Method for improving the accuracy of measuring the deuterium enrichment of DKDP crystal by a thermal gravimetric analyzer

Abstract

The application discloses a method for improving the measurement accuracy of a thermal gravimetric analyzer in measuring the deuteration rate of DKDP crystal. The method performs thermal gravimetric curve scanning on a DKDP crystal sample; wherein the reaction formula of the thermal decomposition of the DKDP crystal sample is K(D x H 1‑x )2PO4→KPO3+(D x H 1‑x )2O; the residual mass of the sample is obtained through the thermal gravimetric curve; and the calculation formula of the deuteration rate x of the DKDP crystal is as follows: x(%)=(58.599 / α-67.539)×100%; wherein α is the mass ratio of the residual mass measured by the thermal gravimetric analyzer to the mass of the sample. The method requires a small amount of sample, the measured deuteration rate is a point value rather than a statistical average value, can be measured in the full range of 0-100%, is simple to operate, and has high precision, and is a true sense of deuteration rate test.

Description

Technical Field

[0001] This application relates to a method for improving the accuracy of thermogravimetric analysis in measuring the deuteration rate of DKDP crystals, which belongs to the field of testing important indicators of DKDP crystals. Background Technology

[0002] Tetragonal potassium dideuterium phosphate (K(D)) x H 1-x 2PO4 (DKDP) crystal is a widely used frequency conversion and electro-optic modulation crystal in laser technology, especially for large-size (430 nm) crystals with different deuteridization rates (i.e., x in the molecular formula). 430mm DKDP crystal blanks have been widely used in high-power laser drivers.

[0003] With the development of inertial confinement fusion (ICF) technology, countries around the world are accelerating research and stockpiling of raw materials needed for laser fusion engineering. High-quality, large-size DKDP crystals are an important component of the optical device assembly in laser fusion devices. DKDP crystals are made by replacing hydrogen atoms in potassium dihydrogen phosphate (KDP) crystals with deuterium atoms, improving certain crystal properties: 1. The electro-optic coefficient of DKDP crystals is twice that of KDP crystals, and the half-wave voltage is half that of KDP crystals, making them more suitable for fabricating electro-optic devices; 2. The transmission band of DKDP crystals is broadened, shifting towards the infrared, expanding the laser application band; 3. A strong stimulated Raman scattering (SRS) band appears in KDP crystals at 915 cm⁻¹. -1 Nearby, it splits into two weaker SRS bands in the DKDP crystal, reducing the intensity of the SRS.

[0004] Advanced countries like the United States widely use DKDP crystals instead of KDP crystals in optical devices for laser fusion engineering to reduce the effects of stimulated Raman scattering. my country began laser fusion engineering research in the 1980s, completing the Shenguang I device in 1987 and the Shenguang II device in 2001. Due to economic and technological constraints, both Shenguang I and Shenguang II devices used potassium dihydrogen phosphate (KDP) crystals for electro-optic and third-harmonic generation components. The Shenguang III device, to be completed in 2015, requires 48 DKDP crystals with 70% deuteration to replace KDP crystals as third-harmonic generation components. Under feasible crystal growth technology and economic conditions, 48 ​​DKDP crystals with 90% deuteration will also be used for electro-optic components, which is of great and far-reaching significance to my country.

[0005] The deuteration rate of DKDP solution can be accurately determined by nuclear magnetic resonance (NMR). Due to the influence of the segregation coefficient during crystal growth, the deuteration rate of DKDP crystal is usually lower than that of its growth solution, and the deuteration rate of DKDP crystal cannot be determined by measuring the deuteration rate in the growth solution.

[0006] The deuterium saturation of a DKDP crystal blank directly affects the phase matching angle and frequency doubling coefficient of the crystal. Accurate measurement of the deuterium saturation of a DKDP crystal blank is a crucial parameter in the fabrication of DKDP crystal components. The deuterium saturation distribution in different regions of large-diameter DKDP crystals is also non-uniform, requiring accurate measurement of the deuterium saturation of crystal blanks cut from different parts of the DKDP crystal. Previous methods for measuring the deuterium saturation of DKDP crystals, such as the transmittance redshift method, determine the deuterium saturation based on the redshift of the DKDP crystal's infrared cutoff edge relative to the KDP crystal. During testing, the sample must be precisely oriented, cut to centimeter-sized dimensions in the Z-axis, and undergo surface polishing, which can easily lead to accumulated and amplified errors. The transmittance method can only guarantee accurate test results in the high deuterium saturation region (>90%). Neutron diffraction, Raman scattering, and Curie point measurement methods, among others, suffer from cumbersome operation and large test deviations, failing to meet practical requirements. Summary of the Invention

[0007] We analyzed the thermal decomposition reaction process of DKDP crystals and found that the deuteration rate of the water produced by the thermal decomposition reaction is the same as that of the crystal sample, and there is a fixed stoichiometric relationship between the products (i.e., water and potassium metaphosphate). Using a thermogravimetric analyzer, we accurately measured the weight loss of a small amount of DKDP crystal sample after thermal decomposition, and precisely calculated the deuteration rate of the DKDP crystals based on the stoichiometric relationship of the gravimetric method.

