CHEMISTRY GLOSSARY

covalent bond    →   kovalentna veza

Covalent bond is a chemical bond between two atoms whose stability results from the sharing of two electrons, one from each atom (H· + ·H = H:H or H-H).

cracking    →   krekiranje

Cracking is the process whereby heavy molecules of petroleum or crude oil are broken down into hydrocarbons of lower molecular weight (especially in the oil-refining process).

critical point    →   kritična točka

In general, critical point is the point on the phase diagram of a two-phase system at which the two coexisting phases have identical properties and therefore represent a single phase. At the liquid-gas critical point of a pure substance, the distinction between liquid and gas vanishes, and the vapour pressure curve ends. The coordinates of this point are called the critical temperature and critical pressure. Above the critical temperature it is not possible to liquefy the substance.

critical pressure    →   kritični tlak

Critical pressure is the pressure of a fluid in its critical point; i.e. when it is at its critical temperature and critical volume.

critical temperature    →   kritična temperatura

Critical temperature is the temperature of the liquid-vapour critical point, that is, the temperature above which a gas cannot be liquefied by an increase of pressure.

cross-linking    →   umrežavanje

Cross-linking is an attachment of two chains of polymer molecules by bridges, composed of either an element, a group, or a compound, that join certain carbon atoms of the chains by primary chemical bonds, as indicated in the schematic diagram

Cross-linking occurs in nature in substances made up of polypeptide chains that are joined by the disulfide bonds of the cysteine residue, as in keratins or insulin. Cross-linking can be artificially effected, either adding a chemical substance (cross-linking agent), or by subjecting the polymer to high-energy radiation. Examples are: vulcanisation of rubber with sulphur, cross-linking of polystyrene with divinylbenzene, or cross-linking of polyethylene by means of high-energy radiation.

Cross-linking has the effect of changing a plastic from thermoplastic to thermosetting. Thus, it also increases strength, heat and electrical resistance, and especially resistance to solvents and other chemicals.

crucible    →   lončić za žarenje

Crucible is used for heating small amounts of solid in an oven to very high temperatures. Crucibles are usually made out of porcelain, platinum, nickel or iron.

crude oil    →   sirova nafta

Crude oil (petroleum) is a fossil fuel formed from plant and animal remains many million of years ago. It is occasionally found in springs or pools but is usually drilled from wells beneath the earth’s surface. Crude oil is a mixture of hydrocarbons with small quantities of other chemicals such as sulphur, nitrogen and oxygen. Crude is the raw material which is refined into petrol, heating oil, jet fuel, propane, petrochemicals, and other products.

cubic close-packed structure    →   kubična gusta slagalina

In a cubic close-packed (ccp) arrangement of atoms, the unit cell consists of four layers of atoms. The top and bottom layers (a) contain six atoms at the corners of a hexagon and one atom at the center of each hexagon. The atoms in the second layer (b) fit into depressions in the first layer. The atoms in the third layer (c) occupy a different set of depressions than those in the first. The cubic close packed structure can be made by piling layers in the a-b-c-a-b-c-a-b-c... sequence.

cubic crystal system    →   kubični kristalni sustav

Cubic crystal system is also known as the isometric system. The Isometric crystal system characterizes itself by its three equivalent crystallographic axes perpendicular to each other.