Calcium sulfate crystals and methods for making the same
A technology of calcium sulfate whiskers and whiskers, applied in crystal growth, chemical instruments and methods, single crystal growth, etc., can solve the problems of slow growth rate of whiskers and difficulty in manufacturing whiskers.
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Embodiment 1
[0051] Calcium sulfate whiskers were prepared according to the procedure described below using alpha and beta hemihydrate particles mined from the same source. Calcium sulfate hemihydrate was combined with water to form a slurry containing 5 wt% calcium sulfate. The slurry was autoclaved at 115°C for 2 hours at a pressure of 10 psig to form whiskers. The resulting whiskers were dehydrated by passing through a mesh filter for 5 minutes. The dehydrated whiskers were heated at 600°C for 3 hours to form stable insoluble calcium sulfate anhydrite whiskers. The resulting alpha and beta calcium sulfate anhydrite whiskers were then photographed.
[0052] figure 1 is a micrograph (600x400 microns) taken by optical microscopy showing alpha-derivatized anhydrite calcium sulfate whiskers prepared according to the method described above. figure 2 is a micrograph (600x400 microns) taken by optical microscopy showing β-derivatized anhydrite calcium sulfate whiskers prepared according to...
Embodiment 2
[0055] According to the method of Example 1, α and β calcium sulfate whiskers were prepared. The whiskers were combined with polypropylene to form composites and the stiffness / flexural modulus of each composite was measured and compared to that of polypropylene alone according to the Chord method. The results are shown in Table 1 below.
[0056] Whiskers are either pre-mixed or side-fed with polypropylene. Precompounding refers to combining whiskers with extruded polypropylene pellets prior to melting to form a composite. Side feeding refers to feeding whiskers into the extruder while the polypropylene is already molten.
[0057]
[0058] These results indicate that polypropylene composites with alpha whisker reinforcement exhibit much better mechanical properties than composites with comparable beta whisker reinforcement. Without being bound by a particular theory, it is believed that the pre-compounding process causes the whiskers to be comminuted by the unmelted polyp...
Embodiment 3
[0061] The commercially available alpha calcium sulfate particles used in the preceding examples had a median particle size of 15.4 μm and a maximum particle size of 120 μm. Relatively fine alpha calcium sulfate particles with a narrow distribution were also prepared and tested. Specifically, commercially obtained alpha calcium sulfate particles were comminuted in a jet mill to a median particle size of 3.06 μm and a maximum particle size of about 12 μm. Therefore, compared to the commercially obtained calcium sulfate particles, there are fewer finer particles and more uniform size, as shown in Table 2.
[0062]
[0063] In a fluid energy mill, compressed air is used to jet mill particles to produce smaller particles. Calcium sulfate particles are impacted particle-on-particle by high-speed rotation in the grinder. The particle size was measured using a laser diffraction particle size analyzer (LA-950 commercially available from HORIBA of Kyoto, Japan). As shown in Table 2...
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