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Crystalline and Non-crystalline Materials report.pptx
1. Crystalline and Non-crystalline
Materials
TOPIC OUTLINE:
• SINGLE CRYSTALS
• POLYCRYSTALLINE MATERIALS
• ANISOTROPY
• X-RAY DIFFRACTION: DETERMINATION OF CRYSTAL
STRUCTURES
• NONCRYSTALLINE SOLIDS
2. SINGLE CRYSTALS
- For a crystalline solid, when the periodic and repeated
arrangement of atoms is perfect or extends throughout the
entirety of the specimen without interruption, the result is a
single crystal. All unit cells interlock in the same way and
have the same orientation. Single crystals exist in nature,
but they may also be produced artificially. They are
ordinarily difficult to grow, because the environment must
be carefully controlled.
3. POLYCRYSTALLINE MATERIALS
- Most crystalline solids are composed of a collection of
many small crystals or grains; such materials are termed
polycrystalline. Various stages in the solidification of a
polycrystalline specimen are represented schematically in
Figure 3.35. Initially, small crystals or nuclei form at
various positions. These have random crystallographic
orientations, as indicated by the square grids. The small
grains grow by the successive addition from the
surrounding liquid of atoms to the structure of each. The
extremities of adjacent grains impinge on one another as
the solidification process approaches
Editor's Notes
Single crystals essential for many modern technologies, such as microcircuits, and they have a distinct geometric shape that is indicative of the crystal structure. It is interesting to note that single crystal exist in nature, as well as being artificially produced. It is also fascinating to think that in order to have a perfect and uninterrupted arrangement of atoms, a lot of care and precision must be taken in the environment in which these crystals are grown.
This sentence explains the process of solidification in polycrystalline materials. Polycrystalline materials are composed of many small crystals or grains, and the solidification process begins with the formation of small crystals or nuclei at various positions. These nuclei have random crystallographic orientations, as indicated by the square grids. As the solidification process progresses, the small grains grow by the successive addition of atoms to the structure of each grain from the surrounding liquid. The extremities of adjacent grains touch each other as the solidification process nears completion.
Small crystallite nuclei. (b) Growth of the crystallites; the obstruction of some grains that are adjacent to one another is also shown. (c) Upon completion of solidification, grains having irregular shapes have formed. (d) The grain structure as it would appear under the microscope; dark lines are the grain boundaries. completion.
This sentence is describing the various stages of solidification for a polycrystalline material. Stage (a) shows small crystallite nuclei forming in the material, which then grow in stage (b). Stage (c) shows the grains forming with irregular shapes, and stage (d) shows how the grain structure looks under a microscope, with the dark lines indicating grain boundaries. Upon completion of solidification, the crystallographic orientation of each grain will vary, and there will be an atomic mismatch in the region where two grains meet, which is known as a grain boundary.
