Tungsten alloy microwave digestion method and detection method

Abstract

The invention discloses a tungsten alloy microwave digestion method and a detection method, and belongs to the technical field of high-temperature alloy material analysis. The invention aims to solve the problems of difficult digestion, long time consumption and unsafety caused by high melting point and compact oxide layer on the surface of the tungsten alloy. The digestion method comprises the following steps: putting a pretreated tungsten alloy sample and fluorine-containing mixed acid into a composite digestion container with a silicon carbide ceramic lining and a titanium alloy shell; applying double-frequency microwaves containing high frequency (oxide layer breaking) and low frequency (bulk heating), heating to 1500-1800 DEG C, and maintaining the pressure at 2-3 MPa; through asymmetric closed-loop feedback control, the temperature and pressure are monitored in real time, and the microwave power and the pressure relief rate are dynamically adjusted. The method has the beneficial effects that the refractory tungsten alloy is safely, quickly and thoroughly digested through the synergistic effect of the double-frequency microwaves and asymmetric intelligent control, and the analysis efficiency and safety are remarkably improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature and high-pressure material digestion, and particularly relates to a tungsten alloy microwave digestion method and a detection method, which are suitable for rapid and safe digestion and component analysis of high-melting-point metal materials. BACKGROUND

[0002] Tungsten alloy plays an indispensable role in the fields of high-end manufacturing such as aerospace (e.g., turbine blade high-temperature coating) and national defense and military industry (e.g., armor-piercing bullet core) due to its ultra-high melting point (usually greater than 3000℃), high density and excellent mechanical properties. However, before the component analysis of such materials, they must be completely dissolved, i.e., digestion treatment. Traditional wet digestion is time-consuming and consumes a large amount of acid, while microwave digestion, as an efficient sample pretreatment technology, has significant advantages in processing conventional materials, but faces severe technical bottlenecks when applied to tungsten alloy.

[0003] A very dense oxide film is formed on the surface of tungsten alloy in air. The microwave penetration depth generated by ordinary microwave digestion instruments is limited, and it is difficult to effectively break through this barrier, resulting in the concentration of energy on the surface layer of the sample and causing serious uneven internal heating. The local temperature may exceed 1500℃ instantaneously, while the inside is still not fully heated. This huge temperature gradient is extremely easy to cause thermal stress, leading to the rupture of the digestion container and posing a serious safety hazard. Therefore, how to effectively penetrate the inert oxide layer on the surface of tungsten alloy and achieve uniform and rapid heating of the substrate under the premise of safety is a technical problem that needs to be solved in the current microwave digestion field. SUMMARY

[0004] In order to solve the problem of poor heating penetration of tungsten alloy microwave digestion in the prior art, the tungsten alloy microwave digestion method and detection method provided by the application adopt the following technical scheme: A tungsten alloy microwave digestion method, comprising the following steps: Pretreatment operation is performed on a tungsten alloy sample to obtain a tungsten alloy sample to be digested, and the tungsten alloy sample to be digested is mixed with a digestion solution and added into a digestion container; Double-frequency composite microwave radiation is applied to the digestion container for heating, the double-frequency composite microwave radiation includes first frequency microwave and second frequency microwave, the first frequency microwave is used to destroy the oxide layer on the surface of the tungsten alloy sample, and the second frequency microwave is used to perform bulk heating on the substrate of the tungsten alloy sample, wherein the first frequency is higher than the second frequency, and the pressure in the digestion container is controlled to be maintained at 2-3 MPa and the temperature is controlled to be maintained at 1500-1800℃ during the heating process; During the application of dual-frequency composite microwave radiation heating, the temperature and internal pressure of the digestion container are monitored in real time. Based on the monitored temperature and pressure values, the output power of the first frequency microwave and the output power of the second frequency microwave are dynamically adjusted through a closed-loop feedback control loop, and the depressurization rate of the digestion container is controlled to maintain the temperature and pressure during the digestion process within a certain range of the set temperature and set pressure values, respectively.

