Molar Alkali Research Articles

Effect of Treatment Age on Mechanical Properties of Geopolymer Concrete

There are the same compound content, fly ash does not have the ability to bind, so it requires an alkaline activator for the polymerization reaction or binding reaction to occur. The alkali activators commonly used are sodium hydroxide and sodium silicate. The use of these materials makes concrete with fly ash known as geopolymer concrete. Geopolymer concrete is an alternative to conventional concrete, so it must have optimal strength like conventional concrete, therefore researchers are interested in testing the value of compressive strength, split tensile strength and mode of elasticity of geopolymer concrete using 10 molar alkali activator with a ratio of 3:2. for variations in the age of concrete 7, 14, 21, and 28 days; and the conversion value of geopolymer concrete using 10 molar alkali activator with a ratio of 3:2 for variations in the age of concrete 7, 14, 21, and 28 days. This research is an experimental study using variations in the age of concrete 7, 14, 21, and 28 days for geopolymer concrete using 10 molar alkali activator with a ratio of 3:2. The results of this study indicate that there is an effect of variations in the age of concrete on the value of compressive strength, split tensile strength, and modulus of elasticity of geopolymer concrete. Where the compressive strength, split tensile strength, and modulus of elasticity of geopolymer concrete at the age of 7 days are 31.40%; 35.44%; and 23.32% which at the age variation of 28 days increased by 100%. In addition, in this study, it is known that the conversion value at the age of 28 days for variations in the age of 7 days, 14 days, 21 days, and 28 days, respectively, is 0.31; 0.73; 0.97; 1.00
 Keywords: Geopolymer Concrete, Compressive Strength, Modulus of Elasticity

Controls on the stability and composition of amphibole in the Earth’s mantle

Presented here is a suite of new experiments aimed at quantifying the effects of pressure, temperature, bulk composition, and H2O content on the stability and composition of amphibole in the Earth’s mantle. Experiments have been performed from 2 to 4 GPa and 950 to 1100 °C on fertile and depleted mantle compositions. H2O contents of most experiments are 0.65 wt%. In the fertile mantle composition, pargasitic amphibole is stable up to ~3.8 GPa at 1000 °C, approximately 0.5 GPa higher than any previous study. The upper stability limit of amphibole in depleted mantle is 0.7 GPa and 40 °C lower than in fertile mantle. The addition of 3 wt% H2O to fertile mantle destabilizes amphibole by 0.5 GPa and 40 °C relative to the 0.65 wt% H2O experiments. Compared to existing experiments on amphibole stability, these experiments indicate that pargasitic amphibole may be stable in mantle lithosphere to almost 4 GPa (0.5 GPa higher (15 km deeper) than previously thought). The extremely strong destabilizing effect of H2O suggests that deeper portions of the strongly fluid-fluxed mantle wedge may be amphibole-free even at low temperatures near the slab–wedge interface. The molar alkali content of amphibole is shown to be a linear function (R 2 = 0.98) of pressure and temperature and is relatively insensitive to bulk compositional differences between fertile and depleted mantle. This relationship is used to produce an empirical thermobarometer for pargasite-bearing spinel and garnet lherzolites. Comparison to existing experimental data shows that this thermobarometer has predictive ability over the pressure range of 1–4 GPa. Comparisons with pressure–temperature estimates of garnet + amphibole peridotites further corroborate the applicability of this thermobarometer for natural samples. Pressure estimates are presented for four examples of metasomatized spinel peridotites otherwise lacking pressure information, and future avenues for refinement of the thermobarometer are discussed.

