Nitrate surface

Accordingly, it can be ruled out that the reaction between NH4N03 and NO and the fast SCR reaction proceed in parallel we have proposed an alternative, sequential scheme, whereby the fast SCR reaction results from the formation of nitrate surface species related to NH4N03, reactions (R7 + R8 + R9, Table V), and their subsequent reduction by NO, reaction (R10 in Table V), which is rate determining at low temperature (Ciardelli et al., 2004b). 

Lourey, M. J., Trull, T. W., and Sigman, D. M. (2003). Sensitivity of delta N-15 of nitrate, surface suspended and deep sinking particulate nitrogen to seasonal nitrate depletion in the Southern Ocean. Global Biogeochem. Cycles 17(3), doi 10.1029/2002GB001973. 

The failure of carbon dioxide to appear at the beginning of the run has been shown not to be due to downstream adsorption by experiments in which the catalyst was exposed to unlabeled carbon dioxide before reaction, and, together with the temperature rise, is persuasive evidence that the oxidation does not begin until adsorption is substantially complete. The reason for the delayed oxidation is not so clear. It seems that a definite population density of acetylene molecules (expressed numerically by a) is required on the silver nitrate surface, either as adsorbed molecules or as a definite surface compound, before oxidation can begin. 

Molecules could be adsorbed on the silver nitrate surface to form an activated complex which then reacts with gaseous oxygen, and this would result in a reaction rate proportional to 1 — reaction rate. There are some indications, however, that neither process is the correct one. It was observed that the evolution of carbon dioxide is very abrupt within the experimental error no carbon dioxide whatever was produced until the silver nitrate-silver acetylide equilibrium had been attained. It is difficult to understand why some catalytic oxidation should not have occurred on either of the two surfaces before this condition was reached. 

Engines of this design, with a working volume of 20 cm, tested during the last six months exhibited an efficiency of up to 75%. Expansion took place from 30 to 1.5 atm, with an outlet temperature of 12°K and within a frequency range of 500 and 1500 cycles/min. The material for the piston and cylinder is a special stainless steel with nitrated surfaces. 

Amblard, I, M. Froment, C. Georgoulis, and G. Papanastasiou (1978). Sur le role de I adde tartrique et des tartrates dans I inhibition de la croissance dendritique de I argent electrodepose a partir d une solution aqueuse de nitrate. Surface Technology 6(6), 409-423. 

Fig. 7. A bead filter, one of many types of biological filters, shown in association with a laboratory-scale recirculating water system. Small plastic beads inside the fiber glass chamber provide surface area for colonisation by bacteria that convert ammonia to nitrate.

A more constrained opportunity for nitrate bioremediation arose at the US-DoE Weldon Spring Site near St. Louis, Missouri. This site had been a uranium and thorium processing faciUty, and treatment of the metal had involved nitric acid. The wastestream, known as raffinate, was discharged to surface inpoundments and neutralized with lime to precipitate the metals. Two pits had nitrate levels that requited treatment before discharge, but heavy rains in 1993 threatened to cause the pits to overflow. Bioremediation by the addition of calcium acetate as a carbon source successfully treated more than 19 million liters of water at a reasonable cost (75). 

For most crops, other than rice, urea in the soil must first undergo hydrolysis to ammonia and then nitrification to nitrate before it can be absorbed by plant roots. One problem is that in relatively cool climates these processes are slow thus plants may be slow to respond to urea fertilization. Another problem, more likely in warmer climates, is that ammonia formed in the soil hydrolysis step may be lost as vapor. This problem is particularly likely when surface appHcation is used, but can be avoided by incorporation of the urea under the soil surface. Another problem that has been encountered with urea is phytotoxicity, the poisoning of seed by contact with the ammonia released during urea hydrolysis in the soil. Placement of urea away from the seed is a solution to this problem. In view of the growing popularity of urea, it appears that its favorable characteristics outweigh the extra care requited in its use. 

Sometimes the formation of oxide films on the metal surface binders efficient ECM, and leads to poor surface finish. Eor example, the ECM of titanium is rendered difficult in chloride and nitrate electrolytes because the oxide film formed is so passive. Even when higher (eg, ca 50 V) voltage is apphed, to break the oxide film, its dismption is so nonuniform that deep grain boundary attack of the metal surface occurs. 

---