Titanium thermochemical data

Table 2. Thermochemical Data for the Formation of Titanium Compounds ...

TABLE A2 Thermochemical Data of Selected Chemical Compounds Titanium oxide (TiO), ideal gas, molecular weight = 63.8794... 

Accurate self-consistent thermochemical data for the copper chlorides up to 200°C are required, in order to improve solubility calculations and electrochemical modelling capabilities for Aspen Plus and OLI software. Experimental work has been initiated at the University of Guelph, Canada and UOIT to determine a comprehensive thermochemical database, for solubility limits of OMIT, and aqueous cupric chloride versus chloride concentration and temperature using UV-VIS spectroscopy (Suppiah, 2008). The chloride ion is obtained by adding LiCl OMIT. The conditions of tests are primarily 25-200°C, up to 20 bars. Specialised equipment for this task is needed to reach elevated temperatures and pressures, because cupric chloride is chemically aggressive, and because changes in the solution concentrations must be made precisely. A titanium test cell has been custom made, including a UV-VIS spectrometer with sapphire windows, HPLC pumps and an automated injection system. The data acquired will be combined with past literature data for the cuprous chloride system to develop a self-consistent database for the copper (I) and copper (II) chloride-water systems. 

TABLE 2 Thermochemical Data of Selected Chemical Compounds Titanium Dioxide (Ti02), crystal-liquid, mol. wt. = 79.8788... 

Titanium Oxide Complex Oxides Sulfide. The dioxide Ti02, has three crystal modifications, rutile, anatase, and brookite, all of which occur in Nature. In rutile, the commonest, the titanium is octahedrally coordinated, and this structure has been discussed on page 51, as it is a common one for MX2 compounds. In anatase and brookite there are very distorted octa-hedra of oxygen atoms about each titanium, two being relatively close. Although rutile has been assumed to be the most stable form because of its common occurrence, thermochemical data indicate that anatase is —8-12 kJ mol more stablenhan rutiler-... 

Further thermochemical work on low-melting-temperature alloys need not be encouraged. Data for high-melting-temperature alloys, on the other hand, are still in short supply. Iron alloys, it is true, have attracted much attention from thermochemists, for obvious reasons, but in view of the large number of elements found in alloyed steels more results are still required. Thermochemists should make sure, however, that the ferrous system they intend to study has not already been adequately investigated. More thermochemical data are needed for alloys of transition metals of technical interest, such as titanium, zirconium, niobium, tantalum, chromium, molybdenum, and tungsten. 

Interest in the metal borides is due mostly to the presence of boron in certain steels and its interaction with other alloying elements. An example of other industrial use of borides is the use of titanium borides for the grain refining of aluminium. Thermochemical data for metal borides are, however, virtually non-existent. The reason, again, is the difficulty of finding suitable experimental methods for enthalpy and Gibbs energy determinations. 

Thermodynamic data in the area of transition metal chemistry is available, but additional studies would be desirable. One of the early indications that C—Ti bonds are not notoriously weak was obtained from the heats of combustion of Cp2Ti(CH3)2 and Cp2Ti(C6H5)2 with subsequent estimation of the a-bond dissociation energies (250 kJ/mol-1 and 350 kJ/mol 1, respectively)49. From heats of alcoholysis of a number of titanium, zirconium and hafnium compounds, and heats of solution of the products as well as subsidiary data, Lappert estimated heats of formation (AHf°) and thermochemical mean bond energy terms (EM X) of metal—X bondsso> (Table 2). 

Aluminum, boron, carbon, iron, nitrogen, oxygen, phosphorus, sulfur and titanium are the common impurities in the SoG-Si feedstock. Arsenic and antimony are frequently used as doping agents. Transition metals (Co, Cu, Cr, Fe, Mn, Mo, Ni, V, W, and Zr), alkali and alkali-earth impurities (Li, Mg, and Na), as well as Bi, Ga, Ge, In, Pb, Sn, Te, and Zn may appear in the SoG-Si feedstock. A thermochemical database that covers these elements has recently been developed at SINTEF Materials and Chemistry, which has been designed for use within the composition space associated with the SoG-Si materials. All the binary and several critical ternary subsystems have been assessed and calculated results have been validated with the reliable experimental data in the literature. The database can be regarded as the state-of-art equilibrium relations in the Si-based multicomponent system. 

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