Alkaline earth sulfide

Data for ionic oxides (alkaline earth oxides) are presented in Chapter 11, although they could be presented in this chapter since they are bonded ioni-cally. The sulfides are closely related, and are presented here. 

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The use of alkali or alkaline-earth sulfides cataly2es the reaction so that it is complete in a few hours at 150—160°C use of aluminum chloride as the catalyst gives a comparable reaction rate at 115°C. When an excess of sulfur is used, the product can be distilled out of the reactor, and the residue of sulfur forms part of the charge in the following batch reaction. The reaction is carried out in a stainless steel autoclave, and the yield is better than 98% based on either reactant. Phosphoms sulfochloride is used primarily in the manufacture of insecticides (53—55), such as Parathion. 

The predominantly ionic alkali metal sulfides M2S (Li, Na, K, Rb, Cs) adopt the antifluorite structure (p. 118) in which each S atom is surrounded by a cube of 8 M and each M by a tetrahedron of S. The alkaline earth sulfides MS (Mg, Ca, Sr, Ba) adopt the NaCl-type 6 6 structure (p. 242) as do many other monosulfides of rather less basic metals (M = Pb, Mn, La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Th, U, Pu). However, many metals in the later transition element groups show substantial trends to increasing covalency leading either to lower coordination numbers or to layer-lattice structures. Thus MS (Be, Zn, Cd, Hg) adopt the 4 4 zinc blende structure (p. 1210) and ZnS, CdS and MnS also crystallize in the 4 4 wurtzite modification (p. 1210). In both of these structures both M and S are tetrahedrally coordinated, whereas PtS, which also has 4 4... 

Alkaline-earth sulfides react vigorously with chromyl chloride, lead dioxide, potassium chlorate (explodes lightly) and potassium nitrate (explodes violently). 

Figure 9.10 Vickers hardness numbers as a function of the molecular volumes of the alkaline earth sulfides.

In the late nineteenth century and early twentieth century, Lenard et al. in Germany carried out systematic research on phosphors. They prepared phosphors based on alkaline earth sulfides and selenides, and also on ZnS, and studied their luminescence. In these studies, they laid down the fundamentals of phosphor research.6 Other significant contributions included those of H. W. Leverenz and colleagues at the Radio Corporation of America (RCA)1 laboratories who investigated many phosphors for use in television tubes which led to detailed work being carried out on ZnS-type phosphors.7... 

The alkaline earth sulfides activated with rare earths are also of importance. They are suitable for use in CRTs because of the linear dependence of their brightness on applied current over a wide range. For example, MgS activated with 0.004% Eu has a very bright maximum emission at 600 nm. 

SrGa S Ce C 14). The motivation for choosing sulfides for de-velopment is, in part, simply that the most efficient families of CRT phosphors are sulfides ZnS, CdS, and the alkaline earth sulfides. However, rare earth based sulfides have not achieved the CR efficiency of the conventional sulfides. 

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. 

Among the long afterglow alkaline-earth sulfides, only (Ca, Sr)S Bi3+, CaS Bi3+, and CaS Eu2+, Tm2+ still have any real importance because their respective blue, violet, and red luminescence cannot yet be achieved with the less hydrolysis-sensitive zinc sulfide phosphors. The last-mentioned phosphor gives an intensive red afterglow and can substitute the red zinc-cadmium phosphor. 

Only the alkalis and alkaline earths form sulfides that appear to be mainly ionic. They are the only sulfides that dissolve in water and they crystallize in simple ionic lattices, for example, an anti-fluorite lattice for the alkali sulfides and a rock salt lattice for the alkaline earth sulfides. Essentially only SH" ions are present in aqueous solution, owing to the low second dissociation constant of H2S. Although S2" is present in concentrated alkali solutions, it cannot be detected below 8 M NaOH owing to the reaction... 

C. Fouassier, Luminescence of Rare-Earth-doped Alkaline-Earth-Sulfides, in Inorganic and Organic Electroluminescence , eds. R. H. Mauch and H. E. Gumhch, W T, Berhn, 1996, p. 313. 

The Polysulfides. Sulfur dissolves in a solution of an alkali or alkaline-earth sulfide, forming a mixture of polysulfides ... 

K) = 9.03 3.0 kcal mol", Is based on the Knudsen mass-spectrometrlc study of Colin et al. ( ). Our reanalysls of their ion intensity data is given below. Although the large drift would suggest a larger uncertainty in the derived quantities (A H, D ), our experience with related work on other alkaline earth sulfides and oxides by the same authors indicates that results derived from a 3rd law analysis are preferred. 

Rare earth element doped alkaline earth sulfides are employed in luminescence-based devices like thin film electroluminescent displays [119,120] and devices for optical data storage [121]. Strontium sulfide, SrS, thin films have been prepared by atomic layer epitaxy from [Sr(tmhd)2] (tmhd" 7) in the presence of HiS [122]. Additionally, solid sources have been employed in a comparable CVD approach [122b]. 

Alkaline earth sulfides can be easily prepared in small quantities (3-5 g.) by heating their pure carbonates (C.P.) for about two hours at about 1000°C in a fast stream of an equimolar mixture of KgS and Hg. When water ceases to evolve, Hg alone is passed through for about half an hour to decompose the polysulfides. The product is left to cool in a stream of ... 

Other preparative methods Larger amounts of sulfides, though of lower purity, can be obtained by heating the carbonates in a crucible with an excess of elemental S. Here, tight closure of the crucible is essential and use of an autoclave Is advantageous. This procedure is mostly used to produce pho hors based on alkaline earth sulfides. 

Although we can conclude from the optical electronegativities that LMCT transitions play a role in the absorption spectra of lead thiolates, it is not currently known to what extent intraatomic transitions may also contribute to these bands, or what orbitals are involved in the transitions. There have been no detailed theoretical studies of lead-thiolate CT bands, and very little work in general has been reported on the absorption spectroscopy of Pb(II) coordination complexes. Although the absorption spectra have been reported for solid-state Pb(ll) alkaline earth sulfides (69-71), these data have not been analyzed extensively. In addition, much of the data that have been reported (69-71) are ambiguous due to insufficient information on sample preparation and composition (95). 

Several complementary pairs of activators have been used, but the most effective are those consisting of cerium-samarium and europium-samarium, the samarium ions furnishing the trapping centers. Phosphors of this type are best prepared from the pure alkaline earth sulfides or selenides by introducing the activators wdth the aid of a flux such as an alkaline earth halide or lithium fluoride. 

Guo CF, Chu BL, Su Q (2004) Improving the Stability of alkaline earth sulfide based phosphors. Appl Surf Sci 225 198... 

Nevertheless, certain conclusions may be drawn from even a brief perusal of this work. These include the necessity of positively identifying electrochemical waves by methods such as the standard addition technique. Moreover, there is a clear need to control the sulfur partial pressure over melts. Lastly, more attention must be given to the role of solvent and solute cation composition, since many of the apparent disagreements in the literature have arisen because authors have employed different alkali and alkaline earth sulfides. 

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