Sinter phosphates

Sinter phosphates Rhenania phosphates with a P2O5 content of ca. 29% are obtained by sintering apatite, silica and sodium carbonate or sodium hydroxide. Their annual production in the Federal Republic of Germany is over 300 10 t (corresponding to ca. 90 10- t/a P2O5). 

Melt and sinter phosphates accounted for ca. 3% of the worldwide production of phosphate fertilizers in 1976, with its share decreasing relative to other types. 

Rhenania phosphate is made by sintering phosphate rock at 1200°C with soda ash and silica, cooling and then grinding. In this way the phosphate rock is opened up and made more suitable for application. Tetracalcium phosphate, Ca4P20g, can be formed as well as calcium sodium phosphates and calcium silicate. The main reaction has been represented as (12.12). 

Another preparation method is a sintering process where phosphate ore, sand, and coal are blended together and ignited on the grates of a sintering machine. Air is pulled through the blend, and the entire mass is allowed to bum. The resulting fused bed of material is then cmshed and screened to the appropriate size distribution, and the undersized material is reprocessed. 

One other method used to size the phosphate ore is disk agglomeration. After preparation, the disk agglomerates are sintered at high temperature in separate process steps, followed by screening to the appropriate size specifications. 

Two methods are available for the preparation of the powder (Smith, 1969). In one, zinc oxide is ignited at 900 to 1000 °C for 12 to 24 hours until activity is reduced to the desired level. This oxide powder is yellow, presumably because zinc is in excess of that required for stoichiometry. Alternatively, a blend of zinc oxide and magnesium oxide in the ratio of 9 1 is heated for 8 to 12 hours to form a sintered mass. This mass is ground and reheated for another 8 to 12 hours. The powder is white. Altogether the powder is similar to that used in zinc phosphate cements. 

Liquid-phase reactions photocatalytic, 19 85 of titanium nitride, 25 10 Liquid-phase sedimentation, 18 142 Liquid-phase sintering, 5 661 Liquid phosgene assay, 18 808 Liquid phosphate esters, 19 51, 68... 

Sintering machines, 26 565 molybdenum, 17 9-10 of polytetrafluoroethylene, 18 300-301 phosphate ore, 19 7 Sintering process, 10 41, 94, 95 for ceramic membranes, 15 814, 815 sulfur recovery from, 23 772 with tin powder, 24 798-799 Sinter processes... 

Low-temperature treatment of low-level mixed wastes has also been accomplished by solidification/stabilization with chemically bonded phosphate ceramics (CBPC). These are made by hydrothermal chemical reaction rather than by sintering. Chemical bonding develops when acid phosphates react with oxides to form crystalline orthophosphate (Singh et al. 1997). The ceramic matrix stabilizes the wastes by microencapsulation. The low temperature of the reaction allows volatile radionuclides to be treated (Singh et al. 1997). 

In France, a number of researchers have explored the washing, phosphate stabilization, and sintering or calcination of residues (Derie 1996 Iretskya et al. 1999 Nzihou Sharrock 2002 Piantone et al. 2003). The formation of more crystalline hydroxyapatite reaction products helps reduce leachability of metals incor-... 

Cr/alumina can be modified like Cr/silica. Adding titania is not particularly useful, but replacing the hydroxyls with fluoride does boost the activity by as much as 10-fold (62). An example is shown in Fig. 22, where activity is plotted versus the amount of fluoride impregnated onto a highly porous alumina. Too much fluoride tends to sinter the alumina and destroy the activity. Other modifications which improve the activity of Cr/alumina include adding chloride, sulfate, boria, phosphate, or 1-5% silica (62, 78). 

Deep Bonding Process (Tiefbonder-Verfahren, in Ger) for AP Projectiles. This method, developed in Germany during WWII by the late Dr. V. Duffek collaborators, consists of deep surface treatment of a sintered iron AP projectile with a phosphate. The method is claimed to diminish the wear of gun barrels and to increase the effectiveness of armor penetration by AP projs... 

The process known in industry as "parkerizing" consists essentially of a treatment of an iron object with an acidic phosphate soln which results in depositing a thin layer of cryst iron phosphate on the surface of iron. When applied to sintered iron projs, the "parkerizing" process decreased only slightly the friction of proj s in the bore, because the amt of phosphate deposited on the surface was so small that it was completely removed even before the proj left the bore. The use of this method did not improve the penetration of armor by AP projs... 

The investigation of Dr Duffek collabs continued and, on the strength of their suggestions, a process was developed at the Metallgesell-schafr AG, Frankfurt a/Main, (Refs 1, 2 3), which permitted the deposition of thicker surface layers of phosphate crysts due to deeper penetration of the phosphate solns into sintered iron objects. The process (called in Ger "Tiefbonder-Verfahren") may be conducted by one of three methods, but the following procedure was preferred by Dr Duffek ... 

Since improvements achievable with bulky electrodes are limited by the structure of the electrode itself, sintered, porous, Teflon bonded, or phosphate-bonded Ni electrodes have been proposed [386, 391, 399, 400]. A mere increase in surface area is observed without any change in Thfel slope. The same is the case with Ni wiskers in spite of their very large surface area and small particle size [401, 402], A decisive modification of the kinetic pattern is indeed obtained as Raney Ni is used [93, 403] (see Fig. 11). This form of Ni is well known also in the field of hydrogenation catalysis. As an electrocatalyst it was proposed by Justi et al. [404] long ago. Raney Ni is obtained by allowing Ni with a component (usually Al or Zn) which is then... 

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