Silicon carbide ‘Globar

Infrared radiation in the range 4 000 to 200 cm-1 is commonly obtained from a silicon carbide globar, heated to near 1 500 K by an electric current. The globar emits radiation with approximately the same spectrum as a blackbody at 1 000 K (Box 20-1). 

Evacuation is not necessary in this region and sources are much less of a problem than they are in the far-infrared. A heated black body emits strongly in the near- and mid-infrared and a Nemst filament, consisting of a mixture of rare earth oxides, or a silicon carbide Globar, emulate a black body quite well. 

Transmitted IR spectra for rocks and minerals are generally measured by making thin sections of samples with thicknesses of from 20 to 200 pm, which depend on concentrations and absorption coefficients based on Beer-Lambert law. A Fourier Transform IR microsjjectrometer totally used in this study is equipped with a silicon carbide (globar) IR source and a Ge-coated KBr beamsplitter. IR light through a sample is measured using a mercury-cadmium-telluride detector. 

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. 

Globars" (silicon carbide rods) are the next most frequently used furnace heating elements. They will operate continuously at 1450 °C. and intermittently at 1500 C. A newer t3q>e of element. Mo wire coated with silicide, i.e.- MoSi2(to protect the Mo wire against oxidation), heis become... 

Radiation in the infrared region of the spectrum is obtained from heated ceramic devices such as the Nemst glower or Globar. The Globar is made of silicon carbide and is heated to approximately 800-1500°C to emit black-body radiation in the infrared region of the spectrum. Coils of nichrome wire also emit infrared radiation when electrically heated. 

Globar Silicon carbide 1300 Mid-IR or Far-IR to 2000 cm Cooled by water, emission can be down to 80cm ... 

Globar [Carborundum], TM for silicon carbide heating elements and resistors and accessories. 

The continuum sources for IR radiation are normally heated inert solids. A Globar source is a silicon carbide rod infrared radiation is emitted when the Globar is heated to about 1500°C by the passage of electricity. Table 25-1 gives the wavelength range of these sources. 

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. ... 

Silicon carbide is a semiconductor material with a resistivity much higher than conventional metallic resistance materials. Resistance measurements taken at room temperature will give no indication of the resistance at higher temperatures (Figure 10.14) and values must be determined. These values are measured by the manufaeturer at a constant temperature (e.g. 1050°C for Hot Rod and 1070°C for Globar LL and Silit ED elements). Elements to be connected in series should be selected within a resistance range of 5%, whereas elements connected in parallel can be 10%. 

Globar. A silicon carbide heating element. (Trade-name Carborundum Co., USA and England.)... 

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. 

All IR spectrometers have a source of infrared radiation which is usually some solid material heated to incandescence by an electric current. The Nemst Glower is a source composed mainly of oxides of rare earths such as zirconium, yttrium and thorium, and the Globar is a silicon carbide rod. Other materials have been used as well. All these sources are fairly efficient emitters of infrared radiation and approach the energy distribution of a theo-rectical black body. 

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. 

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