ELECTROLYSIS

From Big Medical Encyclopedia

ELECTROLYSIS — the chemical changes proceeding under the influence of electric current on the electrodes placed in solutions, fusions or solid electrolytes. AA. it is used at nek-ry physiotherapeutic procedures (see Galvanization), in the polyarografichesky method of the analysis (see Polyarografiya) which is widely applied in biochemistry is the cornerstone of an electrochemical method of receiving a number of important substances and storage of electrical energy in accumulators.

In the industry E. use for receiving from fusions of ores of aluminum (see), magnesium (see), titanium, zirconium, uranium (see) and beryllium (see), and also for receiving chlorine (see), chlorates, perchlorates, persulphates, organic compounds (see), hydrogen (see), oxygen (see), fluorine (see) etc. Besides, by means of E. apply thin metallic coatings on various products, including on medical tools, for protection them from corrosion, increase in wear resistance and thermal stability, improvement of outward. Electrolysis is applied also at production of metal copies.

In addition to E., the electric current passed through solutions, fusions and solid electrolytes (see) can cause various electrokinetic phenomena (see) — electroosmosis (see), an electrophoresis (see) and heat effects.

For the first time quantitative ratios between electrical energy and the related chemical transformations were established by Faraday (M. to Faraday), in 1833 — 1834 formulated fundamental laws of electrolysis: 1) amounts of the substances emitted or dissolved on electrodes are directly proportional to their chemical equivalents (see the Equivalent chemical), and also to amount of the electricity which passed through electrolyte; 2) allocation of grams equivalents of any substance always requires the same amount of electricity (F) equal 9,650 to.

At E. on the anode ions and molecules of electrolyte or material of an electrode (see Electrodes) give electrons (are oxidized), e.g.: 2Al + Z (N 2 O) → Al 2 O 3 + 6H + + 6e, and on the cathode — accept electrons, i.e. are recovered: Fe 3+ + e → Fe 2+ . On the cathode usually there is a category of ions of metals and hydrogen: Cu 2+ +2e → Cu, 2H + + 2e → N 2 . The nature of anode processes depends on material of the anode. In case of the soluble anodes made of silver, copper, zinc, cadmium, atoms of metal give electrons to an external electric chain and become cations, i.e. there is a dissolution of the anode: Ag → e + Ag + . On the insoluble anodes manufactured of platinum, iridium, graphite most often note the category of anions: 2Cl - + 2e → Cl 2 . Nek-ry materials (iron, nickel, cobalt, gold, chrome, aluminum, tin) can be under various conditions as soluble. and insoluble electrodes.

For allocation of any ion in the form of free substance it is necessary to put to an electrode the potential which at least is slightly exceeding own electromotive force (EMF) of the couple formed as a result of E. Eto so-called potentials of decomposition, the category or allocation. The size of such potential is measured experimentally for each electrode, most often by method of polarizing curves. The sum of deposition potentials of substances on the anode and the cathode determines tension of decomposition of electrolyte in these conditions. Accumulation of substances on electrodes leads to emergence of potentials and the polarization current (see) sent to opposite polarizing current. Behind primary electrode processes secondary, purely chemical reactions sometimes proceed: formation of molecules from atoms of the gases which are emitted on electrodes, napr, hydrogen H 2  ; education and crystal growth of metals and formation of continuous metal rainfall, napr, the cathode sedimentation of copper; interaction of products E. with each other, with electrolyte, solvent or with impurity, napr, education hypochloric to - you at E. chlorides due to interaction of the chlorine which is emitted on the anode with water. Allocation on electrodes of elemental oxygen or hydrogen leads to secondary oxidation reactions or recovery (see Redoxreactions); e.g., nitrobenzene (see) on the cathode is recovered in aniline (see), anthracene on the anode is oxidized in anthraquinone.

AA. for the purpose of receiving certain products carry out in special devices — electrolyzers, electrolytic bathtubs, cells. As electrolytes use mineral or organic to - you, salts and their mixes. In some cases electrolyte serves as mother substance for receiving a required product. For an exception of interaction of products E., formed on electrodes, the electrolyzer is divided into two (and more) speak rapidly a porous diaphragm from asbestos, ceramics, ion-exchanger membranes, permeable only for ions of electrolyte. In this case solution in anode space is called anolyte, in the cathode — a catholyte. Efficiency E. estimate on coefficient of useful use of tension, an exit on energy, an exit on substance, etc.

Bibliography: Glinka N. L. General chemistry, page 293, L., 1978; Krishtalik L. I. Electrode reactions, Mechanism of the elementary act, M., 1979; Electrosynthesis and bioelectrochemistry, under the editorship of A. N. Frumkin, etc., M., 1975.

V. A. Pekkel.

Яндекс.Метрика