Short-chain carboxylic acid modified alumina for use as coatings and method for making same - Patents.com

Abstract

The present invention provides a method for producing modified alumina for use in coating compositions, the method comprising hydrothermally treating an alumina suspension under specified conditions before and / or after the addition of an organic modifier. The present invention further provides modified alumina produced according to the method of the present invention and uses of the modified alumina in coating applications, including corrosion protection compositions and adhesive coatings.

Description

Cross-reference to related applications

[0001] This application claims priority to U.S. Patent Application No. 62 / 987,616, filed March 10, 2020, the disclosure of which is incorporated herein by reference for all purposes. [Technical Field]

[0002] FIELD OF THE INVENTION The present invention relates generally to coating compositions. More particularly, the present invention relates to a method for preparing modified alumina compositions, modified alumina compositions, and the use of modified alumina compositions as coatings, especially in corrosion protection and adhesion applications. [Background technology]

[0003] Background of the Invention The protection of surfaces from corrosion is well known and widely practiced. Protection of metal surfaces from corrosion is generally achieved, among other things, by the application of inhibitors to the metal, by the addition of passive alloy elements, and by the application of protective coatings. For the protection of metal surfaces from corrosion, the microstructure of the corrosion-protected material is an important property.

[0004] In the corrosion protection of metal surfaces, modification of the metal microstructure is a practically applied method. For example, the behavior of nanocrystalline nickel (8-28 nm) produced by electrodeposition compared to coarse-grained nickel has been studied and reported in (Non-Patent Document 1, the disclosure of which is incorporated herein by reference for all purposes). It was found that nanocrystalline nickel is more susceptible to corrosion due to imperfections in the film produced by electrodeposition.

[0005] Sol-gel coating methods are often applied to products with complex geometries. Most research in this field uses organic corrosion inhibitors starting from solutions of metal or alkoxide precursors. Sol-gel processes proceed via the hydrolysis and condensation of the precursors. During condensation, a gel forms. Aging accelerates the condensation reaction, which ultimately leads to the formation of thicker film coatings. However, film coatings often have numerous defects. Any weakness in the film coating can become a starting point for corrosion. Typically, organic compounds are embedded in the gel. If the gel weakly interacts with the organic compounds, the bond between the gel and the organic compounds may not be stable against weathering corrosion. Furthermore, while the presence of large amounts of organic compounds leads to the formation of thicker film coatings (which function better as corrosion barriers), high organic compound concentrations can reduce the adhesion of the gel to the substrate, thus adversely affecting the corrosion protection performance of the film coating. The corrosion protection performance of a film coating can also be affected by the reversibility of the precursor's hydrolysis reaction. For example, water penetration can compromise the integrity of the organic layer, reducing corrosion protection performance.

[0006] Various methods have been proposed for incorporating corrosion inhibitors, such as phosphonic acid and 2-mercaptobenzimidazole (MBI), into sol-gel film coatings. However, a problem associated with these corrosion inhibitors is the difficulty of achieving an optimal balance between concentration and solubility. On the one hand, high solubility can limit long-term corrosion protection performance due to potential leaching from the substrate, while on the other hand, low solubility can result in poor corrosion protection performance due to low concentrations of corrosion inhibitor present. This challenge has been addressed, for example, by the use of organic inhibitors that are released by a change in pH, thereby inhibiting corrosion. However, without a pH change, there is no pH-triggered release of the organic corrosion inhibitor, and therefore corrosion protection performance is ineffective even with organic inhibitors. Maybe not.

[0007] Dip and spin coating methods are commonly used for applying corrosion inhibitors. Spin coating can provide thin films, for example, by centrifugal force, but has the obvious drawback that the shape of the substrate strongly influences the ability to effectively coat the substrate. Dip coating is often the most convenient method for irregularly shaped objects or objects with complex shapes. It is generally well understood in the art that the coating method used must be capable of covering the entire surface to be protected with the corrosion inhibitor. Spray and electrodeposition are also widely practiced, although the effectiveness of spray dispersion has not been well documented.

