The Effect of Carbon on the magnetic properties of Aluminum/Iron Alloys

[Folkcafe]

While finishing up some light reading I came across this graph in a book Magnetic and other properties of aluminum-iron alloys.

The dashed line represents the carbon contaminated alloy and the solid line is high purity. The amounts are relatively small (.06-.09%) I leave it to your own analysis to decide its relevance.

I've been trying to answer the few remaining questions I have about the effect of carbon and oxides on the magnetic properties of various materials.

My research is primarily into the production methods and any additions to the alloys there may be and what the possible effect they might have.

What I find the most odd is the relative lack of public domain information on alnico. I can find tons of data on manufacturing methods for just about every other magnet materials. All the alnico papers are pay for view. I wonder if this is in part due to the "mystique" alnico has in the audio world?

I found some information regarding niobium, silicon and titanium as additions in alnico alloys. There is some information I've found regarding the effects of silicon on permeability and hysteresis loss but I've still got more to look at.

So far carbon seem to be the most interesting.

I know this is a rather complicated route I'm taking but I have the time. What I'm not sure of, is anyone interested? If the general consensus is not, I can surely keep my work to myself. Feel free to let me know what you think.

[Folkcafe]

Once I started looking at the effects of chemistry on the magnetic properties of materials it continually brought with it references to the relationship between changes to the mechanical properties and the magnetic properties of materials. In a book dealing with the topic of magnetic properties of alloys I found the following to be thought provoking and led the direction of my search parameters:

“An impurity-based model cannot explain the dependences of magnetic properties on technology, the concentrations of hydrogen or oxygen, the isomeric composition, crystallinity and the hybridization of carbon atoms. We note immediately that magnetic properties can be greatly affected by a mechanical effect without any change in the elemental composition.”

Simply put, the magnetic properties of steel can be varied by how it is processed. By solution treating, annealing, tempering and combinations of these, the magnetic properties are affected without any change to the chemistry of the material. Carbon seems like a suitable start point as it has a great deal to do with the magnetic properties and its properties can be altered via heat treating. An example of this is pearlite in steel can be transformed into graphite through a long heat and slow cool. Both are forms of carbon but graphite is nearly magnetically neutral. You are not changing the chemistry but the state of the carbon and that has a marked effect on its properties. This is how transformer plates are processed. If the magnetic properties in 1018 or 1010 steel (as an example) can be altered with heat treating, wouldn’t this open up options?

Now how to move from the theory to practical experimentation? The main point of this exercise was for gaining some insight but also to shape how I would approach the next phases of pickup building. My initial thought was the magnets but I’ve decided there are too many variables I realistically don’t have any control over. I felt it would have been better to keep the experimentation within two main variables, magnets and coils. For now I am going to focus on coils and standardize on just a few magnets.

Once I get to a point where I am comfortable, I will probably think about looking at running some experiments on back plates. Here the methodology and variables are easier to control. They are also within a reasonable area of resources to bring about. I am thinking about trying to gain access to a small pc controlled lab size vacuum furnace (4”x4”x8” hot zone) capable of temps to 2000C (I also once worked for a company that made vacuum furnaces). Perhaps a reasoned methodology to equate the relationship between these controllable changes in magnetic properties and tone can be put into a definable process.