EP1029953A1 - Process for surface treatment and for deposition of polyaniline for absorbing light - Google Patents

Abstract

Deposition of polyaniline layer on titanium comprises electropolymerization after hydrofluoric/nitric acid pickling, chemical conversion treatment and hydrolysis. Preferred Features: A titanium (alloy) substrate may be initially treated by alkaline degreasing for 10-15 minutes at 55-65 degrees C in a bath containing 36-44 g/l sodium tripolyphosphate (Na5P3O10), 40 g/l sodium tetraborate (Na2B4O7.10H2O), 10 ml/l Ref. 631 surfactant and sodium hydroxide to give pH 8.5-9.5 and by abrasive grit blasting to a surface roughness (Ra) of 10-30 mu m. The hydrofluoric/nitric acid pickling is carried out for 2-2.5 minutes at 18-22 degrees C in a bath containing 100-180 ml nitric acid (41 degrees Be), 40-60 ml hydrofluoric acid (48%), 1 g F68 additive, 1.5 g TA6V (metal) and 11 qsp distilled water. The deposit is baked at 40-160 degrees C for 30 minutes to 2 hours.

Description

Field of the invention

The invention lies in the field of devices with an absorbent coating radiation, especially a polyaniline coating absorbing radiation in a band from ultraviolet to infrared. It also concerns a process for preparing the surfaces receiving the deposit.

Prior art

A wide variety of surface treatments or surface coatings with only a low specular reflection and having only a weak reflection diffuse is known. These treatments or coatings are sought in particular for applications optical or infrared. They help ensure that mechanical elements such as optical supports input of optical devices do not reflect or little light and so do not increase the ratio signal / noise of the optical or infrared signal picked up by the detectors of these devices.

Known issues with these coatings and that obviously we're always looking to resolve through process improvements surface treatment and / or coating deposition are indicated for example in column 1 of the patent U.S-A-4 589 972 of May 20, 1986 issued to Martin Marietta. The problems reported in this patent and that we also seek to resolve according to the present invention are cited below.

Regarding black paints, we know they tend to crack or crack detach from particularly metallic substrate, due to stresses induced by cycles especially for infrared systems who often work with sensors cooled to the temperature of helium or liquid nitrogen.

These phenomena worsen with the thickness of the paint layer, this thickness being generally increasing with the wavelength of the radiation that we want to absorb.

Another problem that we encounter is due to the degassing of the coating, in particular when the coated material operates at high altitude or in space. Degassing products can react chemically and damage components microelectronics or to condense on cooled optical surfaces and darken them.

This patent (4,589,972) by Martin Marietta offers, like a previous patent from Martin Marietta n ° 4 111 762 to which reference is made in the patent 4,589,972, to improve the solution to these problems in two ways. These two improvements are applicable to anodisable metals, previously anodized, in particular aluminum and beryllium.

The method provides a surface treatment by a jet of aluminum oxide with a particle size 100 to 200 mesh. This initial processing is intended to create a roughness of the surface before anodizing.

It is indicated at the top of column 7 of this patent, that the increased roughness of the treated surface has a significant effect on absorption and reflectivity of the surface. Specular reflection is reduced and scattering of incident radiation thanks the relief created, multiplies the absorption opportunities.

The importance of the roughness state of the surface has been recognized by most professionals. We will cite as an example additional, Johnson's patents US-A-4,233,107 and US-A-4,361,630 which is a continuation of the first. In the process described in this patent a substrate is first treated with a veneer made in a phosphorous nickel alloy. The surface as well coated is then roughened by means of a bath in an aqueous solution of nitric acid which achieves an acid attack on the deposited plating. It is so obtained a very good absorption in the range from 320 to 2140 nanometers

So we see that it is generally known in the art that a roughening treatment of the surface to be treated, before (case of the Marietta patent) or after (case Johnson patent) coating or other treatment of surface is likely to improve the qualities absorption. However, for each length range wave to be absorbed and for each treatment and also in function of the substrate, the roughening treatment will have to be adapted.

The present invention is under a first aspect directed towards such a roughening treatment.

In a second aspect it is directed towards a method of depositing an absorbent layer of polyaniline, this deposition preferably being carried out after the surface has been roughened beforehand during the laying operations of the polyaniline layer.

The use of polyaniline as an absorbent electromagnetic radiation is in itself known. In this regard, mention will be made of the patents of EPSTEIN and Al No. US-A-5,079,334 and some of its continuations in particular n ° 5 147 968, 5 294 694 and 5,563,182. In these various patents EPSTEIN explains the reasons for the absorbent qualities of polyaniline and possible applications. Patent 5,294,694 claims a wave absorption method electromagnetic by means of a composition of polyaniline. This patent explicitly contemplates in particular the field of ultraviolet to infrared.

