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
|