CHEMISTRY GLOSSARY

volume    →   volumen

Volume is a space taken by a certain mass of some matter. SI unit for volume is a cubic meter (m³). Changes of temperature or pressure can change volume.

zeotrope    →   zeotrop

Zeotrope is a liquid mixture that shows no maximum or minimum when vapour pressure is plotted against the composition at a constant temperature. (See Azeotrope)

metallic glass    →   metalno staklo

Certain alloys can solidify by extremely rapid cooling out of melt without formation of a crystal lattice, that is in the amorphous form - such, amorphous alloys are so called metallic glasses. The alloy of zirconium, beryllium, titanium, copper, and nickel is one of the first metallic glasses that can be made in bulk and formed into strong, hard, useful objects.

Unlike pure metals and most metal alloys, metallic glasses have no regular crystalline structure. This lack of long range order or microstructure is related to such desirable features as strength and low damping which is one reason why the premier use for zirconium-based metallic glass is in the manufacture of expensive golf club heads. Metallic glasses can be quite strong yet highly elastic, and they can also be quite tough (resistant to fracture). Even more interesting are the thermal properties; for instance, just like an oxide glass, there is a temperature (called the glass transition temperature) above which a metallic glass becomes quite soft and flows easily. This means that there are lots of opportunities for easily forming metallic glasses into complex shapes.

normal conditions    →   normalni uvjeti

Gas is under normal (or standard) conditions when: p₀ = 10⁵ Pa and T₀ = 273.15 K (0 °C). IUPAC recommends that the former use of the pressure of 1 atm as standard pressure (equivalent to 101 325 Pa) should be discontinued. At these conditions, the molar volume of gas V_m0 is 0.022 711 m³ (22.711 L).

phase diagram    →   fazni dijagram

Phase diagram is a graphic representation of the equilibrium relationships between phases (such as vapour-liquid, liquid-solid) of a chemical compound, mixture of compounds, or solution.

The figure shows a typical phase diagram of an element or a simple compound. The stability of solid, liquid and gas phases depends on the temperature and the pressure. The three phases are in equilibrium at the triple point. The gas and liquid phases are separated by a phase transition only below the temperature of the critical point.

piezoelectric effect    →   piezoelektrični efekt

Piezoelectric effect is voltage produced between surfaces of a solid dielectric (nonconducting substance) when a mechanical stress is applied to it. A small current may be produced as well. The effect, discovered by the French physicist Pierre Curie (1859-1906) in 1883, is exhibited by certain crystals, e.g., quartz and Rochelle salt, and ceramic materials. When a voltage is applied across certain surfaces of a solid that exhibits the piezoelectric effect, the solid undergoes a mechanical distortion. Piezoelectric materials are used in transducers, e.g., phonograph cartridges, microphones, and strain gauges, which produce an electrical output from a mechanical input, and in earphones and ultrasonic radiators, which produce a mechanical output from an electrical input.

plasma    →   plazma

Plasma is a highly ionised gas in which the charge of the electrons is balanced by the charge of the positive ions, so that the system as a whole is electrically neutral. Plasmas are created by exposing gases at low pressure to an electric or electromagnetic field. In semiconductor processing, plasmas are used for etching and thin film deposition (the excited state of the gas makes it very reactive). In everyday life plasmas are used to give light in fluorescent light bulbs, neon lamps, and blue insect traps.

plastic    →   plastika

Plastic is a material that can be shaped by the application of heat or pressure. Most are based on synthetic polymers although some are the product of natural substances (such as cellulose derivatives, but excluding the rubbers.). They are usually light and permanent solids, being also heat and electric isolators. If the materials soften again when reheated, they are said to be thermoplastic. If, after fashioning, they resist further applications of heat, they are said to be thermoset.

polymorphism    →   polimorfija

Polymorphism is the ability of a solid substance to crystallise into more than one different crystal structure. Different polymorphs have different arrangements of atoms within the unit cell, and this can have a profound effect on the properties of the final crystallised compound. The change that takes place between crystal structures of the same chemical compound is called polymorphic transformation.

The set of unique crystal structures a given compound may form are called polymorphs. Calcium carbonate is dimorphous (two forms), crystallizing as calcite or aragonite. Titanium dioxide is trimorphous; its three forms are brookite, anatase, and rutile. The prevailing crystal structure depends on both the temperature and the external pressure.

Iron is a metal with polymorphism structure. Each structure stable in the range of temperature, for example, when iron crystallizes at 1 538 °C it is bcc (δ-iron), at 1 394 °C the structure changes to fcc (γ-iron or austenite), and at 912 °C it again becomes bcc (α-iron or ferrite).

Polymorphism of an element is called allotropy.

practical salinity    →   praktični salinitet

Practical salinity S_P is defined on the Practical Salinity Scale of 1978 (PSS-78) in terms of the conductivity ratio K₁₅ which is the electrical conductivity of the sample at temperature t₆₈ = 15 °C and pressure equal to one standard atmosphere, divided by the conductivity of a standard potassium chloride (KCl) solution at the same temperature and pressure. The mass fraction of KCl in the standard solution is 0.0324356 (32.4356 g of KCl in 1 kg of solution). When K₁₅ = 1, the Practical Salinity P S is by definition 35. The conductivity of that reference solution is C(35,1568,0) = 42.914 mS/cm = 4.2914 S/m (Siemens per meter). Note that Practical Salinity is a unit-less quantity. Though sometimes convenient, it is technically incorrect to quote Practical Salinity in "psu". When K₁₅ is not unity, S_P and K₁₅ are related by the PSS-78 equation

At a temperature of t₆₈ = 15 °C, R_t is simply K₁₅ and Practical Salinity S_P can be determined from the above equation. For temperatures other than t₆₈ = 15 °C, Practical Salinity S_P is given by the following function of R_t (k = 0.0162)