Transparent Nanometric Cubic and Tetragonal Zirconia Obtained by High‐Pressure Pulsed Electric Current Sintering

Abstract

Transparent samples of cubic (8 mol % yttria) and tetragonal (3 mol % yttria) zirconia were prepared from nanometric powders by the pulsed electric current sintering process. The crystallite size of the resulting dense samples was about 50 nm in both cases. The consolidation pressure had a positive effect on the occurrence of transparency for both modifications. Transmittance in the near infrared for 1 mm thick samples is above the 60 % for the cubic (8 %YSZ) and above 50 % for the tetragonal (3 % YSZ) zirconia, representing between 70 and 80 % of the theoretical values of the two modifications. Samples had a yellowish‐brown coloration which was attributed to the presence of color centers. Annealing in oxygen improved transmittance initially, but prolonged annealing resulted in translucent samples. The role of porosity in transmittance is analyzed.

Field‐Assisted Sintering Technology/Spark Plasma Sintering: Mechanisms, Materials, and Technology Developments

“…[43] For sintering temperatures below 1000°C, steel and refractory metals such as TZM molybdenum alloys, copper-beryllium, alumina, [243] silica, [244] and even concrete [245] were used. Anselmi-Tamburini et al [141] used binder-free tungsten carbide parts with silicon carbide inserts. Double-walled tool concept with inner ceramic die and outer graphite mantle has also been proposed.…”

“…[142] Optically anisotropic ceramics are even more challenging, as the transparency decreases drastically as grain size increases, and alumina, [143][144][145][146] tetragonal zirconia, [147] or hydroxyapatite [148] have been synthesized with improving success. Compared to standard free sintering in vacuum followed by HIP, the definite advantages of FAST/SPS are: (i) one single set-up required for densification and (ii) shortening of the process cycle.…”

“…Transparent ceramics synthesized by FAST/SPS include a large number of optically isotropic materials [132] like yttrium-aluminum-garnet (YAG), pure or doped with rare earths, [133][134][135][136] yttria, [137] magnesia, [138] magnesium aluminum spinel, [139,140] fully stabilized zirconia, [141] and lutetium based oxides. [142] Optically anisotropic ceramics are even more challenging, as the transparency decreases drastically as grain size increases, and alumina, [143][144][145][146] tetragonal zirconia, [147] or hydroxyapatite [148] have been synthesized with improving success.…”

In Vitro Evaluation and Comparison of the Translucency of Two Different All-Ceramic Systems

“…The zirconia core is less translucent than other dental all-ceramic materials such as glass-infiltrated ceramics, which is known for its good esthetic properties (11,12). Translucency of zirconia is related to the amount and type of additives, the sintering temperature, the atmospheric conditions during the sintering process and the heating methods (13)(14)(15)(16).…”

Light scattering by residual pores in transparent zirconia ceramics

“…17) A recent study using the spark plasma sintering method also showed that a fine-sized pore gives less effect as compared with pores with sizes comparable to wavelength. 14) Therefore, both miniaturization of the residual pores and their elimination are favorable for promoting transparency.…”