Constituents Of Alloy

Swarnprastha Public School Chemistry Project

Study Of Constituents Of Alloys Submitted By:Vineet Singhal

XII A

Introduction An alloy(through the Fr. aloyer, from Lat. alligare, to combine), is a partial or complete solid solution of one or more elements in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal (heat treatment) history. Alloys usually have different properties from those of the component elements. Alloying one metal with other metal(s) or non metal(s) often enhances its properties. For instance, steel is stronger than iron, its primary element. The physical properties, such as density, reactivity, Young's modulus, and electrical and thermal conductivity, of an alloy may not differ greatly from those of its elements, but engineering properties, such as tensile strength[1] and shear strength may be substantially different from those of the constituent materials. This is sometimes due to the sizes of the atoms in the alloy, since larger atoms exert a compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors, helping the alloy resist deformation. Alloys may exhibit marked differences in behavior even when small amounts of one element occur. For example, impurities in semi-conducting ferromagnetic alloys lead to different properties, as first predicted by White, Hogan, Suhl, Tian Abrie and Nakamura. Some alloys are made by melting and mixing two or more metals. Brass is an alloy made from copper and zinc. Bronze, used for bearings, statues, ornaments and church bells, is an alloy of copper and tin.

Unlike pure metals, most alloys do not have a single melting point. Instead, they have a melting range in which the material is a mixture of solid and liquid phases. The temperature at which melting begins is called the solidus and the temperature when melting is complete is called the liquidus. However, for most alloys there is a particular proportion of constituents (in rare cases two) which has a single melting point. This is called the alloy's eutectic mixture.

Some Common Alloys And Their Uses Amalgam Any alloy of mercury is called an amalgam. Most metals are soluble in mercury, but some (such as iron) are not. Amalgams are commonly used in dental fillings because they have been relatively cheap, easy to use, and durable. In addition, until recently, they have been regarded as safe. They are made by mixing mercury with silver, copper, tin, and other metals. The mercury content of dental fillings has recently stirred controversy, based on the potentially harmful effects of mercury. Mercury amalgams have also been used in the process of mining gold and silver, because of the ease with which mercury amalgamates with them. In addition, thallium amalgam is used as the liquid material in thermometers, because it freezes at -58°C, whereas pure mercury freezes at -38°C. Brass

A decorative brass paperweight (left), along with zinc and copper samples. Brass is the term used for alloys of copper and zinc in a solid solution. It has a yellow color, somewhat similar to gold. It was produced in prehistoric times, long before zinc was discovered, by melting copper with calamine, a zinc ore. The amount of zinc in brass varies from 5 to 45 percent, creating a range of brasses, each with unique properties. By comparison, bronze is principally an alloy of copper and tin. Despite this distinction, some types of brasses are called bronzes. Brass is relatively resistant to tarnishing and is often used for decorative purposes. Its malleability and acoustic properties have made it the metal of choice for musical instruments such as the trombone, tuba, trumpet, and euphonium. Although saxophones and harmonicas are made out of brass, the saxophone is a woodwind instrument, and the harmonica, a free reed aerophone. In organ pipes designed as "reed" pipes, brass strips are used as the "reed." Aluminum makes brass stronger and more corrosion-resistant. It forms a transparent, self-healing, protective layer of aluminum oxide (Al2O3) on the surface. Tin has a similar effect and finds its use especially in seawater applications (naval brasses). Combinations of iron, aluminum, silicon, and manganese make brass resistant to wear and tear.

Bronze Bronze refers to a broad range of copper alloys, usually with tin as the main additive, but sometimes with other elements such as

phosphorus, manganese, aluminum, or silicon. Typically, bronze is about 60 percent copper and 40 percent tin. The use of bronze was particularly significant for early civilizations, leading to the name "Bronze Age." Tools, weapons, armor, and building materials such as decorative tiles were made of bronze, as they were found to be harder and more durable than their stone and copper predecessors. In early use, the natural impurity arsenic sometimes created a superior natural alloy, called "arsenical bronze." Though not as strong as steel, bronze is superior to iron in nearly every application. Bronze develops a patina (a green coating on the exposed surface), but it does not oxidize beyond the surface. It is considerably less brittle than iron and has a lower casting temperature. Several bronze alloys resist corrosion (especially by seawater) and metal fatigue better than steel; they also conduct heat and electricity better than most steels. Bronze has myriad uses in industry. It is widely used today for springs, bearings, bushings, and similar fittings, and is particularly common in the bearings of small electric motors. It is also widely used for cast metal sculpture and is the most popular metal for top-quality bells and cymbals. Commercial bronze, otherwise known as brass, is 90 percent copper and 10 percent zinc. It contains no tin.

