Strontium ferrite ion exchange research

Research on nano-additive application in strontium ferrite ion exchange

We do ion exchange experiment on strontium ferrite to research the influence on magnetic properties caused by two different adding method with various exchange amount x by adding rare earth oxide in mi-l and nano-sizes. We found that when the added nano-particle x is 0.2, the effect is the same as that when mil-particle x is 0.3 and get a high property, O8 is 74A m²/kg, and hcj is 374 kA/m. Furthermore, the distribution of exchanged ion with added nano-size particles in crystal is more equal.

1. Forward:

The application of nano materials in magnetic materials can be divided into two catalogs. One is the magnetic material itself has nano structure like nano complex permanent material, nano crystal alloy soft magnetic material etc. The other catalog is to use nano additives to transfer the property of traditional magnetic materials.

Using nano material as additive, the particle size is one thousand times smaller than the mil-size particle and the surface area is very big and the crystal field environment where the surface atom of the particle is located and the bonded power and inner atom is not the same, so there are many active center, which improve the attaching power a lot, has very high property of surface activeness and fixed phase activeness.

Usually the added nano material to change the properties of permanent magnets and soft ferrite magnets is nano CaCo3 and nano SiO2. We add nano rare earth oxide particle to exchange ions in the strontium ferrite. We do experiments by adding mil-size particle and nano-size particle to make comparison; we use TEM and EDS to analyze the micro structure and use a vibration sample meter to measure magnetic properties.

2. Experiments:

  1. Experiment theory
  2. The molecular formula of strontium ferrite magnet is SrFe12O19. According to theory of close exchange on ion radius, Sr2+ ion radius is 1.27 mil, choose A=La3+, Pr3+, Nd3+ partly substitute Sr2+, Fe3+ on an ion radius of 0.83 mil. Choose R=Zn2+, Cd2+, CO2+ partly substitute Fe3+. After the ion substitute the main phase constructed is: Sr 1-x A x Fe 12-x R x O 19. A and R is added as oxide and do ion exchange in the ferrite fixed phase reaction. The value of the x exchanged in the experiment is in a range of 0-0.7. A and R oxide is as additive in mil size and nano size in the experiment for comparison.

  3. Experiment method
  4. Add A2O3 and RO and Fe2O3, SrCO3 into a small ball mill at the same time, mix them in wet, dry press compacting, pre-burn (1265 degree X 2hr), and then crush them to 3.5 um powder. material input: water: ball is 1:1:8. Small ball mill (adding a little CaCO3 and SiO2) grind to 0.65um powder slurry, and the concentration up to 68%. Under an over 10000Oe magnetic field and 400kg/cm2 pressure, it is shaped into standard ring magnets. Sinter it (1230 degree X 1hr) and do grinding on the ring magnet, then do some analysis and test.

  5. Experiment result and analysis
  6. 1). Add two different particles and research relation between the exchange value x and magnetic property

    Strontium ferrite ion exchange experiment

    The picture above shows the relationship between the A2O3, RO in mil size and in nano size and the exchange value x and o s. From the Picture above we can see when the additive is in a mil size and the exchange value x is 0.3, the maximum value of o s is 74 A*m2/kg. However, when the additive is in nano size and the exchange value x is 0.2, the maximum value of o s is 74 A*m2/kg, but when exchange value x is 0.3, the o s value is reduced to 73.7 A*m2/kg.

    strontium ferrite ion exchange experiment

    This picture shows the relation between the A2O3, RO in mil size and in nano size and the exchange value x and Hcj. From the picutre above, we can see when the additive is in mil size and the exchange value x is 0.3, the maximum value of hcj is 4720 Oe; and when the additive is in nano size, the exchange value x is 0.2, the hcj is 4700. But when x is 0.3 the hcj is reduced to 4650 Oe.

    2). Add two different particles to research the relationship between the exchange value x and the Tc

    ferrite ion exchange test result

    Picture 3 shows the result of the test by VSM on Curie temperature of two different additives. From the picture 3 we can see that when the additive is in mil size and the exchange value x is 0.2, the curie temperature is 450 Celsius degree and when the x is 0.3, it is 445 Celsius degree; however, when the additive is in nano size, the exchange value x is 0.2, curie temperature is 445 Celsius degrees and when x is 0.3 the curie temperature is reduced to 437 Celsius degrees.

    3). Analysis on the micro structure of the two different particle samples

    We use TEM to analyze the shape and size of the two different particle samples; we use EDS to analyze the content of element A and element R in different parts inside the particle and its surface. The result is shown as the table below.

    Content table of element A and R

    From this table, we can see when the additive is in a mil size, most of A ion and R ion are on the particle surface and only little of them go to the inside of the particle, especially the A ion which content inside the particle is nearly zero; when the additive is in a nano size, the distribution of A ion and R ion on the particle surface and inside the particle is more equal and their content on the particle surface is a little higher than that inside particle.

  7. Conclusion
  8. We use nano-La2O3, nano-Nd2O3, nano-ZnO, nano-CoO for the ion exchange of strontium ferrite and add particles in mil size and in nano size in experiments and adopt oxidation method to get the ferrite with a main phase of Sr 1-x A x Fe 12-x R x O 19. The test result shows that the effect achieved by additive particles in a nano size when the exchange value x is 0.2 is equal to that achieved by additive particles in a mil size when the exchange value x is 0.3. We achieve a high property. The os value we get is 74A*m2/kg and the hcj value is 374kA/m. At the same time, by adding nano-size particles, it can make SrM solid melted crystal have an equal distribution of exchange ion on the surface and inside the particle. Finally, adding nano-size particle and using the ion exchange method to make high-property strontium ferrite can reduce the consumption of precious rare earth oxide.