End-members

There is often a wide range of crystalline soHd solubiUty between end-member compositions. Additionally the ferroelectric and antiferroelectric Curie temperatures and consequent properties appear to mutate continuously with fractional cation substitution. Thus the perovskite system has a variety of extremely usehil properties. Other oxygen octahedra stmcture ferroelectrics such as lithium niobate [12031 -63-9] LiNbO, lithium tantalate [12031 -66-2] LiTaO, the tungsten bron2e stmctures, bismuth oxide layer stmctures, pyrochlore stmctures, and order—disorder-type ferroelectrics are well discussed elsewhere (4,12,22,23). 

Another important class of titanates that can be produced by hydrothermal synthesis processes are those in the lead zirconate—lead titanate (PZT) family. These piezoelectric materials are widely used in manufacture of ultrasonic transducers, sensors, and minia ture actuators. The electrical properties of these materials are derived from the formation of a homogeneous soHd solution of the oxide end members. The process consists of preparing a coprecipitated titanium—zirconium hydroxide gel. The gel reacts with lead oxide in water to form crystalline PZT particles having an average size of about 1 ]lni (Eig. 3b). A process has been developed at BatteUe (Columbus, Ohio) to the pilot-scale level (5-kg/h). 

The reduction of molybdate salts in acidic solutions leads to the formation of the molybdenum blues (9). Reductants include dithionite, staimous ion, hydrazine, and ascorbate. The molybdenum blues are mixed-valence compounds where the blue color presumably arises from the intervalence Mo(V) — Mo(VI) electronic transition. These can be viewed as intermediate members of the class of mixed oxy hydroxides the end members of which are Mo(VI)02 and Mo(V)0(OH)2 [27845-91-6]. MoO and Mo(VI) solutions have been used as effective detectors of reductants because formation of the blue color can be monitored spectrophotometrically. The nonprotonic oxides of average oxidation state between V and VI are the molybdenum bronzes, known for their metallic luster and used in the formulation of bronze paints (see Paint). 

Solid solution series where x = A/(A End member of series. 

Vermicuhte is an expandable 2 1 mineral like smectite, but vermiculite has a negative charge imbalance of 0.6—0.9 per 02q(0H)2 compared to smectite which has ca 0.3—0.6 per 02q(0H)2. The charge imbalance of vermiculite is satisfied by incorporating cations in two water layers as part of its crystal stmcture (144). Vermiculite, which can be either trioctahedral or dioctahedral, often forms from alteration of mica and can be viewed as an intermediate between UHte and smectite. Also, vermiculite is an end member in a compositional sequence involving chlorite (37). Vermiculite may be viewed as a mica that has lost part of its K+, or a chlorite that has lost its interlayer, and must balance its charge with hydrated cations. 

Chlorite is another mineral that is commonly associated with mixed-layered clays. Complete soHd solutions of chlorite mixed-layer minerals have not been identified. In contrast to iUite—smectite mixed-layer minerals, chlorite mixed-layer minerals occur either as nearly equal proportions of end-member minerals (Rl) or dominated by one end member (RO) (142). Mixed-layer chlorite may consist of any of the di—tri combinations of chlorite and chlorite mixed-layering occurs with serpentine, kaolinite, talc, vermicuhte, smectite, and mica. References of specific chlorite mixed-layer minerals of varied chemical compositions are available (142,156). 

Global uranium flux calculations have typically been based on the following two assumptions (a) riverine-end member concentrations of dissolved uranium are relatively constant, and (b) no significant input or removal of uranium occurs in coastal environments. Other sources of uranium to the ocean may include mantle emanations, diffusion through pore waters of deep-sea sediments, leaching of river-borne sediments by seawater," and remobilization through reduction of a Fe-Mn carrier phase. However, there is still considerable debate... 