Pewter

Pewter plate Pewter is traditionally composed of 85 to 99 percent tin, with the remainder consisting of copper, which acts as a hardener. Lead is added to lower grades of pewter, giving a bluish tint. Traditionally, there were three grades of pewter: fine, for eatingware, with 96 to 99 percent tin and 1 to 4 percent copper; trifle, also for eating and drinking utensils but duller in appearance, with 92 percent tin, 1 to 4 percent copper, and up to 4 percent lead; and lay or ley metal, not for eating or drinking utensils, which could contain up to 15 percent lead. Modern pewter mixes the tin with copper, antimony, and/or bismuth rather than lead. Physically, pewter is a bright, shiny metal that is similar in appearance to silver. Like silver, it oxidizes to a dull gray over time if left untreated. It is a very malleable alloy, being soft enough to carve with hand tools. It also takes good impressions from punches or presses. Given this inherent softness and malleability, pewter cannot be used to make tools. Some types of pewter pieces, such as candlesticks, were turned on a metal lathe, and these items are sometimes referred to as "holloware." Pewter has a low melting point (around 225 to 240°C), depending on the exact mixture of metals. Duplication by casting gives excellent results.

The use of pewter was common from the Middle Ages up until the various developments in glass-making during the eighteenth and nineteenth centuries. Pewter was the chief tableware until the making of china. With the mass production of glass products, glass has universally replaced pewter in daily life. Today, pewter is mainly used for decorative objects such as collectible statuettes and figurines, replica coins, and pendants. Nickel silver (German silver) Nickel silver is an alloy of copper, nickel, and often (but not always) zinc. It is named for its silvery appearance and contains no elemental silver. Other common names for this alloy are German silver, paktong, new silver, and alpacca (or alpaca). Many different formulations of alloys fall in the general category of "nickel silver." Besides containing copper, nickel, and zinc, some formulations may include antimony, tin, lead, or cadmium. A representative industrial formulation (Alloy No.752) is 65 percent copper, 18 percent nickel, and 17 percent zinc. In metallurgical science, such alloys would be more properly termed nickel bronze. Some nickel silver alloys, especially those containing high proportions of zinc, are stainless. The earliest use of nickel silver appears to have been in China. It became known to the West from imported wares called Paktong or Pakfong, where the silvery metal color was used to imitate sterling silver. It was discovered to be an alloy composed of copper, nickel, and zinc in the eighteenth century. Nickel silver first became popular as a base metal for silverplated cutlery and other silverware, notably the electroplated wares called "E.P.N.S." (electro-plated nickel silver). It is used in zippers, costume jewelry, and musical instruments (such as

cymbals). After about 1920, its use became widespread for pocketknife bolsters, due to its machinability and corrosion resistance. In some countries, it is used in the production of coins. Its industrial and technical uses include marine fittings and plumbing fixtures for its corrosion resistance, and heating coils for its high electrical resistance. Steel Steel is an alloy composed mainly of iron, with carbon content between 0.02 and 1.7 percent by weight. Carbon is the most costeffective alloying material for iron, but many other alloying elements are also used. Carbon and other elements act as hardening agents, preventing iron atoms in the crystal lattice from sliding past one another. By varying the amount of alloying elements and their distribution in the steel, one can control its qualities such as hardness, elasticity, ductility, and tensile strength. Steel with increased carbon content can be made harder and stronger than iron, but it is also more brittle. The maximum solubility of carbon in iron is 1.7 percent by weight, occurring at 1130 °C. Higher concentrations of carbon or lower temperatures produce cementite, which reduces the material's strength. Alloys with higher carbon content than this are known as cast iron because of their lower melting point. Steel should also be distinguished from wrought iron, with little or no carbon (usually less than 0.035 percent). Currently, there are several classes of steels in which carbon is replaced with other alloying materials, and carbon, if present, is undesired. More recently, steels have been defined as iron-based alloys that can be plastically formed—pounded, rolled, and so forth.

Experiment - 1 Aim : To analyze a sample of brass qualitatively. Requirements : China dish, test-tube funnel, filter paper and common laboratory reagents. Theory : Brass is an alloy of copper and zinc. with the following. Composition : Cu = 60-90% and Zn. = 10-40%. Thus Cu and Zn. form the main constituents of brass. Both these metals dissolved in 50% of nitric acid due to formation of nitrates which are soluble. 3 Cu + 8HNO3 (Dil) 3 Cu (NO3)2 + 2NO + 4H2O or Cu + 8H+ + 2NO3– 3 Cu+2 + 2NO + 4H2O 4Zn + 10HNO3 (Dil) 4 Zn (NO2)2 + N2O + 5H2O 4Zn + 2NO3– + 10H+ 4 Zn+2 + N2O + 5H2O The solution is boiled to expel the oxides of nitrogen and the resulting solution is tested for Cu2+ and Zn+2 ions. Procedure : 1. Place a small piece of brass in a china dish and heat this with minimum quantity of 50% HNO3 so as to dissolve the piece completely.

