Scattering particulates

R. D. Skocypec, D. V. Walters, and R. O. Buckius, Total Hemispherical Emittances for Isothermal Mixtures of Combustion Gases and Scattering Particulate, Combustion Science and Technology, 47, p. 239,1986. 

Fine scattering particulates within a sample are measured by diffuse transmission or diffuse reflectance methods. The scattering produces a pseudo-pathlength effect that must be compensated for by using scatter correction data processing methods when making quantitative measurements on scattering materials (see description in Appendix B). 

Fine scattering particulates of 5 to 25 times the measuring wavelength are measured using diffuse transmittance or diffuse reflectance methods. The scattering produced by some of the... 

Accuracy Under normal conditions relative errors of 1-5% are easily obtained with UV/Vis absorption. Accuracy is usually limited by the quality of the blank. Examples of the type of problems that may be encountered include the presence of particulates in a sample that scatter radiation and interferents that react with analytical reagents. In the latter case the interferant may react to form an absorbing species, giving rise to a positive determinate error. Interferents also may prevent the analyte from reacting, leading to a negative determinate error. With care, it maybe possible to improve the accuracy of an analysis by as much as an order of magnitude. 

An important question to consider when using a flame as an atomization source, is how to correct for the absorption of radiation by the flame. The products of combustion consist of molecular species that may exhibit broad-band absorption, as well as particulate material that may scatter radiation from the source. If this spectral interference is not corrected, then the intensity of the transmitted radiation decreases. The result is an apparent increase in the sam-... 

Spectroscopic measurements may also involve the scattering of light by a particulate form of the analyte, fn turbidimetry, the decrease in the radiation s transmittance through the sample is measured and related to the analyte s concentration through Beer s law. fn nephelometry we measure the intensity of scattered radiation, which varies linearly with the analyte s concentration. 

The ratio / for a surface composed of particulate matter which scatters isotropically varies with from 1 when = 1 to 0.8 when = 0.07 (see Fig. 5-14). 

Much of the concern about particulate matter in the atmosphere arises because particles of certain size ranges can be inhaled and retained by the human respiratory system. There is also concern because particulate matter in the atmosphere absorbs and scatters incoming solar radiation. For a detailed discussion of the human respiratory system and the defenses it provides against exposure of the lungs to particulate matter, see Chapter 7. 

Particulate emissions have their greatest impact on terrestrial ecosystems in the vicinity of emissions sources. Ecological alterations may be the result of particulate emissions that include toxic elements. Furthermore, the presence of fine particulates may cause light scattering, known as atmospheric haze, reducing visibility and adversely affecting transport safety, property values, and aesthetics. 

Nephelometer A device used to determine the suspended particulate size and concentration by the scattering of light. 

However, since measurements of Tg s and the thermal expansion coefficients are not very sensitive and accurate, the results derived from such model present some scattering and their reliability needs further proof for its validity. Therefore, in the following we shall concentrate to the unfolding models for fiber composites, as they have been extended from the respective models for particulates, which present significant stability and unquestionned reliability. 

The Doppler meter may be used wherever small particulate solids, bubbles or droplets are dispersed in the fluid and are moving at essentially the same velocity as the fluid stream which is to be metered. A continuous ultrasonic wave is transmitted, again at an acute angle to the wall of the duct, and the shift in frequency between the transmitted and scattered waves is measured. This method of measurement of flowrate is frequently used for slurries and dispersions which present considerable difficulties when other methods are used. 

Instruments that measure scattered light, such as the Photo-Nephelometer (Coleman Instruments, Oak Brook, IL), are used to evaluate and set clarity standards for parenteral preparations. It is not possible to establish an overall standard value for all products (e.g., 30 ne-phelos) because the value itself is relative and influenced by many factors, including concentration, aging, stopper extracts, and the solubility characteristics of the raw materials. Nephelometer readings are insensitive to contamination by large (visible) particulates. 

---