Calcium and Strontium

Co-condensation of Ca atoms and ArH vapours at 77K provided (ArH )2Ca (Ar=H, PhMe, PhEt or PhSiMe ). Calcium ultrafine particles, obtained by vapourizing Ca at 900 C in a vacuum vessel, have been successfully used to prepare organocalcium compounds in THF from organic bromides, iodides and alkyl chlorides. Gas phase reactions of M vapour (M=Ca or Sr) with cyclopentadiene produced CpM, which has been investigated using laser spectroscopy. The gas phase molecular structure determination of (C Meg)2Ca (Cp2 Cd), obtained from CpH. .and Cal2, by e.d. revealed that the two Cp rings are not parallel in contrast those In Cp2 Hg. 

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Coatings, Paints, and Pigments. Various slightly soluble molybdates, such as those of zinc, calcium, and strontium, provide long-term corrosion control as undercoatings on ferrous metals (90—92). The mechanism of action presumably involves the slow release of molybdate ion, which forms an insoluble ferric molybdate protective layer. This layer is insoluble in neutral or basic solution. A primary impetus for the use of molybdenum, generally in place of chromium, is the lower toxicity of the molybdenum compound. 

Health and Safety Factors. The strontium ion has a low order of toxicity, and strontium compounds are remarkably free of toxic hazards. Chemically, strontium is similar to calcium, and strontium salts, like calcium salts, are not easily absorbed by the intestinal tract. Strontium carbonate has no commonly recognized hazardous properties. Strontium nitrate is regulated as an oxidizer that promotes rapid burning of combustible materials, and it should not be stored in areas of potential fire hazards. 

Barium [7440-39-3] Ba, is a member of Group 2 (IIA) of the periodic table where it Hes between strontium and radium. Along with calcium and strontium, barium is classed as an alkaline earth metal, and is the densest of the three. Barium metal does not occur free in nature however, its compounds occur in small but widely distributed amounts in the earth s cmst, especially in igneous rocks, sandstone, and shale. The principal barium minerals are barytes [13462-86-7] (barium sulfate) and witherite [14941-39-0] (barium carbonate) which is also known as heavy spar. The latter mineral can be readily decomposed via calcination to form barium oxide [1304-28-5] BaO, which is the ore used commercially for the preparation of barium metal. 

Compared to the hydroxides of calcium and strontiuim, barium hydroxide is the most water-soluble and also the strongest base. Additionally, barium hydroxide is more difficult to convert to the oxide by heating than are the corresponding hydroxides of calcium and strontium. Barium oxide is more readily converted to the peroxide than are the oxides of the other alkaline earths. 

Alkaline-earth metals are often deterruined volumetricaHy by complexometric titration at pH 10, using Eriochrome Black T as indicator. The most suitable complexing titrant for barium ion is a solution of diethylenetriaminepentaacetic acid (DTPA). Other alkaline earths, if present, are simultaneously titrated, and in the favored analytical procedure calcium and strontium are deterruined separately by atomic absorption spectrophotometry, and their values subtracted from the total to obtain the barium value. 

Heating with the following solids, their fusions, or vapours (a) oxides, peroxides, hydroxides, nitrates, nitrites, sulphides, cyanides, hexacyano-ferrate(III), and hexacyanoferrate(II) of the alkali and alkaline-earth metals (except oxides and hydroxides of calcium and strontium) (b) molten lead, silver, copper, zinc, bismuth, tin, or gold, or mixtures which form these metals upon reduction (c) phosphorus, arsenic, antimony, or silicon, or mixtures which form these elements upon reduction, particularly phosphates, arsenates,... 

Thermogravimetry may be used to determine the composition of binary mixtures. If each component possesses a characteristic unique pyrolysis curve, then a resultant curve for the mixture will afford a basis for the determination of its composition. In such an automatic gravimetric determination the initial weight of the sample need not be known. A simple example is given by the automatic determination of a mixture of calcium and strontium as their carbonates. 

Both carbonates decompose to their oxides with the evolution of carbon dioxide. The decomposition temperature for calcium carbonate is in the temperature range 650-850 °C, whilst strontium carbonate decomposes between 950 and 1150°C. Hence the amount of calcium and strontium present in a mixture may be calculated from the weight losses due to the evolution of carbon dioxide at the lower and higher temperature ranges respectively. This method could be extended to the analysis of a three-component mixture, as barium carbonate is reported to decompose at an even higher temperature ( 1300 °C) than strontium carbonate. 

