ISSN:0232-1300    

DOI:10.1002/crat.2170260521

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

ISSN:0232-1300    

DOI:10.1002/crat.2170260522

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

ISSN:0232-1300    

DOI:10.1002/crat.2170260523

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

ISSN:0232-1300    

DOI:10.1002/crat.2170260524

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

ISSN:0232-1300    

DOI:10.1002/crat.2170260525

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

ISSN:0232-1300    

DOI:10.1002/crat.2170260526

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe high‐pressure X‐ray diffraction technique, commonly applied for inorganic crystals, is discussed in a view of its application for laboratory studies on molecular crystals of organic compounds – particularly when the weak X‐ray scattering of such specimens causes experimental difficulties. To minimize the background‐to‐signal ratio, relatively big crystal samples (ca. 0.005 A3) were used and the mechanical properties of the gasket material were applied to obtain the optimum experimental conditions for pressure generation and lowering the background of reflections. The mechanical properties of tungsten, Inconel, and hardened steel gaskets are different and these properties can be helpful in planning high‐pressure measurements with large high‐pressure chamber to contain a big crystal sample. Several characteristic features of organic crystals – like their strong compressibility (depending on the nature of intermolecular interactions) and pressure‐dependence of thermal vibrations of atoms – can have a direct impact on the conditions of high‐pressure experiments. The properties of molecular crystals of organic compounds have been discussed on the basis of several high‐pressure structural studies, mainly on simple cyclic β‐diketoalkanes (enol forms). It has been attempted to assess the feasibility of investigating the details of molecular structure at high pressures by X‐ray laboratory studies. A systematic pressure‐induced change in the length of double C  O bonds is observed in this group of compounds, which can be correlated with the compression of the H

ISSN:0232-1300    

DOI:10.1002/crat.2170260502

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

ISSN:0232-1300    

DOI:10.1002/crat.2170260503

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractAn analysis of the thermodynamics and kinetics of crystal growth and dissolution of slightly soluble salts in physiological solutions in the presence of complexing ions is made, accounting for conditions typical in human urine. It is found that hippuric acid, a normal physiological constituent of urine, acts at increased concentrations as a dissolving agent with respect to calcium oxalate and calcium oxalate calculi. The kinetics of dissolution of crystalline calcium oxalate calculi (CaOx) in physiological solutions containing hippuric acid in different concentrations is studied, using the change in the Archimedean weight of samples, immersed in the solution.The analysis of the experimental results enables the determination of the increased solubility of CaOx in the presence of hippuric acid and to characterize quantitatively this substance as a new and very prospective dissolving agent of CaOx calculi in human urine. A discussion is also given on the possible effect of hippuric acid as a neutral regulator of CaOx‐supersaturation and crystallization in human and mammal urin

ISSN:0232-1300    

DOI:10.1002/crat.2170260504

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe formulae for absoluteRdisapand relativeR reldisapvelocities of disappearance and lifetime τ of faces of growing crystals have been derived for stationary growth. It was shown that the quantities are determined by the relative growth velocityRA/RcritAof the vanishing face A with respect to the critical growth velocityRcritAand by the geometry of a crystal expressed by the trigonometric functions of interfacial angles β and γ formed between face A and the adjacent faces.R reldisapincreases and τ decreases with the increase inRA/RcritAto certain limiting values. The calculations have been verified and illustrated by the experimental results for triclinic potassium bichromate (KBC) crystals. Results enable ones to predict values of velocities of disappearance and lifetimes of undesirable, supplementary faces of any real

ISSN:0232-1300    

DOI:10.1002/crat.2170260505

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY