Coated Titanium Anode
1. Substrate: Titanium
Titanium is a metallic element, gray, with atomic number 22 and relative atomic mass 47.867. Can burn in nitrogen, high melting point. Passive titanium and titanium-based alloys are new structural materials, mainly used in the aerospace industry and the marine industry. Because titanium has the characteristics of high melting point, small specific gravity, high specific strength, good toughness, fatigue resistance, acid and alkali corrosion resistance, low thermal conductivity, good high and low temperature tolerance, and low stress under rapid cooling and rapid heating conditions, its commercial value is in In the 1950s, it was recognized by people and used in high-tech fields such as aviation and aerospace. With the continuous promotion to chemical, petroleum, electric power, desalination, construction, daily necessities and other industries, titanium metal is increasingly valued by people, known as modern metal, smart metal, strategic metal, and is indispensable to improve the level of national defense equipment. important strategic material.
1. Physical properties, pure metal titanium is silvery white. Compared with other metal materials, the characteristics of titanium are as follows:
①The melting point is as high as 1660 degrees.
② Titanium has a close-packed hexagonal lattice at room temperature (below 885 degrees), and a body-centered cubic lattice when it is higher than 885 degrees, and the volume increases by 5.5%.
③The density of titanium is about 4.51g/cm3, which is about 60% of that of stainless steel, more than that of aluminum, and about 60% larger than that of aluminum.
④Although the tensile strength of pure titanium is 350-700MPa, the general titanium alloy can reach 700-1200MPa, or even 1400MPa. Therefore, the specific strength of titanium alloys (that is, the ratio of strength to density) is greater than that of any other material at present.
⑤The specific heat, thermal conductivity and resistivity of titanium are at the same level as those of stainless steel, but the expansion coefficient of titanium is 50% smaller than that of steel. Titanium has poor thermal conductivity and poor electrical conductivity, similar to stainless steel.
⑥The Young's modulus of titanium is smaller than that of stainless steel, and it can bend under lower stress.
⑦Follow stable creep characteristics in the temperature range of 200 to 300 °C.
2. Chemical properties
①Acid with acid At room temperature, titanium is not easy to react with inorganic acid, but it can react after heating.
②Reaction with alkali Titanium reacts very slowly with ordinary alkali solutions and does not react with dilute alkali solutions.
③ Interaction with non-metals In general, titanium is not very active, but at high temperatures, titanium can directly form very stable, hard and insoluble interstitial compounds with many non-metallic elements.
4. An important characteristic of gettering titanium is that it can strongly absorb gases (oxygen, nitrogen, hydrogen). The role of titanium and oxygen and nitrogen is irreversible, so titanium is a good getter. The hydrogen absorbed in titanium can be discharged from the metal when it is heated to 800-900 degrees in a vacuum.
5. Machinability The ratio of strength to density of titanium is higher than that of iron and aluminum. It is 1 times stronger than pure iron and 5 times stronger than pure aluminum.
2. Titanium Electrode Titanium anode is called titanium-based metal oxide coated titanium anode (MMO). Also called DSA anode (dimensionally stable anode). It uses titanium as the substrate, and brushes the noble metal coating on the titanium substrate, so that it has good electrocatalytic activity and electrical conductivity. Compared with pristine graphite anodes and lead anodes, titanium electrodes have the following advantages:
1. The electrode size is relatively stable, and the distance between the electrodes will not change during the electrolysis process, ensuring that the electrolysis operation is carried out under the condition that the cell voltage is stable;
2. High catalytic activity and low working voltage;
3. The working voltage is low, so the power consumption is small, and the DC power consumption can be reduced by 10%---20%;
4. The working life of the titanium anode is long. The metal anode in the chlorine gas production by the diaphragm method is resistant to corrosion by chlorine and alkali. The life of the anode has reached more than 5~7 months, while the graphite anode is only 8 months;
5. It can overcome the dissolution problem of graphite anode and lead anode, avoid the pollution of electrolyte and cathode products, thus greatly improving the purity of metal products;
6. It can improve the current density and increase the electrolysis efficiency;
7. The oxides of noble metals iridium and ruthenium have oxidation resistance, so titanium electrodes have strong corrosion resistance;
8. It can avoid the short circuit problem after the deformation of the lead anode, so as to improve the efficiency of the current;
9. Titanium electrodes are light in weight, which can reduce labor intensity compared with graphite anodes and lead anodes;
10. The shape and manufacture of the titanium matrix are easier, and it can be high-precision;
11. Under the premise of no damage, the substrate can be tried repeatedly;
Titanium anode classification:
1. Distinguish according to the gas evolved from the anode in the electrochemical reaction. The chlorine-evolving anode is called chlorine-evolving anode, such as ruthenium-coated titanium electrode: the oxygen-evolving anode is called oxygen-evolving anode, such as iridium-coated titanium electrode and platinum titanium mesh. /plate. Chlorine evolution anode (ruthenium-coated titanium electrode): The chloride ion content in the electrolyte is high, generally in the environment of hydrochloric acid, electrolysis of seawater, and electrolysis of salt water. The corresponding products of our company are ruthenium iridium titanium anode and ruthenium iridium tin titanium anode.
