Particles needle-like

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 ... 

Figure 1.4 SEM images and EDX data from a Mo9V3W12Ox catalyst after activation during the oxidation of acrolein [35], The pictures indicate that needle-like (A), platelet-like (B), and spherical (not shown) particles are formed during exposure to the reaction mixture. EDX analysis at different spots, two of which are exemplified here, point to V, Mo, and W contents that vary from 19 to 29, 60 to 69, and 11 to 13 atom%, respectively. It was determined that the in situ formation of a (MoVW)5014-type phase accounts for the increase in acrolein conversion observed during the initial reaction stages. (Reproduced with permission from Elsevier.)...

An important consideration of reactions in which a new solid phase appears is the number, source and location of nucleation sites and the form of the new phase. A needle-like new phase can result in a marked apparent expansion of the material leading to particle disintegration in packed beds. 

The nature and relevance of colloids is one of the main current research topics (Birdi, 2002). They are an important class of materials, intermediate between bulk and molecularly dispersed systems. Colloid particles may be spherical but, in some cases, one dimension can be much larger than the other two (as in a needle-like shape). The size of particles also determines whether they can be seen by the naked eye. Colloids are not visible to the naked eye or under an ordinary optical microscope. The scattering of light can be suitably used to see such colloidal particles (such as dust particles, etc.). Their size then may range from 1() 4 to 1() 7 cm. The units used are as follows ... 

Kiyama, M. Akita, T. Shimizu, S. Okuda,Y. Takada,T. (1972) Conditions favourable for the formation of y-FeOOH by aerial oxidation in an acidic suspension of iron metal powder. Bull Chem. Soc. Japan 45 3422—3426 Kiyama, M. Shamoto, S. Horushi, N. Okuda, Y. Takada,T. (1986) Growth of needle-like a-FeO(OH) particles by air oxidation of aqueous suspensions containing Fe(ll) predpi-tates. Bull. Inst..Chem. Res. Kyoto Univ. 46 150-156... 

Various particle morphologies have been reported using scanning electron microscopy (SEM) [7,25,26]. The y-form can exhibit morphologies of dense irregularly shaped particles, or of needle-like particles that result in a more loose-knit matrix [7,25]. Instant sorbitol was found to be an... 

Photomicrographs taken at higher magnifications of representative surfaces of instant sorbitol and crystalline sorbitol particles are presented in Figure 2. For the instant sorbitol lot, the surface appears porous and comprised of needle-like particles. The surface of crystalline sorbitol, however, exhibits some roughness and some fine particles, but the overall surface is compact and non-porous. 

Wollastonite is a form of calcium silicate (CaSiOj). It is a relatively hard (Moh hardness 4.8) white material with needle-like particles. The specific gravity is... 

The above formulation can be readily extended to the two-dimensional diffusion of a Brownian particle in the presence of needle-like obstacles with a mean lifetime x, as has been made by Teraoka and Hayakawa [107], who obtained for the two-dimensional effective diffusion coefficient... 

Needle like crystals are formed while synthesizing ADN and HNF. Spherical particles with a low aspect ratio are desired in order to obtain high solids loading in a propellant. 

In Mode II (feeding time 10 min), the TEM photo of the product shows clumped particles with a little needle-like crystalline, and the data of XRD indicates that the major product is Cu20, with a little Cu only and no CuO. 

Appearance of product from TEM With Ccuci2 =0.1 kmol-m 3, the product is loosely clumped particles and needle-like appearance at Ccucn = 0.2 the product consists essentially of sphere particles without needle-like appearance at CCuci2 = 0.3 the appearance of the product is essentially the same as for Cc ci2 = 0.2 while for Cc ci2 = 0.4 the product is loose particles and needle-like cluster of long length. 

From both the mean sizes and the appearance characteristics it seems that at lower concentrations of CuCl2 solution, normally spherical particles of uniform sizes are produced while for CCuci2 = 0.4 kmol-m 3 needle-like crystalline clusters possibly up to several micrometers long are formed, which consists of the growing particles in the... 

Appearance of product from TEM The product obtained at the reaction temperature of 10°C consists of particles and needle-like crystalline that obtained at 20°C is roughly spherical particles without needle-like crystalline and slightly clumped that obtained at 30°C consists of spherical particles without needle-like crystalline, but significantly clumped together while the product obtained at 40°C consists of completely spherical particles without needle-like crystalline, but seriously clumped together. 

Photomicrographs of solids produced at 2000 ppm total Mg2+ concentration are shown in Figure 11 which indicates that the solid particles are composed of ill-defined, needle-like platelets. Furthermore, Figure lib reveals serious crystal defects. The poor crystal properties were evidenced by an extremely low settling rate (less than 0.1 cm/min) and very few filter cake insoluble solids (less than 30%). 

Unfortunately, this is not an atypical situation. APIs frequently exhibit rod- or needle-like morphology. Using laser diffraction instruments, particle size distributions of these materials appear as multimodal, making it difficult to assert that... 

Needle-like coke has been widely used for the industrial production of graphite electrodes for steel refining. The changes in transverse magnetoresistance (Ap/p0) with the rotation angles 9 and 9 of the magnetic held along and perpendicular to the axis of a needle-like particle (TL and T... 

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