X-Ray Diffraction

Carleton College has Philps PW 18??

Sample Preparation techniques

SAMPLE PREPARATION FOR POWDER DIFFRACTION

In order to obtain a diffraction pattern of a mineral you must grind and sieve your sample to <270 mesh and then mount it in the Philips sample holder.

1. Coarse grinding. Use the “Little Smasher” to reduce the size of larger chips to approximately sand-size (less than 1 or 2 mm).

2. Transfer no more than about 2 grams of the coarse grind to the steel container for grinding in the Spex Mixer. The container should be no more than 20% full.

3. Add a steel ball to the container and put on the lid.

4. Mount the grinding container into the mixer, fasten snugly, close the lid and turn on the mixer for at least 5 minutes. Hard samples may require a longer grinding time.

5. After grinding is complete, transfer the powder to a piece of weighing paper and sieve it through the 270 mesh sieve.

6. Be sure to clean the grinding vessel thoroughly with a Kimwipe and acetone so the next person does not have to clean up after you.

7. If insufficient sample was reduced to <270 mesh, return the oversize fraction to the grinder for another run.

8. Mount the powder in the sample holder according to the procedure in the Philips manual in the drawer beneath the sample preparation materials.

9. Clean the mounting materials and put them away.

10. Please clean the tables, take your samples and your stuff.

PROCEDURE FOR IDENTIFYING UNKNOW N MINERALS BY X-RAY DEFRACTION

Once you have obtained both a printout of the x-ray data file and a plot of the pattern for your unknown mineral, you can key out its identification using the following procedure:

1. Identify the three most intense peaks from the printed peaks file and note the d-spacing for each.

2. In the volume for keying out minerals (Fink Index), find the section containing the d-spacing of the most intense peak.

3. Within that section scan down the second column until you find the d-spacing of the second most intense peak.

4. Compare the values for the three most intense peaks with those minerals listed in the immediate vicinity; usually a total of 6 or 8 possibilities.

5. See how the next 5 most intense peaks in the book compare with your data. Usually one or two minerals will emerge as most likely candidates. Look at the file number printed on the right side of the row for these minerals and find the appropriate file card in the black volumes (Vol. 1 – sets 1-5; Vol. 2 – sets 6-10). Compare your pattern with the pattern printed on the cards. By looking at both the d-spacings and relative intensities you should be able to make a determination. Keep in mind, however, that d-spacing values are more important than the exact ranking of relative intensities for mineral identification. After all, d-spacings relate directly to the crystal structure. Relative intensities, on the other hand, are subject to more variation depending on sample preparation and run conditions. As a result, when your strongest peak intensities are within about 20% of each other, you may need to consider alternative rankings of the peak intensities in order to correctly key out the mineral.

6. Most common minerals are listed in these two volumes, but for uncommon minerals you may have to rely only on the eight most intense lines in the key book.

7. Remember that minerals that undergo solid solution may be difficult to key out owing to a range of d-spacing values. These minerals may be given on several cards covering several different compositions.
Instructions for Operation of the Phillips PW 1800 X-Ray Diffraction Machine

Carleton College Geology Department
Last Updated:
January 21,2003

NOTE: Before beginning these directions, it is important to know the big mistakes to guard against when running this instrument.

The following things will cause serious harm to the instrument:
Running the XRD without the Chiller On – This causes it to overhear. Bad.
Turning off the High Voltage without steppe down the voltages – This will damage the X-ray lamp. Bad.
Not stepping in between voltages: This wears down the lamp – which is very expensive. Bad.
Keep these things in mind when running the instrument and you should be fine.
Getting to the Instrument:

1) The XRD is down in the basement. Get the key from the cabinet where the keys are kept. Remember that the department’s police is that no lab work be done between the hours of 11 PM and 6 AM or when you are tired.
Starting the Instrument:

2) Turn the Chiller On – IMPORTANT
{The chiller is located in the closet at the back of the room. There is only one switch on the machine.}
[The chiller keeps the components of the XRD from overheating, burning up, or exploding]

3) Turn on the computer, monitor and printer {All located next to the XRD. The switch for the monitor is near the front on the bottom right. The computer power is below the CD drive.}

4) Turn on the XRD
{The ON button is located on the front near the bottom left corner.}

5) Open PC_APD on the Computer
{PC_APD is located in the ‘Phillips XRD’ folder in Program Manager}
[press <anykey> to get to the main screen]

6) Turn on the high voltage (HV).
{This button is to the right of the power button.}
[This applies voltage and current to the X-ray lamp. Note that the settings come up on the LED’s, which should read: 14 kV and 10 MA. Also note that turning on the HV activates the X-ray warning light on top of the machine. This is to let you know that there are X-rays spilling around inside the instrument. DO NOT OPWN THE XRD’S PANELS WITH THE HV ON.]

