Differential Dissolution Research Articles

Mineralogy of Palagonitic Material from the Golan Heights, Israel

AbstractSideromelane in Pleistocene lapilli-tuff rocks from the Golan Heights had partly altered into palagonite. X-ray and electron diffraction showed that the major part of the clay alteration product is composed of a dioctahedral micaceous mineral with well organized crystallinity along the a- and b-axes. Very poor basal reflections as well as incomplete expansion upon glycerolation and incomplete collapse upon heating were interpreted as being due to random interstratification with chlorite. Electron microscopy showed the particles to be very similar to montmorillonite tactoids. The thermal behavior as well as surface properties were similar to those of montmorillonite. Differential dissolution analysis and infrared spectroscopy failed to indicate amorphous constituents to any significant extent. Chemically the material was enriched in iron, aluminum and titanium and depleted in alkali and alkaline earth cations.A minor component of the clay was found to consist of ‘onion-like’ halloysite. It is suggested that palagonite is a natural precursor for montmorillonite in the volcanic glass-montmorillonite alteration series.

Measuring and Calculating Heat of Crystallisation

AbstractThe paper deals with problems and methods of the determination of crystallisation heat values either by direct measuring or by calculating based on solubility and activity data or on concentration dependences of differential dissolution heat. A table of hitherto published values of heat of crystallisation from aqueous solutions is presented.

Die Podsolierungsstadien von Braunerden aus Schieferschutt

Stages of Podsolization in Braunerden on SlateA six member pedosequence between Braunerde and Braunerde‐Podzol on slate in the Rheinisch‐Westfälisches Bergland was described and analyzed. Macromorphology of the profiles comprises the transformation from mull‐like mor to raw humus and the appearance of a podzol A and B horizon. The results of a detailed iron fractionation using differential dissolution methods (total, dithionite, oxalate, pyrophosphate, KC1 soluble) clearly reflects change in Fe during podsolization. Silicate Fe (total minus, dithionite) decreases compensating part of Fe loss in the A horizon which accumulates in the B. The Fed maximum is in the strongest podsolized member (Braunerde‐Podsol), whereas the maxima of the more mobile Fe fractions (FeKCI, Fepy and partly Feo) as well as the oxalate soluble carbon occurs in the weaker podsolized members (podsolized Braunerde). Within the profiles the more mobile Fe fractions have their maximum in the horizon of strongest Fe mobilization (A) whereas the less mobile fractions show maxima in the horizon of immobilization (B).The Fe fractionation improves proper horizontation of the profiles and proves the sequence to be a continuum. The change on ecological conditions is better indicated by decreasing amount of P than by changes in C and N although C/N is increasing along the series. Since the Braunerde is already very acid a change in exchangeable cations is not significant except an increase in exchangeable Fe and a decrease in exchangeable Mn. In the equilibrium soil solution an increase in H, Al and Fe and a decrease in Ca was noted. With increasing podsolization the turn over of Ca between soil and plant appears to decrease. The local distribution of the soils with varying degree of podsolization in this mountainous forest region appears to depend on such factors as inclination, exposition and forest history.

RNA ratios in dividing and non-dividing cells of pea root

These experiments were designed to determine RNA ratios in dividing, elongating, and maturing cells of pea seedling roots. Fractionation into high molecular weight ribosomal RNA and a low molecular weight fraction (4-S transfer RNA and 5-S ribosomal RNA) was accomplished by differential dissolution of total RNA in 3.0 M sodium acetate (pH 6.0) in combination with gel electrophoresis. Transfer RNA, when expressed as percent of the total RNA, was present in significantly lower amounts in dividing cells than in non-dividing cells. The level in dividing cells was approx. 50 % of that found in non-dividing cells. Based on known cell sizes in the three types of tissue, the amount of transfer RNA per cell increased markedly when going from the dividing to the non-dividing state while rRNA changed only slightly. Low proportions of transfer RNA are also associated with rapidly dividing cells in soybean callus tissue and synchronously grown Chlorella pyrenoidosa.

