A method for preparing high-purity and highly crystalline CaLa2S4 infrared ceramic powder

Abstract

The present invention discloses a method for preparing CaLa2S4 infrared ceramic powder with relatively high purity and good crystallinity. After synthesizing the precursor through a wet chemical route, a thermal decomposition reaction occurs under relatively low-temperature conditions, followed by low-temperature sulfidation to achieve the formation of the CaLa2S4 phase, and CaLa2S4 infrared ceramic powder with relatively high purity and good crystallinity is prepared. This method uses liquid-phase reaction chemistry to synthesize the CaLa2S4 precursor, uses thioacetamide as a catalyst and a capping agent, removes impurity elements in the precursor through a thermal decomposition reaction, and then combines the low-temperature sulfidation method to restore the stoichiometric ratio of sulfur, and sulfides to obtain submicron CaLa2S4 powder. This method has the advantages of simple preparation process, high synthesis efficiency and low raw material cost. The prepared CaLa2S4 powder has the advantages of high purity, good crystallinity and sinterability, and small particle size.

Description

Technical Field

[0001] The present invention belongs to the technical field of new materials, and particularly relates to a method for preparing high-purity and high-crystallinity CaLa2S4 infrared ceramic powder. Background Art

[0002] In the early 1980s, the CaLa2S4 solid solution compound emerged as an alternative window material for ZnS. CaLa2S4 was prepared by doping Ca 2+ to attempt to improve the infrared performance of γ-La2S3. The CaLa2S4 compound has the characteristics of a thorium phosphide-type cubic structure (Th3P4), a high melting point (Tm = 2300K), a large band gap (E = 2.7eV), and a wide optical transmission band (0.4 - 18μm). Due to the Th3P4-type structural defects, Ca 2+ can be filled in the lattice vacancies, resulting in a small change in the lattice. Adding a large amount of Ca 2+ helps to obtain a stable cubic phase at low temperatures. CaLa2S4 transparent ceramics have excellent infrared transmittance, high melting point, high hardness and other advantages, and have good resistance to wind, sand, rain and erosion. They are ideal candidate materials for future infrared window materials.

[0003] The research on CaLa2S4 mainly focuses on the preparation of CaLa2S4 powder, because high-purity, well-crystallized and highly sinterable CaLa2S4 ceramic powder is one of the key factors for successfully preparing high-quality CaLa2S4 infrared transparent ceramics. At present, most of the methods for preparing and synthesizing CaLa2S4 powder at home and abroad adopt a two-step method: the first step is to synthesize a CaLa2S4 precursor in which calcium and lanthanum ions are closely mixed, and then these precursors are subsequently sulfided and converted into CaLa2S4 powder in an H2S or CS2 atmosphere.

[0004] Current specific methods for synthesizing CaLa2S4 powder at home and abroad: (1) Using lanthanum nitrate, calcium nitrate, and thioacetamide as starting materials, preparing a nitrate solution and heating it to produce a precursor, and then sulfiding the precursor in an H2S atmosphere; (2) Using calcium nitrate and lanthanum nitrate solutions as raw materials to prepare a nitrate solution, then spraying the nitrate solution into an 800 °C hot furnace to produce a precursor, and then sulfiding the precursor in a high-temperature atmosphere of H2S-H2; (3) Adding La metal powder and dry methanol to a pressureless container, using a small amount of mercury chloride and mercury iodide as catalysts, keeping warm for 30 days, and then adding Ca metal powder to the container to form a methoxide; after vacuum decomposing the methoxide, sulfiding it in an H2S atmosphere; (4) Adding lanthanum nitrate and calcium nitrate to distilled water to prepare a stock solution; then stirring ammonium carbonate and ammonium hydroxide solutions and quickly dispersing the stock solution in this solution; ultrasonically dispersing and filtering the precipitate, then performing spray freezing operation, and then drying for several days; the dried precursor is sintered at a high temperature in an oxygen atmosphere and then sulfided in H2S; (5) Dissolving lanthanum acetate (La(CH3COO)3) and calcium acetate (Ca(CH3COO)2) in deionized distilled water, spraying it into a large liquid nitrogen dewatering bottle and freeze-drying for several days, then calcining the precursor in a pure oxygen atmosphere, and finally sulfiding it in an H2S atmosphere to form a sulfide; (6) Mixing calcium carbonate (CaCO3) and lanthanum carbonate (La2(CO3)3) powders in the correct stoichiometric ratio, placing them in a graphite boat and putting them into a silica-glass furnace tube to react for several days, and then sulfiding them in an H2S atmosphere to form a sulfide; (7) Co-precipitating calcium oxalate and lanthanum oxalate from a nitrate solution, filtering and drying the obtained precipitate, then heating the precursor in air to convert it into an oxide, and finally heating the mixed oxide product in an H2S atmosphere to convert it into a sulfide.

