Method for lossless separation of crystals through acid corrosion of molybdenum crucible

Abstract

The invention discloses a method for lossless separation of crystals by corroding a molybdenum crucible with acid, and the method comprises the following specific steps: immersing the crystals adhered with the molybdenum crucible in a corrosive liquid which can dissolve the molybdenum crucible but does not react with the crystals, standing for reaction until the molybdenum crucible is completely dissolved, and realizing crystal separation; and taking out the crystal, cleaning and drying to obtain the lossless separated crystal. According to the method, the molybdenum crucible is selectively etched, cleaning separation of the target crystal and the molybdenum crucible is achieved, compared with a traditional mechanical stripping method or a heating melting method, introduction of mechanical stress or thermal stress is avoided in the whole separation process, secondary damage to a crystal body structure is fundamentally eradicated, and the purity of the crystal is improved. And the integrity and the performance consistency of the crystal structure are ensured.

Description

Technical Field

[0001] This invention relates to the field of separation technology in crystal post-processing, and specifically to a method for non-destructive separation of crystals by acid etching of a molybdenum crucible. Background Technology

[0002] In the current field of commercial crystal growth, horizontal direct crystallization (HDC) has attracted much attention due to its numerous technical advantages: First, the prepared crystals are free of core and side core defects, significantly improving material utilization, with typical dimensions not less than 150×70×10 mm³; Second, it uses molybdenum crucibles, which have a melting point as high as 2600℃, exhibiting excellent high-temperature resistance and low cost; Third, the growth system has weak natural convection and strong solid-liquid interface stability, which is conducive to the formation of high-quality crystals; Fourth, it eliminates mechanical disturbances such as relative movement and rotation between the molybdenum crucible and the raw material, thereby effectively suppressing the formation of rotational streaks and significantly reducing crystal growth defects; Fifth, it can grow high-melting-point commercial crystals such as YAG, LuAG, and sapphire series. The principle of this method for crystal growth is as follows: a horizontal temperature gradient is maintained within the growth furnace, and a molybdenum crucible containing the raw material is passed through the heater at a set rate. As it moves forward, the supercooling caused by the temperature difference causes localized cooling and crystallization of the melt, allowing the crystal to grow slowly and continuously until completion. The final crystal size is determined by the morphology of the molybdenum crucible, which is for single use only.

[0003] Because the crystal is exposed to a high-temperature environment for an extended period during HDC growth, interfacial adhesion easily occurs between its bottom and the molybdenum crucible, forming a tightly bound aggregate that is difficult to separate. Currently, the commonly used separation method relies on manual mechanical peeling using thin blades. This method has significant drawbacks: it is time-consuming, labor-intensive, requires high skill, and consumes substantial human resources. More importantly, mechanical intervention introduces uneven stress, triggering secondary stress release within the crystal, causing damage such as microcracks or dislocation proliferation, severely degrading the structural integrity and performance consistency of the final crystal. While some methods use heating to partially melt the crystal and separate it from the crucible, the introduction of thermal stress also causes secondary damage to the crystal, making non-destructive separation impossible.

[0004] To date, no mature process or dedicated technical equipment has been reported in publicly available patents and academic literature that can achieve efficient and non-destructive separation between crystals grown by the HDC method and molybdenum crucibles. This separation challenge has become a key bottleneck restricting the industrial application of HDC technology, and there is an urgent need to develop a reliable separation solution that can avoid mechanical damage and ensure crystal integrity. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a method for non-destructive separation of crystals by acid etching of a molybdenum crucible, which solves the problem that mechanical stress or thermal stress is introduced when separating crystals and molybdenum crucibles in the prior art, causing microcracks or dislocation proliferation damage and deteriorating crystal performance.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for non-destructive separation of crystals by acid etching of a molybdenum crucible involves immersing the crystals adhering to the molybdenum crucible in an etching solution that can dissolve the molybdenum crucible but does not react with the crystals. The reaction is allowed to proceed until the molybdenum crucible is completely dissolved, thus achieving crystal separation. The crystals are then removed, cleaned, and dried to obtain the non-destructively separated crystals.

[0007] Furthermore, the corrosive liquid contains a highly corrosive acid and a strong oxidizing agent.

[0008] Furthermore, the highly corrosive acid is selected from hydrofluoric acid or concentrated hydrochloric acid; the strong oxidizing agent is selected from concentrated sulfuric acid, nitric acid or hydrogen peroxide.

[0009] Furthermore, the volume ratio of each component in the corrosive solution is as follows: strong corrosive acid : strong oxidant : deionized water = 1 : 0.33~20 : 0~90.

[0010] Furthermore, the concentration of the highly corrosive acid is 35-45 wt.%; and the concentration of the strong oxidant is 60-98 wt.%.

