The hull below the waterline of the ship is immersed in seawater for a long time, and it is not only corroded by seawater, but also adhered by various marine organisms (such as shellfish, seaweed, seaweed, etc.) and other dirt, which causes the hull to be fouled.
The fouling and its influence are mainly manifested in two aspects: first, the adhesion of the hull and the propeller increases the resistance of the hull, which increases the frictional resistance of the ship by 0.25% to 5% per day, resulting in a decrease in speed, an increase in fuel consumption, and a weakening in flexibility. Secondly, marine organisms adhere to the seawater pipe, causing the pipe to be blocked, and the corrosion of the shell is accelerated, causing serious harm.
Titanium alloy has good seawater corrosion resistance, but it is easy to grow sea creatures on the surface of the alloy in seawater. According to research, lime worms, algae and a small amount of oysters grow most inside the titanium alloy cylinder, so long-term use of titanium alloy pipes may cause pipe blockages. However, after removing the marine organisms, there are no corrosion pits left at the attachment, indicating that marine organisms and microorganisms will not cause corrosion to the titanium alloy. Therefore, the seawater antifouling measures for titanium alloy pipes only need to consider how to prevent marine organisms from adhering to the surface of the titanium alloy. There are many ways to prevent marine organisms from attaching, such as: painting antifouling paint, adding poisonous materials to seawater, electrolytic antifouling, and physical methods such as filtration, scorching, and ultrasonic waves.
1. Antifouling technology of titanium and titanium alloys
As an excellent ship material, titanium and titanium alloys have the following characteristics:
(1) Low density, light weight, good toughness and brittle fracture resistance while having high specific strength; (2) Titanium has better properties than other commonly used metals in neutral and oxidizing atmospheres and many harsh environments. Much higher corrosion resistance. It has good corrosion resistance in the marine atmosphere of long-term high temperature, high humidity and seawater splashing; (3) At the same time, it also has low magnetic properties, good sound transmission performance, shock and vibration resistance, heat and low temperature resistance, and good processing performance. Excellent overall performance.
Titanium alloy marine structural parts have been used in the marine environment for a long time, and sea creatures can grow on their surface, but the sea creatures attached to the surface can be removed, and no corrosion pits remain after removal. The sea creatures that attach and grow on the surface of titanium materials are mainly barnacles, oysters, lime worms and algae, and their growth has a certain regularity. Bright and free-flowing seawater conditions are suitable for the growth of marine organisms. Marine organisms are easy to grow on the outer surface, and the inner surface, the farther away from the port, and the smaller the area of the port, the smaller the number of marine organisms growing. Under the conditions of darkness and poor seawater circulation, sea creatures are not easy to attach and grow. The seawater flow rate has an impact on the growth and attachment of marine organisms, and it is difficult to grow and attach if the flow rate is large.
Protective measures such as anti-fouling paint and electrolytic copper are used to prevent marine contamination.
while developing marine resources. Preventing marine fouling has become an urgent problem to be solved. There are more than a dozen methods commonly used to prevent marine fouling organisms from attaching: such as painting anti-fouling paint, adding poisons to seawater, electrolyzing seawater to generate hypohydrogenate, Electrolytic heavy metal method (electrolytic copper, aluminum anode anti-fouling and anti-corrosion and electrolytic hydrogen. Copper, aluminum anti-fouling and anti-corrosion method), mechanical removal method, filtration method, heating method, sealing method or ozone method and ultrasonic anti-fouling method.
1. Applied potential anti-fouling method
The applied potential antifouling method is an electrochemical antifouling method being developed in Japan by applying a certain potential (eg. I.OV) to an electrode titanium nitride (TiN ), an antifouling method that kills marine microorganisms through direct electrochemical reactions between cells and electrodes. Japan has studied the sputtering TiN coating on the titanium substrate in seawater, and the experiment of applying 8V potential and maintaining it for 30 minutes shows that it can kill 98.7% of the microorganisms attached to the electrode, and the change and generation of pH value are observed. Chlorine phenomenon. Tests on fishing nets have confirmed that this will be a promising antifouling method for ship hulls.
2. Low surface energy antifouling coatings
The surface energy of the coating determines the adhesion strength of marine organisms on its surface. The lower the surface energy of the coating, the more difficult it is for organisms to adhere. Even if there is adhesion, the adhesion strength is not large. When the ship coated with the low surface energy coating starts at a certain speed Time. Sea creatures attached to its surface will automatically fall off. Low surface energy antifouling coatings are non-toxic and have a long validity period, and are an important direction to replace toxic antifouling coatings.
When the surface energy of the coating is lower than 2.5×10-4N/m, that is, the contact angle between the coating and the liquid is greater than 98. Only when it has anti-fouling effect. According to Lindner's test results, barnacles can be prevented from sticking only when the surface energy of the coating is lower than 1.2x10-4N/m.
