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Aqueous electrophoretic deposition

a technology of electrophoretic deposition and water, applied in the direction of fluid pressure measurement, liquid/fluent solid measurement, peptide measurement, etc., can solve the problems of low economic value of direct current epd from water at low field, inability to produce coatings, and inability to attract economic value, so as to reduce or prevent water electrolysis, the effect of reducing or preventing water electrolysis

Inactive Publication Date: 2011-07-14
KATHOLIEKE UNIV LEUVEN
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0015]It is an object of present invention to deposit cationic polymers in smooth coatings from an aqueous medium onto anodes or porous substrate placed in front of an anode by subjecting them to unbalanced (asymmetric) alternating current (UAC) electric signals to reduce or prevent electrolysis of water in the aqueous medium.
[0016]It is also an object of present invention to deposit anionic polymers in smooth coatings from an aqueous medium onto cathodes or porous substrate placed in front of a cathode by subjecting them to unbalanced alternating current (UAC) electric signals to reduce or prevent electrolysis of water in the aqueous medium.
[0017]It is also an object of present invention to deposit charged microorganism and living cells or cell components in smooth coatings from an aqueous medium onto a conductive medium or electrode or porous substrate placed in front of an electrode by subjecting them to unbalanced alternating current (UAC) electric signals in which the amplitude differs significantly for the positive and negative part to reduce or prevent electrolysis of water in the aqueous medium.
[0018]It is also an object of present invention to deposited bioactive agents in thin coatings (nanometer scale average thickness) or in thick coatings (micrometer scale average thickness) from an aqueous medium onto a conductive medium or electrode or porous substrate placed in front of an electrode by subjecting them to unbalanced alternating current (UAC) electric to reduce or prevent electrolysis of water in the aqueous medium.
[0019]The present invention further concerns a system of high voltage EPD of colloidal particles suspended in an aqueous medium while the decomposition of water is suppressed below the point of gas bubble formation. The current problem in the art of high voltages water decomposition is solved by applying an unbalanced alternating electric field. Contrary to what one might expect, the particles form an adhering deposit on the selected electrodes (deposition electrodes), the experimental results of present invention clearly demonstrated that by present invention deposits with high green density (>60% in the case of monomodal spherical submicron Alumina particles) and smooth surface can be formed from aqueous suspensions.
[0033]In a particular embodiment of present invention the unbalanced alternating current electrophoretic deposition (UAC-EPD) of present invention to produce a strong lightweight metals and alloys.

Problems solved by technology

Molecules that are charged or partially charged dissolve readily in water while molecules that do not have charges or partial charges on their surface do not mix readily with water.
However these are not the most important advantages that water has to offer if we look at aqueous EPD from a technical point of view.
Most EPD is therefore carried out in non-aqueous solvents, direct current electrophoretic deposition from water being limited to low electric fields.
Since the deposition rate depends directly on the strength of the applied, direct current EPD from water at low field is not attractive from an economical perspective.
sis. With the first two solutions, the production of coatings is impractical because the deposit is not formed on the electrode, or the expensive electrode material is not suitable or economically infeasible as substrate mate
rial. The use of specialty chemicals is expensive, difficult to control and not ecolog
ltages. However, despite the high quality of the deposits claimed using these techniques they display low deposition rates (e.g. 30 minutes to form a mono-layer). Y. Hirata et al. in Journal of the Ceramic Society of Japan, volume 99, 108-113 (1991) reported the use of symmetric AC signals to form deposits by EPD from aqueous suspensions at high frequencies, but the deposition rate was extremely low and seemed to be controlled by the diffusion of alumina in the s
As a result unwanted electrochemical reactions were slowed down, yet not fully stopped.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

Controllability of the Process

[0121]α-Al2O3 was deposited using the technology of present invention. The deposition rate of α-Al2O3 versus the symmetry of the applied signal V1, V2, t1, t2 (as defined in FIG. 1). The suspension consisted of a 200 g / L SM8 in water containing 4.10−4 M HNO3.

[0122]The more symmetric signals the smaller deposition rates observed. For instance symmetry of the signal was varied, by varying the height (amplitude) and width (pulse duration) of the triangular waves while maintaining a total period of 20 ms, a peak to peak height of 500 V and a net integral lower in absolute value than 4V, preferably lower than 1.24V and most preferably equal to zero, over one period. The asymmetry factor is determined as the ratio between the pulse heights, which is equal to the ratio of the pulse widths.