2. Continue heating the solution till a dry solid residue is obtained. 3. Dissolve the solid residue in dil. HCl and filter. Add distilled water to the filtrate. 4. Pass H2S gas through the filtrate. A black precipitate of copper sulphide is obtained. Separate the black ppt. and keep the filtrate for the test of Zn+2 ions Dissolve black ppt. by heating them with 50% HNO3. To this solution add ammonium hydroxide solution. Appearance of deep blue colouration in the solution shows the presence of copper ions in the solution. 5. To test Zn+2 ions, boil the filtrate to remove H2S gas, then add solid NH4Cl to this and heat to dissolve NH4Cl. Add excess of NH4OH so that a solution is ammoniacal. Now pass H2S gas through this ammoniacal solution. Dirty white or grey precipitation indicate zinc. Separate the precipitates and dissolve it in minimum amount of dil. HCl. Boil to expel H2S gas and add potassium Ferro cyanide solution, white or bluish white ppt. confirm Zn+2 ions in the solution. Result : The given sample of brass contains copper and zinc. metals as the main constituents.

Experiment - 2

Aim : To analyze a sample of bronze qualitatively. Requirements : China dish, test-tube funnel, filter paper and common laboratory reagents.

Theory : Bronze is an alloy of copper and tin with the following. Composition : Cu = 88-96% and Sn. = 4-12%. Thus copper and zinc. form the main constituents of bronze. Both these metals dissolved in nitric acid. 3 Cu + 8H+ + 2NO3– 3 Cu2+ + 2NO + 4H2O 4Sn + NO3– + 10 H+ 4 Sn+2 + NH4+ + 3H2O (Cold and Dil. Acid) Sn + 4NO3– + 4H+ H2Sn O3 + 2NO2 + H2O (Conc. acid) (Metastannic Acid) Excess of nitric acid is removed by heating the solution. The resulting solution now would contain Cu+2 ions and metastannic acid. This solution is acidified with dil. HCl and H2S gas is passed when the sulphides of copper and tin are formed. Cu+2 + S2- CuS (Black ppt.) H2SnO3 + 2H2S SnS2 (Black ppt.) + 3H2O The sulphides are separated by boiling the ppt. with yellow ammonium sulphide when SnS2 goes into solution as thiostannate where as CuS is not affected. SnS2 + (NH4)2S (NH4)2 SnS2 (Soluble) Ammonium thiostannate.

CuS + (NH4)2S CuS (Unaffected) Black ppt. The soluble black ppt. is tested for Cu+2 ions and the solution is tested for Sn2+ ions as in elementary qualitative analysis. Procedure : 1. Take about 1g. of small pieces of bronze in a china dish and add to it 5-10 ml. of dil. HNO3. 2. Heat the contents slowly to dissolve copper and tin completely and then boil the contents to a paste to remove excess of HNO3. All this is carried out in cup board. 3. Dissolve this dry mass in distilled water containing HCl (1:1) to get a clear solution. 4. Transfer the solution in a test tube and pass H2S in excess i.e. till the precipitation is complete. Filter and reject the filtrate. 5. Take the black ppt. in a test tube and add to it 2-3 ml. of yellow ammonium sulphide and heat. Filter the contents. Black residue is tested for Cu+2 ions and filtrate is tested for Sn+2 ions. 6. Analysis of black residue : Transfer a little of the black ppt. into a test tube. Add to it 2-3 ml. of 50%. HNO3 and boil the contents of the tube. A light blue or green sol. indicates the presence of Cu+2. Divide this sol. into two parts. (a) To one part add excess of NH4OH a deep blue colouration confirms the presence of Cu+2 ions.

(b) Acidify the second part with acetic acid and add K4 [Fe (CN)6] i.e. potassium ferrocyanide solution. A reddish brown ppt. confirms the presence of Cu+2 ions. 7. Analysis of filtrate : Boil the filtrate with 1 ml. of dil. HCl. A yellow ppt. is obtained. Dissolve in 1 ml. conc. HCl. To this solution add 0.5 g. of zinc. dust and boil it for 2-3 minutes. Filter and to filtrate add 1-2 ml. of mercuric chloride solution. A white ppt. turning grey on standing confirms the presence of Sn+4 ions. Result : The given sample of bronze contains - Cu and Sn as the main constituents.