ASTM E423 Test Method for Normal Spectral Emittance at Elevated Temperatures of Nonconducting Specimens

ASTM E423 test method specifies an accurate method for determining the normal spectral emittance of electrically nonconducting materials at temperatures ranging from 1000 to 1800 K and wavelengths ranging from 1 to 35 m. This test method necessitates the use of particular specimen size and design, as well as particular heating and viewing procedure.

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Introduction

The ASTM E423 test method accurately determines the normal spectral emittance of electrically nonconducting materials at high temperatures. It is primarily helpful for ceramic oxides with lower heat conduction and transparency in some depths. Further, it can be expanded into the range of 1000 to 1800 K and 1 to 35 µm range in the spectrum. The test has specific specimen size, geometry, and heating and viewing conditions that are fully controlled to measure emittance precisely. It is essential for conditions used for high temperatures, especially for materials under such conditions, primarily employed in specific research laboratories where high accuracy is desired.

Scope

ASTM E423 is a standard test technique for identifying typical spectral emittance of nonconducting specimens at extreme temperatures. It is highly suitable for determining typical spectrum emittance of materials like ceramic oxides, which have low heat conductivity and are translucent to some depths below the surface but opaque at 10 mm or less thicknesses. It is used in research labs where extreme precision and accuracy are required and is not advised for ordinary production or acceptance testing. This test method can be utilized as a reference technique for production and acceptance testing in the event of a disagreement because of its high accuracy.

Apparatus used in ASTM E423

The apparatus used in ASTM E423 are as follows:

Apparatus	Description
Spectrophotometer	It is equipped with a wavelength drive and slit servomechanism to scan and minimize radiant flux variations automatically.
Stray Radiation Filter	Black polyethylene filter to limit stray radiation in the 15 to 35 µm range.
Specimen Furnace	High-temperature alumina core with platinum-rhodium wire, water-cooled viewing port, and a platinum foil shield.
Rotation Mechanism	The specimen’s rotation is adjustable from 1 to 300 rpm. The spindle is driven by a 1/8-hp motor coupled to a gear reducer.
Axial Temperature Control	Power to booster coil to minimize temperature gradients in the specimen, measured by a micro-optical pyrometer.
Blackbody Furnaces	The measurement system used two nearly identical blackbody furnaces with a fused alumina-bonded inner cavity.

Test Procedure

In the ASTM E423 test method, a cylindrical sample rotates in an electrically heated furnace with virtually isothermal conditions. Furthermore, electronic controls maintain the host specimen and blackbody reference at the same temperature. In general, the measurement process involves comparing the brightness of a heated object to that of a laboratory blackbody furnace operating at the same temperature as a function of wavelength.

Specimen Size

For ASTM E423, the specimens must be hollow cylinders with wall thicknesses sufficient to be essentially opaque but not exceeding 10 mm and a diameter of 25.4 +0.5 mm. Six replicate specimens of each material should be measured for typical spectral emittance.

Data

For ASTM E423, the calculation follows the equation below,

Where ∈, λ, Sλ, Zλ, and Hλ are the spectral emittance of the specimen, wavelength, height of the specimen line, zero line, and height of the 100%, respectively.

Result

The ASTM E423 test method accurately measures the normal spectral emittance of nonconducting materials at elevated temperatures. This method provides the critical data needed for high-precision applications, mainly with materials having low heat conductivity, such as ceramic oxides.

Conclusion

An ASTM E423 test method is a reliable and precise approach for determining the normal spectral emittance of nonconducting materials at high temperatures. It is essential in research or specialized applications that involve materials like ceramic oxides because only such materials can provide accurate spectral data with low heat conductivity. The method is convenient in advanced material characterization, acting as a reference technique when problems arise from the production or acceptance testing process.