Particle shape roundness

Particle Shape and Size. With few exceptions, resins are supplied as small, round beads having a diameter between 0.3 and 1.2 mm. Some resins are reduced to a smaller size by grinding to satisfy specific requirements in applications for electric power generation (qv) and pharmaceuticals (qv). 

The factor iji < 1 must be determined experimentally for particles of interest. Typical values are iji = 0.77 for particles of rounded shape iji = 0.66 for particles of angular shape iji = 0.43 for particles of a flaky geometry. 

The grain size distribution of spent foundry sand is very uniform, with approximately 85 to 95% of the material between 0.6mm and 0.15mm (No. 30 and No. 100) sieve sizes. Five to twelve percent of foundry sand can be expected to be smaller than 0.075 mm (No. 200 sieve). The particle shape is typically subangular to round. Spent foundry sand gradations are too fine to satisfy the fine aggregate standard specified in specification ASTM C33 Standard Specification for Concrete Aggregates. 

Endosperm constitutes the main part of the corn kernel and consists of 85 to 90% starch, 8 to 10% protein, and a small amount of oil and other compounds. Corn endosperm can be divided into two distinct parts floury and horny endosperm. In floury endosperm, starch particles are round and are dispersed loosely in the protein matrix. In the horny endosperm, the protein matrix is stronger and starch particles are held more firmly. Starch granules are encased in the continuous protein matrix. The tighter setting in horny endosperm gives starch particles a polygonal shape. On average, the amount of horny endosperm in the corn kernel is twice that of the floury endosperm. However, this ratio is a function of the corn kernel protein content (Wolf et al., 1952). 

Particle shape. When examined under the micro scope the fracture of the particles shall be con choidal and there shall be no long needles or round particles... 

Particle size and shape Finer particles tend to be more cohesive and hence more difficult to handle. Similarly, particle shape also affects flowability. Fibrous and angular particles are usually more cohesive than particles that are rounded. 

The ratio of surface to volume factors is a useful measure of particle-shape, as shown by Fair and Hatch (1933). Thus, for rounded particles at/a9 is approximately 6.1 for worn particles, 6.4 for sharp particles 7.0 and for angular particles 7.7. (For spheres ott/a9 = 6.) A similar... 

Narayanan and El-Sayed investigated the effect of the electron-transfer reaction between ferricyanide and thiosulfate on the stability of particle shape [39,40]. The change in shape of the nanoparticle was time-dependent this change was in the form of a thermodynamic rounding of the particle into a sphere due to the dissolution of platinum atoms from the comers and edges of the tetrahedral and cubic platinum nanoparticles. Figure 18.3 demonstrates that the tetrahedral particle evolves into a distorted tetrahedral particle after one reaction cycle (Fig. 18.3a and b). For the cubic platinum nanoparticles (Fig. 18.3c), the rate of dissolution of platinum atoms was slower, and distorted cubic platinum nanoparticles (Fig. 18.3d) were dominant after two reaction cycles. 

Lemery s use of mechanical explanations for chemical phenomena is, in fact, very restricted. Although he deploys a particulate matter theory throughout the book, using it both post and ad hoc to explain chemical processes, he actually talks exclusively of only two kinds of shaped particles - acids which are pointy and alkalies which are porous. This system is in marked contrast to that of Descartes who happily postulated shapes for a great variety of particles - smooth, round, straight, bent, branched, hooked, and helical - to explain the properties of everything from oils and salts to magnetic attraction.11 Moreover, Lemery s explanations based on the shapes of acid and alkali particles alone creates a serious, but hitherto unremarked, tension within his chymical system. For Lemery equally maintains the traditional... 

Particle shape is of the greatest importance for agglomeration. Typical characteristics are particle roundness or the general overall shape and surface roughness. For some binding mechanisms and/or agglomeration methods, the particle shape is the most decisive particle characteristic. 

Powder metallurgy was used to fabricate SiC particle-reinforced and unreinforced QE 22 alloy. The QE 22 + 15vol.%SiC composite was prepared from gas-atomized metal alloy powders of various sizes (ASTM sieve sizes 230 and 600 corresponding to mean particle diameters of 30 and 10 pm, respectively) and various shapes of the SiC particles (bulky particles - BL, rounded particles - HD). 

Particle shape. Most solid particles tend to be nonspherical, which means that their curvature varies along the surface. This is especially obvious for crystals, where most of the surface is flat while the curvature is very high where two crystal faces meet. This then means that the solubility of the material also varies, and this readily causes local dissolution of material, which is likely to become deposited at sites of small curvature. Table 10.4 shows that for a sucrose crystal a considerable solubility ratio (1.09) is found for r = 10 nm. However, where crystal faces meet, the shape would be cylindrical rather than spherical, leading to a solubility ratio of about 1.045. This is certainly sufficient to cause a crystal edge to become rounded in a saturated solution, and if the crystals are very small, they would likely be almost spherical. Indeed, microscopic evidence shows that many crystals of pm size are roughly spherical and that larger crystals often show rounded edges. 

Figures lb and 1c show how the particle shape are predicted to change when the particles are sintered in hydrogen. Pt(100) strongly binds hydrogen. As a result, (100) faces are predicted to grow when the catalyst is sintered in hydrogen. Simultaneously, the Pt(lll) faces are expected to shrink. With l atmosphere of hydrogen, the calculations suggest that the shape should be a rounded cube at 900 K, as indicated in Figure 1c,...

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