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Graphite Monochromators

Graphite Monochromators

 

Momentive graphite monochromators are highly oriented forms of high purity pyrolytic graphite (PG) which diffract x-rays and neutrons with greater efficiency than any other material.  In x-ray analysis, intensity is increased 3 to 5 times over that obtained with conventionally used crystals.  A singly-bent focusing monochromator using graphite yields 3 times the intensity of lithium fluoride at equivalent resolution.  Momentive originally introduced, and still offers, graphite monochromotors with the lowest mosaic spread available.

 

 

Physical Characteristics (@300°K)

 

   Spacing of Reflecting Planes (002)

   3.355 - 3.359å

   Mosaic Spread

   >=0.4°

   Density

   2.255 - 2.265/cm3 

   Thermal Conductivity

  Parallel (002)
  Perpendicular (002)

   1600 - 2000 W/m-K
   ~8 W/m-K

   Thermal Expansion

  Parallel (002)
  Perpendicular (002)

   Slightly negative
   20 x 10-6/°C

   Electrical Resistivity

  Parallel (002)
  Perpendicular (002)

   3.5 - 4.5 x 10-5 ohm-cm
   0.15 - 0.25 ohm-cm

Mosaic spread is half maximum height peak width of the Cu-K a rocking curve

 

  

HOPG plates are produced as flat, singly-bent and doubly-bent shapes.  The monochromators are classified according to mosaic spread.

 

 

Standard Grades & Sizes

Grade

Mosaic Spread

Nom. Thickness
Tol. +0/-0.4 mm

Min. size
+/-0.2mm

Max. size
+/-0.2mm

ZYA

0.4° +/- 0.1°

2

12 x 12

50 x 75

ZYB

0.8° +/- 0.2°

2

12 x 12

50 x 75

ZYD

1.2° +/- 0.2°

2, 4

12 x 12

50 x 75

ZYH

3.5° +/- 1.5°

2, 4, 6, 8

12 x 12

75 x 75

 

Standards for Bent Monochromators

     Radii (mm)

  155, 225, 250, 510, 790, 1300

Size (mm)

   12 x 12, 20, 25, 40
   15 x 15, 25, 40, 50
   20 x 20, 25, 40, 50

   25 x 25, 40, 50, 75

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