Kirkendall

Kirkendall E O 1942 Diffusion of zinc in a-brass Trans. Metall. Soo. AIME 147 104... 

Darken assumed that the accumulated vacancies were annilrilated within the diffusion couple, and that during tlris process, tire markers moved as described by Smigelskas and Kirkendall (1947). His analysis proceeds with the assumption tlrat the sum of tire two concenuations of the diffusing species (cq - - cq) remained constant at any given section of tire couple, and tlrat the markers, which indicated the position of tire true interface moved with a velocity v. 

An example where one metal melts before the densihcation process, is the formation of bronze from a 90 10 weight percentage mixture of copper and tin. The tin melts at a temperature of 505 K, and the liquid immediately wets the copper particles, leaving voids in the compact. The tin then diffuses into the copper particles, leaving further voids due to dre Kirkendall effect. The compact is therefore seen to swell before the hnal sintering temperature of 1080 K is reached. After a period of homogenization dictated by tire criterion above, the alloy shrinks on cooling to leave a net dilatation on alloy formation of about 1%. 

Evidence concerning the identity of the mobile species can be obtained from observation [406,411—413] of the dispositions of product phases and phase boundaries relative to inert and immobile markers implanted at the plane of original contact between reactant surfaces. Movement of the markers themselves is known as the Kirkendall effect [414], Carter [415] has used pores in the material as markers. Product layer thickness has alternatively been determined by the decrease in intensity of the X-ray fluorescence from a suitable element which occurs in the underlying reactant but not in the intervening product layers [416]. 

Figure 3.21 Kirkendall effect shown by the movement of inactive markers originally at the interface between two interdiffusing species.

It is particularly helpful that we can take the Cu-Ni system as an example of the use of successive deposition for preparing alloy films where a miscibility gap exists, and one component can diffuse readily, because this alloy system is also historically important in discussing catalysis by metals. The rate of migration of the copper atoms is much higher than that of the nickel atoms (there is a pronounced Kirkendall effect) and, with polycrystalline specimens, surface diffusion of copper over the nickel crystallites requires a lower activation energy than diffusion into the bulk of the crystallites. Hence, the following model was proposed for the location of the phases in Cu-Ni films (S3), prepared by annealing successively deposited layers at 200°C in vacuum, which was consistent with the experimental data on the work function. 

In humans, one study of a worker accidentally sprayed with acrylonitrile indicated that transient injury to liver and muscle may have occurred, but the data are too limited to draw any firm conclusions (Vogel and Kirkendall 1984). 

Dizziness, redness, nausea, vomiting and hallucinations were reported (Vogel and Kirkendall 1984). The symptoms persisted for 3 days. 

In a case study of a human male accidentally sprayed with acrylonitrile, recurring signs of cyanide poisoning were seen over a 3 day period (Vogel and Kirkendall 1984). This indicates that acrylonitrile is also metabolized to cyanide following predominantly dermal exposure. 

In animals, deaths from acrylonitrile have been reported in several species following inhalation, oral or dermal exposure. In most species, death appears to be related to cyanide poisoning. That the cyanide moiety is involved in human toxicity of acrylonitrile has been reported in a case study in which a human male was sprayed with acrylonitrile when a valve burst (Vogel and Kirkendall 1984). This individual suffered symptoms characteristic of cyanide poisoning, and treatments designed to reduce cyanide levels in the blood were required in order to save his life. 

Some liver damage has been reported in humans after acute exposure to high doses. In workers exposed to high levels of acrylonitrile vapors, mild jaundice was diagnosed (Wilson 1944). In a case of an accidental dermal exposure of a man, enzyme levels in the blood suggestive of liver injury were reported for several days (Vogel and Kirkendall 1984). These effects appeared to be fully reversible. 

Also, transient irritation of scrotal skin has been noted by workers after entering areas with high ambient acrylonitrile concentrations. Direct contact of acrylonitrile with the skin has resulted in erythema, desquamation and slow healing (Dudley and Neal 1942). In both humans and animals, skin redness has been reported subsequent to acute exposures (Dudley and Neal 1942 Vogel and Kirkendall 1984). 

Symptoms which have been associated with acrylonitrile poisoning in humans include limb weakness, labored and irregular breathing, dizziness and impaired judgment, cyanosis and nausea, collapse, and convulsions (Baxter 1979). Case studies of occupational exposure to acrylonitrile suggest that the acute nonlethal effects in humans may be fully reversible (Vogel and Kirkendall 1984 Wilson 1944 Wilson et al. 1948). 

Vogel RA, Kirkendall WM. 1984. Acrylonitrile (vinyl cyanide) poisoning A case report. Tex Med 80 48-51. 

Sometimes interdiffusion between two metals is uneven and may lead to the creation of vacancies or voids. This type of imbalance is the result of possible unequal mobilities between a metal couple. These voids occur individually near the common interface. The voids, like bubbles, coalesce, resulting in porosity and loss of strength. Many thin-fihn couples exhibit this phenomenon, which is referred to as Kirkendall void creation. Al-Au, Cu-Pt, and Cu-Au are just a few examples. To be specific, it has been found (7), for instance, that in the case of Au-Ni, about five times more Ni atoms diffuse into Au than Au atoms diffuse into Ni. 

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