Method for measuring content of free carbon in tantalum carbide or niobium carbide

Abstract

The invention relates to a method for determining the content of free carbon in tantalum carbide or niobium carbide, and belongs to the technical field of material chemical analysis. The method comprises the following steps: reacting a tantalum carbide or niobium carbide sample with protonic acid under a heating condition, so that metal carbide is dissolved and free carbon is not dissolved; filtering the reaction liquid, separating out free carbon solid residues, and carrying out water washing and drying treatment; and then burning the residues in an oxygen atmosphere, and measuring the amount of generated carbon dioxide by utilizing infrared detection or other means, so as to calculate the content of free carbon in the sample. The method disclosed by the invention has the advantages of high determination precision, simplicity and convenience in operation and wide applicability, fills the technical blank of accurate quantitative analysis of free carbon in tantalum (niobium) carbide, and has important significance on preparation and quality control of high-purity tantalum and niobium metal materials.

Description

Technical Field

[0001] The invention belongs to the technical field of material chemical analysis and metallurgical testing, and particularly relates to a method for determining the free carbon content in tantalum carbide or niobium carbide. Background Art

[0002] Tantalum carbide (TaC) and niobium carbide (NbC) are important additives in the cemented carbide industry and play a key role in its production. This is due to the excellent properties of tantalum (niobium) carbide, such as a high melting point, high hardness, good chemical stability, high thermal conductivity, high flexural strength, and low thermal expansion coefficient, which impart excellent high-temperature resistance, wear resistance, and mechanical strength to cemented carbide materials. Furthermore, tantalum (niobium) carbide serves as an intermediate in the production of metallic tantalum. The carbon reduction method, which uses tantalum carbide as an intermediate in tantalum powder production, offers advantages over the sodium reduction method in terms of cost and efficiency. The basic principle is to use carbon black as a reducing agent to reduce tantalum pentoxide (Ta2O5) and gradually convert it into carbide. During the reaction, the oxide is gradually reduced, and the resulting carbon monoxide (CO) gas is released, ultimately yielding tantalum (niobium) carbide. Although a certain amount of hydrogen is introduced during the carbothermal reduction process to protect the carbide and equipment and to aid in the reduction, excess carbon (carbon black) remains in the resulting tantalum carbide melt after the reaction is complete. This elemental carbon is called free carbon, and its presence can severely impact the quality and precision of subsequent tantalum (niobium) metal purification processes, such as high-temperature sintering and electron beam melting. Therefore, accurately measuring the free carbon content in carbides like tantalum (niobium) carbide is essential for improving the purity and performance of these metals.

[0003] Currently, no specific method for measuring the free carbon content in tantalum (niobium) carbide has been reported. Existing techniques typically only measure the total carbon content of the carbide, failing to distinguish between bound carbon and free carbon. This technological gap makes it difficult to effectively monitor and adjust the purity of tantalum (niobium) carbide products, failing to meet the demand for precise control of raw material composition in the production of high-purity metals. Therefore, there is an urgent need to provide an analytical method that can quantitatively determine the free carbon content in tantalum (niobium) carbide to overcome the shortcomings of existing techniques. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for determining the free carbon content in tantalum carbide or niobium carbide to solve the technical problem of the lack of accurate means for determining the free carbon content in tantalum carbide (niobium) in the prior art, thereby meeting the demand for raw material monitoring in the preparation of high-purity tantalum and niobium metal materials.

[0005] To achieve the above objectives, the present invention provides a method for determining the free carbon content in tantalum carbide or niobium carbide. This method separates the free carbon in the carbide sample from the matrix through special pretreatment, and uses high-temperature combustion infrared detection to determine the free carbon content.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for determining the free carbon content in tantalum carbide or niobium carbide, comprising the following steps:

[0008] (1) placing a tantalum carbide or niobium carbide sample to be tested in an acid-resistant container, adding protonic acid and heating, so that the tantalum carbide or niobium carbide in the sample is dissolved, while the free carbon is not dissolved in the protonic acid;

[0009] (2) After the dissolution is completed, the mixture is filtered to separate, retaining the free carbon solid residue, and the residue is washed with deionized water to remove residual acid;

[0010] (3) drying the free carbon residue and burning it in an oxygen atmosphere, detecting the amount of carbon dioxide produced by the combustion, and determining the free carbon content in the sample accordingly.