[0005] However, the CaLa2S4 powder prepared by the above preparation methods has the disadvantages of low purity, low sinterability, large particle size (μm level), and poor crystallinity. At the same time, the sulfiding process is complex, highly dangerous, and the long sintering time leads to excessive growth of powder particles. At the same time, CaLa2S4 will undergo a reduction phenomenon and phase transformation at a high sintering temperature (i.e., T≥1000 °C), resulting in the sample turning black and affecting the transmittance of the final ceramic sample. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing high-purity and high-crystallinity CaLa2S4 infrared ceramic powder. This method has a simple preparation process, can improve the purity, crystallinity, and sinterability of the prepared CaLa2S4 powder, and reduce the particle size of the CaLa2S4 powder.

[0007] To achieve the above purpose, the present invention provides a method for preparing high-purity and high-crystallinity CaLa2S4 infrared ceramic powder, including the following steps:

[0008] S1. Dissolve sodium diethyldithiocarbamate trihydrate powder and phenanthroline monohydrate powder in absolute ethanol respectively. Then mix the sodium diethyldithiocarbamate ethanol solution and the phenanthroline ethanol solution and stir vigorously to fuse them to obtain solution A.

[0009] S2. Dissolve lanthanum chloride heptahydrate powder and calcium chloride dihydrate powder in absolute ethanol respectively. Subsequently, mix the lanthanum chloride ethanol solution and the calcium chloride ethanol solution and stir evenly to obtain solution B. Then add solution B dropwise to the solution A prepared in step S1 and stir vigorously to obtain a yellow solution.

[0010] S3. Dissolve thioacetamide powder in absolute ethanol to prepare a reagent that serves as both a catalyst and a capping agent. Then add the catalyst and the capping agent dropwise to the yellow solution prepared in step S2. After heating and reacting, centrifuge and wash the yellow solution with absolute ethanol multiple times to obtain a yellow precipitate.

[0011] S4. Place the yellow precipitate obtained in step S3 in an oven to dry to obtain a yellow powder. Then heat-treat the yellow powder in air to remove impurities and generate a gray powder.

[0012] S5. Place the gray powder obtained in step S4 in a tube furnace. One end of the tube furnace is connected to a hydrogen-in-argon mixed gas. When the temperature is raised to a specific sulfidation temperature, pass the hydrogen-in-argon mixed gas through CS2 liquid. Start the sulfidation reaction treatment for a period of time, and then cool down to end the sulfidation process. Finally, prepare high-purity and good-crystallinity CaLa2S4 infrared ceramic powder.

[0013] Preferably, in step S1, the concentrations of both the sodium diethyldithiocarbamate ethanol solution and the phenanthroline ethanol solution are 0.2 mol / L; in solution A, the molar ratio between the sodium diethyldithiocarbamate trihydrate powder and the phenanthroline monohydrate powder is 1:1.