7) Step up the voltages {In PC-APD on the computer} If you are running “Geochem” program. The following steps need not be done.
Go to the Utilities Menu.
Go to Diffractometer Commands.
This will bring you to a prompt which looks like “C=”
Slowly step up the voltages by entering a sequence, one line at a time, like the one below:
skm 30 10 <enter>
skm 40 15 <enter>
skm 45 20 <enter>
skm 45 30 <enter>
skm 45 40 <enter>
After each line, check to make sure that the numbers on the front of the XRD match what you set. Your final voltage setting should 45 kV and 40 mA. This is what it should read on the front of the instrument.
Press <Esc> twice to return to the main menu.
[This step slowly increases the potential applied to plate in the X-Ray lamp. It’s important to do this in steps rather than all at once to avoid searing out the lamp. REMEMBER TO STEP THE VOLTAGE BACK DOWN BEFORE TURNING THE INSTRUMENT OFF. If you mistype a line or try to backspace, the computer will prompt you with the previous voltage like so:
**1 Invalid argument
Milliamp = 20 :=
If this happens just type the value you wanted and hit enter.
If the prompt reads “ @=” you are talking to the machine itself, rather than the control card. This is bad and you should have somebody take a look at the instrument.]
You are now ready to run samples.

Running Samples
8) Go into the Data Collection menu.

9) Go into the Identify Measurement menu.

[This is the most useful mode for simply identifying the constituents of a sample. Other analyses will require different modes.]
The machine will prompt you for a method. Hit <F5> to list the available methods. For most analyses the method called Identify should work. F1 = “go to item”

10) Load your sample. {Onto the tray in the front of the XRD, sample side up.}

10a. The computor will ask you for a prgram file, and”Geochem” should be in the lower right corner. If not F5 show names will help you locate the prgram “geochem”

11) Type a sample identification and data file name. Hit F1 to run the sample.
{File names cannot be longer than 8 letters.}

12) To Display your sample while running:
Go back to Data Collection
Select Display Scan
[This will show a plot of your data as it comes in. You may have to wait until the actual scan begins before this option will work.]

Printing Samples

13) Go into the Graphics menu {From the main menu.}
14) Select your file.

Press <F3> to delete any old files listed.
You can either type the name of your file or hit <F5> to show a list of options.

15) Hit <F1> for 2D plot.

16) To Label Peaks, Hit <F2>

You can move the cursor around to the point where you want the label. Pressing <F9> will change the amount the cursor move each time you press an arrow key.
Press <F1> to set the position of the label.
Press <F2> to select the type of label ( <+> or <-> to cycle through options)
If the label looks like its in a funny place, put the cursor on it, hit <F5> move the cursor to where you want to label and hit <F1>.
Hit <esc> to return to the printing screen.
17) Hit <F9> to print your spectrum.
[The software will prompt you for the Caption at the top of the plot.]

Identifying Peaks
This option will automatically generate a list of all the major peaks in your spectrum.

18). Double click on Phillips X-pert Graphics and Identify
19) Open file from PC-APD
20) Find your FileName.RD
21) Scanned graph will appear on the screen
22) Go to analyses
23) Peak Search
24) Selected Peak Search Parameter list
25) As Measured intensities
26) Print

The print out will be a table of all the d values for the peaks in your scan.
Using these d values, identify your unknown from the JCPDS

SHUTDOWN
1) Remove any samples from the instrument’s tray.

[Failure to do this will result in a disturbing, but mostly harmless alarm when you turn off the HV.]

2) Step down the voltages {In PC-APD}

Go to the Utilities Menu.
Go to the Diffractometer Commands.
This will bring you up a prompt which looks like “ C=”.
Slowly step down the voltages by entering a sequence, one line at a time like the one below:
skm 45 30 <enter>
skm 45 20 <enter>
skm 45 15 <enter>
skm 30 10 <enter>
skm 15 10 <enter>
After each line check to make sure that the numbers on the front of the XRD match what you set. After your final voltage should be 15 kV and 10 ma. This is what you should read on the front of the instrument.
Press <esc> twice to return to the main menu.
[This step restores the original, low potential applied to the places in the X-Ray lamp. It is important that you do this in steps rather than all at once to avoid wearing out the lamp. If you mistype a line, the computer will prompt you with the previous voltage.]

3) Exit PC-APD
Choose Exit from the main menu

3a. Until everybody is done we are not going to turn the XRD off. We will leave it under standby, 10Kv, 15Ma.

4) Turn the HV OFF.

5) Set the XRD to Standby {The bottom right next to the ON button (bottom left front panel)}

6) Decide what else to turn off.

If the XRD will be used again in the next week or so, feel free to leave both the chiller and the computer on.
If the XRD will not be used in the near future,
Shut down the computer:
Exit windows (File Menu ‡ Exit Windows)
Turn of the computer, monitor, and printer
Turn off the Chiller.
That’s it. For extra information, consult the nearby drawer of old manuals or talk to a faculty member.