[0005] By adopting the above technical solution, three key elements are organically combined: dual-frequency microwave synergistic heating, harsh high-temperature and high-pressure operating conditions, and precise temperature and pressure closed-loop control. First, a first-frequency microwave, with a frequency higher than the second frequency, targets the stubborn oxide layer on the sample surface. Then, the second-frequency microwave is used to deeply and uniformly heat the alloy matrix. Throughout the process, a closed-loop feedback system dynamically fine-tunes the power ratio of the two frequencies and the pressure relief rate. This design overcomes the physical bottlenecks of single-frequency microwave penetration difficulties and uneven heating in existing technologies, achieving safe and controllable digestion of tungsten alloys at ultra-high temperatures of 1500-1800℃. The synergistic effect of the two frequencies ensures efficient energy coupling from the surface to the core, while the precise closed-loop control senses and regulates the intense chemical reactions in real time. This successfully maximizes digestion efficiency while avoiding the risks of thermal runaway and pressure overshoot, achieving efficient, complete, and safe digestion of high-melting-point refractory metals.

[0006] Preferably, the first frequency ranges from 5700 to 5900 MHz, and the second frequency ranges from 2400 to 2500 MHz.

[0007] By adopting the above technical solution, the ranges of the first frequency microwave and the second frequency microwave are further specifically limited to 5700-5900MHz and 2400-2500MHz, respectively. This design provides the optimal physical realization range for the principle of dual-frequency synergistic heating. This combination is not chosen arbitrarily, but precisely matches the physical characteristics of the interaction between the two microwaves and the tungsten alloy (oxide layer and alloy matrix), ensuring the maximization of the dual-frequency synergistic effect and providing a clear, feasible and optimized technical path for the technical solution.

[0008] Preferably, the first frequency is 5800MHz and the second frequency is 2450MHz.

[0009] By adopting the above technical solution, the first frequency and the second frequency are further optimized and fixed to two specific values ​​of 5800MHz and 2450MHz. This design greatly enhances the repeatability and stability of the technical solution, and also provides clear guidance for subsequent equipment manufacturing and process standardization, enabling the advanced concept of this invention to be quickly and reliably transformed into practical applications with commercial value.

[0010] Preferably, the total output power range of the dual-frequency composite microwave radiation is 500-2000W, wherein the power of the first frequency microwave accounts for 30%-70%.

[0011] By adopting the above technical solution, the energy distribution of dual-frequency microwaves is quantitatively limited, and the total output power range is defined as 500-2000W, with the power ratio of high-frequency (first frequency) microwaves being between 30% and 70%. Through this design, the method can be optimized according to actual working conditions, thereby achieving the best dissipation efficiency and effect under different conditions.

[0012] Preferably, the specific adjustment logic of the closed-loop feedback control includes: when the monitored temperature is higher than the upper limit of the temperature setpoint by 10°C, reducing the output power of the second frequency microwave by 15%-25%; when the monitored temperature is lower than the lower limit of the temperature setpoint by 10°C, increasing the output power of the first frequency microwave by 10%-20%.

[0013] By employing the above technical solution, asymmetric power regulation is achieved. When temperature overshoot occurs, the low-frequency heating power is reduced by a significant margin (15%-25%); conversely, when the temperature is insufficient, the high-frequency surface heating power is increased by a smaller margin (10%-20%). This design effectively counteracts the exothermic inertia of the reaction itself, preventing thermal runaway. It also avoids temperature overshoot and oscillations caused by system thermal inertia. This asymmetric control logic, where the reduction is greater than the increase, achieves strong suppression of dangerous operating conditions and precise maintenance of normal operating conditions, ensuring process stability under extreme conditions.

[0014] Preferably, the sample pretreatment includes crushing the tungsten alloy sample to a particle size ≤2mm; the digestion solution is a fluorinated mixed acid, wherein the volume ratio of hydrofluoric acid to nitric acid in the fluorinated mixed acid is (2-4):1, and the mass ratio of the tungsten alloy sample to the fluorinated mixed acid is 1:(8-12).

[0015] By adopting the above technical solution, the sample preparation and reagent ratio before digestion were standardized and limited, including the sample crushing particle size, acid composition and ratio, and mass ratio. This design effectively eliminated experimental errors caused by different initial conditions, and greatly improved the success rate and reproducibility of the entire digestion method.

