Yttrium reactive element

High reactivity elements (RE e.g., cerium, yttrium, zirconium, hafnium) are sometimes added to the Fe-Cr-Al matrix these help the formation of the alumina protective layer that is, they speed up the transition from the less to the more stable crystallographic lattices [5,6] and increase its adhesion to the substrate. Secondly this action is assisted by the precipitation of "pegs" made up by fhe oxides of fhe reactive elemenfs (RE), partially immersed both in the substrate and in the scale of continuous superficial oxide [6]. However, fhe same authors state that the formation of fhe pegs is nof vital for the resistance to the scaling off of fhe layers of superficial oxide. It is important to note that its crystallographic type is a-Al203, which is much more effective than the 5, y, or 9 types. 

In high-temperature corrosion, the protective oxide hlms—usually either chromia, Cr203, or alumina, AI2O3—that form between the metal and the environment are of critical importance. One of the major advances in corrosion science over the past few decades has been the characterization of the reactive element effect (REE), which identifies the role of small additions of reactive elements, such as yttrium, hafnium, lanthanum, zirconium, and cerium, to improve high-temperature oxidation resistance. 

The reactive element effect (REE) is obtained when lwt.% or less of a reactive element, such as yttrium, hafnium, lanthanum, zirconium, or cerium, is added to... 

Grain refinement during solidification reportedly can also be obtained by additions of reactive elements like alkaline and rare earth elements, such as calcium, barium, yttrium, or nonmetals like Boron [12], In these cases, nuclei for crystallization from the melt are provided by formation of high melting compounds (sometimes intermetallic phases) of these reactive additions with other alloying elements or impurities, particularly oxygen. 

The addition of small amounts of reactive elements such as cerium, yttrium, hafnium, thorium, lanthanum, or their oxide dispersions greatly increases the high-temperature oxidation resistance of Fe-Cr alloys under isothermal or cyclic conditions. [11], Beneficial effects also result from ion implantation of the active element or from surface-applied coatings [11]. The ion implantation work of Bennett et al. [12] concerns the oxidation behavior of a 20Cr-25Ni-Nb stainless steel in CO2 at temperatures in the range of 900 to 1050°C. SIMS can be used to locate the position of the reactive element after oxidation. 

No fewer than 14 pure metals have densities se4.5 Mg (see Table 10.1). Of these, titanium, aluminium and magnesium are in common use as structural materials. Beryllium is difficult to work and is toxic, but it is used in moderate quantities for heat shields and structural members in rockets. Lithium is used as an alloying element in aluminium to lower its density and save weight on airframes. Yttrium has an excellent set of properties and, although scarce, may eventually find applications in the nuclear-powered aircraft project. But the majority are unsuitable for structural use because they are chemically reactive or have low melting points." ... 

Hydrogen reacts at elevated temperatures with many transition metals and their alloys to form hydrides. The electropositive elements are the most reactive, that is, scandium, yttrium, the lanthanides, the actinides and members of the titanium and vanadium groups (Figure 5.20). 

Group 3 elements have emerged as being useful Lewis-acidic metal centers for the ROP of cyclic esters. While these elements are highly reactive for this transformation, one significant challenge remains - the extreme water sensitivity of yttrium and other group 3 metals. [52b]... 

The yttrium concentration in seawater is 17ngkg (Zhang etal. 1994). The solution complexation of Y in seawater is similar to that of Tb, as opposed to the different reactivity with ligands on the particle surfaces (Liu and Byrne 1995). Hence, solution chemistry may help in explaining the distribution of these elements in the oceans, and this field of study might be applicable with regard to the biological effects of yttrium. 

Thus, Mosander s activities led to the originally two-element division into a six-element division. The cerium compounds are yellow at the higher oxidation level and colourless at the lower oxidation level, lanthanum compounds are white, didymium compounds are red, yttrium and erbium compounds are white, terbium compounds are pink. Chemists existed, of course, who disputed the existence of these elements. Unequivocal identification of elements was, however, possible in later times only. In the period in question, the main characteristics on the basis of which a substance could be qualified as a new element were separability, colour, crystal shape and reactivity. Even atomic mass determinations were largely uncertain, particularly in the group of the rare earth elements, it will be seen in the... 

The study of catalytic processes involving rare earths has been advanced by the synthesis and characterization of alkyl and hydride complexes of yttrium (Evans et al., 1984b), which in part were investigated because they provided NMR information via Y-H and Y-C coupling. Although yttrium is not considered a lanthanide, that row of elements exhibits reactivities similar to yttrium, and subsequent comparisons are reasonably valid. 

---