tailieunhanh - Zinc

Introduction In 1791, the first combination of metals in Volta’s battery involved zinc as the negative electrode. A zinc electrode was also used in subsequent Daniell, Grove, and Bunsen cells developed in the early nineteenth century. Those cells were strictly powered by zinc dissolution and cathodic hydrogen evolution. Improvements in battery power and capacity were achieved by increasing the electrode area and the volume of electrolyte, but the ultimate improvement required a new cathodic reaction and new porous cathode materials, leading to increased cathodic voltage and reduced cathodic polarization. . | Zinc J-Y Huot Technical Consultant St-Hubert Canada 2009 Elsevier . All rights reserved. Introduction In 1791 the first combination of metals in Volta s battery involved zinc as the negative electrode. A zinc electrode was also used in subsequent Daniell Grove and Bunsen cells developed in the early nineteenth century. Those cells were strictly powered by zinc dissolution and cathodic hydrogen evolution. Improvements in battery power and capacity were achieved by increasing the electrode area and the volume of electrolyte but the ultimate improvement required a new cathodic reaction and new porous cathode materials leading to increased cathodic voltage and reduced cathodic polarization. Despite competition from aluminum and magnesium primary batteries are predominantly zinc anode-based systems so zinc has remained the most widely used anode material in aqueous primary cells for over a century. Zinc is indeed the anode material of most commercially important primary cells and also finds use in several high-specific-energy secondary cells. The reasons for this are the desirable chemical and electrochemical properties the low cost and the suitable physical characteristics of zinc and more importantly its high corrosion resistance which make zinc batteries very affordable and reliable. Basic Chemistry of Zinc Zinc is not a very abundant element on earth but it is a constituent of a number of minerals. The main source of zinc is sphalerite. Zinc is the first element in group IIB with atomic number 30 and atomic weight g. Its melting point is 419 C and its boiling point is 907 C. The electronic configuration of zinc 3d104s2 has two s electrons outside a filled d shell. The dipositive 2 oxidation state is the most stable as this valence change due to the loss of the 4s2 electrons is favored by the stable d10 core. Zinc II commonly has a coordination number of 4 as the ion can form sp3-hydridized orbitals. It forms a wide variety of compounds and complexes with .