Chemical Forums

Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: Quaff on January 01, 2010, 02:37:36 PM

Title: Making pellets
Post by: Quaff on January 01, 2010, 02:37:36 PM
Years ago I bought a kit from a university for demonstrating the Meissner effect.  The kit contained
a pellet of YBaCuOx, about an inch in diameter and a quarter inch thick.

I'm just wondering how such pellets are made, from powders, wherein the pellets have a really really good structural integrity.
Title: Re: Making pellets
Post by: Borek on January 01, 2010, 03:18:51 PM
Sintering perhaps.
Title: Re: Making pellets
Post by: 408 on January 01, 2010, 04:10:09 PM
The metal oxides are mixed by any number of means.  Physical mixing and grinding, sol-gel, etc.  They are then pressed into pellets under brute force in a pellet press.  The pressing is more important when an inferior mixing method is used (physical mixing) to ensure good reactant mixing and contact between grains.  Then the pellet is heated very high.  The pellets are heated to 930C over 8-12h.  Held at 930C for 12-16h.  The composition at this time isYBa2Cu3O6.5.  The pellet is then cooled to 500C  and held there for 12-16h where it reacts with atmospheric oxygen giving a final composition of YBa2Cu3O6.9
These temps are for making YBCO at atmospheric pressure with ambient oxygen.  The composition of YBa2Cu3O(7-x) is dependent on partial pressures of oxygen.
Title: Re: Making pellets
Post by: Quaff on January 01, 2010, 04:14:33 PM
Right.   But once the powder is prepared, then what ?   

I see pellet presses available for about 1500 bucks, and some simple tool and die types available for about 500.   Guess I'll just have to shell out the cash unless I can come up with something creative.   I have made a novel material having a good thermoelectric coefficient and need to make chunks for a new refrigerator design.  When I put it in my hand and expose it to a strong magnet, I can actually feel it heat up in my hand.