[0011] Preferably, the sample is pre-treated by grinding to a particle size of less than 100 microns before being processed in step (1).

[0012] Preferably, the protonic acid is a mixed acid of acid A and acid B, and the dissolution treatment in step (1) is performed in the order of adding acid A first and then adding acid B, wherein the acid A is hydrofluoric acid and the acid B is a mixed acid of one or more of nitric acid, sulfuric acid and phosphoric acid.

[0013] Preferably, the volume ratio of the sample mass to the mixed acid of acid A and acid B is 1:10-40, acid A is high-grade pure hydrofluoric acid with a density of 1.15 g / mL, and acid B is: high-grade pure nitric acid with a density of 1.42 g / mL, or high-grade pure sulfuric acid with a density of 1.105 g / mL, or high-grade pure phosphoric acid with a density of 1.082 g / mL, or a mixed acid thereof.

[0014] Preferably, the step (2) is performed by vacuum filtration using a platinum suction crucible padded with an acid-washed asbestos, aluminum silicate fiber or quartz fiber filter pad to separate the free carbon residue.

[0015] In the step (3), the free carbon residue is placed in a pure oxygen atmosphere of a high-frequency induction furnace and burned, and the carbon dioxide generated by the combustion is measured by an infrared detector.

[0016] Preferably, the dissolution process in step (1) is carried out at 50-100° C. for 1-5 minutes to ensure that the sample is fully dissolved.

[0017] During the combustion measurement, a flux is added to the free carbon residue, wherein the flux is a tungsten-tin alloy.

[0018] During the acid decomposition of tantalum carbide or niobium carbide samples, using proton acids such as hydrofluoric acid (HF), nitric acid (HNO3), sulfuric acid (H2SO4), or phosphoric acid (H3PO4) alone is difficult to completely dissolve the carbides at room temperature or low temperature conditions. High temperatures and long times are required, resulting in low dissolution efficiency and easily causing changes in the free carbon in the sample. However, when two proton acids are mixed at once and added to the sample, the mixed acid reacts violently, releasing a large amount of heat in a short period of time. This can easily trigger oxidizing acids such as nitric acid to react with elemental carbon, resulting in the loss of free carbon in the sample and affecting the accuracy of the final measurement. Furthermore, the intense heat release can easily cause nitric acid to rapidly volatilize and produce corrosive gases, posing a safety hazard and causing environmental pollution. Furthermore, the proton acids used are all fixed-concentration solutions purchased directly from the industry. During use, the main control is the volume ratio, and no further adjustment of the acid concentration is required.

[0019] For the above problems, the present invention proposes the processing mode of protonic acid dripping step by step, i.e. first dripping the first protonic acid (A acid), after making sample and A acid fully react, then slowly dripping the second protonic acid (B acid). By the method for adding acid step by step, on the one hand, the full dissolution of carbide can be achieved, and decomposition efficiency is improved; On the other hand, the free carbon loss caused by the violent heat release of mixed acid is effectively avoided, thereby ensuring the accuracy of free carbon measurement result. In addition, if the order of adding A acid after adding B acid is adopted, although the reaction intensity can be reduced, the phenomenon that sample is not completely dissolved may still occur under certain circumstances, and it is speculated that it may be relevant with the formation of a passivation layer on the sample surface, which affects the further corrosion of acid to sample. Therefore, the present invention preferably adopts the step-by-step acid addition mode of adding B acid after adding A acid, to take into account the full dissolution of carbide and the effective retention of free carbon, and the reliability and safety of measuring method are improved as a whole.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The method of the present invention successfully separates free carbon from matrix carbon and conducts quantitative analysis by combining chemical decomposition with physical separation, and has high accuracy and reliability.

[0022] The assay process described in the present invention is simple to operate and can be performed using conventional chemical reagents and instruments. It is fast and has a low cost per assay. This method can be used for rapid monitoring of tantalum (niobium) carbide products at production sites or in laboratories, improving production efficiency and quality control, and is of great significance for the preparation of high-purity tantalum (niobium) metal materials. DETAILED DESCRIPTION

[0023] The determination method of the present invention is described in detail below by way of examples, but the present invention is not limited to the following examples.