This patent only very fleetingly mentions the treatments to be applied to the surfaces to be coated and the removal method. Thus it is indicated column 7, lines 55-63 of any of these patents that aniline can be applied practically by any known method. Among these methods, he cites the electrochemical deposition on substrates conductors.

Thin film deposits are also envisaged in column 8, lines 5-20.

The applicant has carried out experiments in which a polyaniline was used as absorbent coating.

Polyaniline was found to have actually good absorbent qualities, however, the total reflection value remains high in the infrared. Adhesion to the substrate is not good. The tendency to laminate the layer is certain.

These experiments showed that there was a need for deposition of a polyaniline layer absorbing electromagnetic radiation in ranges from ultraviolet to infrared which adheres well to the substrate and has no reflection peak in the infrared range.

Brief description of the invention

For all these purposes, the invention relates to a process for preparing the surface of a substrate intended to receive a polyaniline layer, absorbent in the ultraviolet to infrared, characterized in that the surface of the substrate is roughened before the stages of deposition of the polyaniline layer.

It has been found that the best results from the absorption point of view was obtained when the roughness value of the substrate surface is between 10 and 30 µm. This is the value quadratic mean of the differences between the points the farther from the surface and the more points deep corrected for slow surface ripples known as the roughness Ra. With this roughness initial of the substrate we get a good effect of scattering, especially in the range of 0.25 to 16 µm. In addition, this diffusion promotes absorption.

This Ra value can be obtained by example on a titanium substrate by sandblasting with a abrasive. This can be done with corundum with a particle size between 30 and 120 mesh.

In one embodiment, the sandblasting was made with such a corundum, under a pressure of 6 bars at a distance from the surface to be treated of approximately 20 cm. A double pass was made with a rate 100% recovery.

This initial substrate preparation phase is necessary to decrease or even remove the peak specular reflection in the infrared. The deposit aniline, according to a second aspect of the invention can be carried out after this preparatory phase relating to obtaining the roughness of the substrate surface. It may also not be performed if the value specular absorption or reflection obtained without this roughening treatment are judged sufficient.

• un décapage fluonitrique ;
• un traitement de conversion chimique ;
• une hydrolyse ; et
• un dépôt de polyaniline par électropolymérisation.

According to this second aspect, the invention relates to a process for depositing a layer of polyaniline on a substrate of titanium or of a titanium alloy, characterized in that the operating range of the deposition successively comprises:

• fluonitric stripping;
• chemical conversion treatment;
• hydrolysis; and
• deposition of polyaniline by electropolymerization.

If the substrate is not in perfect condition of cleanliness, it is prudent to plan a stage preliminary cleaning (alkaline degreasing, solvent or mechanical).

An example of realization of a coating of polyaniline on a substrate and a description succinct optical results obtained will be now next to the attached drawings in which :

• figure 1a : avec un grossissement de 40
• figure 1b : avec un grossissement de 400
• figure 1c : avec un grossissement de 2000

FIG. 1 comprises FIGS. 1a, 1b, 1c, these figures represent views by scanning electron microscope of a surface of TA6V alloy coated with a deposit of polyaniline at an inclination of 30 °;

• figure 1a: with a magnification of 40
• figure 1b: with a magnification of 400
• figure 1c: with 2000 magnification

• figure 2a : avec un grossissement de 40
• figure 2b : avec un grossissement de 400
• figure 2c : avec un grossissement de 2000

Figure 2 includes Figures 2a, 2b, 2c. These figures represent views with a scanning electron microscope of a TA6V alloy surface coated with a polyaniline deposit, the surface having been roughened beforehand by sandblasting. (30 ° tilt);

• figure 2a: with a magnification of 40
• figure 2b: with a magnification of 400
• figure 2c: with 2000 magnification

• figure 3 pour de la polyaniline déposée selon le procédé de l'invention sans sablage préalable ;
• figure 4 avec sablage préalable.

FIGS. 3 and 4 represent a curve giving a value of total reflection coefficient for wavelengths ranging from 0.25 to 2.5 μm;

• Figure 3 for polyaniline deposited according to the method of the invention without prior sanding;
• Figure 4 with prior sanding.

