Real‐Time Nucleation and Crystallization Studies of a Fluorapatite Glass–Ceramics Using Small‐Angle Neutron Scattering and Neutron Diffraction

Abstract

Real-time small-angle neutron scattering (SANS) and neutron diffraction (ND) studies have been performed on a calcium fluorapatite (Ca 5 (PO 4 ) 3 F) (FAP) glass-ceramic composition. The cast glass exhibited scattering at low q and a peak in I(q) at higher q. The scattering at low q is thought to arise from a larger-scale nucleated structure, while the peak in I(q) is thought to arise from a finer spinodally decomposed structure. High temperature viscoelastic measurements show two reductions in the storage modulus (E 0 ) and two peaks in the damping factor (tan d) consistent with a glass that has undergone amorphous phase separation (APS) during the casting process. On heating to 7801C, the scattering at low q increased in intensity, while the peak in I(q) increased in intensity and moved to lower q, consistent with the coarsening of the finer scale phase separated structure. During isothermal experiments, the scattering at low q increased in intensity and the peak in I(q) moved to lower q, corresponding to a final spacing of about 35 nm. After about 30 min at 7401C, and 12 min at 7501C the coarsening process effectively stopped and is inhibited by the glass transition temperature (T g ) of the second glass phase. ND showed the glass to crystallize on heating to FAP and then mullite (2SiO 2 . 3Al 2 O 3 ). At high temperatures, both the FAP and mullite crystal phases partially re-dissolved, but were found to re-crystallize rapidly on subsequent cooling. The results indicate that the proposed crystal growth hold is actually a crystal dissolution hold, with recrystallization occurring rapidly on cooling. The results indicate that it is important to control not only the heat-treatment cycle but also the cooling cycle.

Apatite Glass-Ceramics: A Review

“…Small angle neutron scattering (SANS) techniques can be used to study LLPS in both spinodally and binodally decomposed glasses. SANS scattering at lower q values correspond to larger phases, which can be attributed to a phase separation under the binodal region of the phase diagram, whereas neutrons scattered at higher q values correspond to a finer scale phase separation, which may be attributed to spinodally decomposed structures (Hill et al, 2007). Spinodal decomposition, unlike nucleation, generally results in sharp scattering maximum often referred to as a "spinodal ring" particularly during the early stages of phase separation.…”

“…They postulated that amorphous glasses that form the A-M system may have undergone phase separation by spinodal decomposition during the casting process on a scale of 25-27 nm (Hill et al, 2007). Similarly, the same cast A-M system isothermally heat treated at 740°C and 750°C initially showed neutron scattering at higher q, which then moved to lower q with increasing temperatures where the scale of the LLPS corresponded to about 35 nm.…”

“…This provides evidence that undercooled liquids can undergo LLPS by nucleation and growth, whereupon the chemical system can overcome the thermodynamic and kinetic energy barriers to nucleation and subsequent amorphous phase growth. It is suggested by Hill et al (2007) that the A-M cast glass is initially phase-separated by spinodal decomposition, whereby rapid cooling creates a barrier to nucleation and growth. However, it may be argued that scattering at lower q in the as-cast glasses may be attributed to a finer LLPS by nucleation and growth.…”

“…Relatively recently, Stamboulis et al (2006), Hill et al (2007), and O'Donnell et al (2010) conducted real-time SANS and neutron diffraction (ND) experiments on the A-M systems developed in the early 1990s. They postulated that amorphous glasses that form the A-M system may have undergone phase separation by spinodal decomposition during the casting process on a scale of 25-27 nm (Hill et al, 2007).…”

Nitrogen plasma surface modification enhances cellular compatibility of aluminosilicate glass

“…understood [29][30][31]. Plasma surface modification on a glass surface (without the addition of coatings) in order to study the cellular compatibility of the modified surface has not previously been conducted.…”