I made Fe2O3 through solution synthesis and it magnetic. However, I sintered at 500C for 3 hours and test magnetic property. It is not magnetic anymore. I was expecting to be more crystalline and highly magnetic. Any reason why this is the case?
Not all iron oxides are strong magnetic and i suspect that after high temperature sintering your iron oxide alpha phase is converted to gamma phase which is not strong magnetic.
If you want it to be more crystalline, then sinter it in inert atmosphere(Argon or Nitrogen).
and this thing is not true for all oxides or alloys because some of them get strongly magnetised after high temperature sintering(like YIG) so try to question in some specific way.
I support the opinion of Dr. Vinay Sharma. You need to carry out the phase analysis of the sample after the synthesis and after heat treatment (as sintered), for example, via XRD. Perhaps you have even mixture of ferrite-spinel phases (magnetite Fe3O4 and/or maghemite g-Fe2O3), and the end product can show a “non-magnetic” hematite a-Fe2O3.
It is useful to provide also magnetic phase analysis and/or differential scanning calorimetry of Your substance to see the phase transformations in the system during heating and cooling.
As suggested and it was also my plan to run XRD and DSC before and after. In the next section, I will try to provide relevant information to phase transformation.
I am equally curious or unaware the thermal stability CNT or graphite if sintered at high temperature? In one preliminary test, I have heat treated MWCNT at 500 C for 3 hrs and lost the CNT at end.
About magnetic phase analysis see, for example,
Article Application of magnetic phase analysis for the study and con...
As explained by several before let me just say that what you had synthesized was Gamma Fe2O3, which is also knoiwn as a defect spinelle. By heating it you have ocnverted it to alpha which is antiferromagneitc. So the heat treatment has to be done a t lower T. also if you had originally magnetite which is Fe3O4 then of course you have oxidised it to Fe2O3 by heating in air. So to check in which case you are you may do the annealing at T< 500. preferably in Ar and see.
First thank you for you input. I am always sintering in air as I d not want to go to expensive inert process. I am also realizing, the magnetic properties depend on the synthesis method. (let me point out my research is not on magnetic properties, it is just something that I want to understand better for the materials I am working with).
Read this article
http://www.sciencedirect.com/science/article/pii/S0304885316301123
Thank you Murtaza and I appreciate for the reference you provided.
What do you mean "it is not magnetic anymore".Does the result come from moment vs temperature or moment vs field? I wonder the temperature you take the measuremeat and what is your sample like, crystal or powder? As far as I konw, the powder of Fe-Oxide shows superparamagnetism while the crystal exhibits FM or AFM.
The material is sintered at 500 C for 3 hours and look intense red. Shows no magnetic effect.
If its Red, and annealed in air at 500C, it should be alpha-Fe2O3 (hematite) that is antiferromagnetic phase.
You are right in many respects. But if the material remains the same, the transition to a multidomain state has no significant effect on Ms. Besides a multi-domain state does not mean the loss of magnetic properties. Every domain is magnetized to saturation Ms.
Dr. Morchenko is perfectly right.I think peple should think carefully before explaining to a question. The idea is to come to a conclusion and not let grow the discussion at a tangent. This is my view.
- Badges
- Science topic
- Similar topics
- Engineering
- Petroleum Engineering
- Oil