Single-crystal – oriented-crystal – and epitaxy growth processes; – Apparatus – For crystallization from liquid or supercritical state
Patent
1996-09-25
1999-12-14
Kunemund, Robert
Single-crystal, oriented-crystal, and epitaxy growth processes;
Apparatus
For crystallization from liquid or supercritical state
117 68, 117 70, 117925, 117926, 117927, 204290R, 204291, C30B 712
Patent
active
060011769
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device for specific formation of nuclei or crystals on the surface of a dielectric in contact with a solution, in particular on the functional groups of a polymer.
The invention further relates to a method for controlling the formation of nuclei or the epitaxial growth of crystals from a solution on a surface of a dielectric, in particular on the functional groups of a polymer.
It is already known that crystal nuclei are formed or epitaxial growth of a mineral phase takes place on dielectric surfaces, wherein the chemical, morphological and sterochemical properties of the surface influence this growth. Such formation of nuclei takes place, for example, in nature, where biopolymers induce and control the growth of shells, skeletons, teeth or the like. The biomineralization is described, for example, in the article "Molecular recognition in biomineralization" by Stephen Mann in Nature, Vol. 332, 10.31988, pages 119 ff, or in the book "Biomineralization" by S. Mann, J. Webb and R. J. P. Williams, CH Publications 1989, pages 35 ff.
Technical applications have as yet remained limited to specially produced macromolecules which, having certain functional surface groups, are able to control precipitation and flocculation reactions (for example, tensides, phosphates); for this, these compounds must, for the most part, be mixed directly with the solution--the control of the reactions is, however, possible only by means of the amount added or by means of addition of certain chemicals which cause certain charge reversal in the polymers.
SUMMARY OF INVENTION
The object of the invention is to provide a device and a method of the type described in the introduction, upon which crystal nuclei or crystals with a defined form, size, structure and orientation can be grown in a specific and controlled manner.
According to the invention this is achieved in a device of the type described in the introduction by a means for generating an electric field in the dielectric.
Polarisation or an increase in the polarisation already present in the dielectric is obtained with the electric field, in particular, the orientation of functional groups (for example carboxylate groups, carbonyl groups or amino groups for the synthesis of CaCO.sub.3, CaPO.sub.4) away from the contact surface of the dielectric towards the solution is also obtained. As a result, a so-called electric double layer is formed. Normally, homogeneous formation of nuclei occurs only when critical supersaturation is reached in the solution. Such critical supersaturation can be obtained locally in the dielectric double layer in that an electric field is created by means of the potential on the field generating electrodes, which changes the proportion of the concentrations of ions in the solution within the double layer.
For example, with a negatively charged electrode the proportion of the concentrations of Ca.sup.2+ and CO.sub.3.sup.2- can be changed in the double layer in favour of the Ca ions. The product of [Ca.sup.2+ ].times.[CO.sub.3.sup.2- ], which has a certain value in the saturation (thermodynamic balance, regardless of pH value and temperature), is, when it is also taken into account that Ca.sup.2+ Ions and CO.sub.3.sup.2- bond with a different number of water molecules and are consequently differently protected (solvated), clearly exceeded in certain areas of the double layer--supersaturation is obtained locally and thereby the homogeneous formation of nuclei can be initiated.
Moreover, it is possible to control, by means of the electric field, a specific accumulation of the dissolved ions in the proximity of the functional groups and the specific involvement of the functional groups in the nucleus forming reaction. This consequently results in a formation of nuclei or crystal growth which can be influenced by means of the electric field. For example, different macromolecular compounds influence the formation of nuclei from mineral phases on their surface through the presence of certain functional groups such as, for example, the ca
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Abstract of JP Application 4-367598 filed by Sumitomo Electric Ind. Ltd. on Jun. 14, 1991, English language abstract provided by Japanese Patent Office, Unexamined Applications May 13, 1993, p. 99C1057.
"Molecular Recognition in Biomineralization" by Stephen Mann in Nature, vol. 332 Oct. 3, 1968, pp. 119 ff; and Biomineralization, S. Mann, J. Webb and R.J.P. Williams, CH Public 1989, pp. 35 ff.
Journal of Physics D: Applied Physics, vol. 24, No. 2 Feb. 14, 1991, Letchworth GB, pp. 154-164; Mann et al. "Structural and stereochemical relationships between Langmuir monolayers and calcium carbonate nucleation."
Leiter Klaus
Walder Gerhard
Kunemund Robert
Leiter Klaus
Walder Gerhard
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