Hi Nabil,


I'm afriad to say using Cu wires (and Pt wires) only is not a good idea since CuO decomposes at T > 825 C. In other words, you deplete your oxygen sink (and stress your reduction tube) even when no samples go through the system.

In the Cu/Ni (+ Pt) system, NiO acts as your oxygen sink while CuO acts as the actual oxygen donor during combustion, hence why increasing the number of Ni wires increases the serviceable life span of your reactor.

My philosophy is to use as many wires as possible since this will also reduce the dead volume of the reactor (look at the difference in ID between the ceramic tube and your capillaries) thus preserving chromatography.

Typically I insert 3+3+2 Cu/Ni/Pt wires, oxidise at 620 C and then ramp the temperature to 940 C. Once this is done, I give the system several hours so excess oxygen can bleed off. Such a reactor if typically good for 120 to 150 individual runs (depending on relative compound concentration). It is possible to re-oxidize such a reactors several time before having to replace it.

Please, note running halogenated compounds will reduce serviceable life span of an ox reactor; even reoxidation will not change that since Ni halides are very stable and have melting points above the operational temperature of the oxidation furnace; certainly well above the (re)oxidation temperature of 620 C; NiCl2 melts somewhere around 1,000 C if memory serves; NiF2's mp is even higher (1450 C) and is not theramlly decomposable. Similar story for copper; CuF2 melts around 840 C but does not decompose while CuCl2 does decompose above 990 C but only to form CuCl plus Cl2.


Best regards,

Wolfram


****************************************
"Facts do not cease to exist because they are ignored."
Aldous Huxley, "Proper Studies", 1927
****************************************
Dr W Meier-Augenstein
Senior Lecturer in Stable Isotope Forensics

Environmental Forensics & Human Health Research Group
EERC, S.P.A.C.E.
Queen's University Belfast
David Keir Building
39-123 Stranmillis Road
Belfast, BT9 5AG
United Kingdom

Tel.: +44 (0)28 9097 4015
Fax: +44 (0)28 9066 3754
Email: [log in to unmask]<mailto:[log in to unmask]>
URL (Isotope Lab): http://www.qub.ac.uk/eerc/facilities/siff.htm
URL (Research): http://www.qub.ac.uk/eerc/people/academic_staff/wma/wm_a/efnhh.htm

________________________________
From: Nabil Saad [[log in to unmask]]
Sent: 08 November 2007 15:10
To: Wolfram Meier-Augenstein
Subject: Wolfram: question about combustion tube packing

Hello Wolfram,

May I ask you how many Cu, Pt & Ni wires you use to pack your combustion tube?

I use one of each but noticed that it doesn't hold O2 charge long enough compared to the ones we buy from Thermo for $$$$

I then started to use 2xCu wire + 1Ni +1 Pt and it works better now.

Thermo recommended that I use 2xNi wires+1Cu+1 Pt in case I wanted to go to a 4wire config.

Traditionally, I have used 3Cu wires ONLY, while oxidizing at 650C and combusting at 850C

Thought I'd check with you.

Thanks,

Nabil


On Nov 6, 2007 11:15 PM, Wolfram Meier-Augenstein <[log in to unmask] <mailto:[log in to unmask]> > wrote:
None whatsoever; all it takes is patience plus copper wires (0.1mm dia) from Alfa Aesar (Puratronic 99.99+) and ceramic tubes.

Best,

Wolfram


*****************************************************************
"Facts do not cease to exist because they are ignored."

Aldous Huxley, "Proper Studies", 1927
*****************************************************************

Dr W Meier-Augenstein
Senior Lecturer in Stable Isotope Forensics

Environmental Forensics & Human Health Research Group
EERC, S.P.A.C.E .
Queen's University Belfast
David Keir Building
39-123 Stranmillis Road
Belfast, BT9 5AG
United Kingdom

Tel.: +44 (0)28 9097 4015
Fax: +44 (0)28 9066 3754
Email: [log in to unmask]<mailto:[log in to unmask]>
URL (Isotope Lab): http://www.qub.ac.uk/eerc/facilities/siff.htm
URL (Research):
http://www.qub.ac.uk/eerc/people/academic_staff/wma/wm_a/efnhh.htm

-----Original Message-----
From: Stable Isotope Geochemistry [mailto: [log in to unmask]<mailto:[log in to unmask]>] On Behalf Of Todd Prior
Sent: 06 November 2007 21:02
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [ISOGEOCHEM] Aging carbon furnace tube in GC-C-IRMS

Thanks Gerry,

Is it difficult to make these as you suggested??

Thanks again ..Todd