[0011] Furthermore, the corrosive liquid should be stored and handled in containers made of compatible materials such as borosilicate glass or polytetrafluoroethylene (PTFE) according to its chemical properties.

[0012] Furthermore, during the preparation of the etchant, the preparation temperature is controlled to be <60℃.

[0013] Furthermore, during the static reaction process, the reaction temperature is controlled to be <100℃.

[0014] Furthermore, the static reaction time is 0.00833~168 h; specifically, the corrosion rate of the molybdenum crucible shall prevail. Furthermore, the crystal is an oxide crystal, a sesquioxide crystal, or a mixed sesquioxide crystal.

[0015] Furthermore, the oxide crystals include Re:YAG, Re:GAGG, Re:YGG, Re:YSGG, and Re:LuAG; the sesquioxide crystals include Re:Y₂O₃ and Re:Al₂O₃; and the mixed sesquioxide crystals include Re:YScO₃ and Re:LuScO₃; wherein Re is a dopant ion selected from Er 3+Tm 3+ Ce 3+ Ho 3+ 、Nd 3+ Cr 3+ Dy 3+ Ti 3+ Yb 3+ One or more of them.

[0016] In practice, the degree of substitution of the dopant ion Re at the corresponding cation site in the matrix crystal is 0 at.% to 100 at.%.

[0017] Furthermore, the cleaning process includes first rinsing the crystal surface with a large amount of deionized water until it is neutral, and then performing ultrasonic cleaning with deionized water. The drying process involves wiping with anhydrous ethanol and then drying with dry nitrogen gas.

[0018] Principle: This invention employs a corrosive solution to selectively etch a molybdenum crucible, achieving non-destructive separation of the target crystal from the crucible. During the etching reaction, a strong oxidizing agent first acts on the surface of the molybdenum crucible, oxidizing it and forming a molybdenum trioxide (MoO3) passivation film. Subsequently, a highly corrosive acid rapidly dissolves this newly formed MoO3 film, forming a soluble compound that eliminates its hindrance to further reactions. Once the passivation film is removed, the fresh molybdenum surface is re-exposed, allowing the strong oxidizing agent to immediately oxidize it again, followed by the continued dissolution of the newly formed oxide film by the highly corrosive acid. This cycle repeats until the molybdenum crucible is completely dissolved.

[0019] Because the target crystal does not react with the etching solution, it is preserved intact, achieving non-destructive separation from the molybdenum crucible. It should be noted that while a strong oxidizing agent alone can rapidly form a MoO3 passivation film on the molybdenum surface, this film is too stable and tightly covers the surface, hindering further reaction between the oxidizing agent and the internal molybdenum, thus preventing effective corrosion on its own. Conversely, strong corrosive acids alone have difficulty initiating the dissolution of metallic molybdenum, resulting in an extremely low corrosion rate. Therefore, strong oxidizing agents and strong corrosive acids must be used in combination.

[0020] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for non-destructive separation of crystals using acid etching of a molybdenum crucible. This chemical separation method selectively etches the molybdenum crucible, achieving clean separation of the target crystal from the crucible. Compared to traditional mechanical peeling or heating and melting methods, this invention avoids the introduction of mechanical or thermal stress throughout the separation process, fundamentally eliminating secondary damage to the crystal structure and ensuring the integrity and performance consistency of the crystal structure. Furthermore, this method eliminates the uncontrollability and inefficiency of traditional manual operations, achieving batch separation through preset chemical reaction conditions, significantly improving process efficiency and consistency, and effectively solving common industry problems in existing technologies such as high manpower requirements, low efficiency, and high peeling difficulty. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the apparatus for the non-destructive separation of crystals using an acid-etched molybdenum crucible according to the present invention; the diagram includes a reaction vessel 1, an etching solution 2, and a molybdenum crucible 3.

[0022] Figure 2 These are comparison images of the crucible and sapphire crystal before and after separation in Embodiment 1 of the present invention; where the left image is before separation and the right image is after separation. Figure 3 This is a comparison image of the crucible and Ce:YAG crystal before and after separation in Example 2 of the present invention; where the left side is before separation and the right side is after separation. Figure 4 The images show a molybdenum crucible and a CTH:YAG crystal product after manual stripping treatment using existing technology. Detailed Implementation

[0023] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0024] This invention relates to highly corrosive, highly oxidizing, and highly toxic chemicals such as hydrofluoric acid and concentrated sulfuric acid. When implementing this invention, a thorough understanding of the safety risks involved in the operation is essential, and strict adherence to the laboratory safety procedures of the institution is mandatory. Operations must be conducted in a well-ventilated fume hood, the correct acid mixing sequence must be followed, and containers and personal protective equipment compatible with the aforementioned chemicals must be selected. Before operation, all Material Safety Data Sheets (MSDS) for the chemicals involved should be reviewed, and emergency equipment should be ensured to be readily available. The proposed implementation methods of this invention should not be construed as exemptions from relevant health and safety regulations.

