Reduction of NiO
Daniel Monceau
Just From a knowledge of high temperature oxidation and
thermodynamics :
-at 1100°C, you have to decrease the oxygen partial pressure
of oxygen below 1E-10 atmospheres (see Ellingham diagram)
To reduce the PO2 under 1E-10 atm, you have to use a very good
vaccum (not very easy to do). The best way to do it is to use
an atmosphere with a low equilibrium value of PO2:
mixture between CO and CO2, or H2 and H2O. If you use
a flow of pure CO, obviously, you can prevent the oxidation.
-from a kinetic point of view, decreasing PO2 will decrease the
thickness of your oxide scale, as diffusion in NiO is decreasing
with decresing PO2 (I can give you more details if you want)
======================================================
Daniel Monceau
Ecole Nationale Supérieure de Chimie de Toulouse (ENSCT)
DMON...@ENSCT.FR
======================================================
>----------
>De : Henry_L...@brushwellman.com[SMTP:Henry_L...@brushwellman.com]
>Date : mardi 30 septembre 1997 13:46
>A : metall...@mtu.edu
>Objet : Reduction of NiO
>
>
>A question I hope someone can help me with.
>
>If I cast a Nickel containing alloy using element nickel I am introducing
>NiO into the melt on the surface of the elemental Nickel.
>
>Will using a Carbon Monoxide cover reduce the NiO if I am casting at
>approximate 1100-1200 C? What about casting in a vacuum, will the NiO be
>reduced with the oxygen coming out of the melt?
>
>Any experience or thoughts is appreciated.
>
>Hank Grohman
>
>
>
>
Doug Swinbourne
> You don't seem to be a metallurgist which means you're happier than the
> rest of us and your chances for re-employment during the corporate turmoil
> are better. Well, let me pull you a bit on our side.
So there is corporate turmoil in the US of A too eh?? We in Australia
are experiencing the same sort of insanity! I've seen so many very
good young engineers and researchers given the sack in the name of
economic rationalism. Rational? Ha!
Still, this seems to be the way corporations think..... cost
problems? sack labour! develop new products, new ways? what for??
Doug
Dr.Doug Swinbourne, Discipline Leader
Chemical & Metallurgical Engineering
Royal Melbourne Institute of Technology
P.O. Box 2476V, Melbourne 3001
AUSTRALIA
d...@rmit.edu.au Ph: +61 03 9660 2201 Fax: +61 03 9660 3746
Harris Lowenhaupt
In article <625un0$cmf$1...@campus1.mtu.edu>,
Henry_L...@brushwellman.com wrote:
>A question I hope someone can help me with.
>
>If I cast a Nickel containing alloy using element nickel I am introducing
>NiO into the melt on the surface of the elemental Nickel.
>
>Will using a Carbon Monoxide cover reduce the NiO if I am casting at
>approximate 1100-1200 C?
There are some good answers already posted, so I won't add to them. A
word of caution, though: if you're using CO, beware of the formation of
nickel carbonyl, a volatile and toxic compound. It forms above about 180
deg and decomposes above about 600.
Regards,
--
Harris Lowenhaupt
Cast Earth
Nickel Laterites
<http://www.lvnexus.net/nimud>
If replying by eMail, please remove the .xx in my URL before sending. They are there to obfusticate spammers.
zuzia
Dear Hank:
rest of us and your chances for re-employment during the corporate turmoil
are better. Well, let me pull you a bit on our side.
alloying additions (Cr? Al? Si?) are more reactive than Ni and will reduce
NiO via redox. This isn't good at all for recovery, economics, inclusions,
etc. Since Ni is relatively noble/doesn't corrode so fast, the amount of
superficial NiO film introduced to your melt with elemental Ni might be
quite low (unless you use Ni fines or powder) and you'd be well advised to
search the other melt re-oxidation sources as well.
(2) Any book on metallurgical thermodynamics or JANAF tables (Bureau of
Mines tables, etc.) will give you easy answers on how to reduce NiO, and if
you need just a crude estimate w/o the need for a pocket calculator or
application software like F*A*C*T from McGill Univ.
(http://www.uic.edu/~mansoori/Thermodynamic.Data.and.Property_html) you may
consult so called Ellingham diagram which is about the same thing as
Richardson diagram and can be found even in the ASM handbook
(http://www.asm-intl.org/) on heat-treating atmospheres. In any case, you
could reduce NiO with C, CH4, or heavier hydrocarbons, CO or a mixture of
CO and CO2, just as well as H2, and a mixture of H2 and H2O not to mention
metallic deoxidizers like Ca, Mg, Li, etc. Note, CO is toxic, H2 and CHx
explosive and alkali/a-e metals make fireworks.
(3) The same thermodynamics will let you calculate the dissociation
temperature of NiO which (I'm guessing) is orders of magnitude higher than
your casting temperature. Thus, vacuum will help you to minimize
re-oxidation resulting from the ambient air but that's pretty much all.
Also, you'd be better off using an inert Ar blanket over the melt surface
since it's cheaper than vacuum and you could still continue melt
charging/charge meltdown, superheating and treatment operations w/o the
physical obstruction imposed by the chamber.
To recap, your problem with a high oxygen in the melt can be most
effectively minimized by (a) bubbling a reducing gas through this melt
while protecting its surface from reoxidation with an Ar-gas blanket. At
least that's what I'd do. ZZ
PS: If your e-mail address is ...brushwellman... you must be melting Cu-Be
as well - there ain't too many deoxidizers for Be as you know.
----------
> From: Henry_L...@brushwellman.com
> To: metall...@mtu.edu
> Subject: Reduction of NiO
> Date: Tuesday, September 30, 1997 8:46 AM
>
> A question I hope someone can help me with.
>
> If I cast a Nickel containing alloy using element nickel I am introducing
> NiO into the melt on the surface of the elemental Nickel.
>
> Will using a Carbon Monoxide cover reduce the NiO if I am casting at