Magnetite spheres

Bums, M., Kvesitadze, G. I., and Graves, D., "Dried alginate/magnetite spheres a new support for chromatographic separations and enzyme immobilization" Biotech. Bioeng. 1985. 27 137-145. 

Burns, M. A. and Kvesitadze, G. I. Dried calcium alginate/magnetite spheres A new support for chromatographic separations and enzyme immohilization. Biotechnol. Bioeng. 27 (1985) 137. 

Further heating at 350°C for 1 h under hydrogen atmosphere finally led to hollow magnetite spheres displaying superparamagnetic behavior, with Ms close to that of bulk material (67emug ). 

Kato (K3) measured so-called critical gas velocities corresponding to the complete suspension of solids, and presents a graphical correlation of the results for glass spheres (diameters from 0.074 to 0.295 mm), magnetite particles (particle size from 0.038 to 0.175 mm), and sand particles (particle size 0.147 to 0.295 mm). 

Magnetite Octahedra Intergrown octahedra (twins), rhombic dodecahedra, cubes, spheres, bullets... 

It is no wonder that the particles are spherical but crystalline, if one considers the formation mechanism. The rather smooth surface of the spherical magnetite may be due to the rapid contact recrystallization of the constituent primary particles (5), forming the rigid polycrystalline structure. Flowever, it must be noted that polycrystalline spheres are also prepared by normal deposition of monomeric solute, as shown in the formation of the uniform spherical polycrystalline particles of metal sulfides in Chapters 3.1-3.3. Thus, while we may be able to predict the final particle shape and structure from the formation mechanism, it is risky to conclude the formation mechanism only from characterization of the product. As a rule, scrupulous analyses are needed for concluding the growth mechanism in a particle system. 

Kitamoto and Abe applied power ultrasonic waves (19.5 kHz, 600 W) to 300 ml of FeCh aqueous solution (pH 7.0) at 70 °C, and succeeded in encapsulating polyacrylate spheres of 250 nm diameter with magnetite ferrite coatings [49]. From TEM observations of the cross sections it was seen that the polymer spheres were covered with uniform columnar crystallites of 30-40 nm in diameter at the bottom and 60-70 nm at the top. The ultrasound waves produce OH groups on the polymer surfaces which work as ferrite nucleation sites this improves the quality of the ferrite coatings. The ferrite-encapsulated particles will greatly improve the performance of the enzyme immunoassay as a cancer test reagent. The above possible mechanism for the formation of the blue oxide is consistent with explanations in the literature for a sonochemical reaction. 

Fig. 44 Swelling kinetics of a iron- and b magnetite-loaded mPDMS spheres. The arrow shows the direction of the applied magnetic field during preparation...

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