Ferric hydroxide polymer

Other physical parameters of the micelle also suggest that the cores of ferritin and ferric nitrate polymer are closely related. The magnetic susceptibility of the iron micelle is 3.84 Bohr magnetons. The Mossbauer spectrum for ferritin observed by Boas and Window (39) and by Blaise et al. 40) are in close agreement with the spectrum for the ferric nitrate polymer as well as the ferric citrate and ferric fructose polymers. Most interesting is the fact that the size of the ferric hydroxide polymer in the ferritin molecule is practically identical to that observed for the ferric nitrate and ferric citrate spheres. 

Fe " ) forms Fe " and Fe species can only be produced under experimental conditions. Because ferrous iron is spontaneously oxidized and forms highly insoluble ferric hydroxide polymers (= rusf , solubility products 10 ), life has developed ironbinding proteins and low molecular-weight chelators called siderophores" in order to make iron available for its purposes (Ull-mann 1989). 

Rohrsetzer, S. et al.. Colloidal stability of electrostatically stabilized sol particles. Part 1. The role of hydration in coagulation and repeptization of ferric hydroxide sol. Colloid Polym. Sci., 270, 1243. 1992. 

The discussion above has assumed a Fe /OH stoichiometry of 1/3 for the oxyhydroxides. There is convincing evidence, however, that the freshly precipitated oxyhydroxides formed in acid salt solutions, especially above 0.05M, are initially deficient in OH (38,39). According to Murphy et al. (40), the initial precipitate upon neutralization is comprised of spherical polycations, 15 to 35 A in diameter. These are presumably the small ferric-hydroxy polymers described by Dousma and deBruyn ( ) which form reversibly and rapidly from precursor monomers and dimers. The next step is the formation of large polymers (, 39). The hydroxide deficiency (+ charge) of the small and large polymers is compensated for by adsorbed and/or coprecipitated anions such as Cl, N03, and CIO. Several studies have shown that such anion-enriched polymers can persist at ambient temperatures, particularly at high anion concentrations in acid solution. Thus, Biedermann and Chow (42) report a two-month old precipitate with the composition Fe(OH)2 yClg 3 formed from 0.5 M NaCl solutions, and Fox... 

In a study of the surface modification of poly(bisphenol A carbonate) by sul-fochromic acid, application of this approach to the Is/Ic intensity ratio led to a density of 4-10 sulphur atom cm, which was found unrealistic and lead to the conclusion that the polymer was attacked and that sulfate was incorporated over a certain depth. This pretreatment made the zeta potential of the material more negative. It increased the uptake of ferric hydroxide colloids in subsequent adsorption tests, which in turn made the zeta potential more positive. As a consequence the promotion of yeast cell adhesion by the ferric hydroxide treatment was less affected by drying. 

Scale prevention methods include operating at low conversion and chemical pretreatment. Acid injection to convert COs to CO2 is commonly used, but cellulosic membranes require operation at pH 4 to 7 to prevent hydrolysis. Sulfuric acid is commonly used at a dosing of 0.24 mg/L while hydrochloric acid is to be avoided to minimize corrosion. Acid addition will precipitate aluminum hydroxide. Water softening upstream of the RO By using lime and sodium zeolites will precipitate calcium and magnesium hydroxides and entrap some silica. Antisealant compounds such as sodium hexametaphosphate, EDTA, and polymers are also commonly added to encapsulate potential precipitants. Oxidant addition precipitates metal oxides for particle removal (converting soluble ferrous Fe ions to insoluble ferric Fe ions). 

Alum dosages between 200 and 500 mg/1 were not significantly different. Table II also Illustrates that sedimentation Is effective In lowering the concentration of the pesticides to the solubility limit. Metrlbuzln Is soluble In water to a concentration of about 1200 mg/1 and the sedimentation step reduced the concentration from 2000 and 3000 mg/1 to about 1000 mg/1. At lower concentrations sedimentation was not effective. Other coagulants and flocculant aids such as hydroxide and ferric chloride, were tested but alum with an anionic polymer (Watcon 1255) was the most effective. 

Kandori, K. Tamura, S. Ishikawa.T. (1994) Inner structure and properties of diamondshaped and spherical a-Fe203 particles. Colloid Polym. Sci. 272 812-819 Kandori, K. Uchida, S. Kataoka, S. Ishikawa, T. (1992) Effects of silicate and phosphate on the formation of ferric oxide hydroxide particles. J. Mater Sci. 27 719-728 Kandori, K. Yasukawa, A. Ishikawa,T. (1996) Influence of amines on formation and texture of uniform hematite particles. J. Colloid Interface Sci. 180 446-452 Kaneko, K. Inouye, K. (1974) Electrical properties of ferric oxyhydroxides. Bull. Chem. 