[0008] Patent Document 1, the disclosure of which is incorporated herein by reference for all purposes, is directed to a corrosion inhibitor comprising particles of an inorganic oxide selected from the group consisting of silica and alumina, with corrosion-inhibiting metal cations chemically bonded to the surface of the particles. Patent Document 1 reports the ion exchange of alumina with calcium hydroxide and describes a paint formulation using the exchanged silica.

[0009] Patent Document 2, the disclosure of which is incorporated herein by reference for all purposes, discloses a corrosion inhibitor composition comprising alumina trihydrate Al(OH)3 having a particle size of less than 20 μm, another oxide in an amount of 10-100 parts by weight, and calcium and / or magnesium carbonate in an amount of 0-40 parts by weight.

[0010] Patent Document 3, the disclosure of which is incorporated herein by reference for all purposes, describes a corrosion inhibitor that selectively adsorbs to a metal surface and creates a barrier that prevents access of corrosive agents to the surface. It states that a nanostructured support, such as alumina, can be used to deliver the corrosion inhibitor, but the use of alumina is not exemplified.

[0011] Patent Document 4, the disclosure of which is incorporated herein by reference for all purposes, is directed to composite inorganic particles and methods for their manufacture and use. Although the use of metal oxides as corrosion inhibitors is mentioned, only the use of silica is exemplified.

[0012] Clearly, there are drawbacks associated with corrosion inhibitors and coating methods: the performance of a corrosion inhibitor is highly dependent on the corrosion inhibitor itself (e.g., method of manufacture) and the effectiveness of the coating method used to apply the inhibitor to the substrate.

[0013] Against this backdrop of problems associated with corrosion inhibitors and coating methods in the art, the present inventors have discovered nanocrystalline coatings in the form of organically modified boehmite compositions that exhibit favorable corrosion protection properties. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] U.S. Patent No. 4,419,137 [Patent Document 2] International Publication No. 86 / 07371 Brochure [Patent Document 3] International Publication No. 2012 / 050984 Brochure [Patent Document 4] International Publication No. 2011 / 081874 Brochure [Non-patent literature]

[0015] [Non-Patent Document 1] “Effect of nanocrystalline grain size on the electrochemical and corrosion behavior of nickel”,Corrosion Science 46(12):3019-3029 Summary of the Invention

[0016] Summary of the invention Throughout this application, when discussing ranges, the use of the term "between" is intended to include the ends of the range, for example, between 3 nm and 5 nm includes 3 nm and 5 nm.

[0017] According to a first aspect of the present invention, there is provided a method for producing a modified alumina, said method comprising: i) providing an alumina suspension comprising alumina and water, wherein the alumina suspension is optionally hydrothermally treated at a temperature between 20°C and 90°C for a time period between 0.5 hours 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 between 20°C and 90°C for a time between 0.5 hours and 5 hours to form a hydrothermally treated modified alumina suspension; and iv) drying the hydrothermally treated modified alumina suspension to form modified alumina; Includes stages.

[0018] The method may include the further step of heating the alumina suspension prior to the addition of the organic modifier. In such a case, the alumina suspension is heated to a temperature of less than 90°C, preferably 85°C, and for a time period preferably between 1 and 2 hours. The time and temperature are independently selected.

[0019] The alumina can be aluminum oxide, aluminum oxide hydroxide, or a mixture thereof. The alumina is preferably aluminum oxide hydroxide. The aluminum oxide hydroxide is preferably boehmite. Boehmite can be produced from the Ziegler process using aluminum alkoxide as a feed material. Alternatively, boehmite can be produced by precipitation.

[0020] The boehmite can have cubic, plate- or needle-like crystallite morphology. Preferably, the boehmite has plate- or needle-like crystallite morphology.

[0021] Boehmite crystals can have an aspect ratio ranging from about 1.1 to 6.0, preferably from 1.5 to 6.0, where the aspect ratio is the ratio of the crystal's length in the (002) plane to the crystal's width in the (020) plane, as measured by conventional x-ray diffraction (XRD). The aspect ratio is measured by X-ray diffraction (XRD), a common method used in the art. The Scherrer equation can be used to calculate the aspect ratio from the crystallite size, as determined in a direction perpendicular to the plane of the X-ray diffraction pattern. The Scherrer equation allows for the calculation of crystallite size by analyzing the diffraction peaks and using peak broadening.

