Partially stabilised zirconia

Despite earlier doubts, (Willmann, 1993) zirconia materials, in particular tetragonal zirconia partially stabilised with yttria (Y-PSZ), magnesia (Mg-PSZ) and calcia (Ca-PSZ), have found various applications in biomedical devices, most importantly as hard and tough structural ceramic material for femoral balls in hip endoprostheses (Cales and Stefani, 1995) and as material for restorative... 

A more complicated, and more effective, mechanism operates in partially stabilised zirconia (PSZ), which has general application to other ceramics. Consider the analogy of a chocolate bar. Chocolate is a brittle solid and because of this it is notch-sensitive notches are moulded into chocolate to help you break it in a fair, controlled way. Some chocolate bars have raisins and nuts in them, and they are less brittle a crack, when it... 

Bioinert materials are materials that display minimal, if any, interaction with surrounding tissues examples of these are titanium and its alloys, alumina, partially stabilised zirconia, carbon and possibly ultrahigh molecular weight polyethylene (UHMWPE). In the case of bioinert materials bone remodelling occurs by a shape-mediated contact osteogenesis. 

Figure 4.6 Transmission electron micrograph (TEM) showing spindle-shaped tetragonal zir-conia precipitates within a monoclinic zirconia matrix phase in Mg-partially stabilised zirco-nia (Birkby and Stevens, 1996). ( With permission by Trans Tech Publ., Millersville, DA, USA.)...

Figure 4.9 R-curve behaviour of Mg-partially stabilised zirconia (Mg-PSZ) compared to that of alumina (Bleise and Steinbrech, 1994 Inghels, Heuer and Steinbrech, 1990). ( With permission by John Wiley and Sons.)...

Yttria-partially stabilised zirconia coatings were manufactured by SPS of submicrometre-sized particles (50 and 400 nm) with several sets of spray operating parameters (Bacciochini et al., 2010). The average void size was comparable to the solid precursor structure showing nanometre-size scale with multimodal size... 

Hoffman, M.J., Dauskardt, R.H., Ager, J., Mai, Y.-W., and Ritchie, R.O. (1995) Grain size effects on cyclic fatigue and crack-growth resistance behaviour of partially stabilised zirconia. J. Mater. Set., 30, 3291. 

The value of Gjc for PMMA is 500 J/m, that of a brittle thermoset is typically 100 J/m and G]c for polycarbonate is 1100 J/m. Note that, just because a material has a high value of K q, it does not follow that Gj is also high. Certain ceramics have high values of K,r but low values of Gjc. For example, partially stabilised zirconia has a of 6 MPa.m ... 

Carter, G.A., Hart, R.D., Rowles, M., Ogden, M.I., and Buckley, C.E. (2009) Industrial precipitation of yttrium chloride and zirconyl chloride effect of pH on ceramic properties for yttria partially stabilised zirconia. J. Alloys Compd., 480 (2),... 

Oxygen sensors are now widely used in food storage, in metal processing and in flame controllers, but the main market is automobiles. Zirconia technology for sensors has been very successful in the marketplace, and it has pushed forward the development of solid oxide fuel cell materials. The main difference is that the power output of sensors is low so that partially stabilised zirconia can be used. At higher power, fully stabilised zirconia must be used if the electrolyte is to remain stable for long periods. The supply of this electrolyte material is discussed next. 

Yoshida et al. made systematic investigations on the effect of using partially stabilised zirconia (PSZ, Y2O3 content = 3 mol%) on the electrochemical performance of cathodes with different dopants and their concentrations [52], The overpotential of the LSM/PSZ is always and systematically higher than that of the same LSM with fully stabilised YSZ. This is apparently due to the chemical interaction between LSM and PSZ that is, the tetragonal phase (on the surface of the PSZ electrolyte) is transformed into the cubic phase after manganese dissolution into the tetragonal phase [53]. This increases the overpotential of the LSM cathode. 

Figure 6.24 (a) Spinner housings of homebuilt MAS NMR probes for 4 and 7 mm outer-diameter rotors. (From Daugaard, P. et al.. High speed spinner for NMR spectrometer. US Patent 4739270, April 19, 1988.) The outer shields of the probes have been removed. The cupper coil for rf excitation and detection can be seen in the centre of the 7 mm stator (left), (b) Rotors with a diameter of 4 (homebuilt), 2.0 (Bruker) and 1.6 mm (Varian) capable of spinning at 20, 35 and 45 kHz, respectively. The 4 mm rotor is made of Si3N4 and has a sample volume of 80 pL, whereas the 2 and 1.6 mm rotors are made of partially stabilised zirconia with sample volumes of 12 and 8.1 pL, respectively. 

Hannink, R.H.J. and Swain, M.V., Magnesia-Partially Stabilised Zirconia The Influence of Heat Treatment on Thermomechanical Properties. J. Australian Ceram. Soc. 18 [3] 53-62 (1982). 

A key factor in the possible applications of oxide ion conductors is that, for use as an electrolyte, their electronic transport number should be as low as possible. While the stabilised zirconias have an oxide ion transport number of unity in a wide range of atmospheres and oxygen partial pressures, the BijOj-based materials are easily reduced at low oxygen partial pressures. This leads to the generation of electrons, from the reaction 20 Oj + 4e, and hence to a significant electronic transport number. Thus, although BijOj-based materials are the best oxide ion conductors, they cannot be used as the solid electrolyte in, for example, fuel cell or sensor applications. Similar, but less marked, effects occur with ceria-based materials, due to the tendency of Ce ions to become reduced to Ce +. 

Several oxygen sensors based on oxygen pumping with stabilised zirconia have been reported (Hetrick, Fate and Vassell, 1981). This type of oxygen sensor is able to measure the oxygen partial pressure in the exhaust gas from the engine in lean burn. The operating principle of the... 

The electrolyte in an SOFC must consist of a good ion conductor, which has essentially no electronic conductivity. Otherwise the cell will be internally short-circuited. An often-used electrolyte material is yttria-stabilised zirconia (YSZ). The electrodes must pos.scss good electron conductivity in order to facilitate the electrochemical reaction and to collect the current from the cell. The fuel electrode usually contains metallic nickel for this purpose. The anodic oxidation of the fuel (H or CO) can only take place in the vicinity of the so-called three-phase boundary (TPB), where all reactants (oxide ions, gas molecules and electrons) are present. Thus, it is advantageous to extend the length and width of the TPB zone as much as possible. One way to do this is by making a composite of Ni and YSZ called a Ni-YSZ-cermet. Another way is to use a mixed ionic and electronic conductor, which in principle can support the electrochemical reaction all over the surface as illustrated in Fig. 15.1. Partially reduced ceria is a mixed ionic and electronic... 

To finish, similar other sensors using stabilised zirconia are also developed to measure the partial pressure of oxygen to be found in gases (air, and waste gas) or in molten metals (in metallurgy). However, these sensors have a reference electrode made of a metal which is mixed with its oxide inside the zirconia tube. 

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