Calcium carbonate There are 3
Calcium carbonate, or CaCO3, comprises more than 4% of the earth’s crust and is found throughout the world. Common natural forms are chalk, limestone, and marble, produced by the sedimentation of the shells of small fossilized snails, shellfish, and coral over millions of years. Although all three forms are identical in chemical terms, they differ in many other respects, including purity, whiteness, thickness and homogeneity. Calcium carbonate is one of the most useful and versatile materials known to man.
Most of us meet calcium carbonate for the first time in the school classroom, where it is use blackboard chalk. Chalk has been used as a writing tool for over 10,000 years and is a fine, microcrystalline material.
As limestone, calcium carbonate is a biogenic rock, and is more compacted than chalk.
As marble, calcium carbonate is a coarse-crystalline, metamorphic rock, which is formed when chalk or limestone is recrystallised under conditions of high temperature and pressure. Large deposits of marble are found in North America and in Europe; e.g., in Carrara, Italy, the home of the pure white "statuario" from which Michelangelo created his sculptures.
Calcium carbonate, as it is used for industrial purposes, is extracted by mining or quarrying. Pure calcium carbonate can be produced from marble, or it can be prepared by passing carbon dioxide into a solution of calcium hydroxide. In the later case calcium carbonate is derived from the mixture, forming a grade of product called “precipitated calcium carbonate,” or PCC. PCC has a very fine and controlled particle size, on the order of 2 microns in diameter, particularly useful in production of paper. The other primary type of industrial product is “ground calcium carbonate,” or GCC. GCC, as the name implies, involves crushing and processing limestone to create a powdery-like form graded by size and other properties for many different industrial and pharmaceutical applications.
Calcium carbonate is used widely as an effective dietary calcium supplement, antacid, phosphate binder, or base material for medicinal tablets. It also is found on many grocery store shelves in products such as baking powder, toothpaste, dry-mix dessert mixes, dough, and wine. Calcium carbonate is the active ingredient in agricultural lime, and is used in animal feed. Calcium carbonate is also used in agriculture as a fertilizer. It is used to stabilize the pH of the soil. Calcium carbonate also benefits the environment through water and waste treatment.
PCC is the most widely used mineral in the paper, plastics, paints and coatings industries both as a filler – and due to its special white color - as a coating pigment. In the paper industry it is valued worldwide for its high brightness and light scattering characteristics, and is used as an inexpensive filler to make bright opaque paper. Filler is used at the wet-end of paper making machines, and calcium carbonate filler allows for the paper to be bright and smooth. As an extender, calcium carbonate can represent as much as 30% by weight in paints. Calcium carbonate also is used widely as a filler in adhesives, and sealants.
Its primary function in the paper industry is to reduce furnish costs and increase the brightness of paper, while still being inexpensive.
Main functions of PCC as a paper filler are:
Improving printing quality by changing the smoothness,
Show through, ink absorption.
Formation and sheet structure.
Texture and feel.
In the plastics industry it is used as filler in polymer composites such as plasticized and rigid PVC, unsaturated polyesters, polypropylene and polyethylene.
In coatings, calcium carbonate is used as the main extender. The opacity of coatings is influenced by fineness and particle size distribution. Also, calcium carbonate enhances properties of the coating such as:
• Weather resistance.
• Rheological properties.
• Low abrasiveness.
In water based coating calcium carbonate also reduces the drying time.
Calcium carbonate is critical to the construction industry, both as a building material in its own right (e.g. marble), and as an ingredient of cement. It contributes to the making of mortar used in bonding bricks, concrete blocks, stones, roofing shingles, rubber compounds, and tiles. Calcium carbonate decomposes to form carbon dioxide and lime, an important material in making steel, glass, and paper. Because of its antacid properties, calcium carbonate is used in industrial settings to neutralize acidic conditions in both soil and water.
Currently used conventional PCC is 1-3 micrometers particle size and nanosized PCC has PCC nanoparticles smaller than 100 nm.
Nanosized PCC has shown many unique properties compared to microsized PCC particles. Studies on the effects of using nanosized PCC fillers in sealants and PVC materials have been made. It has been indicated that fatty acid-treated PCC of particle size less than 100 nm is particularly useful for filling sealants. Studies on the impact fracture energy of mineral-filled polypropylene and copolymer with and without calcium carbonate fillers showed that nanometer fillers increased the stiffness of both the homopolymer and copolymer.
Calcium carbonate nanocomposites exhibit unique and improved properties in polymer composites appeared. In poly (vinyl acetate) (PVAc) matrix, the morphology of the composite is dependent on the filler particle size. The nanoparticles form‘net like’ dispersion in the matrix, whereas the particles in the micron scale structures in ‘islands’.
The application of nano CaCO3 nanoparticles as additives in lubricating oils are base n the fact that CaCO3 nanoparticles exhibit good load-carrying capacity, antiwear and friction-reducing properties.
• Personal Health
• Food Production
• Building Materials and Construction