Surface saturation state

The upper plateau of the isotherm of sulfur chemisorption allows definition of a surface saturation state of sulfur for each metal. Such a state can be reached in a large range of temperatures and partial pressures of hydrogen sulfide. Using 35S, Oudar (21) listed the values obtained on different metals for a maximum concentration of sulfur before the appearance of solid sulfide. On the (100) faces of nickel and platinum, this saturation state corresponds to one sulfur atom for two accessible metallic atoms. On the (111) faces, it is slightly lower than one sulfur atom for two metal atoms. On the (110) faces, it is, respectively, equal to 0.71 on nickel... 

When the airflow meets a surface whose temperature is lower than the dewpoint, water vapor from the air condenses on the surface of the cooling coil. If all air comes into contact with the cold surface, the state of the air after the process will be at point 3. Some air always escapes the cold surface, and therefore the state of air after contact with the coil is a mixture of saturated air (3) and escaped air (1). The mixing point (2) lies on the line connecting points 1 and 3, as shown in Example 8. The nearer point 2 is to point 3, the more effective is the cooling coil. 

Figure 6-8 shows how the partial pressure of carbon dioxide in equilibrium with surface water oscillates in phase with the fluctuations in precipitation rate, saturation state, and temperature. The oscillations in alkalinity and bicarbonate concentrations have shifted in phase by about 90° because these quantities decrease when precipitation and evaporation are removing carbon from the system at above-average rates. 

Up to now we have presented this example without any regard for consistency, i.e. satisfying thermodynamic and conservation principles. This fuel mass flux must exactly equal the mass flux evaporated, which must depend on q and h(g. Furthermore, the concentration at the surface where fuel vapor and liquid coexist must satisfy thermodynamic equilibrium of the saturated state. This latter fact is consistent with the overall approximation that local thermodynamic equilibrium applies during this evaporation process. 

Low temperature etching. Our data suggests that, under hydrothermal conditions the rate of pit formation is dramatically reduced, although perhaps not completely stopped, at C = Ccrjt. Etch pits on a natural, hydrothermally-etched quartz surface therefore indicate extended dissolution times, but not necessarily etching at C < Ccrit This is because the rate of etch pit formation even above Ccr t can be significant at elevated temperatures (as shown by crystal R9). However, at low temperatures, formation of etch pits when C > C would be less likely, and natural surfaces etched at low temperature should record the saturation state of the etching fluid. 

Supersaturated a solution containing more solute than is present in its saturated state Surface Tension property of liquid causing it to contract to the smallest possible area due to the unbalance of forces at the surface of the liquid... 

S100A13 differs from the other family members in its very broad expression pattern and the absence of a surface-exposed hydrophobic patch in the Ca2+-saturated state. Its 3-dimensional structures (Sivaraja et al., 2005) deposited in the RCSB Protein Data Bank supports the unique properties of this S100A13 protein. 

The equations and methods given in this chapter can be used to calculate the distribution of carbonic acid system components and the saturation state of a solution with respect to a carbonate mineral under varying temperature, pressure, and composition. To illustrate the type of changes that occur, a calculation has been done for seawater, and the results summarized for nine different cases in Table 1.12. Case 1 is used as a reference typical of surface, subtropical, Atlantic seawater in equilibrium with the atmosphere. In all other cases the salinity and total... 

The applicability of scanning Auger spectroscopy to the analysis of carbonate mineral surface reactions was demonstrated by Mucci and Morse (1985), who carried out an investigation of Mg2+ adsorption on calcite, aragonite, magnesite, and dolomite surfaces from synthetic seawater at two saturation states. Results are summarized in Table 2.5. 

Table 2.5. The Mg to Ca concentration ratio on the surface of four carbonate mineral crystals after extended exposure to synthetic seawater at two different saturation states. (After Mucci and Morse, 1985.)...

The Mg to Ca surface ratios for calcite in both supersaturated seawater solutions were nearly identical. The lower Mg to Ca surface ratio obtained in the less supersaturated solution may be the result of incomplete coverage of the pure calcite crystal by the magnesian calcite overgrowth. The Mg to Ca surface ratio on calcite exposed to both saturation state solutions is in close agreement with the value of 1 obtained in a solution with a Mg2+ to Ca2+ ratio of 5 by Moller and his associates. 

It should be kept in mind that, in spite of these major variations in the CO2-carbonic acid system, virtually all surface seawater is supersaturated with respect to calcite and aragonite. However, variations in the composition of surface waters can have a major influence on the depth at which deep seawater becomes undersaturated with respect to these minerals. The CO2 content of the water is the primary factor controlling its initial saturation state. The productivity and temperature of surface seawater also play major roles, in determining the types and amounts of biogenic carbonates that are produced. Later it will be shown that there is a definite relation between the saturation state of deep seawater, the rain rate of biogenic material and the accumulation of calcium carbonate in deep sea sediments. 

Let us now consider the problem from the standpoint of calcite precipitation kinetics. At saturation states encountered in most natural waters, the calcite reaction rate is controlled by surface reaction kinetics, not diffusion. In a relatively chemically pure system the rate of precipitation can be approximated by a third order reaction with respect to disequilibrium [( 2-l)3, see Chapter 2]. This high order means that the change in reaction rate is not simply proportional to the extent of disequilibrium. For example, if a water is initially in equilibrium with aragonite ( 2c=1.5) when it enters a rock body, and is close to equilibrium with respect to calcite ( 2C = 1.01), when it exits, the difference in precipitation rates between the two points will be over a factor of 100,000 The extent of cement or porosity formation across the length of the carbonate rock body will directly reflect these... 

NO desorption from the alloy surface saturated at 80 K is observed at X = 193 nm and is a singlephoton process. The rotational energy distributions in the Boltzmann plot are shown in Fig. 30 and satisfy an almost linear relation, the gradient of which gives Tt 350 K. The two spin-orbit states look... 

Carbonate 1. Surface water nearly always supersaturated with respect to CaC03 (200-500%) favored by high pH values and moderate temperatures 2. Variation with depth saturation state with respect to CaC03 decreases as the result of lower temperature and pH. Under saturated in deep waters (e.g., below 200-300 m)... 

Unless a wet cell or cryo stage is used, the fine microstructure is much altered by dehydration in the instrument (J10,S41). However, localized drying occurs in any paste even before it is placed in a high vacuum, as soon as the RH falls below saturation. The water is lost initially from the wider pores, which are probably represented disproportionately on fracture surfaces. The state of the cement paste in a practical concrete may thus vary on both a macro and a micro scale between dry and saturated. 

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