SpectralEmissivity & Emittance

| Useful Data | Practices Measuring or Avoiding | Background & Theory|

Influence of KMnO4 Concentration on Infrared Emissivity of Coatings

On TC4 Alloys by Micro-Arc Oxidation (Materials EISSN 1996-1944)

Abstract:

Figure 8. Infrared emissivity curves of the MAO ceramic coatings with different KMnO4 concentrations within a waveband of 5–20 μm.

Figure 8. Infrared emissivity curves of the MAO ceramic coatings with different KMnO4 concentrations within a waveband of 5–20 μm.

Ceramic coatings with high emissivity were fabricated on TC4 alloys by micro-arc oxidation technique (MAO) in mixed silicate and phosphate electrolytes with varying KMnO4 addition.

The microstructure, phase and chemical composition were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and the infrared emissivity of the MAO coatings was measured in a waveband of 5–20 μm.

The results show that the thickness of the coatings increased with the addition of KMnO4, but the roughness of the coatings first decreased and then increased slightly due to the inhibitory effect of KMnO4 on Na2SiO3 deposition. Read More

Raytek’s Online Spectral Emissivity Guide

Screen Shot of Webpage

Santa Cruz CA, USA — As part of the IR Education section, the Raytek Corporation website contains some useful and well-presented information on Spectral Emissivity, one of the few instrument makers who do so.

Although they just call it plain “emissivity” they then present values for three or four different wavebands, according to the table viewed, “A Rose by any other name…”. There are two pages with disclaimers.

Here’s a summary of the opening statements and links to the actual data pages.Read More

Table of Emissivities in Three Popular Spectral Regions

The Table of Emissivity on the INFRAPOINT Messtechnik GmbH website, posted in 2009 (No longer available online) had summary data for a wide variety of materials broken down into three distinct spectral regions for the wavelength regions where the majority of infrared radiation thermometers and Infrared Thermal Imaging cameras operate.

First and second are tables that deal with the narrow spectral bands about 0.9 µm and 1.6 µm, the regions where many Silicon (Si) photovoltaic detectors (peak wavelength response: (0.9 µm) and both Germanium (Ge) and Indium Gallium Arsenide (InGaAs) (nominal wavelength region (0.7 – 1.6 µm) are used.

The third table cover the 8 – 14 µm waveband where most “low” (near ambient) temperature IR thermometers and thermal imaging sensors operate.

It has been reproduced here below in the spirit of Internet openness from our archives. We hope there is no problem in doing so and if any heir or assigns of INFRAPOINT Messtechnik GmbH wishes to keep this information secret, obviously against the original intent of INFRAPOINT, please contact us according to our webpage contact information.


   Table of emissivity        
  The emissivity ? (radiant emittance factor) is the relationship of the radiated intensity of a body to the intensity of a blackbody of the same temperature.
It is the most important factor, in order to determine of an item exactly.

If you want to measure the surface temperature with an infrared thermometer the emissivity must be known and correct adjusted
on the instrument.

               
   Material  Emissivity     Material  Emissivity  
  Metals Wavelength
0.9 µm 
Wavelength
1.6 µm 
  Non metals Wavelength
8 – 14 µm  
 