In crystalline oxides and hydroxides of iron (III) octahedral coordination is much more common than tetrahedral 43). Only in y-FegOs is a substantial fraction of the iron (1/3) in tetrahedral sites. The polymer isolated from nitrate solution is the first example of a ferric oxyhydroxide in which apparently all of the irons are tetrahedrally coordinated. From the oxyhydroxide core of ferritin, Harrison et al. 44) have interpreted X-ray and electron diffraction results in terms of a crystalline model involving close packed oxygen layers with iron randomly distributed among the eight tetrahedral and four octahedral sites in the unit cell. In view of the close similarity in Mdssbauer parameters between ferritin and the synthetic poljmier it would appear unlikely that the local environment of the iron could be very different in the two materials, whatever the degree of crystallinity. Further study of this question is needed. 

Although hydrolyzed iron (III) solutions are unstable with respect to eventual precipitation of hydroxides (sec. II A 3), Feitknecht and Mi-chaelis (29) observed no correlation between the time required for precipitate formation and the degree of hydrolysis. Furthermore, while on standing the polymeric fraction in hydrolyzed ferric nitrate solutions increases slowly in sedimentation coefficient, this process is not parallel to precipitate formation (37). Apparently the polymer is not an intermediate in precipitate formation. 

In fact, the polymer is quite stable with respect to precipitation. Once isolated it can be kept in aqueous solution indefinitely (37). This stability is presumably kinetic in origin. Since all evidence points to a different internal structure for the polymer from all crystalline ferric oxide or hydroxide phases, the reorganization required for precipitation would be expected to have a high activation energy. Addition of base to pol5maer solutions does produce an immediate precipitate, presumably by cross-linking the polymer particles. In hydrolyzed ferric nitrate solutions with less than 2.5 base equivalent per mole of iron the eventual precipitates observed are probably formed directly from low molecular weight components. The low rate of dissociation would then be another factor in polymer stability. 

The high polymer fraction is not on the pathway to precipitate formation, as long as the degree of hydrolysis is less than about 2.5. Its internal structure is different from all known crystalline ferric oxides or hydroxides. These must be precipitated directly via low molecular weight components. 

When the asymmetric carbon is a part of a heterocyclic monomeric system, the polymerization of such a compound may lead to optically active products. For example, in the case of the polymerization of 1-propylene oxide with potassium hydroxide as catalyst, a low molecular weight crystalline optically active polymer formed. When the same monomer was polymerized by use of a ferric chloride-propylene oxide complex catalyst, a high molecular weight product was formed. This polymer could be separated into an amorphous form with little or no optical activity and a crystalline resin with optical rotation similar to that observed for the potassium hydroxide-catalyzed process [106]. 

When the polymerizations was carried out with a separately prepared ferric chloride-propylene oxide catalyst, the 1-monomer formed a high molecular weight polymer which could be separated into an amorphous fraction with low optical rotation and a crystalline form with the same optical rotation as had been obtained with potassium hydroxide initiation. 

Approximately 50 mg of the polymer are cut into small pieces and reacted with a few drops of 2n potassium hydroxide in methanol plus phenolphthalein. The mixture should be kept alkaline as indicated by the phenolphthalein. A few drops of a saturated solution of hydroxylamine hydrochloride in methanol are added and the mixture heated to a maximum of 50°C for a few seconds. The mixture is then acidified with In hydrochloric acid and one drop of a 3% solution of ferric chloride in water... 

Propylene oxide has an asymmetric carbon atom. The normal commercial epoxide is a racemic mixture of the d- and 1-isomers. Osgan and Price did extensive work with both the 1-propylene oxide and the d,l-propylene oxide in both potassium hydroxide and ferric chloride/propylene oxide-initiated polymerizations. Their results are summarized in Table 5 (48). C. C. Price and coworkers first demonstrated that polymerization of pure 1-propylene oxide with an anhydrous potassium hydroxide (solid KOH) initiator led to a crystalline, rather than the usual amorphous, liquid, polymer. After extensive study by a number of researchers (69), this polymerization was shown to proceed by a stepwise anionic mechanism. The uses found for polymers of propylene oxide largely have been those requiring the amorphous polymer in elastomeric applications. Stereospecificity, however, has proved to be a key tool in understanding the polymerization mechanisms. 

TABLE 5 Comparison of Polymers Prepared by Potassium Hydroxide and by Ferric Chloride/Propylene Oxide Complex Initiated Polymerizations of 1-Propylene Oxide and d,1-Propylene Oxide... 

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