Crucibles, electric

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The source can be heated by a variety of techniques. Resistance heating can be used, employing W, Mo, or Ta heater wire or tape. These have the advantage that their low vapour pressures do not cause contamination of the deposit. The source can be contained in a crucible made of boron nitride or titanium diboride. Induction heating can also be used to heat a susceptor source contained in a nonsusceptor crucible. Electric-arc and laser-beam sources can also be used to heat the evaporant. 

As platinum is stable to most reagents, it is used in crucibles for analytical chemistry. But, B, Si, Pb, P, As, Sb and Bi, produce low melting point compounds with platinum under a reductive atmosphere, so platinum vessels are not used with these elements. A main use of platinum is ornaments, thermocouples, crucibles, electric contact points, electrodes, electric furnaces, chemical apparatuses, dental materials, catalysts for hydrogenation, dehydrogenation, isomerization, etc. Platinum black is used as a catalyst in the petroleum-refining industries and for catalytic car waste gas treatment [3—10]. 

Crucible, electrically conductive (evaporation) A cmcible of an electrically conductive material such as carbon or TiB2 plus BN that can be heated resistively or by accelerated electrons. 

Although its principal use is as a hardening agent for platinum, iridium is also used to make crucibles and devices requiring high temperatures. It is also used for electrical contacts. 

Glass in the form of fibres is relatively inexpensive and is the principal form of reinforcement used in plastics. The fibres are produced by drawing off continuous strands of glass from an orifice in the base of an electrically heated platinum crucible which contains the molten glass. The earliest successful glass reinforcement had a calcium-alumina borosilicate composition developed... 

II should noi be overlooked that platinum has played a crucial role in ihe development of many branches of science even though the amounts of metal involved may have been small. Reliable Pt crucibles were vital in classical analysis on which the foundations of chemistry were laid. It was also widely used in the development of the electric telegraph, incandescent lamps, and thermionic valves. 

Perchlorate as potassium perchlorate (ca 400 mg as the sodium salt in 25 mL solution). Warm the solution to 80-90 °C and treat with a slight excess of a cold saturated solution of potassium acetate. Allow to cool and after 1 hour collect the precipitate on a weighed porcelain filtering crucible. Wash twice with 0.05M potassium chloride and then with four 5 mL portions of equal volumes of anhydrous ethyl acetate and anhydrous butan-l-ol. Dry the precipitate at 110°C for 30-60 minutes and then heat at 350 °C in an electric furnace for 15 minutes. Weigh as KC104 (Section 11.68). 

Calcium Oxide (lime, Quicklime, Burnt Lime, Calx, Unslaked Lime, Fluxing Lime). CaO, mw 56.08, white or greyish-white lumps or powd, mp 2580°, bp 2850°, d 3.25-3.40g/cc. SI sol in w with formation of calcium hydroxide and evolution of large amts of heat sol in acids, and insol in ethanol. Coml prepn consists of heating calcium carbonate in kilns at 1000—1100° until all of the C02 is driven off. Lab prepn is by burning calcium carbonate or calcium oxalate at about 800° using a quartz crucible in an electric furnace... 

Elements dissolved in boron influence its crystal structure. Dissolved impurities also influenee the physical and chemical properties of boron, especially the electrical properties, because boron is a semiconductor. Preparation of solid solutions in jS-rh boron requires a careful choice of crucible material. To avoid contamination, boron nitride or a cold, coinage-metal crucible should be used or the levitation or floating-zone melting techniques applied. 

If a susceptor such as a metal crucible is placed within the coil. The R.F. power induces "eddy-currents" in the crucible, causing it to heat up. Eddy-currents are circular electrical currents induced within the metal by the R.F. field of the coil. It is essentially a "skin" effect, and the depth of penetration, l.e.- depth of eddy-current generation within the crucible is defined by ... 

Pulse-mode pyrolyzers include resistively-heated electrical filaments or ribbons and radio frequency induction-heated wires [841,842,846,848,849]. The filament or ribbon-type pyrolyzers are simple to construct. Figure 8.45, and typically consist of an inert wire or ribbon (Pt or Pt-Rh alloy) connected to a high-current power supply. Samples soluble in a volatile solvent are applied to the fileutent as a thin film. Insoluble materials are placed in a crucible or quartz tube, heated by a basket-lilce shaped or helical wound filiunent. The coated filament is contained within a low dead volume chamber through which the carrier gas flows, sweeping the pyrolysis products onto the column. The surface temperatui of the filament is raised rapidly from ambient temperature to He equilibrium pyrolysis temperature. This... 

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