Oxide powder calcination

Ceramic-grade beryllium oxide has also been manufactured by a process wherein organic chelating agents (qv) were added to the filtered beryllium sulfate solution. Beryllium hydroxide is then precipitated using ammonium hydroxide, filtered, and carefully calcined to obtain a high purity beryllium oxide powder. 

Calcination or dead burning is used extensively to dehydrate cements (qv) and hygroscopic materials such as MgO, and to produce a less water sensitive product. Calcination is also used to decompose metal salts to base oxides and to produce multicomponent or mixed oxide powders for... 

Cobalt pigments are usually produced by mixing salts or oxides and calcining at temperatures of 1100—1300°C. The calcined product is then milled to a fine powder. In ceramics, the final color of the pigment maybe quite different after the clay is fired. The materials used for the production of ceramic pigments are... 

Brown et al. [494] developed a method for the production of hydrated niobium or tantalum pentoxide from fluoride-containing solutions. The essence of the method is that the fluorotantalic or oxyfluoroniobic acid solution is mixed in stages with aqueous ammonia at controlled pH, temperature, and precipitation time. The above conditions enable to produce tantalum or niobium hydroxides with a narrow particle size distribution. The precipitated hydroxides are calcinated at temperatures above 790°C, yielding tantalum oxide powder that is characterized by a pack density of approximately 3 g/cm3. Niobium oxide is obtained by thermal treatment of niobium hydroxide at temperatures above 650°C. The product obtained has a pack density of approximately 1.8 g/cm3. The specific surface area of tantalum oxide and niobium oxide is nominally about 3 or 2 m2/g, respectively. 

The most important characteristic of the magnesium oxide powder used in these cements is its reactivity (Glasson, 1963). Magnesium oxide needs to be calcined to reduce this, otherwise the cement pastes are too reactive to allow for placement. Surface area and crystal size are important and relate to the calcination temperature (Eubank, 1951 Harper, 1967 Sorrell Armstrong, 1976 Matkovic et ai, 1977). The lower reactivity of calcined magnesium oxide relates to a lower surface area and a larger crystallite size. 

Alkoxides (titanium ethoxide, titanium n-propoxide, titanium n-butoxide, titanium sec-butoxide, titanium ethylhexoxide, aluminum sec-butoxide, zirconium n-propoxide, and their mixtures), typically 3 ml, sonicated with propylene carbonate, typically 17 ml, for 20-30 to form uniformly turbid emulsions. Immediate addition of water (10 mol excess) hydrolyzed the alkoxides. Precipitated oxide powders washed (in a Soxhlet extractor) with THF or 2-propanol for 21-30 h, dried, calcinated... 

During the course of studying the effect of crystallite sizes, attempts were made to produce very small unsupported iron oxide powders by lowering the calcination temperature of the iron hydroxyl gel that was precipitated from iron nitrate with ammonium hydroxide. However, catalysts calcined below 300°C still contain hydroxide, and they show high selectivity in butadiene production. For this reason, two catalysts, calcined at 250°C and 300°C, respectively, were studied in more detail. 

Beryllium sulfate, [CAS 13510-49-1], BeSO 4H2O, is an important salt of beryllium used as an intermediate of high purity for calcination to beryllium oxide powder for ceramic applications. A saturated aqueous solution of beryllium sulfate contains 30.5% BeSC>4 by weight at 303C and 65.2% at 111"C. 

The old phosphorus boxes contained preparations which absorbed moisture from the air with the evolution of heat. The resulting rise of temp, favoured combustion. For example, the mixture of yellow and red phosphorus, and phosphoric and phosphorous oxides and acids, obtained by blowing a jet of air into a flask with some warmed phosphorus, may ignite when exposed to moist air. The phosphoric oxides keep the phosphorus in a fine state of subdivision. J. Pelouze obtained a luminous mixture by melting phosphorus with phosphoric oxide, or calcined magnesia, or lime. M. Saltzer melted phosphorus with about one-third its weight of wax sent a jet of air into the flask until the phosphorus inflamed and then closed the flask. E. Benedix fused a mixture of powdered cork, beeswax, phosphorus, and naphtha. The mass fired spontaneously at 20°, or at a lower temp, if breathed upon. 

Other alkalis will also work to dissolve the stibnite, such as potassium hydroxide, even liquid ammonia. By altering the concentrations, and order of mixing the acid and alkali solutions, the powder can be made to take on shades of canary yellow to brilliant orange to crimson red as the particle size varies. Kermes is much easier to calcine to a light oxide powder because of its greater purity. 

For high-temperature applications, sauereisen cement (Omega CC cement) and zinc oxychloride (dental cement) are useful irreversible cements. Sauereisen cement is made by suspending ceramic powders in sodium silicate solution ( water glass ). This cement sets very hard and withstands temperatures up to 1000°C. Zinc oxychloride is made by mixing calcined zinc oxide powder with concentrated zinc chloride solution. One can also use a ceramic putty (Omega CC high-temperature cement), which must be cured at 180°C and is then serviceable up to 850°C. 

The combustion synthesis technique consists of bringing a saturated aqueous solution of the desired metal salts and a suitable organic fuel to the boil, until the mixture ignites a self-sustaining and rather fast combustion reaction, resulting in a dry, usually crystalline, fine oxide powder. By simple calcination, the metal nitrates can, of course, be decomposed into melt oxides upon heating to or above the phase transformation temperature. 

The starting point for the suspension process is a finely divided aluminum oxide powder suspended in water. An additive provides the necessary viscosity. Spinning of this finely divided suspension with the help of additives provides raw aluminum oxide fibers, which by calcining and treatment at high temperature is converted into non-porous sintered a-aluminum oxide fibers. 

The most common technique used to prepare the /i-type (i.e., or / ") alumina is to mechanically blend the component oxides or precursor compounds in powder form prior to a calcination or prereaction step at temperatures between 1000 and 1260°CT Commercially available aluminum oxide powders (0.3-0.5 pm average crystallite size) in the alpha (corundum) polymorph are typically usedT They are derived from three common sources decomposition of gibbsite [Al(OH)3], which is precipitated from soda liquors in the Bayer process preparation and decomposition of alum salts and preparation from aluminum chloride precursors NaaCOs is usually the source of Na20. Sources of Li20 have included Li2C03, LiNOs, and Li2C204- MgO is usually added as the commercially available oxide. 

The synthesis of lithium aluminates for tritium production requires formation of nanostructured phases. These can be made by solid-state reaction, by appropriate mixing of oxide powders [84] or by sol-gel methods [80, 85-87], One technique is the peroxide route where y-Al203 and LiC03 are dissolved in a peroxide (H202) solution. Evaporation of water and calcining the solid residue results in nanophase LiA102. 

Fig. 4. The XRD patterns of samples, (a) Metal support oxidized at 1100 C (b) Sample 9 (c) Sample 3 (d) Sample 6 (e) Precursor powder calcined at 1000 °C...

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