[0008] We obtained good repeatability of the deuteration (theoretically 0) test results for slowly grown KDP crystals. Based on the residual mass obtained from the thermogravimetric curves, the deuteration rates were 0.109, -0.046, -0.202, and 0.101. The average of the four test results was -0.0095%, with a standard deviation of 0.0014. All four results were within ±0.5%, significantly improving the accuracy compared to the previous 5.66%. Using the method of this patent, the deuteration rate test results are highly accurate.

[0009] Thermogravimetric analysis (TGA) is accurate, highly repeatable, and easy to operate for determining the deuteration rate of DKDP crystals.

[0010] A method for improving the accuracy of thermogravimetric analysis (TGA) measurements of deuteration rate in DKDP crystals includes the following steps:

[0011] S1. Use a thermogravimetric analyzer to perform a baseline scan on the empty crucible;

[0012] S2. Add the DKDP crystal sample to the empty crucible, and record its mass as m1.

[0013] Among them, the chemical formula of the DKDP crystal sample is K(D x H 1-x)2PO4;

[0014] S3. Perform programmed temperature increase and scan the thermogravimetric curve of the DKDP crystal sample.

[0015] The reaction formula for the thermal decomposition of the DKDP crystal sample is as follows:

[0016] K(D x H 1-x )2PO4 KPO3+(D x H 1-x )2O;

[0017] S4. Obtain the residual mass m2 of the sample through thermogravimetric curves;

[0018] The formula for calculating the deuteration rate x of DKDP crystals is as follows:

[0019] x (%) = (58.599 / α-67.539) 100%

[0020] Where α = m2 / m1.

[0021] Potassium dideuterium phosphate can be completely decomposed when heated to a certain temperature. The reaction formula is: K(D) x H 1-x )2PO4 KPO3+(D x H 1-x )2O. Due to the generated (D X H 1-X The deuterium-to-hydrogen ratio in O₂ and K(D) x H 1-x The deuterium-to-hydrogen ratio in K2PO4 is the same, and the generated KPO3 and (D X H 1-X Since the molar ratio of α to α is 1:1, the formula for calculating the deuteration rate X of DKDP crystal can be derived as follows: X (%) = (58.599 / α - 67.539) 100%, where α is KPO3 and K(D) x H 1-x The mass ratio of 2PO4, i.e. the residual mass measured by thermogravimetric analyzer.

[0022] Optionally, in step S1, corundum fragments with the same or similar mass as the DKDP crystal sample are placed in the empty crucible.

[0023] Optionally, in step S1, the size of the empty crucible is Φ10~16. 20~30mm.

[0024] Optionally, in step S1, the size of the empty crucible is Φ16. 22mm.

[0025] Optionally, in step S2, the mass m1 of the DKDP crystal sample ranges from 60 to 150 mg.

[0026] Optionally, in step S2, the mass m1 of the DKDP crystal sample ranges from 110 to 150 mg.

[0027] Optionally, in step S2, the mass m1 of the DKDP crystal sample is 110 mg.

[0028] Optionally, in step S2, the range of the DKDP crystal sample mass m1 is selected from any value or range between any two points from 60 mg, 70 mg, 80 mg, 90 mg, 100 mg, 110 mg, 120 mg, 130 mg, 140 mg, and 150 mg.

[0029] First, a baseline scan is performed using an empty crucible to eliminate the buoyancy effect caused by airflow. A corundum fragment with a weight approximately equal to that of the sample to be tested is then placed in the empty crucible to accurately account for the buoyancy effect. Finally, 110–150 mg of DKDP crystal sample is added to the empty crucible to improve the accuracy of the deuteration measurement.

[0030] When taking samples, be sure to take intact fragments from inside the DKDP crystal and immediately place them in a crucible to prevent the deuterium atoms on the crystal surface from being replaced by hydrogen atoms in the air, which would affect the accuracy of the test.

