Alkaline Earth Hydroxides Research Articles

ChemInform Abstract: Heats of Formation of Alkali and Alkaline Earth Oxides and Hydroxides: Some Dramatic Failures of the G2 Method.

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Heats of Formation of Alkali and Alkaline Earth Oxides and Hydroxides: Some Dramatic Failures of the G2 Method

High-level ab initio calculations with a variety of G2-based methods have been used to determine the structures and heats of formation of the alkali and alkaline earth oxides and hydroxides (M2O, MOH with M = Li, Na, and K; M‘O, M‘(OH)2 with M‘ = Be, Mg, and Ca). Standard G2 theory, which is normally very reliable for the prediction of molecular thermochemistry, is shown to be quite unsuitable for the prediction of the heats of formation of several of these highly polar species, with errors greater than 100 kJ mol-1 in some cases. Our calculations confirm that for systems containing the third-row atoms K and Ca, it is essential to include the 3s and 3p orbitals in the correlation space. Interestingly, an analogous relaxed-inner-valence (denoted riv) procedure is more beneficial for the Li- and Be-containing oxides and hydroxides than for the Na- and Mg-containing molecules. Inclusion of all orbitals in the correlation space (denoted full) generally provides only a slight further improvement to the results...

Test Method for the Potential Release of Hydrogen Gas from Silica Fume

Abstract Most silica fumes contain a small amount of silicon metal. Silicon reacts with alkali or alkaline-earth hydroxides when water is present to yield hydrogen. The reaction mechanism is similar to the one used to produce cellular concrete or expanding grout with aluminum powder. There is concern that hydrogen release can cause problems when silica fume is used in grouting prestressing tendons because atomic hydrogen embrittles steel, thereby shortening the life of the prestressed concrete structure. Moreover, if the partial pressure of hydrogen in air attains a certain level, there is a risk of explosion in the presence of a source of heat or spark. Portland cement-based materials with silica fume that contains some silicon do not present an induction period that could delay hydrogen release. Therefore, users of silica fume should be aware of this potential danger. Because most users of portland cement are unfamiliar with techniques for measuring the silicon content of silica fume, a simple and rapid measurement method is shown here to evaluate the amount of hydrogen that can be released from a given silica fume. This value can be used to calculate the amount of silicon contained in the silica fume.

Cyanoethylation of methanol catalyzed by alkaline earth oxides and alumina-supported K catalysts

Cyanoethylation of methanol with acrylonitrile to form 3-methoxypropanenitrile proceeds effectively over solid basic catalysts such as alkaline earth oxides and hydroxides, and alumina supported potassium fluoride and hydroxide at a reaction temperature of 323 K. The catalytic activity of magnesium oxide was scarcely affected by exposure of the catalyst to air before use for the reaction.

Isotope exchange between alkaline earth metal hydroxide and HTO water in the equilibrium state

In order to reveal to what extent tritium (3H or T) can be incorporated into hydroxides, the isotope exchange reaction (OT-for-OH exchange reaction) between each alkaline earth metal hydroxide (M(OH)2), where M means alkaline earth metal (M=Ca, Sr or Ba) and HTO water was observed homogeneously at 30 °C under equilibrium after mixing. Consequently, the followings were obtained: (1) a quantitative relation between the electronegativity of each M ion and the ability (of the M ion) incorporating OT− into the M hydroxide can be found and the ability is small when the temperature is high, (2) the exchange rate for the OT-for-OH exchange reaction is small when the electronegativity of the M ion in the M hydroxide in great, (3) as for the dissociation of HTO water, it seems that fomula (HTO⇆T++OH−) is more predominant than the fomula (HTO⇆H++OT−) when the temperature is high and (4) the method used in this work is useful to estimate the reactivity of a certain alkaline material.

Hydrodesulfurization of Dibenzothiophene Catalyzed by Supported Metal Carbonyl Complexes (Part 7) Hydrodesulfurization Catalysts Prepared from Alumina-supported Ruthenium Carbonyl-Alkaline-earth Metal Hydroxide Systems.

