CHEMISTRY GLOSSARY

ferrite    →   ferit

Ferrites are ceramic materials of the nominal formula MO·Fe₂O₃, where M is a divalent metal (Co, Mn, NI, or Zn). The ferrites show either ferrimagnetism or ferromagnetism, but are not electrical conductors, and they are used in high-frequency circuits as magnetic cores, in rectifiers on memory and record tapes, and various related uses in radio, television, radar, computers, and automatic control systems.

Fischer-Tropsch process    →   Fischer-Tropschov postupak

Fischer-Tropsch process is an industrial method of making hydrocarbon fuels from carbon monoxide and hydrogen. The process was introduced in 1933. and used by Germany in World War II. to produce motor fuel. Hydrogen and carbon monoxide are mixed in the ratio 2:1 (water gas was used with added hydrogen) and passed at 200 °C over a nickel or cobalt catalyst. The resulting hydrocarbon mixture can be separated into a higher-boiling fraction for Diesel engines and a lower-boiling petrol fraction. The petrol fraction contains a high proportion of straight-chain hydrocarbons and has to be reformed for use in motor fuel. Alcohols, aldehydes, and ketones are also present. The process is also used in the manufacture of SNG from coal. It is named after the German chemist Franz Fischer (1852-1932) and the Czech Hans Tropsch (1839-1935).

volt    →   volt

Volt (V) is the SI derived unit of electric potential. One volt is the difference of potential between two points of an electric conductor when a current of 1 ampere flowing between those points dissipates a power of 1 watt. It was named after the Italian physicist Alessandro Volta (1745-1827).

weak electrolyte    →   slabi elektrolit

Weak electrolytes are those electrolytes which in water solutions dissociate only partially, giving ions and which are in equilibrium with undissociated molecules. Their water solutions conduct electric current weakly. For example, acetic acid partially dissociates into acetate ions and hydrogen ions, so that an acetic acid solution contains both molecules and ions.

flammable limit    →   granica zapaljivosti

Flammable limits refer to the conditions under which a mixture of a flammable material and air may catch fire or explode. When vapour s of a flammable or combustible liquid are mixed with air in the proper proportions in the presence of a source of ignition, rapid combustion or an explosion can occur. The proper proportion is called the flammable range and is also often referred to as the explosive range. The flammable range includes all concentrations of flammable vapour or gas in air, in which a flash will occur or a flame will travel if the mixture is ignited.

The lower flammable limit (LEL) or the lower explosive limit is the lowest concentration of a flammable vapour or gas in air that will propagate a flame from an ignition source. The upper flammable limit (UEL) or the upper explosive limit is the highest concentration of a flammable vapour or gas in air that will propagate a flame from an ignition source. Any concentration between these limits can ignite or explode.

fossil fuel    →   fosilno gorivo

Fossil fuels (coal, oil, and natural gas) are the fuels used by man as a source of energy. They are formed from the remains of living organisms and all have a high carbon or hydrogen content. They have value as fuels on the exothermic oxidation of carbon to form carbon dioxide

and the oxidation of hydrogen to form water

fuel cell    →   gorivi članak

Fuel cell is a device that converts chemical energy into electrical energy. It is different from a battery in that the energy conversion continues as long as fuel and oxidising agent are fed to the fuel cell; that is, in principle indefinitely. (A battery is manufactured with a limited amount of chemicals, and it is exhausted when all the chemicals have reacted.) It is a galvanic cell where spontaneous chemical reactions occur at the electrodes. The fuel is oxidised at the anode, and the oxidising agent (almost always oxygen or air) is reduced at the cathode. Presently, the most commonly used fuel is hydrogen. More conventional fuels (e.g., petrol or natural gas) must be converted (reformed) into hydrogen before they can be utilised in a fuel cell.

Some fuel cells employ an aqueous solution as electrolyte, that can be either acidic or basic (alkaline), or an ion-exchange membrane soaked in aqueous solution can act as the electrolyte. These fuel cells operate at relatively low temperatures (from room temperature to not much above the boiling point of water). Some fuel cells employ molten salts (especially carbonates) as electrolytes and have to operate at temperatures of several hundred degrees centigrade (Celsius). Others employ ionically conductive solids as electrolyte and must operate close to 1 000 °C.

gallium    →   galij

Gallium was discovered by Lecoq de Boisbaudran (France) in 1875. The origin of the name comes from the Latin word Gallia meaning France. It is soft, blue-white metal. Stable in air and water. Reacts violently with chlorine and bromine. Gallium is found throughout the crust in minerals like bauxite, germanite and coal. Used in semiconductor production. It us used in making LED’s (light-emitting diodes) and GaAs laser diodes.

galvanic celll    →   galvanski članak

Galvanic cell (voltaic cell) is a simple device with which chemical energy is converted into electrical energy. Galvanic cells consist of two separate compartments called half cells containing electrolyte solutions and electrodes that can be connected in a circuit. Two dissimilar metals (e.g., copper and zinc) are immersed in an electrolyte. If the metals are connected by an external circuit, one metal is reduced (i.e., gains electrons) while the other metal is oxidized (i.e., loses electrons).

In the example above, copper is reduced and zinc is oxidized. The difference in the oxidation potentials of the two metals provides the electric power of the cell.

A voltaic cell can be diagrammed using some simple symbols. In the diagram the electrodes are on the outer side of the diagram and a vertical line (|) is used to separate the electrode from the electrolyte solution found in the compartment. A double vertical line (||) is used to separate the cell compartments and is symbolic of the salt bridge. Usually in a diagram the species oxidized is written to the left of the double slash. Here is an example of the Daniell cell:

The names refer to the 18th-century Italian scientists Alessandro Volta (1745-1827) and Luigi Galvani (1737-1798).

germanium    →   germanij

Germanium was discovered by Clemens Winkler (Germany) in 1886. The origin of the name comes from the Latin word Germania meaning Germany. It is greyish-white semi-metal. Unaffected by alkalis and most (except nitric) acids. Stable in air and water. Germanium is obtained from refining copper, zinc and lead. Widely used in semiconductors. It is a good semiconductor when combined with tiny amounts of phosphorus, arsenic, gallium and antimony.