[0031] Air bubbles may appear in the residue after decomposition, affecting the accuracy of the test results. The experiment used a Φ16... The 22mm corundum crucible allows for complete release of generated gas, significantly reducing the impact of air bubbles on test results.

[0032] The crucible was soaked in nitric acid for more than 24 hours and boiled in pure water for 30 minutes during cleaning. The baseline was scanned after multiple cleanings to ensure the accuracy of the test.

[0033] Optionally, in step S3, the conditions for the programmed temperature rise are: the initial temperature is set to 25~35ºC, the temperature is increased to 370~550ºC at a rate of 4.5~5.5 ºC / min, and then the temperature is held constant for 60~120 minutes.

[0034] Optionally, in step S3, the conditions for the programmed temperature rise are: the initial temperature is set to 30ºC, the temperature is increased to 500ºC at a rate of 5ºC / min, and then the temperature is held constant for 90 minutes.

[0035] Optionally, the same heating procedure as in step S3 may be used in step S1.

[0036] Thermogravimetric analysis (TGA) of the sample was performed using the same temperature ramping procedure as the baseline scan. The TGA curve in the isothermal region is a straight line parallel to the X-axis. The residual mass of the sample can be obtained from the curve. Substituting this value into the curve, the deuteration rate of the DKDP crystal sample can be calculated.

[0037] Optionally, the thermogravimetric analyzer used is equipped with a high-sensitivity balance system and an electromagnetically compensated microbalance, with its support sensor in direct contact with the bottom of the crucible.

[0038] The thermogravimetric analyzer used is equipped with a high-sensitivity balance system, featuring larger weighing capacity and higher precision. It achieves a weighing resolution of 0.25 μg and maintains high sensitivity across the entire weighing range. The instrument operates in the temperature range of 0–1500 ºC with a heating rate range of 0–50 K / min. Through a vacuum and flow control system, it can perform tests under any atmosphere (inert, dynamic, static, oxidizing, vacuum). Equipped with an electromagnetically compensated microbalance, it boasts high accuracy, μg-level resolution, and excellent stability. The sensor is in direct contact with the bottom of the crucible, ensuring accurate temperature measurement.

[0039] The beneficial effects that this application can produce include:

[0040] The method provided in this application for improving the accuracy of thermogravimetric analysis (TGA) measurement of deuteration rate of DKDP crystals, compared with other methods, requires a small sample weight, and the measured deuteration rate is a point value rather than a statistical average. It can be used to measure the deuteration rate in the full range of 0-100%, is easy to operate, and has high accuracy, making it a true deuteration rate test. Attached Figure Description

[0041] Figure 1 The thermogravimetric analyzer used was the STA449F1 thermogravimetric analyzer from the German company NETZSCH.

[0042] Figure 2 For the Φ16 used 22mm corundum crucible.

[0043] Figure 3 The thermogravimetric curves were obtained from four measurements of the KDP crystal.

[0044] Figure 4 The thermogravimetric curves were obtained from three measurements of the high-deuterium DKDP crystal. Detailed Implementation

[0045] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0046] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased commercially, and the instrument operation was performed using the manufacturer's recommended settings.

[0047] The thermogravimetric analyzer used is the STA449F1 thermogravimetric analyzer from NETZSCH, Germany. Figure 1 As shown, this instrument is equipped with a high-sensitivity balance system, achieving a weighing resolution of 0.25 μg and maintaining high sensitivity across the entire weighing range. The instrument operates in the temperature range of 0–1500ºC with a heating rate range of 0–50 K / min. Through a vacuum and flow control system, it can perform tests under controlled atmospheres (inert, dynamic, static, oxidizing, and vacuum). It features an electromagnetically compensated microbalance with μg-level resolution. The sensor is in direct contact with the bottom of the crucible.

[0048] The crucible is Φ16 A 22mm corundum crucible, such as Figure 2 As shown, the crucible was soaked in nitric acid for more than 24 hours and boiled in pure water for 30 minutes during cleaning. The baseline was scanned once after multiple cleanings.

[0049] Example 1: DKDP Crystal Testing

[0050] For a slowly growing DKDP crystal (chemical formula K(D) x H 1-x Test with 2PO4.

[0051] The accuracy required for deuteration rate testing is within ±0.5%, making instrument stability (including stability under airflow, water bath conditions, and the external environment) crucial. We scanned three baselines using an empty crucible, and the baseline repeatability obtained from the three tests was excellent, indicating stable instrument performance. Therefore, in subsequent tests, we can use one of the baselines for buoyancy effect correction, eliminating the need for repeated baseline scanning, simplifying the testing procedure, shortening the testing cycle, and improving efficiency.

