07MANcrystalsolids - Crystalline Solids Revised: 8/12/04...

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Crystalline Solids Revised: 8/12/04 1 CRYSTALLINE SOLIDS Adapted from Experiments by A.B. Ellis et al, ICE OBJECTIVES To investigate materials containing cubic unit cells by studying three dimensional models and the properties of two crystalline solids: an alloy, NiTi, and a superconductor, YBa 2 Cu 3 O 7 . SAFETY PRECAUTIONS Safety goggles and lab aprons must be worn in lab at all times. Liquid nitrogen is extremely cold (–321°F!). Contact with skin may result in severe frostbite. If any liquid nitrogen spills on clothing, remove the clothing immediately, as the trapped liquid will cause severe frostbite to the skin beneath the clothing. Do not touch any metal dipped into liquid nitrogen until it has warmed to room temperature. Do not place liquid nitrogen in a closed container; it can rapidly expand and explosively shatter a container that is not properly vented. Use plastic tweezers to handle superconductors and rare earth magnets; the solids may be toxic. The solid state models contain small spheres and rods - if any are dropped on the floor, pick them up to prevent slips or falls. Wash your hands before leaving lab. Report any spills, accidents, or injuries to your TA. INTRODUCTION Many exciting discoveries are found at the interfaces between traditional scientific disciplines such as the interaction between researchers in chemistry, physics, and engineering that has led to the emerging field of material science: the study of the synthesis, composition, and properties of solids. In this experiment we will investigate the composition and properties of one class of material – crystalline solids containing cube-like building blocks called cubic unit cells. Primitive and body centered cubic unit cells are created from two different arrangements of square array layers. Layering of close packed arrays creates face centered cubic unit cells. (You
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Crystalline Solids Revised: 8/12/04 2 should read “Crystal Structures with Cubic Unit Cells” before proceeding further.) Students will investigate models to determine composition and observe the properties of actual samples of a metal alloy called nitinol and a superconductor with the formula YBa 2 Cu 3 O 7 . Nitinol (NiTi) “Smart” materials have the ability to respond to physical stimulus in a predictable, preprogrammed way. One such material, the metal alloy NiTi, is called a “memory metal” because it can be twisted or bent without causing crystal defects and returns to its original shape when heated. This alloy is referred to as "nitinol", a name derived from the lab where it was discovered in 1965: Ni ckel Ti tanium - N aval O rdinance L aboratory. At high temperatures, the atoms of the nitinol are arranged in the orderly crystalline austenite form that resists distortion. At low temperatures, the atoms of nitinol are arranged in the more disordered
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07MANcrystalsolids - Crystalline Solids Revised: 8/12/04...

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