Thermocouple sheaths

A bench-scale study of the hydrogenation of nitrobenzene was investigated by Wilson [2]. In this study, nitrobenzene and hydrogen were fed at a rate of 65.9 gmol/lir to a 30 cm internal diameter (ID) reactor containing the granular catalyst. A thermocouple sheath, 0.9... 

Hardness on the Mohs scale is often above 8 and sometimes approaches 10 (diamond). These properties commend nitrides for use as crucibles, high-temperature reaction vessels, thermocouple sheaths and related applications. Several metal nitrides are also used as heterogeneous catalysts, notably the iron nitrides in the Fischer-Tropsch hydriding of carbonyls. Few chemical reactions of metal nitrides have been studied the most characteristic (often extremely slow but occasionally rapid) is hydrolysis to give ammonia or nitrogen ... 

In contact with molten salts, the nickel-base alloys behave much more satisfactorily than is the general experience with molten metals. For this reason they are considered as structural materials in atomic reactors using fluoride mixtures as coolants and are used as vessels for heat-treatment salt baths, as thermocouple sheaths and in similar applications. 

Nickel thermocouple sheaths have been used satisfactorily in salt baths, e.g. in barium chloride at 1 000-1 100°C and in sodium and potassium chlorides at up to 980°C. If the salt is contaminated with sulphur then an Inconel sheath is preferred to one of nickel. The latter type is also satisfactory in cyanide baths used for case-hardening. 

The reactants are loaded in a magnesia crucible and heated by a resistance furnace to 800°C (Figure 3). Once the CaCl2 is molten, a tantalum stirrer and a Ta-Ni thermocouple sheath are lowered into the melt. While stirring, the reaction is monitored with a thermocouple. Once the reaction is complete, the stirrer and thermocouple well are retracted and the melt is allowed to cool. Figure 4 shows a typical DOR product and salt/crucible residue. A typical product button weighs 600 g and the process yield is >99%. Essentially no purification takes place in the reduction step, meaning that the product button is no purer than the feed. 

The temperature of molten polymer process streams is commonly measured using a thermocouple positioned through a transfer line wall and partially immersed in the polymer stream. Process stream temperature measurements that use an exposed-tip thermocouple, however, can be misleading since the temperature of the thermocouple junction is a balance between the heat transferred from the polymer stream and from the thermocouple assembly [39]. Due to the low heat transfer rate between the polymer and the exposed tip and the high thermal conductivity of the thermocouple sheath, the temperatures measured can be different by up to 35°C depending on conditions. Extrudate temperatures, however, can be accurately measured using a preheated, handheld thermocouple probe. This method minimizes thermal conduction through the probe sheath. 

There are multiple types of thermocouples that can be used. The most common thermocouples used in combustion applications are type K, type S, and type B. The temperature rating for type S and type B are higher than type K but are significantly more expensive and not quite as accurate. The thermocouple sheathing material and length also needs to be selected to be compatible with a given test. 

Since HF is formed as a by-product of the reaction, glass should not come into contact with the reaction mixture, and the reaction vessel, fluorine delivery tube, thermocouple sheath, and filtration apparatus should all be made of Teflon. The delivery tube is made from /4-in. o.d. x yie-in. i.d. FEP tubing [Zeus]. One end of the tube should be heated and drawn to a narrow tip (ca. 1 mm i.d.). 

After reaction vessel a has been opened, the filled crucible is placed in it and the vessel sealed directly above the side tube (dotted line in figure), leaving as little dead space as possible. The reaction vessel is placed inside the heater o and its top is wrapped as well as possible in asbestos wool, to prevent cold spots where later on the alkali metal vapor could condense. Heating under high vacuum is then started. The temperature is checked with a thermocouple, protected by a thin ceramic sheath and inserted between the vessel wall and the heater. The thermocouple sheath must not touch the vessel wall and is prevented from adhering to the latter by a few tufts of asbestos. 

Articles of sintered alumina are hard, not readily attacked by acids or alkalis at high temperatures, and can withstand considerable changes of temperature without fracturing, consequently sintered alumina is used for making crucibles, thermocouple sheaths and sparking-plugs it also has a very high electrical resistance and so insulators are made from it. 

Fig. 7.7. Titanium electrolytic cell constructed from graphite 1, gnqihite cell 2, graphite cell top 3, furnace 4, cathode 5, anode connection and thermocouple sheath 6, heating element 7, titanium trichloride reservoir (Bett, F. L.c/a/.Ref. 33).

Autostic. A water-based, air-setting cement much used for small tasks such as mounting thermocouple sheaths. (Tradename of Carlton, Brown Partners, Sheffield). 

A Kanthal wire-wound furnace enabled the temperature to be controlled to 5 °C at 700, 725, 750, 775 and 800 °C. The cell assembly consisted of a round-bottomed silica container with a ground fiat flange at the upper open end, tightly connected to a flanged Pyrex manifold, through which a thermocouple sheath and various... 

J.D. Tkach and R.H. Meservey, Corrosion of Thermocouple Sheath Materials in a Pressurized Water Reactor Environment, Aerojet Nuclear Company, 1971... 

Kislyi, P. S., Kuzenkova, M. A. (1965). Gas-impermeable protective thermocouple sheaths from zirconium boride. Powder Metallurgy and Metal Ceramics, 4,23-26. doi 10.1007/BF00773783. 

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