Brasses & Bronzes
Brass is an alloy made of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties. Bronze is an alloy consisting primarily of copper, usually with tin as the main additive. It is hard and tough, and it was so significant in antiquity that the Bronze Age was named after the metal. Admiralty brass contains 30% zinc, with 1% tin to inhibit dezincification in many environments. Alpha brasses with less than 35% zinc, are malleable, can be worked cold, and are used in pressing, forging, or similar applications. They contain only one phase, with face-centered cubic crystal structure. Alpha-beta brass (Muntz metal), also called duplex brass, is 35–45% zinc and is suited for hot working. It contains both α and β' phase; the β'-phase is body-centered cubic and is…
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard and brittle metal which takes a high polish, resists tarnishing, and has a high melting point. Chromium oxide was used by the Chinese in the Qin dynasty over 2,000 years ago to coat metal weapons found with the Terracotta Army. Chromium was discovered as an element after it came to the attention of the western world in the red crystalline mineral crocoite (lead(II) chromate), discovered in 1761 and initially used as a pigment. Louis Nicolas Vauquelin first isolated chromium metal from this mineral in 1797. Since Vauquelin's first production of metallic chromium, small amounts of native (free) chromium metal have been discovered in rare minerals, but these are not used commercially. Instead, nearly all chromium is commercially extracted from the single commercially viable orechromite, which is iron chromium oxide Chromite is also now the chief source of chromium for chromium pigments. Applications The strengthening effect of forming…
Zinc
Zinc (symbol Zn), in commerce also spelter, is a metallic chemical element. It has atomic number 30. It is the first element of group 12 of the periodic table. In some respects zinc is chemically similar to magnesium: its ion is of similar size and its only common oxidation state is +2. Zinc is the 24th most abundant element in the Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral. The largest mineable amounts are found in Australia, Asia, and the United States. Zinc production includes froth flotation…
Aluminum
• Aluminum is a light metal & easily machinable; has wide variety of surface finishes; good electrical and thermal conductivities; highly reflective to heat and light. • Versatile metal - can be cast, rolled, stamped, drawn, spun, roll-formed, hammered, extruded and forged into many shapes. • Aluminum can be riveted, welded, brazed, or resin bonded. • Corrosion resistant - no protective coating needed, however it is often anodized to improve surface finish, appearance. • Al and its alloys - high…
Copper Alloys
• Brasses and Bronzes are most commonly used alloys of Cu. Brass is an alloy with Zn. Bronzes contain tin, aluminum, silicon or beryllium. • Other copper alloy families include copper-nickels and nickel silvers. More than 400 copper- base alloys are recognized. Applications - Electrical wires, - roofing, nails, rivets - Automotive radiator - core, lamp fixture, - clutch disk,…
NON FERROUS METAL & ALLOYS
Copper - Copper is one of the earliest metals discovered by man. - The boilers on early steamboats were made from copper. - The copper tubing used in water plumbing in Pyramids was found in serviceable condition after more than 5,000 years. - Cu is a ductile metal. Pure Cu is soft and malleable, difficult to machine.…
Factors that influence diffusion
As stated above, there is a barrier to diffusion created by neighboring atoms that need to move to let the diffusing atom pass. Thus, atomic vibrations created by temperature assist diffusion. Also, smaller atoms diffuse more readily than big ones, and diffusion is faster in open lattices or in open directions. Similar to the case of vacancy formation, the effect of temperature in diffusion is given by a Boltzmann factor: D = D0 × exp(–Qd/kT).
Nonsteady-State Diffusion
This is the case when the diffusion flux depends on time, which means that a type of atoms accumulates in a region or that it is depleted from a region (which may cause them to accumulate in another region).
Steady-State Diffusion
The flux of diffusing atoms, J, is expressed either in number of atoms per unit area and per unit time (e.g., atoms/m2-second) or in terms of mass flux (e.g., kg/m2-second).Steady state diffusion means that J does not depend on time. In this case, Fick’s first law holds that the flux along direction x is: J = – D dC/dx Where dC/dx is the gradient of the concentration C, and D is the diffusion constant. The concentration gradient is often called the driving force in diffusion (but it is not a force in the mechanistic …
Diffusion
Diffusion Mechanisms Diffusion is the process of mass flow in which atoms change their positions relative to neighbors in a given phase under the influence of thermal and a gradient. The gradient can be a compositional gradient, an electric or magnetic gradient, or stress gradient. Many reactions in solids and liquids are diffusion dependent. Diffusion is very important in many industrial and domestic applications. E.g.: Carburizing the steel, annealing homogenization after solidification, coffee mixing, etc. From an atomic perceptive, diffusion is a step wise migration of atoms from one lattice position to another. Migration of atoms in metals/alloys can occur in many ways, and thus corresponding diffusion mechanism is defined.…
