Synthetic method of large-size alpha-aluminum hydride

Abstract

The invention discloses a synthesis method of large-size alpha-aluminum hydride. The synthesis method comprises the following steps: carrying out ball-milling activation on NaAlH4 slurry, and then adding an initiator to obtain a turbid liquid A; dropwise adding an anhydrous AlCl3 solution into the turbid liquid A, stirring and reacting, and filtering the reaction liquid to obtain an etherate solution; dropwise adding the etherate solution into the solution containing the ether removal aid, stirring and reacting to obtain turbid liquid B, and washing and drying precipitates obtained by filtering to obtain the large-size alpha-aluminum hydride. According to the method, low-cost NaAlH4 is adopted to replace expensive LiAlH4, so that the purposes of reducing the production cost and improving the aluminum hydride product quality are achieved, the product crystal form purity is high and can reach 99% or above at most, the crystal particle size is 50 microns or above, various performance indexes are more excellent, and the application of alpha-AlH3 in the civil field and the tip field of rocket boosters and the like can be expanded.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of hydrogen storage materials, in particular to a synthesis method of large-size alpha-trihydroaluminum. BACKGROUND

[0002] The Gibbs free energy of AlH3 is 48.5+ / -0.4 kJ / mol, and according to thermodynamics, AlH3 is a very unstable binary hydride which will slowly decompose into Al and H2 at room temperature. Through differential thermal analysis, it is shown that when the temperature reaches 175 DEG C to 200 DEG C, the decomposition will intensify, and hydrogen will be rapidly released. The hydrogen content of AlH3 is very high, and the mass hydrogen storage density can reach 10.08 wt%, which is the second highest mass hydrogen storage density among the binary hydrides found at present, and the volume hydrogen storage density reaches 148 g / L, which is twice the volume hydrogen storage density of liquid hydrogen. The products of AlH3 combustion in air are Al2O3 and water, which are both non-toxic and harmless products, and AlH3 is a very clean fuel, and is widely used in solid propellants and solid-liquid mixed propellants, and is popular in the field of fuel cells.

[0003] There are seven different crystal forms of AlH3, and four crystal forms of alpha, alpha', beta and gamma have successfully prepared single crystal products. Among the four crystal forms, the thermodynamic stability of the alpha form is the highest, and the alpha form is the only crystal form with practical value at present, the beta form and the gamma form can be converted into the alpha form under certain conditions, and the alpha' form cannot be converted.

[0004] Patent No. CN106957046A discloses an improved process for preparing alpha-trihydroaluminum. The etherate is prepared at low temperature, the clear etherate solution is filtered out by using a filtering device, and then hot toluene solution is added to remove ether. Patent No. CN109970030A discloses a synthesis process of alpha-trihydroaluminum. The clear filtrate is filtered out, and the filtrate is heated to prepare a slurry, and then the lower solid is put into heated toluene to remove ether. Patent No. CN107098313A discloses a preparation method of alpha-trihydroaluminum. The clear filtrate is filtered out, and then added into heated toluene solution to remove ether, and the reaction system needs to be heated after adding the filtrate twice.

[0005] The above-mentioned patents all adopt the conventional "wet method" synthesis process route, and two-step synthesis is needed in the process, LiAlH4 and AlCl3 are used as raw materials, and an etherate is synthesized in an ether or ether / aromatic hydrocarbon solution. Then, the etherate is removed by thermal cracking in an inert aromatic hydrocarbon solution or under vacuum to obtain alpha-AlH3, and the representative chemical reaction process is as follows.

[0006] AlCl3+nEt2O→AlCl3·nEt2O

[0007] 3LiAlH4+AlCl3·nEt2O→4AlH3·nEt2O+3LiCl

[0008] AlH3·nEt2O→AlH3+nEt2O

[0009] The aforementioned AlH3 still has many problems. For example, the reaction uses LiAlH4 as the synthesis raw material, which costs more than one million yuan per ton. The high price severely limits the application of α-AlH3 in the civilian field. During the deetherification and crystallization process, non-α-type AlH3 is easily generated or incomplete deetherification occurs. These are mixed in the product and are difficult to separate and purify, which reduces the purity and performance of the product. The α-AlH3 crystals prepared are small in size and have poor storage stability. Summary of the Invention

[0010] This invention addresses the problems of low purity, small crystal size, and high preparation cost of α-AlH3 in existing technologies by providing a method for preparing α-AlH3 using NaAlH4 as a reactant. The resulting α-AlH3 has high purity, large crystal size, and a particle size of over 50 μm, which can well meet the needs of more application scenarios.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A method for synthesizing large-sized α-aluminum trihydride includes the following steps:

[0013] Step 1: In an inert environment, NaAlH4 is dissolved and filtered to remove 90-95% of the solvent. The remaining NaAlH4 slurry is ball-milled and activated. After activation, it is dispersed in a solvent, and an initiator is added to obtain suspension A, which is stored at low temperature for later use.

[0014] Step 2: Under an inert environment, anhydrous AlCl3 solution is added dropwise to suspension A and stirred to react. The reaction solution is filtered to obtain an ether compound solution.

