Sciencemadness Discussion Board - Pt with Hf

Pt with Hf

aeacfm - 26-12-2011 at 00:54

we measure sand % (as silicon dioxide) in our labs by dissolving sample with Hf in pt crucible and calculate the weight loss then determine sand %

in the last period the results looks hazy and fluctuated

and we find that when Hf heated a lone in the crucible it got increase in weight !!!!

we find also that the weight of the crucible decreased from its original wt .....!!!!

does this mean a reaction occur between Pt crucible and Hf and so ppt in the crucible ???

LanthanumK - 26-12-2011 at 04:39

This website states the following: "Some materials resist the corrosive action of the acid, such as platinum, wax, polypropylene, polyethylene, and Teflon."

http://corrosion-doctors.org/Acids/Hydrofluoric.htm

Unless your hydrofluoric acid was impure, no platinum should have dissolved.

[Edited on 26-12-2011 by LanthanumK]

Bot0nist - 26-12-2011 at 05:45

Or the Pt crucible has non platinum impurities.

[Edited on 26-12-2011 by Bot0nist]

Neil - 26-12-2011 at 05:52

Or the Pt crucible has a surface imperfection and the Hf is getting to the nickle underneath.

Are you suurrreeee you are using pure Pt and not Pt coated nickle? I had a friend who had an exciting deviation on an experiment when a crucible full of material in an induction heater turned out to be a Nickle coated Pt crucible not pure Pt.

Apparently they managed to chip the slag/nickle/bits of Pt out without to much damage to the furnace.

AJKOER - 26-12-2011 at 06:11

Before seeking a chemical related explanation, check out your scale.

If you have access to more than one scale, use a different scale to verify results of weight gain. If not, perform some test weightings on a truly inert object in the weight range of your filled crucible. Repeat several times at different times of the day and heat the test object. This would address any variations due to electric wattage flow (assuming an electric scale), temperature sensitivity to the scale of a hot object and humidity variances. Also, operator error could be an issue with respect to placement positions on the scale and force with which object is place.

Chemical explanation not address include some oxide formation or reaction with heating gases most likely from new impurities now in the sand. Heating in a nitrogen enclosure one way to check and also vary heat source.

Other reason is that repeated heating enlarges new cracks in the now old crucible and it just accumulates hard to clean residue (solution, try a different crucible).

Good luck.

[Edited on 26-12-2011 by AJKOER]

bbartlog - 26-12-2011 at 07:05

Opened the thread thinking I would read something interesting about Hafnium. Disappointed. HF != Hf.

aeacfm - 26-12-2011 at 14:16

Quote: Originally posted by Neil

Or the Pt crucible has a surface imperfection and the Hf is getting to the nickle underneath.

Are you suurrreeee you are using pure Pt and not Pt coated nickle? I had a friend who had an exciting deviation on an experiment when a crucible full of material in an induction heater turned out to be a Nickle coated Pt crucible not pure Pt.

Apparently they managed to chip the slag/nickle/bits of Pt out without to much damage to the furnace.

NNNNNNNNOOOOOOOOOO

it is pure Pt
its wt was 21.7451 when first purchsed
now it is 21.7021
what happened ????
erosion ???
corrosion ????
chemical dissolution ????
complex formation ????

Ephoton - 26-12-2011 at 16:38

I would say that the Silicon Dioxide is oxidising the HF to a small degree making HOF which does eat
Pt at high temps.

ie your making an oxidising halogen acid somehow and this will eat platinum at higher temps.

I say this as from what you have posted the Silicon Dioxide is the only source of oxygen other than
the atmosphere.

maby heat your crucible with HF in it under a reducing enviroment.

it could also be that your HF has let some F2 out into the solution also making HOF as HCl does "the reason it goes greeny yellow over time" I belive that HF is less likely to do this due to its extreamly strong bond to Hydrogen but still it is a halide so there would be some equalibrium I would think.

[Edited on 27-12-2011 by Ephoton]

phlogiston - 27-12-2011 at 16:37

Quote:

in the last period the results looks hazy and fluctuated

So, if it did work at first but you are getting fluctating results now, check what changes were made to the protocol/materials just before you started to encounter problems? Check lab notes, log books, etc.
Are you using the same crucible and HF as before?

[Edited on 28-12-2011 by phlogiston]

aeacfm - 28-12-2011 at 03:09

Quote: Originally posted by phlogiston

Quote:

in the last period the results looks hazy and fluctuated

yes , i am using the same crucible (Pt crucible) , the same HF (40% from the same vendor) but a problem encountered with it that when heating and evaporating it a lone in the crucible ( with no sample) it precipitate 0.004 grams , from where these 0.004 grams came ?????????

note :
these 0.004 gram consists 10% error because we take 0.04 gram sample while measuring

[Edited on 28-12-2011 by aeacfm]

Endimion17 - 28-12-2011 at 03:36

Moderators should rename this thread. I honestly thought it was about an alloy of platinum and hafnium.

aeacfm, if you really work in the lab, you should know how a formula of hydrofluoric acid is written. It's like talking about carbon(II) oxide and writing a formula: Co (cobalt).

aeacfm - 28-12-2011 at 03:39

Quote: Originally posted by Endimion17

Moderators should rename this thread. I honestly thought it was about an alloy of platinum and hafnium.

aeacfm, if you really work in the lab, you should know how a formula of hydrofluoric acid is written. It's like talking about carbon(II) oxide and writing a formula: Co (cobalt).

sorry , I was urgently........... just a mistake