ISSN:0934-0866    

DOI:10.1002/ppsc.19960130502

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130503

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper gives a theoretical basis for calculating Fraunhofer diffraction patterns of arbitrary polyhedron particles. It is shown that this solution can be used for calculating a scatter matrix adapted to the particle shape in a straightforward manner. Some simulations were made to show the difference between the size distribution by volume obtained with a scatter matrix for spheres and with that for the appropriate shape. Finally, some experimentally measured signatures from platelets and rods are evaluated in order to show that the spherical equivalent diameter could be accurately retrieved.

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130504

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractWithin the past 20 years, particle size analysis with laser diffraction (LD) has been subject to rapid development, extending the size range stepwise from 1–200 μm to about 0.1–3500 μm. The limits of LD are discussed in terms of light sources, the influence of the beam diameter, special Fourier optics and a new detector design.It is shown that thesize rangeis not only restricted by the wavelength of the laser and the transmission limits of the medium. Its extension is mainly related to improvements in the measurement of the angular intensity distribution. Influences from stability and flow dominate on the coarse side of the measuring range. On the fine side, the spatial extension of aerosols and the resulting demand for extended working distances can be covered only in a parallel laser beam. Extended Fourier optics in combination with an adapatable beam expansion technique and a detector with virtual borders between semicircular elements overcome the existing limits and extend the size range to a lower limit of about 0.05 μm and an upper limit above 10 mm.Thesensititivitylimit of LD is approaching that of single particle counting techniques. For medical spray and inhaler applications, a 0.1% optical concentration can be converted to particle size distributions even for time‐resolved analyses with sample intervals of a few milliseconds.Thereproducibilityof the sensor, with a standard deviation typically much less than 0.5%, is no longer the limiting factor. The reproducibility of the results is mainly dominated by the reproducibility of sampling, sample splitting, dispersion and the contamination of the optical path. The latter can be improved by the control of flow, especially for in‐line and inhaler ap

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130505

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractMany different methods for size measurement are known and since they differ in their physical principles, different results are also obtained. In the recent past, there were rapid developments in new measurement techniques and one can now quickly and routinely determine particle sizes in the very fine range. Smaller particle sizes, on the other hand, tend to increase the probability of agglomeration. The measurement of the particle sizes for magnetic materials is not well understood and this paper reports results regarding the size determination of very fine magnetic materials. Because of their dipole moment, these particles tend to agglomerate even more, which in turn causes certain difficulties during the measurements. Wet and dry laser measurement systems were compared and also magnetic materials with different permeabilities in order to establish the influence of individual factors on the measurement process and on the accuracy of the results obtained.

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130506

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractDynamic light scattering has become a standard technique of investigating colloidal suspensions and polymer solutions. The experimental field autocorrelation function ĝ1(t) can often be well modelled by a Laplace transform relating ĝ1(t) to a distribution of decay times A(τ). In simple systems A(τ) can usually be directly related to a distribution of molecular weights, particle sizes, diffusion coefficients or other physically relevant quantities, With constrained regularization methods, the parameter‐free estimation of A(τ) has become straightforward. In complex systems, the resulting A(τ) may contain several components the identification of which is not always obvious. The problem often originates in a superposition of diffusive and angle‐independent components that have different variations of their respective decay times with the scattering vector. A method is presented based on a simultaneous fit of several autocorrelation functions measured at several different scattering angles, which, using simple and reasonable assumptions, yields a robust analysis of the spectra of decay times. The application of the method is illustrated on simulated autocorrelation functions and also on real experimental data obtained on a variety of different polyme

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130507

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractA light‐scattering instrument that is normally used for particle size analysis was applied to obtain information about particle shape. Micro‐cuboids of dimensions a × b × c in the range between 10 and 1000 μm, which can be accurately manufactured employing special technology, were used as labelled samples for the determination of 3‐D features. Particle projections at different orientations due to turbulent motion were measured sequentially. The laser diffraction of cuboids rotating in a turbulent flow is described theoretically using a simplified model, i.e. rotation of a rectangle. The change in the projection areas of rotating cuboids is connected with their rotational velocity. The power spectrum density of rotational velocity of cuboids and spheres was determined and the influence of particle shape on the power spectrum density established. The frequency distribution of projection sizes was found to be suitable for particle shape es

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130508

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractLaser diffraction (LD), with reference to the analysis time, is highly advantageous for the automation of particle size analysis. The high measuring frequencies alloy quasi‐continous measuring operation. The fineness values obtained form the particle size distribution (PSD) can be transformed into electrical signals for automatic process control.For industrial purposes, an encapsulated measuring cell was developed where the laser beam penetrates the dispersed fines stream via two optical windows. Thus, hazardous materials can also be measured, specifically pharmaceutical or chemical products, or applications requiring explosion‐proof plant design are possible. Great efforts had to be made to keep the inner side of the windows clean form product dust. Ultimately, batches running for more than 8 h could be analysed continuously without any contamination of the windows. For the PSD measurements, a standard LD instrument was used with a measuring range of 0.5/0.9–175 μm.As product fineness is monitored continuously in‐stream, and virtually without delay, any changes in the fineness during classifier operation can be detected immediately. On the one hand, this opens up a new field for studies of classifier performance. On the other, immediate quality control of even very small batches is possible during the micronization process. The results demonstrate very clearly, for example, the importance of controlling the feed rate to the classifier. Therefore, fineness control by means of this in‐line technique gives superior advantages for direct adjustment of the classi

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130509

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractExperimental investigations were carried out with mainly a Mogensen‐Sizer, compared with test screening and additionally laser diffraction and light extinction, in order to check the qualification for on‐line determination of particle size distribution under the specific conditions of feed milling. The different components of compound feed, the degree of milling, the difference in measured particle characteristics and the possibility of sample dispersion affect the comparability of the results. The results show that laser diffraction is a manysided method with accurate recording of the distribution. The modified Mogensen‐Sizer can be a robust low‐price alternative if the control of selected distribution parameters is suf

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130510

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe precipitation of barium sulfate was investigated by photon correlation spectroscopic (PCS) measurements of the growing crystals combined with electrical conductivity measurements of the mother solution. Small silica seeds (36nm) were added to the solution. Therefore, heterogeneous nucleation did not take place on the walls and on the stirrer, which is usually the case, but on the seeds. Hence the growth of the crystals which had nucleated on the seeds could be studied by PCS. In order to avoid the ill‐conditioned inversion of the measured raw data, the autocorrelation functions, a population balance model was used to calculate these functions with the help of a kinetic model taken from the literature. The measured an the calculated autocorrelation functions could coincide and adjustable parameters were found from a least‐squares fit. The measurements revealed that nucleation is strongly enhanced by PMA‐PVS (polymaleic acid–polyvinylsulfonic acid). However, a simple model which assumes langmuir adsorption of PMA‐PVS on the crystal surface did not describe the kinetics very well. The nucleation rate in the absence of the additive was found to beJ=1.3·1010exp(−27/In2S) [m−3s−1], while the growth rate wasG=2.6·10−8(S−1)2/3S1/3exp(−29/3 InS) [ms−1]. These results match results taken from t

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130511

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY