A exchanged with

O atoms from N20 photolysis at 1849 A exchange with those in C02 (1060). 

It is also of interest to use MAS NMR for the study of the thermal treatment of zeolites which are not in the ammonium-exchanged form. In an X-ray study, Pluth and Smith (179) found electron density at the center of the sodalite cages in dehydrated zeolites Ca-A and Sr-A and attributed this to a partial occupancy of these sites by a four-coordinated aluminous species. No such effect was found in zeolite A exchanged with monovalent cations. Corbin et al. (180) used 27A1 MAS NMR to examine commercial samples of K-A, Na-A and (Ca,Na)-A, as received (see Fig. 41). For K-A and Na-A, only framework tetrahedral Al species were observed, with chemical shifts of 57 and 52 ppm respectively. However, in (Ca,Na)-A an additional intense resonance at 78 ppm, typical of AlfOH) but definitely not due to framework aluminum, was also found (see Fig. 41). A much weaker signal, also at 78 ppm, was detected in zeolite Sr-A its intensity increased greatly on heating the sample to 550°C. Freude et al. (183) came to very similar conclusions in their NMR study of heat-treated zeolite Ca-A. They found that maximum framework dealumination occurs at 500°C and corresponds to ac. 17% of total Al. 

Figure 9 Illustration of the relative gravity parameter, (a) Occupant A may move to an empty cell with probabilities north 0.174, east 0.445, south 0.379, or west 0.000, or it may also exchange positions with cell B with probability 0.379. (b) The grid configuration after cell A exchanges with cell B. The parameters used are Pb(AB) = 0.8, /(AB) = 0.5, /(AB) = 2.0, absG(A) = 0, and G D(AB) = 1.5.

Figure 21 Raman spectra of hydrated zeolite A exchanged with LI, Na, K, Tl, and NH4 Ions laser line, 457.9 nm laser power, 150 mW slit width, 5 cm The dots denote plasma llnes. ...

Competition between the analyte ion and the eluent ion is stoichiometric, with both concentration and valency influencing the equilibrium. Equation (1) can be generalized for y moles of A " " exchanging with x moles of as demonstration in Eq. (2) ... 

As for cation exchanged zeolites A and Y, the condition for selectivity is different. For the zeolites A exchanged with Mg, Ca, Cd, Zn etc. whose pore size is 3 — 5 A, large molecules such as ethylene polymer cannot be formed in hydration of ethylene despite the fact that the zeolites possess strong acid sites of Ho S —8.2 active for polymerization of ethylene. However, with zeolites Y which have large pore size (ca. 9A),... 

Example 7.3 A hot stream is to be cooled from 410 to 110°C by exchange with... 

To predict the capital cost of a network, it must first be assumed that a single heat exchanger with surface area A can be costed according to a simple relationship such as... 

Condition (3) applies to Eq. (C.2) when R = 1. Both conditions (1) and (2) are always true for a feasible heat exchange with positive temperature differences. 

The C exchanges with C in living organisms, but exchange ceases on death. The radioactive content decays with a half-life of 5730 years. Hence the age of a once living material may be established by determining the amount of C. 

If the two sites exchange with rate k during the relaxation, tiien a spin can relax either tlirough nonnal spin-lattice relaxation processes, or by exchanging witli the other site, equation (B2.4.45) becomes (B2.4.46). 

Figure B2.4.8. Relaxation of two of tlie exchanging methyl groups in the TEMPO derivative in figure B2.4.7. The dotted lines show the relaxation of the two methyl signals after a non-selective inversion pulse (a typical experunent). The heavy solid line shows the recovery after the selective inversion of one of the methyl signals. The inverted signal (circles) recovers more quickly, under the combined influence of relaxation and exchange with the non-inverted peak. The signal that was not inverted (squares) shows a characteristic transient. The lines represent a non-linear least-squares fit to the data.

The grand canonical ensemble corresponds to a system whose number of particles and energy can fluctuate, in exchange with its surroundings at specified p VT. The relevant themiodynamic quantity is the grand potential n = A - p A. The configurational distribution is conveniently written... 

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