I need a very hot surface to do CVD experiments for Carbon nanotube production
Hot surface is in a vacuum tank
I am using a AC Transformer which gives 1,5 Volt and 500Watts.
Secondary coil is designed to heat a thin (0,4 mm thickness) graphite plate width 20mm
poles are made of copper plates and on top of copper comes steel supporters due to the softness of the copper.
I would expect to have the graphite heated up but instead the iron supports are getting heated??
graphite surface reaches max 250C degrees but the poles reach 400C degrees
what could be the reason for that? Connections? Type of graphine? Anything else?
What other materials would you suggest for reaching 700 degrees?
Is AC or DC matters? (I think not but what are your comments?)
Hello Onur Ozan Çilsal ,
Can you tell us how you are measuring the temperatures of the graphite and the steel?
Regards,
Tom Cuff
I measure ıt with a non-contact thermometer from a distance of 30 cm
I move the thermometers laser on the surface and record the max value
Hello Onur Ozan Çilsal ,
Is it possible that the non-contact thermometer is giving you systematic errors due to the difference in emissivity of the graphite (dull and black) versus the steel (shiny and silver colored)? Or another possibility is that because the graphite probably has a higher emissivity than the steel, the graphite is radiating heat away faster than the steel. That would cause the graphite to be cooler than the steel.
Regards,
Tom Cuff
Hello Onur Ozan Çilsal ,
Third possibility is both systematic error in temperature measurement and graphite radiating away more heat than the steel.
Regards,
Tom Cuff
Thanks a lot for quick answers Mr. Thomas Cuff.
If graphite is radiating more heat than steel which material would be an alternative to reach higher temparatures on surface?? Usually I see graphite as solution due to its high temparatue resistivity. e.g. Iron melting rods in big furnaces.
I have chance to try ni-cr plates.
Hello Onur Ozan Çilsal ,
I would recommend tungsten or molybdenum instead of graphite, see Chapter 4 of the book by Holland.
[1] L. Holland; Vacuum Deposition of Thin Films; John Wiley & Sons, Inc.; 1961; pp. 104-140.
Note, according to Holland, see pp. 131-132, the resistivity of carbon and graphite decrease dramatically with increasing temperature, then eventually begin to increase again. In contrast, the resistivity of tungsten and molybdenum always increase with increasing temperature. For detailed information on tungsten, molybdenum, carbon, and graphite, Holland recommends the book by Kohl.
[2] Walter H. Kohl; Materials Technology for Electron Tubes, 1st Ed.; Reinhold Publishing Company; 1951; see Chapters 8 (Tungsten), 9 (Molybdenum), and 13 (Carbon and Graphite). Note, this book can be downloaded free-of-charge from the following web site: https://archive.org/details/Kohl_1960_Materials_and_Techniques_for_Electron_Tubes
Note, you can purchase tungsten and molybdenum filaments and strips (boats) commercially.
Regards,
Tom Cuff
Hello Onur Ozan Çilsal ,
How did using nichrome or chromel, in place of the graphite strip, work in your apparatus?
Regards,
Tom Cuff
Calderón, Alejandro, Camila Barreneche, Anabel Palacios, Mercè Segarra, Cristina Prieto, Alfonso Rodriguez‐Sanchez, and Ana Inés Fernández. "Review of solid particle materials for heat transfer fluid and thermal energy storage in solar thermal power plants." Energy Storage 1, no. 4 (2019): e63.
Update:
I have discovered several potentials at the setup and now I reach 700 and more degrees
1 - copper was oxidizing and causing loss of conductivity and heatind up so causing some loss of energy, so I cleaned up all contact surfaces by brushing and grinding.
2- according to a very primitive physics rule, I increased the length of the graphite to increase resistance. So I clamped from farther ends.
3 same transformator but i made one additional spin at the secondary side and instead of 1,5 it now gives 2,5 V but this is much better to push the electrons over the raphite so very low voltages are preventing a strong current flow.
Iron side was getting hot because initial contact was happening under this iron plate with a smallcontact surface. Those small surfaces were acting as bottlenecks for the current flow and heating extremely. That’s why on the top surface I was measureng around 400C
Hello Onur Ozan Çilsal ,
Thanks for the update. It sounds like you have solved all your problems, congratulations!
Regards,
Tom
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