The P Phase

Poirier G E, Tariov M J and Rushmeier H E 1994 Two-dimensionai iiquid phase and the p phase of aikanethioi seif-assembied monoiayers on Au(111) La/rgmu// 10 3383-6... 

Alloys of the P type respond to heat treatment, are characterized by higher density than pure titanium, and are more easily fabricated. The purpose of alloying to promote the P phase is either to form an aE-P-phase aEoy having commercially useful quaUties, to form aEoys that have duplex a- and P-stmcture to enhance he at-treatment response, ie, changing the a and P volume ratio, or to use P-eutectoid elements for intermetallic hardening. The most important commercial P-aEoying element is vanadium. 

A progressive etching technique (39,40), combined with x-ray diffraction analysis, revealed the presence of a number of a polytypes within a single crystal of sihcon carbide. Work using lattice imaging techniques via transmission electron microscopy has shown that a-siUcon carbide formed by transformation from the P-phase (cubic) can consist of a number of the a polytypes in a syntactic array (41). 

Conditions that favor dezincification include stagnant solutions, especially acidic ones, high temperatures, and porous scale formation (2). Additions of small amounts of arsenic, antimony, or phosphoms can increase the resistance to dezincification. These elements are, however, not entirely effective in preventing the dezincification of the two-phase (cc—P) brasses because dezincification of the P-phase is not prevented (31). Another area of corrosion concern involves appHed or residual stresses from fabrication that can lead to EIC of brasses in the form of stress-corrosion cracking. 

An alloy is cooled from a temperature at which it has a single-phase structure (a) to a temperature at which the equilibrium structure is two-phase (a -i- ji). During cooling, small precipitates of the P phase nucleate heterogeneously at a grain boundaries. The nuclei are lens-shaped as shown below. 

The investigation of the stability of P -alumina in ZEBRA cells, which always contain some iron, showed an increase of resistance under certain extreme conditions of temperature (370 °C) and of voltage. This is related to the interaction of the P alumina with iron and it was shown that iron enters / -alumina in the presence of an electric field when current is passing, if the cell is deliberately overheated. However, it was found that only the P -phase but not the P"-phase was modified by the incursion of iron. The resistance of the iron-doped regions was high. It was shown that the addition of NaF inhibits access of the iron to the / " -alumina ceramic. By doping practical cells these difficulties have now been overcome and lifetime experiments show that the stability of / "-alumina electrolytes are excellent in ZEBRA cells. 

More complex phenomena occur when current crosses interfaces between semiconductors. The most typical example is the rectification produced at interfaces between p- and n-type semiconductors. Electric current freely flows from the former into the latter semiconductor, but an electric field repelling the free carriers from the junction arises when the attempt is made to pass current in the opposite direction Holes are sent back into the p-phase, and electrons are sent back into the n-phase. As a result, the layers adjoining the interface are depleted of free charges, their conductivities drop drastically, and current flow ceases ( blocking the interface). 

An alternative graphical solution makes use of the biphasic exponential nature of the plasma concentration function ineq. (39.16). At larger time values, when the effect of absorption has decayed, the function behaves approximately as monoexponential. Under these conditions, and after replotting the concentration data on a (decimal) logarithmic scale, one obtains a straight line for the later part of the curve (Fig. 39.8a). This line represents the P-phase of the plasma concentration and is denoted by C ... 

In practice, the half-life time of the dmg in the plasma compartment is derived from the P-phase, and is therefore denoted as rf/2 ... 

A least squares linear regression has been applied to the data pertaining to the p-phase, yielding the values of 1.745 and 0.005166 for the intercept log B and slope Sp, respectively. Using these results, we can compute the extrapolated plasma concentrations between 0 and 20 minutes. From the latter, we subtract the observed concentrations C which yields the concentrations of the a-phase C ... 

First, we determine the P-phase function on a semilog plot by means of linear regression on the later part of the concentration curve for which the time course is most linear (Fig. 39.13a). This yields ... 

The ratio of the intercepts to indicates that the amplitude or peak value of the a-phase is 2.7 times larger than the one of the P-phase, while the ratio of a to P (or t 2 to tfi2) shows that the a-phase decays at a rate which is 17 times larger than that of the P-phase. 

This magnetic behavior is very sensitive to the chemical structure of the spin carrier and to the crystal packing. For instance, for the para-nitro substituted derivative, Nit(p-NO )Ph, which crystallizes in four different phases, the p phase only orders ferromagnetically (Tc = 0.6 K) [8,9], Moreover, attaching the nitro group in the meta-, rather than the / ara-position of the phenyl, leads to an antiferromagnetic compound [2],... 

Scheme 2 Four common packing motifs of the BEDT-TTF molecule. The black bars represent and end-on view of the molecule, looking down the long molecular axis. The a-phase, which is quite similar to the 0-phase, is characterized as a herringbone structure, the P -phase contains stacks of slipped dimers, the K-phase contains orthogonally arranged dimers, and the P"-phase is characterized by canted stacks of donor molecules...

The answer is c. (Katzung, p 35.) The apparent Vd is defined as the volume of fluid into which a drug appears to distribute with a concentration equal to that of plasma, or the volume of fluid necessary to dissolve the drug and yield the same concentration as that found in plasma. By convention, the value of the plasma concentration at zero time is used In this problem, a hypothetical plasma concentration of the drug at zero time (7 mg/mL) can be estimated by extrapolating the linear portion of the elimination curve (the p phase) back to zero time. Therefore, the apparent is calculated by... 

Another issue with ScSZ is that there is a decrease in conductivity at around 580°C as indicated by broken lines in two of the curves for higher scandia contents, 10.0 to 12.0 mol%. With high scandia contents, the cubic phase transforms to a lower conductivity rhombohedral phase, the p phase, at lower temperatures [25], The phase change can be avoided by limiting the scandia content to 8 mole% [25] or by codoping with other oxides, such as those of bismuth [36] or ytterbium [37],... 

The description of a thermodynamic system formed by C components present in P phases needs the specification of temperature, pressure and composition of all the P phases. 

Each of the P phases must be at the same temperature and pressure so there are P — 1 equalities of temperature and P — 1 of pressure. As for the concentration, the C values of each component in each phase must be related to the corresponding C values in the other phases (technically this means the same activity of each component in all the phases) so C(P — 1) relations are found. The total number of equilibrium conditions, therefore, is given by ... 

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