School of GeoSciences

Cathodoluminescence

When bombarded with high energy electrons, epoxy resins give off light in the visible region of the spectrum. This light can dominate the cathodoluminescence of some minerals and should be minimised or eliminated.

 

Sample preparation

Ten of the resins were mounted into a specially made aluminium block with twenty, 2mm holes, each hole being filled with a different resin. The resins were mixed and cured according to the manufacturers specification by first mounting the high temperature cure resins followed by the cold cure, allowing sufficient cure time. There was no post cure heating of any of the resins. Zircon and apatite crystals were also mounted to compare their cathodoluminescence with the resins. The zircon (91500) was mounted in epothin and the apatite (Durango) in specifix. Araldite, Araldite rapid set, Varian Torr Seal and the Beuhler hot press mounts were not tested.

The Al-mount was then ground using 1200, 2500 and 4000 silicon carbide paper with water. It was then polished with 6, 3 and 1 micron diamond (Buehler Metadi Supreme diamond suspension) and then washed and ultrasonically cleaned with Pet-ether (Poduct spec). The samples were finally cleaned with ethanol prior to carbon coating using a Denton (BTT-IV) coater to produce a thin conducting film across the sample surface.

 

Analytical Procedure

The cathodoluminescence of the resins were measured using a Philips XL30CP Scanning Electron Microscope (SEM) with a KE-cathodoluminescence detector. All images were acquired at 20kV and a beam current of 5nA measured in a Faraday cup using a Keithley picoammeter (model 486).

Image acquisition time was 32.5 seconds. The grey level was adjusted so that a fragment of 91500 zircon mounted in a block of Epothin gave a white level of 256 on the zircon and a grey level of 0 on the Al sample holder. The contrast and brightness were not adjusted after this calibration. An image of each resin was acquired under identical instrumental conditions in a single slow scan.

Only areas that were void of bubbles and were representative of the sample were selected for grey level analysis. The analysis was conducted using XL-Docu whereby an average of 230 pixels were selected in the centre of resin from which an average was calculated.

 

Results

 Epoxy Resin

Average Grey Value (0-255)

Cathodoluminescence Image

Petropoxy 18
Petropoxy Specimen
EpoxiCure (Cured at 55'C) 58
EpoxiCure Specimen
EpoThin 69
EpoThin Specimen
EpoFix 82
Epofix Specimen
EpoHeat 86
EpoHeat Specimen
Ciba Geigy  MY778 & HY951 127
Ciba Geigy
SpeciFix-20 144
Specifix 20
Robnor Resin  PX771c 255
Robnor Resin
Korapox 439 255
Korapox
Zircon (mounted in EpoThin) 255
Zircon Specimen
Apatite (mounted in Specifix 20) 255
Photo of Apatite Specimen