1.What are abrasives?2.What are macromolecules?3.What are hygroscopic and hydrophobic substances?

1) Abrasives : An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away. While finishing a material often means polishing it to gain a smooth, reflective surface it can also involve roughening as in satin, matte or beaded finishes.

Some naturally occurring abrasives are:

• Calcite (calcium carbonate),Emery (impure corundum),Diamond dust (synthetic diamonds are used extensively), Novaculite, Pumice dust, Rouge, Sand

2)macromolecules: Any very large molecule, composed of much larger numbers (hundreds or thousands) of atoms than ordinary molecules. Some macromolecules are individual entities that cannot be subdivided without losing their identity (e.g., certain proteins, with molecular weights into the millions). Others (polymers) are multiples of a repeating building block (monomer) in chains or networks (e.g., plastics, cellulose). Most macromolecules are in the size range typical of colloids.

3)hygroscopic and hydrophobic substances:

Hygroscopic substances are those substances that absorb water vapour from the air. The process is called Hygroscopicity.Hygroscopic substances include sugar, honey, glycerol, ethanol, methanol, iodine, many chloride and hydroxide salts, and a variety of other substances

All substances that are water repelling are considered hydrophobic substances.Ex: Oil, Waxes, etc..

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regards

Ramesh

Approved