Crystallographic Centenary Celebration

It’s a 100 years since something to do with the Bragg’s discovery of X-rays. The Royal Society have made a cartoon about it.

Shear Relief

I’m very happy that my paper was accepted for publication in Metallurgical and Materials Transactions A. It took a long time from performing the experiment to presenting the results, mainly because I needed to repeat the analysis which was something I wasn’t able to make time for until I had to submit the thesis.

Surface relief caused by shear transformation of bainite

Surface relief caused by shear transformation of bainite

In the paper atomic force microscopy is used to measure the shear component of extremely thin plates of bainitic ferrite in superbainite. The shear component is surprisingly large compared to the value we expected of 0.23–0.28 based on previous experiments carried out after transformation at higher temperatures (such as the results by Swallow and Bhadeshia).

It seems like the higher strain may help to explain why the bainitic ferrite plates are so thin and slender. It would now be really interesting to test if that is true or not, which is something I couldn’t really do by looking at the TEM and SEM images I have already.

More details on my web-page at Mathew Peet| Papers| Surface Relief Due to Bainite Transformation at 200°C

Article is currently available electronically by using DOI

Ferrite crystal structure in cmd format for jmol


<?xml version="1.0"?>
<molecule xmlns="http://www.xml-cml.org/schema">
<crystal>
<scalar title="a">2.882</scalar>
<scalar title="b">2.882</scalar>
<scalar title="c">2.882</scalar>
<scalar title="alpha">90.00</scalar>
<scalar title="beta">90.00</scalar>
<scalar title="gamma">90.00</scalar>
</crystal>
<atomArray>
<atom id="Fe1" xFract="0.0" yFract="0.0" zFract="0.0" elementType="Fe"/>
<atom id="Fe2" xFract="0.5" yFract="0.5" zFract="0.5" elementType="Fe"/>
</atomArray>
</molecule>

After viewing cmlexplained.
Jmol is a an open-source Java viewer for chemical structures

Density of Iron Carbide (Fe3C)

There are 4 molecules of Fe3C per unit cell. The cell is orthorombic, typical lattice parameters at room temperature are given below from Mehl etal, Trans AIMME, 1933.

Mass
——-

m = mass of 1 mole of unit cells
= 12 x FeRAM + 4 x CRAM
= 12 x 55.845 + 4 x 12.011 = 670.14 + 48.044
= 718.184 g/mol

Fe3C unit cell is 718.184 g/mol

Volume
——-
v = volume of 1 mole of unit cells
= AV x a x b x c
= 6.0221415 × 1023 x 4.518 x 5.069 x 6.736 x 10-30
= 9.2901×10-5 m3

Density
——-
d = density
= m/v
= 0.71814 kg / 9.2901 x 10-5 m3
= 7730.14 kg/m3

View FCC Austenite in three dimensions

Channel 4 seem to be showing some 3d programs on t.v. the consequence is you can get 3d glasses for free in sainsburys, and you can use them with the Jmol sorfware to view molecular models in three dimensions.

3 dimensional model of 2 FCC unit cells

2 FCC unit cells (click image to enlarge)

Using GSAS and EXPGUI in debian

EXPGUI is a graphical interface for the GSAS software, allowing structural refinement using the Reitveld technique.

EXPGUI/GSAS can be downloaded in binary form from http://www.ncnr.nist.gov/programs/crystallography/software/downloads.html

You need to install tcl/tk and also blt all of which can be found in debian package repositories. (Or whatever for your system!)

in debian:
apt-get tk8.4 blt

tcl/tk is the scripting language used to write EXPGUI.
failing to install blt will result in the error “Error — Unable to load the BLT package; cannot run liveplot”.

View crystal structures

There is a very nice java package which lets you view crystal structures on any computer platform that supports java (Linux, Mac, etc).

Jmol can be downloaded from sourceforge here. Download the latest binary or full package, unpack it and you are good to go.

Either cd into the directory and run ./jmol or add the directory to your $PATH environment and run jmol.

some molecule

I have a feeling I have referred to Jmol in a previous post but I think I’d only used it as an applet then.

The full version alloys export of the images to graphics formats, as well as lots of options that I don’t understand. You can view molecules in 3D if you have the proper pair of glasses, and you can load crystal structures in the xyz format from sites such as Crystal Lattice*Structures at the U.S. naval research laboratory (note this is very different to navel research). I’m particularly impressed by the ability to change the background colour to white, which is particularly useful if you ever want to print something.