[0014] Preferably, in step S2, the concentration of the lanthanum chloride ethanol solution is 0.05 mol / L, and the concentration of the calcium chloride ethanol solution is 0.02 mol / L; in solution B, the molar ratio between the lanthanum chloride heptahydrate and the calcium chloride dihydrate is (2 - 2.5):1.

[0015] Preferably, in step S3, the heating reaction temperature is 60 - 80 °C, and the reaction time is 1 - 2 h.

[0016] Preferably, in step S3, in the catalyst and the capping agent, the concentration of the thioacetamide powder is 0.1 mol / L.

[0017] Preferably, in step S3, centrifuge and wash at least 4 times.

[0018] Preferably, in step S4, the heat treatment temperature is 450 - 650 °C, and the heat treatment time is 3 - 6 h.

[0019] Preferably, in step S4, the drying temperature is 50 - 70 °C, and the drying time is 24 - 36 h.

[0020] Preferably, in step S5, in the argon - hydrogen mixed gas, the volume ratio of argon to hydrogen is 95:5; the gas flow rate is 25 - 75 ml / min.

[0021] Preferably, in step S5, the specific sulfidation temperature is 600 - 1000 °C, the sulfidation reaction temperature is 600 - 1000 °C, and the sulfidation reaction time is 3 - 6 h.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention first synthesizes the CaLa2S4 powder precursor by liquid - phase reaction, uses thioacetamide as a catalyst and a capping agent, then removes impurity elements in the precursor by thermal decomposition reaction, and then combines with low - temperature sulfidation method to restore the stoichiometry of sulfur, and sulfides to obtain micron - scale CaLa2S4 powder. The present invention only performs sulfidation treatment within a specific temperature range, avoiding carbon element pollution while ensuring the stoichiometry of sulfur, effectively solving the problem of easy sulfur deficiency in the preparation of CaLa2S4 infrared ceramic powder; the preparation process of this method is simple, the synthesis efficiency is high, and the raw material cost is low. The prepared CaLa2S4 powder has the advantages of high purity, good crystallinity and sinterability, and small particle size. Description of the Drawings

[0024] Figure 1 It is the X - ray diffraction pattern of the CaLa2S4 powder precursor prepared in step S4 of the embodiment of the present invention;

[0025] Figure 2 It is the TG - DSC pattern of the CaLa2S4 powder precursor prepared in step S4 of the embodiment of the present invention;

[0026] Figure 3 It is the scanning electron microscope image of the CaLa2S4 powder precursor prepared in step S4 of the embodiment of the present invention;

[0027] Figure 4 It is the Fourier transform infrared spectrum pattern of the CaLa2S4 powder precursor prepared in step S4 of the embodiment of the present invention;

[0028] Figure 5 It is the X - ray diffraction pattern after thermal decomposition of the CaLa2S4 powder precursor prepared in step S4 of the embodiment of the present invention;

[0029] Figure 6 The X-ray diffraction pattern of the CaLa2S4 powder prepared in the embodiment of the present invention;

[0030] Figure 7 The SEM and elemental EDS patterns of the CaLa2S4 powder prepared in the embodiment of the present invention;

[0031] Figure 8 The physical picture of the precursor of the CaLa2S4 powder prepared in step S4 of the embodiment of the present invention;

[0032] Figure 9 The physical picture of the CaLa2S4 powder prepared in the embodiment of the present invention. Detailed implementation manners

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] The raw materials and reagents used in the following embodiments are all conventional commercially available products unless otherwise specified.

[0035] The Na(Ddtc)·3H2O powder, phen·H2O powder, LaCl3·7H2O powder, CaCl2·2H2O powder, and TAA powder used in the following embodiments are all analytical pure grade powders, and CS2 is an analytical pure grade reagent.

