Powder characterization milling

The time of milling depends on the degree of fineness desired overlong milling, however, leads to excessive contamination due to wear. Comminution theory relates particle size and distributions to the work imparted from the mill. The theories require certain constants to be determined. In practice, size and size distribution after milling are obtained by a powder characterization technique. 

Microfocus film radiogi aphy was employed to nondestructively evaluate as-received and milled powders for the baseline process. Samples of the as-received powder showed no indications of high density inclusions. This result was consistent with Task 1 powder characterization which quantified iron contamination as less than 50 ppm. 

XRD Characterization The powder x-ray diffraction of the mechano-chemically milled complex borohydride has been carried out by the Philips X pert diffractometer with Cu-Koi radiation of X= 5.4060 A. The incident and diffraction slit width used for the measurements are 1° and 2° respectively. The sample holder was covered with Polyethylene tape (foil) with an O-ring seal in an N2 filled glove box in order to avoid or at least minimize the 02/moisture pickup during the XRD measurements. The diffraction from the tape was calibrated without the actual sample and found to be occurring at 29 angles of 22° and 24°, respectively. The XRD phase identification and particle size calculation has been carried out using PANalytical X pert Highscore software, version l.Of. 

Two important morphological parameters characterizing ball-milled powders are the particle and grain size of constituent phases within the powders. In our laboratory, the size measurement of the powder particles is carried out by attaching loose powder to sticky carbon tape and taking pictures under secondary electron (SE) mode in the SEM. The images are then analyzed by an image analysis software. The size of the powders is calculated as the particle equivalent circle diameter, ECD = AA/nf, where A represents the projected particle area. Usually from -300 to 700 particles are analyzed for each batch. 

Center and Behai (49) have resolved 5 -nucleotidase from calf intestinal mucosa into three fractions using DEAE-cellulose chromatography. One of these was obtained free of nonspecific phosphatase. It had a pH optimum of 6-6.5, Mn2+, Mg2+, and Co2+ (1-10 mill) all enhanced activity and complete inactivation was produced with 1 mM EDTA. This enzyme hydrolyzes all 5 -ribonucleotides at similar rates and hydrolyzes 5 -deoxribonucleotides more slowly. These properties indicate that it is strikingly similar to the one obtained from acetone powder preparations of chicken and rat liver (32, 33) and from soluble supernatants of rat liver (36). The other two activities (which were not fully characterized) (49) could possibly have originated from particulate material or membranes because the authors employed deoxycholate in the early phase of purification. 

One of the main problems in investigation of mechanochemical transformations consists in the relations between product yield and mechanical energy consumed by the process. Butyagin and Pavlychev [8] proposed to characterize mechanochemical yield by the ratio of the moles of product to the amount of the energy consumed (mol/MJ), similarly as in radiation chemistry. In reality, the researches most often record the dependence of the transformation degree a versus the time of mechanical treatment of powder mixture in mills. If the power of apparatus is known,... 

Metal-free phthalocyanine (H2PC) exists in the a, P, r, and X polymorphic forms. The a,P, and X forms have been characterized by electrochemistry [36a], fluorescence spectroscopy [36b], and optical absorption [36c] and a,p, and t forms by C-NMR spectroscopy [36d], optical absorption, and X-ray powder diffraction [36e]. Figure 19 shows the optical absorption spectra of the four forms. The t form has been further characterized as to particle shape (Types I and II) [36f]. The as-synthesized y9-H2Pc is converted to a-H2Pc by acid pasting and this can be converted to the X or T forms with mechanical milling under specific conditions. The X and r forms convert to the P with thermal, solvent, or extended mechanical treatment. 

However, it is not easy to evaluate the particle size of a powder. For a large lump, it is possible to measure it in three dimensions. But if the substance is milled, the resulting particles are irregular with different numbers of faces and it would be difficult or impracticable to determine more than a single dimension.For this reason, a solid particle is often considered to approximate to a sphere characterized by a diameter. The measurement is thus based on a hypothetical sphere that represents only an approximation to the true shape of the particle. The dimension is thus referred to as the equivalent diameter of the particle. 

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