Polyaniline deposition was carried out on TA6V type titanium alloys, the different stages of the operating range are as follows:

ALKALINE DEGREASING

• Sodium tripolyphosphate Na ₅ P ₃ O ₁₀ : 40 g / l
• Sodium tetraborate Na ₂ B ₄ O ₇ , 10 H ₂ O: 40 g / l
• Surfactant ref. 631: 10 ml / l
• NaOH soda: pH = 9
• Operating temperature: 60 ° C
• Duration: 10 minutes

FLUONITRIC STRIPPING

• Nitric acid 41 ° Be HNO ₃ : 141 ml
• Hydrofluoric acid (48%) HF: 50 ml
• Additive F 68: 1 g
• TA6V (metal) 1.5 g
• Distilled water qs: 11.
• Operating temperature: 20 ° C
• Duration: 2 mins 15s

CHEMICAL CONVERSION BATHS

• Sodium bifluoride NaFHF: 13 g / 1
• Operating temperature: 20 ° C
• Duration 1 min 45s

HYDROLYSIS

• Demineralized Water
• Operating temperature: 90 ° C
• Duration 15 minutes

ELECTROPOLYMERIZATION

• Liquid aniline 0.1 mole / liter
• Sodium sulfate Na ₂ SO ₄ , 10 H ₂ O: 0.5 M
• Sulfuric acid H ₂ SO ₄ qs pH = 1

The durations, concentrations of products, and types of products which have been used and which are mentioned above, can of course be modified in a way known in the art to obtain the same results. The inventors have not experienced all ranges of usable products and durations needed for treatments but they think has a priori than for example for alkaline degreasing with the same products, the proportions or durations below could be used.

ALKALINE DEGREASING

• Sodium tripolyphosphate Na ₅ P ₃ O ₁₀ : 36 to 44 g / l
• Sodium tetraborate Na ₂ B ₄ O ₇ , 10 H ₂ O: 40 g / l
• Surfactant ref. 631: 10 ml / l
• NaOH soda: pH = 8.5 to 9.5
• Operating temperature: 55 to 65 ° C
• Duration: 10 to 15 minutes

Regarding the fluonitric stripping, the acid proportions could be increased and the duration of the bath decreased, or they could be reduced, the duration of the bath remaining equivalent, but the temperature of the bath being increased.

Again, the durations and proportions could to be :

FLUONITRIC STRIPPING

• Nitric acid 41 ° Be HNO ₃ : 100 to 180 ml
• Hydrofluoric acid (48%) HF: 40 to 60 ml
• Additive F 68: 1 g
• TA6V (metal) 1.5 g
• Distilled water qs: 11.
• Operating temperature: 18 to 22 ° C
• Duration: 2 to 2.5

In the electropolymerization bath, the part to be processed, in the laboratory these were test tubes, is the working electrode of a three cell electrodes (against stainless steel electrode and saturated calomel reference electrode (ECS)). The alloy is polarized at -0.5 V / DHW for 3 min, then then subjected to anodic scanning at the speed of 10 mV / s until the imposed voltage reaches +2 V / DHW. The scanning is then stopped, but the polarization maintained for 20 minutes.

The indicated voltages are measured between the calomel reference electrode and the job.

After electropolymerization, the test pieces can be steamed at a temperature between 40 ° and 160 ° for a period of between 30 min and 2 hours, for example 1 hour at 160 ° C.

• qu'après un simple décapage fluonitrique, la polyaniline électropolymérisée n'adhère pas à la surface de l'alliage de titane,
• que le traitement de conversion chimique favorise l'adhérence de la polyaniline, mais la répartition de la couche est hétérogène,
• que le traitement d'hydrolyse est indispensable à la réalisation d'un film adhérent et homogène.

Each step of the preparation range is important, polyaniline polymerization tests were carried out after each of these steps. It was highlighted:

• that after a simple fluonitric pickling, the electropolymerized polyaniline does not adhere to the surface of the titanium alloy,
• that the chemical conversion treatment promotes the adhesion of the polyaniline, but the distribution of the layer is heterogeneous,
• that the hydrolysis treatment is essential for the production of an adherent and homogeneous film.

The NaFHF conversion treatment leaves the surface of the alloy a small amount of fluorine than the hydrolysis treatment makes it possible to decrease but not to totally eliminate. This hydrolysis treatment seems favor the speed of formation of the deposit of polyaniline. The induction time is shorter and the quantity deposited after a given holding time more important.

In order to simplify the operating range, additional electropolymerization tests were performed on TA6V test pieces beforehand anodized in sulfuric medium. It was not possible to make an adherent polymer film.

Optical characterization tests of treated test pieces showed good absorption characteristics and low reflection specular. However, there was still a peak specular for wavelengths of 10.6 µm.

In order to remove this peak, the roughness of the surface of the titanium alloy was changed by sandblasting.