               
  Aluminium, bright 0.05 – 0.25  0.05 – 0.25    Asphalt  0.95   
  Aluminium, anodized 0.2 – 0.4  0.1 – 0.4    Concrete 0.95  
  Chrom, bright 0.28 – 0.32  0.25 – 0.3    Gypsum 0.85 – 0.95   
  Iron, oxidised 0.4 – 0.8 0.5 – 0.9    Graphite  0.75 – 0.92   
  Iron, not oxidised 0.35 0.1 – 0.3    Glass*, pane  0.80   
  Gold, bright 0.02 0.02    Rubber 0.85 – 0.95   
  Copper, bright 0.06 – 0.20 0.06 – 0.20    Wood, natural 0.8 – 0.95   
  Copper, oxidised  0.5 – 0.8  0.7 – 0.85    Chalk 0.98   
  Magnesium 0.03 – 0.8  0.05 – 0.3    Ceramics 0.85 – 0.95   
  Brass, bright  0.8 – 0.95  0.01 – 0.05    Plastics 0.85 – 0.95   
  Brass, oxidised  0.65 – 0.75  0.65 – 0.75    Masonry 0.85 – 0.95   
  Nickel, oxidised  0.8 – 0.9  0.4 – 0.7    Human skin 0.98   
  Platinum, black  –  0,95    Oil paints 0.85 – 0.95   
  Silver  0.02  0.02    Paper  0.85 – 0.95   
  Steel, melted 0.30  0.20 – 0.25    Porcelain 0.85 – 0.95   
  Steel, oxidised  0.8 – 0.9  0.8 – 0.9    Quartz  0.8   
  Steel, bright 0.40 – 0.45  0.30 – 0.4    Carbon black 0.95   
  Titanium, bright 0.5 – 0.75  0.3 – 0.5    Chamotte  0.85 – 0.95   
  Titanium, oxidised  –  0.6 – 0.8    Textile, Drapery 0.85 – 0.95   
  Zinc, bright 0.6  0.4 – 0.6    Tone 0.95   
  Zinc, oxidised  0.5  0.05    Water 0.95  
  Tin 0.25  0.1 – 0.3    Cement  0.9   
* The emissivity of glass (0.95 – 0.97 µm) is in the range of 4.5 – 7 µm particularly high.
Glass has there an absorption band (spectral range, where materials absorb radiation).
To measure glass surface temperatures, the best wavelength is at 5.14 µm, because
the measurement at this range is not affected by absorption bands such as carbon or hydrogen.

Prediction of the thermal radiative properties of an X-Ray µ-tomographied porous silica glass

Prediction of the thermal radiative properties of an X-Ray µ-tomographied porous silica glass
B.Rousseau, D.De Sousa Meneses, P.Echegut, M.Di Michiel, J.-F.Thovert
Prediction of the thermal radiative properties of an X-Ray µ-tomographied porous silica glass
Applied Optics 46 4266-4276, (2007)

ABSTRACT
“A Monte Carlo ray tracing procedure is proposed to simulate thermal optical processes in heterogeneous materials. It operates within a detailed 3D image of the material, and it can therefore be used to investigate the relationship between the microstructure, the constituent optical properties, and the macroscopic radiative behavior. The program is applied to porous silica glass. A sample was first characterized by 3D x-ray tomography; then, its normal spectral emittance was calculated and compared with the experimental spectrum measured independently by high-temperature infrared emittance spectroscopy. We conclude with a discussion of the light-scattering mechanisms occurring in the sample.”

Work performed at and reported by: Centre National de la Recherche Scientifique (CNRS), France.

Texture and porosity effects on the thermal radiative behavior of alumina ceramics

Texture and porosity effects on the thermal radiative behavior of alumina ceramics
Int. J. Thermophys. (in press) [view]

New Article
By: O.Rozenbaum, D.De Sousa Meneses; P.Echegut
Texture and porosity effects on the thermal radiative behavior of alumina ceramics
Int. J. Thermophys. (in press) [view]

ABSTRACT
“Thermal and optical properties of ceramics are dependent on radiation scattering and cannot be determined by the only knowledge of their chemical composition as for single crystals. In this paper, we investigate extrinsic effects such as roughness, porosity and texture on spectral emissivity of alumina ceramics. Roughness effects have an influence mainly in the opaque zone; an important porosity dependence and the presence of a critical porosity threshold were also pointed out in the semi-transparent zone. Furthermore, it was shown that two ceramics with similar total porosity but with different textures possess radically different emissivities, showing that grain size, pore size and spatial repartition of the grains is also crucial for the comprehension of the ceramics thermal properties”

Work performed at and reported by: Centre National de la Recherche Scientifique (CNRS), France.