II.2.3. X-ray diffraction (XRD)

XRD is one of the most powerful techniques for qualitative and quantitative analysis of crystalline compounds.

The technique provides information that cannot be obtained by any other way. The information obtained includes types and nature of crystalline phases present, structural make-up of phases, degrees of crystallites, amount of amorphous content, microstructure size and orientation of crystallites.

Figure 5: Simple theory of XRD analysis[13].

Figure 5 shows the principle of XRD.

In this work the crystalline phases of the catalysts as well as crystalline sizes were determined by powder X-ray diffraction.

A Siemens D-500 X-ray diffractometer with nickel-filtered CuKα₁ radiation was used to record the X-ray powder diffraction (XRD) patterns of the samples. The XRD profiles were collected between 2θ = 20 – 100˚., at a step scan of 0.05˚ counting 3˚at each step. The mean crystallite size of cobalt and copper particles was calculated with the Debye-Scherrer equation,

t=Kλ /  β cos( θ)

where K is the shape factor, λ is the x-ray wevelength, β is the line broadening at half the maximum intensity in radians and θ is the Bragg angle.

For catalysts prepared by microwave method the following experimental conditions were used:

PANalytical X’Pert PRO MPD Alpha1 powder diffractometer (radius = 240 millimetres)

Cu K₁ radiation ( = 1.5406 Å).

Work power: 45 kV – 40 mA.

Focalizing Ge (111) primary monochromator

Sample spinning at 2 revolutions per second.

Variable automatic divergence slit to get an illuminated length in the beam direction of 10 millimetres.

Mask defining a length of the beam over the sample in the axial direction of 12 millimetres

Diffracted beam 0.04 radians Soller slits

X’Celerator Detector: Active length = 2.122 º; PHD lower level: 45% (iron discrimination)

/2 scan from 4 to 100º 2 with step size of 0.017º and measuring time of 150 seconds per step.