Thanks, Mike! I used aqueous solution at 10 pH and it was still unstable. For calcined stoichiometric hydroxyapatite the isopropyl alcohol was the most stable. But for green samples it was not. According to TEM micrograph the crystals are needle like and smaller than 100 nm. I forgot to mention that the dispersion was made with probe sonicator.

1. Have you tried dispersing with bath sonication instead (maybe coupled with 2 s probe sonication just before DLS analysis)?

2. As Mike suggested, you may need a stabilizer since pH adjustment did not really help.

Best wishes.

I once dispersed freshly sinthesized HA  i.e. green HA (obtained by acid base method mechanically activated which only  by product is water and also a bit of water was used in the milling) in anhydrous ethanol and it suspended very well. Before suspending the HA was washed three times in absolute ethanol to eliminate water traces, then suspended in fresh same solventcentrifuged. The size and heSize was well below one micrometer and DRX corresponded to very amorphous   material with very wide "peaks" centered around HA 2 theta main peaks. You can also use other anhydrous ketones. The point is to use a dry liquid with a low dielectric constant such as those mentioned, water traces increase polarity.DRX peaks height and particle size increase almost by the minute.

Hello, Edgar and Mike

My best results were obtained with 100% isopropanol for calcined samples and the  Z-Ave was around 300 nm. I used the probe sonicator (5 s ON 10 s OFF for 15 min) then I waited for 1 h. But the repeatability was very low. The green samples were worst. Thank you for suggestions.

Lidia

Lidia

As long as you have solids and liquids in contact  there will be Ostwald ripening. It is a dynamic system. You can sonicate but is almost impossible to return to the conditions you had before. Ultrasound will reduce agglomerates size but not predictable. Of course green solids will change more than sintered materials because green ones have a higher solubilty and surface energy.

Check Ralph Nelson´s  book "dispersing powders in liquids" it is old but I am sure you will enjoy it and make good use of it.

Edgar D.

Grind well with motar and pestle and use a ASTM mesh to sieve it , you would be able to get uniform particle size and then prepare the suspension or use ball milling.

Thank you, Edgar and Shidhar tm.