[0015] Step 3: Under an inert environment, the etherified solution is added dropwise to a solution containing a deetherifying agent, and the reaction is stirred to obtain suspension B;

[0016] Step 4: Filter the suspension B, and wash and dry the resulting precipitate to obtain the large-sized α-aluminum trihydride.

[0017] This invention uses NaAlH4 as the raw material for synthesis, replacing the expensive LiAlH4 and reducing synthesis costs. The reaction rate is increased through purification and activation of NaAlH4. An appropriate amount of initiator is added during the reaction. By using low-cost NaAlH4 instead of expensive LiAlH4, the goal of reducing production costs and improving the quality of aluminum hydride products is achieved. The product has high crystal purity, reaching up to 99% or more, with crystal particle sizes exceeding 50 μm, and even exceeding 90 μm or 100 μm. Its performance indicators are superior, expanding the application of α-AlH3 in civilian fields and cutting-edge fields such as rocket propellants. The reaction formula is as follows:

[0018] 3NaAlH4+AlCl3·nEt2O→4AlH3·nEt2O+3NaCl

[0019] The initiator includes one or more of LiAlH4, LiBH4, LiH, LiCl, and BH3; preferably, the initiator is LiAlH4.

[0020] The molar ratio of the initiator to NaAlH4 is 0.1 to 1.2:1.

[0021] The solvent in step 1 includes one or more of tetrahydrofuran, dimethyl ether, diethyl ether, propyl ether, butyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, benzene, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, and pentane. Retaining a portion of the solvent is to prevent direct contact between the gaseous components and the NaAlH4 surface, which could deactivate the active sites on the NaAlH4 surface. Keeping the slurry moist before ball milling prevents heat buildup during the process that could lead to NaAlH4 decomposition. This eliminates the need for ultra-low temperatures (e.g., 77K), effectively reducing equipment requirements and energy consumption.

[0022] Preferably, the solvent in step 1 is one or more of tetrahydrofuran, dimethyl ether, diethyl ether, propyl ether, butyl ether, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether.

[0023] The solvents used in the anhydrous AlCl3 solution include one or more of tetrahydrofuran, dimethyl ether, diethyl ether, propyl ether, butyl ether, ethylene glycol dimethyl ether, benzene, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, and pentane. AlCl3 can dissolve in a variety of polar solvents and form complexes. In the dissolution process of AlCl3, different organic reagents can be selected as ligands for the complexes. Preferred solvents include one or more of tetrahydrofuran, dimethyl ether, diethyl ether, propyl ether, butyl ether, and ethylene glycol dimethyl ether.

[0024] The ball-to-material ratio during ball milling activation is 30–40:1, the ball milling temperature is -5–5℃, and the ball milling time is 30–90 min.

[0025] The dropping rate of anhydrous AlCl3 solution is 10–40 mL / min;

[0026] In step 2, the temperature for dropwise addition and reaction is -15 to -5℃, and the reaction continues for 0.5 to 1.5 hours after the dropwise addition is completed.

[0027] In step 2, the molar ratio of NaAlH4 to AlCl3 is 4.6 to 2:1.

[0028] In step 2, a sand-plate filter tube is used to filter out the clear ether compound filtrate to prevent insoluble byproducts generated during the preparation of the ether compound and unreacted insoluble raw materials from entering the deetherification solution and affecting the purity of the product.

[0029] The deetherifying aid includes one or more of LiAlH4, LiBH4, LiH, and LiCl; the mass of the deetherifying aid is 5 to 40 wt% of the mass of NaAlH4.

[0030] The solution containing the deetherifying agent uses an inert solvent, including one or more of benzene, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, pentane, and n-heptane. An inert solvent allows for more uniform heating of the entire system and rapidly removes the ligand molecules generated after deetherification, preventing them from complexing with AlH3 molecules again. Preferably, the solvent used in the solution containing the deetherifying agent is toluene, resulting in higher product purity.

[0031] The etherified compound solution is added dropwise to the solution containing the deetherifying agent at a rate of 2–10 mL / min. The etherified compound is insoluble in the inert solvent and rapidly precipitates as seed crystals. Subsequent drops of the etherified compound continue to grow on these seed crystals, completing the deetherification and crystal transformation process. A slower dropping rate is more conducive to the growth of α-AlH3 and results in better purity; however, too slow a rate also affects the overall process flow and increases time costs.

[0032] In step 3, the temperature for dropwise addition and reaction is 60-100℃, and the reaction continues for 1-4 hours after the dropwise addition is completed. Preferably, the temperature for dropwise addition and reaction in step 3 is 75-100℃, more preferably 80-100℃, and even more preferably 85-95℃.

[0033] Step 4 is replaced by: using the suspension B as an electrolyte for electrodeposition, followed by ultrasonication of the electrode sheet after electrodeposition, collecting the ultrasonically desorbed solid, washing and drying to obtain the large-sized α-aluminum trihydride.

[0034] Selective adsorption of α-AlH3 via electrophoretic deposition further enhances the crystal purity and performance of the product. Applying voltage to the electrophoretic cell causes AlH3 molecules to move directionally and deposit on specific silicon wafers on the electrode plates. The magnitude of the voltage affects the deposition rate; controlling the voltage within a certain range allows for better control of the deposition rate.

