How and why did it break?

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Every year around this time, I teach a bunch of freshmen engineers in my university through a project that we call "How and why did it break?”. It is an effort to introduce them to failure analysis an important (and profitable) endeavor for engineers. I give them some broken items and they have to find what material they are made, how they were manufactured, and if possible why they broke. Their tools are … Google, a loupe, an optical microscope and a scanning electron microscope.  This year the items were a cork screw which broke in the cork, a veterinarian medical suture, a paper clip and the nib from an antique fountain pen.  The students don’t know that I am the one who enjoys this class the most.

Here are the photos from the broken tip of a fountain pen tip.  The nib is a Warranted 14K gold and at the tip the material is “iridium” – actually not iridium but a hard, wear resistant material like iridium, osmium, ruthenium or their alloys, etc.) .  Iridium was used in the early days but it was soon replaced by other less expensive materials.  The tip is welded to the nib by applying electrical current that heats up the tip and nib and locally partially melts the gold.  Sometimes this difficult weld is weak. In this sequence of photos we see an nib that lost its tip on one tine.

(1-2)  This is the pen nib with the 14K mark probably from late 30s early 40s.  The photo was taken by my mobile phone.  (not an iphone)

(3) Magnified view of the tip taken by my phone through an optical microscope.

(4) This is the scanning electron microscope with the students – it uses electrons rather than light.

(5) X-ray spectrum cause by electrons that collide with the material we examine.  Here is shows maybe gold (Au), Copper (Cu) and a little bit of silver (Ag).

(6) Detail of the tip under the electron microscope.

(7) This is the nib tip.  It should be smooth for proper writing but what seems smooth in the eye or feels smooth in the hand it is never totally smooth.  Here it is slightly rougher than usual.

(8) This is the spectrum from the tip of the nib.  It shows mainly Ruthenium and a hint of tungsten, also some  salts maybe KCl and NaCl – probably from residuals of ink(?)

(9)No, it is not the comet Philae, it is the tip of the nib. Incidentally, the microscope can increase this magnification by  200-1000 times.

Now, probably you understand why I am enjoying this class more than the students.

This is a good opportunity to look at a prior picture also.