Calcium titanate

PEROVSKITE. The mineral perovskite is calcium titanate, essentially CaTiCL, with rare earths, principally cerium, proxying for Ca, as do both ferrous iron and sodium, and with colunibiuni substituting for titanium, ll crystallizes in die orthorhombic system, but witli pseudo-isometric character fracture subconchoidal to uneven brittle hardness, 5.5 specific gravity. 4 luster, adamantine color, various shades of yellow to reddish-brown or nearly black transparent to opaque. It is found associated with chlorite or serpentine rocks occurring in the Urals, Baden, Switzerland, and Italy, It was named for Von Perovski. 

MacNevin and Ogle (87) investigated the effects of impurities on the photochromism of barium and calcium titanates as shown in Table V. Pure samples of barium and calcium titanate were not photochromic and doping with Ag+1, Cu+2, Sb+3, Sn+4, Zn+4, and Co+2 produced no enhancement of photochromism. However, increases in the concentrations of impurities such as Fe+3, Zn+2, Sb+5, and V+6 promote photochromic activity. MacNevin and Ogle concluded that the photochromism in these systems depends on the insertion into the lattice of an impurity ion having, (a) an ionic radius near that of Ti+4, and (b) an oxidation number other than 4 to make electron transfer possible. 

Salts of these elements, on treatment with soda, yield no precipitate, for they are dissolved by the alkali the compounds formed are indefinite, but it may be supposed that they contain aurate, MAuOg.Aq, or platinate, titanate, zirconate, or thorate, MPtOg.Aq, c. Iron and calcium titanates occur native FeTiOg is termed ilmenite, and CaTiOg perowskite. The first is isomorphous with and crystallises along with native ferric oxide the ore is known as titanic iron ore. It is the commonest compound of titanium. 

As has been mentioned, ternary compounds having polyatomic ions such as NO3-, C032-, NFLt+, and so on often have the same types of structures as binary compounds in which a polyatomic ion occupies a lattice site as a unit. The mineral perovskite, CaTiOs, calcium titanate, however, is a somewhat different type of ternary compound that has the structure shown in Figure 3.8(a). Most ternary compounds are oxides, and the general formula ABO3 corresponds to many compounds because A = Ca, Sr, Ba, and so forth, and B = Ti, Zr, Al,... 

Calcium titanate. Calculations of Gibbs energy for the synthesis of calcium titanate, given below, show that from the thermodynamic point of view the reactions involving hydrated titanium dioxide (HTD) are the most profitable ... 

The authors [46] investigated the effect of mechanical activation on the synthesis of calcium titanate starting from anhydrous and hydrated calcium and titanium oxides. 

Kosova N.V., Avvakumov E.G. Mechanochemical synthesis of calcium titanate on the basis of hydrated oxides. Sib. Khim. Zhurn. 1992 3 121-27. 

Sasaki K., Masuda T., IshidaH., MitsudaT. Synthesis of calcium silicate hydrate with Ca/Si=2 by mechanochemical treatment. J. Am. Ceram. Soc. 1996 80 472-76. KosovaN.V., Avvakumov E.G., Malakhov V.V. et al. About nature ofphases formed in soft mechanochemical synthesis of calcium titanate. Doklady Akad. Nauk, 1997 356 350-53. 

CaOsTi (s) CaO Ti02 (s) Calcium Titanate Perowskite 03O3Ti (s) CaO Ti02 (s)... 

ER fluids are typically are suspensions of 1- to 100- um particles of cornstarch, silica, calcium titanate, or other semiconductors at volume fractions of0.05-0.50 in a hydrophobic liquid, such as mineral oil or com oil. For an electric field E of 50-5000 V/mm, the particles form chains that span the gap between the field-generating electrodes (see... 

Compounds that have been proposed to react by this mechanism include barium titanate, calcium titanate, calcium carbonate, strontium titanate and magnesium oxides[8,9,10]. All these basic compounds should theoretically react with vanadic acid and bind it in the trap and have proved effective in laboratory evaluations. However, sulfur competition negatively affects the performance of these traps in commercial units[8,l 1],... 

