Particle size standards

National Institute of Standards and Technology (NIST). The NIST is the source of many of the standards used in chemical and physical analyses in the United States and throughout the world. The standards prepared and distributed by the NIST are used to caUbrate measurement systems and to provide a central basis for uniformity and accuracy of measurement. At present, over 1200 Standard Reference Materials (SRMs) are available and are described by the NIST (15). Included are many steels, nonferrous alloys, high purity metals, primary standards for use in volumetric analysis, microchemical standards, clinical laboratory standards, biological material certified for trace elements, environmental standards, trace element standards, ion-activity standards (for pH and ion-selective electrodes), freezing and melting point standards, colorimetry standards, optical standards, radioactivity standards, particle-size standards, and density standards. Certificates are issued with the standard reference materials showing values for the parameters that have been determined. 

AB), which are colored cross-linked dextran particles with defined buoyant densities, were used to determine the evolution and the final shape of the quasiequilibrium density gradients in TLF. Several samples of polystyrene (PS) latex microspheres (Duke Scientific Corporation, Palo Alto, CA), supplied by manufacturer as particle size standards, were used in focusing FFF experiments. 

Figures 19 and 20 show experimental data recently obtained by Siebenburger et al. [33] on polydisperse dispersions of the thermosensitive core-shell particles introduced in Sect. 3.1.2 [31]. In all cases stationary states were achieved after shearing long enough, proving that ageing could be neglected even for glassy states. Because of the appreciable poyldispersity in particle size (standard deviation 17%) crystallization could efficiently be prevented and flow curves over extremely wide windows could be obtained. Two flow curves from their work can be used to test the asymptotic results.

Reasonable and justifiable acceptance criteria for the particle size distribution of samples from a future study, either scale-up or validation, would be the following each sample median should fall within the range 5.28-6.22 urn, and the particle size standard deviation should fall with the range 0.40-0.56 jim. 

The particle size standards (PSS) used to test the dependence of the reflectance measurements to the particle size were purchased from Duke scientific. Table 2 shows the information on the particle size distribution (NIST mean diameter, standard deviation, a, and coefficient of variation) of the particles given by the manufacturer. 

Table 2. Polystyrene (ID 1-11) particle size standards from Duke Scientific...

Sample preparahon requires auxiUaries which are not required for macrotechniques. Sample preparation is parhcularly important in order to reduce artefacts by handling. The need for leUable standards for both microanalysis and imaging is great. Cer-tihed PS particle size standards (100 nm-30 u.m) are available for calibrahon (TEM, SEM, OM). For the current status on standardisahon in microbeam analysis techniques (EPMA, SEM, AEM, EDS), cfr ref. [8]. 

D. R. Alliet, A Study of Available Particle Size Standards for Calibrating Electrical Sensing Zone Methods, Powder Technology. 13 (1976) 5—7. 

Powder Preparation. The goal in powder preparation is to achieve a ceramic powder which yields a product satisfying specified performance standards. Examples of the most important powder preparation methods for electronic ceramics include mixing/calcination, coprecipitation from solvents, hydrothermal processing, and metal organic decomposition. The trend in powder synthesis is toward powders having particle sizes less than 1 p.m and Httie or no hard agglomerates for enhanced reactivity and uniformity. Examples of the four basic methods are presented in Table 2 for the preparation of BaTiO powder. Reviews of these synthesis techniques can be found in the Hterature (2,5). 

Fumaric acid is shipped ia soHd form, the particle size varying based upon the specification. The standard shipping containers are 50-lb bags (25 kg bags outside the United States), supersacks containing up to 2500 lbs, and occasionally bulk hopper tmck. 

Analysis. Excellent reviews of phosphate analysis are available (28). SoHds characterization methods such as x-ray powder diffraction (xrd) and thermal gravimetric analysis (tga) are used for the identification of individual crystalline phosphates, either alone or in mixtures. These techniques, along with elemental analysis and phosphate species deterrnination, are used to identify unknown phosphates and their mixtures. Particle size analysis, surface area, microscopy, and other standard soHds characterizations are useful in relating soHds properties to performance. SoHd-state nmr is used with increasing frequency. 

The most commonly measured pigment properties ate elemental analysis, impurity content, crystal stmcture, particle size and shape, particle size distribution, density, and surface area. These parameters are measured so that pigments producers can better control production, and set up meaningful physical and chemical pigments specifications. Measurements of these properties ate not specific only to pigments. The techniques appHed are commonly used to characterize powders and soHd materials and the measutiag methods have been standardized ia various iadustries. 

In contrast to sodium chloride, langbeinite has an extremely slow rate of solution. Upon control of agitation time, essentially all the sodium chloride dissolves but most of the langbeinite remains as a soHd. Langbeinite is separated from the brine, dried, and then screened into granular, standard, and special-standard particle sizes. These fractions are marketed directiy. In one plant, the unsalable fines are used as the source of sulfate reactant for the production of potassium sulfate. 

Fig. 11. Particle size analyzer based on ultrasonic spectroscopy where DSP = digital signal processor, and RS 232 is a standard serial connection that allows...

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