It is reported that sulfate can be incorporated in the vaterite polymorph of calcium carbonate. I am interested to know how the incorporation influences the physical properties, strength/hardness of calcium carbonate?
Hello Prof.
As I understand your question-
The incorporation of sulfur and sulfate in calcium carbonate (CaCO3) profoundly influences its hardness and strength. These impacts rely on the particular methodologies and extent of substitution or incorporation. The effects below explain how sulfur/sulfate incorporation can influence these properties:
1. Solid solution substitution:
- Carbonate ions (CO3^2-) in the calcium carbonate lattice are replaced by sulfate ions (SO4^2-), thus forming a solid solution.
- This causes distortions and stresses in the crystal structure, thereby elevating its hardness and strength.
- At any rate, excessive substitution may result in lattice destabilization, which weakens the material.
2. Interstitial incorporation:
- Sulfur atoms or sulfide ions (S^2-) can be incorporated interstitially into the calcium carbonate lattice.
- This too can induce lattice strain and distortion that could increase its hardness and strength respectively.
- Nonetheless, high concentration of interstitial species leads to instability of the lattice hence weakening it
3. Surface adsorption/substitution:
- In case of surface carbonate ions, sulphate ions will either be adsorbed onto calcium carbonate crystals or substitute them.
- Changes made at this level affect surface energy as well as crystallinity; thereby altering material’s hardness/ strength as well
4. Impurity effects:
- Calcium carbonate crystals may have impurities such as sulfur-containing compounds or ions that modify their growth patterns as well as defects concentrations.
Certain impurities may increase dislocation pinning while others hinder dislocation movement leading to increased hardness/ strength levels.
Presence of structural defects, however, arising from other impurities may lead to weakening of materials and promotion for undesirable phase transformations.
On the whole effect of sulfur/sulfate inclusion on CaCO3’s hardness/strength is determined by specific mechanisms implicated herein, distributed concentration levels incase of incorporated species and consequential structural and compositional changes. In general, moderate levels of substitution or incorporation can increase hardness and strength but excessive inclusion can lower the material’s strength through lattice destabilization. The influence of sulfur/sulfate incorporation can also be varied by other factors such as calcium carbonate polymorph (e.g., calcite, aragonite, vaterite), presence of other impurities or additives, processing conditions (e.g., temperature, pressure).
Thanks, Rajesh ji for the comprehensive response. This is certainly helpful. In this regard, can you share any article(s) for my reference?
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