[0035] Preferably, the electrode sheet is a silicon wafer with a Ti layer electroplated on its surface.

[0036] The electrodeposition voltage is 0.45–2.80 V, and the electrodeposition time is 30–90 min;

[0037] The ultrasonic treatment involves sonicating the electrode sheet in an inert solvent, which includes one or more of benzene, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, and pentane. The ultrasonic treatment lasts for 1-5 minutes at a power of 600W-800W, disrupting the weak physical adsorption forces and allowing the α-AlH3 solid to detach rapidly from the silicon wafer. The ultrasonically treated silicon wafer can be reused after cleaning.

[0038] Preferably, a larger silicon wafer size is more advantageous, as increasing the surface area of ​​the silicon wafer facilitates the deposition of α-AlH3. During electroplating, it is necessary to control the voltage stably to ensure a more uniform coating thickness and a denser, smoother surface.

[0039] The washing process includes washing with one or more of the following: diethyl ether and inorganic acid, water, and ethanol. Preferably, the precipitate is washed sequentially with diethyl ether, inorganic acid, water, ethanol, and then back to diethyl ether to remove as much unreacted raw material and impurities as possible. The inorganic acid includes one or more of dilute hydrochloric acid, phosphoric acid, and hypochlorous acid.

[0040] The inert environment refers to an environment in the form of nitrogen, argon, or helium. This includes the preparation of raw material solutions and the reaction process, which employs repeated vacuuming and refilling with inert gas to ensure that the reaction process continues under the protection of inert gas, thus preventing air and moisture from affecting the reaction.

[0041] The aforementioned low-temperature preservation refers to storing the product in an inert environment at -15 to -5°C to avoid oxidation or decomposition.

[0042] The α-AlH3 prepared by this invention has a yield of over 96%, an α-crystal purity of over 99%, and a size of over 50 μm, preferably 50-120 μm.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] This invention utilizes relatively inexpensive NaAlH4 instead of the traditionally expensive LiAlH4 as a raw material, and proposes a method for activating NaAlH4 to obtain high-purity, large-size α-AlH3 crystals, thus improving the product's various performance indicators. This synthesis technology is expected to significantly reduce production costs and expand the application of α-AlH3 in the civilian sector. Attached Figure Description

[0045] Figure 1 The image shows the XRD data of AlH3 prepared in Example 1.

[0046] Figure 2 The image shows the XRD data of AlH3 prepared in Example 2.

[0047] Figure 3 The image shows the XRD data of AlH3 prepared in Example 3.

[0048] Figure 4 The image shows the XRD data of AlH3 prepared in Example 4.

[0049] Figure 5 The image shows the XRD data of AlH3 prepared in Example 5.

[0050] Figure 6 The XRD data of AlH3 prepared in Example 6 is shown.

[0051] Figure 7 The image shows the XRD data of AlH3 prepared in Example 7.

[0052] Figure 8 The XRD data of AlH3 prepared for Comparative Example 1 is shown.

[0053] Figure 9 The XRD data of AlH3 prepared for Comparative Example 2 is shown.

[0054] Figure 10 TGA-DSC data images of AlH3 prepared for Example 1(a) and Comparative Example 3(b).

[0055] Figure 11 SEM images of AlH3 prepared in Example 1 (A) and Comparative Example 3 (B). Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0057] All raw materials used in the following specific implementation methods were purchased from the market.

[0058] Example 1

[0059] Step 1: In a glove box, place 12.4g of NaAlH4 into a single-necked flask, add 200mL of tetrahydrofuran, stir to dissolve, and then filter the clear filtrate using a sintered glass funnel. Place the filtrate under dynamic vacuum to remove 95% of the tetrahydrofuran, forming a mud-like slurry, for later use.

[0060] Step 2: In a glove box, add the NaAlH4 slurry to a stainless steel cylinder pre-cooled to 0°C. Add 40g of 10mm ceramic balls and ball mill for 40 minutes, maintaining the temperature between -5°C and 0°C during the milling process. Pour the slurry into a single-necked bottle and rinse off the solids adhering to the cylinder and ceramic balls with 100mL of toluene and 100mL of diethyl ether. Add 3.31g of LiAlH4 to the suspension and place it in a -10°C cold bath for later use.

[0061] Step 3: Place 8.8g of AlCl3 into a single-necked bottle in a glove box, and slowly add 60mL of a mixed solution of toluene and diethyl ether with a volume ratio of 1:1. Stir continuously during the addition until the solid is completely dissolved. Place the bottle in a cold bath at -10℃ for later use.

[0062] Step 4: At a temperature of -10℃, slowly add AlCl3 solution dropwise to a mixed suspension of NaAlH4 and LiAlH4, maintaining a dropping rate of 10 mL / min. After the addition is complete, continue the reaction for 1.5 h, then filter the clear ether compound solution using a sand-plate filter tube and place it in a cold bath at -10℃ for later use.

