CHEMISTRY GLOSSARY

blanching    →   blanširanje

1. Blanching is a heat treatment of foodstuffs to partially or completely inactivate the naturally occurring enzymes prior to freezing.

2. Blanching is a washing process for coins cleaning. The black surface layer of cupric oxide is removing by dipping the coins in hot dilute sulphuric acid (w(H₂SO₄) = 10 %).

bomb calorimeter    →   kalorimetrijska bomba

Bomb calorimeter is a type of constant-volume calorimeter used in measuring the heat of combustion of samples which can be burned in oxygen. Four essential parts are required in any bomb calorimeter:

1. a bomb or vessel in which the combustible charges can be burned,
2. a bucket or container for holding the bomb in a measured quantity of water, together with a stirring mechanism,
3. an insulating jacket to protect the bucket from transient thermal stresses during the combustion process, and
4. a thermometer or other sensor for measuring temperature changes within the bucket.

conduction    →   kondukcija

This process occurs most significantly in solids. The atoms or molecules in a solid state do not leave their mean positions, but continue to vibrate about their mean positions. They transfer heat energy from one atom to another. This happens because of the coupling between them due to mutually attractive forces.

flame    →   plamen

Flame is a mixture of heat and light energy which occurs when sudden combustion occurs.

Glauber’s salt    →   Glauberova sol

Glauber’s salt is sodium sulphate decahydrate (Na₂SO₄·10H₂O). Loses water of hydration at 100 °C. Energy storage capacity is more than seven times that of water.

heat transfer    →   prijenos topline

From observations and experiments it has been found that heat energy can be transferred from one position to another through three different modes: conduction, convection and radiation.

Lewis number    →   Lewisova značajka

Lewis number (Le) is a dimensionless quantity used in fluid mechanics, defined by

where a is thermal diffusivity and D is diffusion coefficient.

brass    →   mjed

Brasses are alloys of copper and zinc (generally 5 % to 40 %). Brass has been known to man since prehistoric times, long before zinc itself was discovered. It was produced by melting copper together with calamine, a zinc ore. Its ductility reaches a maximum with about 30 % zinc and its tensile strength with 45 % although this property varies greatly with the mechanical and heat treatment of the alloy. Typical applications included gears, plumbing ware fittings, adapters, valves and screw machine products. The French horn is a valved brass wind instrument.

Brass may contain small amounts of other alloying elements, such as aluminum, lead, tin, or nickel. Lead can be added as an alloying element resulting in a brass that can be rapidly machined and produces minimal tool wear. Additions of aluminium, iron and manganese to brass improve strength, whilst silicon additions improve wear resistance. Brass containing tin (< 2 % ) is less liable to corrosion in seawater; it is sometimes called naval brass and is used in naval construction.

copper    →   bakar

Copper has been known since ancient times. The origin of the name comes from the Latin word cuprum meaning the island of Cyprus famed for its copper mines. It is malleable, ductile, reddish-brown metal. Resistant to air and water. Exposed surfaces form greenish carbonate film. Pure copper occurs rarely in nature. Usually found in sulfides as in chalcopyrite (CuFeS₂), coveline (CuS), chalcosine (Cu₂S) or oxides like cuprite (Cu₂O). Most often used as an electrical conductor. Also used in the manufacture of water pipes. Its alloys are used in jewellery and for coins.

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.