GLY433/533
SEM Laboratory
Part I: Introduction
to the Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer
(EDS) by Peter Bush, director of the laboratory
Electron
optics
Interaction of electron beam with specimen
Secondary electrons
Backscattered electrons
X-rays
Auger electrons
Energy dispersive spectrometer (EDS)
Wave-length dispersive spectrometer (WDS)
Part
II: Sample inspection and preparation. The purpose of this exercises
is to give you some experience in:
a. Stereo microscope viewing
b.
Sample labeling
c.
Carbon coating
Samples of tephra from four samples representing different classic eruptions
are mounted on a stub for SEM viewing and analysis. Carefully examine some
unmounted grains with a stereo microscope and describe the grain charaxteristics
(and identiy if possible) in your notebook. The mounted grains have
been photographed before carbon coating and this image will be available
for you to use as a map.
The
samples are:
a.
COT-0301A Cotopaxi
b. MSH-8405
Mount St. Helens
Part
III: Introduction to the instrument
Click here to see the
various instruments in the South
Campus Instrument Center.
The techniques that
you will practice today include:
a.
Loading the sample
b.
Viewing the sample
c.
Saving the image
d.
Making an EDS analysis
Part IV: Hands-on
SEM analysis of the pyroclasts that you mounted
a.
Examine
each particle from the four samples with the SEM
b.
Choose
an appropriate magnification and make a digital image of each grain
c.
Use
the EDAX to get a general composition of the various particles and sub-particles.
d.
For
the appropriategrains describe their bubble structure and microlite texture.
Then make an interpretation of the features that you see in terms of eruption
dynamics in the conduit. All of the examined images and data will be available
on the web site for analysis following the lab.
Part V: Homework
exercise on “unknown” grains
You have available data
from a single stub divided into four areas. Each area contains five grains
selected to show a variety of types from their sample and deposit. These
four stub areas represent four unique deposits:
1)
1888-90 Vulcanian deposit of Vulcano, Sicily
2) 1906 blast deposit of Ksudach Volcano, Kamchatka
3) 1964 debris flow of Shiveluch Volcano, Kamchatka
4) 1965 surge beds of Surtsey Volcano
You
can view the images and their EDX spectra in the
Image
file. In the week following your laboratory work you should analyze
this data make a report giving your results. Besides the identification
of each particle you should identify which area on the stub is occupied
by each of the four deposits listed above. Please give the reasoning for
your conclusions.