Alkaline earth halide

Systematic studies of the concentration dependence of Br and I relaxation in aqueous solutions of alkaline earth bromides and iodides were reported by Hertz [237] and later the bromine relaxation of aqueous alkaline earth bromide solutions was investigated by Richards and co-workers [51 52], In comparison with the alkali ions, these divalent ions cause a considerably stronger increase in halide ion relaxation rate with concentration. The shape of the plots of relaxation rate versus concentration resembles that obtained with the smaller alkali ions. The different alkaline earth ions have similar influence on Br and I relaxation. The sequence of increasing effect on Br relaxation 

No attempts, corresponding to those described above for the alkali halides, have been made to separate the relaxation rates for the alkaline earth halides into ion-ion and ion-solvent contributions and to analyze these in terms of the electrostatic and electronic distortion models of ion quadrupole relaxation. To do so, certain presently lacking information would be needed such as halide ion chemical shift data. It can, however, be said from the well-established structure-stabilizing effect on water of the alkaline earth ions and from studies of water translational [281] and rotational motions [79] in aqueous alkaline earth halide solutions that a modification of the ion-solvent contribution to halide ion relaxation due to the cations is of great importance. In line with this, in their analyses based on the macroscopic viscosity, Deverell et al. [52] found the ion-ion contributions to Br relaxation to be small at least at not too high electrolyte concentration. Such an interpretation is also suggested by the 

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Table 5.3 Crystal structures of alkaline earth halides ...

Erdalkali, n. alkaline earth, -halogen, n. alkaline-earth halide, -metall, n. alkaline-earth metal, -salze, n.pl. salts of the alkaline-earth metals. 

In this method " - the melt eontains boric oxide and the metal oxide in a suitable electrolyte, usually an alkali or alkaline-earth halide or fluoroborate. The cell is operated at 700-1000 C depending on electrolyte composition. To limit corrosion, the container serving as cathode is made of mild steel or of the metal whose boride is sought. The anode is graphite or Fe. Numerous borides are prepared in this way, e.g., alkaline-earth and rare-earth hexaborides " and transition-metal borides, e.g, TiBj NijB, NiB and TaB... 

Low-temperature solvents are not readily available for many refractory compounds and semiconductors of interest. Molten salt electrolysis is utilized in many instances, as for the synthesis and deposition of elemental materials such as Al, Si, and also a wide variety of binary and ternary compounds such as borides, carbides, silicides, phosphides, arsenides, and sulfides, and the semiconductors SiC, GaAs, and GaP and InP [16], A few available reports regarding the metal chalcogenides examined in this chapter will be addressed in the respective sections. Let us note here that halide fluxes provide a good reaction medium for the crystal growth of refractory compounds. A wide spectrum of alkali and alkaline earth halides provides... 

About a dozen recent publications have appeared in the literature or are in press. These describe other evaluations for the alkaline earth halides (Goldberg and Nuttall, 1978) the biunivalent compounds of iron, nickel and cobalt (Goldberg, Nuttall, and Staples, 1979) lead, copper, manganese and uranium (Goldberg, 1979). Several other publications are in preparation (Goldberg, 1980a, 1980b). 

The osmotic coefficients calculated from Eq. (9) can be brought into good agreement with solution data up to about 1M for aqueous solutions of alkali (26) and alkaline earth halides, (30) tetraalkyl ammonium halides, T3l) mixed electrolytes, where the Harned coefficients are measured, (32) and electrolyte-non electrolyte mixtures, where Setchenow coefficients are measured. 

Fig. 5.5. Free energies of solution (Johnson 1968, p. 70) of alkali metal and alkaline earth halides as a function of cation bonding strength. F = fluorides, C = chlorides, B = bromides, and I = iodides. The lines represent eqn (5.3), the solid line is for F , the broken line for CP, the dense dotted line for Br, and the light dotted line for P.

With some of the alkali- and alkaline-earth halides, ammonia forms complexes that, in their general behaviour, strongly resemble the hydrates. Since neither the positive nor the negative ions have unoccupied orbitals available for bond formation, it has to be assumed that in these ammoniates the ammonia is bonded by the electrostatic attraction of the ions of the halide on the dipole of the ammonia molecule. 

Alkaline-Earth Sulfides and Sulfoselenides. Activated alkaline-earth sulfides have been known for a long time their luminesence is very varied. Emission bands between the ultraviolet and near infrared can be obtained by varying the activation. They are produced by precipitation of sulfates or selenites from purified solutions, followed by reduction with Ar-H2. The addition of activators, for example, copper nitrate, manganese sulfate, or bismuth nitrate, is followed by firing for 1 - 2 h. Alkaline-earth halides or alkali-metal sulfates are sometimes added as fluxes. 

Alkaline-Earth Halides. Of the alkaline-earth halide phosphors, those doped with manganese or rare earths have been used industrially (Section 5.5.4.7) (e.g., CaF2 Mn CaF2 Dy). 

Inorganic Adsorbents. These have two general classifications (a) inorganic salts (e.g., alkali metal nitrates and halides (45), alkaline earth halides (46), vanadium, manganese, and cobalt chlorides (47), and barium sulfate (48). (b) inorganic salts... 

The majority of inorganic systems reported to exhibit photochromism are solids, examples being alkali and alkaline earth halides and oxides, titanates, mercuric chloride and silver halides.184 185 The coloration is generally believed to result from the trapping of electrons or holes by crystal lattice defects. Alternatively, if the sample crystal is doped with an impurity capable of existing in variable oxidation states (i.e. iron or molybdenum), an electron transfer mechanism is possible. 

White [7] gives a general review that includes information about the preparation and purification of a variety of alkali and alkaline earth halide melts. Information about fluorides can also be found in an earlier review article by Bamberger [8]. Many different halide melts have been used as solvents for electrochemistry, and a complete discussion of all of these melts is outside the scope of this chapter. However, two systems that have generated continuous interest over the years are the LiCl-KC1 eutectic (58.8-41.2 mol%, mp = 352°C) [9] and the LiF-NaF-KF (46.5-11.5-42.0 mol%, mp = 454°C) also known as FLINAK [10]. The former is an electrolyte commonly used in thermal batteries, whereas the latter molten salt is of interest for refractory metal plating. 

The reactions producing alkaline earth halides are comprehensively reviewed by Herm [216]. Table 3 summarises measurements of energy disposal in these reactions. 

When working with a solution of an alkali or alkaline-earth halide, the anode is generally made of silver coated with the same metal in a finely-divided state, and the cathode is of silver covered with silver halide. In this case the discharged halogen at the anode combines with the silver to form the insoluble silver halide, and so is effectively removed from the anode compartment. At the cathode, however, the silver halide is reduced to metallic silver and halide ions pass into solution there is consequently a gain in the concentration of the cathode compartment for which allowance must be made. 

Calcium, Sr, Ba and presumably Ra react directly with to form ionic hydrides that have the orthorhombic PbClj structure resembling the heavier alkaline-earth halides (e.g., BaClj, BaBtj, Balj, SrBtj). 

Preparation and Identification of Divalent Lanthanide Ions as Dilute Solutes in Alkaline Earth Halide Solid Solutions... 

In the fused state, the straightforward method is to allow either the lanthanide metal or the alkaline earth metal to react with a melt of the alkaline earth halide and the lanthanide trihalide. This approach yields the desired divalent ions if inert containers are used. Satisfactory reduction has been obtained in molybdenum, tungsten, and tantalum. The... 

Trivalent rare earth or actinide ions can be incorporated in the alkaline earth halides in sites of various symmetries. Since the crystal as a whole must be electrically neutral, charge-compensating ions must also... 

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