[0123]FIG. 3 shows that the deposition rate is zero when the applied field is symmetric (asymmetry factor equal to one) because no net electrophoresis occurs under the influe...

example 2

Material and Methods

[0127]Fresh deionised water with an initial conductivity of 0.04 μS / cm and prepared with a commercial ion exchange setup (Sation Aqualab 50) was used for all suspensions. Commercially available α-Al2O3 (Baikowski grade SM8), TiB2 (H.C.Starck grade F) and rutile TiO2 (Kemira grade Rutilex) powders were used for experimentation. The TiO2 was boiled and washed in a dialysis cell prior to use. No charging agent was added to the TiB2 suspension while the TiO2 was charged using KOH (Chem Lab 0.1 mol / l standard). HNO3 (Fluky 65%) was used as a charging agent for the experiments with alumina. For each experiment a new suspension was prepared using 50 ml freshly prepared water and the indicated amount of powder and charging agent (Table 1). The suspensions were magnetically stirred for 15 minutes; followed by 15 minutes of treatment in an ultrasonic bath (Branson 2510), subsequently followed by 15 minutes of stirring on a magnetic plate. A programmable function generator ...

example 3

Characterization

The Archimedes Method for Green Density Determination:

[0132]The green density is a value that relates to the particle packing in the formed object, and therefore is often used as a measure of the quality of the formed object. This value is traditionally stated as a percentage of the theoretical density of the material. For the measurement, the mass of the object is recorded. In order to include the interparticle porosity the object is coated with a lacquer that seals off this porosity, and after drying the mass of the coated object is registered as well. The volume of the coated object is measured by submerging it in a solvent of known density and measuring the buoyancy. The Archimedes principle is used to calculate the total volume of the coated object. From the weight difference before and after coating, the volume of the lacquer can be calculated and subtracted from the total volume. The density of the sealing lacquer is determined previously by coating a substrat...

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Abstract

From an environmental, safety and economic perspective water should be the solvent of choice for electrophoretic deposition under industrial circumstances. However, because of the electrolytic decomposition of water, the majority of EPD is carried out in non-aqueous solvents.Approaches of the art for aqueous deposition involve the separation of the reaction and deposition front by means of a membrane, the use of palladium electrodes to absorb the formed hydrogen, addition of chemicals to suppress the electrolysis reaction, or lowering voltages below the threshold for water electrolysis. With the first two solutions, the production of coatings is impractical since the deposit is not formed on the electrode, or the electrode material is not suitable since the substrate is usually prescribed by the application. The use of specialty chemicals is expensive and difficult to control. Low voltages have been used to form high quality deposits from aqueous systems but they display very low deposition rates, which are not attractive from an economical perspective.Present invention provides a system and a means for which high voltages can be used in the electrophoretic deposition from aqueous suspensions without decomposition of water at satisfying deposition rates. It shows that the deposits obtained show a high green density with excellent surface quality.

Description

TECHNICAL FIELD OF THE INVENTION[0001]The present invention relates generally to the process of the deposition of 1) colloidal particles suspended in an aqueous medium or in an aqueous medium slurry or 2) organic or metallo-organic molecules dissolved in an aqueous medium, (preferably concentrated systems and most preferably highly concentrated systems) under the influence of an electric field onto an electrode or porous substrate placed in front of an electrode.[0002]More particularly the present invention relates to a controllable system and method for electrophoretic deposition in unbalanced AC electric fields (UAC-EPD) to form smooth deposits with no visible defects or to form a coating or a deposit.BACKGROUND OF THE INVENTION[0003]Electrophoretic deposition (EPD) is a colloidal processing technique in which a suspension or solution of charged particles or charged organic or metallo-organic molecules is placed in an electric field. The charged particles move towards one of the e...

Claims

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Application Information

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IPC IPC(8): C25D13/04C25D13/00C09D7/65
CPCA23L1/0047C08L89/00C09D5/024C25D13/18C09D7/125C25D13/04C09D5/448A23P20/10C09D7/65
Inventor FRANSAER, JANNEIRINCK, BRAMVAN DER BIEST, OMERVLEUGELS, JOZEF
Owner KATHOLIEKE UNIV LEUVEN
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