Why are alloys made 1

Big Bang HTL 2, textbook

Basics of Chemistry (2nd year, 3rd semester) 49 The chemical bonds 4 4.3.2 Alloys Alloys are mixtures of 2 or more metals. Sometimes non-metals such as B. carbon C or sulfur S involved, but the main component is always a metal. The aim is to strengthen desired properties (toughness, hardness), to eliminate undesired ones (susceptibility to corrosion) or simply to vary colors (F16). Other metals are added to the starting metal. This happens in a liquid state, i.e. in molten form at correspondingly high temperatures. As a result, the metals mix and when they crystallize (solidify), mixed crystal structures are formed. A distinction can be made between different types: 1. Inclusion mixed crystals: The foreign atoms of the alloy partner are also embedded in the metal lattice (between the regular lattice sites). These additional atoms make it more difficult to shift the lattice planes and the alloys become harder. Example: steel (Fe-C). 2. Substitution mixed crystals: In the metal lattice, some metal atoms are replaced by atoms of the alloying partner, these instead sit in the same, predetermined lattice positions. This only works if the alloy partners have atoms of approximately the same size. Example: Brass (Cu-Zn) Reasons for the types of bond Define the terms: atomic core, electron gas, metal lattice L Explain how metal atoms achieve noble gas configuration. L Complete the table and add a technical application for each property. L Metal property Explanation through the metal bond model Deformability Electrical conductivity Thermal conductivity 4.3.1 F12 A1 F13 A1 F14 A1 A1 Which alloys do you know? What elements do they consist of? Why do you alloy? What is lead pouring? F15 F16 F17 3. Mixtures of pure crystals: Small, pure crystals of the individual components are present here, but they are microscopically distributed in small groups. Therefore the mixture appears as an alloy in the macroscopic area. Example: Pb-Zn Examples and applications of alloys: The melting point of alloys in a certain composition is often far below the melting point of pure metals. Such so-called "eutectic" alloys are often used for soldering. Tin solder is an alloy of 95–99% tin, up to 5% silver and up to 2% copper and has a melting point of only 183 ° C. The metal used to cast lead is a lead-tin alloy that contains only a small amount of lead. This alloy has a much lower melting point than pure lead and “lead pouring” is much faster. (F17) In Austria approx. 90% of all lead cast goods are manufactured by the traditional company Perzy in Vienna-Hernals. Wood's metal, an alloy of bismuth-lead-cadmium-tin, even melts at around 60 ° C. To make the composition of an alloy visible in the formula, first write the base metal and then the alloy component (s) with the respective percentage. CuZn 38 means an alloy made of copper with a zinc content of 38%. Alloys made of copper and zinc are called brass. Doorknobs, musical instruments, fittings, but also antennas and waveguides are often made of brass. Bronze is also one of the copper alloys, but here copper is alloyed with tin. Nowadays, pure tin bronzes are used almost exclusively as coin material and bells. Alloyed with other metals, e.g. B. phosphorus or silicon, there are applications as overhead lines and machine parts. Fig. 4.6: Alloy forms Fig. 4.7: Lead cast goods Fig. 4.8: French horn made of brass For testing purposes only - property of the publisher öbv

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