Factors affecting the differential dissolution of human enamel in acid and EDTA. A scanning electron microscope study

Surfaces of sound, human permanent teeth, either natural surfaces or surfaces cut in various planes, were etched with a variety of agents. In general, acids preferentially removed prism centres and ethylene diamine tetra-acetic acid (EDTA), at neutral pH, preferentially removed prism peripheries. A relationship between time and concentration was suggested by the observations that application of very dilute EDTA solutions resulted in the formation of narrow clefts at prism junctions which progressed to destroy the prism peripheries. Short exposures to dilute acids produced similar clefts as well as shallow concavities within the body of the prism; these concavities deepened with length of exposure leaving the prism cortex relatively unaffected. Etching with organic acids at neutral pH, where they might be expected to manifest some chelating activity, and etching with EDTA at acid pH, produced variable results with features typical of both acid and neutral EDTA attack. When the ionization of acids was inhibited by preparation in non-aqueous solvents, prism junctions appeared to be preferentially attacked. The role of crystal orientation and regional differences in chemical composition of enamel are discussed as possible explanations for the findings. It is suggested that the major factor which determines the differential etching by different agents is the greater permeability of prism junctions, which admits the large EDTA molecule and acid anions more readily than the bodies of the prisms. The pattern of tissue destruction seen in enamel caries could be explained on the basis of acid dissolution alone, or by a mixture of acid dissolution and calcium complexation.

Assessment of gibbsitic material in soil clays by differential thermal analysis and alkali dissolution methods

Precision differential thermal analysis (DTA) equipment provides a sensitive and accurate means of detecting and estimating gibbsite in soil clays. A combination of DTA and sodium carbonate dissolution procedures enables well-ordered gibbsite to be distinguished from poorly-ordered aluminous material.

The nature and composition of amorphous material and free oxides in some temperate region and tropical soils

Abstract Amorphous clay separated from pedons of a highly weathered soil previously classified as Oxisol and an Ultisol of the Southern States and, from the surface horizons of an Oxisol and two Andepts of the tropics were studied by chemical, DTA, infrared and X‐ray analysis. Considerable amounts of amorphous material, 20–37% in temperate region and 29–40% in tropical soils, were extracted by differential dissolution using 0.5 N NaOH. The molar SiO2/Al2O3 ratios of the dissolved material varied from sesquioxidic to siliceous (0.36–9.1) in temperate region soils, whereas those of the Andepts were allophonic (1.5–1.7). DTA and infrared analysis confirmed these results, however the strong gibbsite peaks in the X‐ray analysis of temperate region soils suggested that the aluminum fraction dissolved was in part, if not all, crystalline in nature. Indications were obtained with DTA and infrared that Na‐dithionite treatment might have altered the nature of the clay.

Enhancement of Solubility and Dissolution Rate of Poorly Water Soluble Drug using Cosolvency and Solid Dispersion Techniques

The low aqueous solubility of celecoxib (CB) and thus its low bioavailability is a problem. Thus, it is suggested to improve the solubility using cosolvency and solid dispersions techniques. Pure CB has solubility of 6.26±0.23µg/ml in water but increased solubility of CB was observed with increasing concentration of cosolvents like PEG 400, ethanol and propylene glycol. Highest solubility (791.06±15.57mg/ml) was observed with cosolvency technique containing the mixture of composition 10:80:10%v/v of water: PEG 400: ethanol. SDs with different polymers like PVP, PEG were prepared and subjected to physicochemical characterization using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffractometry (XRD), differential scanning calorimetry (DSC), solubility and dissolution studies. These studies reveals that CB exists mainly in amorphous form in prepared solid dispersions of PVP, PEG4000 and PEG6000 further it can also be confirmed by solubility and dissolution rate studies. Solid dispersions of PV5 and PV9 have shown highest saturation solubility and dissolution rate

Chemical and Mineralogical Properties of an Orangeburg Profile

AbstractThe Orangeburg soil used in this study was formed from unconsolidated sand of the Kosciusko formation. Weathering of this profile has been intense due to the porous nature of the sand and warm, humid climatic conditions. Methods used in this study consisted of X‐ray diffraction, DTA, an alkali differential dissolution technique for amorphous constituents, heavy mineral analysis of sand, total elemental analysis of the clay fractions, and surface area measurements. Minerals present in clay fractions are kaolinite, amorphous material, mica, a 14Å. montmorillonite‐vermiculite‐chlorite intergrade and quartz, in approximate order of abundance. Kaolinite and amorphous material increases whereas quartz decreases with profile depth in the coarse clay fraction. According to Jackson's weathering sequence this would place the lower horizons in a higher weathering stage than the surface horizon. The evidence gained in this study suggests that coarse quartz particles are being broken down to smaller particles resulting in this apparently anomalous sequence. The 14Å. intergrade mineral is more prevalent and stable in the surface horizons and apparently forms from montmorillonite.