[0036] Embodiment

[0037] A method for preparing high-purity and high-crystallinity CaLa2S4 infrared ceramic powder, comprising the following steps:

[0038] S1. Dissolve 20 mmol of sodium diethyldithiocarbamate trihydrate powder (Na(Ddtc)·3H2O) and 20 mmol of phenanthroline monohydrate powder (phen·H2O) in 100 ml of absolute ethanol respectively, then mix the Na(Ddtc) ethanol solution and the phen ethanol solution and stir vigorously at a speed of 300 r / min to obtain solution A;

[0039] S2. Dissolve 5 mmol of lanthanum chloride heptahydrate powder (LaCl3·7H2O) and 2.174 mmol of calcium chloride dihydrate powder (CaCl2·2H2O) in 100 ml of absolute ethanol respectively, then mix the lanthanum chloride ethanol solution and the calcium chloride ethanol solution and stir evenly at a speed of 300 r / min to obtain solution B, and then add solution B dropwise to the solution A prepared in step S1 and stir vigorously at a speed of 400 r / min to obtain a yellow solution;

[0040] S3. Dissolve 10 mmol of thioacetamide (TAA) powder in 100 ml of absolute ethanol to prepare a catalyst and a capping agent. Then, drop the catalyst and the capping agent into the yellow solution prepared in step S2, heat it to 70 °C and react for 2 h, and then centrifuge and wash the yellow solution 4 times with absolute ethanol to obtain a yellow precipitate;

[0041] S4. Place the yellow precipitate obtained in step S3 in an oven at 70 °C and dry it for 24 h to obtain yellow powder, which is the CaLa2S4 powder precursor. Its physical picture is as Figure 8 shown; then heat-treat the yellow powder in air to remove impurities to generate gray powder. The heat-treatment temperature is 500 °C and the heat-treatment time is 5 h;

[0042] S5. Place the gray powder obtained in step S4 in a tube furnace. One end of the tube furnace is connected to a hydrogen-in-argon mixed gas (the volume ratio of argon to hydrogen is 95:5), and the gas flow rate is 30 ml / min; when the temperature rises to the sulfidation specific temperature of 700 °C, pass the hydrogen-in-argon mixed gas through CS2 liquid to start the sulfidation reaction. After holding at 1000 °C for 3 h, end the sulfidation process when the temperature drops to 700 °C, and finally prepare high-purity and well-crystalline CaLa2S4 infrared ceramic powder. Its X-ray diffraction pattern, SEM and elemental EDS spectra, and physical picture are respectively as Figure 6 、 Figure 7 and Figure 9 shown.

[0043] Perform X-ray diffraction analysis, TG / DSC test, electron microscopy scanning, and infrared spectroscopy analysis on the CaLa2S4 powder precursor obtained in step S4 in sequence. The obtained results are respectively as Figures 1-4 shown; perform X-ray diffraction analysis on the gray powder obtained in step S4, and the obtained result is as Figure 5 shown.

[0044] From Figure 1 it can be seen that the precursor is an oxide and has poor crystallinity, and post-treatment is required to make it form the required sulfide with high crystallinity; from Figure 2 it can be seen that the precursor undergoes two weight loss processes of removing impurities in the range of 1200 °C. Set the thermal decomposition temperature of the precursor and the post-sulfidation treatment temperature according to the two weight loss temperatures; from Figure 3 it can be seen that the precursor is nanoscale powder; from Figure 4 it can be seen that there are many organic elements in the precursor and purification is required; from Figure 5 it can be seen that sulfur oxides appear in the powder after thermal decomposition and the crystallinity is better than that of the precursor, but further purification and improvement of crystallinity are still required.

[0045] From Figure 6It can be seen that the powder after vulcanization treatment has the desired phase, high purity and good crystallinity; from Figure 7 It can be seen that the powder after vulcanization treatment is composed of submicron-sized particles, and the presence of the expected cations and anions can also be seen.