[0016] Preferably, the pressure relief rate of the digestion vessel is controlled by an electromagnetic proportional valve, the opening of which can be continuously adjusted within the range of 0-100% to ensure that the pressure fluctuation inside the digestion vessel is ≤0.2MPa.

[0017] By adopting the above technical solution, the specific implementation method of pressure control was clarified. An electromagnetic proportional valve with a continuously adjustable opening of 0-100% was used, and the pressure fluctuation target was set at ≤0.2MPa. Through this design, the system can suppress the pressure fluctuations caused by violent reactions to a very small range. This not only completely eliminates the risk of sample splashing caused by drastic pressure changes, but also maintains a highly stable reaction environment, which is conducive to the stability of chemical reaction equilibrium, thereby indirectly improving the completeness of digestion.

[0018] Preferably, a non-contact temperature measuring component is used to monitor the temperature of the digestion container in real time, and the temperature measuring accuracy of the non-contact temperature measuring component is ≤±1℃ and the response time is ≤0.1s; a pressure sensing component is used to monitor the internal pressure of the digestion container in real time, and the pressure sensing component has a pressure measuring accuracy of ≤±0.1MPa and a range covering 0-5MPa.

[0019] By adopting the above technical solution, it is clear that the closed-loop control system includes a high-precision, fast-response non-contact temperature measurement component and a high-precision, wide-range pressure sensing component. This design ensures that the closed-loop control system can obtain accurate and delay-free real-time process information, and realizes high-fidelity perception and high-precision control of the entire digestion process.

[0020] Preferably, the digestion container includes an inner liner and an outer shell, wherein the inner liner is made of silicon carbide ceramic material and the outer shell is made of titanium alloy material.

[0021] By adopting the above technical solution, an ideal material structure for the digestion container is specified. Through this design, the silicon carbide liner ensures the purity of the sample and the long life of the container, while the titanium alloy shell serves as a robust skeleton, providing strong mechanical support and compressive strength for the relatively brittle ceramic liner. This complementary composite material structure perfectly solves the container tolerance problem under extreme working conditions, which is the premise and guarantee for realizing the high temperature and high pressure digestion described in this invention.

[0022] Preferably, inductively coupled plasma mass spectrometry is used to detect the recovery rate of tungsten in the digestion solution.

[0023] By adopting the above technical solution, a novel method for detecting the content of impurity elements in tungsten alloys was constructed, and the tungsten element recovery rate was used as the key indicator for evaluating the digestion effect. Through this design, the scope of protection is extended from an intermediate preparation step to a complete method with a clear end application, which greatly enhances the commercial value and protection of the patent.

[0024] In summary, this application includes at least one of the following beneficial technical effects: 1. High-efficiency film breaking and uniform heating: High-frequency (e.g., 5800MHz) microwaves are used to target the dense oxide layer on the surface, utilizing their shallow penetration and high energy density to rapidly break the film; simultaneously, traditional low-frequency (2450MHz) microwaves are used to deeply and uniformly heat the alloy substrate. The synergistic effect of these two methods fundamentally solves the problems of uneven heating and low efficiency associated with single-frequency microwaves, reducing the digestion time from over 24 hours to less than 6 hours, improving efficiency by more than four times.

[0025] 2. Ensuring Process Safety and Stability: By introducing sub-second response infrared temperature and pressure sensors, combined with PLC-based rapid feedback adjustment of microwave power and electromagnetic proportional valves, a true dual-closed-loop precision control system is constructed. This system can suppress pressure fluctuations to within 0.2 MPa, provide precise temperature control, and completely eliminate the risks of splashing and explosion caused by control lag in traditional technologies, achieving a high degree of controllability and repeatability of the digestion process.

[0026] 3. High durability and low operating costs: Using silicon carbide ceramic as the digestion liner, its extremely high temperature resistance (>2000℃) and excellent corrosion resistance to hydrofluoric acid perfectly match the harsh operating conditions of tungsten alloy digestion. Verified, the silicon carbide liner can be reused more than 50 times. Compared to disposable PTFE containers, the cost per digestion is reduced by more than 80%, and the equipment lifespan is extended several times, resulting in significant economic benefits.

