KR20030096252A - Improved electrophoretic deposition - Google Patents

Abstract

The present invention relates to electrodeposition of ceramics by electrophoresis, wherein the anode incorporates the same metal as the metal in the metal salt dissolved in the solvent, and the salt is preferably magnesium nitrate.

Description

Improved Electrophoretic Electrodeposition {IMPROVED ELECTROPHORETIC DEPOSITION}

Electrophoretic electrodeposition is increasingly used in electrodeposition and other electronics applications in which phosphors are coated with ceramic powder. The basic technique of this method involves the use of stainless steel anodes, and the conductive cathode is also immersed in an organic liquid such as isopropanol in which a small amount of magnesium nitrate is dissolved. After the ceramic powder is added to the electrolyte, a high DC voltage is applied to electrodeposit the ceramic powder on the cathode. Upon application of voltage, the ceramic powder becomes positively charged and attracted toward the cathode. At the same time, Mg (OH) ₂ is formed at the cathode and acts as a binder for the ceramic powder.

Mg (NO ₃ ) ₂ is added as Mg (NO ₃ ) _{2 ·} 6H ₂ O, and isopropanol does not become completely anhydrous, so a small amount of water present in the organic liquid exhibits some ionic conductivity. Most of the studies on electrophoretic electrodeposition are based on the electrolysis of water to produce oxygen and hydrogen, based on the following equation.

Anode _{reaction: 2H 2 O = O 2 +} 4H + + 4e -

Cathode ^{reaction: 4H + + 4e - = 2H} 2

In practice, when an anode potential is applied to a metal anode, before oxygen is generated, the metal M is first oxidized at the anode to give the following equation on the anode surface.

_{M + H 2 0 = MOH +} H + + e -

For isopropanol containing extremely limited amounts of water, even when 300-350 volts are applied throughout the cell so that most of the anode current is used to oxidize the anode, the very high resistance of the electrolyte causes a current of ~ 1 mA through the cell. Restrict to flow at / cm3. Because of the unavoidable dissociation phenomenon at the anode, the isopropanol electrolyte is contaminated. The cations generated at the anode are electrodeposited into the ceramic powder at the cathode. Previous studies were conducted by the University of Greenwich (Carol Gibbons, Xiping Jing, Jack Silver, Aron Vecht, and Robert Withnall, Elctrochemicals and Solid State Letters, (1999), 2 (7), 357). In the case of the stainless steel anode, it was proved that the electrodeposition of the iron is not suitable for the electrodeposition of the luminous material because the electroluminescent property of the luminous material is reduced.

The present invention relates to an improved electrophoretic electrodeposition method.

This figure is a graph measuring the luminescence at 12 points on the glass substrate in the presence or absence of a reducing additive according to the present invention.

The present invention is embodied in the Examples.

The present inventors have found that when copper is used as an anode instead of stainless steel, inactivation of the copper plated zinc sulfide emitter is prevented because Cu ⁺² ions are not reduced in the Zns: Cu emitter but are reduced in the electrolyte. Magnesium nitrate is consumed during the electrophoretic electrodeposition process, but using magnesium anode can ensure that the Mg ⁺² cation is continuously supplied in solution. This is because the amount of Mg ⁺² cation is made constant, resulting in a more consistent electrophoretic electrodeposition coating in a continuous production process. In addition, the reaction at the cathode reduces the generation of hydrogen as well as the electrodeposited emitter. When hydrogen is generated at the cathode, the electrodeposition efficiency is reduced, and the reduction of the ceramic powder at the cathode potential results in a change in composition which may be harmful. In addition, when hydrogen evolution is one of the cathode reactions, water is consumed in the process causing changes in electrolyte composition and conductivity.

