Coated particles basic carbonate

Again, decomposition of urea in an acidic metal salt solution in the presence of preformed particles can yield homogeneous layers of variable thicknesses of metal basic carbonates on the core materials of different chemical composition. In order to obtain uniformly coated particles (rather than a mixture of the latter and of the independently precipitated coating material), a balance between the amount of the initial dispersed matter and the concentration of the reacting solutes must be optimized. 

One important aspect of such coating processes is the generality of the procedure. It would appear that specific surface characteristics of the preformed particles are not necessarily essential for the successful deposition of the new layer. For example, yttrium basic carbonate coatings were produced on zirconium basic sulfate... 

Using the same procedure, spherical nanosize particles of hematite were coated with yttrium basic carbonate and showed that various surface thermodynamic properties of these systems were essentially those of yttria (37). 

In most cases the coating alone may be changed on subsequent treatments (e.g., by calcination at elevated temperatures), such as by converting basic carbonates into oxides. However, in some instances the shell and the core may interact to yield a different compound. For example, silica particles coated with Y(0H)C03 on heating to IOOO°C reacted to yield yttrium silicate, Y2Si207, which was restricted to the shell, as long as the amount of silica in the core was in molar excess (32). 

Aiken B, Matijevic E (1988) Preparation and properties of uniform coated inorganic colloidal particles, 4. Yttrium basic carbonate and yttrium-oxide on hematite. J Colloid Interface Sci 126 645-649... 

Figure 2.28 Transmission electron micrograph of yttrium basic carbonate (YOHCO3) particles coated with Si02 showing (a) smooth Si02 coating when the reaction was carried out at room temperature and (b) rough Si02 coating formed at higher reaction temperature (SOT). (From Ref. 86.)...

Fuel clad material - the material of the tube containing the fuel pellets or rods. Basically, there are three types of cladding - magnesium alloys (e.g. Magnox), stainless steel, or various zirconium alloys. HTGR reactors use fuel particles coated with pyrolitic carbon and silicon carbide in two layers. Data providers should choose the appropriate option from the multiple-choice menu magnesium alloy, stainless steel, zirconium alloy, zirconium-magnesium alloy, carbide compound. 

Zinc coatings on steel (galvanised) are attacked in the same way Jis iron, but usually more slowly. Very alkaline waters are usually aggressive to zinc and will often remove galvanised coatings the corrosion products consist of basic zinc carbonate or other basic compounds and may take the form of a thick creamy deposit or hard abrjisive particles. 

Sodium carbonate is an alkali, a strongly basic compound that has a pH of 9 or more in solution. Boiling an alkali with fat makes soap. Chemically, soap contains a long chain of hydrocarbons that repels water but has an affinity for other fatty substances. When treated with alkali, the ends of the fatty chains are modified so that they are attracted to water. A molecule with one end that attracts fatty substances and another end that likes to dissolve in water is ideal for coating dirt particles and floating them away in water. Soap can be made from any kind of fat, whether from kitchen scraps or whale, olive, or palm oil. 

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