[0052] The initial temperature of the heating program was set to 30ºC, and the temperature was increased to 500ºC at a rate of 5ºC / min. Then, the temperature was held for 90 minutes. A baseline scan was performed on the empty crucible. The baselines obtained from the three tests showed good repeatability. In subsequent tests, one of the baselines can be used for buoyancy effect correction, and it is not necessary to repeat the baseline scan.

[0053] 110 mg of corundum fragments were placed in an empty crucible. Intact fragments from within a DKDP crystal were immediately placed into the crucible, along with the added DKDP crystal sample. Thermogravimetric analysis (TGA) curves were then performed using the same temperature program. The resulting TGA curves are shown below. Figure 4As shown, the mass m1 of the DKDP crystal samples added three times were 135.1169 mg, 117.7148 mg, and 117.1686 mg, respectively, and the corresponding residual mass m2 was 115.5833 mg, 100.6881 mg, and 100.2123 mg, respectively. The instrument can directly calculate the m2 / m1 ratio, which is 85.5432%, 85.5356%, and 85.5283%. Substituting these values ​​into the formula x (%) = (58.599 / α - 67.539) 100%, where α = m2 / m1, the corresponding calculated deuteration rates are: 96.3230%, 96.9317%, and 97.5164%. As shown in the curves in the figure, the repeatability of the three measurements is good, with average values ​​and standard deviations of 96.9237% and 0.00597, respectively.

[0054] Example 2: KDP Crystal Testing

[0055] The deuteration rate (theoretically zero) of slowly grown KDP crystals was determined to further verify the reliability and accuracy of the testing method. The theoretical deuteration rate of KDP crystals is zero, which is the same as the thermal decomposition property of DKDP crystals, decomposing into KPO3 and H2O at around 230ºC. The above calculation formula is also applicable to calculating the deuteration rate of KDP crystals.

[0056] The procedure is the same as in Example 1, and the thermogravimetric curves obtained from the four tests are as follows: Figure 3 As shown in the figure, the test results have good repeatability. Based on the residual mass obtained from the thermogravimetric curve, the deuteration rates are 0.109, -0.046, -0.202, and 0.101. The average value of the four test results is -0.0095%, and its standard deviation is 0.0014. The results of the four tests are all within ±0.5%, which is significantly higher than the previous 5.66%, indicating a substantial improvement in test accuracy.

[0057] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for improving the accuracy of DKDP crystal deuteration rate measurement by thermal gravimetric analyzer, characterized in that, Includes the following steps: S1. Use a thermogravimetric analyzer to perform a baseline scan on the empty crucible; S2. Add the DKDP crystal sample to the empty crucible, and record its mass as m1. wherein the chemical formula of the DKDP crystal sample is K(D x H 1-x )2PO4; S3. Perform programmed temperature increase and scan the thermogravimetric curve of the DKDP crystal sample. The reaction formula for the thermal decomposition of the DKDP crystal sample is as follows: K(D x H 1-x )2PO4→ KPO3+ (D x H 1-x )2O; S4. Obtain the residual mass m2 of the sample through thermogravimetric curves; The formula for calculating the deuteration rate x of DKDP crystals is as follows: x (%) = (58.599 / α-67.539) ×100% Where α = m2 / m1; In step S1, corundum fragments with the same or similar mass as the DKDP crystal sample are placed in the empty crucible. In step S2, the mass m1 of the DKDP crystal sample ranges from 60 to 150 mg. In step S3, the conditions for the programmed temperature rise are: the initial temperature is set to 25~35ºC, the temperature is increased to 370~550ºC at a rate of 4.5~5.5 ºC / min, and then the temperature is held constant for 60~120 minutes. The same heating procedure as in step S3 is used in step S1.

2. The method according to claim 1, characterized in that, In step S1, the dimensions of the empty crucible are Φ10~16×20~30mm.

3. The method according to claim 1, characterized in that, In step S1, the dimensions of the empty crucible are Φ16×22mm.

4. The method according to claim 1, characterized in that, In step S2, the mass m1 of the DKDP crystal sample ranges from 110 to 150 mg.

5. The method according to claim 1, characterized in that, In step S3, the conditions for the programmed temperature rise are: the initial temperature is set to 30ºC, the temperature is increased to 500ºC at a rate of 5ºC / min, and then the temperature is held constant for 90 minutes.

6. The method according to claim 1, characterized in that, The thermogravimetric analyzer used is equipped with a high-sensitivity balance system and an electromagnetically compensated microbalance, with its support sensor in direct contact with the bottom of the crucible.

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