resin and found that the wearability of both materials improved. When the content of aluminum borate whiskers was 8%, the wear rate of the material declined from 4.39 X 10" mmVCN irO to 1.42 x 10 mmV(N-m). When the content of calcium sulfate whiskers was 10%, the wear rate of the material declined from 2.89 x 10" mmy(N-m) to 1.28 x 10" mmVCN-m). Thus it can be seen that the high hardness of inorganic whiskers determines their broad application prospects in the field of polymer wear-resistant materials. 

Jian Zhou, Jiqin Tang. Study on PP/calcium sulfate whisker composite. Engineering Plastics Application, 36(ll) 19-22, 2008. 

Debo Wang, Jiping Yang, Pengcheng Huang. Adhesive properties of calcium sulfate whisker-modified polyurethane-epoxy resins. Acta Materiae Compositae Sinica, 25(41 1-6, 2008. 

Chao Zhao, Jian Zhou. Application of calcium sulfate whisker in HIPS. Modem Plastics Processing and Application, 21(4) 45-48, 2009. 

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