Mineralogy of Soils on Basalt in North Queensland

AbstractData from X‐ray diffraction, elemental, differential thermal analyses, and differential dissolution were used to correlate the relationship between rainfall and clay mineral formation in the < 2 µ fraction of latosolic soils of North Queensland, Australia. Rainfall varied from 36 to 147 inches per year. Application of the weathering mean showed that the weathering intensity increased with increasing rainfall, being most pronounced in the surface layers. Poorly crystalline kaolinite is the dominant clay mineral (79 to 52%). Halloysite may be present in the higher rainfall areas. Total iron content moderately increased with rainfall (12 to 20%). No positive evidence for allophane was found. Gibbsite content varied (0 to 19%). The mineral composition of the silt fractions was also estimated.

Significance of Kaolinite Intersalation in Clay Mineral Analysis

AbstractRecent development of the intersalation method by which kaolinite (as well as dickite and halloysite) is expanded makes possible the application of X-ray diffraction to qualitative and semiquantitative determinations of these mineral species. It also permits their distinction from the X-ray-thermally similar intergradient 2:1–2:2 layer silicates which are not affected by the treatment. Intergradient 2:1–2:2 layer silicates are developed by interlayer precipitation of hydroxides of aluminum, iron, and magnesium during pedogeochemical weathering and probably also during burial in sediments. The quantitative determination of kaolinite-halloysite by NaOH differential dissolution is completely corroborated by the qualitative, semiquantitative X-ray diffraction intersalation technique with respect to their clear differentiation from chlorite and intergradient clays.

Mineralogical Analysis of Soil Clays Involving Vermiculite-Chlorite-Kaolinite Differentiation

AbstractThe content of kaolinite plus halloysite is differentiated quantitatively from chlorite by differential dissolution, even in those samples wherein each mineral has 500°C heat instability of the 7 Å peak. This differentiation is possible because the structures of kaolinite and halloysite are destroyed on loss of the 7 Å peak, producing amorphous material which is rapidly soluble in 0.5 N NaOH, whereas the chlorite structure remains largely intact with only partial dehydration of the octahedral layer. The amorphous residue of kaolinite-halloysite is dissolved from the other mineral components of the heated sample with sodium hydroxide and the dissolved silica and alumina are allocated to kaolinite. The percentages of kaolinite thus obtained for Elliott, B3–C horizon, 2–0.2 μ fraction, are 3.8 and 3.7 based on silica and alumina, respectively. Similarly, the percentages of kaolinite obtained for Buchanan, B1 horizon, 2-0.2 μ fraction, are 14.9 and 13.8 based on silica and alumina, respectively. Collapse of the vermiculite basal spacing to 10 Å on K saturation and heating to 300°C, together with the clear differentiation of kaolinite by differential dissolution analysis (D.D.A.) above, removed the possibility of misinterpretation of the chlorite-like diffractometer tracing by kaolinite and vermiculite occurring together. Other clays, from Davidson and Susquehanna soils, had 44 and 42 to 43 percent kaolinite, based on silica and alumina, respectively. The vermiculite and montmoril-lonite contents of soil clay samples are quantitatively determined by specific surface. The mica percentages are based on the K2O after exclusion of potassium in feldspars. Water loss in the 400°C-to-ignition range gives an important quantitative basis for chlorite.

Rapid Dissolution of Allophane and Kaolinite-Halloysite After Dehydration

AbstractDifferential dissolution in NaOH solution was investigated as a means of purification of clay. It was discovered that a large quantity of allophane and free alumina and silica were dissolved from clay preparations in 0.5 N NaOH solution by boiling for as little as 2.5 min, provided the ratio of clay weight to solution volume was kept less than 100 mg to 100 ml. Reprecipitation of dissolved silica occurred if a more prolonged digestion or higher sample to solution ratio was employed. Also, prolonged digestion in the NaOH solution (for 80 min) dissolved as much as 50 percent of kaolinite (Merck) and 25 percent of Wyoming montmorillonite, but only a small quantity of these crystalline minerals was dissolved during the 2.5 min digestion period. Subsequent dithionite-citrate-bicarbonate treatment removed the released iron. Marked improvement of x-ray diffraction patterns of the clays resulted. This rapid and selective dissolution of allophane and free oxides greatly improves the quantitative analysis of crystalline minerals by conventional methods.After dehydroxylation at 500°C, kaolinite and halloysite became amorphous and also dissolved by the same differential dissolution procedure. Heat-stable (aluminous) montmorillonite and chlorite were only slightly dissolved by this treatment. The selective removal of the 1 : 1 layer aluminosilicates greatly improves the quantitative analysis of the remaining crystalline components of clays by conventional methods.