CaO-ZrO

We shall here consider a densely sintered ZrOi doped with 15 mol% CaO (Zro.ssCao.isOi.ss)-... 

CaO has been used to some degree as a stabilizer and is attractive due to its low cost. Its ionic conductivity, however, is approximately an order of magnitude less than an equivalent yttria stabilized body. There has also been some question about the chemical stability of a CaO stabilized body, although this may be more of a factor with a partially stabilized body than a fully stabilized body. Calcia fully stabilized ZrO has been and may still be used in commercial production of oxygen sensors. 

Figure 1.43 shows the electrical conductivity o versus oxygen pressure Po. curves at fixed temperatures for Zro gjCao ijOj 5 or (Zr02)o.85(CaO)o,i5 (called stabilized zirconia), as an example. In the oxygen pressure range... 

We noted above that if Zr02 is doped with 15 at% CaO we can stabilize the cubic phase. The resulting material can be described as Zro,85Cao.i50i,85. Experimentally we find that Do decreases as the concentration of oxygen vacancies increases. Hence we know that oxygen diffuses by a vacancy mechanism. 

Catalytic properties find uses in the oil industry. Zeolite ZSM-5 (an aluminosilicate) in refining oil by the reaction methanol— octane. Other functionalities The oxygen as sensor ZrO/CaO in solid solution, and a lot more other applications. 

Pure and mixed metal oxides have been widely investigated as Lewis acid and/or Lewis base for the reaction epoxides with CO to form the corresponding cyclic carbonates. Bhanage et al. [31] investigated several kinds of basic metal oxides (MgO, CaO, ZnO, ZrO, La Oj, CeO, Al Oj and K CO ) for the reactions of EO and PO with CO to the corresponding cyclic carbonates and for the transesterification reactions of the cyclic carbonates with methanol to DMC and the corresponding glycols. The catalytic performance of the various metal oxides for the synthesis of PC (express in Yp ) was (54.1%) >MgO (32.1%) > ZrO (10.9%) > K CO (8.7%) =... 

ZnO (8.7%) >CaO (0.8%). Among the metal oxides investigated MgO presented the larger number of moderately basic sites on the surface shown by CO -TPD. ZrO, ZnO and Al O also possessed moderately basic sites but the amounts were smaller than that of MgO. According to CO -TPD, the basic sites present in the La O are mainly strong ones in smaller quantify compared to MgO. The strong nature of the basic sites has been identified as the critical factor in the reaction. 

Today, heterogeneous catalysts used for biodiesel production (NaOH, KOH, CHO Na, and O, CH3OK) are cheap and readily available (Atapour Kariminia, 2011 Demirbas, 2011). Heterogeneous catalysts, such as solid catalysts (Ca (NO)/Al O, CaO/Al O Sr (N03)2/Zn0, ZrO/SO and zeolite HY, zeolite X) and enzymes Pseudomonas fluorescens, Rhizopus oryzae, Candida rugosa, and Pseudomonas cepacia), are currently applied for the production of biodiesel. 

Figure 4. Transmission electron micrographs (1 cm = 20 nm) of pure and doped zirconia calcined at 723K in air (a) ZrOj, (b) 5.2 mol% CeOj/ZrOj, (c) 5.1 mol% LazOs/ZrO, (d) 8.6 mol% CaO/ZrOj...

Thermodynamic stability of the interface with silicon is also important for correct selection of sensor material. According to Hubbard and Schlom (1996), for MgO and ZrO, thermodynamic stability of their interfaces with silicon was predicted. For HfO, AI2O3, CaO, and Y2O3, experimental evidence showed that these oxides also form stable interfaces with silicon. The CeO /Si interface is thermodynamically unstable, in accordance with experimental observations of formation of a Ce203 interlayer at the CeO /Si interface. Present analysis shows that, for the majority of metal oxides used, the interface with Si is stable. However, ZrO or YSZ thin films are permeable for oxygen at elevated temperatures, so that oxygen diffuses to the silicon substrate and a SiO layer is formed at the interface (Jia et al. 1995). It should be noted that this problem exists for all metal oxides used for gas sensor design. 

ETSELL and FLENGAS studied oxygen solubility in molten copper and silver. An impervious ZrO - CaO tube, closed at one end is immersed in liquid metal. The inner surface of the tube is platinized and a platinum wire serves as a conducting lead. Air or oxygen are used as reference. Another metallic wire establishes the contact with liquid metal. The tube is vibrated vertically. 

The high temperature electrolytes are mostly oxides of composition MO based upon the fluorite, structure. The best investigated is "calcia stabilized zirconia (CSZ) which consists of a solid solution of 12-15% CaO in ZrO. The addition of calcia transforms ZrO from the monoclinic to tne cubic (fluorite) structure and also introduces anion vacancies for charge compensation. Conduction is by 0 ion diffusion through anion vacancies and ZrO -CaO has a resistivity of 30 ohm-cm at 950 C. Trivalent cations may also be used to stabilise ZrO with resistivities at 950 C of 12 ohm-cm for ZrO -Y 0 and - 6 ohm-cm for ZrO -Yb O or ZrO -Sc O (Figure l). Staoilized zirconia is of interest as an electrolyte for fuel cells, but no battery applications have been proposed and the temperature of conduction is too high to be of real interest. 

Disproportionation ratios of wiistite doped with oxides calculated from Fig. 3.12 are listed in Table 3.7. It will be seen from Table 3.7 that the disproportionating ratio of sample yo without doped oxides is the highest, reaching 45.93%, while all that of other samples doped with oxides are much lower, in which the samples doped with CaO and MgO are the most marked ones. The reason is, after doping with oxides, especially with CaO, large amounts of metal ion enters the lattice of Fei xO and inhibits the disproportionation of Fei xO effectively. The inhibition of studied oxides on disproportionation is ordered as CaO > MgO > MnO > BaO > ZrO and the disproportionating ratios increase obviously with increasing temperature. 

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