Solid solution examples

The forms of active components present in heterogeneous catalysts are of importance to catalysis. A supported catalyst usually consists of an active component dispersed on a support with a highly specific surface. According to current opinions (/), an active component dispersed on a support may end up in one of three forms (1) it may retain its chemical identity as a separate crystalline or amorphous phase, (2) it may form a new stoichiometric compound with the support or additive, or (3) it may dissolve in the support to give a solid solution. Examples of these forms are readily available from the literature. 

Example 9. Kinetic oxidation of dissolved ferrous iron with oxygen Example 10.—Aragonite-strontianite solid solution Example 11.-Transport and cation exchange Example 12—Advective and diffusive flux of heat and solutes Example 13.-ID transport in a dual porosity column with cation exchange Example 14.-Advective transport, cation exchange, surface complexation, and mineral equilibria... 

An interstitial solid solution is obtained when the solute (guest) molecule occupies the interstitial space (Fig. 4) in the solvent (host) lattice. For this to occur, the solute molecule diameter should be less than 0.59 times that of the solvent molecule therefore, the volume of the solute molecule should be less than 20% of the solvent molecule. Owing to their large molecular size, polymers favor the formation of interstitial solid solutions. Examples of this type include solid solutions of digitoxin, methyltestosterone, prednisolone acetate, and hydrocortisone acetate in the matrix of PEG-6000. They all exhibit a fast rate of dissolution. 

C. Equilibrium between Solid and Liquid Phases only. I. The Components are Completely Miscible in the Liquid State. a) The pure components only occur as solid phases. Polymorphism of components. Determination of the equilibrium curve. Example, b) Compounds are formed with a congruent meltings point. The indifferent point. Determination of the composition of a compound by thermal analysis. Examples, (c) Compounds are formed with an %ncongruent melting-point. Determination of the composition of the coinpound by thermal analysis. Example. (d) Solid solutions or " mixed crystals are formed, i) The two components can form an unbroken series of solid solutions. Examples. Melting-point curve. Example. Fractional crystallisation of solid solutions, h) The two components do not form a continuous series of solid solutions. Examples. Changes in solid solutions with the temperature. II. The Components are not Completely Miscible in the Liquid State. Suspended transformation. 

Undoubtedly the rare earth metals, with the continuous change of size within the series, offer a highly promising field of study for these new, partly interstitial solid solutions. Examples of the variety of defect structures that can be obtained are the Y(Cu) and the Gd(Cu, Fe) systems. In the former, splat quenching (Giessen et al., 1971) yielded a purely interstitial solid solution in the latter, (Ray, et al., 1972) the solutes were in the form of bi-substitutionals i.e. associated solute pair at one lattice site. 

System in which the two components form a continuous series of solid solutions. In all the preceding examples the individual components (A or B or A By) form separate crystals when solidifying from the melt. There are, however, a number of examples of the separation of a homogeneous solid solution of A and B (or A and A By, etc.). 

Two other types of equilibrium curves are occasionally encountered with the system of two components forming a continuous series of solid solutions. These are shown in Figs. 1,16, 3 and 1,16, 4. In the former the freezing or melting curve passes through a minimum (examples p-chloroiodobenzene, m.p. 57° - p-dichlorobenzene, m.p. 53° naphtha-... 

To prepare the solid phenyldlazonlum chloride or sulphate, the reaction is conducted in the absence of water as far as possible. Thus the source of nitrous acid is one of its organic esters (e.g., amyl nitrite) and a solution of hydrogen chloride gas in absolute alcohol upon the addition of ether only the diazonium salt is precipitated as a crystalline solid, for example ... 

Phenomena at Liquid Interfaces. The area of contact between two phases is called the interface three phases can have only aline of contact, and only a point of mutual contact is possible between four or more phases. Combinations of phases encountered in surfactant systems are L—G, L—L—G, L—S—G, L—S—S—G, L—L, L—L—L, L—S—S, L—L—S—S—G, L—S, L—L—S, and L—L—S—G, where G = gas, L = liquid, and S = solid. An example of an L—L—S—G system is an aqueous surfactant solution containing an emulsified oil, suspended soHd, and entrained air (see Emulsions Foams). This embodies several conditions common to practical surfactant systems. First, because the surface area of a phase iacreases as particle size decreases, the emulsion, suspension, and entrained gas each have large areas of contact with the surfactant solution. Next, because iaterfaces can only exist between two phases, analysis of phenomena ia the L—L—S—G system breaks down iato a series of analyses, ie, surfactant solution to the emulsion, soHd, and gas. It is also apparent that the surfactant must be stabilizing the system by preventing contact between the emulsified oil and dispersed soHd. FiaaHy, the dispersed phases are ia equiUbrium with each other through their common equiUbrium with the surfactant solution. 

