Metal wire seals

Some items not usually described in elementary glass blowing texts, but frequently useful in vacuum apparatus, are magnetic seal-breakers, universal joints, and metal wire seals. Therefore their construction is described here. 

Friedrich Otto Schott (1851-1935). In a closed glass tube a mercury drop contacted by a metal wire sealed into the end of the tube is used as an anode, a piece of... 

Hladik and coworkers studied the reduction of cadmium chloride and nickel chloride in solid LiCl-KCl eutectic. The WE was metallic wire, sealed in a glass tube, and arased, for only the cross section of the wire be into contact with the electrolyte. Reverse transition times are equals to direct electrolysis times. Thus nickel metal is deposited at the electrode surface during reduction. Reverse transition time is about equal one third of the direct electrolysis current. In order to explain this fact, Hladik suggested the formation of cadmium I-chloride diffusing from the electrode to the electrolyte. 

Stia counter — Mercury coulomb meter invented by Friedrich Otto Schott (1851-1935). In a closed glass tube a mercury drop contacted by a metal wire sealed into the end of the tube is used as an anode, a piece of graphite or more recently another wire sealed into the other end of the tube serves as cathode. Upon ffow of a direct (DC) current mercury is dissolved into the aqueous electrolyte solution containing KCl and Hgl and deposited at the cathode. A porous diaphragm prevents metallic drops of mercury to reach the anode. According to Faradays law the amount of deposited mercury... 

A simple, but efficient reactor concept was developed based on the insertion of metallic wires that serve as a catalyst into a micro channel. The wire extends over the channel length and can thus be contacted electrically for heating purposes. It is sealed by graphite seals at both reactor ends. In this way, an easy, flexible and cheap concept for catalyst exchange and reactor assembly is provided. 

A 4.9 g sample of the liquid siloxane in a glass dish was put into a bomb calorimeter (on an open bench) containing 5 ml of sodium hydroxide solution to absorb combustion gases. The electric igniter system consisted of a metal wire in contact with a cotton-wool wick which dipped into the siloxane sample. The bomb was sealed, pressured up to 39-44 bar with oxygen, and the igniter was fired. A violent explosion blew the lid off the bomb (rated at 190 bar working, 250 bar test), and examination of the deformed bomb indicated that a maximum detonation pressure of around 900 bar had been attained. 

Detailed Examination of Parts. Sometimes it is necessary to take the igniter apart and submit the shell (metal or plastic), the wires, sealing compound and igniter compound to a physical and chemical examination. The disassembly operation should be carried out behind a barricade, preferably by remote control. The tests are usually different for each type of igniter and are described in the corresponding specifications... 

A simple HMDE was developed by Gerischer [17]. Using his approach, one or two mercury drops falling from the classical DME are collected on a miniature spoon and transferred to a small metal contact sealed in glass or plastic (Fig. 14.2). Platinum or gold-plated platinum wires are used. The length of the exposed contact wire is usually 0.1-0.5 mm and its diameter is about 0.5 mm. 

UMEs used in our laboratory were constructed by sealing of carbon fibre into low viscosity epoxy resin (see Fig. 32.4) [118]. This method is simple, rapid and no specialised instrumentation is required. Firstly, the fibres are cleaned with this aim. They are immersed in dilute nitric acid (10%), rinsed with distilled water, soaked in acetone, rinsed again with distilled water and dried in an oven at 70°C. A single fibre is then inserted into a 100- iL standard micropipette tip to a distance of 2 cm. A small drop of low-viscosity epoxy resin (A. R. Spurr, California) is carefully applied to the tip of the micropipette. Capillary action pulls the epoxy resin, producing an adequate sealing. The assembly is placed horizontally in a rack and cured at 70°C for 8h to ensure complete polymerization of the resin. After that, the electric contact between the carbon fibre and a metallic wire or rod is made by back-filling the pipette with mercury or conductive epoxy resin. Finally, the micropipette tip is totally filled with epoxy resin to avoid the mobility of the external connection. Then, the carbon fibre UME is ready. An optional protective sheath can be incorporated to prevent electrode damage. 

Obtain 1cm long PYC flexible tube (1.5 mm o.d.x 0.5 mm i.d.). Insert a cleaned metal wire across the tube. Seal both exterior parts of the metal wire with a drop of conductive epoxy. 

The largest amount of tin used in the United States goes to the production of solder (typically pronounced SAH der in the United States). Solder is an alloy, usually made of tin and lead, with a low melting point. It is used to join two metals to each other. For example, metal wires are attached to electtical devices by means of solder. Solder is also used by plumbers to seal the joint between two metal pipes. 

The metal reduction of the polycyclic system is usually carried out in an ether solvent and by an alkali metal at low temperature (—78 °C). When potassium metal is applied it is best to prepare a metal mirror. Sodium and lithium react, either directly in the form of a metal wire, or after treatment in an induction furnace. Cesium is prepared by thermolysis of cesium azide. It has recently been found that the application of an ultrasonic bath facilitates the reaction and avoids side reactions. The reaction can be carried out in a modified NMR tube or in an ESR cavity. Diamagnetic ions are prepared in extended NMR tubes to which the metal is extruded and sealed under vacuum. Reaction rates are difficult to compare as the electron-transfer process depends on various experimental conditions such as concentration, temperature, the presence of impurities, the solvent and the nature of the metal surface. It may take from minutes to days to form the first radical-anion the second step then follows and can sometimes be rather slow 10 13). 

An apparatus for reaction of solutions of alkali metals in NHg with solid materials (G. Brauer and V. Stein D.0]) is shown in Fig. 72. The alkali metal is sealed in a small ampoule which is provided with a small hook at one end. The seal point is broken off the ampoule is suspended by the hook from a thin wire and introduced into the apparatus. The ampoule contents are melted in a stream of Ng and flow to B. Then NHg is condensed in B. The solid is already in A, and both substances are combined by tipping the apparatus. After evaporation of the NHg the reaction product is transferred to analysis flasks, Mark capillaries, or to containers such as shown in Fig. 54a. From these it can be further transferred, as required. 

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