Scandium binary compounds

Other Binary Compounds.—Scandium nitride and zirconium and titanium carbide do not conform with the theoretical radii. It is possible that these crystals do not consist essentially of Sc+3, N 3, Ti+4, Zr+4 and C-4 ions, especially since zirconium and titanium nitride, ZrN and TiN, also form crystals with the sodium chloride structure but possibly also the discrepancy can be attributed to deformation of the anions, which have very high mole refraction values. 

When considering binary compounds of boron, it should be kept in mind that boron does not always behave as if the atom forms compounds in which the octet rule is obeyed. For example, compounds formed with scandium and titanium are ScB2 and TiB2, but other... 

Table 7.3 lists in parallel corresponding binary compounds and complexes of scandium, lanthanum, and lutetium. As expected on steric grounds, the smaller scandium generally... 

Scandium, a soft and silvery metal, was first isolated (1937) electrolytically, but it is generally obtained metal-lothermically, typically by reduction of the trifluoride with calcium, ft is electropositive, tarnishing rapidly in air and reacting with water. It forms a wide range of binary compounds. 

Considering the crystal structures of the compounds it is possible to conclude that the presence of scandium leads to the formation of various kinds of superstructures to the structure types of the binary compounds (Sm5Gc4, Ca2As). RScGe ternary germanides are isostructural and are formed with the elements of the cerium subgroup (La, Ce, Pr, Nd, Sm, Eu), i.e. at the ratio r /rsc 1.1 for R=Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu the compounds of this composition are not observed. 

There are no data about the interaction of scandium with the alkaline metals. Taking into consideration the large differences in the melting temperatures of Sc and lA elements the occurrence of immiscibility gaps in liquid and solid binary alloys are possible as they occur in the Sc-E (E = alkaline-earth element) alloys (see sect. 2.2). The absence of binary compounds in these systems is very likely. 

The interaction of scandium with the earth alkaUne elements is similar. An immis-cibility gap occurs in the liquid alloys and no binary compound exists in any of these systems. 

Savitskii et al. (1966) reported on the Sc-Re phase diagram. It follows from the figure in their paper that the liquidus curve in the phase diagram and the boundaries of some phase fields need additional refinement. Two binary compounds occur in this system (table 4). pSc dissolves <1 at.% Re, and the solubility of scandium in solid rhenium does not exceed 5-6at.%. Gschneidner (1975) presented the data of Savitskii et al., however he corrected in the figure of the phase diagram the temperatures of some phase transitions with the accepted values. 

The 0-14 at.% Sc part of the Sc-Au phase diagram was reported over three decades ago (Rider et al. 1965). The figure is also presented by Gschneidner (1975). The maximmn solubility of scandium (8.8 at.%) in solid gold occurs at the eutectic temperature of 1040°C. Four binary compounds have been synthesised in the system. Their crystal structure data are presented in table 7. 

Kotur et al. (1991) reported on part of the Sc-Sm-Si isothermal section at 600"C which is shown in fig. 54. All the samarium and scandium binary silicides dissolve different amounts of the third component, fi om 2at.% Sm (ScSi compound) up to 13at.% Sc (Sms Sis compound). Five ternary compounds exist in the system, and the crystal structure is known for all of them (see table 19). 

Muratova (1978) studied the Sc-Ge-Si isothermal section at 600 C, however, no figure was presented in her paper. A continuous series of solid solutions exist between pairs of isotypic binary compounds ScsGea and ScsSis, ScGe and ScSi. The scandium germanide... 

The elements of all other groups form binary compounds with scandium. The number of binary compoxmds in each system is indicated in table 1 (above). Within each large period Sc forms the largest number of binary compounds with 8A and 3B elements. In the rows of the p-elements the number of binary compoimds decreases with the increase of the group number of the element. The number of binary compounds changes inconsiderably with the increase of the period s number. 

There is also a relation between the interval of stoichiometries (i.e. the composition range where the intermetallic phases are formed in the binary Sc-E system, see fig. 92) of binary compounds and the position of element in the periodic table. The widest intervals of compositions of the binary compounds with Sc display 8A and 3B elements (fig. 92). These are the elements which form the largest number of binary compounds with scandium. In the rows of d elements the least scandium content in compounds increases from 7A to IB element and then sharply decreases for the 2B elements. A similar relation... 

The second group is characterized by a smaller number of ternary compounds, which may be explained by the similarity of the crystallochemical behaviours of the two components Be, Mg, Ga or Ge, and Al. As one can see, scandium generally forms a small number of compounds in the investigated systems (Sc is rather similar with a 3d transition metal, than with the other rare earths). All of the ternary compounds with solved crystal structures are characterized by structure types of the binary compounds or closely related ones. Systems with Ge and Al show the La202S type of crystal structure. This may be explained by the partially semimetallic properties of Al in these systems. 

The lanthanide and actinide halides remain an exceedingly active area of research since 1980 they have been cited in well over 2500 Chemical Abstracts references, with the majority relating to the lanthanides. Lanthanide and actinide halide chemistry has also been reviewed numerous times. The binary lanthanide chlorides, bromides, and iodides were reviewed in this series (Haschke 1979). In that review, which included trihalides (RX3), tetrahalides (RX4), and reduced halides (RX , n < 3), preparative procedures, structural interrelationships, and thermodynamic properties were discussed. Hydrated halides and mixed metal halides were discussed to a lesser extent. The synthesis of scandium, yttrium and the lanthanide trihalides, RX3, where X = F, Cl, Br, and I, with emphasis on the halide hydrates, solution chemistry, and aspects related to enthalpies of solution, were reviewed by Burgess and Kijowski (1981). The binary lanthanide fluorides and mixed fluoride systems, AF — RF3 and AFj — RF3, where A represents the group 1 and group 2 cations, were reviewed in a subsequent Handbook (Greis and Haschke 1982). That review emphasized the close relationship of the structures of these compounds to that of fluorite. 

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