Precipitation condition

Steam and calcium hydroxide is formed. If the cooling water tends to form acid ia the boiler, either caustic or phosphate may be added to counteract the effect. When the cooling water tends to form base, only phosphate treatment is appropriate. Many dmm boilers that are operated on AVT have provision for phosphate or caustic treatment duriag condenser leaks because the amines used ia AVT have neither significant bufferiag capacity nor precipitate conditioning properties ia the boiler. 

Hydrolysis of solutions of Ti(IV) salts leads to precipitation of a hydrated titanium dioxide. The composition and properties of this product depend critically on the precipitation conditions, including the reactant concentration, temperature, pH, and choice of the salt (46—49). At room temperature, a voluminous and gelatinous precipitate forms. This has been referred to as orthotitanic acid [20338-08-3] and has been represented by the nominal formula Ti02 2H20 (Ti(OH). The gelatinous precipitate either redissolves or peptizes to a colloidal suspension ia dilute hydrochloric or nitric acids. If the suspension is boiled, or if precipitation is from hot solutions, a less-hydrated oxide forms. This has been referred to as metatitanic acid [12026-28-7] nominal formula Ti02 H2O (TiO(OH)2). The latter precipitate is more difficult to dissolve ia acid and is only soluble ia concentrated sulfuric acid or hydrofluoric acid. 

Temperature, pH, precipitation conditions, and the drying process determine the amount of water in the sohd. In addition the species Ce(OH)... 

Equations (141) and (142) describe the equilibrium between the hydrolysis of complex fluoride acids (shift to the right) and the fluorination of hydroxides (shift to the left). Near complete precipitation of hydroxides can be achieved by applying an excessive amount of ammonia. Typically, precipitation is performed by adding ammonia solution up to pH = 8-9. However, the precipitate that separates from the mother solution can be contaminated with as much as 20% wt. fluorine [490]. Analysis of niobium hydroxides obtained under different precipitation conditions showed that the most important parameter affecting the fluorine content of the resultant hydroxide is the amount of ammonia added [490]. Sheka et al. [491] found that increasing the pH to 9.6 toward the end of the precipitation process leads to a significant reduction in fluorine content of the niobium hydroxide. 

The resulting product depends on the precipitation conditions, and in particular, on the over-saturation level of the solution. Formation of ammonium oxyfluorometalate crystalline compounds occurs at a relatively low pH of the solution. From the standpoint of the interactions described in Equation (143), this means that the interaction between NH4F and Me205 (denoted as interaction 1) is stronger than the interaction denoted as interaction 2. In this case, subsequent processes of the hydroxide treatment lead to some defluorination of the product, but the performance of such processes is usually very problematic. Precipitation at high pH values leads to a strong oversaturation of niobium- or tantalum-containing compounds, which in turn... 

The hydration of polyoxyethylene (POE) is dramatically affected by the anion present(J 0) in the aqueous phase. The adsorption of HEC (both 2.0 and 4.3 M.S.) was therefore studied in Na SO and Na PO, at equivalent normalities. The multivalent anions are more effective in precipitating POE than is the chloride ion. The amounts adsorbed and the interlayer expansions at normalities below precipitation conditions are given in Table III. The influence of multivalent anions on the intrinsic viscosity of variable M.S. HECs is illustrated in Figure 6. The increased amounts adsorbed are within experimental error, but the decrease in d. with the 4.3 M.S. HEC is notable. The d. changes in the absence of increased adsorption are not explainable in terms of solvation effects. 

Auto-Acceleration in Free-Radical Polymerizations Under Precipitating Conditions... 

Methacrylic acid also polymerizes in bulk under precipitating conditions. It forms molecular associations very similar to those of acrylic acid. However, the conversion curves were found to be linear under a variety of experimental conditions temperatures of 16.5 to 60°C and broad ranges of initiation rates and monomer concentration in numerous solvents (7). It was assumed that structures of type III do arise but owing to steric hindrance and to the rigidity of the poly(methacrylic acid) molecule the monomer cannot align to form a "pre-oriented" complex as in the case of acrylic acid and propagation is not favored. 

Further experiments were therefore carried out with polar solvents which do not dissolve the polymer. Most striking results were obtained with trichloroacetic acid. The polymerization of acrylonitrile in this solvent was found to proceed under precipitating conditions at all concentrations. In spite of this, the conversion curves were perfectly linear in solutions containing 60 volume per cent monomer or less (18). Moreover, these systems exhibit marked post-polymerization showing the presence of long-lived radicals. 

Early adolescent smoking onset is a risk factor for severe addiction and difficulty in smoking cessation in adulthood (Breslau and Peterson 1996). Therefore, it is significant that nicotine has more potent rewarding effects in adolescent as opposed to adult rodents (Adriani et al. 2004 Belluzzi et al. 2004 Vastola et al. 2002). However, several studies suggest that adolescent rodents develop physical nicotine dependence less readily than adults, as indicated by less severe nicotine withdrawal syndrome. Unlike adult rats, continuously nicotine-infused adolescent rats failed to display mecamylamine-precipitated withdrawal behaviors (O Dell et al. 2004, 2006). They also displayed less mecamylamine-precipitated conditioned place aversion than adults (O Dell etal. 2007). In addition, nicotine-infused adolescent rats experienced smaller mecamylamine-precipitated ICSS threshold elevations than adults (Kota et al. 2007). Nicotine-infused adolescent mice also displayed fewer spontaneous and mecamylamine-precipitated somatically expressed withdrawal behaviors... 

The influence of methanol precipitation conditions on water absorbencies of final products is lown in Ted le I, and results of this stuc may be sunnarized as follows 1) If the se xxiificate is stirred for 1 h open to the atmo here to allow some of the anmonia to esce before methanol precipitation, the polymer has about the... 

Table I. Influence of Precipitation Conditions and Aging of Saponificate ...

Finally, control of fluorapatite particle size (from 15 nm to 200 pm) and morphology can be achieved by varying precipitation conditions using aqueous precipitation from a micro-emulsion or by biomimetic synthesis in a gelatin matrix [129],... 

A seemingly similar process of polymerization - the radiation induced polymerization of methyl acrylate in n-hexane - shows also auto-acceleration and post-polymerization. Polymerization was carried out under precipitating conditions. Using the results of kinetics examination, the authors showed that all effects can be explained by the mechanism based on trapped radical reactions in particles of precipitated polymer. No influence of any template effect was detected in these systems. 

Only at calcination temperatures above 800°C does the density increase to the literature value of amorphous silica of 2.2 to 2.25 g cm-1. The exact microstructure within the Stober silica particles depends very much on the specific precipitation conditions, which are discussed in more detail in section 2.1.4. 

Powders containing bismuth compounds have long been used for decorative purposes to generate a shiny luster or lustrous colors (e.g., facial cosmetic powder in ancient Egypt, imitation pearls made by coating glass and ceramic beads). Bismuth oxychloride [7787-59-9], BiOCl, Mr 260.4, was the first synthetic nontoxic nacreous pigment. It is produced by hydrolysis of acidic bismuth solutions in the presence of chloride ions. Precipitation conditions may be varied (concentration, temperature,... 

Particles of precipitate should not be so small that they clog or pass through the filter. Large crystals also have less surface area to which impurities can become attached. At the other extreme is a colloidal suspension of particles that have diameters in the approximate range 1-500 nm and pass through most filters (Figure 27-1 and Demonstration 27-1). Precipitation conditions have much to do with the resulting particle size. 

Casting solution composition Precipitation conditions Application and comments... 

Fouling prevention under fast precipitating conditions... 

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