In hyrdrodesulfurization of dibenzothiophene (DBT) catalyzed by alumina-supported ruthenium carbonyl systems, the effects of alkaline-earth metal hydroxides (Ca(OH) 2 , Sr(OH) 2 , and Ba(OH) 2 ) on catalytic activity and product selectivity were investigated. The catalytic activity and the selectivity for biphenyl increased with the increase in the amount of alkaline-earth metal hydroxides added. With the use of Ba(OH) 2 , the conversion of DBT exhibited a maximum at Ba/Ru=1. In contrast, Ca(OH) 2 did not show a clear maximum in the range of Ca/Ru from 0 to 2. The conversion of DBT increased in the order Ca(OH) 2 <Sr(OH) 2 <Ba(OH) 2 at M/Ru=1 (M=Ca, Sr, or Ba). When the activity with the use of Ba(OH) 2 was compared with that of CsOH, the maximum activity was obtained in both cases in which the ratio of the added hydroxide ion to ruthenium was 2 (OH - /Ru=2). XPS spectra showed that the addition of an appropriate amount of alkaline-earth metal or cesium stabilized ruthenium sulfide on alumina even under hydrogen pressure.

Occurrence, abundance and origin of minerals in coals and coal ashes

The mineralogy of coal and coal ash samples from a wide variety of deposits worldwide has been studied by X-ray diffractometry, light microscopy, SEM, TEM, and DTA-TGA methods. The common major minerals identified in the crystalline matter of coals are quartz, kaolinite, illite, calcite, pyrite, plagioclase, K-feldspar and gypsum, and occasionally dolomite, ankerite, siderite, Fe oxyhydroxides and sulphates. A number of minor and especially accessory minerals are also present. The modes of occurrence and some genetic peculiarities of the minerals found are described and summarized. Minerals and phases of probable detrital origin include mainly silicates, volcanic glass, oxyhydroxides and phosphates. Authigenic minerals of syngenetic origin may be sulphides, clay minerals, carbonates and rarely sulphates and phosphates. Epigenetic minerals, formed by the infiltration of low-temperature hydrothermal solutions, may include sulphides, carbonates, sulphates, clay minerals, quartz, chlorides, and probably alkaline-earth hydroxides and zeolites. The alteration products of detrital and authigenic minerals may be Fe and Al oxyhydroxides, sulphates, kaolinite, illite, chlorite, muscovite, zeolites and calcite. The behaviour of these minerals and phases during low- and high-temperature ashing is also discussed.

Rest Frequencies for Alkaline Earth Hydroxide Radicals (X 2 Sigma +)

Rest Frequencies for Alkaline Earth Hydroxide Radicals (X 2 Sigma +)

Highly Dispersed Partially Stabilized Zirconias: Synthesis, Bulk and Surface Properties, Performance in the Selective Reduction of Nitrogen Oxides by Propane in the Excess of Oxygen

ABSTRACTBulk and surface properties of dispersed partially stabilized zirconias (PSZ) prepared via coprecipitation of zirconium and alkaline-earth metal hydroxides have been studied by XPD, SIMS, IR spectroscopy of surface hydroxyls and adsorbed C.O. For Sr- and Ca-PSZ, the number of the Lewis acid centers, surface concentration of the guest cation and Zr-O bonding strength at the surface have been found to deviate substantially from the values predicted by a bulk truncation model, while for Ba-PSZ it seems to be valid. A local reconstruction of the near-surface layer into the perovskite-like structure was proposed for the first two systems, which explained satisfactorily their surface properties including catalytic performance in the selective reduction of nitrogen oxides by propane in the excess of oxygen. Such reconstruction is probably facilitated by segregation of the guest cations in the subsurface layer. The driving force for this process depends upon site preference of the alkaline-earth cations to cubooctahedrons and steric factors.

Activated Carbons from Spanish Coals. 2. Chemical Activation

Activated carbons from Spanish coals have been prepared by chemical activation with alkali and alkaline-earth hydroxides. The paper analyzes the following aspects: presence of water during pyrolysis, extension of the impregnation and drying processes, activating agent, temperature and time of pyrolysis, activating agent/coal ratio, coal rank, and mineral matter content. KOH and NaOH activation provides very successful results in which N2 apparent surface areas of 2500 m2/g are obtained; contrarily, Ca(OH)2 produces a small porosity development. A pyrolysis temperature of 700 °C yields activated carbons with a wider pore size distribution than those prepared at 500 °C. The pyrolysis time does not affect the microporosity development but an important reduction in the ash content is observed when the time is increased. The use of an activating agent/coal ratio of 2/1 compared to 1/1 has favorable effects: (i) a decrease in the ash content and (ii) a wider pore size distribution. The addition of a drying st...