In given work the possibilities enumerated above of varieties of thermal analysis used to reseai ch of solid solutions of hydrated diphosphates with diverse composition. So, for example, the results of differential-thermal analysis Zn Co j P O -SH O showed, that it steady in the time of heating on air to 333 K. A further rise of temperature in interval 333 - 725 K is accompanied with the masses loss, which takes place in two basic stages, registered on crooked TG by two clear degrees, attendant to removal 4,0 and 1,0 mole H O. On crooked DTA these stages dehydration registers by two endothermic effects. In interval 603 - 725 K on crooked DTA is observed an exothermal effect. 

Questions of the analytic control of maintenance of the bivalent metals cations to their joint presence in materials of diverse fixing always were actual. A simultaneous presence in their composition of two cations with like descriptions makes analysis by sufficiently complicated process. Determination of composition still more complicates, if analyzed object is a solid solution, in which side by side with pair of cations (for example, Mg " -Co ", Mn -Co, Zn -Co ) attends diphosphate anion. Their analysis demands for individual approach to working of methods using to each concrete cations pair. 

An effect which is frequently encountered in oxide catalysts is that of promoters on the activity. An example of this is the small addition of lidrium oxide, Li20 which promotes, or increases, the catalytic activity of dre alkaline earth oxide BaO. Although little is known about the exact role of lithium on the surface structure of BaO, it would seem plausible that this effect is due to the introduction of more oxygen vacancies on the surface. This effect is well known in the chemistry of solid oxides. For example, the addition of lithium oxide to nickel oxide, in which a solid solution is formed, causes an increase in the concentration of dre major point defect which is the Ni + ion. Since the valency of dre cation in dre alkaline earth oxides can only take the value two the incorporation of lithium oxide in solid solution can only lead to oxygen vacaircy formation. Schematic equations for the two processes are... 

In the examples given below, the physical effects are described of an order-disorder transformation which does not change the overall composition, the separation of an inter-metallic compound from a solid solution the range of which decreases as the temperature decreases, and die separation of an alloy into two phases by spinodal decomposition. 

Example. (Ca, ZrO) nitrates - - (COOH)2 — (Ca, ZrO)(COO)2 calcium and zirconyl nitrates solution to which oxalic acid is added. The oxalate solid solution of cations is then fired to 1300 K... 

These two processes provide examples of the moving boundary problem in diffusing systems in which a solid solution precedes the formation of a compound. The diickness of the separate phase of the product, carbide or... 

The most successful way of combating exhaust-system corrosion is, in fact, stainless steel. This is a good example of how - just as with dry oxidation - the addition of foreign atoms to a metal can produce stable oxide films that act as barriers to corrosion. In the case of stainless steel, Cr is dissolved in the steel in solid solution, and Cr203 forms on the surface of the steel to act as a corrosion barrier. 

As you can see from the tables in Chapter 1, few metals are used in their pure state -they nearly always have other elements added to them which turn them into alloys and give them better mechanical properties. The alloying elements will always dissolve in the basic metal to form solid solutions, although the solubility can vary between <0.01% and 100% depending on the combinations of elements we choose. As examples, the iron in a carbon steel can only dissolve 0.007% carbon at room temperature the copper in brass can dissolve more than 30% zinc and the copper-nickel system - the basis of the monels and the cupronickels - has complete solid solubility. 

A phase is a region of material that has uniform physical and chemical properties. Phases are often given Greek symbols, like a or fi. But when a phase consists of a solid solution of an alloying element in a host metal, a clearer symbol can be used. As an example, the phases in the lead-tin system may be symbolised as (Pb) - for the solution of tin in lead, and (Sn) - for the solution of lead in tin. 

Take the silica-alumina system as an example. It is convenient to treat the components as the two pure oxides SiOj and AI2O3 (instead of the three elements Si, A1 and O). Then the phase diagram is particularly simple, as shown in Fig. 16.6. There is a compound, mullite, with the composition (Si02)2 (Al203)3, which is slightly more stable than the simple solid solution, so the alloys break up into mixtures of mullite and alumina, or mullite and silica. The phase diagram has two eutectics, but is otherwise straightforward. 

The PTC materials already mentioned depend directly on the ferroelectric phase transition in solid solutions based on BaTi03, suitably doped to render them semiconducting. This is a typical example of the interrelations between different electrical phenomena in ceramics. 

Mixed 6),Af-donor ligands such as Schiff bases are of interest in that they provide examples not only of square-planar coordination but also, in the solid state, examples of square-pyramidal coordination by dimerization (Fig. 28.6(b)). A similar situation occurs in the bis-dimethylglyoximato complex, which dimerizes by sharing oxygen atoms, though the 4 coplanar donor atoms are all nitrogen atoms. Copper(II) carboxylates are easily obtained by crystallization from aqueous solution or, in the case of the higher carboxylates, by precipitation with the appropriate acid from ethanolic solutions... 

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