Properties of Calcium Carbonate

Particle Shape:

• Due to its low aspect ratio (length-to-thickness ratio), calcium carbonate is considered a filler, not a reinforcement.
• Limestone processing affects the shape of the particles:

Dry powder: more irregular shape but higher specific surface area
Wet powder: more uniform and smoother shape due to water centrifugation
Precipitated: smaller and more uniform size

Composition of Calcium Carbonate

• Calcium carbonate is usually selected from specific grades of calcite ore (crystalline limestone).
• Typical composition of calcium carbonate used as filler:

Types of Calcium Carbonate

• Fine Powder: from calcite ore with 94% purity, particle size ranges from 0.7 microns (fine) to 20 microns (coarse)

– Hydrated

– Dry

• Precipitated: from aragonite ore with 98% purity, particle size from 0.01 microns (ultrafine) to 5 microns (coarse)

Particle Size and Size Distribution

• Equivalent Spherical Diameter (ESD)

– Diameter of a sphere having the same volume as the particle

Particle Size Distribution

• Average particle diameter d50%

– The diameter at which at least 50% of the particle mass is smaller

– ۵۰% by weight are larger than d50%, and 50% are smaller

• Top Cut d98%

– ۹۸% of the particles are smaller than d98%

– Since coarse and rough particles cause stress concentration,

   Reducing the top cut is desirable and improves the following properties:

       –   Impact Strength
U-PVC:
d98% < 5µm
d50% < 1µm

       –   Tensile Strength
       –   Surface Gloss