Calcium hydroxide characterization

Calcium hydroxide is an excellent adsorbent for resolving carotenoid cis-trans isomers compared with alumina, it is less retentive and less sensitive to temperature and moisture content of the mobile phase. However, calcium hydroxide columns are not commercially available, and separations using them can be difficult to reproduce, owing to extreme sensitivities to mobile-phase composition and temperature. Nine cis-/3-carotenes were characterized from a chromatogram of 18 peaks after isocratic elution of a mixture obtained by thermal isomerization and photoisomerization of /3-carotene (162). Chandler and Schwartz (10), using a calcium hydroxide column and a mobile phase of hexane containing 0.3% acetone, separated six carotene isomers from canned carrots. These were, in order of elution, two cw-a-carotenes, all-tram-a-carotcnc, 13-m-/3-carotcnc, all- ram-/3-carotene, and 9-cw-/3-carotene. A mobile phase of hexane modified with 2% p-methylanisole separated all-rram-/3-carotcnc and its 9-, 13-, and 15-cis isomers in an iodine isomerized mixture (163). 

Figure 16.13 shows that the surface of calcium hydroxide-coated glass spheres is characterized by a strong porosity and cavities, and this results in a worsened heat transfer. 

The effect of a reducing sodium borohydride treatment followed by a mildly alkaline wash on the physical properties and stability of paper was studied. Test papers were characterized by measuring their initial pH value, brightness, and folding endurance. Then they were subjected to borohydride treatment and washed with dilute calcium hydroxide solution or deionized water. The concentrations of sodium borohydride... 

Concrete is a multiple-phase material and the overall mechanical properties not only depend on each phase, but also upon the interface between them. Prior study shows that the interfacial transition zone (ITZ) which is characterized by the prevalence of calcium hydroxide and higher porosity, is the weakest region in a cementitious material. Interactions that take place there control many important properties such as strength, permeability and durability [1]. Methods have been... 

A number of laboratory studies have been recorded recently aimed at characterizing the kinetics of both the chemical reaction and crystallization steps in a reaction crystallization process. Examples of liquid phase reactions studied for this purpose are the crystallization of salicylic acid from aqueous solutions of sodium salicylate using dilute sulphuric acid (Franck et al, 1988) and the crystallization of various calcium phosphates by reacting equimolar aqueous solutions of calcium nitrate and potassium phosphate (Tsuge, Yoshizawa and Tsuzuki, 1996). Several aspects of crystal size distribution control in semi-batch reaction crystallization have been considered by Aslund and Rasmuson (1990) who studied the crystallization of benzoic acid by reacting aqueous solutions of sodium benzoate with HCl. An example of crystallization arising from a gas-liquid reaction in an aqueous medium is the precipitation of calcium carbonate from the reaction between calcium hydroxide and CO2 (Wachi and Jones, 1995). 

The texture of cement pastes containing microsilica is characterized by the presence of agglomerates of individual microsilica particles. Such agglomerates are present even when a superplasticizer has been added to the mix (Mitchell et al., 1998), but in smaller numbers. Within these agglomerates a reaction with calcium hydroxide and formation of the C-SH phase also occurs, but the rate of this process is significantly reduced, especially in the central part, and the reaction is not completed even after 180 days. 

The texture of cement pastes in high-performance concretes is characterized by high density and very low porosity. Owing to the pozzolanic reaction between the added microsilica and calcium hydroxide, the amount of ciystalline portlandite in the hardened paste is reduced, and the formed C-S-H phase has a lower C/S ratio (Cheong et al, 1997). The mature cement paste contains a significant fraction of non-hydrated cement. 

The first applications of glass fibres in concrete-like composites were published by Biryukovitch et al. (1965), who carried out tests on elements with high alumina cement. The paste made with that cement is characterized by pH from 11.8 up to 12.05 with total amount of alkalis from only 0.15% to 0.20% and during hydration calcium hydroxide does not appear. In the... 

