Characterisation of particles

Trimborn et al. (2000) have developed a mobile system for the on-line analysis of single airborne particles and for the characterisation of particle populations in aerosols, using a transportable laser mass spectrometer. A schematic diagram of their setup is shown in Figure 3.12. 

Scarlett B (1996) Characterisation of Particles and powders. In Brook RI (ed) Processing of Ceramics, Part I.VCH, Weinheim, p 99... 

As an irreversible flocculation occurred with a drop-wise approach for both cationic and anionic PEC particles when the mixing ratio was close to unity, a more versatile and simpler method was found to be the one-shot addition of one solution to the other. Characterisation of particles obtained via this path revealed very similar properties to those obtained by a slow drop-wise approach [155]. 

The starting point of any study of particle systems is the characterisation of particles in terms of their size, shape and density. Figure 1 shows the range of sizes of some commonly encountered particulate materials compared with other quantities, such as the wavelengths of electromagnetic radiation and the sizes of molecules. 

A variety of techniques are available for the characterisation of particle size distributions but, because of the large size distribution of solids in water and wastewater, no single analytical method can be used. Besides their physico-chemical properties (stability, settleability, etc.), heterogeneous fractions have interesting optical properties. This is the reason why optical methods take an important place among granulometric methods (Table 5). 

At first, the effect of ageing time on precipitation and growth of particles has been studied. The characterisation of particles aged for various duration shows that one week aged boehmite particles have reached their thermodynamic stability (table 1), so that their different morphologies do not result from any kinetic effect. Hereafter, we discuss only boehmite materials obtained for one week ageing. 

Cheng, R. J., V. A. Mohnen, T. T. Shen, M. Current J. B. Hudson, 1976. Characterisation of particles from power plants. J. Air Poll. Cont. Assoc. 26 787-783. 

The SFM is usually employed for the characterisation of films and surfaces (e.g. roughness), whereas the morphological characterisation of particles is of minor relevance. Its real strength is the sensitivity to the forces between probe and sample, which allows an evaluation of surface chemistry (e.g. functional groups, hydrophobicity) and the quantification particle interactions, or interactions between particles and surfaces (e.g. adhesion, friction Heim et al. 1999 Butt et al. 2007). 

Many macroscopic phenomena of colloidal suspensions arc related to the light scattering and the Brownian motion of the single particles. Both properties depend largely on particle size they are, therefore, frequently employed for the characterisation of particle systems (cf. previous chapter). Additionally, the small size of colloids enhances the significance of the interface to the particles physical behaviour. The interfacial properties additionally affect the interaction between particles and are, thus, cmcial for the macroscopic suspension behaviour (e.g. stability). A particular characteristic of interfaces is the electric double layer (EDL), which camiot be ignored in most situations. Its formation and sttucture is closely related to dissolved ionic species and their interaction with the particle surface (e.g. adsorption, precipitation). Last but not least, the interfacial properties can be affected by the solubility behaviour of the particle phase. 

Evans J.W. Beddow, J.K (1987). Characterisation of Particle Morphology and Rheological Behaviour in Solder Paste. IEEE Trans. Compo. Hybrids Manufac. Tech., pp. 224-231. 

Standard practice for characterisation of particles. ASTM Standards Committee F1877-05 2005. 

The penultimate chapter. Chapter 10, details techniques for the characterisation of particles and surfaces. Although this chapter does not directly relate to the microstructure of hardened cementitious materials, the characterisation of the powders that will transform into the cement is of great importance. Binder properties such as particle packing and rheology critically depend on the accurate characterisation of the powder mix. Again, the study of cementitious materials requires specifically adapted methodologies and care to overcome common problems. 

Heuer, M. and Lesclioiiski, K., 1985. Results obtained with a new instrument for the measurement of particle size distributions from diffraction patterns. Particle Characterisation, 2, 7-15. 

Kaye, B.H., 1981. Direct characterisation of fine particles. New York Wiley. 

