Primary solid solutions

In a primary solid solution M(O) (phase (I)) as appears in this system, the oxygen atoms take up positions between the lattice sites of metals, i.e. the interstitial positions. The chemical composition of phase (II) is usually expressed as In the case of <5 / 0, the crystal has various kinds of... 

The structure of alloys— When two or more metals are melted together in suitable proportions a homogeneous solution often results. On cooling, the homogeneous solid is termed a solid solution, since as in a liquid solution, the atoms are distributed in a random fashion. If the structure of the solid solution is identical with that of one of the components (the solvent) the solution is termed a primary or a solid solution. Primary solid solutions are of two types interstitial solid solutions, in which the atoms of the dissolved substance are situated in the holes between the atoms of the solvent and substitution solid solutions in which the solute atoms have taken the place of solvent atoms in the lattice of the latter. 

When the a phase, i.e, the primary solid solution, has only a limited range of stability, other intermediate phases are formed. At particular concentrations of the second component a transformation from one crystal structure to another takes place. In a large number of binary systems, e.g. Gu-Au, Cu-Al, Cu-Sn, a transition from the cubic close packed structure of copper to a body centred cubic structure ()3 phase) occurs at a particular concentration. The phase is stable over a particular range of concentration and at higher concentrations is generally converted to the y-phase which has a complex structure, followed by the e and >) phases which are... 

Correlation of X-ray Diffraction Patterns from MoFe-UFe Mixtures with the Phase Diagram. X-ray diffraction patterns from mixtures with 5 mole % UFe at 6°C. and 14 mole % UFe at 0° to 7°C. appeared to be the same as those obtained from the high-temperature form of MoFe, suggesting a cubic structure. According to Figure 1, the stable phase in these mixtures is the primary solid solution Si which would be expected to have the lattice of the high temperature form of pure MoFe. 

More commonly, the two metals A and B are only partially soluble in the solid state. The first additions of B to A go into solid solution in the A lattice, which may expand or contract as a result, depending on the relative sizes of the A and B atoms and the type of solid solution formed (substitutional or interstitial). Ultimately the solubility limit of B in A is reached, and further additions of B cause the precipitation of a second phase. This second phase may be a B-rich solid solution with the same structure as B, as in the alloy system illustrated by Fig. 12-2(a). Here the solid solutions a and P are called primary solid solutions or terminal solid solutions. Or the second phase which appears may have no connection with the B-rich solid solution, as in the system shown in Fig. 12-2(b). Here the effect of supersaturating a with metal B is to precipitate the phase designated y. This phase is called an intermediate solid solution or intermediate phase. It usually has a crystal structure entirely different from that of either a or P, and it is separated from each of these terminal solid solutions, on the phase diagram, by at least one two-phase region. 

Effect of Increasing Valency of Solute. It has been found that when size-factors are favourable extended solid solutions are most lilcely to be formed when the metals concerned have atoms with the same number of outer-layer electrons, i.e. when they have the sa ne valency. When size-factors arc favourable and valencies unequal tin4 extent of solid solubility will decrease as the difference between the respective valencies increases. To examine the effect of the valency-factor we may consider the extent of the solid solubility in copper ((1u).of the favourable size-factor but increasing valency metals, zinc (Zn), gallium (Ga), germanium (Ge) and arsenic (As), and in silver (Ag) of the corresponding favourable size-factor metals, cadmium (Cd), indium (In), tin (Sn) and antimony (8b). The necessary atomic diameters and valency data (vide p. bl), and the results of experimental work on these1 alloys, as far as the primary solid solutions are concerned, an1 summarised in Fables IX (a) and (h). 

Structures of Abnormal Valency or Electron Intermetallic Compounds. We have seen how in many alloy systems the / -. y- and e-phases are based on electron compounds the formula of which differ very widely but which have in common electron atom ratios of 8 2, 21 18 and 7 4. The range of existence of the particular phases is really a range of solid solution in the compound concerned, and this tends to decrease, as it does in primary solid solution, with increase of valency of the second metal. The j3-, y- and -phases have, however, more in common than mere electron concentration, for they have, in addition, the same lattice structure, although the atomic arrangement is usually a purely random one. Thus, the 8 2 / -compound phase is normally body-centred cubic, although it may have a modified cubic structure known as the /3-manganese one the 21 18 y-compound phase, known as the y-brass structure,... 

Interstitial primary solid solutions are rare among inclusion compounds but not unknown. Thus a-quinol contains small amounts of gas in solid solution, while Dianin s compound forms inclusion compounds of primary solid solution-type, with only small differences in cell dimensions between neat crystals and interstitial solid solutions. The same situation occurs in a-TMA. 

For compositions and crystal structures, see Tables 3.1-122-3.1-124 [1.217,218,223,224]. Primary solid solutions have the fee structure of Ag and the lattice parameters correspond roughly to Vegard s rule with a few exceptions. Alloys with Pt, In, Mg, Cd, and Zn form superlattice phases with tetrahedral and rhombo-... 

Eshelby, J. D. (1954). Distortion of a Crystal by Point Imperfections. Journal of Applied Physics, Vol. 25, No. 2, (February 1954), pp. 255-261. ISSN 0021-8979 Eshelby, J. D. (1956), The continuum theory of lattice defects. Solid State Physics Advances in Research and Applications. Frederick Seitz and David Turnbull, (Ed.), Vol. 3, (1956), pp. 79-144, Elsevier, ISBN 978-0-12-374292-6, Amsterdam, the Netherlands Friedel, J. (1954). Electronic structure of primary solid solutions in metals. Advances in Physics, Vol. 3, No. 12, (October 1954), pp. 446-507, ISSN 0001-8732 Fan, G. J. Choo, H. Liaw, P. K. (2007). A new criterion for the glass-forming ability of liquids. Journal of Non-Crystalline Solids, Vol. 353, No.l, (January 2007), pp. 102-107, ISSN 0022-3093... 

Friedel J (1954) Electronic stmcture of primary solid solutions in metals. Adv Phys 3 446-507... 

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