[0022] The boehmite crystals have a crystallite size between 2 nm and 200 nm on the (020) plane, preferably between 3 nm and 5 nm on the (020) plane, and most preferably about 3.5 nm to 5.0 nm on the (020) plane, as measured using XRD.

[0023] The boehmite crystals further have i) crystallites greater than 1, preferably between 1.0 and 3.2 ( ii) a crystallite (002) / (020) ratio greater than 3.0, preferably between 3.0 and 4.0; and iii) a crystallite (200) / (002) aspect ratio of 0.5 to 1.5. These crystallite ratios are also measured using XRD.

[0024] The alumina suspension can include aluminum oxide, aluminum oxide hydroxide, or a mixture thereof, and at least water. Preferably, the alumina suspension includes aluminum oxide hydroxide and at least water. Even more preferably, the alumina suspension includes boehmite and at least water. The percentage of solids in the alumina suspension is between 2% and 30% by weight, preferably between 2% and 12% by weight. The alumina suspension can be provided at an initial or starting pH in the range of about 8 to about 10, for example, about 9.

[0025] The method of the present invention comprises hydrothermal treatment of a modified alumina suspension, and optionally hydrothermal treatment of an alumina suspension together with said hydrothermal treatment. The hydrothermal treatment is preferably carried out at a temperature above 25°C, more preferably above 30°C, more preferably above 60°C. Preferably, the hydrothermal treatment is carried out at a temperature below 85°C. The hydrothermal treatment is preferably carried out at a temperature between 30°C and 85°C, more preferably between 60°C and 85°C. The hydrothermal treatment is preferably carried out for a time period between 1 hour and 3 hours.

[0026] Preferably, only the modified alumina suspension is hydrothermally treated.

[0027] The inventors have found that the temperature of the hydrothermal treatment, and in particular the temperature of the hydrothermal treatment of the modified alumina suspension, is important for the production of the modified alumina of the present invention. As shown by Comparative Example 3, if the hydrothermal conditions are not followed, the modified alumina will not be useful for coating applications, including corrosion protection applications.

[0028] The organic modifier may contain a carboxyl group and thus may be a carboxylic acid with or without an amino group, an acrylic modifier, a high molecular weight amine, an organic compound with a quaternized ammonium group (e.g., a quaternized ammonium salt), a quaternized alkyl, a quaternized pyridine, a surfactant such as an ethoxylate, a silane, an aminosilane, an amino acid, or a bifunctional amino acid.

[0029] The organic modifier preferably contains a carboxyl group, an amino acid, or a bifunctional amino acid.

[0030] When the organic modifier contains a carboxyl group, i.e., a carboxylic acid, the carboxylic acid can be a hydrophobic carboxylic acid. The carboxylic acid can be a short-chain carboxylic acid having a carbon chain length of between 6 and 10, preferably between 6 and 9, and most preferably between 8, a medium-chain carboxylic acid having a carbon chain length of between 11 and 17, or a long-chain carboxylic acid having a carbon chain length of between 18 and 30. The carbon chain of the carboxylic acid can be linear or branched. Preferably, the organic modifier is a short-chain carboxylic acid. Even more preferably, the organic modifier is a linear short-chain carboxylic acid. Most preferably, the organic modifier is a C8 linear carboxylic acid, i.e., octanoic acid.

[0031] When the organic modifier is an amino acid or a bifunctional amino acid, the amino acid is preferably a hydrophobic amino acid such as alanine, leucine, or a mixture thereof. The bifunctional amino acid is preferably cysteine, taurine, thiourea, or a mixture thereof.

[0032] When the organic modifier is a carboxylic acid, and particularly when the organic modifier is octanoic acid, the organic modifier is preferably added to the alumina in the range of 12 to 25 wt. %, most preferably in the range of 20 to 23 wt. %, calculated as Al2O3 of the total alumina.

