Dissolution of precipitates

Bio)chemical reactions may take place prior to or after the continuous separation module and are intended to enhance or facilitate mass transfer, detection or both. The earliest and simplest approach to integrated analytical steps in continuous-flow systems involves a combination of chemical reactions and continuous separations [4,5]. Such is the case with the formation of soluble organic chelates of metal ions in liquid-liquid extractions with the ligand initially dissolved in the organic stream [6], the formation and dissolution of precipitates [7], the formation of volatile reaction products in gas difiusion [8] and that of volatile hydrides in atomic absorption spectro-... 

The knowledge of the solubility products of solids enables us to solve problems related to the formation, or dissolution of precipitates in chemical reactions. 

Complex formation is responsible for the dissolution of precipitates in excess of the reagent ... 

When plutonium in a nitrate form enters soil it precipitates very soon due to hydrolytic reactions. It becomes attached where-wherever a pH-gradient occurs on the surface of the wetted mineral particles and at the top of the advancing acid front. After such an Irreversible type of adsorption it is improbable that the amount of plutonium 1n the soil water depends on ion exchange. Therefore one would suspect a relatively higher contribution coming from the dissolution of precipitated Pu(0H>4. 

The equilibrium formation and dissolution of precipitates can be illustrated with silver chloride. Ag+forms a series of chloro complexes, at least up to AgCI4 v. In the presence of solid AgCl the formal description is most readily characterized by the following formalism ... 

It has been demonstrated that the release of citric acid from PHEMA hydrogels hinders the formation of calcium phosphates, especially hydroxyapatites. Because of this inhibitory effect, the calcium phosphate phases formed during in vitro calcification were mainly present as non-apatite phases, possibly MCPM and DCPD. The porous morphology of the outer surface of the spherical calcium phosphate deposits could be due to the dissolution of precipitates in the presence of citric acid. The results obtained after subcutaneous implantation ofPHEMA and PHEMA containing citric acid in rats confirmed the resistance of PHEMA-citric acid to calcification. The calcium phosphate deposits which formed in vivo consisted mainly of Ca2+ and OH deficient hydroxyapatites. However, it is not yet known whether or not the differences between the calcium phosphate phases found in vivo and in vitro arise from the presence of proteins/peptides in the in vivo calcifying medium. 

Hydrazine hydrate is the key material for the preparation of this type of explosive. Hydrazine dinitrate has to be first prepared following the production of hydrazine nitrate through the recrystallization of hydrazine hydrate. As shown in Fig. 7.6, the preparation involves nitric acid 65 % and hydrazine hydrate 50 %, of which an equimolar mixture in methanol stirred at room temperature and ambient pressure. Upon the reaction, the mixture is aged and filtered before white hydrazine dinitrate precipitation is received. Adding hydrazine hydrate 85 % then leads to the dissolution of precipitation. Tuning the solution to a PH level of 8 can induce recrystallization at temperatures lower than 10 °C where white needle Uke or rod like hydrazine nitrate. 

Figure 5.8. Cyclic voltammogram of a Hg-film electrode in contact with 100 mM NaC104 (pH 4) equilibrated with 20% CO2 (A, C) or N2 (B). B and C were recorded with the electrolyte solution also containing 0.2 mM Ni(cyclam) +. (1) Reductive adsorption of Ni(cyclam) + (2) Electrocatalytic reduction of CO2 (3) H2-evolution (4) electrocatalytic reduction of H+ (5) anodic dissolution of precipitated Ni(cyclam)-CO. Hg-film on rotating Au-disk electrode (diameter 1.5 mm), / = 3000 min , v = 100 mV s Reprinted from Figure 1 R Jacquinot and RC. Hauser, Ni(II) cyclam Catalyzed Reduction of CO2 Towards a Voltammetric Sensor for in Gas Rhase, Electronalysis 15(8), 1437-1444 (2003). With permission of Wiley-VCH, Germany.

The mechanical properties of the Mg alloys can be improved by heat treatment. Mainly T4, T5, and T6 heat treatments are in use. A T4 treatment means dissolution of precipitates. In general, a T4 treatment is followed by an artificial aging (T6). Stress relieving can also be applied to the cast alloys. Major variables which affect the heat-treatments are section size and heating time, annealing time and temperature, and the protective atmosphere. Welded parts made of Mg alloys can be stress relieved. In general, the heat treatments can be applied to castings with the exception of HPDCs. It is not rec-... 

The dissolution of precipitates of glycogen and diraethyldodecylbenzyl-ammonium chloride complexes in an excess of a solution of the salt, and the dependence of the process on pH have been studied, and the possible utilization of these properties for the separation of a mixture of a-o-glucans has been evaluated. ... 

It is important to know the elementary properties of selfinterstitials, if we want to understand in detail and model the behavior of intermetallic compounds under technological irradiation conditions, e.g. disordering and dissolution of precipitates in steels used in nuclear reactors, or amorphization by implantation. 

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