jvdv
Harmless
Posts: 2
Registered: 10-6-2004
Member Is Offline
Mood: No Mood
|
|
Diamond
I'm sawing a diamond with a laser. The surface of the sawplane is black. Graphite? I want the surface to be transparent, so I need to remove the
layer of graphite. Polishing brings additional weightloss. Heating the diamond to 700-750°C removes the graphite but also affects the diamond
(surface burns and gets "milky" . Boiling the diamond in sulphuric acid
helps, but still a black layer remains. Ultrasonic cleaning: no result... Could electrolysis be the key? Can I somehow transform the graphite to CO,
CO2...????
Any suggestions more than welcome!
|
|
|
Marvin
National Hazard
Posts: 995
Registered: 13-10-2002
Member Is Offline
Mood: No Mood
|
|
Rumor has it that a hydrogen plasma (just a low pressure discharge) will etch back graphite preferentially to diamond.
What laser are you using? Being transparent and highly conductive thermally I'm curios as to what works.
Since diamond isnt conductive at ordinary temps I dont see how electrolysis could be made to work.
Is it possible the laser heating has affected the diamond beyond the surface?
|
|
|
Proteios
Hazard to Others
Posts: 109
Registered: 7-3-2004
Member Is Offline
Mood: No Mood
|
|
just a point of trivia......in one of the labs i worked in they were using a CO2 laser to melt metals at about 1-2000 C.... the laser was in the far
IR.... very powerful... and had diamond windows.... because they had excellent transmission... apparentaly to almost all EM radiation.
|
|
|
jvdv
Harmless
Posts: 2
Registered: 10-6-2004
Member Is Offline
Mood: No Mood
|
|
I'm not a laserguru, but I think it's a YAG, diode pumped system. It works at very low power (less than a regular household iron), but the
beam is extremely concentrated, and focus-depth is extremely limited. I suppose it's the heat that burns the diamond. Focusing slightly under the
surface at the start can cause the beam to reflect in the diamond and as a result shatter it to pieces (not a pretty sight;-). The diamond under the
graphite layer is not affected by the heat of the laser. It remains as hard as before and polishing characteristics remain unchanged.
Diamond and graphite are to my knowledge the only two cristal structures of pure carbon. So I suppose there is no transition zone between the diamond
and the graphite layer. But how to divide between the two layers????
|
|
|
Esplosivo
Hazard to Others
Posts: 491
Registered: 7-2-2004
Location: Mediterranean
Member Is Offline
Mood: Quantized
|
|
Besides diamond and graphite another form of carbon exists, which is known as amorphous carbon. This is probably also present in the black layer on
the diamond, since it is reported to occur by irradiation of diamonds by atoms - I know lasers do not emit atoms but maybe the high ionizing power
emitted by a laser might gimmic the results obtained by irradiation by atoms.
The link below may help you:
http://phycomp.technion.ac.il/~david/thesis/node12.html
[Edited on 10-6-2004 by Esplosivo]
Theory guides, experiment decides.
|
|
|
Proteios
Hazard to Others
Posts: 109
Registered: 7-3-2004
Member Is Offline
Mood: No Mood
|
|
shattering diamonds by heating is very hard work..... it has the highest thermal conductivity known!
One prospective use for CVD diamond (chemical vapor deposition)... is as a cooling condiut for CPU chips.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
