Zuckermann, Transport Properties (Electrical Resistivity, Thermoelectric Effect, and Thermal Conductivity) of Rare Earth Intermetallic Compounds 117. Transition Temperatures, Phases, and Melting Points of Rare Earth Metals (after Beaudry and Gschneidner, 1978, unless otherwise noted).
Intra Rare Earth Phase Diagrams 1. Introduction
This suggests that the d h c p ~ f c c transformation lines may go through a minimum in the middle of the diagram. The A-axis grid parameter for all the grid spacing data is shown in Fig.
LANTHANUM - HOLMIUM
ATOMIC PERCENT HOLMIUM 100 Ho
Lundin (1970), in a study of the formation of a samarium-like structure in intra-rare-earth binary alloys, included six compositions in the lanthanum-scandium system ranging from 10 to 85 at% La. I (Centre National de la Recherche Scientifique, Paris ) P. 1962), but has been slightly revised in light of Lundin's (1966) research on the formation of the samarium-like structure in intra-rare-earth binary alloys.
Sm-PHASE I
Altunbas and Harris correlated the predominance of the fcc structure with the hysteresis characteristics of these alloys. Lattice spacings at the cerium-rich I 2 3 4 5 end of the cerium-ATOM IC PERCENT PRASEODYM IUM praseodymium system.
3.6290 DHCP
23 and 24, along with a line showing the relationship of Vegard's law for each part of the plot. All three a distance data points in the fcc region show positive deviations that increased with s a m a r i u m content.
Lattice spacings for some cerium-rich alloys in the c e r i u m - e u r o p i u m system were reported by Arajs et al. A positive deviation from the Vegard's law line is observed in the 8-phase region for the C e - 5 5 a t % H o alloys as determined by Lundin and b y Jayaraman et al.
LIQUID /~ZZ
They stated that the room temperature solid solubility limit of scandium in cerium is about 17 at% Sc and that of cerium in scandium is about 12 at% Ce. The melting points and transformation temperatures of pure metals are adjusted according to the accepted values listed in Table 1.
Thermodynamic properties
Essentially identical results were obtained at 1475 and 1525°C. 1966) measured lattice spacings for a selection of alloys that included various compositions in the P r - G d system. Tissot and Blaise (1970) also studied magnetic and crystallographic properties of alloys in the P r - G d system.
HcP~
The lattice spacings of the alloys have been adjusted by prorating the variations from the spacing of the pure metals on the basis of the mole fraction of each constituent in the alloy. All a-spacing data for the neodymium-rich dhcp phase show a negative deviation from Vegard's law. All a-spacing data in the hcp-phase region showed large positive deviations from Vegard's law line.
In the hcp region, all data show a negative deviation from Vegard's law behavior, with the deviations being much larger for the reported alloys. The phase diagram presented by these authors covers only the high temperature (above 850°C) portion of the system. 69 have been slightly modified to reconcile these properties of the pure metals with the accepted values in Table 1.
73 is a reproduction of their diagram with minor adjustments to the melting point and transition temperatures of the end members to bring these temperatures into agreement with the accepted values for pure metals as listed in Table 1. Adjustments to the reported data were made by prorating the deviations between the accepted values for the lattice spacings of the pure metals and reported values for the corresponding end members based on alloy composition. Therefore, their data were adjusted to bring the endmember grid spacings into agreement with accepted values for pure metals.
5.70- HCP " ~
Amorphous alloys
Laridjani and Sadoc (1981) studied amorphous G d - Y alloys in the composition range 10 to 90 at% Y by X-ray diffraction. These authors found that the radial distribution function can be accounted for by a mixture of tetrahedra and octahedra. At low concentrations of Y in Gd or Gd in Y there were four tetrahedra to one octahedra, but the number of tetrahedra increased as the concentration approached an equiatomic mixture of yttrium and gadolinium.
Thermodynamic properties
The Vegard lines are based on accepted values for pure metals as listed in Table 2. Smidt and D a a n e (1963) reported lattice spacings for four alloy compositions and for pure metals in the T b - L u system. The straight lines illustrate Vegard's law relationships and are based on accepted values for the lattice spacings of pure metals shown in Table 2. a positive deviation from Vegard's law behavior over most of this compositional range.
The lattice spacings for the alloy reported by Mc W h a n and Stevens h a d a negative deviation in the a separation. The data presented in fig. 99 have been adjusted so that the spacings for terbium and scandium agree with the accepted values for these pure metals as shown in Table 2. The terbium-scandium compounds have hcp structure and the a lattice spacings appear to follow Vegard's law within experimental error. Since their value for the melting point of yttrium (1502°C versus the accepted value of 1522°C) and for the transition temperature (bcc ~ hcp) of both metals (Tb: 1317°C and Y: 1490°C) did Disagree with the accepted values for pure metals (1289 and 1478°C, respectively) as listed in Table 1, the melting and transition temperatures of alloys are adjusted based on composition.