The main component of the low surface energy antifouling coating is a system composed of organic silicon or organic fluorine low surface energy resin as the base material, together with a crosslinking agent, a low surface energy additive and other auxiliaries. There are many patents for low surface energy antifouling coatings at home and abroad. According to the different base materials, the currently developed low surface energy coatings can be divided into 4 types:
Silicone low surface energy antifouling coatings, including two types based on silicone rubber and silicone resin; organic fluorine low surface energy coatings, including high fluorine content fluorinated polyurethane antifouling coatings and low fluorine content antifouling coatings Coatings; Silicon-fluororesin low surface energy antifouling coatings; other resin low surface energy antifouling coatings, such as low surface energy antifouling coatings based on chlorosulfonated polyethylene.
The U.S. Naval Research Laboratory successfully developed and applied for a patent for silicone elastic low surface energy antifouling paint. At present, low surface energy antifouling coatings have been reported in real ships for 5 years.
Low surface energy antifouling coatings have not been widely used in the US Navy, mainly due to three factors:
One is the high cost; the second is that the construction requirements are very strict. The third is that it is easily damaged, and the defects at the damaged place are easily fouled by marine organisms and are not easy to repair.
3. Conductive coating antifouling coating
The conductive coating antifouling technology is a relatively advanced environmental protection antifouling technology, which does not pollute the seawater environment.
The principle is on the steel plate of the hull that is in contact with the sea water. The insulating coating film is applied first, and then the conductive coating film is applied thereon. Using this coating as an anode, if a tiny electric current is passed through, the seawater will be electrolyzed on its surface. The polar surface of the conductive coating is covered with hypochlorite ions, which can prevent the adhesion of microorganisms, algae, shellfish and other marine organisms. Japan has begun to apply it to ship anti-fouling, and my country has been conducting research on conductive polymer anti-fouling coatings since 1991, and some progress has also been made. Conductive coatings to improve electrical conductivity and resistance to seawater electrolysis still need to continue to be studied.
4. Natural bionic antifouling coating
(1) Natural synthetic antifouling paint
Using the anti-fouling mechanism of marine animals, plants and microorganisms, natural products (natural biological anti-fouling agents) with anti-fouling activity are extracted and separated from marine organisms, and natural synthetic anti-fouling coatings are prepared by self-polishing and other technologies. The research on natural antifouling agents is the key to synthesizing natural antifouling coatings. As of 1993, 52 antifouling active substances have been found in marine organisms. antifouling agent;
(2) Bionic paint
Most organisms living in the ocean can resist the attachment of marine organisms, especially large mammals such as dolphins, whales, etc. Their epidermis can secrete special mucus, forming a hydrophilic low surface energy surface, making it difficult for marine organisms to attach , According to the research on the mechanism of these large mammals preventing biological adhesion, non-toxic biomimetic anti-target coatings can be developed.
5. Electrochemical antifouling method
The electrochemical antifouling method is a method that uses the electrochemical principle to generate antifouling products to achieve the purpose of antifouling.
Electrochemical antifouling methods mainly include electrolysis of seawater to produce chlorine antifouling method, electrolytic Cu-Al/Cu-Fe anode antifouling and antifouling method, and chlorine-copper and aluminum combined antifouling and antifouling method.
6. Micro-arc oxidation nano antifouling coating on titanium alloy surface
Nanometer antifouling ceramic coatings were successfully prepared on the surface of Ti-6Al-3Nb-2Zr alloy by micro-arc oxidation technology. The thickness of the anti-fouling coating can reach more than 20μm, the coating is composed of amorphous and 20-50mn nanocrystalline TiO 2 and Cu 2 O, the bonding strength of the film base reaches 50MPa, the insulation and wear resistance of the coating are good, and the anti-fouling performance is obtained. Significant improvement, only a small amount of marine organisms adhered to the surface of the coating after 6 months of hanging, while the bare titanium alloy sample was completely adhered by marine organisms after 3 months, the coating has a certain ability to prevent the adhesion of marine organisms .
Different from electroplating, thermal spraying, self-propagating high-temperature synthesis, etc., microarc oxidation (MAO) does not introduce ceramic materials from the outside, but directly on the surface of the base metal / in-situ (In-Situ) 0 oxidation and sintering to obtain oxides The ceramic layer overcomes the shortcomings of the ceramic membrane layer, such as poor compactness and weak bonding force with the substrate.
2. Status Quo of Titanium and Titanium Alloy Antifouling Technology at Home and Abroad
Status of foreign titanium and titanium alloy anti-fouling technology In the application of foreign anti-fouling coating technology, anti-fouling agent-releasing anti-fouling paint dominates the market, and Wuxi self-polishing anti-fouling paint has become the leading anti-fouling product for ocean-going and deep-sea ships; controllable dissolution As the market supplement of Wuxi self-polishing antifouling paint, the type antifouling paint is mainly used in the coating protection of offshore ships; the low surface energy antifouling paint has entered the market, with the continuous development and maturity of its technology, and people's concern for environmental protection And the growing concern of energy consumption and other issues, its market application?
has shown an expanding trend.
