Alloy A mixture of two or more elements or compounds Cu Sn Cu Zn Pb Sn Fe C Bronze Brass Solder Carbon Steel Where do metals come from in the rst place and how do we mix them 1 Where You Can Find Metallic Iron it s out of this world 2 Where Iron Ore Comes From 3 Making Steel 4 The Washington Monument and its Lightening Rod 5 Aluminum SmelTng Turning Al2O3 into Al metal using Hall Cells 6 IntersTTal Solid SoluTons IntersTTal solid soluTons when the solute atoms are much smaller than the host For example carbon r 0 071 nm mixed with iron r 0 124 nm As the name suggests solute atoms reside at intersTTal sites in the crystal la ce Generally the host la ce can accommodate only a small amount of the solute more details to come 7 SubsTtuTonal Solid SoluTons When the host la ce and the solute atoms are of similar size within about 15 and have the same crystal structure the solute atoms may sit at the host s la ce sites forming a solid soluTon Nickel and copper readily form solid soluTons whereas the solubility of silver in copper and copper in silver is limited due to their di erent atomic radius 8 A SubsTtuTonal Solid SoluTon 9 Solid SoluTons in Ionic Compounds Now we have the added twist that charge neutrality must be maintained in addiTon to nding solute ions of similar size Consider LiF r Li 0 068 nm r F 0 133 nm Candidate ions to subsTtute for Li include Ionic Radius nm Cs 0 170 K 0 138 Na 0 102 Mg2 0 072 Looks like Mg2 is the best t but it has a 2 charge rather than 1 10 F How can we maintain charge neutrality 11 LiF crystal structure 12 This is not a Schogky defect which is a Li vacancy paired with a F vacancy but rather a vacancy that forms to maintain charge neutrality due to the introducTon of an aliovalent solute Compounds like CaO are alloyed with ZrO2 to increase the concentraTon of oxygen vacancies in the ZrO2 This makes its response Tme faster when it is used as an oxygen sensor or increases its performance as a fuel cell membrane due to its ability to allow rapid di usion of oxygen ions 13
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