Cleaning junctions

Hard soldering is applicable in most cases. Spelter solder, silver solder (m.p. about 700°C) and pure silver (m.p. 960°C) are used. The cleaned junctions are sprinkled with a generous amount of borax, and when they are sufficiently hot the solder (as powder or as wire) is added. With a large amount of borax and pure silver, even Mo and W can be hard soldered. 

The method has been successfully applied to steroids. The fnms AB ring junction in 612 can be generated cleanly from the. i-allylic formate 611 the cis junction in 614 is formed by the hydrogenolysis of the a-allylic formate 613... 

If metal surfaces are thoroughly cleaned in vacuum it is almost impossible to slide them over each other. Any shearing force causes further plasticity at the junctions, which quickly grow, leading to complete seizure (p > 5). This is a problem in outer space, and... 

Fig. 25.4. Oxide-coated junctions can often slide more easily than ones which are clean.

Tops made from solid epoxy compounds are resistant to just about any kind of chemical abuse but are very expensive. They are often sold with an integral backsplash and curved junction, which makes cleaning easy. They are much easier on glassware than either stone or cement composition. 

To minimize microbial contamination, all floors should be easy to clean, impervious to water and laid on a flat surface, hi some areas it be necessary for the floor to slope towards a drain, in which case the gradient should be such that no pools of water form. Any joints in the floor, necessary for expansion, should be adequately sealed. The floor-to-wall junction should be coved. 

The thermometer is held in the flask by means of a I clean bored cork the bulb of the thermometer must be completely immersed in the vapour and hence must be below the junction of neck and side tube. 

There are also electrodes available which have a ground glass junction between the reference electrode and the solution being measured. These probes would probably be most suitable because they can be dismantled and cleaned. A probe arrived as our measurements were being completed so this type of probe has not yet been tested in our laboratory. 

We can employ the following technique. A clean silver electrode is immersed in a solution of chloride ion of known concentration, while a calomel electrode (SCE) is immersed in a second solution of saturated KNO3. The two containers are connected via a salt bridge (to minimize junction potentials, Ej), thus constructing the circuit shown in Figure 4.6. 

Fig. 6. Schematic illustration of a photoassisted corrosion phenomenon during the post CMP cleaning of damascene interconnections. At the electrode connected to the p-side of the junction, the metal is corroded by the oxidation reaction M - M" + n.e , while the produced soluble M"" species diffuse to the other electrode where the opposite reaction can occur.

As seen in Fig. 7, the metal can be even fully removed in 1 min at the line connected to the p-side of the junction — one can see the plugs — and the redeposition of the metal can be observed on the lines connected to the n-side of the same junction. The better method of reducing this phenomenon consists of adding corrosion inhibitors and reducing the light as far as possible using for example close chamber cleaning equipments. 

Alkali, on the contrary, should he a solid earthy body the particles of which have between, their junctions pores of different structure. It is for this reason it can he dissolved by an acid, and that it effervesces with it and blunts its points that it cleans cloth and is capable as alkali of some other actions that experience teaches us to recognize. But it is only by reason of this particular contexture that it accomplishes these. ... 

A needle source consists of a hairpin filament (M80 pm diameter), usuafly of a refractory metal such as tungsten, with a short length of smaller diameter (M25 pm) wire spot-welded to it, Figure lb. The tip of the latter wire, the emitter, is electrochemically etched to a point with a radius of curvature at the apex of 2-5 pm the etching technique for tungsten has been described in detail by others (7,29). As quickly as possible after the assembly is thermally cleaned under vacuum (n<10 " Pa), the emitter is dipped into a molten pool of liquid metal and then withdrawn. If done correctly, the junction formed by the bend in the filament and the emitter wire will hold a small bead of metal, and the emitter will appear shiny from the thin film of metal on its surface. 

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