2. Oxygen evolution anode (iridium-coated titanium electrode): The electrolyte is generally a sulfuric acid environment. The corresponding products of our company are iridium tantalum anode, iridium tantalum tin titanium anode, high iridium titanium anode.
3. Platinum-coated anode: titanium is the base material. The surface is coated with platinum, the thickness of the coating is generally 0.5-5μm, and the mesh size of the platinum titanium mesh is generally 12.5×4.5mm or 6×3.5mm.
3. Introduction to the production process
1. Select TA1 grade titanium substrate, and make sure that the surface of the substrate is smooth and smooth, without scratches, peeling, cracking, delamination and other defects.
2. Machining the selected titanium substrate to the specifications and dimensions required by customers.
3. The titanium substrate is annealed and leveled at a temperature of 600°C.
4. During the annealing and leveling treatment, a dense titanium oxide layer will be formed on the surface of the titanium substrate, which will be polished mechanically to make the surface of the titanium metal luster.
5. The titanium substrate is acid-washed and etched with 10% oxalic acid for 10 hours in a slightly boiling state, so that the surface oxide layer is etched into a titanium hydride surface.
6. Carry out reasonable qualitative and quantitative configuration of precious metal solution according to the anode environment used by customers.
7. Check that the acid-washed titanium substrate is qualified, that is, the surface layer is a gray and uniform pockmarked surface structure, and then artificially coated, sintered at a suitable temperature, and cooled naturally after sintering, and the second coating is carried out when it is cooled to room temperature. Apply, and so on, until more than 18 to 22 times the configuration solution is applied.
8. After the sintering of the above processed parts is completed, the life test test is carried out with the furnace test piece, and the test is qualified and packaged for delivery.
Fourth, the main application areas
1. Electrolytic production of sodium hypochlorite in chlor-alkali industry and chlorate industry
The chemical industry that extracts chlorine, hydrogen and caustic soda by means of electrolysis of salt solution is called the chlor-alkali industry, which is the largest sector in the modern electrochemical industry and occupies an important position in the national economy. In addition to the above, downstream products such as hydrogen chloride, sodium hypochlorite, chlorite, polyvinyl chloride (referred to as PVC Polyvinyl chloride polymer = PVC molecular structure), hydrogen peroxide, etc. can also be prepared. In the production of chlor-alkali, pure saturated brine is used as the electrolytic solution, titanium electrode is used as the anode, and asbestos wool with iron mesh is used as the cathode. The anode chamber produces chlorine gas, and the cathode chamber produces hydrogen and sodium hydroxide. in production. The application of titanium anode has greatly promoted the development of the chlor-alkali industry and is an epoch-making contribution to the field of electrochemistry. The electrode has high catalytic activity for chlorine evolution, good electrocatalytic activity, mechanical stability and chemical stability for chlorine evolution reaction. It is an irreplaceable electrode material in today's chlor-alkali industry, with a service life of more than five years.
2. Electrolyzed functional water
Functional water is defined as water that can obtain various useful functions through artificial treatment. Electrolyzed water is popular as a sterilization treatment technology with good sterilization effect, strong practicability and no secondary pollution. The functional water is produced by electrolyzing drinking water or a trace amount of salt water through titanium electrodes, which is widely used in electrolysis water machines.
①Using electrolysis to generate hypochlorite, new ecological oxygen, hydroxyl radicals and other strong oxidizing substances to kill microorganisms.
②Using the electrolytic electrode to directly act on the microorganism to make it die.
③Alkaline ionized water can directly treat a variety of diseases, effectively improve the metabolic function of the human body, eliminate free radicals of harmful acidic metabolites, and enhance physical fitness to prevent and improve disease resistance.
