Alumina Modified With a Short Chain Carboxylic Acid for Use as a Coating and a Method for Producing the Same

Abstract

The invention provides for a method of producing a modified alumina for use in a coating composition, the method being characterised by hydrothermally treating an alumina suspension under specific conditions before and/or after adding an organic modifier. The invention further provides for a modified alumina made according to the method of the invention and to uses of the modified alumina in coating applications including anti-corrosive compositions and adhesive coatings.

Claims

1. A method of producing a modified alumina, the method comprising the steps of: i) providing an alumina suspension comprising alumina and water, the alumina suspension optionally being hydrothermally treated at a temperature of between 20° C. and 90° C. for a period of between 0.5 and 5 hours to form a hydrothermally treated alumina suspension; ii) adding an organic modifier to the alumina suspension or the hydrothermally treated alumina suspension to form a modified alumina suspension; iii) hydrothermally treating the modified alumina suspension at a temperature of between 20° C. and 85° C. for a period of between 0.5 and 5 hours to form a hydrothermally treated modified alumina suspension; and iv) drying the hydrothermally treated modified alumina suspension to form the modified alumina.

2. The method of claim 1 in which the alumina is boehmite.

3. The method of claim 2 in which the boehmite have crystallite sizes on the (020) plane of between 2 nm and 200 nm.

4. The method of claim 1 in which the modified alumina suspension is hydrothermally treated at a temperature of between 30° C. and 85° C.

5. The method of claim 1 in which the modified alumina suspension is hydrothermally treated for a period of between 1 and 3 hours.

6. The method of claim 1 in which the organic modifier is a carboxylic acid.

7. The method of claim 6 in which the carboxylic acid is a short chain carboxylic acid having a carbon chain length of less than 10 and at least 6.

8. A modified alumina prepared according to the method of claim 1.

9. A modified alumina which is a modified boehmite having: i) a crystallite size on the (120) plane ranging from 2 nm to 200 nm; ii) an aspect ratio on the (120)/(020) plane of between 1 and 2; iii) an aspect ratio on the (200)/(020) plane of between 1.0 and 6.0; iv) an aspect ratio on the (002)/(020) plane of between 3.0 and 6.0; and v) a carbon content in the range of 3 to 10 mass%.

10. A coating composition including the modified alumina of claim 8 and a dispersant.

11. A coating composition including the modified alumina of claim 9 and a dispersant.

Description

EXAMPLES

[0065] The invention will now be exemplified with reference to the following non-limiting examples and with reference to the Figures in which:

[0066] FIG. 1 shows the plate of Comparative Example 1 and the plate of Example 1 after corrosion testing;

[0067] FIG. 2 shows the plate of Comparative Example 2 after corrosion testing; and

[0068] FIG. 3 shows the plate of Comparative Example 3 after corrosion testing.

Example 1

Preparation of Modified Alumina Composition as Per the Present Invention

[0069] A suspension including Ziegler-derived boehmite and water (2000 g of slurry) was heated, 178.6 g boehmite and the remainder water An organic modifier, in this case octanoic acid (33 g), was added and the suspension was hydrothermally treated at 80° C. for 2h in a round bottom flask, under reflux. The modified boehmite suspension obtained after the hydrothermal treatment was diluted with deionized water (3000 g). No adjustment of pH was made. The modified boehmite suspension was dried in a standard spray dryer to form a modified alumina.

[0070] The starting boehmite had a platelet-like shape with size from the X-ray (020) reflex of about 3.4 nm, and a size of about 4.3 nm (120) reflex.

[0071] The modified boehmite had a platelet-like shape with size from the X-ray (020) reflex of about 3.7 nm, and a size of about 4.7 nm (120) reflex. The crystallite morphology was platelet-elongated in length, with an aspect ratio 200/020 (width: thickness) of about 2.7 and an aspect ratio 002/020 (length : thickness ratio) of about 3.4.

Coating of Plates

[0072] 0.2 g of an anti-corrosion composition comprising the modified alumina prepared as above was added to 40 g of isopropyl alcohol (IPA) and stirred for between 5 and 10 minutes with a magnetic stirrer to form an anticorrosive suspension.

[0073] A stainless steel plate of approximately 4 cm x 15 cm was coated with the modified alumina corrosion composition. The plate was prepared by washing with at least 25 ml methylethylketone (MEK) as a degreasing solvent, and then air drying.

[0074] The anticorrosive suspension was spray coated onto the test plate using a 10ml spray bottle. The spray bottle had a spray head with a small opening in order to create a mist of the anti-corrosion composition in a stream of nitrogen flowing through the nozzle, thereby to form a wet film on the test plate. The spray coating process was repeated 2 or 3 times, such that between 20 ml and 30 ml of the anti-corrosive suspension was used to coat the plate. The spray coated test plate was air dried for about 10 minutes and subsequently thermally treated at 150° C. for 1h under a nitrogen atmosphere.

[0075] The coating on the test plate was transparent, which demonstrates the ability of the anti-corrosion composition to coat the substrate thinly and uniformly with nano-sized particles.

Comparative Example 1

[0076] A control plate washed only with MEK and air dried, but not coated with the anticorrosive suspension was also thermally treated under the same conditions (150° C. for 1h under a nitrogen atmosphere).

[0077] Corrosion resistance of the two plates from Example 1 and Comparative Example 1 were determined according to the method described below:

Corrosion Testing

[0078] Corrosion testing of Example 1 and Comparative Example 1 was performed by subjecting each plate to a water vapor environment inside a water bath chamber, using a Precision stainless steel water bath chamber Model 183. Both plates were placed inside the chamber which was set at 60° C. and left for a period of at least 5 hours.