Only values, data points not reported. The name "perovskite, which usually denotes calcium titanate, was used in [2598] for LaNiO, and a series of its analogs with Ni replaced by Co, Fe, Mn, Cr, or V, and La partially replaced by Sr, Ca, Gd, or Nd. 

Coreno, J. and Coreno, O., Evaluation of calcium titanate as apatite growth promoter, 7. Biomed. Mater. Res. A, 75A, 478, 2005. 

Mixed oxides are exemplified by CaTi03, which, although often called calcium titanate , does... 

US patent 5,763,630 claims silver catalysts supported on other alkaline earth metal compounds than carbonates, such as calcium titanate, tribasic calcium phosphate, calcium molybdate, or calcium fluoride, as well as the magnesium and strontium analogues. Such supports provide significantly higher selectivity to the desired epoxide than would be expected from the performance of related materials. Selectivities are lower than those reported in the original Union Carbide patent. 

During plasma spraying of hydroxyapatite onto titanium alloy substrate surfaces minor amounts of highly reactive CaO are being formed by thermal decomposition that react with the native titanium oxide layer to form calcium titanate, CaTiOs. This thin reaction layer has been implicated to be an important... 

Figure 3.8 Epitaxial relationship between the (0 2 2) plane of calcium titanate and the (0001) plane of hydroxyapatite (Wei et al., 2007). ( With permission by Elsevier.)...

Structure of calcium titanate/titania bioceramic composite coatings on titanium alloy and apatite deposition on their surfaces in a simulated body fluid. Surf. Coat. Technol., 201, 8715-8722. 

Later work was centred on the chemical activation of titanium surfaces with alkalis that lead to precipitation of amorphous sodium titanate the Na+ ions of which will be exchanged against Ca2+ ions to form amorphous calcium titanate (Kokubo et al., 1996). This compound in turn will be transformed into ACP acting as a template for the subsequent precipitation of nano-crystalline hydroxyapatite (Kokubo, Kim and Kawashita, 2003). The sequence of events is shown schematically in Figure 5.2a-e. 

Reactions (1) and (2) have been postulated by Kokubo (1997) and subsequently electrochemically confirmed. The conversion of amorphous calcium titanate to calcium phosphate (Figure 5.2d,e) may be initiated by the formation of a thin layer of calcium phosphate with the configuration of the Posner s cluster, Ca3(P04)2 3 (reaction (5)) that has been shown to have the energetically most stable configuration (Onuma et al., 2000). This amorphous layer takes up more calcium and phosphate ions from the SBF to form OCP (reaction (6)) with Ca/P = 1.33 and finally stoichiometric hydroxyapatite (reaction (7)) with... 

Figure 5.2 Schematic of the sequence of apatite formation at a titanium surface activated with NaOH (a) and subsequently soaked in SBF (b-e). The originally formed amorphous sodium titanate (a) hydrolyses (b) and transforms by ion exchange to amorphous calcium titanate (c) and finally to...

Ca/P = 1.67 (Figure 5.2e). It should be noted that this sequence is at odds with that postulated by Liu et al. (2001) who assumed early precipitation of OCP that in turn takes up more calcium ions to convert to ACP with Ca/P = 1.5 and then transforms to hydroxyapatite with Ca/P = 1.67 via a Ca-deficient hydroxyapatite phase. It was noted that the activation energy for this sequence appears to be very large. Hence, it is reasonable to assume that a transformation path via amorphous sodium titanate and calcium titanate as described by the equations (1) - (7) above may constitute an energetically more favourable situation. 

The main idea of this sequence of chemical events was confirmed in principle by Webster et al. (2003) who showed that osteoblasts preferentially adhered to nanometre-rough calcium titanate formed as a consequence of the reaction between HAp and titanium during coating annealing. As bioadhesion is a crucial prerequisite for mineralisation of osteoblasts towards bony tissue,... 

Kizuki, T., Matsushita, T., and Kokubo, T. (2014) Antibacterial and bioactive calcium titanate layers formed on Ti metal and its alloys. / Mater. Sci. Mater. Med., 25 (7), 1737-1746. 

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