Tantalum, whose English name is Tantalum, is mainly found in tantalite and is symbiotic with niobium.
Tantalum has very good chemical properties and is extremely resistant to corrosion.
Tantalum is a transition metal element with the chemical symbol Ta and atomic number 73. It has some unique physical and chemical properties that make it very important in many high-tech and industrial applications. Here are some of the key properties of tantalum and an overview of global storage:
Properties of tantalum
- High melting point: Tantalum has a high melting point of 3017°C, making it very valuable in high-temperature applications.
- Corrosion resistance: Tantalum is highly resistant to many chemicals, including acids and bases, which makes it widely used in the chemical and medical fields.
- High density: Tantalum has a density of 16.65 g/cm³, which is close to the density of gold.
- Good electrical conductivity: Tantalum has good electrical and thermal conductivity.
- Biocompatibility: Tantalum exhibits good compatibility in the biological environment, so it is often used in the manufacture of medical implants.
Applications of tantalum
- Electronics industry: used in the manufacture of tantalum capacitors and high-power resistors.
- Aerospace: used in the manufacture of superalloys and jet engine components.
- Medical field: used in the manufacture of surgical implants and medical devices.
- Chemical industry: used in the manufacture of corrosion-resistant equipment and containers.
Global tantalum reserves and distribution
According to the United States Geological Survey (USGS), the world's proven reserves of tantalum are mainly distributed in the following countries:
- Australia: Australia has the world's largest tantalum reserves, accounting for a large portion of global reserves.
- Brazil: Brazil is also an important producer of tantalum and has rich tantalum ore resources.
- Rwanda and the Democratic Republic of the Congo (DRC): These two African countries are major sources of tantalum ore, particularly in Rwanda, where tantalum is an important export commodity.
- Canada: Canada also has some tantalum reserves, but the mining is relatively small.
Tantalum supply and potential depletion issues
Although tantalum is a relatively rare element, the global demand for tantalum continues to grow due to its important industrial use. Here are some of the challenges facing tantalum supply:
- Supply concentration: The main source of supply for tantalum is concentrated in a few countries, which makes the supply chain vulnerable to geopolitical and economic fluctuations.
- Environmental and social issues: Particularly in African countries, tantalum mining can involve illegal mining and conflict minerals, which pose challenges to the stability and sustainability of supply chains.
- Limited resources: While proven tantalum reserves are sufficient to meet short-term demand, in the long term, demand for tantalum is likely to increase further as the high-tech industry develops, leading to the risk of resource depletion.
Sustainability and alternatives
In order to deal with the problem of potential depletion of tantalum resources, the following strategies and research directions are proposed:
- Resource recovery: Improving the recovery rate of tantalum, and recovering tantalum from waste electronic equipment is an important direction.
- Alternative materials: Research and development of alternative materials to tantalum, such as high-performance ceramic materials or other metal alloys, to reduce reliance on tantalum.
- Improve mining efficiency: Adopt advanced mining and refining technologies to improve the efficiency of tantalum mining and refining.
In summary, tantalum, as a key industrial metal, has relatively limited global reserves, and its supply is facing certain challenges. However, through technological innovation and sustainable development measures, the risk of depletion of tantalum resources can be mitigated.
Although tantalum is highly resistant to corrosion, its corrosion resistance is due to the formation of a stable tantalum pentoxide (Ta2O5) protective film on the surface.
To put it simply, the solid tantalum capacitor is to press the tantalum powder and sinter it into an anode body in a high-temperature furnace, and its dielectric is to put the anode body into the acid to empower it to form a porous amorphous Ta2O5 dielectric film, and its working electrolyte is manganese nitrate solution decomposed at high temperature to form MnO2, which is used as a lead-out connection through the graphite layer.
Tantalum capacitors, like aluminum electrolytic capacitors, need two large enough plane areas and a sufficiently small and controllable plane spacing if they need to form a large enough capacitance value.
Tantalum capacitors are a type of capacitor widely used in electronic circuits and are known for their high capacitance, low leakage current, and high stability. The process of manufacturing tantalum capacitors involves the following main steps:
1. Preparation of raw materials
Tantalum is extracted from tantalum ore and tantalum powder is obtained through a chemical treatment and reduction process. The purity of the tantalum powder and the particle size have a great impact on the performance of the final capacitor.
2. Anode preparation:
1. Pressed into shape
- Compression molding: Tantalum powder is pressed into a blank of the desired shape, usually cylindrical or rectangular.
The purpose of this process is to mold tantalum powder and tantalum wire together and have a certain shape.
