<i>Optical Crystallography</i>

SUMMARYThe concentration of orthophosphate ions released from Fe-K-P compounds (Fe 3 KH 8 (PO 4 ) 6 .6H 2 O and Fe 3 KH 14 (PO 4 ) 8 .4H 2 O) present in superphosphates increases with pH, which initially suggests that the agronomic effectiveness of P fertilizers containing high amounts of these compounds would also increase with soil pH but studies considering activity, instead of concentration, are necessary. With this purpose, both compounds were synthesized under laboratory conditions, characterized by elemental chemical analysis, optical microscopy, X ray diffractometry, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), and used in a solubility study. Solutions of 0.01, 0.05 and 0.1 mol L -1 NaCl with pH adjusted to 3.0, 4.0, 5.0, 5.5, 6.0, 6.5, 7.0 and 7.5 were prepared for the solubility study of H8-syn, H14-syn and a phosphate rock (PR) from Brazil. The orthophosphate activity as H 2 PO 4 -and HPO 4 2-was calculated in each situation as related to pH and ionic strength using software MINTEQ. The remaining precipitates after equilibrium were chemically analyzed and subjected to X ray, SEM and EDS. Results of chemical analysis and instrumental techniques confirmed the preparation method. The activity of orthophosphate ions of both compounds tended to decrease under increasing pH and/or ionic strength of the solution, which in turn suggests that an increase in the solution pH does not necessarily promote an increase in the P bioavailability for plant uptake. This can be important when evaluating agronomic data of P fertilizers with high contents of these two Fe-K-P compounds.Index terms: Phosphate fertilizers, cationic impurities, phosphorus activity, phosphorus bioavailability.(

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“…Refractive indices were measured by the Becke line method (Wahlstrom, 1979) with certified refractive index oils.…”

Section: Methodsmentioning

confidence: 99%

Activity of phosphorus of synthetic Fe-K-P compounds in superphosphate fertilizers as affected by pH and ionic strength

Prochnow¹,

Biasioli²,

Rodella³

et al. 2006

Rev. Bras. Ciênc. Solo

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“…-Apothecia and their associated crystals were immersed in optical index oils n = 1.57, 1.59 and observed between crossed polarizers at 1000X on a microscope with a rotating stage to measure extinction angles of the crystals. The Becke line technique and oblique illumination were used to determine the refractive indices of the crystals (Wahlstrom, 1960;Bloss, 1961). Whole leaves were viewed and photographed with a macro-dia apparatus using reflected light.…”

Section: Methodsmentioning

confidence: 99%

Formation of Calcium Oxalate Crystals Associated with Apothecia of the Discomycete Dasyscypha capitata

1983

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Calcium oxalate dihydrate crystals form at or near the tips of sterile hairs on the apothecia of the oak leaf litter discomycete Dasyscypha capitata. Early in their development, the crystals appear to be covered by a wall or membrane, whereas later they appear external. The crystals on each hair form a mass of crystals called a druse. Quite often the smaller crystals near the apex of the tip form a rosette, whereas the more peripheral crystals are much larger and display shapes possibly related to environmental factors. Calcium oxalate dihydrate crystals form at or near the tips of sterile hairs on the apothecia of the oak leaf litter discomycete Dasyscypha capitata. Early in their development, the crystals appear to be covered by a wall or membrane, whereas later they appear external. The crystals on each hair form a mass of crystals called a druse. Quite often the smaller crystals near the apex of the tip form a rosette, whereas the more peripheral crystals are much larger and display shapes possibly related to environmental factors. The formation and development of Dasyscypha crystals are compared with recent studies of other litter and soil fungi and their presence in other biological systems is put into perspective.

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“…The real part, n, is called the refractive index while k is the absorption (or extinction) coefficient. Both coefficients are dependent on the frequency of light and standard refractive index measurements (n) are often tabulated for wavelengths emitted by a sodium flame or a sodium vapor lamp (589.3 nm) designated ''D'' [38]. The absorption coefficient 'k' is 0 or very close to 0 for transparent or translucent material, and becomes important for opaque media.…”

Section: Optical Parametersmentioning

confidence: 99%

“…In fact, only a limited number of materials have a single, isotopic refractive index: crystals belonging to the cubic crystal system, glasses and amorphous substances. Minerals in other crystallographic systems are anisotropic, with different refractive indices depending on crystal alignment with 2 or 3 main values described as a, b and c in tabulations of reference data [38,40]. The real part of the complex index of refraction can be determined under an optical microscope using the immersion method, in which the index of a solid is compared with that of a liquid of known index [9].…”

Section: Optical Parametersmentioning

confidence: 99%