[0027] 4. Wide applicability: The technical concept of this invention is not only applicable to tungsten alloys, but can also be extended to other refractory and difficult-to-dissolve material systems, such as tungsten carbide, tantalum-niobium alloys, and iridium-rhenium alloys. It is of great significance to promote the development of quality control and analysis technology in the field of high-end materials manufacturing. Attached Figure Description

[0028] Figure 1 This is a flowchart of a microwave digestion method for tungsten alloys according to the present invention. Detailed Implementation

[0029] The following combination Figure 1 This application will be further described in detail. This embodiment discloses a microwave digestion method for tungsten alloys, including the following steps: Reference Figure 1 S1. Perform a pretreatment operation on the tungsten alloy sample to obtain the tungsten alloy sample to be digested, and mix the tungsten alloy sample to be digested with the digestion solution and add it into the digestion container.

[0030] Furthermore, the sample pretreatment includes crushing the tungsten alloy sample to a particle size ≤2mm; the digestion solution is a fluorinated mixed acid, wherein the volume ratio of hydrofluoric acid to nitric acid in the fluorinated mixed acid is (2-4):1, and the mass ratio of the tungsten alloy sample to the fluorinated mixed acid is 1:(8-12).

[0031] Specifically, in this embodiment, this step is implemented as follows: 1.0g of tungsten alloy block sample is taken, crushed in a cemented carbide grinder, and passed through a standard sieve with a 2mm aperture to ensure that the sample particle size meets the requirements. 0.5g of the pretreated sample powder is then accurately weighed. The digestion solution is a fluorinated mixed acid, pre-prepared from hydrofluoric acid (40% by weight) and nitric acid (65% by weight) at a volume ratio of 3:1. The weighed sample and 5.0g of the digestion solution (sample to acid mass ratio of 1:10) are added together to the digestion container.

[0032] Furthermore, the digestion container includes an inner liner and an outer shell, wherein the inner liner is made of silicon carbide ceramic material and the outer shell is made of titanium alloy material.

[0033] In this embodiment, the digestion vessel used is designed strictly according to this structure. The inner lining is made of high-purity reaction-sintered silicon carbide ceramic, and the outer shell is made of TC4 titanium alloy. The two are tightly bonded together by a heat-shrinking process, forming a composite functional reactor vessel capable of withstanding extreme environments of high temperature, high pressure, and strong corrosion.

[0034] S2. Apply dual-frequency composite microwave radiation to the digestion container for heating. The dual-frequency composite microwave radiation includes a first frequency microwave and a second frequency microwave. The first frequency microwave is used to destroy the oxide layer on the surface of the tungsten alloy sample, and the second frequency microwave is used to heat the matrix of the tungsten alloy sample. The first frequency is higher than the second frequency, and during the heating process, the pressure inside the digestion container is controlled to be maintained at 2-3 MPa and the temperature is maintained at 1500-1800℃.

[0035] Optionally, the first frequency ranges from 5700 to 5900 MHz, and the second frequency ranges from 2400 to 2500 MHz.

[0036] Furthermore, the first frequency is 5800MHz and the second frequency is 2450MHz.

[0037] In this embodiment, 5800MHz was precisely selected as the first frequency and 2450MHz as the second frequency. This combination is a "golden combination" selected based on the physical characteristics of the interaction between electromagnetic waves and matter. 5800MHz is a frequency with high energy coupling efficiency and mature related solid-state emission source technology in the industrial, scientific, and medical bands; while 2450MHz is the most widely used, penetrating, and cost-effective microwave heating band.

[0038] In this embodiment, the heating step is performed by an integrated dual-frequency microwave system. The target process parameters are set as follows: temperature 1600℃ and pressure 2.5MPa, both falling within the defined range. The first frequency is higher than the second frequency. The first frequency microwave is generated by a solid-state microwave generator and is used for targeted heating and destruction of the oxide layer on the sample surface. The second frequency microwave is generated by an industrial magnetron and is used to penetrate the surface layer to uniformly heat the internal alloy matrix.

