Wetting completely oxidized surfaces

Several problems were encountered with crystal growth from the platinum crucibles. The liquid wet the Pt surface and could not be completely contained. In addition, the liquid reacted extensively with the crucible, forming mixed platinates. Consequently, the charges were depleted of yttrium and barium oxides, lowering the YBC crystal yield. A search was therefore made for other crucible materials. 

In addition to wet chemical methods, some coupons were exposed to ozone under an ultraviolet lamp to promote complete oxidation and hydration of the silicon surface. Coupons were held within 1 cm of an ultraviolet lamp for 1 hour in ambient air. 

The functional limitations placed on solderable finish/protective finish systems are illustrated in Fig. 21 [5]. As noted above, spreading of the solder front requires that the surface of the protective finish be solderable (free of contamination or oxidation). The protective finish is sacrificial as it is dissolved into the solder. Therefore, the protective finish must be sufficiently thick to protect the solderability of the underlying solderable layer, but not excessively thick to pose a significant contamination concern for the subsequent solder joint (e.g., Au in Pb-Sn solder). The solder then wets to the surface of the solderable layer. The requirements placed on the solderable layer are the following it must be solderable it must have adequate thickness so as not to be completely dissolved by molten solder during the initial assembly process or during subsequent process steps (including repair or rework cycles) and the layer must adhere to the base metal surface. 

The metallic substrate, clean and rinsed, is immersed wet in the plating cell. The base metals which are usually plated present an essentially metallic surface to the electrolyte, and the slight corrosive action of the rinse water in preventing the formation of any substantial oxide film is important. A critical balance of corrosion processes in the initial stages is vital to successful electroplating, and for this reason there is a severe restriction on the composition of the electroplating bath which may be used for a particular substrate. This will be discussed later. The substrate is made the cathode of the cell it may be immersed without applied potential ( dead entry) or may be already part of a circuit which is completed as soon as the substrate touches the electrolyte ( live entry). Live entry reduces the tendency for the plating electrolyte to corrode the substrate in the period before the surface... 

It is perhaps worthwhile noting that the promoter patches on the metal can be either created during the wet steps of the catalyst preparation, or when a transition metal oxide is used as a support, they can be created by migration of the support material on the metal upon high temperature reduction. The metal surface can be kept almost completely covered in vacuo (SMSI effect) [52], but in the presence of CO or of the reaction mixture, the layer of oxide recrystallizes and the metal surface becomes accessible again from the gas phase [33]. 

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