Spark Plasma Sintering of Highly Transparent Hydroxyapatite Ceramics

Abstract

Highly transparent hydroxyapatite ceramics were fabricated by using the electrically conductive SiC mold during spark plasma sintering. Compared to the conventional graphite mold, the SiC mold lowered the sintering temperature by 50°C at least. The in-line transmission of the sintered ceramics is 82% at a wavelength of 600 nm. The high transmission is a result of fine and dense microstructures. The light scattering behavior was examined to show the Rayleigh and Mie scattering at low and high wavelengths, respectively. The appearance of the Rayleigh scattering, which is caused by nano-sized pores, indicates that the Mie scattering by anisotropic grains was sufficiently suppressed by the fine microstructures.

Transparent tetragonal-cubic zirconia composite ceramics densified by spark plasma sintering and hot isostatic pressing

“…The total forward transmission (TFT) was measured in the wavelength range of 240-1600 nm using a double beam spectrophotometer (SolidSpec-3700DUV, Shimadzu Co. Ltd., Kyoto, Japan) equipped with an integration sphere. To simplify comparison, the measured TFT on an arbitrary thickness was converted to the corresponding TFT for 1 mm thick samples using the following relation [16]:…”

Transparent non-cubic laser ceramics with fine microstructure

“…In transparent non-cubic ceramics, two scattering sources can be considered: birefringent grains and pores. Since hydroxyapatite ceramics prepared in a way similar to the present techniques exhibited nano-sized pores of 5–30 nm 13 , it is likely that the Nd:FAP ceramics also contain such pores. The nano-sized pores are considerably smaller than the wavelengths to cause Rayleigh scattering γ p 18 , whereas the birefringent grains comparable to the wavelengths cause Mie scattering γ g 19 .…”

“…A carbon sheet was used between SiC and Nd:FAP powder. The die and punch, which are electrically conductive 13 , were heated at a rate of 5 °C/min under a uniaxial pressure of 80 MPa in vacuum. The sintering temperature was 950 °C and the holding time was 20 min.…”

“…Besides alumina, Kim et al . obtained highly transparent hydroxyapatite ceramics using a SiC mould during SPS 13 . The microstructure had a grain size of 120 nm, and the transmittance was close to a theoretical value.…”

Crystallization of glass materials into transparent optical ceramics

“…Nevertheless, although most research in the transparent ceramics field has been performed on ceramics with a cubic crystal structure (e.g. Y 3 Al 5 O 12 , Y 2 O 3 , MgAl 2 O 4 , MgO, CaF 2 , SrF 2 , and other), recent advances in this field have enabled the fabrication of ceramics with non-cubic symmetries, such as Al 2 O 3 [58], Nd:Ca 10-(PO 4 ) 6 F 2 [39], hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ) [59], and others. Substantial progress in this area has been enabled by novel ceramic processing technologies, which have allowed for the fabrication of ceramics with nanosized grains [39,59] or with highly oriented grains under a strong magnetic field [60].…”