Analytical solutions of equation 9.44 in the form of infinite series are available for some simple regular shapes of particles, such as rectangular slabs, long cylinders and spheres, for conditions where there is heat transfer by conduction or convection to or from the surrounding fluid. These solutions tend to be quite complex, even for simple shapes. The heat transfer process may be characterised by the value of the Biot number Bi where ... 

The investigations [27,44-49] carried out with model particle sytems allow the characterisation of many technical and model reactors and their comparison. Some of the results given there are summarised here since they contain the most important, systematic knowledge about stress in reactors existing so far. 

Complete characterisation of complex samples thus becomes possible, and the SAM is used to identify embedded defects and surface particles in semiconductor devices, as well as the study of metal matrix composites and grain boundary analysis. 

Because of the extreme importance of regularity and freedom from failure which must characterise safety fuse, detailed and exhaustive tests must be carried out on the product. Certain controls are obvious, namely, measurement of powder charge and of burning speed, both before and after immersion in water. Other tests usually carried out include resistance to cracking on flexing at low temperatures round a mandrel, coil tests in which the fuse is bunched into flat or complex coils and freedom from failure after immersion in water is determined. New types of fuse are usually tested to indicate the amount of smoke produced and also to determine the adequacy of the end spit. The end spit is the projection of particles of burning powder from a cut end and is of importance because it provides the mechanism which enables the fuse to ignite a detonator. 

Preparation and Characterisation of Novel pH Responsive Microgel Particles. Matt Hearn, Department of Chemistry, University of Bristol, http //www.chm.bris.ac.uk/vincent/matt.html... 

The dark clouds were responsible for the discovery of ISM, as they absorb the light from stars which lies behind these clouds of interstellar matter. It is difficult to obtain reliable information on the dust particles. They are probably about 0.1 pm in diameter, consisting of a silicate nucleus and an envelope of compounds containing the elements C, O and N, which, with H and He, are the main elements present in interstellar space. There are only two sources of information for more exact characterisation of the dust particles ... 

Lespes G, Gigault J. Hyphenated analytical techniques for multidimensional characterisation of submicron particles a review. Anal. Chim. Acta 2011 692 26-41. 

In some cases the interaction between the particles and the surrounding fluid is of little significance, although at other times this can have a dominating effect on the behaviour of the system. Thus, in filtration or the flow of fluids through beds of granular particles, the characterisation of the porous mass as a whole is the principal feature, and the resistance to flow is dominated by the size and shape of the free space between the particles. In such situations, the particles are in physical contact with adjoining particles and there is... 

Much less is known about the settling of particles in fluids exhibiting a yield stress. Barnes (39) suggests that this is partly due to the fact that considerable confusion exists in the literature as to whether or not the fluids used in the experiments do have a true yield stress 39. Irrespective of this uncertainty, which usually arises from the inappropriateness of the rheological techniques used for their characterisation, many industrially important materials, notably particulate suspensions, have rheological properties closely approximating to viscoelastic behaviour. 

The general structure of a bed of particles can often be characterised by the specific surface area of the bed SB and the fractional voidage of the bed e. 

The last term in equation 4.28 is not a simple geometric characterisation of the flow passages, as it also depends on the rheology of the fluid (n). The constant b is a function of the shape of the particles constituting the bed, having a value of about 15 for particles of spherical, or near-spherical, shapes there are insufficient reliable data available to permit values of b to be quoted for other shapes. Substitution of n = 1 and of /x for k in equation 4.28 reduces it to equation 4.13, obtained earlier for Newtonian fluids. 

The minimum fluidising velocity is a function of both emf and 4>s, neither of which is easily measured or estimated, and Wen and Yu have shown that these two quantities are, in practice, inter-related. These authors have published experimental data of emf and relation between these two quantities is essentially independent of particle size over a wide range. It has also been established that the following two expressions give reasonably good correlations between emf and [Pg.297]

The early Universe can be reasonably described as a dilute gas of particles and radiation in thermal equilibrium, uniquely characterised by its instantaneous density and temperature. The expansion of space causes further dilution and coohng of this gas. 

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