Hydrothermal Degradation Behavior of Y‐TZP Ceramics Sintered by Nonconventional Microwave Technology

Abstract

Different factors such as the characteristics of starting powders, their processing, the sintering technique and the final sintering temperature were assessed with the goal to improve the low temperature degradation (LTD) resistance of 3Y-TZP materials without compromising on the mechanical properties. The degradation of hydrothermally treated specimens was studied by AFM, nanoindentation technique, micro-Raman spectroscopy and electron microscopy.3Y-TZP previously prepared in laboratory by colloidal processing, and sintered by microwave method at low temperature (1200 ºC) led to excellent mechanical and LTD resistance, as compared to dental restorations based on Y-TZP commercial material. In the former, the presence of m-phase was almost non-existent even after 200 h of exposure to LTD conditions and the initial mechanical properties were maintained, giving 16 GPa and 250 GPa mean values for hardness and Young's modulus, respectively. The influence of the fast-technology by microwave heating is presented with a non-conventional sintering method to fabricate 3Y-TZP 2 ceramics for dental application with very high resistance against LTD and optimized mechanical properties.

LOW TEMPERATURE DEGRADATION BEHAVIOUR OF 10Ce-TZP/Al2O3 BIOCERAMICS OBTAINED BY MICROWAVE SINTERING TECHNOLOGY

“…Moreover, the effect of the sintering method on the aging could not be verified in this work, because until 80 h exposed to LTD does not appear monoclinic. However, it is possible that at higher times, differences between CS and MW can be observed 3 .…”

“…Despite stabilizing zirconia with the addition of an oxide, phase transformation can occur spontaneously under humid conditions at temperatures of 20 ºC-300 ºC, leading to a drastic drop in its long-term mechanical properties. This phenomenon is generally known as low temperature degradation (LTD), hydrothermal degradation or aging 3 . Different factors can affect the aging behavior in zirconia materials, such as grain size and shape, porosity or stabilizer content, among others 4 .…”

Progress on Hydrothermal Stability of Dental Zirconia Ceramics

“…4 [47] 研究发现氧化锆老化行为不仅与烧结 方法和晶粒尺寸相关, 还取决于初始粉末的性能。 Lawson 等 [48] 发现采用不同的方法制备的 3Y-TZP 粉 末, 其抗低温老化能力存在明显差异。 虽然, 共沉淀 法和气相反应-等离子包覆法已应用于 Y-TZP 粉末 的制备, 但制备的粉末因粒径及稳定剂 Yttria 分布 不均匀易发生 t-m 相变老化。 相比于传统球磨混合方法, Deville 等 [49] 采用溶 胶法制备的氧化锆粉末无团聚现象, 烧结体具有较 小的晶粒尺寸和良好的致密性。Smirnov [50] 证实了 粉末合成方法在 Y-TZP 陶瓷 LTD 行为中扮演重要 图 6 Y-TZP 陶瓷微观形貌 [45] Fig. 6 SEM images of the Y-TZP ceramic [45] (a) before and (b) after LTD [52] 采用微波烧结(MW)技术 制备的氧化锆陶瓷致密性高, 且 c 相含量降低, 样 品在水热条件下暴露处理 200 h, 几乎没有 m 相产 生, 表现出良好的抗水热老化性能。 Chintapalli 等 [53] 采用等离子烧结(SPS)技术获得小晶粒尺寸的陶瓷, 晶粒边缘呈圆形, 降低了晶界交汇处的残余应力, 提高了相变势垒 ΔG t-m 从而抑制 LTD。 此外发现, 孔 隙率对样品耐水热老化性能无明显影响。 图 7 2Y-TZP 陶瓷晶粒尺寸 [50] Fig. 7 2Y-TZP ceramic [50] (a) SEM images together with the corresponding grain size distribution, and (b) semi-quantitative Y 2 O 3 distribution…”

Effect of frequency on MW assisted sintering: 2.45 GHz versus 5.8 GHz

“…In this work, tetragonal zirconia polycrystalline (TZP) is stabilized with cerium oxide (CeO2), a less known dopant, as the commonly used for the stabilization of zirconia is yttrium oxide. With the use of CeO2 as a stabilizer, it is possible to improve the fracture toughness and reduce the low hydrothermal degradation (LTD) suffered by the TZP sample [11]. Low hydrothermal degradation is considered a big problem for biomaterials, especially zirconia is prone to ageing in presence of water [5].…”