A certain proportion of binder is added to the tantalum powder during the molding process.
Tantalum powder conducts electricity in full contact with tantalum wire as a metal, forming an anode.
Because it is granular, the area can be large enough.
2. Sintering
Sintering: Blanks are sintered at high temperatures to form a strong porous structure. This step results in a good electrical contact between the tantalum powder particles.
Under high temperature and high vacuum conditions, the newly pressed tantalum billet is fired into a tantalum block with a certain mechanical strength.
3. Anodizing:
Tantalum oxide layer formation: The sintered tantalum anode is electrochemically oxidized in the electrolyte to form a layer of tantalum oxide (Ta2O5). This oxide layer is the dielectric layer of the tantalum capacitor and determines the electrical properties of the capacitor.
1. Empowerment
The enabling process is a key process, which uses electrochemical methods to generate a dense insulating Ta2O5 (tantalum pentoxide) oxide film on the surface of the anode, which serves as the dielectric layer of the tantalum electrolytic capacitor.
The process is that the product of the frame is immersed in the formation solution (usually dilute nitric acid solution) at a certain depth, and the nitric acid solution will penetrate into the pores inside the tantalum block, and then the tantalum block will be used as an anode to pass through the current, and the nitric acid will decompose oxygen, and the Ta2O5 (tantalum pentoxide) oxide film will be generated on the surface of the tantalum particles in contact with nitric acid.
Oxide film thickness: The higher the voltage, the thicker the thickness of the oxide film, so the increase of the enabling voltage, the thickness of the oxide film increases, and the capacity decreases.
The higher the spacing, the smaller the capacitance value according to the capacitance formula, but the greater the withstand voltage value that can be realized, because the voltage required for breakdown becomes larger.
4. Cathodic preparation:
1. Manganese dioxide deposition: The oxidized tantalum anode is soaked in manganese dioxide solution, and a layer of manganese dioxide (MnO2) is formed on the surface of the anode through chemical reaction, which is used as the cathode of the capacitor.
Film
Film: The process of preparing manganese dioxide by multiple impregnation of manganese nitrate and decomposition.
The film is a cathode in which the tantalum capacitor that has been empowered is cleaned and dried, immersed in manganese nitrate solution, which penetrates deep into the internal holes of the tantalum block, and heats and decomposes manganese nitrate into manganese dioxide to form a capacitor. This process must be repeated several times until the internal gap is filled with manganese dioxide, so as to ensure that the manganese dioxide coverage is sufficient and the capacitance of the capacitor is large enough.
Here manganese dioxide is the cathode of the capacitance, which adheres to the dielectric layer so that there can be enough area S.
At the same time, we expect the resistivity of the electrode to be relatively small, so that there can be a small enough ESR.
With the above description and animation, we can see that the anode is tantalum metal, the dielectric layer is tantalum pentoxide, and the cathode is manganese dioxide. Because tantalum powder is granular pressed, the surface area is large enough, and tantalum pentoxide is achieved through chemical reaction, so it is wrapped on the surface of tantalum powder, and manganese dioxide is also wrapped on the surface of tantalum pentoxide through multiple treatments.
A layer of MnO2 is applied to the Ta2O5 film as the cathode of the capacitor. This is what we described in the previous structural characteristics of electrolytic capacitors, and the cathode is ---- "electrolyte" of non-metallic materials.
In addition to tantalum capacitors with MnO2 electrolyte, there are also tantalum capacitors with polymer as electrolyte. Polymer tantalum capacitors only change the cathode material from MnO2 to Polymer, and the rest of the process is basically the same, but many characteristics are changed:
1) The high-frequency characteristics of the capacitor are significantly improved, and the frequency range of the electrolytic capacitor is expanded. The conductivity of conductive polymer material is 10~1000 times that of MnO2, which effectively reduces the ESR of capacitors.
2）Polymer材料柔软有弹性，被膜过程最高温度+120℃，Polymer钽电容的失效率比MnO2钽电容的失效率更低。
3) Another advantage of Polymer is its low oxygen content, which greatly reduces the chance of combustion due to the combination of tantalum block with oxygen.
Polymer translated into Chinese is polymer. As for what polymers are?
Click: What are polymer solid capacitors, what are polymers?
The full name of tantalum capacitor is called manganese tantalum dioxide capacitor, and it is this structural feature that forms the "tantalum capacitor" and the failure mode is sparks:
Why don't you choose "tantalum capacitors"?
In what scenario must "tantalum capacitor" be selected?
