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Metal Hydroxide and Oxide Nanocages
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Kirkendall effect: This effect is a classical phenomenon in metallurgy, which describes the nonequilibrium mutual diffusion process of the boundary layer between two metals that occurs as a consequence of the difference in diffusion rates of the metal atoms. In 1942, Kirkendall for the first time suggested a difference in diffusion rates of two components based on interdiffusion experiments on copper and brass diffusion couple, which were welded together and subjected to an elevated temperature [122,123]. From the traditional point of view, the formation of Kirkendall voids in alloy and solder is not an ideal process for metallurgical manufacturing, because porosity reduces the mechanical properties of the interface or leads to the failure of welding line in integrated circuits. However, since the first report in 2004 on the preparation of hollow CoO and CoS nanocrystals by oxidation and sulfidation of Co nanocrystals, the Kirkendall effect has recently shown positive effects in the design and synthesis of various hollow nanomaterials [86].
Diffusion Bonding
Published in Yoseph Bar-Cohen, Advances in Manufacturing and Processing of Materials and Structures, 2018
Bonding pressure is an important parameter for diffusion bonding, especially for the bonding of dissimilar materials. For example, it can assist in avoiding the formation of diffusion voids due to the Kirkendall effect (DoITPoMS, 2015a; Zhou, 2004). The applied pressure is used to make the asperities on the interface between the two bonded substrates to be plastically deformed, hence to increase the contact area, to promote the activation of the diffusion of the interfacial atoms, to accelerate the void closure, and ultimately to eliminate the voids, as well as to facilitate cracking of the oxide films over the initial mating surfaces. In general, for a given temperature and time, the higher the pressure, the higher the strength and toughness of the joint will be. But the applied pressure should not cause macroscopic deformation. For example, when diffusion bonding Al2O3 ceramic to Ti bulk, if the applied pressure is more than 5 MPa, the Ti substrate experiences macroscopic deformation at the interface, as shown in Figure 13.4b–d. After the pressure is decreased to 5 MPa, no macroscopic deformations at the interface are visible, as shown in Figure 13.4e. In addition, there is a critical value of pressure to be applied. Beyond the critical value of the pressure, any further increase in pressure will not affect the quality of the joint. So, the pressure should be as low as possible. The pressure in most cases is not beyond 350 MPa. The commonly used pressure is in the range of 2–40 MPa (see Tables 13.1 and 13.2).
Metals
Published in Andrea Chen, Randy Hsiao-Yu Lo, Semiconductor Packaging, 2016
Andrea Chen, Randy Hsiao-Yu Lo
The Kirkendall effect is named after Ernest Kirkendall who was an assistant professor at Wayne University from 1941 to 1946, during which time he wrote his now-famous paper titled “Zinc Diffusion in Alpha Brass,” coauthored with Alice Smigelskas and published in 1947. Essentially, the Kirkendall effect describes that the diffusion of two solids into each other is not done at equal rates with the atoms of one replacing the atoms of the other in any one-to-one correlation. Instead, one solid will have a faster diffusion rate than the other, and the mixture/alloy of the two will grow into the faster diffusing material. Unfilled voids are left behind in the faster diffusing solid and eventually coalesce into large pores. Figure 7.7 shows an example of zinc and copper joined together. As diffusion occurs and a zinc-copper alloy is created, the zinc is consumed by the brass (the faster moving species), leaving behind larger and larger voids.
The evaluation of oxide scale formation during hot corrosion of Rene-80 superalloy under thermal shock at different dwell times
Published in Corrosion Engineering, Science and Technology, 2022
Arman Rabieifar, M.Reza Afshar, Hamidreza Najafi, Said Nategh
In the initial cycles of hot corrosion, molten salt was decomposed according to reaction (1) and due to the high partial pressure of oxygen (pO2). Moreover, NiO and Co3O4 transient oxides were formed with a high growth rate [33]. The growth of these oxides is associated with the cationic lattice diffusion (Figure 6(a)). This means that the nickel and cobalt cations and oxygen anions diffused in opposite directions and across the salt layer, forming cationic voids [28]. Kirkendall effect intensified the reduction of adhesion between the substrate/oxide scale interface; this could result from the downward diffusion rate of oxygen to the substrate, which was higher than the upward diffusion rate of substrate elements [34]. The formation of these compounds in the initial cycles of hot corrosion led to the formation of pores and cavities in the substrate/oxide scale interface [35].
Evaluation of diffusion mechanism and structural characterizations of ZnS compound during chemical reaction of Zn and S in liquid phase
Published in Journal of Sulfur Chemistry, 2018
Ehsan Karami, Majid Tavoosi, Ali Ghasemi, Gholam Reza Gordani
In fact, the formation of Kirkendall voids near the ZnS/S interface can be related to the higher diffusion coefficient of sulfur atoms in the ZnS layer than zinc atoms. If the diffusion phenomenon takes place on a large scale, then a flux of atoms will occur in one direction and a flux of vacancies in the other [20]. The Kirkendall effect arises when two distinct materials (such as S and Zn) are placed next to each other and diffusion is allowed to take place between them. Generally, the diffusion coefficients of the two materials in each other are not the same (DS > DZn) [20]. In the Zn/S diffusion couple, the net movement of atoms will be from sulfur toward zinc. In this condition, vacancies will diffuse in the ZnS phase from zinc toward the sulfur layer. One important result derived from increasing the vacancies’ density is the formation of pores in the tZnS/S interface [28]. The formed voids act as sinks for the vacancies, and when enough accumulate they can become substantial and expand in an attempt to restore equilibrium [20,28]. It is important to note that, the formation of Kirkendall voids has been reported in other diffusional couples such as Al/Ti [29], Cu/Sn [30] and Ni/Al [31].