[0024] Example:

[0025] The free carbon content in a batch of tantalum carbide powder samples was determined. To ensure test accuracy, a blank test and a calibration test with a standard sample were performed before the formal analysis of the sample. The specific steps are as follows:

[0026] Blank sample analysis: Simulate the testing of the reagents and apparatus without adding sample to determine the system's background carbon content. To a clean platinum dish, add 2 ml of pure water, then approximately 2 ml of protic acid A and 2 ml of protic acid B. Mix gently, let the mixture react for approximately 3 minutes, and heat on a hot plate at 50-100°C to simulate sample decomposition. Remove the dish and rinse the container's interior with a small amount of pure water. Pour the resulting solution into a platinum crucible pre-filled with acid-washed asbestos filter media with a small perforated bottom. Connect a vacuum pump for vacuum filtration. Rinse the platinum dish and filter media several times with hot pure water until the filtrate is neutral. Stop filtration, carefully remove the acid-soaked asbestos filter media, place it in a ceramic crucible, and dry it on a hot plate to remove moisture. After cooling, spread the dried filter media evenly on the bottom of the crucible, add 1.3 g of tungsten-tin flux, and gently shake to mix. The crucible was placed in a high-frequency induction furnace, a simulated sample mass of 1.0000 g was entered as the basis for calculation, high-purity oxygen was introduced, and the instrument was started for combustion analysis. After infrared detection, the carbon content reading was recorded. This blank operation was repeated three times. The results showed that the blank free carbon content reading remained stable at approximately ±0.0002%, indicating that the system background was extremely low and negligible.

[0027] Standard Sample Analysis: The method is calibrated using a standard reference sample with a known free carbon content. Weigh 0.2000±0.0010g of a standard carbide sample (with a known free carbon content, such as a batch of previously measured tantalum carbide standard samples) into a platinum dish. Add 2ml of pure water and follow the same procedure as for the blank, adding protonic acids A and B for a decomposition reaction (1-5 minutes, heating at 50-100°C). Vacuum filtration and hot water washing are then performed. The filter medium containing the free carbon from the standard sample is dried and mixed with a tungsten-tin flux. The carbon content is then determined by combustion in a high-frequency induction furnace. The measurement is repeated three times, and the free carbon content of the standard sample is within ±0.0005% of the reference value, demonstrating the accuracy and stability of the method.

[0028] Analysis of the test sample: Take the tantalum (niobium) carbide powder sample to be tested and determine the free carbon content in it according to the following steps:

[0029] Grinding and Pulverization: If the sample particles are large (e.g., initial particle size exceeding several hundred microns), first grind the tantalum (niobium) carbide sample using a ball mill. Ceramic balls or zirconia balls can be used as grinding media to avoid the introduction of impurities such as iron. The particle size of the sample after grinding should be as uniform as possible, preferably within 1000 μm, and preferably within 100 μm, to ensure sufficient acid decomposition.

[0030] Protonic acid decomposition: Weigh 0.2000 g (accurate to 0.0001 g) of the ground sample into a platinum dish and add about 2 ml of pure water to wet the sample. Then add 1 to 4 ml of protonic acid A, followed by slowly adding 1 to 4 ml of protonic acid B, so that the acid solution fully submerges the sample and reacts. The reaction lasts for about 1 to 5 minutes. During this period, the platinum dish can be placed on a hot plate at 50 to 100 ° C to accelerate the dissolution and decomposition reaction of the carbide. During the reaction, the matrix of tantalum carbide (niobium) is gradually dissolved or converted by the acid solution, and the free carbon in the sample does not participate in the chemical reaction and is released in the form of fine carbon particles. After the reaction is completed, remove the platinum dish and rinse along the wall of the dish with a small amount of pure water to collect all the residual liquid.

[0031] Filtration, washing and drying: Pour the above solution containing free carbon particles into the prepared platinum crucible with filter medium and connect a vacuum pump for filtration. The filter medium used is the same as the blank step, such as an acid-washed asbestos fiber pad, which can effectively retain carbon particles. Turn on the vacuum for reduced pressure filtration, so that the solution flows out through the small holes at the bottom of the crucible, and the free carbon is retained on the asbestos fiber. Then rinse the platinum dish and filter device repeatedly with hot deionized water for at least 3 times until the filtrate is neutral and does not contain any acid residue. Then stop filtration, remove the asbestos filter medium and place it in a clean ceramic crucible. Dry it on a hot plate for several minutes to ensure that the filter material and the carbon in it are completely dry.

