Transient liquid phase bonding

This technique employs a thin and chemically different metal or metal alloy interlayer placed between the surfaces of metallic components so that contact results in interdiffusion and the transient production of a composition that is liquid and wets the solids, (Zhou et al. 1995). 

Such excellent or at least adequate capillary behaviour is also typical of the process variant known as eutectic bonding in which the transient creation of a liquid phase is caused by the interdiffusion of two chemically different metal alloy component materials. In the laboratory variant process known as partial transient liquid phase bonding, (Shalz et al. 1992), a coated interlayer is used for ceramic-ceramic or ceramic-metal joints. In this process the interlayer is a ductile metal or alloy whose surface is coated with a thin layer of a lower melting temperature metal or alloy, for example Ni-20Cr coated with 2 microns of Au. The bonding temperature is chosen so that only the coating melts and the ductility of the interlayer helps to accommodate mismatches in the coefficient of thermal expansion of the component materials. 

A particular advantage of the transient liquid phase bonding technique is that the joints are produced at relatively low temperatures but have elevated service temperature capabilities comparable to those of diffusion bonded structures, (Locatelli et al. 1995). 

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Roman, J.W. Eagar, T.W. Low stress die attach by low temperature transient liquid phase bonding. Proceedings of ISHM, San Francisco, CA, October 1992 52-57. 

More productive chemical results, which stiU harness the destructive action of ultrasound on certain bonds, can be attained when sonication is applied to biological fluids (e.g. protein solutions) en route to bionanomaterials [15], A conspicuous example can be found in sonochemically-prepared protein microspheres, in which the interplay of mechanical effects (emulsification) and chemical effects (formatiOT of transient species) is noticeable. A protein emulsion is readily created at the interface between two immiscible liquid phases, while radicals generated by water sonolysis promote disulfide bond cross-linking between cysteine residues. Surface modifications, via conjugation with monoclonal antibodies or RGD-containing peptides, can also be carried out [102, 103]. The sonochemical preparation of chitosan microspheres also exploits the intermolecular cross-linking of imine bonds from the sugar precursor [104]. 

Thiazyl monomer is a radical with one unpaired electron. In contrast to nitric oxide, it polymerizes so readily that it cannot be isolated as a monomeric solid or liquid and has only a transient existence in the gas phase. Thiazyl monomer may be generated in a number of ways, including the volatilization of (SN) c (2) or pyrolysis of S4N4 (1) over quartz wool above 300 °C. The emission spectrum and ESR spectrum have been reported. The bond length is calculated to be 149.7 pm from its spectroscopic moment of inertia. This indicates a bond order of between two and three. The dissociation energy of this strong sulfur-nitrogen bond is estimated to be 463 kj mol from spectroscopic data. Nevertheless, like other sulfur nitrides, NS is endothermic and unstable with respect to its elements. Thiazyl monomer exhibits an IR band at 1209 cm T The experimental dipole moment is 1.83 0.03 D and the ionization potential is 9.85 eV. 

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