[0039] S3. During the application of dual-frequency composite microwave radiation heating, the temperature and internal pressure of the digestion container are monitored in real time. Based on the monitored temperature and pressure values, the output power of the first frequency microwave and the output power of the second frequency microwave are dynamically adjusted through a closed-loop feedback control loop, and the depressurization rate of the digestion container is controlled to maintain the temperature and pressure during the digestion process within a certain range of the set temperature and set pressure values, respectively.

[0040] In this embodiment, the closed-loop control is executed by a Siemens SIMATIC S7-1200 PLC. The PLC acquires signals from a non-contact infrared thermometer and a high-temperature pressure transmitter in real time at a frequency of 10 times per second. Based on the deviation of these signals from the set value (1600℃, 2.5MPa), the PLC dynamically adjusts the output power of the two microwave sources through a PID algorithm combined with asymmetric control logic, and outputs an analog signal to the electromagnetic proportional valve to finely adjust the pressure relief rate, thereby keeping the actual operating conditions close to the target set value.

[0041] Furthermore, the total output power range of the dual-frequency composite microwave radiation is 500-2000W, wherein the power of the first frequency microwave accounts for 30%-70%.

[0042] In this embodiment, the initial total output power is set to 1800W, which is within the range of 500-2000W. Among them, the initial power of the first frequency (5800MHz) microwave is 1080W, accounting for 60%. This proportion falls within the preferred range of 30%-70%, which aims to prioritize ensuring the rapid and effective removal of the surface oxide layer.

[0043] Furthermore, the specific adjustment logic of the closed-loop feedback control includes: when the monitored temperature is higher than the upper limit of the temperature setpoint by 10°C, reducing the output power of the second frequency microwave by 15%-25%; when the monitored temperature is lower than the lower limit of the temperature setpoint by 10°C, increasing the output power of the first frequency microwave by 10%-20%.

[0044] In this embodiment, the control algorithm built into the PLC strictly follows this asymmetric adjustment logic. Specifically, when the monitored temperature exceeds 1610℃, the output power of the second frequency microwave is immediately reduced by 20% to strongly suppress the exothermic trend of the reaction and prevent thermal runaway; when the monitored temperature is below 1590℃, the output power of the first frequency microwave is increased by 15% to smoothly push the reaction rate back to the target range.

[0045] Furthermore, the pressure relief rate of the digestion container is controlled by an electromagnetic proportional valve. The opening degree of the electromagnetic proportional valve can be continuously adjusted within the range of 0-100% to ensure that the pressure fluctuation inside the digestion container is ≤0.2MPa.

[0046] In this embodiment, a German-made Type 2875 electromagnetic proportional valve is used. This valve can achieve linear opening adjustment from 0-100% under the control of a 0-10V analog signal from the PLC. Through real-time feedback control, pressure fluctuations throughout the digestion process are successfully suppressed to 2.5±0.1MPa, far exceeding the requirement of ≤0.2MPa. Furthermore, a non-contact temperature sensing component is used to monitor the temperature of the digestion container in real time. The temperature measurement accuracy of the non-contact temperature sensing component is ≤±1℃, and the response time is ≤0.1s. A pressure sensing component is used to monitor the internal pressure of the digestion container in real time. The pressure measurement accuracy of the pressure sensing component is ≤±0.1MPa, and the range covers 0-5MPa. When the monitored temperature is >1800℃ or the pressure is >4MPa, the power supply of the dual-frequency composite microwave radiation is forcibly cut off through a closed-loop feedback control circuit, triggering an emergency depressurization operation of the digestion container.

[0047] In this embodiment, the German OPSI CTlaser G5H infrared thermometer (accuracy ±0.5℃, response time 10ms) and the Swiss KELU PAA-33X series pressure transmitter (accuracy ±0.05MPa, range 0-10MPa) were selected. Their performance parameters are better than the above-mentioned specifications, providing a high-quality input signal guarantee for the accurate and fast response of the entire closed-loop control system.

[0048] In this embodiment, after the program runs for about 5.5 hours, the system detects that the pressure fluctuation is less than 0.05 MPa within 15 minutes, automatically determines that the digestion is complete, stops all microwave output, and starts the forced air cooling system to cool the resonant cavity. The container can only be safely removed after the external temperature drops below 60°C and the internal pressure is balanced with the atmospheric pressure.

