I wonder if you couldn't couple this system with say a solar heater on one end to gain more power at peak sun time or even a Fresnal lens maybe... Well I suppose each project is always a step at a time but your results are rather interesting.

Aluminum oxide has a very good (for this application) thermal conductivity number. (Meaning low conductivity)  But, there are many, many types of Al203.  We used to purchase a number of different mixtures and purity in the ceramics business.  Purities of 99.7% vary greatly from purities of 99.8%, and 97% and 96% as well as 95%.  Each, like steel, has their own set of physical properties and vary greatly from each other.  Usually, depending on the manufacturer, (we purchased most of ours from Coors) the remaining ingredients in the Al203 is usually glass.  That is why, for metalization purposes, we used 95% because the glass allowed the metal to bond with the Al203.

So, I would make sure you know the content of the aluminum oxide you are using as just a little bit of difference make a huge change in physical properties.  And, if your supplier tells you it is 100% Al203, do not believe them as Coors 99.8% cost us (20 years ago) $100.00/ft of 1/4" rod.  This is very specialized stuff.

I don't know if this helps or not but, I was tossing it out there.

I can post the specs on this stuff if I can dig them out of my library.

Bill