Manganese-tantalum dioxide capacitors (often referred to simply as tantalum capacitors) can explode under certain conditions because tantalum capacitors are prone to failure when electrical and environmental conditions are harsh. Here are some of the possible causes of tantalum capacitor explosion:
Overvoltage
Tantalum capacitors have a limited tolerance to voltage, and if the applied voltage exceeds their rated voltage, the insulation of tantalum capacitors may break down. This causes a surge in current, generating a large amount of heat, which can cause a capacitor explosion.
Reverse voltage
Tantalum capacitors are typically polar capacitors that need to be properly connected to the positive and negative poles. If the connection is reversed, the tantalum capacitor will operate at a reverse voltage, which can cause the insulation to deteriorate and heat to accumulate, causing an explosion.
Overcurrent
When the current through the tantalum capacitor exceeds its design value, the internal resistance heats up. This heat may cause the chemical reaction between the tantalum oxide layer and the manganese dioxide layer inside the tantalum capacitor to intensify, eventually leading to capacitor failure and explosion.
The temperature is too high
Tantalum capacitors have a certain tolerance range to ambient temperatures. At high temperatures, the internal structure of tantalum capacitors may change, especially the manganese dioxide layer will decompose, resulting in capacitor failure and explosion.
Capacitance defects
During the manufacturing process, if the oxide layer of the tantalum capacitor is uneven or defective, these defects may become hot spots during operation, resulting in local overheating, which can cause an explosion.
Impulse loads
Tantalum capacitors are sensitive to rapidly changing pulsed loads. If there is a large current pulse in the circuit, the tantalum capacitor may not be able to adapt quickly, resulting in excessive current, overheating, and explosion.
The process of the explosion
When the tantalum capacitor is overheated inside, manganese dioxide (MnO2) decomposes, releasing oxygen. This oxygen further reacts with tantalum (Ta) to produce more heat and tantalum oxide (Ta2O5). When this heat accumulates to a certain extent, it can cause the capacitor housing to crack and potentially cause a flame or explosion.
Precautionary measures
In order to avoid the explosion of tantalum capacitors, the following measures can be taken:
- Proper selection and use of tantalum capacitors: Ensure that the rated voltage, current rating, and operating temperature range of the tantalum capacitor are appropriate for the specific application.
- Correct connection polarity: connect the positive and negative poles in strict accordance with the identification, and avoid reverse connection.
- Avoid overload and overvoltage: When designing the circuit, ensure that the voltage and current applied to the tantalum capacitor are within its rated range.
- Environmental control: Avoid using tantalum capacitors in extreme temperature environments.
2. Graphite layer and silver layer coating: Graphite layer and silver layer are coated on top of the manganese dioxide layer to improve electrical conductivity and provide good electrical contact.
Graphite silver paste
The graphite layer acts as a buffer layer, the main purpose of which is to reduce the ESR and at the same time prevent the silver paste from coming into contact with manganese dioxide and causing silver oxidation.
The purpose of the silver paste layer is to come into contact with the graphite layer, providing an equipotential surface.
5. Encapsulation:
Encapsulation material selection: Choose the appropriate encapsulation material, usually epoxy or plastic.
Encapsulation process: The processed anode and cathode are encapsulated in the encapsulation material to form the final capacitor shape.
Cutting, assembly
The product after silver is cut off at a fixed distance, and the oxide film on the surface of the tantalum wire is scraped off before cutting off to prevent virtual soldering, and then the anode is welded to the frame, and the cathode is cured by silver paste and combined with the frame bracket.
Molding
The assembled frame strip product is molded and encapsulated.
Sandblasting
Print the product's nominal capacitance capacitance, capacitor voltage rating, and anode identification, as well as manufacturer information.
Trimming
6. Testing and Grading:
Electrical performance testing: Test the capacitance, leakage current, equivalent series resistance (ESR), etc. of the capacitor to ensure that it meets the design specifications.
Quality inspection: Conduct visual and physical property inspections to ensure the quality and reliability of capacitors.
Aging screening
Test
The products after the surge test will be tested for four parameters of electrical performance, capacity, loss, leakage current and ESR, and the unqualified products will be automatically rejected to the collection box.
Capacity: The test frequency is 100Hz
Loss: The test frequency is 100Hz
漏电流:IL判定标准为不大于0.02CU(C为标称容量,U为测试电压).
Taping
Note: The animation in this article is excerpted from the AVX tantalum capacitor production introduction video
Learn more about passives
The system can be understood through the hard ten passive devices