④Acid ionized water has the functions of inhibiting bacterial growth, disinfection and astringency.
3. Sodium hypochlorite generator, chlorine dioxide generator electrode manufacturing.
The electrolysis temperature of sodium hypochlorite should be maintained below 40°C. If the temperature is too high, NaClO will decompose, reducing the solubility of Cl2, which is not conducive to the generation of NaClO. The solution is alkaline, and the anode O2 increases, reducing the current efficiency of chlorine evolution. The electrode distance is selected from 3 to 10mm, and the reduction of the electrode distance can reduce the tank pressure and power consumption. The current density is 13~20A/dm2 when using the coated titanium electrode. The power consumption of sodium hypochlorite generator is generally about 3.7~7kW·h/kg.
The chlorine dioxide generator uses a diaphragm electrolytic cell to electrolyze the sodium chloride solution to generate a mixed gas including chlorine dioxide, which is dissolved in water to form a sterilization and disinfection liquid. The molecular formula of sodium hypochlorite is ClO2, which is easily soluble in water, decomposes in water, and easily reacts with water. The solubility in water is 5-8 times that of chlorine. Dissolved in alkaline solution to generate chlorite and chlorate.
4. Cathodic protection
Due to the use of steel in the ocean, hull, bridge and other environments, due to the corrosion effect of impurities in the steel and micro-battery, and the complex natural environment, although corrosion-resistant alloy steel is selected and the thickness of the material is increased to coat high-quality corrosion-resistant paint, but The corrosion of these structures is still very serious, which greatly threatens the safety of production, and cathodic protection is a convenient and important measure to effectively protect the permanent steel structures in the ocean.
①Using an applied current to make the entire surface of the protected metal structure become a cathode, which is called impressed current cathodic protection.
②Connect a metal or alloy with a more negative potential to the metal equipment to be protected, called sacrificial anode protection.
Applied to the following areas:
1) In fresh water and sea water, prevent corrosion of ships, docks, platforms, gates and cooling equipment.
2) In alkali and salt solutions, prevent the corrosion of storage tanks, evaporation tanks, boiling alkali pots, etc.
3) Prevent corrosion of pipelines and cables in soil and sea mud.
5. Gold-plated, steel galvanized and tin-plated
Titanium electrodes have excellent electrical conductivity and corrosion resistance, and their service life is much higher than that of lead anodes. They can work stably for more than 4,000 hours and have low costs. It will be an inevitable trend in the development of electro-galvanizing and tin production at home and abroad. Titanium electrodes are currently used in Japan, the United States, Germany, and China, which not only greatly saves the energy consumption of electroplating, but also creates conditions for the production of thick galvanized and tin steel plates because it can increase the current density of electroplating.
6. Non-ferrous metal extraction
Electrolytic metallurgy occupies a large proportion in the hydrometallurgy industry. The non-ferrous metals produced by electrolytic metallurgy include Zn, Cd, Cu, Mn, Co, Ni, Cr, etc.
The advantage of electrolytic metallurgy is that it has high selectivity, can obtain high-purity metals, and can recover useful metals. Therefore, it can process low-grade minerals and polymetallic ores with complex components, which is beneficial to the comprehensive utilization of resources. In addition, the pollution to the environment is small, and the production is easier to be continuous and automated. Coated titanium electrodes have been widely used in the field of electrolytic extraction of metals in recent years, and it has become the second industrial field to use titanium electrodes on a large scale.
7. Electrolytic copper foil
With the development of science and technology, the degree of automation is increasing day by day, which has promoted the rapid development of the electronics industry. The application of large-scale integrated circuits has increased the demand for copper foil in the electronics and instrumentation industry, and the quality requirements of copper foil are also getting higher and higher. According to the thickness, it can be divided into 105µm, 70µm, 35µm, 18µm, 12µm, 9µm and 5µm, among which copper foil below 12µm is generally called ultra-thin copper foil. The electrolytic copper foil uses a metal roller partially immersed in a copper sulfate solution that rotates continuously as the cathode, and the foil is produced by continuous electrolysis. Internationally, the production of copper foil is mainly controlled by Japan, and there are about 15 domestic production enterprises with a production capacity of about 35,000 tons.
8. Sewage treatment
With the rapid development of industry and agriculture and population growth, the amount of sewage discharged by humans has increased sharply, resulting in many waters suffering from different degrees of pollution. Electrochemical treatment of sewage is divided into direct electrolysis and indirect electrolysis.