[0033] The method preferably includes monitoring and adjusting the pH of the alumina suspension or hydrothermally treated alumina suspension when the organic modifier is added to the alumina suspension or hydrothermally treated alumina suspension to form the modified alumina suspension. Using a pH meter, the pH of the alumina suspension or hydrothermally treated alumina suspension can be controlled to be within the range of about 2 to about 9, preferably within the range of about 4 to about 6. If necessary, the pH of the alumina suspension or hydrothermally treated alumina suspension when the organic modifier is added can be adjusted by adding a base. The base is preferably ammonia or a derivative thereof, including, but not limited to, aqueous ammonia, urea, hydrazine, hydroxylamine, or hexamethylenetetramine, or an alkali metal hydroxide and / or alkaline earth metal hydroxide, with ammonia and its derivatives being more preferred.

[0034] Drying of the hydrothermally treated modified alumina suspension to form the modified alumina can be by spray drying, contact drying, vacuum / mixer drying, spin flash drying, etc. These methods are known to those skilled in the art.

[0035] The modified alumina preferably comprises a platelet crystallite morphology. The crystallite size of the modified alumina preferably ranges from 2 nm, preferably 2.5 nm to about 200 nm, preferably between 3 nm and 5 nm. Without wishing to be bound by theory, the inventors believe that the temperature of the hydrothermal treatment claimed in the present invention limits the extent of crystal growth, resulting in a modified alumina having crystallites within the preferred range.

[0036] The modified alumina preferably has a carbon content in the range of 3 to 10% by weight, more preferably 5 to 8% by weight.

[0037] The modified alumina is preferably 250 to 300 m 2 / g, more preferably 270 to 290 m 2 / g, the BET surface area is measured after heat treating the modified alumina at 550°C for 3 hours in air.

[0038] The modified alumina is preferably modified boehmite. The crystallite size of the modified boehmite on the (120) plane is preferably 2 nm, preferably 2.5 nm to about 200 nm, preferably between 3 nm and 5 nm. The modified boehmite preferably has i) an aspect ratio on the (200) / (020) plane between 1.0 and 6.0, preferably between 1.0 and 3.2, and more preferably between 2.5 and 3.2; ii) an aspect ratio on the (002) / (020) plane between 1.1 and 6.0, preferably greater than 3, and most preferably between 3.0 and 4.0; and iii) an aspect ratio on the (120) / (020) plane between 1 and 2, preferably between 1.10 and 1.40. The aspect ratios are measured using XRD.

[0039] The geometric relationship between the crystallite sizes of the (020), (200), and (002) planes can be used to describe some aspects of the crystal morphology. Modified boehmite crystals are preferably longer in the (002) plane than in the (200) plane, and shorter in the (020) plane than in any other axis. The preferred (020) size is from about 3 nm to about 5 nm.

[0040] It has been found that the modified alumina can be used in a variety of applications including coating applications, particularly adhesive coating applications, including corrosion protection compositions and primer formulations (eg, bridge, automotive, etc.).

[0041] According to a second aspect of the present invention, there is provided a modified alumina produced according to the method of the present invention.

[0042] According to a third aspect of the present invention: i) crystallite size on the (120) plane ranging from 2 nm to 200 nm; and ii) Aspect ratio on the (120) / (020) plane between 1 and 2 The present invention provides a modified alumina which is a modified boehmite having the formula:

[0043] Modified boehmite is: i) aspect ratio on the (200) / (020) plane between 1.0 and 6.0; ii) Aspect ratio on the (002) / (020) plane between 1.1 and 6.0 can have:

[0044] The aspect ratio is measured using XRD.

[0045] The modified boehmite preferably has a carbon content in the range of 3 to 10% by weight, more preferably 5 to 8% by weight.

[0046] The modified boehmite is preferably 250 to 300 m 2 / g, more preferably 270 to 290 m 2 / g, the BET surface area is measured after heat treating the modified alumina at 550°C for 3 hours in air.

[0047] The crystallite size of the modified boehmite on the (120) plane preferably ranges from 2.5 nm to about 200 nm, preferably between 3 nm and 5 nm. The modified boehmite preferably has i) an aspect ratio on the (200) / (020) plane between 1.0 and 3.2, and more preferably between 2.5 and 3.2, ii) an aspect ratio on the (002) / (020) plane greater than 3, and most preferably between 3.0 and 4.0; and iii) an aspect ratio on the (120) / (020) plane between 1.10 and 1.40. The aspect ratios are measured using XRD.