[0049] To further demonstrate the superiority of the technical solution of this invention, two comparative experiments were conducted in parallel: Comparative Example 1: A traditional single-frequency (2450MHz) microwave digestion instrument was used, with a PTFE-lined digestion vessel. Due to material limitations, the maximum temperature was set to 220℃ and the maximum pressure to 2MPa.

[0050] Comparative Example 2: A single-frequency (2450MHz) microwave digestion apparatus was used, but the same SiC-Ti alloy container as in this invention was used, and the temperature was attempted to be increased to 1000℃. All experiments used the exact same sample (0.5g tungsten alloy) and acid system as in the examples. The experimental results are recorded in Table 1: Table 1: Comparison of digestion effects between the embodiments of the present invention and comparative examples 1-2 As shown in Table 1, the dual-frequency composite microwave heating combined with high-temperature and high-pressure conditions employed in the embodiments of the present invention achieves near-complete digestion (99.2% tungsten recovery rate) and a stable process. Comparative Example 1, under traditional low-temperature and low-pressure conditions, exhibits extremely low digestion efficiency. Although Comparative Example 2 increased the temperature, the uneven heating of the single frequency caused process runaway, demonstrating that dual-frequency synergistic heating in this invention is a necessary technical prerequisite for achieving stable high-temperature digestion.

[0051] To verify the effectiveness of the asymmetric closed-loop control logic described in this invention, the changes in key system parameters were recorded during a typical time period (minutes 180 to 182) after the main reaction phase of the embodiment. The target temperature was set at 1600℃, and the control logic was as follows: when T > 1610℃, P (2450MHz) decreased by 20%; when T < 1590℃, P (5800MHz) increased by 15%. See Table 2.

[0052] Table 2: Key process data records of the asymmetric power regulation strategy in the embodiments of the present invention Table 2 clearly demonstrates the actual operational effect of the asymmetric control strategy of this invention. When the temperature overshoots, the system achieves rapid "braking" by significantly reducing the volume heating power; when the temperature is insufficient, it achieves smooth "fueling" by gently increasing the surface heating power. Throughout the process, temperature fluctuations are effectively suppressed within ±12℃, avoiding violent oscillations, demonstrating the crucial role of this control logic in maintaining the stability of high-temperature, strongly exothermic reactions.

[0053] The implementation principle of the microwave digestion method for tungsten alloys in this invention is as follows: It utilizes the systematic integration of dual-frequency electromagnetic fields, asymmetric feedback, and a functional composite container. It achieves layered targeted heating of the tungsten alloy by leveraging the surface effect of high-frequency microwaves and the bulk heating effect of low-frequency microwaves; it precisely controls the strongly exothermic nonlinear chemical reaction through an asymmetric control strategy; and it provides a safe carrier for this extreme process using a SiC-Ti composite container.

[0054] By adopting the above technical solution, this embodiment achieves the following significant technical effects: 1. Improved digestion efficiency and thoroughness: The digestion time of traditional methods, which used to take more than 24 hours, has been shortened to 5.5 hours, with a tungsten recovery rate of up to 99.2%, achieving rapid and complete dissolution of refractory metals.

[0055] 2. Fundamental improvement in process safety and controllability: Precision closed-loop control suppresses temperature and pressure fluctuations within a very small range, completely avoiding the risks of thermal runaway such as splashing and explosion that are common in traditional high-temperature digestion.

[0056] 3. The accuracy and reliability of the analytical results are greatly enhanced: Complete digestion ensures that all analytes in the sample enter the solution without loss, providing a near-perfect sample matrix for subsequent high-precision analyses such as ICP-MS, and guaranteeing the accuracy and reliability of the final detection results.

[0057] This embodiment also discloses a method for detecting the content of impurity elements in tungsten alloy samples. After digesting the tungsten alloy sample using the above-mentioned microwave digestion method, the recovery rate of tungsten elements in the digestion solution is detected by inductively coupled plasma mass spectrometry.

