Titanium content

Amount if too little titanium dioxide is added, the distance between particles is too large and there is not enough opacity, while if the titanium content is too high, the particles interfere with each other and poor efficiency is obtained. 

Titan-gehalt, m. titanium content. -halogen, n, titanium halide. 

Tantalum-Titanium Bishop examined the corrosion resistance of this alloy system in hydrochloric, sulphuric, phosphoric and oxalic acids and found that alloys containing up to about 50% titanium retained much of the superlative corrosion resistance of tantalum. Under more severe conditions, a titanium content of below 30% appears advisable from the standpoint of both corrosion resistance and hydrogen embrittlement, although contacting or alloying the material with noble metals greatly decreases the latter type of attack. Tantalum-titanium alloys cost less than tantalum because titanium is much cheaper than tantalum, and because the alloys are appreciably lower in density. These alloys are amenable to hot and cold work and appear to have sufficient ductility to allow fabrication. 

Fig. 38. Infrared spectra of adsorbed CO for samples with similar titanium contents (1) Ti-MMM and (2) Ti-SBA-15 (sample 1) [from Trukhan et al. (234)].

Ilmenite has variable titanium content, depending on the iron content and other impurities, and ranges from 45% to 52% Ti02. It can be found in a variety of ore types, along with rutile, apatite, zircon, columbite, etc. 

Figure 8 in Ref. 213, reproduced on the right, displays diffuse-reflectance UV-Vis spectroscopic data obtained for titanium-substituted mesoporous (Ti-SBA-15) catalysts as a function of titanium content. Assign the main absorption feature observed at 200 to 220 mu and the shoulder seen at about 300 nm. What can we learn from this figure in terms of the different titanium species present on the solid ... 

Elemental composition Ti 59.95%, O 40.05%. The oxide may be identified by its physical properties and by x-ray methods. Titanium content may be measured by AA or ICP. The compound is digested in nitric acid or aqua regia, solubdized, and diluted sufficiently for metal analysis. 

Comparison of titanium contents of lunar mare basalts, as measured from neutrons by the Lunar Prospector gamma-ray spectrometer and from reflectance spectra by the Clementine spacecraft. After Prettyman et al. (2006). 

Titanium is a reasonably common element which has been known for over 170 years. The average titanium content of the earth s crust is 0.63% by weight, which makes it the ninth most abundant element in the earth s crust, 20 times more abundant than carbon, and only outranked by oxygen, silicon, aluminum, iron, magnesium, calcium, sodium and potassium. It is only really in this century that elemental titanium has developed any industrial potential, partly because of difficulties associated with its refinement. 

The concentration of the acid recycled to the digestion process depends on the quality of the titanium-containing raw material. For raw materials with a high titanium content, the 65-70% sulfuric acid separated from the metal sulfates must be further concentrated to give 80-87% acid (stage 5). 

Fig. 5 shows the UV-VIS diffuse reflectance spectra for the Ti-MCM-41 samples. In this figure, a strong band at ca. 220 nm, which has been assigned to isolated framework titanium in tetrahedral coordination, is observed for the sample of higher Si/Ti mole ratios. Ti-MCM-41 synhesized at the lower Si/Ti mole ratio(40) showed a broad shoulder at ca. 270nm. This band is attributed to the extraframework titanium. In contrast. Ti-MCM-41 with a low titanium content proved to be free of occluded TiO, in the pores. Thus this result indicates that the rapid evaporation method is favorable for the synthesis of Ti-MCM-41 to incorporate the titanium into the framework. 

In addition to potassium hydrogen sulphate and sodium hydrogen sulphate8 for opening up the ore, potassium carbonate,9 sodium peroxide, and alkali hydroxides 10 have been employed. The use of potassium hydroxide is preferred in the case of a high-grade ore of low titanium content 11 it has the advantage over sodium hydroxide that potassium tantalates are soluble in solutions which contain excess of the alkali, whereas sodium tantalates are insoluble. 