[0063] Step 5: Evacuate the three-necked flask, then purge it with nitrogen to remove air. Repeat this process three times. Add 1 L of anhydrous toluene and 3.3 g of LiAlH4, heat to 95 °C, and stir to form a suspension. Slowly add the ether compound solution to the hot toluene solution at a dropping rate of 2 mL / min. After the addition is complete, continue the reaction for 1 h.

[0064] Step 6: Prepare a silicon wafer with dimensions of 5cm×5cm×2mm, place the silicon wafer in an electrolytic cell, and electroplate a layer of metallic titanium evenly and densely on the silicon wafer.

[0065] Step 7: Lay the silicon wafer flat at the bottom of the electrostatic precipitator, pour the deetherified suspension into the electrostatic precipitator, control the voltage at 2.0V, electrodeposit for 40 minutes, remove the silicon wafer, place it in an ultrasonic cleaner, sonicate for 1 minute, and filter out the solid powder. Wash successively with diethyl ether, dilute hydrochloric acid, deionized water, anhydrous ethanol, and diethyl ether, and dry in a vacuum drying oven at 50℃ for 2 hours. The prepared AlH3 has a purity of 99.9% and a particle size of 82μm.

[0066] Example 2

[0067] Step 1: In a glove box, place 10.8g of NaAlH4 into a single-necked flask, add 200mL of tetrahydrofuran, stir to dissolve, and then filter the clear filtrate using a sintered glass funnel. Place the filtrate under dynamic vacuum to remove 95% of the solvent, forming a mud-like slurry, for later use.

[0068] Step 2: In a glove box, add the NaAlH4 slurry to a stainless steel cylinder pre-cooled to 0°C. Add 35g of 10mm ceramic balls and ball mill for 40 minutes, maintaining the temperature between -5°C and 0°C during the milling process. Pour the slurry into a single-necked bottle and rinse with 100mL of toluene and 100mL of diethyl ether to remove the solids adhering to the cylinder and ceramic balls, forming a suspension. Add 3.29g of LiAlH4 to the suspension and place it in a -10°C cold bath for later use.

[0069] Step 3: Place 8g of AlCl3 into a single-necked bottle in a glove box, and slowly add 60mL of a mixed solution of diethyl ether and toluene with a volume ratio of 1:1. Stir continuously during the addition until the solid is completely dissolved. Place the bottle in a cold bath at -10℃ for later use.

[0070] Step 4: At -10℃, slowly add AlCl3 solution dropwise to the mixed suspension of NaAlH4 and LiBH4, maintaining a dropping rate of 10 mL / min. After the addition is complete, continue the reaction for 1.5 h, then filter the clear ether compound solution using a sand-plate filter tube and place it in a cold bath at -10℃ for later use.

[0071] Step 5: Evacuate the three-necked flask, then purge it with nitrogen to remove air. Repeat this process three times. Add 1 L of anhydrous toluene and 2.5 g of LiAlH4, heat to 90 °C, and stir to form a suspension. Slowly add the ether compound solution to the hot toluene solution at a dropping rate of 2 mL / min. After the addition is complete, continue the reaction for 1 hour.

[0072] Step 6: Prepare a silicon wafer with dimensions of 5cm×5cm×2mm, place the silicon wafer in an electrolytic cell, and electroplate a layer of metallic titanium evenly and densely on the silicon wafer.

[0073] Step 7: Lay the silicon wafer flat at the bottom of the electrostatic precipitator, pour the deetherified suspension into the electrostatic precipitator, control the voltage at 2V, electrodeposit for 40 minutes, remove the silicon wafer, place it in an ultrasonic cleaner, sonicate for 5 minutes, and filter out the solid powder. Wash successively with diethyl ether, dilute hydrochloric acid, deionized water, anhydrous ethanol, and diethyl ether, and dry in a vacuum drying oven at 50℃ for 2 hours. The prepared AlH3 has a purity of 98% and a particle size of 65μm.

[0074] Example 3

[0075] Step 1: In a glove box, place 9.6g of NaAlH4 into a single-necked flask, add 200mL of ethylene glycol dimethyl ether, stir to dissolve, and then filter the clear filtrate using a sintered glass funnel. Place the filtrate under dynamic vacuum to remove 95% of the ethylene glycol dimethyl ether, forming a mud-like slurry, for later use.

[0076] Step 2: In a glove box, add the NaAlH4 slurry to a stainless steel cylinder pre-cooled to 0°C. Add 38g of 10mm ceramic balls and ball mill for 40 minutes, maintaining the temperature between -5°C and 0°C during the milling process. Pour the slurry into a single-necked bottle and rinse off the solids adhering to the cylinder and ceramic balls with 100mL of toluene and 100mL of ethylene glycol dimethyl ether. Add 0.57g of LiH to the suspension and place it in a -10°C cold bath for later use.

[0077] Step 3: Place 7.6g of AlCl3 into a single-necked bottle in a glove box, and slowly add 60mL of a mixed solution of toluene and ethylene glycol dimethyl ether (toluene to dimethyl ether in a volume ratio of 1:1). Stir continuously during the addition until the solid is completely dissolved. Place the bottle in a cold bath at -10℃ for later use.