[0048] The modified boehmite crystals are preferably longer in the (002) direction than in the (200) direction and shorter in the (020) direction than in any other direction. The preferred (020) size is from about 3 nm to about 5 nm.

[0049] The modified aluminas of the present invention are used in coating applications including corrosion protection compositions and primer formulations.

[0050] The modified alumina of the present invention may be dispersible in a mildly polar solvent, such as isopropanol. Alternatively or additionally, the modified alumina may be dispersible in a mildly hydrophobic ether, such as propylene glycol methyl ether acetate (PGMEA). The modified alumina may also be dispersible in water-based or solvent-borne paints. The modified alumina may be dispersible in a mixture of a water-miscible ether and water, such as a mixture of ethylene glycol butyl ether (EGBE) and water.

[0051] Conventional methods such as stirring or wet milling can be used to disperse the modified alumina of the present invention.

[0052] According to a fourth aspect of the present invention there is provided a coating composition comprising the modified alumina of the present invention and a dispersant.

[0053] The dispersant can be a crosslinker or a coating.

[0054] Crosslinkers may include acrylic esters, methacrylic esters, acrylates, methacrylates (including trimethylpropane trimethacrylate (TMPTMA) and trimethylpropane triacrylate (TMPTA)), epoxy acrylates, and urethane acrylates. The crosslinker is preferably a methacrylate and most preferably TMPTMA.

[0055] The paint can be a water-based or non-water-based solvent-based paint.

[0056] The coating compositions can be used in anticorrosion applications, paints, coatings, low molecular weight polymers such as alkyds, polyepoxides, polyurethanes, acrylics, thermoplastics and elastomeric resins.

[0057] In corrosion protection applications, the coating compositions advantageously inhibit corrosion of metals such as hot and cold rolled mild steel and carbon steel, copper and aluminum, among others, in moist environments.

[0058] The modified alumina compositions obtained by the method of the present invention can also be used in the preparation of nanocoatings to be used in various technological applications. These coatings can exhibit the unique property of having acid centers dispersed over a large surface area, and can host highly dispersed catalytic centers with various functions. These properties are highly desirable for improving catalytic activity. Further applications include the use of resistant coatings in catalytic reactors or industrial processes for energy conservation, to improve heat transfer between liquid or gas surfaces, to control or modify thermal expansion, and in abrasives, optical and electronic applications, and semiconductors. [Example]

[0059] The invention will now be illustrated by reference to the following non-limiting examples and with reference to the figures in which: FIG. 1 shows the plate of Comparative Example 1 and the plate of Example 1 after corrosion testing; FIG. 2 shows the plate of Comparative Example 2 after corrosion testing; and FIG. 3 shows the plate of Comparative Example 3 after corrosion testing.

[0060] Example 1: Preparation of modified alumina compositions according to the present invention: A suspension (2000 g of slurry) containing Ziegler-derived boehmite and water was heated (178.6 g of 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 2 hours under reflux in a round-bottom flask. The modified boehmite suspension obtained after hydrothermal treatment was diluted with deionized water (3000 g). No pH adjustment was performed. The modified boehmite suspension was dried in a standard spray dryer to form modified alumina.

[0061] The starting boehmite had a plate-like shape and a size from the X-ray (020) reflection of about 3.4 nm and a size from the (120) reflection of about 4.3 nm.

[0062] The modified boehmite had a platelet shape with an X-ray (020) reflection size of about 3.7 nm and an X-ray (120) reflection size of about 4.7 nm. 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) of about 3.4.

[0063] Plate coating: 0.2 g of the anticorrosion composition containing the modified alumina prepared as described above was added to 40 g of isopropyl alcohol (IPA) and stirred using a magnetic stirrer for between 5 and 10 minutes to form an anticorrosion suspension.

[0064] A modified alumina corrosion composition was coated onto a stainless steel plate approximately 4 cm x 15 cm in size. The plate was prepared by cleaning with at least 25 ml of methyl ethyl ketone (MEK) as a degreasing solvent, followed by air drying.