Claims

1. A method for preparing high-purity and highly crystalline CaLa2S4 infrared ceramic powder, characterized in that, It includes the following steps: S1. Dissolve sodium diethyldithiocarbamate trihydrate powder and phenanthroline monohydrate powder in absolute ethanol respectively. Then mix the sodium diethyldithiocarbamate ethanol solution and the phenanthroline ethanol solution and stir vigorously to fuse them to obtain solution A; S2. Dissolve lanthanum chloride heptahydrate powder and calcium chloride dihydrate powder in absolute ethanol respectively. Subsequently, mix the lanthanum chloride ethanol solution and the calcium chloride ethanol solution and stir evenly to obtain solution B. Then add solution B dropwise to the solution A prepared in step S1 and stir vigorously to obtain a yellow solution; S3. Dissolve thioacetamide powder in absolute ethanol to prepare a reagent that serves as both a catalyst and a capping agent. Then add the catalyst and the capping agent dropwise to the yellow solution prepared in step S2. After heating and reacting, centrifuge and wash the yellow solution with absolute ethanol for multiple times to obtain a yellow precipitate; S4. Place the yellow precipitate obtained in step S3 in an oven for drying to obtain a yellow powder. Then heat-treat the yellow powder in the air to remove impurities to generate a gray powder; S5. Place the gray powder obtained in step S4 in a tube furnace. One end of the tube furnace is connected to a hydrogen-in-argon mixed gas. When the temperature is raised to a specific sulfidation temperature, pass the hydrogen-in-argon mixed gas through CS2 liquid. After starting the sulfidation reaction for a period of time, cool down to end the sulfidation process, and finally prepare CaLa2S4 infrared ceramic powder with high purity and good crystallinity; the specific sulfidation temperature is 600 - 1000 °C, the sulfidation reaction temperature is 600 - 1000 °C, and the sulfidation reaction time is 3 - 6 h.

2. A method for preparing high-purity and high-crystallinity CaLa2S4 infrared ceramic powder according to claim 1, characterized in that, In step S1, the concentrations of both the sodium diethyldithiocarbamate ethanol solution and the phenanthroline ethanol solution are 0.2 mol / L; in solution A, the molar ratio between the sodium diethyldithiocarbamate trihydrate powder and the phenanthroline monohydrate powder is 1:

1.

3. A method for preparing high-purity and highly crystalline CaLa2S4 infrared ceramic powder according to claim 1 or 2, characterized in that, In step S2, the concentration of the lanthanum chloride ethanol solution is 0.05 mol / L, and the concentration of the calcium chloride ethanol solution is 0.02 mol / L; in solution B, the molar ratio between the lanthanum chloride heptahydrate and the calcium chloride dihydrate is (2 - 2.5):

1.

4. A method for preparing high-purity and highly crystalline CaLa2S4 infrared ceramic powder according to claim 1 or 2, characterized in that, In step S3, the heating reaction temperature is 60 - 80 °C, and the reaction time is 1 - 2 h.

5. A method for preparing high-purity and high-crystallinity CaLa2S4 infrared ceramic powder according to claim 1 or 2, characterized in that, In step S3, in the catalyst and the capping agent, the concentration of the thioacetamide powder is 0.1 mol / L.

6. A method for preparing high-purity and highly crystalline CaLa2S4 infrared ceramic powder according to claim 1 or 2, characterized in that, In step S3, centrifuge and wash at least 4 times.

7. A method for preparing high-purity and high-crystallinity CaLa2S4 infrared ceramic powder according to claim 1 or 2, characterized in that, In step S4, the heat-treatment temperature is 450 - 650 °C, and the heat-treatment time is 3 - 6 h.

8. A method for preparing high-purity and high-crystallinity CaLa2S4 infrared ceramic powder according to claim 1 or 2, characterized in that, In step S4, the drying temperature is 50 - 70 °C, and the drying time is 24 - 36 h.

9. A method for preparing high-purity and high-crystallinity CaLa2S4 infrared ceramic powder according to claim 1 or 2, characterized in that, In step S5, in the hydrogen-in-argon mixed gas, the volume ratio of argon to hydrogen is 95:5; the gas flow rate is 25 - 75 mL / min.

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