This sanding carried out prior to the steps The aim of polyaniline deposition is to to obtain a surface roughness Ra of between 10 and 30 µm.

The results obtained in terms of appearance are shown in Figures 1 and 2.

Hemispheric reflection coefficients on the one hand, the curves represented Figures 3 and 4 and, on the other hand, Annexes 1 and 2 which give the values of the reflection coefficients corresponding to curves 3 and 4 respectively.

These curves correspond to lengths incident waves between 0.25 and 2.5 µm.

For the wavelengths corresponding to infrared and far infrared (up to 20 μm), very low levels have been measured, in particular on the roughness test pieces. For example at 10.6 µm a reflection coefficient of 0.03 for a 25 ° direction and 0.06 for a 60 ° direction. ANNEX 1 Average reflection: 4% Nm R 250 0.03 300 0.03 350 0.03 400 0.03 450 0.03 500 0.03 550 0.03 600 0.03 650 0.03 700 0.03 750 0.03 800 0.03 850 0.04 900 0.04 950 0.04 1000 0.04 1050 0.04 1100 0.04 1150 0.04 1200 0.04 1250 0.04 1300 0.04 1350 0.04 1400 0.04 1450 0.04 1500 0.04 1550 0.04 1600 0.04 1650 0.04 1700 0.04 1750 0.04 1800 0.04 1850 0.04 1900 0.04 1950 0.04 2000 0.04 2050 0.04 2100 0.04 2150 0.04 2200 0.04 2250 0.04 2300 0.04 2350 0.04 2400 0.04 2450 0.04 2500 0.05 APPENDIX 2 Average reflection: 2% Nm R 250 0.01 300 0.01 350 0.01 400 0.01 450 0.01 500 0.01 550 0.01 600 0.01 650 0.01 700 0.01 750 0.02 800 0.02 850 0.02 900 0.02 950 0.02 1000 0.02 1050 0.02 1100 0.02 1150 0.02 1200 0.02 1250 0.02 1300 0.02 1350 0.02 1400 0.01 1450 0.01 1500 0.02 1550 0.02 1600 0.02 1650 0.02 1700 0.02 1750 0.02 1800 0.02 1850 0.02 1900 0.02 1950 0.02 2000 0.02 2050 0.02 2100 0.02 2150 0.02 2200 0.02 2250 0.02 2300 0.03 2350 0.02 2400 0.02 2450 0.02 2500 0.02

Claims (9)

Process for depositing a layer of polyaniline on a titanium or titanium alloy substrate, characterized in that the operating range of the deposition successively comprises: fluonitric stripping; chemical conversion treatment; hydrolysis; and deposition of polyaniline by electropolymerization. Method according to claim 1, characterized in that the fluonitric pickling is carried out in a bath, the ingredients and proportions of which are defined by the quantities below: Nitric acid 41 ° Be HNO ₃ : 100 to 180 ml Hydrofluoric acid (48%) HF: 40 to 60 ml Additive F 68: 1 g TA6V (metal) 1.5 g Distilled water gsp: 11 for a time between 2 and 2.5 minutes and an operating temperature between 18 and 22 ° C. Method for depositing a polyaniline layer on a titanium or titanium alloy substrate, according to one of claims 1 or 2, characterized in what the operating range of the depot includes a step preliminary cleaning. Method according to claim 3, characterized in that the preliminary cleaning step is a alkaline degreasing. Process according to Claim 4, characterized in that the proportions and ingredients of the degreasing are defined by the following quantities: Sodium tripolyphosphate Na ₅ P ₃ O ₁₀ : 36 to 44 g / l Sodium tetraborate Na ₂ B ₄ O ₇ , 10 H ₂ O: 40 g / l Surfactant Ref. 631: 10 ml / 1 NaOH soda: pH = 8.5 to 9.5 for a period between 10 and 15 minutes and an operating temperature between 55 and 65 ° C. Method for depositing a polyaniline layer on a titanium or titanium alloy substrate, according to one of claims 1 to 5, characterized in that that the operating range of the depot includes a step steaming terminal at a temperature between 40 and 160 ° C for a period of between 30 minutes and 2 hours. Method for depositing a polyaniline layer on a titanium or titanium alloy substrate, according to one of claims 1 to 6, characterized in that that the operating range of the depot includes a step of roughness of the surface prior to pickling fluonitric. Deposition method according to claim 7, characterized in that the roughness at the end of the roughness is between 10 and 30 µm. Deposition method according to claim 7 or 8, characterized in that the roughness is obtained by sandblasting with an abrasive powder under conditions which allow to obtain a roughness Ra of 10 to 30 µm.

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