①Direct electrolysis means that pollutants are directly oxidized or reduced on the electrode to be removed from the wastewater. Direct electrolysis can be divided into cathodic process and anodic process. The anode process refers to the oxidation of pollutants on the anode surface and the conversion into less toxic substances or easily biodegradable substances, and even the inorganicization of organic matter, so as to achieve the purpose of reducing pollution. The cathode process refers to the reduction of pollutants on the cathode surface to remove them. Mainly used for reductive dehalogenation of halogenated hydrocarbons and recovery of heavy metals.
②Indirect electrolysis refers to the use of electrochemically generated redox substances as reactants or catalysts to convert pollutants into less toxic substances. Indirect electrolysis can be divided into reversible and irreversible processes. The reversible process refers to the electrochemical regeneration and recycling of redox substances in the electrolysis process; the irreversible process refers to the oxidation of organic substances with substances produced by irreversible electrochemical reactions. It is used in printing and dyeing wastewater treatment, landfill leachate treatment, drying sewage treatment, cyanide-containing wastewater treatment, pharmaceutical wastewater treatment, hospital sewage treatment, and organic wastewater treatment.
9. Etching solution regeneration and copper recovery
Etching is an important process in the production of printed circuit boards. As the etching proceeds, the waste etching solution contains a large amount of copper ions or other metal ions, which can be recycled by electrolysis. Through this recycling process, enterprises not only increase economic benefits by recovering metals such as copper, but also achieve long-term social benefits by meeting emission standards and recycling resources. The waste liquid includes: acid etching waste liquid, alkaline etching waste liquid, low copper-containing waste liquid, waste fixing liquid, waste frame material, nickel-containing waste liquid, waste liquid containing gold and palladium, waste tin stripping water.
5. Precautions for the use of electrodes
1. The titanium electrode has a black surface after oxidation and sintering. The uncoated surface is blue and has no electrode performance. The black side corresponds to the cathode.
2. Once the titanium electrode substrate is pickled, all subsequent production and processing procedures and use procedures must be carried out strictly and carefully. Wear clean gloves to get stuck at both ends or edges of the anode during transportation, preferably in contact with the uncoated part. Any foreign objects are strictly prohibited from scratching the coating surface.
Note: The titanium substrate itself is not conductive, and its outer layer is coated with a noble metal oxide coating that has electrocatalytic activity, conductivity, and oxidation resistance, but its thickness is only about 30 microns. During the process, the electrode will first corrode from the damage, which will affect the quality and effect of the entire electrode.
3. The electrolyte maintains stability, especially can not contain cyanide ions and fluoride ions, these impurities will seriously corrode the titanium matrix;
4. Add a filter device before the electrolyte enters the electrolytic cell, and cannot contain metal particles with a diameter greater than 0.1mm to prevent excessive aggregation and lead to short circuit of anode and cathode.
5. When recovering copper, nickel, gold, silver, cobalt and other metals by electrolysis, the cathode attachment should not be too thick to prevent the short-circuit breakdown of the cathode and anode caused by too small electrode spacing or the formation of sharp metal.
6. The spacing between cathode and anode can be set according to actual production, generally 5-25mm. Generally speaking, the pole distance will increase the voltage drop, but it should not be too small, otherwise the cathode scale generated on the cathode surface will easily cause the short circuit of the plate;
7, to avoid the use of inverted poles. Once the noble metal oxide coating is used as a cathode, the surface undergoes a reduction reaction and is easily converted into a metal element, which cannot be effectively combined with the titanium base, causing the coating to fall off.
8. It is not advisable to soak in the solution in the power-off mode for a long time when the machine is stopped. It is best to load a small current of about 5A to protect the plate.
9. During shutdown or other maintenance conditions, add dilute acid or clean the surface of the electrode with clean water, but do not wash it with nylon or mechanical substances.
10. The temperature of the electrolyte should not be too high when working, the ideal temperature is 25-40 °C, and a heat exchange device can be added to maintain the best use environment for the electrode.
11. The normal working current density is within 2000A/m², the excessive current will cause the reaction to be too intense and shorten the life of the anode;
12. When starting up, load the current to the electrolytic cell step by step, do not raise it to the position at one time, and the same is true when it is stopped.
13. Keep the anode clean during production and use, and can not be contaminated with oil or other attachments, so as not to affect the electrolysis effect and the life of the electrode.
