Out- diffusion

Radon can also enter buildings when there are no pressure differences. Place a drop of food coloring in a glass of water eventually, the coloring will spread out (diffuse) and color the water— even without stirring. Radon will do the same thing—spread from an area of higher concentration to an area of lower concentration until the concentrations are equal. Radon movement in this way is called diffusion-driven transport. 

Hexafluoroiridate(IV) salts are again obtained by hydrolysis of the corresponding M(V) species, MFe (48). For caesium hexafluoroiridate (IV) Cs2IrFe, a magnetic moment of 1.42 B.M. at 298 °K has been reported (48), confirming that the ground state is the low-spin 2T2g (t g). For the hexafluoroiridate(IV) anion Hepworth et al. (48) reported two bands in the solution spectrum — an intense absorption at 46.9 kK. and a much weaker band at 31.6 kK. — but Brown et al. and Allen et al. have both carried out diffuse reflectance measurements. 

Therefore it appears that proton implantation is not an appropriate way to calibrate the oscillator strength of the LVMs of hydrogen defects as, on one hand, all the implanted protons are not infrared active and, on the other hand, some hydrogen might out diffuse from the sample during the implantation. 

Figure 5.11 Diffusion mechanisms (a) exchange (e) and ring (r) diffusion (b) kick-out diffusion, leading to (c) a substitutional defect and a self-interstitial.

Another example of phase change is the one exhibited by electrodeposited cobalt. In this case the transformation is from fee- to hep-tj pe lattice structure as a result of hydrogen inclusion during depKJsition on the one hand and subsequent out-diffusion on the other hand. 

Wang et al. (1996) studied diffusion of the hydrous component in pyrope. A natural pyrope wafer initially contains uniform OH content. The wafer was 1.636 mm thick. The total amount of OH in the wafer (average C below) was determined by an IR absorption band at 357 mm. After a heating period, the amount of OH in the wafer was redetermined. The new OH content is less than the initial because some OH diffused out. Repeated heating and measurements yield a relation between average concentration and time. Assume that the surface concentration of OH is zero. Find the diffusivity of the hydrous component using the data below. Explain whether this diffusivity is diffusion-in or diffusion-out diffusivity. Under what conditions would the two differ ... 

This modei is based on a very simpie premise if the partiai pressure of Si atoms above the SiC surface during anneaiing is greater than the vapor pressure Si in the SiC matrix, then out-diffusion of Si from the iattice wiii be suppressed. To theoreti-caiiy obtain the most suitabie conditions for Siiane overpressure anneaiing, a modei was constructed by J.T. Woian at the University of South Fiorida to caicuiate both the vapor pressure of Si in SiC and the partiai pressure of Si as a function of anneaiing temperature and gas pressure [85]. 

Figure 4.26 The solubility limit for aluminum versus reciprocal temperature as extracted from SIMS measurement of out-diffusion from heavily doped 4H-SIC [1 3].

Fig. 2. Deuterium (D) and free carrier concentration (n) profiles of a n-type GaAs Si bulk sample exposed to a rf deuterium plasma for 90 min. at 250°C (rf power density = 0.2W/cm2). The loss of free carriers occurring only in.the deuterated region suggests that hydrogen plays a major role in the free carrier concentration decrease. The deuterium concentration drop in the near surface region is attributed to a deuterium out-diffusion during the cooling stage of the sample with the plasma off. J. Chevallier et al., Materials Science Forum, 10-12, 591 (1986). Trans. Tech. Publications.

Investigations of the mechanism of the a/3 reaction by steady-state and transient kinetic methods have determined the rate constants for intermediate steps in the reaction.I04 The transient kinetic results show that diffusion of indole and condensation of indole with the aminoacrylate intermediate (ES III in Fig. 7.6) are rapid steps that occur without a lag reprotonation of the nascent tryptophan carbanion (ES IV in Fig. 7.6) is the rate-limiting step. The data rule out diffusion of free indole through the bulk solvent and support the channeling mechanism. 

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