[0078] Step 4: At -10℃, slowly add AlCl3 solution dropwise to the mixed suspension of NaAlH4 and LiH, maintaining a dropping rate of 10mL / min. After the addition is complete, continue the reaction for 1.5h, then filter the clear ether compound solution using a sand-plate filter tube and place it in a cold bath at -10℃ for later use.

[0079] Step 5: Evacuate the three-necked flask, then purge it with nitrogen to remove air. Repeat this process three times. Add 1 L of anhydrous xylene and 3.1 g of LiAlH4, heat to 95 °C, and stir to form a suspension. Slowly add the ether compound solution to the hot xylene solution at a rate of 3 mL / min. After the addition is complete, continue the reaction for 1 hour.

[0080] Step 6: Prepare a silicon wafer with dimensions of 5cm×5cm×2mm, place the silicon wafer in an electrolytic cell, and electroplate a layer of metallic titanium evenly and densely on the silicon wafer.

[0081] Step 7: Lay the silicon wafer flat at the bottom of the electrostatic precipitator, pour the deetherified suspension into the electrostatic precipitator, control the voltage at 1.5V, electrodeposit for 50 minutes, remove the silicon wafer, place it in an ultrasonic cleaner, sonicate for 5 minutes, and filter out the solid powder. Wash successively with diethyl ether, hypochlorous acid, deionized water, anhydrous ethanol, and diethyl ether, and dry in a vacuum drying oven at 50℃ for 2 hours. The AlH3 prepared has a purity of 96% and a particle size of 88 μm.

[0082] Example 4

[0083] Step 1: In a glove box, place 11.6g of NaAlH4 into a single-necked flask, add 200mL of ethylene glycol dimethyl ether, stir to dissolve, and then filter the clear filtrate using a sintered glass funnel. Place the filtrate under dynamic vacuum to remove 95% of the solvent, forming a mud-like slurry, for later use.

[0084] Step 2: In a glove box, add the NaAlH4 slurry to a stainless steel cylinder pre-cooled to 0°C. Add 40g of 10mm ceramic balls and ball mill for 60 minutes, maintaining the temperature between -5°C and 0°C during the milling process. Pour the slurry into a single-necked bottle and rinse off the solids adhering to the cylinder and ceramic balls with 200mL of diethyl ether. Add 2.92g of LiAlH4 to the suspension and place it in a -10°C cold bath for later use.

[0085] Step 3: Place 8.4g of AlCl3 into a single-necked bottle in a glove box, slowly add 60mL of diethyl ether solution, stirring constantly during the addition process, until the solid is completely dissolved, and place it in a cold bath at -10℃ for later use.

[0086] Step 4: At -10℃, slowly add AlCl3 solution dropwise to a mixed suspension of NaAlH4 and LiAlH4, maintaining a dropping rate of 10 mL / min. After the addition is complete, continue the reaction for 1.5 h, then filter the clear ether compound solution using a sand-plate filter tube and place it in a cold bath at -10℃ for later use.

[0087] Step 5: Evacuate the three-necked flask, then purge it with nitrogen to remove air. Repeat this process three times. Add 1 L of anhydrous toluene and 3.9 g of LiAlH4, heat to 95 °C, and stir to form a suspension. Slowly add the ether compound solution to the hot toluene solution at a dropping rate of 3 mL / min. After the addition is complete, continue the reaction for 1 hour.

[0088] Step 6: Prepare a silicon wafer with dimensions of 5cm×5cm×2mm, place the silicon wafer in an electrolytic cell, and electroplate a layer of metallic titanium evenly and densely on the silicon wafer.

[0089] Step 7: Lay the silicon wafer flat at the bottom of the electrostatic precipitator, pour the deetherified suspension into the electrostatic precipitator, control the voltage at 1.75V, electrodeposit for 40 minutes, remove the silicon wafer, place it in an ultrasonic cleaner, and sonicate for 1 minute to filter out the solid powder. Wash successively with diethyl ether, dilute hydrochloric acid, deionized water, anhydrous ethanol, and diethyl ether, and dry in a vacuum drying oven at 50℃ for 2 hours. The AlH3 obtained has a purity of 99.2% and a particle size of 77 μm.

[0090] Example 5

[0091] Step 1: In a glove box, place 12.6g of NaAlH4 into a single-necked flask, add 200mL of propyl ether, stir to dissolve, and then filter the clear filtrate using a sintered glass funnel. Place the filtrate under dynamic vacuum to remove 95% of the propyl ether, forming a mud-like slurry, for later use.

[0092] Step 2: In a glove box, add the NaAlH4 slurry to a stainless steel cylinder pre-cooled to 0°C. Add 40g of 10mm ceramic balls and ball mill for 80 minutes, maintaining the temperature between -5°C and 0°C during the milling process. Pour the slurry into a single-necked bottle and rinse off the solids adhering to the cylinder and ceramic balls with 100mL of pentane and 100mL of propyl ether. Add 3.96g of LiCl to the suspension and place it in a -10°C cold bath for later use.