An alternative preferred method is to introduce a reducing species, such as oxygen, into the electrolyte by bubbling small amounts of air or oxygen or adding dilute hydrogen peroxide, where the cathode reaction is a reduction reaction of oxygen:

02 + 4e + 4H ⁺ = 2H ₂ O

Therefore any H ₂ O consumed in the anode reaction will be replaced, which ensures that the electrolyte remains constant in such a system. Also, since the reduction of oxygen occurs at a much higher potential than other reducible species in electrophoretic electrodeposited coatings, the reduction of indium doped tin oxide glass or electrodeposited powders commonly used as substrates for light-emitting coatings does not occur.

According to the present invention, there is provided a method of electrodepositing a ceramic by electrophoresis, the method comprising sending a current into a liquid in which the ceramic is suspended, wherein the liquid contains a solvent in which the metal salt is dissolved, The metal contains the same anode metal as the metal in the metal salt.

All metal anodes are oxidized and release cations in the organic liquid.

For example, magnesium and / or aluminum are preferred anodes in electrophoretic electrodeposition, each containing a magnesium salt or an aluminum salt such as nitrate in an organic liquid.

If other metal compositions need to be included in the coating by electrophoresis, oxygen is introduced in the form of bubbling oxygen or air into the electrolyte, or by adding oxygen-releasing compounds (eg, dilute hydrogen peroxide). Lower surface electrophoretic coating and reduction of the substrate (eg, indium doped tin oxide glass substrates commonly used in emitter coatings) are prevented.

In practice, it is desirable to introduce a compound capable of releasing oxygen in a suspension or solution, such as hydrogen peroxide, into the electrolyte, because it is uniformly distributed throughout the electrolyte and also free of bubbles to prevent electrodeposition by efficient electrophoresis. Because it happens.

Reduction of oxygen is possible only if a small amount of water is in the organic liquid. Therefore, when hydrogen peroxide is added, it is preferably in the form of water containing hydrogen peroxide. If air or oxygen is used, it needs to be added to the organic liquid in a small amount of water.

In use, the ceramic is electrodeposited on the cathode with metal hydroxide as binder.

The solvent used may be any solvent commonly used, such as isopropanol.

The anode may be formed of an anode metal or a metal alloy, or an anode metal layer or strip which at least partially covers the anode may be formed from a support metal having a higher potential than the anode metal on the support metal. In this case, the anode metal flows into the solution before the support metal. This support may also be a conductive material such as carbon.

As the current flows, the anode metal flows into the solution, and the metal ion neutralized at the cathode is replaced by the ceramic to electrodeposit the metal while forming the metal ion. This keeps the concentration of metal ions in solution at a more constant level, thus producing a coating electrodeposition by more constant electrophoresis. Preferred are systems in which isopropanol is used as the solvent, magnesium nitrate is used as the salt, and metal magnesium is used as the anode.

The concentration of metal salts in the solvent is the same concentration as used in conventional electrophoretic processes.

Example 1 Effect on Indium Doped Tin Oxide Glass Cathode

The luminescent phosphor powder was electrodeposited by electrophoresis on a glass coated with a transparent film of indium doped tin oxide using a standard electrolyte consisting of magnesium nitrate in isopropanol at a potential of 350 volts.

Reduction of the indium doped tin oxide coating with tin without the addition of hydrogen peroxide or other reducing species in the electrolyte resulted in discoloration on the glass during electrophoretic electrodeposition. This adversely affects the transparency of the glass and also affects the quality of the display brightness.

Example 2-Magnesium Anode

An indium doped tin oxide glass substrate was coated with a copper and aluminum doped zinc sulfide (ZnS: Cu, Al) emitter, in which case an additive was added to the standard electrolyte of magnesium nitrate in isopropanol at a potential of 350 volts at the magnesium anode. did not use.

The light-emitting body coated with the glass substrate was irradiated with ultraviolet rays having a wavelength of 366 nm. Photoluminescence measurements appeared similar throughout the glass substrate. The values given in Table 1 are expressed in candelas per square meter and are for the 12 measurement points on the glass substrate, with the mean values given.

