I wrote:
The aluminosilicate matrix is a nifty method of keeping the particles apart, so they do not sinter into a large particle with less surface area.
By the way, Takahashi disputes the use of the term "sintering" to describe this effect. He says the clumping effect is caused by hydrogen effects . . . somehow bonding the particles together. I do not recall the details. He says they do not stick together because of heat. He points out that before the experiment, they heat up Pd-black to higher temperatures than they reach during the experiment, in order to purge gases from them, and yet the particles do not stick together in this pre-treatment.
Duncan and others refer to the particles glommed together as "sintered." Perhaps this is not technically correct.
I wonder if the individual particles are not become extremely hot in tiny local areas, and sintering together, even though the overall temperature of the powder rises only a little. With bulk Pd cathodes there are areas that appear to melt or vaporize, although Storms and others have questioned this evidence. If that happened with a particle it might stick to its neighbor.
People have been trying many different methods of holding the nanoparticles apart, so that the gas reaches all of them and they do not glom together as the reaction continues. The NRL method of capturing 2 nm particles inside a matrix is tricky but once you trap the particles the method seems to work incredibly well. The hard part is to make sure the particles go inside the matrix, rather than sticking to the side of it. If the particle is bigger than 2 nm it doesn't fit inside the box so it isn't used. They want small particles. I think they get only a small fraction of the matrix boxes to engulf (swallow? assimilate?) a particle. I think they said 3%. This is why I wish I had the DVD of the lecture right now.
The NRL people use tiny samples of material inside a microcalorimeter that can measure a few hundred joules with high confidence. As stated in the abstract, they have "routinely" repeated these experiments to produce "hundreds of reactions." I have the highest regard for Navy researchers. They wring out procedures; think of everything; do it hundreds of time; they use topnotch equipment, and they produce bulletproof results. When they something works, you can be darn sure it does.
The same goes for SRI and the ENEA, by the way. But I am pleased to see Uncle Sam's people playing a vital role in this research. You have to hand it to the military.
- Jed
