Acicular particles

Historically, strontium metal was produced only in very small quantities. Rapid growth of metal production occurred during the late 1980s, however, owing to use as a eutectic modifier in aluminum—silicon casting alloys. The addition of strontium changes the microstmcture of the alloy so that the siUcon is present as a fibrous stmcture, rather than as hard acicular particles. This results in improved ductility and strength in cast aluminum automotive parts such as wheels, intake manifolds, and cylinder heads. 

At this point, we are most interested in the size of particles and how the other factors relate to the question of size. The next most important factor is shape. Most of the particles that we will encounter are spheroidal or oblong in shape, but if we discover that we have needle-like (acicular) particles, how do we define their average diameter Is it an avereige of the sum of length plus cross-section, or what ... 

Fig. 10 Electron micrograph of an ultramicrotome-cut thin section of a layer of paint, seen perpendicular to the orientation of acicular particles and to the surface of the layer.

Sometimes the dispersion process may inadvertently result in destruction of the aggregates and the primary particles, which happens particularly with pigment powders consisting of coarse or acicular particles - not to forget the effect of intensive shear [59]. 

In view of the high uniformity of the acicular particles, it is likely that their nucleation has finished by the time when the precipitation of the tabular particles is completed, followed by their growth under a low supersaturation, in equilibrium with the tabular particles, without renucleation. 

The goal of the following discussion is to study the low-frequency dynamic birefringence induced by an alternating field in a suspension of acicular particles with dipole moments, that is, the system of type 1 according to the classification given above. The results presented are obtained avoiding any... 

Multiangle Measurements. More information is potentially available from multiangle measurements. Zero-angle extrapolated data are more amenable to proper data transformation. Separation of translational and rotational motion of highly acicular particles is possible. Verification of peaks at more than one angle lends credence to their existence. Simultaneous deconvolution of angular data may provide a useful constraint. 

Cohesion has often been attributed to the interlocking of fibrous or acicular particles. This could be important in the more porous parts of the material, but in the material as a whole, attractive forces between those parts of adjacent layers of C-S-H or other phases that are in contact are probably more important, both within particles and, in so far as the material is particulate, between them. The attractive forces could be direct, of the types mentioned above, or indirect, through interposed HjO molecules forming ion-dipole attractions and hydrogen bonds. Even for D-dried material, analogies with crystalline tobermorite and jennite indicate that much interlayer water is still present (Section 5.4). 

Knowels, J.E., Magnetic properties of individual acicular particles, IEEE. Trans. Magn., 17, 3008, 1981. 

Long, thin particle with a width and thickness that are greater than those of an acicular particle... 

However further increase of pressure may result in particle size increases and a more acicular particle shape because of increasing solubility in modified CO2. Most applications require pressures below 20 MPa. 

Some materials can exhibit negative solid state transformations—for example, formation of different unstable solvate forms or polymorphs and acicular particles. For respiratory applications, the challenge is to achieve many formulation goals with a single-step process. 

Three crystal forms (two polymorphs and one hydrate) of an oxazoli-done antimicrobial, RWJ-337813, were processed by means of the SEDS technique at different pressures (80-200 bar) and temperatures (36-120 °C) from dimethylformamide (containing 20 and 30 mg/mL of the drug) (27). For the preparation of the hydrate, water was added to the CO2 stream at up to 16% by volume. The two polymorphs of RWJ-337813 (forms A and B) generated are anhydrous and monotropic to each other, with A as the stable form. Form C is a hemihydrate generated at 200 bar and 40°C with modified CO2 flow. Form A was produced (as acicular particles) at 200 bar and 120°C, while form B was obtained (as small platelets) at lower pressure and temperature (80 bar and 36°C). 

BLADE similar to acicular particles, except wider and longer... 

We have already discussed measurement of particle size by the use of particle dimensions in Section II. where particle shape as relating to particle size was a major concern. Note that even though the shape of the particle may be quite elongated, the stated size wiU be predicated upon a spheroidal shape. The stated (measured) size of a PSD based upon weight will depend upon how well the particles were separated into fractions. For example, if we use a set of sieves to separate particle fractions, the fractions of particles measured may, or may not, be a function of shape. Acicular particles will not pass through a given screen the same way as... 

Evidence for the formation of acicular particles within larger p grains of the TMAZ of the weld on the p-annealed sample was also... 

Acicular particles, as demonstrated in Figure 9.3.b, are formed of needles or with pointy shaped rods protruding from a nuclear mass. Among the dimensions... 

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