Introduction
Zirconia (ZrO2) is an oxide ceramic material that has a wide range of applications due to its light weight, chemical inertness, high strength, and low thermal conductivity. It is often used in applications such as high temperature chemical processing, implants, and dental prostheses. Because of its unique properties, zirconia is also of scientific interest for its ability to undergo a crystal structure transformation with changes in temperature, which is known as the monoclinic to tetragonal phase transition.
Background
Zirconia is composed of an oxygen anion and a zirconium cation. The oxygen networks in the crystal structure form four-connected corner sharing, eight- connected edge sharing, and twelve-connected face sharing bonds. The atom positions near the oxygen anion are arranged in a threefold coordinated octahedral configuration. These octahedral sites are categorized into three types: the α- site, the β-site, and the γ-site. Zirconia can undergo a transformation from the low-temperature monoclinic (M) phase to the high-temperature tetragonal (T) phase as the temperature changes. This transformation occurs due to the reorientation of oxygen octahedral sites due to the rearrangement of the oxygen atoms.
At lower temperatures, the monoclinic phase is energetically favored. In this phase, the oxygen octahedral sites adopt tilted configurations with an eight-connected edge and twelve-connected face sharing arrangement. As the temperature rises, the octahedral sites become more symmetric, and the twelve-connected face sharing arrangement becomes favored. This is the tetragonal phase, which is energetically favored at higher temperatures and is characterized by a four-connected corner and eight-connected edge sharing arrangement.
Experimental Techniques and Measurements
To study the monoclinic to tetragonal phase transformation of zirconia (ZrO2), materials scientists have employed a number of experimental techniques. Differential thermal analysis (DTA) is one such technique that is used to examine this transformation. DTA involves the use of a DTA device that consists of a high-precision thermocouple and a power-controlled heater. Samples of zirconia are heated in a controlled fashion by the DTA device, and the temperature at which a phase change occurs is measured. This technique can be used to ascertain both the temperature at which the phase transformation commences (Tc) and the temperature at which it is completed (Tct).
Another common technique used to study the M-T transformation in zirconia is X-Ray diffraction (XRD). XRD uses X-rays to probe the crystal structure of a material to determine its diffraction pattern analyses. X-ray diffraction studies of zirconia can be used to quantify the transformation temperatures, as the diffraction patterns of the two phases are quite distinct.
Conclusions
The M-T transformation in zirconia is a complex and intriguing phenomenon. The transformation occurs due to the rearrangement of the oxygen octahedral sites with changes in temperature. Differential thermal analysis and X-ray diffraction studies are two experimental techniques that have been used to understand this transformation. For example, both techniques can be used to measure the transformation temperature, and XRD can be used to quantify the transformation. The study of the M-T transformation in zirconia is important as it provides insight into many practical applications of zirconia.
In conclusion, the monoclinic to tetragonal phase transformation of zirconia (ZrO2) is an important phenomenon that has been studied extensively. It occurs due to the rearrangement of the oxygen octahedral sites with changes in temperature. Differential thermal analysis and X-ray diffraction studies have been used to study this transformation, providing invaluable information about its nature and behavior. This knowledge is critical for the successful utilization of zirconia in many practical applications.