Cations exchanged into the interlayers of expandable clays (smectites) are comparatively easy to study with NMR methods because the cations become major components of the phase and their concentrations are often several wt %. In addition to Cs Li, Na, K, and Cd have been studied by NMR. We have chosen to investigate Cs because it is a significant component of nuclear waste, because it provides an end-member case as the least electronegative cation, and because it has desirable nuclear properties (100% abundance, relatively high frequency, 65.5 MHz at H = 11.7 T, and small quadrupole moment)... 

Because seawater signatures of temperature and salinity are acquired by processes occurring at the air-sea interface we can also state that the density characteristics of a parcel of seawater are determined when it is at the sea surface. This density signature is locked into the water when it sinks. The density will be modified by mixing with other parcels of water but if the density signatures of all the end member water masses are known, this mixing can be unraveled and the proportions of the different source waters to a given parcel can be determined. 

Hydrothermal vents have been sampled at 21 along the East Pacific Rise. The pure end member hydrothermal solutions have a temperature of 350°C and the following major ion composition (von Damm et al. (1985). Geochim. Cosmochim. Acta 49, 2197-2220). All concentrations are in mM and the pH is 3.4. Discuss the... 

VsGcsB is the end member of a homogeneous solid solution V5Ge3Bx (0 < x 1, 700°C) starting from binary V5Ge3-... 

Magar VS, GW Johnson, RFC Brenner, JF Quensen, EA Foote, G Durell, JA Ickes, C Peven-Mccarthy (2005a) Long-term recovery of PCB-contaminated sediments at the Lake Hartwell superfund site PCB dechlorination. 1. End-member characterization. Environ Sci Technol 39 3538-3547. 

The variations in Fe and Mg contents of the 14 A Fe-chlorite-14 A Mg-chlorite solid solution are considered here. However, structural formulae for chlorite are not as simple as those considered here. As mentioned by Walshe and Solomon (1981), Stoesell (1984), Cathelineau and Nieva (1985) and Walshe (1986), chlorite solid solution may be represented by six components, and accurate thermochemical data on each end-member component at the hydrothermal conditions of concern are necessary to provide a far more rigorous calculation of the equilibrium between chlorite and hydrothermal solution. However, the above argument demonstrates that the composition of chlorite is a highly useful indicator of physicochemical conditions of hydrothermal solution and extent of water-rock interaction. 

Few data on the chemical compositions of feldspars (albite, K-feldspar) are available. Fuji (1976) indicated that K-feldspar and albite in the propylite of west Izu Peninsula, middle Honshu are of nearly end member composition. Nagayama (1992) showed that K-feldspars in the Hishikari Au-Ag vein and in the host andesitic rock have different composition Na/K ratio of K-feldspars from the vein is lower than that from the host rocks. 

Chemical compositions of end member hydrothermal solution venting from back-arc basins and midoceanic ridges are summarized in Table 2.14 and Table 2.15 (Ishibashi and Urabe, 1995 Gamo, 1995). 

Submarine hydrothermal fluid end-member data observed at various plate boundary regions (end-member values are those obtained by extrapolation to an assumed value of zero magnesium, except for the values at site 2). BAB back-arc basin (Game, 1995)... 

Fig. 2.40. Relationship between Mn and Fe concentrations in hydrothermal end-member fluids so far observed. Numbers correspond to the site No. in Table 2.15. Hatched areas show the data of sediment-hosted hydrothermal sites (Gamo, 1995).

Fig. 2.41. Relationship between (a) Li and Rb, and (b) Li and Cs concentrations of the fluid end-members from Table 2.15. Filled circles and open circles stand for. sediment-hosted sites and sediment-starved sites, respectively. Numbers mean the site No. in Table 2.15 (Gamo, 1995).

Sulfates (barite and anhydrite) precipitate due to the mixing of discharging hydrothermal solution with cold seawater above the seafloor at an early stage of hydrothermal activity. Ca and Ba in hydrothermal solution react with SO in cold seawater, leading to the precipitations of anhydrite and barite. It is observed that anhydrite precipitated earlier than barite. This may depend on the initial Ca and Ba concentrations of end member hydrothermal solutions, temperature and degree of mixing of hydrothermal solutions and... 

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