Note point Standard electrolyte One 226 2 339 3 268 4 247 5 253 6 208 7 164 8 192 9 206 10 110 11 101 12 135 Average 204

Example 3-Addition of Hydrogen Peroxide

Effect of adding 0.3% hydrogen peroxide in the electrolyte for the photoluminescent ZnX; Cu, Al emitter:

In the absence of hydrogen peroxide, or in the absence of other suitable reducing species, the luminescence decreases when CU ⁺² in the emitter lattice structure is reduced. When hydrogen peroxide was present, there was no decrease in luminescence. When irradiated with UV light at a wavelength of 366 nm, the luminescence of the indium-doped tin oxide sample without discoloration measured at many points was significantly higher than that of the discolored sample.

Experiment result

An indium doped tin oxide glass substrate was coated with a copper and aluminum doped zinc sulfide (ZnS: Cu, Al) emitter, which was added to a standard electrolyte consisting of magnesium nitrate in isopropanol at a potential of 350 volts at the magnesium anode. Was used.

The light-emitting body coated through the glass substrate was irradiated with ultraviolet rays at a wavelength of 366 nm. Photoluminescence measurements appeared similar throughout the glass substrate. The values given in Table 2 are expressed in candelas per square meter and are for the 12 measurement points on the glass substrate, with the mean values given.

Note point A, standard electrolyte B, standard electrolyte + water C, standard electrolyte + 0.3 w / v hydrogen peroxide One 226 381 436 2 339 354 425 3 268 337 446 4 247 364 440 5 253 395 470 6 208 372 445 7 164 368 417 8 192 374 452 9 206 364 436 10 110 368 440 11 101 358 434 12 135 354 430 Average 204 366 439

This is shown graphically in FIG. 1:

A = standard electrolyte (high discoloration of glass substrate)

B = standard electrolyte + water (less discoloration of glass substrate than in A)

C = standard electrolyte + hydrogen peroxide (no discoloration of the glass substrate)

As described above, discoloration of the glass substrate lowers the overall performance of the light emitter.

Since all previous studies on electrolyte electrodeposition have not taken into account the cathode reduction effect of coatings and substrates (indium-doped tinned tin glass), the present invention is directed to electrophoretic coatings, gas sensors, processed ceramics, Oxide powders, composites, fuel cells, field divergent displays, superconducting thin and thick film films, zeolite modified electrode preparation, composite coatings, electrolytes for secondary solid fuel cells, polymer chains, mixed materials for electrodepositing long divergent displays, catalysts Bonding reaction of carrier, silicon carbide and silicon nitride ceramics, fine powder electrodeposition, electrode production of lithium batteries, production of ceramic / ceramic and metal / ceramic composite coatings, layered coatings, bacterial controlled electrodeposition for the production of biofilms, from aqueous emulsions Electrophoretic Electrodeposition, Preparation of Superconducting Tape, Control of Sedimentation Rate, Size of Nanoparticles It is used in a method for producing a ceramic composite composed of cutouts, electrodeposition of clay films, and multicomponents.

Claims (11)

A method for electrodepositing a ceramic by electrophoresis, the method comprising passing a current through a liquid in which the ceramic is suspended, wherein the liquid comprises a solvent in which a metal salt is dissolved, and the anode is the same anode as the metal salt. A method comprising the metal. The method of claim 1, wherein the anode metal is magnesium or aluminum. The method of claim 2, wherein the metal salt is nitrate. The method of claim 1, wherein the anode is formed from an anode metal or an alloy of the anode metal. The anode according to any one of claims 1 to 3, wherein the anode is made of a support metal having a higher potential than the anode metal, wherein a layer or strip of anode metal covering at least partially the anode is present on the support metal. How. 5. The method of claim 1, wherein the solvent is isopropanol, the salt is magnesium nitrate, and the anode contains metal magnesium. The method of claim 1, wherein the liquid contains a compound that releases oxygen. 8. The method of claim 7, wherein the compound is hydrogen peroxide. The method of claim 1, wherein oxygen or air is bubbled through the solvent near the cathode. The method of claim 1, wherein the ceramic is a light emitter. The method of claim 10, wherein the ceramic is a copper doped zinc sulfide emitter and the anode contains copper.