Earth composition of, 52

A limited number of rare-earth minerals are mined for large-scale rare-earth production mona2ite, bastnaesite, loparite [12173-83-OJ, xenotime [13817-22-6]. In addition, siace the 1980s rare-earth-containing clays called ionic ore are mined ia China. Table 4 shows the rare-earth composition of typical mineral concentrates. 

The rare earth composition of commercial electrodes is also related to electrode corrosion. This was noted by Sakai et. al. [44], who found that the presence of Nd or Ce inhibited corrosion when substituted in part for La in La, fZt(NiCoAl)5 (Z = Ce or Nd) electrodes. However no explanation for the effect was noted. Willems [22] prepared an electrode of La0XNd02Ni25Co24 Si0l which retained 88% of its storage capacity after 400 cycles. He attributed its long cycle life to a low VH of 2.6 A3. 

Since the early days of Goldschmidt or Vernadsky, geochemistry has become a mature science which now plays a central role in the Earth Sciences. More particularly, it has evolved considerably over the last fifty years. From an analytical approach with a goal of establishing the chemistry of the Earth compositions of rocks, soils, water, crust and mantle, geochemistry has become an explanatory science. 

The LaRochelle capacity for ore cracking is over 5000 tons as rare earths oxides per year and in Table VIII we show the average production capabilities for the heavier rare earths. It should be noted that the above figures are average values as the rare earths composition of monazite varies somewhat depending on the source. 

The bulk Earth compositions of Rb-Sr and Th-U-Pb are less well known, complicated by the... 

Alfe D, Gillan M J and Price G D 2000 Constraints on the composition of the Earth s core from ab initio calculations Nature 405 172-5... 

Occurrence in Nature. About 99.6% of the earth s mass results from 32 of the chemical elements. The remaining 0.4% is apportioned among 64 elements, all of which are present as traces. Iodine is one of these 64. Estimates about abundance of the constituent elements of the Hthosphere place iodine 46th on a restricted Hst of 59 elements (37 very rare elements are excluded) and 61st on a Hst in which 96 elements are included. Iodine is, indeed, one of the scarcest of the nonmetaUic elements in the total composition of the earth (3). 

Basic oxides of metals such as Co, Mn, Fe, and Cu catalyze the decomposition of chlorate by lowering the decomposition temperature. Consequendy, less fuel is needed and the reaction continues at a lower temperature. Cobalt metal, which forms the basic oxide in situ, lowers the decomposition of pure sodium chlorate from 478 to 280°C while serving as fuel (6,7). Composition of a cobalt-fueled system, compared with an iron-fueled system, is 90 wt % NaClO, 4 wt % Co, and 6 wt % glass fiber vs 86% NaClO, 4% Fe, 6% glass fiber, and 4% BaO. Initiation of the former is at 270°C, compared to 370°C for the iron-fueled candle. Cobalt hydroxide produces a more pronounced lowering of the decomposition temperature than the metal alone, although the water produced by decomposition of the hydroxide to form the oxide is thought to increase chlorine contaminate levels. Alkaline earths and transition-metal ferrates also have catalytic activity and improve chlorine retention (8). 

Their contribution to the total dissolved load in rivers can be estimated by considering the mean composition of river water and the relative importance of various rocks to weathering. Estimates (18) indicate that evaporites and carbonates contribute approximately 17% and 38%, respectively, of the total dissolved load in the wodd s rivers. The remaining 45% is the result of the weathering of siUcates, underlining the significant role of these minerals in the overall chemical denudation of the earth s surface. 

The foremnner of the modern methods of asphalt fractionation was first described in 1916 (50) and the procedure was later modified by use of fuller s earth (attapulgite [1337-76-4]) to remove the resinous components (51). Further modifications and preferences led to the development of a variety of fractionation methods (52—58). Thus, because of the nature and varieties of fractions possible and the large number of precipitants or adsorbents, a great number of methods can be devised to determine the composition of asphalts (5,6,44,45). Fractions have also been separated by thermal diffusion (59), by dialysis (60), by electrolytic methods (61), and by repeated solvent fractionations (62,63). 

The X-ray microanalysis is the basic method of study of rare-metal and rare-earth minerals of micron size. The multi-component composition, instability of minerals under the electron beam, overlap of X-ray characteristic lines, absence of reference samples of adequate composition present difficulties in the research of mineral composition. 

The gaseous composition of unpolluted tropospheric air is given in Table 2-1. Unpolluted air is a concept, i.e., what the composition of the air would be if humans and their works were not on earth. We will never know the... 

Air The composition of gases that make up the earth s atmosphere, approximately 79% nitrogen and 21% oxygen. Pure air has no definite meaning regarding the proportion of these gases this term is used to imply the absence of industrial particulate matter. 

Composition of the Earth s Crust, Seawater, and the Human Body ... 

Air is the source of six industrial gases, N2, O2. Ne, Ar, Kr and Xe. As the mass of the earth s atmosphere is approximately 5 X 10 million tonnes, the supply is unlimited and the annual industrial production, though vast, is insignificant by comparison. The composition of air at low altitudes is remarkably constant, the main variable component being water vapour which ranges from 4% by volume in tropical jungles to very low values in cold or arid climates. Other minor local variations result from volcanism or human activity. The main invariant part of the air has the following composition (% by volume, bp in parentheses) ... 

The method is based on the complete dissolution of the raw material. Only alkali earth metals and rare earth metals that form insoluble salts do not usually provide any significant preliminary concentration of the material during decomposition. In addition, concentration of tantalum and niobium in the final solution yielding by dissolution depends on the composition of the raw material. 

The composition of the earth s atmosphere differs from day to day, from altitude to altitude, and from place to place. The largest variation is in the concentration of water vapor. Water evaporates continually from the hydrosphere, from the soil, from leaves, from clothes drying, etc. At intervals, parts of the atmosphere become chilled until the dew point or frost point is reached and then any vapor in excess of the saturation amount is precipitated as rain or snow. 

Needless to say, the extreme difficulty we experience in probing the composition of the earth beneath us suggests that little is known about the inner composition of the planets. The evidence available is indirect (average density, sur-... 

Geological surveys require the services of analytical chemists to determine the composition of the numerous rock and soil samples collected in the field. A particular instance of such an exercise is the qualitative and quantitative examination of the samples of moon rock brought back to Earth in 1969 by the first American astronauts to land on the moon. 

---