They reported the lattice spacings in terms of the lattice spacing ratio of the alloy with.
Thermodynamic properties
The straight lines represent Vegard's law relationships and are based on accepted values for pure metal separations as listed in Table 2. The straight lines represent Vegard's law relationships and are calculated from accepted values for pure metals pure as listed in Table 2. The estimate of bcc phase termination at 8.5 at% Y is subject to a fairly wide error (i.e., the termination point may lie anywhere in the range 1 to 30 at% Y) and must be determined experimentally.
The straight lines representing Vegard's law behavior are based on the accepted values for the pure metals as given in Table 2. The straight lines represent Vegard's law based on the accepted values for the pure metals as shown in Table 2. The straight lines represent Vegard's legal relationship. Vegard's law based on the accepted values for the pure metals as listed in Table 2.
The straight lines represent Vegard's law relationships and are based on accepted values for pure metals as listed in Table 2.
Systematics 1. Introduction
- Thermodynamics
High pressure diagrams are based almost entirely on the behavior of pure metals at high pressure. At higher pressure, the transformation of fcc aCe into a U-type structure is shown in fig. 25 °C isotherm section of the generalized binary intra rare earth phase diagram from 0 to 24 GPa (0 to 240 kbar).
121, The dashed line in the fcc region indicates the formation of the distorted fcc or tight hexagonal (thcp) phase from the normal fcc phase with increasing pressure. The extremely high pressure behavior of the lanthanides at room temperature, as shown in fig. The fcc and Sm type phase fields expand with increasing pressure at the expense of the dhcp and hcp phase fields, respectively.
Skriver, H.L., 1983, në: Sinha, S.P., ed., Systematics and the Properties of the Lanthanids (Reidel, Dordrecht, The Netherlands) f.
Acknowledgments
The unique chemical similarity of the rare earth group elements and their undesirable electrochemical properties make the determination of individual members of this group by polarographic analysis extremely difficult with only a few exceptions. The first study of the polarography of the rare earth group elements was made on Sc by N o d d a c k et al. 1937), and they concluded that the reduction takes place in two steps, first to the 2 + stare and then to the metal. However, in light of the experiments by Leach et al. 1937), this conclusion appears to be incorrect, and the first wave observed by N o d d a c k et al.
Until recently, the development of polarographic analysis of rare earths has been quite slow, O'Laughlin notes. Polarographic methods are neither as sensitive nor as accurate as spectrometric methods and are rarely used at this time.” POLAROGRAPHIC ANALYSIS OF RARE EARTHS 165 have been successfully used in ore analyzes (Gao et al., 1977). In 1978, our group, in cooperation with the Chinese Academy of Geological Sciences, began to study the electroanalytical chemistry of elements of the rare earth group, especially polarographic methods.
To date, we have proposed more than ten sensitive systems for the analysis of rare earths.
Literature survey of the polarographic analysis of the rare earths 1. Polarographic analysis in simple base electrolytes
For analytical purposes, the sensitivity of the determination of rare earth ions in non-aqueous solutions is only about 10 -4 to 10 -3 M due to the low conductivity of non-aqueous media. Several institutes in China have synthesized some new organic reagents with the aim of increasing the sensitivity and selectivity of rare earth analysis. The height of the discrete wave is proportional to the concentration of y 3 + or lanthanide ions.
Such waves, which arise due to the reduction of a ligand coordinated with a metal ion and adsorbed on the surface of the mercury electrode, are called "adsorption complex waves". Many examples of catalytic prewave are given in a book written by Tur'yan (1980). POLAROGRAPHIC ANALYSIS OF RARE EARTHS 169 studied the polarographic behavior of N O 3 , NO 2 and N H 2 O H in buffered and unbuffered solutions with DPP.
The second mechanism, involving direct reduction of the nitrate ion on the mercury electrode coated with a small amount of Y(OH)3, gives a new peak at -1.3 V SCE in the second cathodic scan of cyclic voltammograms.
Recent developments of polarographic adsorptive complex waves and catalytic waves of the rare earths
These experimental facts indicate that the wave peak in this system is an adsorptive complex wave; its high sensitivity may be due to the strong adsorbability of the complex. This also shows the effect of adding the organic solvent dioxane on the adsorptive complex waves of rare earths. Furthermore, the fraction of the N d ( I I I ) - C N A complex adsorbed on the H M DE surface already saturated with CNA was also determined, and the result supports the assumption that the adsorbability of Nd ( I I I ) - C N The A complex is stronger than that of CNA.
This sensitive m e t h o d has been applied to the determination of trace amounts of light rare earths in plant leaves. This means that the reduction of the complex to a more negative potential is an irreversible process. Light rare earth-OCP complexes exhibit a new wave, which can be used to determine the concentration of light rare earths.
The O system is proportional to the square root of the XO concentration, indicating that the wave is also catalytic in nature.