[0025] like Figure 1As shown, the present invention provides a method for non-destructive separation of crystals by acid etching of a molybdenum crucible. This method is a chemical separation method. The molybdenum crucible 3 with crystals adhering to it is placed in a reaction vessel 1 containing an etching solution 2 and allowed to stand for reaction until the molybdenum crucible and the crystals are completely separated. The separated crystals are then cleaned and dried to obtain non-destructively separated crystals.

[0026] The present invention will be further described below with reference to specific embodiments: Example 1. Non-destructive separation of sapphire (Al2O3) crystals This embodiment provides a method for non-destructive separation of sapphire (Al2O3) crystals by acid etching of a molybdenum crucible, including the following steps: S1. Preparations before the experiment S11. Wear full personal protective equipment, including Teflon (PTFE) gloves, a Teflon apron and boots, splash-proof sealed goggles and a face shield. Also, confirm that the specific antidote for hydrofluoric acid (such as hexafluoroquinolone or calcium gluconate gel), as well as emergency showers and eyewash stations, are located and functioning properly.

[0027] S12. Prepare the consumables required for the corrosion solution, such as deionized water; 40 wt.% hydrofluoric acid; 98 wt.% concentrated sulfuric acid; dry and uncontaminated polytetrafluoroethylene (PTFE) stirring rod, PTFE container, and borosilicate glass beaker.

[0028] S2. Preparation of corrosive solution To control the corrosion rate and exothermic reaction and avoid an overly vigorous reaction, the solution was prepared according to a volume ratio of deionized water: concentrated sulfuric acid: hydrofluoric acid = 6:3:1, with a total volume of 5L.

[0029] Open the fume hood and begin preparing the acid etching solution. Weigh 3L of deionized water into a borosilicate glass beaker and slowly pour it into a PTFE container. While continuously stirring with a PTFE rod, slowly add 1.5L of concentrated sulfuric acid (98wt.%) along the stir bar. After the diluted concentrated sulfuric acid cools to room temperature, add 0.5L of hydrofluoric acid (40wt.%) while continuously stirring and cooling in an ice-water bath. Strictly control the addition rate of hydrofluoric acid according to the intensity of the reaction. Ensure the temperature remains below 60℃ throughout the entire preparation of the etching solution.

[0030] S3, Corroded Molybdenum Crucible A sapphire (Al₂O₃) crystal adhering to a molybdenum crucible was immersed in a freshly prepared etching solution and allowed to react in a fume hood. After one hour, molybdenum metal was observed to detach from the surface of the sapphire crystal, and the crystal showed no signs of corrosion (e.g., Figure 2 (As shown).

[0031] S4, Crystal Processing Wearing Teflon (PTFE) gloves, quickly remove the sapphire crystal and immediately rinse its surface with plenty of deionized water until neutral. Then, wearing dry Teflon (PTFE) gloves, place the sapphire crystal in deionized water for ultrasonic cleaning to thoroughly remove any residual acid. Subsequently, wipe with anhydrous ethanol and dry with a stream of dry nitrogen to obtain a non-destructive separated crystal.

[0032] S5, Waste Liquid Treatment Carefully transfer the waste mixture of concentrated sulfuric acid and hydrofluoric acid into a corrosion-resistant special waste liquid collection container, clearly label it, and hand it over to a qualified hazardous waste treatment organization for further disposal.

[0033] Example 2. Non-destructive separation of Ce:YAG crystals This embodiment provides a method for non-destructive separation of Ce:YAG crystals by acid etching of a molybdenum crucible, including the following steps: S1. Preparations before the experiment S11. Wear full personal protective equipment, including rubber gloves, a rubber apron and boots, splash-proof goggles and face shield. Also, confirm that the emergency shower and eyewash station are in place and functioning properly.

[0034] S12. Prepare the consumables required for the corrosion solution, such as concentrated hydrochloric acid with a concentration of 38 wt.%; nitric acid with a concentration of 68 wt.%; dry and uncontaminated Teflon stirring rods, Teflon containers, and borosilicate glass beakers.

[0035] S2. Preparation of corrosive solution To control the corrosion rate and exothermic reaction and avoid an overly vigorous reaction, the solution was prepared according to a volume ratio of concentrated hydrochloric acid to nitric acid of 3:1, with a total volume of 600 mL.

[0036] Open the fume hood and begin preparing the acid etching solution. Weigh 450 mL of concentrated hydrochloric acid (38 wt.%) into a borosilicate glass beaker and slowly pour it into a Teflon container. While continuously stirring with a Teflon rod and cooling in an ice-water bath, slowly add 150 mL of nitric acid (68 wt.%) along the stirring rod, strictly controlling the addition rate of nitric acid depending on the intensity of the reaction. Allow the mixture to cool to room temperature and stand for 10-15 minutes. Ensure the temperature remains below 60°C throughout the entire etching solution preparation process.

