[vex]

Hi all,

The lab I work in is interested in performing some electrical measurements on semiconductor materials pressed into dense, stable pellets with good electrical contact. We are equipped with a 15-ton room temperature press and 0.5" die, so we've calculated that we have enough pressure-per-area to match what is reported for the fabrication process in the papers we are trying to follow. Our model system for designing these experiments is Degussa TiO2. For some reason, when we try to press a pellet out of this powder, we fail to get a stable pellet. It usually crumbles upon handling; a few times we've gotten it to stick together long enough to get it up to the instrument and paint contacts onto it, but the electrical readings we get are nonsense. (I know TiO2 isn't very conductive, but our instrument isn't even zeroing correctly.)

So, I'm wondering if anyone has pressed pellets for similar applications in the past and if there's any advice you'd be willing to offer for us. Thanks!

[curiouscat]

Is that moulding or extrusion? If it is moulding, how long do you keep the pressure on the powder?

[vex]

I think it's molding; all we do is grind up the powder and put it into the die. We keep it under pressure for about a minute. Our press isn't the greatest and doesn't hold the pressure for long, but I suppose if a longer time is necessary that we could just keep pumping it back up.

[curiouscat]

I think it's molding; all we do is grind up the powder and put it into the die. We keep it under pressure for about a minute. Our press isn't the greatest and doesn't hold the pressure for long, but I suppose if a longer time is necessary that we could just keep pumping it back up.

I have no credentials to say if it'd work; but if it's not going to be too hard I'd give longer press times a shot.

[vex]

Thanks for the input, curiouscat. Turns out we were actually applying too much pressure for the material and die we were using, and the bottom of the pellet was breaking. With less pressure we've been more successful.

[curiouscat]

Thanks for the input, curiouscat. Turns out we were actually applying too much pressure for the material and die we were using, and the bottom of the pellet was breaking. With less pressure we've been more successful.

Glad you worked it out!