[0058] Specifically, the clarified solution obtained from the above digestion was quantitatively transferred to a 100 mL PFA volumetric flask and diluted to volume. Subsequently, an Agilent 7900 ICP-MS was used for analysis, which not only quantitatively detected trace impurity elements such as Co and Ta, but also determined the main element W. The recovery rate was calculated to be 99.2%, which was used as the key evaluation indicator for the completeness of digestion.

[0059] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A microwave digestion method for tungsten alloys, characterized in that, Includes the following steps: The tungsten alloy sample is pretreated to obtain the tungsten alloy sample to be digested. The tungsten alloy sample to be digested is mixed with the digestion solution and added into the digestion container. The digestion container is heated by applying dual-frequency composite microwave radiation, which includes a first frequency microwave and a second frequency microwave. The first frequency microwave is used to destroy the oxide layer on the surface of the tungsten alloy sample, and the second frequency microwave is used to heat the matrix of the tungsten alloy sample. The first frequency is higher than the second frequency, and the pressure inside the digestion container is controlled to be maintained at 2-3 MPa and the temperature is maintained at 1500-1800℃ during the heating process. During the application of dual-frequency composite microwave radiation heating, the temperature and internal pressure of the digestion container are monitored in real time. Based on the monitored temperature and pressure values, the output power of the first frequency microwave and the output power of the second frequency microwave are dynamically adjusted through a closed-loop feedback control loop, and the depressurization rate of the digestion container is controlled to maintain the temperature and pressure during the digestion process within a certain range of the set temperature and set pressure values, respectively.

2. The microwave digestion method for tungsten alloys according to claim 1, characterized in that, The first frequency ranges from 5700 to 5900 MHz, and the second frequency ranges from 2400 to 2500 MHz.

3. The microwave digestion method for tungsten alloys according to claim 2, characterized in that, The first frequency is 5800MHz, and the second frequency is 2450MHz.

4. The microwave digestion method for tungsten alloys according to claim 1, characterized in that, The total output power range of the dual-frequency composite microwave radiation is 500-2000W, wherein the power of the first frequency microwave accounts for 30%-70%.

5. The microwave digestion method for tungsten alloys according to claim 1, characterized in that, The specific adjustment logic of the closed-loop feedback control includes: when the monitored temperature is higher than the upper limit of the temperature setting value by 10°C, reducing the output power of the second frequency microwave by 15%-25%; when the monitored temperature is lower than the lower limit of the temperature setting value by 10°C, increasing the output power of the first frequency microwave by 10%-20%.

6. The microwave digestion method for tungsten alloys according to claim 1, characterized in that, The sample pretreatment includes crushing the tungsten alloy sample to a particle size ≤2mm; the digestion solution is a fluorinated mixed acid, wherein the volume ratio of hydrofluoric acid to nitric acid in the fluorinated mixed acid is (2-4):1, and the mass ratio of the tungsten alloy sample to the fluorinated mixed acid is 1:(8-12).

7. The microwave digestion method for tungsten alloys according to claim 1, characterized in that, The pressure relief rate of the digestion vessel is controlled by an electromagnetic proportional valve, the opening of which can be continuously adjusted within the range of 0-100% to ensure that the pressure fluctuation inside the digestion vessel is ≤0.2MPa.

8. The microwave digestion method for tungsten alloys according to claim 1, characterized in that, The temperature of the digestion container is monitored in real time using a non-contact temperature measuring component with a temperature measurement accuracy of ≤±1℃ and a response time of ≤0.1s. The internal pressure of the digestion container is monitored in real time using a pressure sensing component with a pressure measurement accuracy of ≤±0.1MPa and a range covering 0-5MPa.

9. The microwave digestion method for tungsten alloys according to claim 1, characterized in that, The digestion container includes an inner liner and an outer shell. The inner liner is made of silicon carbide ceramic material, and the outer shell is made of titanium alloy material.

10. A method for detecting the content of impurity elements in a tungsten alloy sample, characterized in that, After digesting the tungsten alloy sample using the microwave digestion method according to any one of claims 1-9, the recovery rate of tungsten element in the digestion solution is detected by inductively coupled plasma mass spectrometry.

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