Millimeter-wave rotational spectroscopy of MgOD and CaOD (X 2Σ+)

Pure rotational spectra of CaOD and MgOD have been recorded in the range 200–390 GHz using millimeter/sub-mm direct absorption spectroscopy. Transitions arising from the (000), (010), (020), and (100) modes have been measured for the 2Σ+ ground electronic states of these free radicals. The data were analyzed successfully using a linear 2Σ+ model for CaOD; for MgOD, only the (000) and (010) states could be fit with this Hamiltonian. Moreover, the (010) data required the addition of a substantial pΠ term to account for contamination of excited 2Π electronic states. For both species, the α2 vibration–rotation term was found to be negative, in contrast to MgOH and CaOH, suggesting a less anharmonic contribution to the bending potential in CaOD and MgOD. These measurements also indicate a shorter O–H bond in MgOH than the other alkaline earth hydroxide radicals, which likely results because this species is quasilinear.

Changes in the Basicity and Species on the Surface of Me(OH) 2-SiO 2 ( Me = Ca, Mg, Sr) Mixtures Due to Mechanical Activation

Mechanical activation increased the surface basicity of the alkaline earth hydroxides in the order Sr(OH) 2 > Ca(OH) 2 > Mg(OH) 2, as determined by titration, temperature-programmed, desorption, and FT-IR. The increase and the difference in the basicity between the hydroxides became more significant in the case of grinding Me (OH) 2-SiO 2 mixtures, as a result of mechanochemical interactions between the ingredients. Bidentate adsorption of CO 2, found exclusively on the ground mixture with SiO2, is only explained by the formation of new - Me-O-Si- bonding. This indicates the incipient formation of alkaline earth silicates as a result of charge transfer during grinding.

Reply to “Comment on ‘Activation of Ground Blast‐Furnace Slag by Alkali‐Metal and Alkaline‐Earth Hydroxides’”

Reply to “Comment on ‘Activation of Ground Blast‐Furnace Slag by Alkali‐Metal and Alkaline‐Earth Hydroxides’”

Comment on “Activation of Ground Blast‐Furnace Slag by Alkali‐Metal and Alkaline‐Earth Hydroxides”

Comment on “Activation of Ground Blast‐Furnace Slag by Alkali‐Metal and Alkaline‐Earth Hydroxides”

Decomposition kinetics of alkaline-earth hydroxides and surface area of their calcines

Thermal decomposition of Mg(OH) 2 and Ca(OH) 2 particles produces highly porous calcines that react rapidly with acidic gaseous pollutants at moderate temperature. Increasing- and constant-temperature gravimetric methods were employed to measure the rates of decomposition of hydroxide particles at temperatures 290–430°C. The measured data wree tested empirically by fitting to the nth-order rate equation of Arrhenius type, and the values of the kinetic parameters were estimated. Differences are explored in the course of the decompo sition of magnesium hydroxide and that of calcium hydroxide. The sintering rate of the nascent, hydroxide-derived oxides was measured in a nitrogen atmosphere at temperatures from 400 to 700°C. An empirical kinetic model has been proposed to correlate the experimental data on the specific surface area of solids. Comparison of the results indicates that particles of MgO exhibit a surface area which is half an order greater than that of CaO sintered under the same conditions.

Cyclic voltammetric studies of nickel hydroxide and cobalt hydroxide thin films in alkali and alkaline earth metal hydroxides

Cyclic voltammetric studies of thin films of electrosynthesized (ES)-Ni(OH)2 and Co(OH)2 in different alkaline electrolytes suggest that the mechanism of oxidation is different from the mechanism of reduction. While the metal ion (alkali or alkaline earth metal) intercalation-deintercalation from the electrolyte into the film provides the driving force, the reduction reaction takes place heterogeneously independent of the electrolyte concentration, whereas oxidation takes place homogeneously across a nebulously defined electrode-electrolyte interphase. ES-Ni(OH)2 permits facile intercalationdeintercalation of alkali metal ions Li+, Na+ and K+, irrespective of their ionic size, while the reactions of ES-Co(OH)2 are sensitive to ionic size, requiring larger potentials in KOH compared to LiOH. In the alkaline earth metal hydroxides, both Ni(OH)2 and Co(OH)2 films show greater reversible characteristics in the order Ba(OH)2 > Sr(OH)2 > Ca(OH)2. This may be trivially related to the order of the solubilities of the three hydroxides.