[0065] The anticorrosion suspension was spray coated onto the test plate using a 10 ml spray bottle. The spray bottle had a spray head with a small opening to create a mist of the anticorrosion composition in a nitrogen stream flowing through a nozzle, thereby forming a wet film on the test plate. The spray coating process was repeated two or three times, using between 20 ml and 30 ml of anticorrosion suspension to coat the plate. The spray-coated test plate was air-dried for approximately 10 minutes and then heat-treated at 150°C under a nitrogen atmosphere for 1 hour.

[0066] The coating on the test plate was transparent, which indicates that the anticorrosion composition can thinly and uniformly coat the substrate with nano-sized particles.

[0067] Comparative Example 1: A control plate that was only washed with MEK and air-dried but not coated with the anticorrosion suspension was also heat-treated under the same conditions (150° C. for 1 hour under nitrogen atmosphere).

[0068] The corrosion resistance of the two plates from Example 1 and Comparative Example 1 was determined according to the method described below:

[0069] Corrosion Testing Corrosion testing of Example 1 and Comparative Example 1 was performed using a Precision Stainless Steel Water Bath Chamber Model 183 by subjecting each plate to a water vapor environment within the water bath chamber. Both plates were placed in the chamber, which was set to 60°C, and left for at least 5 hours.

[0070] FIG. 1 shows that no rust formed on the plate of Example 1 coated with the anticorrosion composition of the present invention, while the plate of Comparative Example 1 clearly showed rust formation.

[0071] The inventors have noticed that the contact angle of deionized water on the corroded surface is lower than on the non-corroded surface.

[0072] Contact angles were measured using a deionized "DI" water droplet on the sample surface using a Kruess DSA 25 instrument. A droplet of DI water was dispensed onto the sample surface. A video image of the droplet was analyzed, and the contact angle was measured as the angle between the droplet's outline and a line representing the surface (baseline).

[0073] The contact angle test conditions were as follows: ●Droplet method Young-Laplace fitting method Automatic baseline 8.0μL drop volume 60 seconds measurement time / 1 frame per second ●Measurement temperature 20-21℃ (room temperature) Use a steel plate as the solid measurement surface and DI water as the test liquid.

[0074] The water contact angle is taken as the average of three water drops. Data from contact angle measurements using water as the probe solvent are shown in Table 1.

[0075] [Table 1]

[0076] The water contact angle of Example 1, which can indicate corrosion resistance, was just above 80°, and it showed no change after the surface was exposed to the steam test despite the thin coating. This indicates that the surface of Example 1 was not corroded in a humid atmosphere. On the other hand, the contact angle of Comparative Example 1 decreased from 55 to 32°, indicating that significant corrosion occurred.

[0077] Comparative Example 2: Comparative Example 2 shows the technical effect of the present invention when compared to the prior art document, US Pat. No. 4,419,137, i.e., modification with Ca2+ etc.

[0078] 100 g of boehmite powder was vigorously stirred in 400 mL of DI water, and the pH of the mixture was 6.75. Calcium hydroxide was then slowly added until the pH reached 12. Once the pH was stable at a value of 12 + / - 0.01 for 1 hour, no further addition of calcium hydroxide was made. The resulting mixture was filtered and washed. The resulting material was then ground after dilution with water. The product exhibited a calcium content of 4.7 wt. %. The particle size of the resulting product was less than 30 μm before drying.

[0079] A stainless steel plate of approximately 4 cm x 15 cm was coated with the sample obtained using the method of Comparative Example 2 using the same method as used for Example 1, including the same steps of degreasing, drying, spray coating, dry coating and heat treatment.

[0080] The resulting plates were subjected to corrosion testing according to the method described for Example 1. Figure 2 shows that rust formed on the sample coated plates obtained using the method of Comparative Example 2. Contact angles were measured using the method described for Example 1 and are reported in Table 2.

[0081] [Table 2]

[0082] Comparative Example 3: This comparative example demonstrates the importance of the hydrothermal treatment conditions for the present invention and its use in corrosion protection compositions when compared to the modified alumina exemplified in applicants' application U.S. Patent No. 2020 / 0056049, the disclosure of which is incorporated herein by reference for all purposes.

