Nernst filament

Mid- and near-infrared Nernst filament globar NaCl or KBr Grating interferometer Golay cell thermocouple bolometer pyroelectric photoconductive semiconductor... 

Absorption in the Infra-red.—The methods of determining this property are briefly described as follows.8 The radiation from a Nernst filament was passed through a rock-salt lens, then through either of two similar tubes, one of which was evacuated and the other filled with the gas at a known pressure. A rocking arrangement allowed either tube to be thrown quickly into the path of the rays. The beam was focussed on the collimator slit of an infra-red spectro-... 

The method used to observe the infrared spectra of the deposits is relatively simple. The optics of a single-beam infrared spectrometer have been modified so that light from the Nernst filament is incident nearly normally on the drum and the light that is reflected directly from the surface of the drum is focused on the slit of the spectrometer. Because of the nature of the optics and the detector it is not feasible to divide the deposit into two bands as for the ultraviolet and visible spectra. Thus a blank run in which no alkali metal is deposited has to be made to provide a reference spectrum. 

IR spectroscopy appears to be a very promising tool for oxidation studies. The rate of formation of carbon monoxide, carbon dioxide and formic acid and the disappearance of ozone was measured this way with the O3/O2 + CH4 system . The system used by Burt and Minkoff for the combustion studies is shown in Fig. 61. Light from a Nernst filament is split in two and passed alternately through two heated cells and F2 containing either fuel + N2 or fuel + Oj. The beams are rejoined and fed into a Wadsworth monochromator containing a CaF2 prism and finally focussed onto a thermopile, from which a particular signal may be amplified and recorded. 

Sources of infrared emission have included the Globar, which is constructed of silicon carbide. There is also the Nernst filament, which is a mixture of oxides of zirconium, yttrium and erbium. However, a Nernst filament only conducts electricity- at elevated temperatures. ... 

Typical light source Laser Silicon carbide or Nernst Filament ... 

One of the earliest sources was the Nernst filament. This is a mixture of rare earth oxides, primarily of zirconium, made into rods 20-50 mm in length and 1-2.5 mm in diameter. These are fired at 1800°C and have platinum wire connections at both ends. The resultant output at 1800-2000°C is approximately blackbody. However, while relatively cheap to produce these have a very unpredictable life and are very sensitive to environmental factors including draughts. Refractory coated platinum-rhodium wire has been used as a more robust solution but is very expensive. 

Two common sources of infra-red radiation are the Nernst filament, an element of rare earth oxides, mainly zirconium oxide, fused together in a rod between 1 mm and 2 mm diameter, and the Globar, a larger diameter rod of silicon-carbide. Both elements are heated electrically, and at temperatures between 1,200° and 2,000° emit radiation with a maximum between 1 5// and 2 5// rather like a black body radiator. 

Figure 4 Plan view of a Hilger IR spectrometer made in 1918. A constant-deviation Wadsworth optical arrangement with a 60° rock salt prism was employed. The detector was a thermopile and the source a Nernst filament. From Hilger Journal, August 1955. Photograph courtesy Professor N. Sheppard, FRS, and reproduced with permission from Hilger Analytical.

The main sources of infrared radiation used in spectrophotometers are (1) a nichrome wire wound on a ceramic support, (2) the Nernst glower, which is a filament containing zirconium, thorium and cerium oxides held together by a binder, (3) the Globar, a bonded silicon carbide rod. These are heated electrically to temperatures within the range 1200- 2000 °C when they will glow and produce the infrared radiation approximating to that of a black body. 

In the mid-IR several type of sources are used. They are either a lamp filament (Figure 10.13), or a hollow rod, 1-3 mm in diameter and 2 to 4 cm long, made of fused mixtures of zirconium oxide or rare earth oxides (Nernst source) heated by Joule effect by the means of an internal resistor (for example Globar ). These sources are heated to 1500 °C, without a protective shield. They dissipate power of the order of a hundred watts by emitting radiation over a large domain ranging from visible to thermal IR. A maximum is observed for A = 3000/T (A in... 

Nernst, Walther (1864-1941 ) A German physical chemist, physicist, and inventor, Nernst discovered the Third Law of Thermodynamics—defining the chemical reactions affecting matter as temperatures drop toward absolute zero—for which he was awarded the 1920 Nobel Prize in Chemistry. He also invented an electric lamp, and developed an electric piano and a device using rare-earth filaments that significantly advanced infrared spectroscopy. He made numerous contributions to the specialized fields of electrochemistry, solid-state chemistry, and photochemistry. 

Carbon or metallic filaments had limited life because of poor sealing technique of the glass bulb. A filament stable in air seemed indeed an elegant solution. Nernst having realised the adequate conductivity of mixtures of oxides at high temperature and amongst them probably stabilised zirconia, demonstrated also that the conductivities were ionic. 

Source. This usually consists of a filament or rod of some refractory material, heated to a temperature of around 1500 K so as to emit infrared radiation. The Globar is probably the most common source of mid-infrared radiation, consisting of synthetic silicon carbide. This usually has to be water-cooled, however. Filament (Nernst), and nichrome wires are also popular—and may not require water cooling. Water-cooled sources should deliver a higher and more stable output, which is better suited to quantitative applications. 

The development of the ideas mentioned above has taken place over more than a century, in 1890, it was not yet clear what electrical conduction was. The electron had not quite been defined. Metals were known to conduct electricity in accord with Ohm s law, and aqueous ionic solutions were known to conduct larger entities called ions. Nernst then made the breakthrough of observing various types of conduction in stabilised zirconia, that is zirconium oxide doped with several mole per cent of calcla, magnesia, yttria, etc. Nernst found that stabilised zirconia was an insulator at room temperature, conducted ions in red hot conditions, from 600 to 1000°C and then became an electronic and ionic conductor at white heat, around 1500°C, He patented an incandescent electric light made from a zirconia filament and sold this invention which he had been using to illuminate his home [1-3], He praised the simultaneous invention of the telephone because it enabled him to call his wife to switch on the light device while he travelled back from the university. The heat-up time was a problem even then [4],... 

The Nernst zirconia rods were similar to metallic conductors in that decomposition did not occur with the passage of direct current. Nevertheless. Nernst was convinced that his filaments were ionic conductors, and he assumed that, e.g. in yttria-stabilised zirconia (YSZ), the yttria provided the necessary charge carriers [16]. He observed evidence of oxygen transport, but believed that metal cations were also deposited by the direct current, later oxidising and diffusing back into the filament. 

It was not until 1943 that Wagner [22] (in memory of Walther Nernst who died on 18 November 1941) recognised the existence of vacancies in the anion sublattice of mixed oxide solid solutions and thus explained the conduction mechanism of the Nernst glowers. We now know that Nernst lamp filaments... 

Nemst [1,2] studied the behavior of solid ionic conductors— high temperamre ceramics—for use as filaments in light bulbs. Nernst made a breakthrough discovery based on the observation of different types of conductivity in stabilized zirconia, or zirconium oxide doped by a few mole per cent of calcia, magnesia, yttria, etc. At that time, the use of other materials for this purpose was problematic due to their unfavorable resistance characteristics—a rise in temperature caused an increase in resistance, and thus the metal wires were not able to obtain a... 

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