For minerals in which the titanium content is high it has been found preferable to attack the ore with potassium hydrogen fluoride, KHF2, or concentrated hydrofluoric acid.13 In one such process the powdered... 

FtG. 8. TS-l unit cell volume expansion as a function of titanium content. (From Taramasso et at., 1983.)... 

Another property that distinguishes TS-1 from silicalite is the 29Si MAS NMR spectrum. The multiplet characteristic of silicalite-1 broadens in TS-1 into a major signal at - 113 ppm relative to TMS, while a shoulder appears at - 116 ppm, the intensity of which increases with increasing titanium content (Perego et al., 1986). 

The maximum amount of Tilv that can be accommodated in framework positions in TS-1 has been evaluated by numerous authors, and the subject is still actively debated. The problem is mainly of scientific, rather than practical interest. Although a relationship between titanium content and catalytic activity certainly exists, a direct proportionality is limited to very low titanium concentrations because other factors, notably diffusion, limit higher catalytic activity. 

An upper limit to the value x = Ti/(Ti + Si) of 0.04 on a molar basis was indicated in the original patent, although a good fit of experimental data with calculated values was limited to x = 0.025. Attempts made to synthesize TS-1 with titanium content exceeding 0.025 with the synthesis methods known at the time caused the formation of a Ti02 phase, and the UCV did not follow the correlation with x described by Eq. (5). It was therefore assumed that the limit for TilV in framework positions should be found in the range 0.0-0.04 (Taramasso et al., 1983). 

Fig. 17. Maximum anodic electrochemical current as a function of titanium content of samples synthesized by the classical method [TS-1(1) to TS-1 (4)] and by the modified procedure of Thangaraj el at. [TS-1 (5) to TS-1 (7)]. (From de Castro-Martins el al., Zeolites, 14, 1994, pp. 130-136. Reprinted with permission from the Publisher.)...

Attempts have been made to synthesize Ti-ZSM-48 with even higher titanium contents, but it was reported that no more than 2% titanium could be incorporated into framework positions. UV-Visible spectroscopic analysis of materials prepared with more titanium precursor indicates the presence of extra-framework Ti02, which in some cases is present also in the materials with low titanium contents. From these observations it is concluded that for Ti-ZSM-48 a limit exists in the amount of Tilv that can substitute for Silv in framework positions (Reddy, K. M. et al., 1994b). 

Through the NN-GA optimisation process, an important improvement in the activity and selectivity of the starting materials has been achieved (Fig. 5.5). The figure shows the cyclohexane epoxide yields for the eight evolved generations (8x21 samples). The best materials have low titanium contents, and were extracted and silylated. These materials have a Ti-MCM-41 structure and a very hydrophobic surface. 

The effect of zeolite porosity on the reaction rate was also well demonstrated in liquid-phase oxidation over titanium-containing molecular sieves. Indeed, the remarkable activity in many oxidations with aqueous H2O2 of titanium silicalite (TS-1) discovered by Enichem is claimed to be due to isolation of Ti(IV) active sites in the hydrophobic micropores of silicalite.[42,47,68 69] The hydrophobicity of this molecular sieve allows for the simultaneous adsorption within the micropores of both the hydrophobic substrate and the hydrophilic oxidant. The positive role of hydrophobicity in these oxidations, first demonstrated with titanium microporous glasses,[70] has been confirmed later with a series of titanium silicalites differing by their titanium content or their synthesis procedure.[71] The hydrophobicity index determined by the competitive adsorption of water and n-octane was shown to decrease linearly with the titanium content of the molecular sieve, hence with the content in polar Si-O-Ti bridges in the framework for Si/Al > 40.[71] This index can be correlated with the activity of the TS-1 samples in phenol hydroxylation with aqueous H2C>2.[71] The specific activity of Ti sites of Ti/Al-MOR[72] and BEA[73] molecular sieves in arene hydroxylation and olefin epoxidation, respectively, was also found to increase significantly with the Si/Al ratio and hence with the hydrophobicity of the framework. 

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