Precious stone Structures

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Slide 1

´╗┐Precious stone Structures Types of gem structures Face focused cubic (FCC) Body focused cubic (BCC) Hexagonal close pressed (HCP) Close Packed Structures Different Packing of HCP and FCC Crystallographic Directions and Planes cubic frameworks

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Face Centered Cubic (FCC) Atoms are organized at the corners and focal point of every 3D square face of the cell. Particles are expected to touch along face diagonals

Slide 3

Face Centered Cubic (FCC) The cross section parameter, a , is identified with the span of the molecule in the cell through: Coordination number: the quantity of closest neighbors to any iota. For FCC frameworks, the coordination number is 12.

Slide 4

Face Centered Cubic (FCC) Atomic Packing Factor: the proportion of nuclear circle volume to unit cell volume, expecting a hard circle display. FCC frameworks have an APF of 0.74, the greatest pressing for a framework in which all circles have break even with distance across.

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Body Centered Cubic Atoms are orchestrated at the edges of the solid shape with another particle at the 3D square focus.

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Body Centered Cubic Since molecules are expected to touch along the 3D square slanting in BCC, the grid parameter is identified with nuclear range through:

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Body Centered Cubic Coordination number for BCC is 8. Every middle iota is encompassed by the eight corner particles. The lower coordination number additionally brings about a somewhat bring down APF for BCC structures. BCC has an APF of 0.68, as opposed to 0.74 in FCC

Slide 8

Hexagonal Close Packed Cell of a HCP cross section is imagined as a top and base plane of 7 particles, framing a standard hexagon around a focal iota. In the middle of these planes is a half-hexagon of 3 iotas.

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Hexagonal Close Packed There are two cross section parameters in HCP, an and c , speaking to the basal and stature parameters separately. In the perfect case, the c/a proportion is 1.633, in any case, deviations do happen. Coordination number and APF for HCP are precisely the same as those for FCC: 12 and 0.74 individually. This is on account of they are both viewed as close pressed structures.

Slide 10

Close Packed Structures Even however FCC and HCP are close pressed structures, they are very extraordinary in the way of stacking their nearby stuffed planes. Close pressed stacking in HCP happens along the c bearing ( the (0001) plane). FCC close pressed planes are along the (111). To begin with plane is pictured as a particle encompassed by 6 closest neighbors in both HCP and FCC.

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Close Packed Structures The second plane in both HCP and FCC is arranged in the "openings" over the primary plane of molecules. Two conceivable arrangements for the third plane of iotas Third plane is put specifically over the primary plane of particles ABA stacking - HCP structure Third plane is set over the "openings" of the main plane not secured by the second plane ABC stacking - FCC structure

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Close Packed Structures

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Crystallographic Directions Cubic frameworks headings are named based upon the projection of a vector from the birthplace of the gem to another point in the phone. Expectedly, a right hand Cartesian organize framework is utilized. The picked source is subjective, however is constantly chosen for the simplest answer for the issue.

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Crystallographic Directions Points inside the grid are composed in the shape h,k,l, where the three records compare to the portion of the cross section parameters in the x,y,z bearing.

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Miller Indices Procedure for composing bearings in Miller Indices Determine the directions of the two focuses in the course. (Improved in the event that one of the focuses is the cause). Subtract the directions of the second point from those of the first. Clear divisions to give least whole number qualities for all directions

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Miller Indices are composed in square sections without commas (ex: [hkl]) Negative qualities are composed with a bar over the number. Ex: if h<0 then the heading is

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Miller Indices Crystallographic Planes Identify the organize captures of the plane the directions at which the plane blocks the x, y and z tomahawks. In the event that a plane is parallel to a pivot, its block is taken as ┬ą . On the off chance that a plane goes through the root, pick a comparable plane, or move the starting point Take the complementary of the captures

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Miller Indices Clear portions because of the proportional, however don't diminish to most minimal number qualities. Planes are composed in enclosures, with bars over the negative records. Ex: (hkl) or if h<0 then it gets to be ex: plane An is parallel to x, and captures y and z at 1, and in this manner is the (011). Plane B goes through the source, so the starting point is moved to O', along these lines making the plane the

Slide 19

Miller Indices

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