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Home >> Chemistry Dictionary >> Cathodic Portection Cerium
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Catalase.
A collective name for enzymes which destroy hydrogen peroxide and so prevent the accumulation of other toxic peroxides that might be formed. They contain haematin or related compounds as the prosthetic group. Their activity is related to the oxidation and reduction of the iron in the molecule. (See also peroxidases).
Cathode.
The electrode which carries the negative charge in an electrochemical cell. In electrolysis the positively charged ions are discharged at the cathode.
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Cathodic protection.
A zinc coating on iron provides Cathodic protection, as the iron cathode does not rust; zinc is a sacrificial coating.
Cation.
An atom which has lost one or more electrons or a positively charged group of atoms, e.g. [NH4]+ . Cations are present in the solid state, e.g. Na+ in Nacl, and in solutions and metals. In electrolysis cation travel to the cathode.
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Caustic soda.
NaOH, Sodium structures.
Cd.
Cadmium
C.D.
Circular dichroism.
Ce.
Cerium.
Celestine.
SrSO4. Native strontium sulphate, a major source of Sr compounds.
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Cell.
A system used a source of electrical energy. Electrochemical cells consist of two electrodes dipping into one or more electrolyte solutions. If the electrodes ar in separate solutions, electrical contact between solutions is achieved by means of a salt bridge; porous disc or ionic conductor. The electrodes may be of the same metal as the electrolyte or of an other inert material, e.g. platinum.
Cellophane.
A transparent sheet cellulose prepared by extruding cellulose xanthate solutions into a bath of acid. Used as a wrapping material for foodstuffs and cigarettes etc.
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Celluloid.
A transparent highly flammable substance made from cellulose nitrate with a camphor plasticizer. It was formerly widely used as a thermoplastic materials, especially for film, (a use now discontinued owing to the inflammability of celluloid).
Cellulose nitrate.
A higly flammable material which is obtained by treating cellulose with concentrated nitric acid. The alternative name is nitrocellulose.
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Cement.
Any of various substances used for bonding or setting to a hard material. Portland cement is a mixture of calcium silicates and aluminates made by heating limestone (CaCO3) with clay (containing aluminosilicates) in a kiln. The product is ground to a fine powder. When mixed with water it sets in a few hours and then hardens over a longer period of time due to the formation of hydrated aluminates and silicates.
Cementation of steel.
A process in which the surface of an object made of low carbon steel is saturated with carbon to increase its hardness and wearability.
Centi.
Symbol C. A prefix used in the metric system to denote one hundredth e.g. 0.01 metre = 1 centimeter (cm).
Centrifugal Pump.
The most widely used pump in the chemical and process industries. It consists of a rotor with a number of curved vanes rotating inside a flat cyclindrical casing. Liquid enters the centre of the casing along the rotor axis and is swept along the vanes into the volute which is a ring shaped chamber.
Ceramics.
Inorganic materials, such as pottery, enamels, and refractories. Ceramics are metal silicates, oxides, nitrides, etc.
Ceresin.
The name formerly given to a hard, white, odourless wax obtained from fully refined ozokerite. The term now often refers to certain forms of hard, brittle waxes obtained from petroleum.
Cerium.
Symbol Ce. A silvery metallic element belonging to the lanthanoids; a.n. 58; r.a.m. 140.12; r.d.6.77 (20°C); m.p. 798°C b.p. 3433°C. It occurs in allanite, bastnasite, cerite, and monazite. Four isotopes occur naturally: cerium- 136; -138, -140, and -142; fifteen radioisotopes have been identified. Cerium is used in mischmetal, a rare-earth metal containing 25% cerium, for use in lighter flints. The oxide is used in the glass industry. Now a days cridely.
Cermetes.
Pressed or sintered ceramic metal mixtures, e.g., Cr = Al2O3, used in high temperature applications, e.g. jet engines.
Cf
Californium
Chain carrier.
Atoms, molecules or radicals which take part in and enable a chain reaction to continue.
Chain reaction.
A reaction that is self sustaining as a result of the products of one step initiating a subsequent step. Chemical chain reactions usually involve free radicals as intermediates. An example is the reaction of chlorine with hydrogen initiated by ultra-violet radiation. A chlorine molecule is first split into atoms:
Cl2 --> Cl +Cl
These react with hydrogen as follows:
Cl + H2 --> HCl + H
H + Cl2 --> HCl + Cl etc
Combustion and explosion reactions similar free radical chain reactions.
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