Particle size detection

Figure 4 Techniques of particle size detection and their limits.

Haaf, W., and R. Jaenicke (1977). Determination of the smallest particle size detectable in condensation nucleus counters by observation of the coagulation of S02 photo-oxidation products. J. Aerosol Sci. 8, 447-456. 

In the past, specifications for metal ion content and particles have been arbitrarily reduced for each new generation (smaller geometry) of devices. Recently, research has been conducted on the correlation of device performance with various impurities. While impurity specifications will continually drop, only troublesome impurities will be reduced. This change in strategy of purity management will reduce the burden on chemical suppliers, especially as specifications move toward 1 part per trillion (ppt) for metals and to the theoretical limits of particle size detection of optical counters. Semiconductor Equipment and Materials International (SEMI) has recently initiated an effort to reduce the number of specified metals down to 17 (Table 15.4) from over 30. 

The range of particle sizes detectable by this technique depends on the refractive index of the chosen solvent system, on the characteristics (intensity and wavelength) of the incident light and on the instrumental conditions, and it is usually in the submicrometer-micrometer range. 

The term particle and particle size are so highly ambiguous as to require precise definition. As used in this article particles will.be limited by size to those distinct entities which have physically detectable boundaries in any direction within the limits of 0.05 and 10 microns (1 micron, p -0.001mm). This size range covers those particles which can be directly measured without magnification down to those which exhibit colloidal behavior... 

If the phases present can be unambiguously identified, microscopy can be used to determine the geometry of interface initiation and advance, and to provide information about particle sizes of components of mixed reactants in a powder. Problems of interpretation arise where materials are poorly crystallized and where crystallites are small, opaque, porous or form solid solutions. With the hot-stage microscope, the progress of reactions can be followed in some instances and the occurrence of sintering and/or melting detected. 

A particle size effect has been detected by Chou and Olson [486] in the isothermal decomposition of isothiocyanatopentammine cobalt(III) perchlorate. Below a = 0.09, the larger crystals decompose relatively more rapidly than the smaller, whereas for a > 0.09, the reverse is true. This behaviour was attributed to enhanced nucleation in the larger particles due to strain, but this favourable factor was later offset by the inhibiting influence of the product ammonia which accumulated in the larger crystals. 

K2C03 3 H202 contains hydrogen peroxide of crystallization and the solid phase decomposition involves the production of the free radicals OH and HOi, detected by EPR measurements [661]. a—Time curves were sigmoid and E = 138 kJ mole-1 for reactions in the range 333—348 K. The reaction rate was more rapid in vacuum than in nitrogen, possibly through an effect on rate of escape of product water, and was also determined by particle size. From microscopic observations, it was concluded that centres of decomposition were related to the distribution of dislocations in the reactant particles. 

The reaction of Na with B, detectable at 850°C, becomes complete at 900°C after 24 h. At 1000°C, the reaction rate is independent of the variety of boron (a- or -rh), if the particle size is the same. The B-Na system contains two borides with the... 

Transmission electron microscopy is one of the techniques most often used for the characterization of catalysts. In general, detection of supported particles is possible, provided that there is sufficient contrast between particles and support - a limitation that may impede applications of TEM on well-dispersed supported oxides. The determination of particle sizes or of distributions therein is now a routine matter, although it rests on the assumption that the size of the imaged particle is truly proportional to the size of the actual particle and that the detection probability is the same for all particles, independent of their dimensions. 

In terms of the accuracy of measurement, it appears from Tables III - V that detection of a narrow distribution particle mixture at 350 or 280 nm is just as advantageous as detection at 25U nm. However for a broad particle size distribution sample, detection at 25U nm or lower where particles absorb, provides a distinct improvement in small particle detection (T.) ... 

The detailed size dependence at the Fermi level is shown in Figure 12 [171]. Although the Fermi cutoff is already detectable even at the smallest particle size (curve (c)), there is change near the Fermi level in the 0-0.6 eV BE... 

Important changes in particle size have been observed by varying the amount of the reducing agent (Table 6 and Figure 2). ICP analysis of the filtered water did not detect any important gold residue after immobilization on... 

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