[0079] FIG. 1 shows that no rust was formed on the plate of Example 1 coated with the anti-corrosion composition of the invention, whereas the Comparative Example 1 plate clearly showed rust formation.

[0080] The inventors noticed that contact angles of deionized water on corroded surfaces is lower than on non-corroded surfaces.

[0081] A Krüss DSA 25 apparatus was used to measure contact angles using deionized “DI” water droplets on sample surfaces. A drop of DI water was dispensed on the sample surface. A video image of the drop was analyzed and the contact angle was measured as the angle between the drop’s contour and the line representing the surface (baseline).

[0082] The Contact angle test conditions were as follows: [0083] Sessile drop method [0084] Young LaPlace fitting method [0085] Automatic baseline [0086] 8.0 .Math.L drop volume [0087] Measurement time of 60 seconds/ 1 frames per second [0088] Measurement temperature 20 - 21° C. (room temperature) [0089] Steel plate used as solid measurement surface and DI water test liquid

[0090] The water contact angle was taken as the average of three water droplets. Data from the contact angle measurements using water as a probe solvent is shown in Table 1.

TABLE-US-00001 Contact angle measurements Stainless Steel Plate Contact Angle (before corrosion testing) Contact Angle (after corrosion testing) Comparative Example 1 55 32 Example 1 85 94

[0091] The water contact angle of Example 1 that was able to display corrosion resistance properties was just above an angle of 80 and it did not show any change after the surface was exposed to a steam test, despite the thin coating. This is indicative that the surface of Example 1 has not corroded in a wet atmosphere. On the other hand, the contact angle of Comparative Example 1 dropped from 55 to 32, indicating that considerable corrosion had taken place.

Comparative Example 2

[0092] Comparative Example 2 demonstrates the technical effect of the present invention when compared with prior art document US 4,419,137 i.e. modification with Ca2+ etc.

[0093] 100 g of boehmite powder was vigorously stirred in 400 mL of DI water, the pH of the mixture was 6.75. Calcium hydroxide was then added slowly until the pH reached 12. Once the pH was stable for 1 hour at the value of 12 +/- 0.01 no further addition of calcium hydroxide was carried out. The resultant mixture was filtered and washed. The resulting material was then milled after dilution with water. The product showed an amount of calcium of 4.7%wt. The resulting particle size of the product, before drying, was below 30 .Math.m.

[0094] A stainless steel plate of approximately 4 cm x 15 cm was coated with the sample obtained using the procedure of Comparative Example 2, using the same method as was used for Example 1, including the same steps of degreasing, drying, spray coating, dry coating and thermal treatment.

[0095] Corrosion testing of the resulting plate was performed according to the procedure described for Example 1. FIG. 2 shows that rust was formed on the plate coated with the sample obtained using the procedure of Comparative Example 2. Contact angles were measured using the procedure described for Example 1 and are reported in Table 2.

TABLE-US-00002 Contact angle measurements, Comparative Example Stainless Steel Plate Contact Angle (before corrosion testing) Contact Angle (after corrosion testing) Comparative Example 2 55 24 (area 1 — significantly corroded) 43 (area 2 — less corroded)

Comparative Example 3

[0096] This Comparative Example shows the importance of hydrothermal treatment conditions for the present invention and its use in anti-corrosive compositions as compared with the modified alumina exemplified in the Applicants application US2020/0056049, incorporated herein by reference for all purposes.

[0097] A product, obtained according to the procedure described in the Example 1 of US2020/0056049 (Hydrophobic Surface Modified Aluminas and Method for Making Thereof), was coated on a steel plate according to the procedure of Example 1.

[0098] According to the procedure described in US2020/005649, a starting boehmite slurry which has a block-like shape is first prepared. An amount of organic composition, in this case octanoic acid, is then added to the stirred vessel with the boehmite slurry at 105° C. for 2 hours to form an acidic modified slurry that is spray dried to give oblong crystallites.

[0099] FIG. 3 shows that rust was formed, whereas the Example 1 plate clearly showed no rust formation.

[0100] This shows the importance of the hydrothermal treatment.

Example 2

[0101] Example 2 demonstrates the dispersibility of the modified alumina of the invention. As is modified boehmite prepared in accordance with example 1 was mixed with a 50:50 by mass mixture of ethylene glycol butyl ether (EGBE) and deionized water for 30 minutes using a stir bar. It was found that a 5 mass% sol of modified alumina in a 50:50 EGBE:water mixture prepared in this manner was stable for more than a week with only slight sedimentation taking place.

Example 3

[0102] Example 3 demonstrates the dispersibility of the modified alumina of the invention and to illustrate particle size and zeta potential distribution in the solvent when using wet milling.

[0103] A Netzsch mill was used to wet mill 5 wt. % of the modified boehmite prepared in accordance with example 1 in isopropyl alcohol (IPA). The following milling conditions were used: [0104] Zeta bead plus 0.5 -0.6 mm Yittrium stabilized [0105] Pump speed = 125 rpm [0106] Agitator speed = 1200 rpm [0107] Milling time = 1 hour [0108] Screen size = 0.2 mm

[0109] The milled product exhibited very good dispersion of alumina in IPA that stayed stable for at least 10 days. No sedimentation of alumina particles was visually observed.

[0110] Particle size and zeta potential distributions of the milled product exhibited nano-particle size distributions, while measuring the zeta potentials showed a broad zeta potential distribution (-80 to 100 mV). The high zeta potential is indicative of a stable dispersion.

[0111] A corrosion test was performed using the milled product following an approach similar to that set out in example 1. No corrosion spots were observed.