Two reviews on the synthesis and utilization of sugars produced by the formose reaction have appeared. The use of chemical ionization - m.s. to characterize the products of the formose reaction has been described. A report of a study on the catalytic activity of rare earth element hydroxides, M(0H), where M is Er, Pr, Sm, Ho or Ce, together with calcium hydroxide on the formose reaction, includes measurements of the ratios of three- and four-carbon... 

Abstract— Thermal analysis of hydroxyapatite formation through dry mechanochemical method has heen stndied. The calcium phosphate was synthesized using calcinm hydroxide and di-ammonium hydrogen phosphate as the precnrsors. The ball milling of 1/6 ball-powder mass ratio was employed on mixtures of calcium hydroxide and di-ammoninm hydrogen phosphate in three different speeds 170, 270 and 370 rpm for 15 h. As ball-milled powders were then sintered at 1150, 1250 and 1350°C for 2 h, then subjected to TGA, XRD and FTIR for phase characterization. Calcium phosphates with ammonium are phases of the material. The ammonium is trace of phosphorus precursor. Choosing condition of the process and type of precursors determines type of reactions and its products. 

A selection of common rock-forming and fracture-coating minerals were reacted with calcium hydroxide solution in accelerated tests for up to 800 hours. Since the focus of the experiment was to generate and characterize secondary products, closed-system batch tests were carried out to encourage extensive precipitation. The tests were accelerated by raising the temperature to 85 C, somewhat higher than would be expected around a radioactive waste repository. 

In general the term dispersion characterizes a two phase system consisting of finely dispersed solid particles in a continuous hquid phase. An example of a dispersion is whitewash, calcium hydroxide above the solubility Kmit in water. If the finely dispersed phase and the continuous phase, both are Hquid, the term emulsion will be used. An example is milk, which essentially consists of fat droplets in water the droplets are stabilized by proteins. In both cases, in dispersions and emulsions, the continuous phase is therefore a Hquid in aU of our examples, the Hquid is water. In dispersions, the finely disperse substance is soHd, while in emulsions it is Hquid. 

A method for the preparation of HA fibers was established using a solid phase reaction [66]. With this method, the HA fibers were fabricated by heating a compact consisting of calcium metaphosphate fibers with calcium hydroxide panicles at 1000°C in air atmosphere, and subsequently treated with dilute aqueous HCl solution to remove unwanted secondary phase substitution such as CaO. The obtained HA fibers were characterized and found that the nanostructural characteristic features of HA are quite similar to the natural bone mineral apatite phase. Therefore, the solid-state reaction can be considered as one of the capable methods for the production of nanostructure HA. 

In 1807, Davy made an important discovery when he subjected slightly moistened potash (potassium carbonate) to electrolysis. He noticed that a silvery matter was deposited at the negative pole, while at the positive pole oxygen was liberated. Davy surmised that the silvery matter observed at the negative pole was of a metallic nature and called it potassium. In similar experiments with sodium hydroxide he also characterized the metal sodium. He then went on to electrolyze the so-called alkaline earths, which led to the isolation of magnesium, calcium, strontium and barium. Davy announced his remarkable discoveries in a series of Bakerian Lectures (he gave all in all no less than five such lectures) and his fame... 

Using ordinary and sulfate-resistant Portland cement to represent differing chloride environments, short-term electrochemical monitoring and SEM were used to characterize corrosion behavior [34]. Steel electrodes attained passivity in mortar with high levels of calcium aluminate, up to 1% wt. chloride. At 1.75% wt. chloride, steel electrodes corrode. All chloride levels resulted in steel corrosion for low levels of calcium aluminate. Pore solution was also impacted by mortar exposure conditions. Atmosphere exposure had a high influence on hydroxide concentration in pore solution but no impact on chloride concentration. Carbonation was also investigated samples in a sealed container had a chloride/hydroxide ratio half that of unsealed samples. 

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