In situ particle size measurement

The advantage of the technique is that the particle size may be determined with the sample in a controlled atmosphere and at a temperature different from 300 K, i.e., in situ particle size measurement, and measurement of changes in particle size may be possible. The problem, however, is that the quantitative relation between the Mossbauer parameters and particle size is rather complex and in some cases not theoretically available. Therefore, the application of the Mossbauer effect to particle size measurement is often facilitated through an experimental calibration of the Mossbauer parameters to particle size for the particular catalyst system of interest, i.e., the measurement of the parameters for a set of samples of known particle size as determined by other experimental methods. This point will become clearer below, as the effects of particle size on the Mossbauer parameters are discussed. 

In order to measure the in-situ particle size of flowing streams, this firm has developed a rather reliable imit for dilute phase flows. The device has been tested by Bell, et al. [18, 19] with promising results. 

A wide variety of particle size measurement methods have evolved to meet the almost endless variabiUty of iadustrial needs. For iastance, distinct technologies are requited if in situ analysis is requited, as opposed to sampling and performing the measurement at a later time and/or in a different location. In certain cases, it is necessary to perform the measurement in real time, such as in an on-line appHcation when size information is used for process control (qv), and in other cases, analysis following the completion of the finished product is satisfactory. Some methods rapidly count and measure particles individually other methods measure numerous particles simultaneously. Some methods have been developed or adapted to measure the size distribution of dry or airborne particles, or particles dispersed inhquids. 

In parallel with the emission measurements, in situ Mossbauer absorption measurements on hematite suspensions treated in a similar manner as in the emission measurements were performed to check the effects of aqueous phase pH on the substrate. The absorption spectra obtained in the pH region 5-12 consisted of the same well-defined sextet as dry hematite powder, indicating that no appreciable change occurred in the state of dispersion and particle size of hematite in the studied pH range. 

Particle size measurement is one of the essential requirements in almost all uses of colloids. However, our discussion in Section 1.5 makes it clear that this is no easy task, especially since even the definition of particle size is difficult in many cases. A number of techniques have been developed for measuring particle size and are well documented in specialized monographs (e.g., Allen 1990). Optical and electron microscopy described in the previous section can be used when ex situ measurements are possible or can be acceptable, but we also touch on a few nonintrusive methods such as static and dynamic light scattering (Chapter 5) and field-flow fractionation (see Vignette II Chapter 2) in other chapters. 

In summary, particle size distributions measured at similar conditions using optical and sampling probe-impactor methods are vastly different. No conclusions can be drawn concerning the relative accuracy of these two techniques because of experimental differences. All indications are that the optical counter is operating properly and is applicable and advantageous for in situ measurements. Further experiments comparing the two techniques directly on a common engine will be performed soon to substantiate the particulate formation hypotheses. 

The first evidence of in situ particle formation in the atmosphere was provided by John Aitken at the end of the nineteenth century (Aitken 1897). He built the first apparatus to measure the number of dust and fog particles in the atmosphere. However, little progress was made in understanding what causes new particle formation or how widespread it might be for almost a century. In the 1990s the development of instruments capable of measuring the size distribution of particles as small as 3 nm led to the discovery that nucleation and growth of new particles is a rather common event in many areas around the world (Kulmala ct al. 2004). Areas where frequent nucleation bursts have been observed include... 

Reichel, A., Gerber, M., Sehwartz, F. H., Waggeling, R., In-situ Particle Measurements in High Concentrations, a Novel approach for Particle Size Measurement, in Preprint of Partec 98. / European Symp. Part. Charact, Nunberg, 1998, pp.561-570. 

Knollenberg, R. G., In Situ Optical Particle Size Measurements in Liquid Media, in Proc. Pure Water Conf., Palo Alto, CA, 1983. 

The lithium morphology at the beginning of the deposition was measured by in-situ atomic force microscopy (AFM) [42], When lithium was deposited at 0.6 C cm2, small particles 200-1000 nm in size were deposited on the thin lines and grain boundaries in LiC104-PC. Lump-like growth was observed in LiAsF6-PC along the line. 

A mechanistic model for the kinetics of gas hydrate formation was proposed by Englezos et al. (1987). The model contains one adjustable parameter for each gas hydrate forming substance. The parameters for methane and ethane were determined from experimental data in a semi-batch agitated gas-liquid vessel. During a typical experiment in such a vessel one monitors the rate of methane or ethane gas consumption, the temperature and the pressure. Gas hydrate formation is a crystallization process but the fact that it occurs from a gas-liquid system under pressure makes it difficult to measure and monitor in situ the particle size and particle size distribution as well as the concentration of the methane or ethane in the water phase. 

Hydrogen uptake of reduced catalysts (X) was measured by volumetric method with an AUTOSORB-l-C analyzer (Quantachrome Instruments). Hydrogen adsorption was carried out at 373 K after in situ H2 reduction at 773 K for 6 h in the adsorption cell. The dispersion and particle size of metallic Co were calculated by the following equations, assuming that the stoichiometry for hydrogen adsorption on the metallic site is unity ... 

---