Question

"Zone-refining" is a technique to make high-purity crystals of a pure element. Without zone-refining of silicon, it is unclear whether there would be a semiconductor industry. In this technique, a heater melts a small zone of material, and the heater and zone move along a bar of material (see Fig. 5.17a). The solutes segregate to the far end of the bar. The technique works for removing B-solutes from A-metal when the A-rich part of the A-B phase diagram is as is shown in Fig. 5.17b. Why does zone-refining work? Would the material become more pure alter a second pass of the heater? For what combination of slopes of the liquidus and solidus would zone-refining work best?

Answer 1

(e) Zone - Refining Shis method is particularly used hen metols one regelired in high degree of purity st is based on the Principle that cuhen an impure metol in a molton state is alloued to cool, only the metal cnystalizes chle the impunthies vemain present un the molton State(mass) or melhf UT ) Smpune metal converted into a yod cshidh is heated at one end artha circular heater. A narrowスone 4 metal is melted. The heater is slouly moved along the rod The pure metal reergstallizes out of metol meit ohile the impurites Yerrain m the melt ωhich moves along with the meited zone of the rod ourith Tre movement heater. The process is repeated Several times The end of rod cwhere impurities have collected is catt off This method is employed for the pumfi catiam of germanum silicon, gallium, ouhichs used i semi cond Pure metal novable heate impure metal molton zome Contaming

virtually any (e) gt can be ortended to virtually any solate solvent system having an appreciable conentratiern diferene ctueen solld and liaaud phasesat at eqeulibrium This proress is also Knoun as the flcat zone process parthcalavly in semiconductor met material pro cess i