Characterization of the compounds formed from the interaction of divalent cations with inorganic molecular metal—oxygen cluster compounds

Infrared spectroscopy, powder X-ray diffraction, differential thermal analysis and nitrogen adsorption—desorption measurements were carried out on a series of solids prepared from 12-molybdophosphoric and 12-tungstophosphoric acids and the alkaline earth hydroxides. A single crystal investigation and data analysis were done for the Ba 2+ /PMo 12O 40 3− system. It is concluded that the reaction of simple divalent salts with 12-molybdophosphoric acid produces a mixture of the parent acid and a divalent compound rather than a divalent heteropoly salt.

Preparation of determining fat dispersing efficiency contains sulphanol, alkali or alkaline earth metal hydroxide, and water-soluble or fat-soluble dye : Lith. Sect. Butter Cheese Ind. SU-1689846; 7 November 1991

Simple, rapid and sensitive spectrophotometric methods were developed for the determination of carbamazepine and mosapride citrate drugs in pure and pharmaceutical dosage forms. These methods are based on ion pair and charge transfer complexation reactions. The first method is based on the reaction of the carbamazepine drug with Mo(V)–thiocyanate in hydrochloric acid medium followed by an extraction of the coloured ion-pair with 1,2-dichloroethane and the absorbance of the ion pair was measured at 470 nm. The second method is based on the formation of ion-pairs between mosapride citrate and two dyestuff reagents namely bromothymol blue (BTB) and bromocresol green (BCG) in a universal buffer of pH 4 and 3, respectively. The formed ion-pairs are extracted with chloroform and methylene chloride and measured at 412 and 416 nm for BTB and BCG reagents, respectively. The third method is based on charge transfer complex formation between mosapride citrate (electron donor) and DDQ (π-acceptor reagent) and the absorbance of the CT complexes was measured at 450 nm. All the optimum conditions are established. The calibration graphs are rectilinear in the concentration ranges 10–350 for carbamazepine using Mo(V)–thiocyanate and 4–100, 4–60 and 10–150 μg mL−1 for mosapride citrate using BTB, BCG and DDQ reagents, respectively. The Sandell sensitivity (S), molar absorptivity, correlation coefficient, regression equations and limits of detection (LOD) and quantification (LOQ) are calculated. The law values of standard deviation (0.04–0.09 for carbamazepine using Mo(V)–thiocyanate and 0.022–0.024, 0.013–0.018 and 0.013–0.020 for mosapride citrate using BTB, BCG and DDQ, respectively) and relative standard deviation (0.630–2.170 for carbamazepine using Mo(V)–thiocyanate and 0.123–1.43, 0.102–0.530 and 0.226–1.280 for mosapride citrate using BTB, BCG and DDQ, respectively) reflect the accuracy and precision of the proposed methods. The methods are applied for the assay of the two investigated drugs in pharmaceutical dosage forms. The results are in good agreement with those obtained by the official method.

Lyoluminescence of luminol in aqueous alkaline metal hydroxides

The lyoluminescence emission spectra of luminol, induced by γ-irradiated NaCl in aqueous alkaline earth metal hydroxides, are recorded. Continuous emission bands are observed in the visible region from 390 to 535 nm. These emission bands on resolution showed two peaks at 430 and 460 nm, respectively in all hydroxides. An additional band of 490 appears in the case of calcium hydroxide. The colour centres released during disintegration of irradiated NaCl crystals in aqueous solution react with luminol to produce various excited molecular species, which are responsible for observed lyoluminescence of luminol.

Lattice vibration spectra Part LXXII. OH stretching frequencies of solid hydroxides — correlation with structural and bonding data

The OH stretching frequencies of OH − ions in solid hydroxides can be either higher or lower than the free ion value. The high-energy shift found for OH − ions which are not involved in H-bonds like OH −⋯X (OH −, H-bond donor) has been analysed with respect to metal-oxygen interactions, repulsion of the lattice potential and H-bonds of the type XH⋯OH −. The upshift of ν OH increases with a decrease in (i) the mean M⋯O distances, (ii) the relative volume increment of OH − and (iii) the mean H⋯O distances (OH −, H-bond acceptor). In the case of alkali and alkaline earth metal hydroxides, ν OH obeys the function ν OH = A + C/( r M-O ) 2 + D/( r M-O ) 3. In the case of transition metal hydroxides, covalent parts of the metal-oxygen interactions counteract the high-energy shift. H-bonding of the type OH −⋯X gives rise to a downshift of ν OH. These H-bonds are strengthened in the case of metal-oxygen interactions (synergetic effect, H.D. Lutz, Struct. Bonding (Berlin), 69 (1988) 97). The criteria of ascertainment whether H-bonds OH −⋯X are present or not are discussed and extended to weak bonds.