Sintering peculiarities for hydroxyapatite with different degrees of crystallinity

Abstract

It has been shown that reduction of sintering temperature of hydroxyapatite is connected to the use of a powder, the particles of which consist of crystalline and amorphous-like constituents. Shrinkage of the pressings made of the powder starts at the middle temperatures (600-700 degrees C) and is realized by a mechanism of a mutual sliding of the particles. If the firing temperature of the pressings increases, the second stage, realized by a diffusion mechanism (over approximately 900 degrees C), begins. A shrinkage curve on the sliding stage has a stepped character. It is caused by a stopping effect on the shrinkage of the pressure of a gas, which is exuded as a result of crystallization of the amorphous-like constituent, and partly accumulates in closed cavities and pores. The contribution of the two mechanisms to the shrinkage process is determined by the degree of crystallinity of the powder (i.e. the ratio of the crystalline and the amorphous-like constituents). If a powder has a higher degree of crystallinity, higher temperatures result, and the stepped character of the shrinkage curve is smoothed. The sliding stage is practically lacking for pressings of crystalline powder, and a noticeable shrinkage starts at high temperatures (over approximately 900 degrees C) as diffusive processes develop.

Calcium Orthophosphates in Nature, Biology and Medicine

“…As metals usually do not undergo bone bonding, i.e. do not form a mechanically stable link between the implant and bone tissue, ways have been sought to improve the mechanical contact at the interface [708,709]. The major way is to coat the metal with calcium orthophosphate ceramics that generally exhibit bone-bonding ability between the metal and bone [636,710,711].…”

Mechanical and cytotoxicity evaluation of nanostructured hydroxyapatite-bredigite scaffolds for bone regeneration

“…ACCEPTED MANUSCRIPT 4 Despite the excellent biocompatibility, the applications of porous HA scaffolds in the load-bearing situations have been restricted due to its weak fracture toughness and brittle nature [11][12][13]. A well-known technique to improve the mechanical characteristics of HA scaffold is the development of HA matrix composites (CMCs) scaffolds [14,15].…”

Crystallinity Engineering of Hematite Nanorods for High‐Efficiency Photoelectrochemical Water Splitting

“…Hence, the temperature required for hematite activation is higher than the sintering temperature, resulting in significant morphology change. Given that the sintering temperature is closely related to the crystallinity of hematite,14, 15, 16 we reason that finely tuning the crystallinity of hematite nanostructures provides a feasible way to reduce lattice defects that are usually present in hematite nanostructures17 and increase their sintering temperature ( Figure 1 ). To achieve this, we employed commercially available antimony‐doped tin oxide (ATO) nanoparticles to decorate FTO substrate for the growth of vertically aligned hematite nanorods with high crystallinity.…”