[0093] Step 3: Place 9.4g of AlCl3 into a single-necked bottle in a glove box, and slowly add 60mL of a mixed solution of pentane and propyl ether with a volume ratio of 1:1. Stir continuously during the addition until the solid is completely dissolved. Place the bottle in a cold bath at -10℃ for later use.

[0094] Step 4: At a temperature of -10℃, slowly add AlCl3 solution dropwise to a mixed suspension of NaAlH4 and LiCl, maintaining a dropping rate of 10mL / min. After the addition is complete, continue the reaction for 1.5h, then filter the clear ether compound solution using a sand-plate filter tube and place it in a cold bath at -10℃ for later use.

[0095] Step 5: Evacuate the three-necked flask, then purge it with nitrogen to remove air. Repeat this process three times. Add 1 L of anhydrous ethylbenzene, 1 g of LiBH4, and 3.1 g of LiAlH4. Heat to 95°C and stir to form a suspension. Slowly add the ether compound solution dropwise to the hot ethylbenzene solution at a rate of 3 mL / min. After the addition is complete, continue the reaction for 1 hour.

[0096] Step 6: Prepare a silicon wafer with dimensions of 5cm×5cm×2mm, place the silicon wafer in an electrolytic cell, and electroplate a layer of metallic titanium evenly and densely on the silicon wafer.

[0097] Step 7: Lay the silicon wafer flat at the bottom of the electrostatic precipitator, pour the deetherified suspension into the electrostatic precipitator, control the voltage at 2.6V, electrodeposit for 40 minutes, remove the silicon wafer, place it in an ultrasonic cleaner, sonicate for 2 minutes, and filter out the solid powder. Wash sequentially with diethyl ether, phosphoric acid, deionized water, anhydrous ethanol, and diethyl ether, and dry in a vacuum drying oven at 50℃ for 2 hours. The AlH3 obtained has a purity of 99.5% and a particle size of 92 μm.

[0098] Example 6

[0099] Step 1: In a glove box, place 11.7g of NaAlH4 into a single-necked flask, add 200mL of tetrahydrofuran, stir to dissolve, and then filter the clear filtrate using a sintered glass funnel. Place the filtrate under dynamic vacuum to remove 95% of the tetrahydrofuran, forming a mud-like slurry, for later use.

[0100] Step 2: In a glove box, add the NaAlH4 slurry to a stainless steel cylinder pre-cooled to 0°C. Add 40g of 10mm ceramic balls and ball mill for 40 minutes, maintaining the temperature between -5°C and 0°C during the milling process. Pour the slurry into a single-necked bottle and rinse off the solids adhering to the cylinder and ceramic balls with 100mL of pentane and 100mL of tetrahydrofuran. Add 1.52g of LiAlH4 to the suspension and place it in a -10°C cold bath for later use.

[0101] Step 3: Place 8.3g of AlCl3 into a single-necked bottle in a glove box, and slowly add 60mL of a mixed solution of pentane and diethyl ether with a volume ratio of 1:1. Stir continuously during the addition until the solid is completely dissolved. Place the bottle in a cold bath at -10℃ for later use.

[0102] Step 4: At a temperature of -10℃, slowly add AlCl3 solution dropwise to a mixed suspension of NaAlH4 and LiAlH4, maintaining a dropping rate of 10 mL / min. After the addition is complete, continue the reaction for 1.5 h, then filter the clear ether compound solution using a sand-plate filter tube and place it in a cold bath at -10℃ for later use.

[0103] Step 5: Evacuate the three-necked flask, then purge it with nitrogen to remove air. Repeat this process three times. Add 1 L of anhydrous n-hexane and 4.1 g of LiAlH4, heat to 85 °C, and stir to form a suspension. Slowly add the ether compound solution to the hot n-hexane solution at a dropping rate of 3 mL / min. After the addition is complete, continue the reaction for 1 h.

[0104] Step 6: Prepare a silicon wafer with dimensions of 5cm×5cm×2mm, place the silicon wafer in an electrolytic cell, and electroplate a layer of metallic titanium evenly and densely on the silicon wafer.

[0105] Step 7: Lay the silicon wafer flat at the bottom of the electrostatic precipitator, pour the deetherified suspension into the electrostatic precipitator, control the voltage at 1.55V, electrodeposit for 40 minutes, remove the silicon wafer, place it in an ultrasonic cleaner, sonicate for 2 minutes, and filter out the solid powder. Wash successively with diethyl ether, hypochlorous acid, deionized water, anhydrous ethanol, and diethyl ether, and dry in a vacuum drying oven at 50℃ for 2 hours. The AlH3 prepared has a purity of 99.6% and a particle size of 114 μm.

[0106] Example 7

[0107] Step 1: In a glove box, place 9.7g of NaAlH4 in a single-necked flask, add 200mL of dimethyl ether, stir to dissolve, and then filter the clear filtrate using a sintered glass funnel. Place the filtrate under dynamic vacuum to remove 95% of the tetrahydrofuran, forming a mud-like slurry, for later use.