[0083] The product obtained according to the method described in Example 1 of US Patent Publication No. 2020 / 0056049 (Hydrophobic surface-modified alumina and its manufacturing method) was coated onto a steel plate according to the method of Example 1.

[0084] A starting boehmite slurry having a block shape was first prepared according to the method described in US 2020 / 005649. An amount of an organic composition, in this case octanoic acid, was then added to the stirred vessel containing the boehmite slurry at 105°C for 2 hours to form an acid-modified slurry, which was spray-dried to give ellipsoidal crystallites.

[0085] FIG. 3 shows that rust formed, whereas the plate of Example 1 clearly showed no rust formation.

[0086] This shows the importance of the hydrothermal treatment.

[0087] Example 2: Example 2 demonstrates the dispersibility of the modified alumina of the present invention. Neat modified boehmite prepared according to Example 1 was mixed with a 50:50 by weight mixture of ethylene glycol butyl ether (EGBE) and deionized water using a stir bar for 30 minutes. A 5 wt. % sol of modified alumina in a 50:50 EGBE:water mixture prepared in this manner was found to be stable for more than a week with only slight settling occurring.

[0088] Example 3: Example 3 demonstrates the dispersibility of the modified alumina of the present invention, showing the particle size and zeta potential distribution in a solvent when wet milling is used.

[0089] A Netzsch mill was used to wet-mill 5 wt. % of the modified boehmite produced according to Example 1 in isopropyl alcohol (IPA). The following milling conditions were used: Zeta bead plus 0.5-0.6mm Ittori Um stabilization Pump speed = 125 rpm Agitator speed = 1200 rpm Grinding time = 1 hour Screen size = 0.2 mm

[0090] The milled product showed a very good dispersion of alumina in IPA, which remained stable for at least 10 days, with no visible settling of the alumina particles.

[0091] The particle size and zeta potential distribution of the milled product showed a nanoparticle size distribution, while the zeta potential measurement showed a wide zeta potential distribution (-80 to 100 mV). A high zeta potential indicates a stable dispersion.

[0092] A corrosion test was carried out using the ground product according to a method similar to that shown in Example 1. No corrosion spots were observed. [Brief explanation of the drawings]

[0093] [Figure 1] 4 shows a plate of Comparative Example 1 and a plate of Example 1 after corrosion testing. [Figure 2] 1 shows the plate of Comparative Example 2 after corrosion testing. [Figure 3] 4 shows a plate of Comparative Example 3 after corrosion testing.

Claims

1. A modified alumina which is a modified boehmite modified with an organic modifier, Modified boehmite is i) crystallite size on the (120) plane ranging from 2 nm to 200 nm; ii) an aspect ratio on the (120) / (020) plane between 1 and 2; iii) an aspect ratio on the (200) / (020) plane between 1.0 and 6.0; and iv) an aspect ratio on the (002) / (020) plane between 3.0 and 4.0; and v) a carbon content in the range of 3 to 10% by weight having Modified alumina.

2. i) providing an alumina suspension containing boehmite having a crystallite size on the (020) plane between 2 nm and 5 nm and water; ii) adding to the alumina suspension an organic modifier which is a short chain carboxylic acid having a carbon chain length of less than 10 and at least 6 to form a modified alumina suspension; iii) hydrothermally treating the modified alumina suspension at a temperature between 20°C and 85°C for a time 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 modified alumina; 10. A method for producing the modified alumina of claim 1, comprising the steps:

3. 3. The method of claim 2, wherein the alumina suspension is hydrothermally treated at a temperature between 20°C and 90°C for a time between 0.5 and 5 hours prior to adding the organic modifier to form a hydrothermally treated alumina suspension, wherein the organic modifier is added to the hydrothermally treated alumina suspension to form a modified alumina suspension.

4. 4. The method of claim 2 or 3, wherein the modified alumina suspension is hydrothermally treated at a temperature between 30°C and 85°C.

5. 5. A method according to any one of claims 1 to 4, wherein the modified alumina suspension is hydrothermally treated for a time period between 1 hour and 3 hours.

6. A coating composition comprising the modified alumina of any one of claims 1 to 5 and a dispersant.

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