The relation is obvious, for the same amount of powder, larger diameter of the pellet means thinner pellet. 90 mg of YAG powder for 13 mm mold sounds like 3 mm thick sample, it's no wonder it breaks easily. Though I believe it is feasible, you just have to reduce friction so that the pressed pellet in the mould would have less internal stress and would not stick to the mould. There are several ways to be tried out. First, you can use liners. I heard there are specal graphite foils for this purpose but you also can use simple wax kitchen paper. As an alternative, you can use non-sticking coatings to treat the mold before you start, for example apply so-called teflon spray.

The relation is obvious, for the same amount of powder, larger diameter of the pellet means thinner pellet. 90 mg of YAG powder for 13 mm mold sounds like 3 mm thick sample, it's no wonder it breaks easily. Though I believe it is feasible, you just have to reduce friction so that the pressed pellet in the mould would have less internal stress and would not stick to the mould. There are several ways to be tried out. First, you can use liners. I heard there are specal graphite foils for this purpose but you also can use simple wax kitchen paper. As an alternative, you can use non-sticking coatings to treat the mold before you start, for example apply so-called teflon spray.

By contamination, i mean that elements from the mould are incorporated in the surface of the pellet. I have been cleaning the moulds using a ultrasound bath for one hour, and then with ethanol. However the surface of the pellet has some dark spots.

If you have any idea of density of the material, then you can correlate it with density, because it relates diameter and mass of the materials

It appears that the amount of powders (90 mg) is too low to make a compact with handling strength (based on the theoretical density of YAG, 4.55 g/cc and the volume of the die mold).

1) If you dont want to add any binder to bind the particles together to make the green compact, try to optimize the processing conditions using smaller mold and amount of the powder. Also, have a look at the particle size distribution.

2) The uniaxial load what you applied on the particles which has no binder seems little too much (~ 370 MPa). Even though, loading rate, hold time, releasing rate plays a role on the compact defects, vertical pressure applied through the die punches will partially transferred horizontally to the die walls as well. Hence, shear stress at the die wall oppose compaction pressure and eventually reduce densification locally around the die wall.

3) Unevenly filled powders (not properly taped) will also result delamination or End/Ring cap defects mainly due to spring back effect.

4) If addition of organics is not an issue for your study, consider adding binders and plasticizers to the powder (but less than 2 Wt% in total). Otherwise, applying stearic acid to the die and punch wall may help to reduce the friction to certain extend.

Give a try and share your experience.

Thank you all for your answers. Armando Loni i will try to clean them like you said, but i am affraid that doesn't work, do you know anymore techniques? Pathikumar Sellappan if a want to keep the same diameter how much amount of powder should i use? What kind of binders do you recommend, beyond PVA?

José,

Plan for 2-3 mm thick sample if you want to stick with the same diameter. Binders? it depends on so many parameters like Particle size and shape distributions, agglomeration of primary particles, surface roughness, and porosity within individual particles. Also, how you are going to mix the binders with the particle? Instead, I simply refer "Ceramic Processing" by M. N. Rahaman http://books.google.com/books?id=GC85CKs7URkC&source=gbs_book_similarbooks

Pathikumar Sellappan,

Thank you so much for your help.

@Roman Kubrin , what kind of Teflon mold you use in the experiment, where can i buy it? Can you send a picture to me? Thank you.