Slag modifiers raise the fusion point or sintering temperature of the ash and directly neutralize any S03 formed. They are based on alkaline-earth metals such as magnesium, calcium, and strontium, or rare-earth metals such as cerium they are available as oxides, salts, or soaps. 

Comar, C.E. 1963 Some over-all aspects of strontium-calcium discrimination. In Wasserman, R.H., ed.. The Transfer of Calcium and Strontium Across Biological Membranes. New York, Academic Press 405 18. 

Pecher, C. 1941 Biological investigations with radioactive calcium and strontium. Proceedings of the Society for Experimental Biology Medicine 46 86-91. 

Wasserman, R.H., Lengemarm, F.W. and Comar, C.L. 1958 Comparative metabolism of calcium and strontium in lactation. Journal of Dairy Science 41 812-821. 

A long time passed between the first discovery of AE3(BN2)2 phases [17] (AE = Ca, Sr) and their structural characterizations [18, 19]. Two distinct phases are known to exist for both calcium and strontium nitridoborate, denoted as low-temperature y9-AE3(BN2)2 and high-temperature a-AE3(BN2)2 [20]. Their phase transitions have been studied by temperature-dependent XRD, thermo-... 

Recently, Wilson Combe (1991) have studied the reactivity of magnesium, zinc, calcium and strontium boroaluminate glasses towards poly(acrylic acid) solutions. The controlling factor would seem to be the alumina content of these glasses which serves to moderate the setting rate of the cements. 

As with calcium and strontium oxides, barium oxide reacts very exothermically with water, forming hydrogen.The heat which is released is such that it can, like... 

Fig. 11.11, p. 112). Incommensurate structures related to bismuth-III are also observed for strontium and barium. Magnesium, calcium and strontium are remarkable in that they transform from the normal closest-packing of spheres to a body-centered packing upon exertion of pressure. Even more remarkable is the following decrease of the coordination number to 6 for calcium and strontium (Ca-III, a-Po type Sr-III, /3-tin type). 

Alkali-earth metals sodium, magnesium, potassium, calcium, and strontium... 

Barium sulfide explodes weakly on heating with lead dioxide or potassium chlorate, and strongly with potassium nitrate. Calcium and strontium sulfides are similar. 

Treatment of the amine 173 (LBu H) in a 2 1 ratio with M[N(SiMe3)2]2(THF)2 (M = Ca, Sr, Ba) in toluene at ambient temperatures affords ( 5-LBut)2M 174 in >93% yields.395 All three compounds possess bent-sandwich structures with -coordinated /3-diketiminato ligands. Similar treatment of the Pr analog of 173 (i.e., LPr H) yields the corresponding calcium and strontium complexes (r 2-LPr )2Ca 175 and (r/s-LPr )2Sr, respectively, in high yield. The reaction of Ba[N(SiMe3)2]2(THF)2 with LPr H yield the -symmetric dinuclear complex 176 (Figure 90). The... 

Lanthanum chromite is a p-type conductor so divalent ions, which act as electron acceptors on the trivalent (La3+ or Cr3+) sites, are used to increase the conductivity. As discussed above, the most common dopants are calcium and strontium on the lanthanum site. Although there is considerable scatter in the conductivities reported by different researchers due to differences in microstrucure and morpohology, the increase in conductivity with calcium doping is typically higher than that with strontium doping [4], The increase in conductivity at 700°C in air with calcium additions is shown in Figure 4.1 [1, 2, 28-44], One of the advantages of the perovskite structure is that it... 

FIGURE 4.4 Coefficients of thermal expansion of calcium- and strontium-doped lanthanum... 

Paulik SW, Baskaran S, and Armstrong TR. Mechanical properties of calcium- and strontium-substituted lanthanum chromite. J. Mater. Sci. 1997 33 2397-2404. 

Menzel, R.G., Heald, W.R., 1955, Distribution of potassium, rubidium, caesium, calcium and strontium within plants grown in nutrient solutions. Soil Sci. 78 (5) 287-293. 

Davy also discovered several other elements (potassium, barium, calcium, and strontium) by isolating the metals from their compounds through electrolysis. His work led to the development of electrochemistry, which is the use of electricity as the energy source to break up the oxides of these alkali and alkali earth elements. 

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