The rheology of peralkaline rhyolites from Pantelleria Island

The viscosity of pantelleritic melts from the Khaggiar lava flow (5.5ka — Pantelleria Island) was investigated as a function of temperature and water content. High (1673–1323K) and low (973–613K) temperature dry and hydrous liquid viscosities were determined by a combination of concentric cylinder (102.44 to 104.56Pas) and micropenetration (108.67 to 1011.37) viscometric techniques. The effect of water, from 0.02 to 3.55wt.% H2O, was explored in the temperature range of 973–613K. Liquid viscosities have been parameterized by means of a modified Vogel–Fulcher–Tammann equation (VFT) which describes viscosities and derivative properties (glass transition temperature Tg, fragility m) of silicic liquids as a function of T–X (H2O). The results yield the expected strong decrease of viscosity with temperature and water content. Fragility, as a measure of the deviation from Arrhenian behavior, increases with H2O content from m=23 to m=28. The peralkalinity (molar alkali excess over alumina), which characterizes the pantelleritic magmas, exerts a primary control over the rheological behavior of these melts. The excess of alkalies over alumina content is responsible for the peculiarly low viscosities of pantelleritic liquids compared to their metaluminous counterpart in the high temperature range, and leads to an even more dramatic decrease in the viscosities of these rhyolites in the low temperature range.Comparison with available models shows substantial differences between the measured and calculated viscosities. Based on our new viscosity results combined with existing literature data, we propose a new parameterization based on a modified Vogel–Fulcher–Tammann equation, accounting for the effect of water and composition, which can be used to determine the viscosity of pantelleritic melts. The derived relationship reproduces the experimental data (58 in total) in the viscosity range from 102.44 to 1011.37Pas and in the temperature range from 613 to 1673K within a root-mean-square-error (RMSE) of 0.12 log units. Application of this calculation model for high temperature low viscosity hydrous melt is limited by the lack of experimental data and needs verification by additional measurements. Volcanological implications for welding and rheomorphic processes as well as conduit dynamic modeling are also discussed in light of the results presented in this work.

Effect of alkali cations, halides and thiocyanate on the Mn(Hg)/Mn(II) electrode reactions

The title subject has been studied by galvanostatic single-pulse, chronopotentiometric and equilibrium measurements on the Mn(Hg)/Mn(II) electrode (mainly saturated managanese amalgams) in one molar alkali chloride (LiCl, KCl and CsCl) and potassium iodide and thiocyanate solutions of pH 4 to 5 at 25°C. The Mn(Hg)/Mn(II) reactions are found to occur in two consecutive steps with monovalent ions as intermediate in all these solutions. The rates of both the ion-transfer step Mn(Hg)/Mn(I) and the electron-transfer step Mn(I)/Mn(II) appear independent of the cations Li + and K + and of the anions Cl −, I − and SCN −, when differences in bulk activities of electroactive species are corrected for. The Cs + ion, however, seems to retard the reactions more than expected from bulk activity changes, and this can be explained by Cs + specific adsorption or by variations in the properties of the inner layer with the cation.

THE SEPARATION, ESTIMATION, AND CHARACTERIZATION OF ALKALI-STABLE OLIGONUCLEOTIDES DERIVED FROM COMMERCIAL RIBONUCLEATE PREPARATIONS

Methods are described which are suitable for the quantitative analysis of the alkali-stable oligonucleotides which result from the hydrolysis of ribonucleates in molar alkali at room temperature for 90 hours. The alkali-stability of the oligonucleotides is presumed to result from 2′-O-methyl substitution of ribose residues and this assumption is supported by the relatively slight reactivity of the purine 2′-O-methyl ribosides in the orcinol color reaction for pentoses. The existence of all of the 16 possible dinucleotides as part of ribonucleate chains has been established. The quantity of alkali-stable trinucleotides is much greater than would be expected for a random spatial distribution of 2′-O-methyl ribosides in ribonucleate chains.

ELECTROPHORETIC HOMOGENEITY OF POLYSACCHARIDES IN MOLAR ALKALI

The usefulness of electrophoretic patterns of polysaccharides in molar alkali as a general criterion of the purity of these substances has been studied. No clear separation of the components of a hemicellulose, of wheat starch, or of potato starch could be demonstrated. Similarly, mixtures of wheat starch and inulin, pectin and sodium alginate, laminarin and sodium alginate, inulin and wheat starch plus sodium alginate could not be resolved in 1 M potassium hydroxide. Nonetheless, mixtures of laminarin and sodium alginate separated rapidly at pH 6.8 and 10.4. Contrary to previous reports, it is shown that the electrophoretic technique cannot be used with confidence as a general criterion of the purity of polysaccharides in molar alkali. However, it may be applicable for the characterization and fractionation of a limited class of polysaccharides which are soluble close to neutrality.