If you want to measure the electrical conductivity of NiO, it is far easier to use a wire that you'll prepare yourself by slow oxidation in air at moderate temperature of a pure nickel wire (attached with Pt wires for conductivity monitoring). I did it in the past and it works quite well, especially you can follow the changes of conductivity in air as a function of temperature or, at a fixed temperature, the changes of conductivity as a function of oxygen partial pressure. You just have to pay attention that the oxidation of the Ni wire is complete, and it may take a few weeks spent in air at 400 - 500°C. By following daily the changes of electrical resistance, you'll know when the oxidation is complete.

Alain

There could be various reasons, why you are unable to make pellet by using press. First one needs to look at properties of powder in hand. If it's primary particle size range in order of nanometers and it has lot of agglomeration then you may want to first deagglomerate it by ultrasonic dispersing methods. One can use non-aqueous liquid medium for dispersion and after ultrasonication carry out careful drying. Freeze drying is one of the method for avoiding re-agglomeration. Take care that powder is stored in desiccator and moisture accumulation or adsorption is avoided. Flowability of powder may be maintained. One can use powder in their original particle size distribution after ultrasonication and drying. But some times researchers use spray drying to make larger sized spherical particles with suitable particle size distribution which will help in pressing powder into pellet.

Pressing the powder is again not only about using higher pressures but pressure cycle profile; wherein pressure application, holding and removal of pressure to be done in systematic manner and sufficient time must be taken in all three steps and process should be gradual with no sudden jerks. Experimenting with different pressure and pressure profile should also be done.

In short, without binder, pellet making is difficult but not impossible. But one should device strategy as per properties of oxide powder being used. Precautions such as cleaning the press die and use of lubricants/releasing agents, for ex. applying inner surface of die with stearic acid etc., can also be tried. Care must be taken to avoid air-pockets. Two-step strategy can be used to avoid air pockets wherein in first pressing not to go full pressure and removing pressure with as little time as possible and then carrying out main full pressure cycle, will help in avoiding air pocket.

Hope it helps.

Have you tried to determine via 4-way method?

you have to use binder solution and make dow out of it,,then extrude it in a extruder. Further, it must be dried and calcined.