Quantitative Determination of the Scattering and Absorption Coefficients from Diffuse Reflectance and Transmittance Measurements: Application to Pharmaceutical Powders

Burger, Tobias; Kühn, Joachim; Caps, R.; Fricke, J.

doi:10.1366/0003702971940404

Cited by 78 publications

(55 citation statements)

References 20 publications

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“…Directional hemispherical transmission and re ectance measurements can be obtained on these samples as a function of wavelength in the near UV, visible, and/or infrared spectral ranges by using an integration sphere (Burger et al 1997;Kuhn et al 1993). The integration sphere acts as an integrating detector to collect and spatially integrate the total radiant ux re ected from or transmitted by the sample.…”

Section: Introductionmentioning

confidence: 99%

An Empirical Method for the Determination of the Complex Refractive Index of Size-Fractionated Atmospheric Aerosols for Radiative Transfer Calculations

Marley¹,

Gaffney²,

Baird³

et al. 2001

Aerosol Science and Technology

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To adequately assess the effects of atmospheric aerosols on climate, their optical constants (scattering and absorption coef cients) must be known. The absorption and scattering coef cients of the aerosols are derived from the real and imaginary parts of the complex refractive index and are dependent on their size and chemical composition. Because aerosol properties vary signi cantly with location, it is dif cult to assign values for the absorption and scattering of solar radiation by aerosols in models of global climate change. This study reports a new method of collecting size-fractionated atmospheric aerosol samples for the purpose of directly measuring their transmission and re ectance spectra followed by the determination of the complex refractive index across the entire atmospherically relevant spectral range. The samples were collected with a modi ed Sierra high-volume cascade impactor with the usual lter collection surfaces replaced with Te on sheets machined to hold quartz (ultraviolet [UV]/visible transparent) and/or silver chloride (infrared transparent) sample collection plates. Re ectance and transmission spectra can be obtained on the aerosol samples directly as a function of wavelength, from 280 nm to 2.5 m, with an integrating sphere coupled to an UV/visible or a Fourier transform infrared (FTIR) spectrophotometer. The effective real and imaginary components of the refractive index of the bulk sample material can then be approximated, as a function of wavelength, from the sample spectra. Preliminary results are presented for carbon soot samples generated in the laboratory and for standard diesel soot samples in the UV/visible spectral range. These are compared to results obtained for size-fractionated atmospheric aerosol samples collected near Pasco, WA, West Mesa, AZ, and Argonne, IL.

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Section: Introductionmentioning

confidence: 99%

An Empirical Method for the Determination of the Complex Refractive Index of Size-Fractionated Atmospheric Aerosols for Radiative Transfer Calculations

Marley¹,

Gaffney²,

Baird³

et al. 2001

Aerosol Science and Technology

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“…The transmission of thermal radiation through semitransparent materials and the emission of radiation from semitransparent materials can be described by the equation of radiative transfer [6], which gives the variation of the spectral intensity I with the path x parallel to the radiation propagation within a plane-parallel sample:…”

Section: Equation Of Radiative Transfermentioning

confidence: 99%

Development and Characterization of Low-Emitting Ceramics

et al. 2007

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The infrared-optical properties of ceramics are correlated with the complex index of refraction of the material and the structure of the ceramic. By changing these parameters, the infrared-optical properties can be changed over a relatively wide range. The correlation of the structural properties (like the porosity or the pore sizes) and the material properties (such as the complex index of refraction on the one hand and the infrared-optical properties such as emittance on the other) are described by a solution of the equation of radiative transfer and the Mie-theory. Within this work, low-emitting ceramics, which have significantly lower emittances than conventional ceramics, were prepared by optimizing their composition and structure. The spectral emittance of these ceramics was measured, and a total emittance dependent on temperature was calculated from the spectral emittance. As a result, one obtains ceramics which have a total emittance of 0.2 at a temperature of 1,100 K. In comparison to conventional ceramics with a typical total emittance of 0.8 at 1,100 K, the use of such low-e ceramics leads to a reduction in heat transfer of about 70% via thermal radiation. The results of our calculations were compared with experimental data to validate the theory.

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“…The directional-hemispherical transmittance T dh of both the diffusely scattered radiation and the transmitted direct beam through the sample was measured by an integrating sphere [12]. Also determined was the directional-hemispherical reflectance R dh of the diffusely scattered radiation and the direct beam, which is reflected at the surface.…”

Section: Sample Production and Experimental Set Upmentioning

confidence: 99%

Characterization of the Pore Structure of Ceramics via Propagation of Light and Infrared Radiation

2005

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The pore size distributions of alumina and magnesia ceramics were determined by measuring the directional-hemispherical transmittance and reflectance. These values are highly sensitive to changes of the pore structure. The partially sintered alumina samples were measured at room temperature in a wavelength range from 0.5 to 6 µm. The equation of radiative transfer can be solved for absorbing and scattering media by a three-flux solution. With this three-flux solution the scattering coefficients were derived from the measured directional-hemispherical transmittance and reflectance. The scattering coefficients can also be calculated theoretically by the Mie theory, if the pore size distribution is known. Finally, the quantitative pore size distribution was determined by fitting the theoretical scattering coefficients to the experimental scattering coefficients. To check the correctness of the derived pore-size distribution, scanning electron microscopy (SEM) and atomic force microscopy (AFM) pictures of the alumina samples were taken. The pore-size distribution was then derived by counting the pores and determining the diameters D of the spherical pores. Both results agree well and show that the new procedure is a valuable tool to extract structural information during the final sintering state.

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Quantitative Determination of the Scattering and Absorption Coefficients from Diffuse Reflectance and Transmittance Measurements: Application to Pharmaceutical Powders

Cited by 78 publications

References 20 publications

An Empirical Method for the Determination of the Complex Refractive Index of Size-Fractionated Atmospheric Aerosols for Radiative Transfer Calculations

An Empirical Method for the Determination of the Complex Refractive Index of Size-Fractionated Atmospheric Aerosols for Radiative Transfer Calculations

Development and Characterization of Low-Emitting Ceramics

Characterization of the Pore Structure of Ceramics via Propagation of Light and Infrared Radiation

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