[0108] Step 2: In a glove box, add the NaAlH4 slurry to a stainless steel cylinder pre-cooled to 0°C. Add 40g of 10mm ceramic balls and ball mill for 90 minutes, maintaining the temperature between -5°C and 0°C during the milling process. Pour the slurry into a single-necked bottle and rinse off the solids adhering to the cylinder and ceramic balls with 100mL of cyclohexane and 100mL of dimethyl ether. Add 2.22g of LiAlH4 to the suspension and place it in a -10°C cold bath for later use.

[0109] Step 3: Place 7.3g of AlCl3 into a single-necked bottle in a glove box, and slowly add 60mL of a mixed solution of cyclohexane and dimethyl ether with a volume ratio of 1:1. Stir continuously during the addition until the solid is completely dissolved. Place the bottle in a cold bath at -10℃ for later use.

[0110] Step 4: At a temperature of -10℃, slowly add AlCl3 solution dropwise to a mixed suspension of NaAlH4 and LiAlH4, maintaining a dropping rate of 10 mL / min. After the addition is complete, continue the reaction for 1.5 h, then filter the clear ether compound solution using a sand-plate filter tube and place it in a cold bath at -10℃ for later use.

[0111] Step 5: Evacuate the three-necked flask, then purge it with nitrogen to remove air. Repeat this process three times. Add 1 L of anhydrous cyclohexane and 4.1 g of LiAlH4, heat to 88 °C, and stir to form a suspension. Slowly add the ether compound solution to the hot n-hexane solution at a rate of 3 mL / min. After the addition is complete, continue the reaction for 1 hour.

[0112] Step 6: Prepare a silicon wafer with dimensions of 5cm×5cm×2mm, place the silicon wafer in an electrolytic cell, and electroplate a layer of metallic titanium evenly and densely on the silicon wafer.

[0113] Step 7: Lay the silicon wafer flat at the bottom of the electrostatic precipitator, pour the deetherified suspension into the electrostatic precipitator, control the voltage at 1.5V, electrodeposit for 60 minutes, remove the silicon wafer, place it in an ultrasonic cleaner, sonicate for 3 minutes, and filter out the solid powder. Wash successively with diethyl ether, dilute hydrochloric acid, deionized water, anhydrous ethanol, and diethyl ether, and dry in a vacuum drying oven at 50℃ for 2 hours. The AlH3 obtained has a purity of 99.6% and a particle size of 98 μm.

[0114] Comparative Example 1

[0115] The experimental conditions for this comparative example were the same as in Example 1, the only difference being that electrophoretic deposition was not performed on the silicon wafer. After step five, the reaction solution was filtered to obtain a solid granular grayish-white powder. It was washed sequentially with diethyl ether, dilute hydrochloric acid, deionized water, anhydrous ethanol, and diethyl ether, and then dried in a vacuum drying oven at 50°C for 2 hours. The AlH3 obtained had a purity of 97% and a particle size of 63 μm.

[0116] Comparative Example 2

[0117] The experimental conditions for this comparative example were the same as in Example 1, except that the NaAlH4 used was directly applied without the purification and activation treatments in steps 1 and 2. It was directly dissolved, and 3.31 g of LiAlH4 was added. The mixture was then placed in a -10°C cold bath for later use. Subsequent steps were the same as in Example 1, resulting in AlH3 with a purity of 54% and a particle size of 77 μm.

[0118] Comparative Example 3

[0119] The experimental conditions for this comparative example were the same as those for Example 1, except that NaAlH4 was replaced with LiAlH4 as the reaction raw material. The AlH3 prepared had a purity of 92% and a particle size of 20-40 μm.

[0120] Results Analysis

[0121] The XRD patterns of AlH3 prepared in Examples 1 and 2 are as follows: Figure 1 and Figure 2 The XRD pattern of AlH3 prepared in Example 4 is as follows: Figure 4 As shown in the results, the XRD data in Example 2 shows a diffuse peak in the small angle range. This diffuse peak is due to the fact that some ether compounds did not complete the deethering process during the deethering and crystallization process. This indicates that the deethering temperature in the example was low, which is not conducive to the deethering and crystallization of the ether compounds.

[0122] The XRD patterns of AlH3 prepared in Examples 1, 3, and 5 are shown below. Figure 1 , Figure 3 and Figure 5 As can be seen from the results, the XRD data in Examples 3 and 5 show diffuse peaks in the small angle range. These diffuse peaks are due to the fact that some ether compounds were not completely deetherified during the deetherification and crystallization process. This indicates that different initiators have a slight impact on the purity of the samples. The preferred initiator is LiAlH4.

[0123] The XRD patterns of AlH3 prepared in Examples 1, 6, and 7 are shown below. Figure 1 , Figure 6 and Figure 7 The results show that the samples still have incomplete deetherification and low product purity, indicating that the solution of the deetherification aid is very important for the deetherification process, and toluene is the preferred solution of the deetherification aid.

[0124] The XRD patterns of AlH3 prepared in Example 1 and Comparative Example 1 are shown below. Figure 1 and Figure 8 As can be seen from the results, the product of Comparative Example 1 contains a small amount of α′ type product. Electrophoretic deposition can avoid the contamination of a small amount of unstable α′ type product in the sample and effectively improve the purity of the product.