[0037] S3, Corroded Molybdenum Crucible The Ce:YAG crystals adhering to the molybdenum crucible were immersed in freshly prepared etching solution and allowed to react in a fume hood. After 3 hours, molybdenum metal was observed to detach from the surface of the Ce:YAG crystals, and the crystals showed no signs of corrosion (e.g., Figure 3 (As shown).

[0038] S4, Crystal Processing Wearing rubber gloves, quickly remove the Ce:YAG crystals and immediately rinse the surface of the Ce:YAG crystals with plenty of deionized water until neutral. Then, wearing dry rubber gloves, place the Ce:YAG crystals in deionized water for ultrasonic cleaning to thoroughly remove residual acid. Subsequently, wipe with anhydrous ethanol and dry with a stream of dry nitrogen to obtain non-destructively separated crystals.

[0039] S5, Waste Liquid Treatment Carefully transfer the waste mixture of concentrated hydrochloric acid and nitric acid into a corrosion-resistant special waste liquid collection tank, clearly label it, and hand it over to a qualified hazardous waste treatment organization for further disposal.

[0040] Figure 4 The images show a molybdenum crucible after artificial processing and a physical product of CTH:YAG crystal. Figure 4 It is easy to see that crystals processed by manual peeling methods have many micro-cracks on their surface, making it impossible to achieve non-destructive separation of crystals. The present invention solves the problem of micro-cracks caused by manual peeling by etching molybdenum crucibles with an etchant. Compared with manual operation, the etching method of the present invention is controllable and efficient, enabling batch separation of crucibles and crystals, significantly improving process efficiency and consistency, and effectively solving common industry problems such as high manpower consumption, low efficiency, and peeling difficulty in the prior art.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for non-destructive separation of crystals by acid etching of a molybdenum crucible, characterized in that, The crystals adhering to the molybdenum crucible are immersed in an etchant solution that can dissolve the molybdenum crucible but does not react with the crystals. The reaction is allowed to proceed until the molybdenum crucible is completely dissolved, thus achieving crystal separation. The crystals are then removed, cleaned, and dried to obtain non-destructively separated crystals.

2. The method for non-destructive separation of crystals by acid etching of a molybdenum crucible according to claim 1, characterized in that, The corrosive liquid contains a highly corrosive acid and a strong oxidizing agent.

3. The method for non-destructive separation of crystals by acid etching of a molybdenum crucible according to claim 2, characterized in that, The highly corrosive acid is selected from hydrofluoric acid or concentrated hydrochloric acid; the strong oxidizing agent is selected from concentrated sulfuric acid, nitric acid or hydrogen peroxide.

4. The method for non-destructive separation of crystals by acid etching of a molybdenum crucible according to claim 3, characterized in that, The volume ratio of each component in the corrosive solution is as follows: strong corrosive acid : strong oxidant : deionized water = 1 : 0.33~20 : 0~90.

5. The method for non-destructive separation of crystals by acid etching of a molybdenum crucible according to claim 2, characterized in that, The concentration of the highly corrosive acid is 35-45 wt.%; the concentration of the strong oxidant is 60-98 wt.%.

6. The method for non-destructive separation of crystals by acid etching of a molybdenum crucible according to claim 2, characterized in that, During the preparation of the etchant, the preparation temperature should be controlled to be <60℃.

7. The method for non-destructive separation of crystals by acid etching of a molybdenum crucible according to claim 2, characterized in that, During the static reaction process, the reaction temperature should be controlled to be <100℃.

8. The method for non-destructive separation of crystals by acid etching of a molybdenum crucible according to claim 1, characterized in that, The crystal is an oxide crystal, a sesquioxide crystal, or a mixed sesquioxide crystal.

9. The method for non-destructive separation of crystals by acid etching of a molybdenum crucible according to claim 8, characterized in that, The oxide crystals include Re:YAG, Re:GAGG, Re:YGG, Re:YSGG, and Re:LuAG; the sesquioxide crystals include Re:Y₂O₃ and Re:Al₂O₃; the mixed sesquioxide crystals include Re:YScO₃ and Re:LuScO₃; wherein Re is a dopant ion selected from Er₂O₃. 3+ Tm 3+ Ce 3+ Ho 3+ 、Nd 3+ Cr 3+ Dy 3+ Ti 3+ Yb 3+ One or more of them.

10. The method for non-destructive separation of crystals by acid etching of a molybdenum crucible according to claim 1, characterized in that, The cleaning process includes rinsing the crystal surface with a large amount of deionized water until it is neutral, followed by ultrasonic cleaning with deionized water. The drying process involves wiping with anhydrous ethanol and then drying with dry nitrogen gas.

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