[0032] High-frequency combustion analysis: Use tweezers to spread dried asbestos filter material (containing the sample's free carbon) flat on the bottom of a ceramic crucible. Add approximately 1.3 grams of tungsten-tin alloy flux and gently shake the crucible to thoroughly mix the flux and filter material. Place the crucible in the analysis position of a high-frequency induction furnace. Set the instrument to the sample mass (0.2000 grams) you actually weigh. After flowing high-purity oxygen, start the high-frequency induction furnace for combustion analysis. In this high-temperature, high-oxygen environment, the free carbon on the filter material is rapidly oxidized to produce CO2 gas. The carbon infrared analyzer's detection cell measures the intensity of the CO2 infrared absorption signal in real time and calculates the corresponding carbon content. The instrument ultimately displays the sample's free carbon percentage. To ensure reliable results, the above analysis is repeated three times for the same sample. The resulting free carbon content values ​​show minimal fluctuation (e.g., within ±0.002%), and the average value is taken as the free carbon content of the tantalum (niobium) carbide sample batch. The experimental parameters and sample free carbon content for each experimental example and comparative example are shown in Table 1.

[0033] Table 1

[0034]

[0035]

[0036] After testing using the above method, the free carbon content of the tantalum carbide powder sample selected in this embodiment can be accurately determined. For example, if the free carbon content of a batch of samples is measured to be 0.015%, it indicates that 0.015% of carbon exists in the form of free elemental matter in the tantalum carbide sample. The results obtained by the method of the present invention can be used to guide adjustments to the production process: if the free carbon content is too high, it may be considered to reduce the carbon ratio during the carbonization process or strengthen the subsequent refining treatment; if the free carbon content meets the requirements, it indicates that the carbonization reaction is sufficient and the product quality is high. This example demonstrates the feasibility and accuracy of the method of the present invention, which can meet the requirements for the determination of trace free carbon in refractory metal carbides such as tantalum carbide (niobium).

Claims

1. A method for determining the free carbon content in tantalum carbide or niobium carbide, characterized in that: The steps include: (1) placing a tantalum carbide or niobium carbide sample to be tested in an acid-resistant container, adding protonic acid and heating, so that the tantalum carbide or niobium carbide in the sample is dissolved, while the free carbon is not dissolved in the protonic acid; (2) After the dissolution is completed, the mixture is filtered to separate, retaining the free carbon solid residue, and the residue is washed with deionized water to remove residual acid; (3) drying the free carbon residue and burning it in an oxygen atmosphere, detecting the amount of carbon dioxide produced by the combustion, and determining the free carbon content in the sample accordingly.

2. The method according to claim 1, characterized in that The sample is pre-treated by grinding to a particle size of less than 100 microns before being processed in step (1).

3. The method according to claim 1, characterized in that The protonic acid is a mixed acid of acid A and acid B, and the dissolution treatment in step (1) is performed in the order of adding acid A first and then adding acid B. The acid A is hydrofluoric acid, and the acid B is a mixed acid of one or more of nitric acid, sulfuric acid and phosphoric acid.

4. The method according to claim 1, wherein The volume ratio of the sample mass to the mixed acid of acid A and acid B is 1:10-40 (g / mL). Acid A is high-grade hydrofluoric acid with a density of 1.15 g / mL. Acid B is: high-grade nitric acid with a density of 1.42 g / mL, or high-grade sulfuric acid with a density of 1.105 g / mL, or high-grade phosphoric acid with a density of 1.082 g / mL, or a mixed acid thereof.

5. The method according to claim 1, characterized in that In the step (2), vacuum filtration is performed using a platinum suction crucible padded with acid-washed asbestos, aluminum silicate fiber or quartz fiber filter pad to separate the free carbon residue.

6. The method according to claim 1, characterized in that In the step (3), the free carbon residue is placed in a pure oxygen atmosphere of a high-frequency induction furnace and burned, and the carbon dioxide generated by the combustion is measured by an infrared detector.

7. The method according to claim 3, characterized in that The dissolution process in step (1) is carried out at 50-100° C. for 1-5 minutes to ensure that the sample is fully dissolved.

8. The method according to claim 1, characterized in that During the combustion measurement, a flux was added to the free carbon residue, and the flux was WSn.

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