After nearly 30 years of development, hydration, hydrolysis, and hybrid non-self-polishing antifouling paints have been applied to Shiyang in foreign countries, and their antifouling periods are 3 years, 5 years, and 3-5 years, respectively. Major multinational companies have a series of Wuxi self-polishing antifouling paint products to meet the antifouling protection of various ocean-going ships. However, for naval ships, due to their low voyage rate and long berthing time, marine organisms are more likely to adhere when berthing in ports. Generally, the antifouling agent output rate of Wuxi self-polishing antifouling paint cannot meet the antifouling requirements.
Dissolving antifouling coating. The release rate of cuprous oxide and auxiliary antifouling agent is ensured by the slow dissolution of the soluble resin in the slightly alkaline environment of seawater. As the oxidized copper on the surface oozes out, micropores filled with seawater will be left, so that the cuprous oxide and antifouling agent inside the coating will continue to decompose and ooze out, and the surface roughness of the coating will continue to increase. It applies to ships that have been suspended for more than 2 consecutive weeks or whose speed is lower than 12 knots.
Low surface energy antifouling coatings, also known as fouling release antifouling coatings. International Coatings is the first to market Intersleek 700 silicone elastomer fouling release antifouling coating for use on high voyage boats between 15-30 knots HempasilX-3 Silicone Hydraulic Coatings Adhesive antifouling paint for ships over 8 knots. South Korea's KCC also has A/F 100 silicone rubber coatings on the market. In 2007, AkzoNobel launched the Intersleek900 fluoropolymer fouling-removing antifouling paint, which expanded the application field of its fouling-removing antifouling paint to ships with more than 10 knots.
With the arrival of the complete ban on the use of organotin self-polishing antifouling coatings in 2008, and the growing voice of global environmental protection, the development of high-efficiency non-toxic or low-toxic environmental protection antifouling coatings has a bright future. Among them, low surface energy antifouling coatings is one of the most attractive options.
Experiments have found that when the coating is in contact with seawater > 98. That is to say, when the surface energy is less than 25mJ/m 2, the coating surface has anti-fouling effect, but at the same time, due to the complex diversity of marine organisms, it is impossible for the same coating to meet different surface energy requirements at the same time, such as Barnacles are most easily adhered to surfaces with a surface energy of 30-35mJ/m 2 , and moss are most easily attached to surfaces with a surface energy of 10-30mJ/m 2 , and simple low-surface-energy coatings can often only make marine organisms adhere. prison, need to be cleaned regularly. In addition, once the attached organisms grow up, it will be difficult to remove, and it is easy to damage the lacquer during the cleaning process.
This has resulted in a long period of research on low surface energy antifouling coatings. In order to further enhance the antifouling performance of the coating, the combination of natural antifouling agents and low surface energy antifouling coatings is one of the first choices for environmentally friendly antifouling coatings. On the basis of previous research work, bactericidal nano-TiO2 and small molecular silicone oil with antifouling effect are used as antifouling active substances, which are used in combination with low surface energy antifouling coatings in order to achieve better environmental protection and antifouling effect.
The new product IntersmoothEcoloflex tin-free self-polishing antifouling coating developed by International Paint and Nippon Paint Marine Coatings Co., Ltd. is a high-performance tin-free antifouling coating that has been proven to replace TBT, and can provide good antifouling performance during its life. .
Sigma has recently developed an antifouling coating called Sigmaseal that does not contain biocides and is a low surface energy coating that relies on poor adhesion and seawater flow to avoid marine biofouling.
The United States has developed a nanostructured paint for ships that uses nanopatterns of the widely used traditional aluminum-titanium ceramic hybrid material, applied by a thermal spray process. This ultra-fine-structured material has unprecedented material properties and is widely used to prevent different types of corrosion, wear, and rust.
Japan has used conductive coatings to prevent marine organisms from adhering to seawater cooling pipes, which proves that there is no pollution to the marine environment. Application on seaside power station.
The conductive antifouling paint developed by the Nagasaki Research Institute of Mitsubishi Heavy Industries in Japan in the late 1980s has been tested on 40-ton, 100-ton and 200-ton boat hulls. After more than 1 year of tests, it shows that the anti-fouling effect is good, and then the anti-fouling test on the hull of large oil tankers is carried out. Recently, Japan has conducted a 2-year and 4-month test on the cooling seawater pipeline of the coastal power station, and the anti-fouling effect is good. The anode technology combining conductive coating film and titanium foil is used, and the anti-fouling period can reach 4 years. At the same time, the anti-fouling principle of the conductive coating film is theoretically explained, and it is believed that it will not cause pollution to the marine environment, and it is an effective new technology to prevent marine biological fouling.
Titanium oxide paint is non-toxic and harmless, has strong penetration resistance, high surface finish, water and oil amphiphilicity, corrosion resistance, antifouling, wear resistance, and good mechanical strength. Makes it a very promising foreign-type antifouling paint. It can be used in various parts of ships, offshore buildings, etc. As the TiO2 superhydrophilic surface-modified solid moves underwater, its frictional resistance can be reduced by 10%-15%. This means that under the same power, the sailing speed of ships and boats can be increased by 10% per hour. Therefore, as an antifouling paint for ships, it can not only prevent marine foulants from adhering, but also improve the sailing speed of ships. This new type of marine paint will soon be accepted and can save a lot of economic costs.