[0125] The XRD patterns of AlH3 prepared in Example 1 and Comparative Example 2 are as follows: Figure 1 and Figure 9 The results show that the product in the comparative example contains a large amount of α′ type product, indicating that the purification or activation process can effectively avoid the generation of unstable α′ type product during the deetherification and crystallization process.

[0126] The TGA-DSC data of AlH3 prepared in Example 1 and Comparative Example 3 are as follows: Figure 10 As shown, the hydrogen content of AlH3 in Example 1 is 10 wt%, while the hydrogen content in Comparative Example 3 is 9.5 wt%. It can be seen that under the same conditions, AlH3 obtained by using sodium aluminum hydride as raw material has a higher hydrogen content. At the same time, the TGA-DSC curve of AlH3 in Comparative Example 3 shows obvious fluctuations and instability, indicating that it contains other impurities or AlH3 with different crystal forms, and the product purity is low.

[0127] SEM images of AlH3 prepared in Example 1 and Comparative Example 3 are shown below. Figure 11 As shown, the sample crystal obtained in Example 1 exhibits a cubic crystal structure and a clean crystal surface, indicating that no small amount of impurities are attached. The sample crystal obtained in Comparative Example 3 exhibits a near-cubic crystal structure and shows agglomeration, with obvious impurities attached to the crystal surface.

Claims

1. A method for synthesizing large-sized α-aluminum trihydride, characterized in that, Including the following steps: Step 1: In an inert environment, NaAlH4 is dissolved and filtered to remove 90-95% of the solvent. The remaining NaAlH4 slurry is ball-milled and activated. After activation, it is dispersed in a solvent, and an initiator is added to obtain suspension A, which is stored at low temperature for later use. Step 2: Under an inert environment, anhydrous AlCl3 solution is added dropwise to suspension A and stirred to react. The reaction solution is filtered to obtain an ether compound solution. Step 3: Under an inert environment, the etherified solution is added dropwise to a solution containing a deetherifying agent, and the reaction is stirred to obtain suspension B; Step 4: Filter the suspension B, and wash and dry the resulting precipitate to obtain the large-sized α-aluminum trihydride.

2. The method for synthesizing large-size α-aluminum trihydride according to claim 1, characterized in that, The initiator includes one or more of LiAlH4, LiBH4, LiH, LiCl, and BH3; The molar ratio of the initiator to NaAlH4 is 0.1 to 1.2:

1.

3. The method for synthesizing large-size α-aluminum trihydride according to claim 1, characterized in that, The solvent in step 1 includes one or more of the following: tetrahydrofuran, dimethyl ether, diethyl ether, propyl ether, butyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, benzene, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, and pentane. The solvents used in anhydrous AlCl3 solutions include one or more of the following: tetrahydrofuran, dimethyl ether, diethyl ether, propyl ether, butyl ether, ethylene glycol dimethyl ether, benzene, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, and pentane.

4. The method for synthesizing large-size α-aluminum trihydride according to claim 1, characterized in that, The ball-to-material ratio during ball milling activation is 30–40:1, the ball milling temperature is -5–5℃, and the ball milling time is 30–90 min.

5. The method for synthesizing large-size α-aluminum trihydride according to claim 1, characterized in that, The dropping rate of anhydrous AlCl3 solution is 10–40 mL / min; And / or, the temperature of the dropwise addition and reaction in step 2 is -15 to -5℃, and the reaction continues for 0.5-1.5 hours after the dropwise addition is completed.

6. The method for synthesizing large-size α-aluminum trihydride according to claim 1, characterized in that, In step 2, the molar ratio of NaAlH4 to AlCl3 is 4.6 to 2:

1.

7. The method for synthesizing large-size α-aluminum trihydride according to claim 1, characterized in that, The deetherifying aid includes one or more of LiAlH4, LiBH4, LiH, and LiCl; the mass of the deetherifying aid is 5 to 40 wt% of the mass of NaAlH4. And / or, the solvent used in the solution containing the deetherifying agent includes one or more of benzene, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, pentane, and n-heptane.

8. The method for synthesizing large-size α-aluminum trihydride according to claim 1, characterized in that, The solution containing the deetherifying agent is added at a rate of 2–10 mL / min; And / or, the temperature of the dropwise addition and reaction in step 3 is 60-100℃, and the reaction continues for 1-4 hours after the dropwise addition is completed.

9. The method for synthesizing large-size α-aluminum trihydride according to claim 1, characterized in that, Step 4 is replaced by: using the suspension B as an electrolyte for electrodeposition, followed by ultrasonication of the electrode sheet after electrodeposition, collecting the ultrasonically desorbed solid, washing and drying to obtain the large-sized α-aluminum trihydride.

10. The method for synthesizing large-size α-aluminum trihydride according to claim 9, characterized in that, The electrodeposition voltage is 0.45–2.80 V, and the electrodeposition time is 30–90 min; And / or, the ultrasound is performed by sonicating the electrode sheet in an inert solvent, the inert solvent including one or more of benzene, toluene, xylene, ethylbenzene, n-hexane, cyclohexane, pentane, and n-heptane; the ultrasound time is 1-5 min.

Images