Lanthanum calcium sulfide transparent ceramic powder material with wide spectrum transmittance and preparation method of lanthanum calcium sulfide transparent ceramic powder material

Abstract

The invention is suitable for the technical field of ceramic materials, and relates to lanthanum calcium sulfide transparent ceramic powder with wide spectrum transmittance and a preparation method of the lanthanum calcium sulfide transparent ceramic powder. The preparation method specifically comprises the following steps: weighing nitrate containing La and Ca according to a specific molar ratio, respectively dissolving the nitrate containing La and Ca into deionized water, and fully mixing to obtain a solution A; adding a thiourea solution into the solution A, and stirring to obtain a mixed solution; heating and continuously stirring the mixed solution, and carrying out hydrolysis and polymerization reaction to form white sol; then, the sol is placed in a drying oven to be subjected to dehydration treatment until the sol is converted into dry gel; and heating the dried gel at high temperature to obtain lanthanum calcium sulfide precursor powder. And putting the lanthanum-calcium sulfide precursor powder into an atmosphere furnace, and carrying out vulcanization reaction in a sulfur-containing atmosphere to prepare the lanthanum-calcium sulfide powder. The preparation method has the advantages that the operation process is simple, the prepared powder is uniform in particle size, high in purity and excellent in dispersity, and the optical performance of the transparent ceramic can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic powder, and particularly relates to a lanthanum calcium sulfide transparent ceramic powder with broad spectral transmittance and a preparation method thereof. Background Art

[0002] To adapt to the future complex and changeable battlefield environment, military infrared optoelectronic systems have put forward unprecedentedly stringent requirements for key optical components. As the front-end barrier of the infrared imaging system, infrared windows and radomes not only need to withstand the huge aerodynamic loads generated during the high-speed maneuvering of aircraft, but also need to resist the tests of harsh environments such as sand impact and raindrop erosion. An ideal military infrared window material must simultaneously meet seven key performance indicators: high transmittance to ensure excellent optical performance, high mechanical strength to resist mechanical impact, high thermal shock resistance to cope with drastic temperature changes, low emissivity to ensure detection sensitivity, high-temperature stability to maintain optical and mechanical properties, excellent sand erosion and rain erosion resistance, and excellent acid and alkali corrosion resistance. According to the different working bands, infrared materials are mainly divided into two categories: mid-wave infrared (3-5 μm) and long-wave infrared (8-14 μm). Among them, the optional range of long-wave infrared materials is relatively limited. Currently, it mainly relies on transparent ceramic materials such as zinc sulfide (ZnS), zinc selenide (ZnSe), and cadmium telluride (CdTe). Although these materials have good infrared transmission characteristics, there are still obvious deficiencies in terms of mechanical strength, environmental stability, etc. Therefore, it is urgent to develop alternative materials with more excellent performance to meet the needs of future high-tech wars.

[0003] Calcium lanthanum sulfide (CaLa2S4) ceramics, as a new generation of high-performance infrared optical transparent ceramic materials, have become key materials with great development prospects in military optoelectronic systems due to their unique isotropic optical properties, wide spectral transmission range (covering the visible light to long-wave infrared band), high hardness (twice as hard as ZnS), and excellent anti-rain erosion and wear resistance. These materials show broad application prospects in high-end military equipment fields such as infrared guidance windows, missile fairings, transparent armor protection systems, and optoelectronic detection devices in extreme environments. However, the performance of calcium lanthanum sulfide ceramics is closely related to the quality of their precursor powders. Currently, the mainstream preparation methods include solid-state reaction method, co-precipitation method, alkoxide hydrolysis method, and wet chemical pyrolysis method, etc., but all have deficiencies: the solid-state method is prone to introducing impurities and the reaction is incomplete; the co-precipitation method is difficult to control the stoichiometric ratio; the alkoxide method has a high preparation cost; the wet chemical pyrolysis method faces the problem of uneven particle size distribution. These preparation processes generally have problems such as harsh reaction conditions, insufficient powder purity (usually below 99%), wide particle size distribution range (0.1 - 10 μm), irregular particle morphology, etc. The prepared ceramics have defects such as optical scattering centers and unstable mechanical properties, which severely restrict the industrial application of calcium lanthanum sulfide in high-precision infrared optical windows, high-performance electronic devices and other fields. Therefore, it is necessary to develop a new process for preparing calcium lanthanum sulfide powders with high purity (>99.9%) and narrow particle size distribution (sub-micron level). Summary of the Invention

[0004] 1. Object of the Invention

[0005] The object of the present invention is to provide a simple and efficient method for preparing calcium lanthanum sulfide ceramic powders with high purity and uniform particle size to meet the application requirements of transparent ceramic materials in high-performance fields.

[0006] 2. Technical Solution

[0007] A calcium lanthanum sulfide transparent ceramic powder with a wide spectral transmittance and a preparation method thereof, comprising the following steps:

[0008] S1: Preparation of Raw Material Solution

[0009] Accurately weigh the nitrate raw materials of lanthanum and calcium, dissolve them in deionized water respectively according to a preset molar ratio, and control the total metal ion concentration within a predetermined range to prepare solution A.

[0010] S2: Addition of Complexing Agent

[0011] Dropwise add an aqueous solution of thiourea to solution A to obtain a uniformly mixed solution. The molar ratio of the total metal ions in the system to thiourea is controlled at 1:1 - 1:5.

[0012] S3: Sol-Gel Transformation

[0013] The mixed solution is continuously stirred and heated at a constant temperature. By controlling the hydrolysis and polymerization processes, the solution gradually transforms into a white sol. The sol is then transferred to a constant temperature drying oven and dehydrated to form a dry block gel.

[0014] S4: Preparation of precursors by self-combustion method

[0015] The gel is placed in a muffle furnace and kept at a set temperature. After the gel undergoes a self-ignition reaction, a white submicron-sized lanthanum calcium sulfide precursor powder is obtained.

[0016] S5: Sulfurization

[0017] The precursor powder is evenly spread in a crucible, placed in an atmosphere furnace, and subjected to a sulfurization reaction in a sulfur-containing atmosphere to finally obtain high-purity lanthanum calcium sulfide powder.

[0018] Furthermore, in the first step, the nitrates containing La and Ca are lanthanum nitrate hexahydrate and calcium nitrate tetrahydrate, respectively, the molar ratio of La / Ca is 2.0-10.0, and the molar concentration of the metal ions is 0.1-1.0 mol / L.

[0019] Furthermore, in the second step, the ratio of the total molar number of the metal ions to the thiourea is 1:1 to 5.

[0020] Furthermore, in the third step, the mixture is heated for 2-6 hours to obtain a transparent colloid, and the oven drying temperature is 60-90° C. and the drying time is 6-24 hours.

[0021] Furthermore, in the fourth step, the temperature of the muffle furnace is 500-900° C., and the holding time is 0.5-3 h.

[0022] Furthermore, the sulfur-containing atmosphere in the fifth step is hydrogen sulfide, carbon disulfide, a mixture of hydrogen sulfide and hydrogen, a mixture of hydrogen sulfide and nitrogen, and a mixture of carbon disulfide and nitrogen. The sulfurization time is 1-9 hours, and the sulfurization temperature is 800-1300°C.

[0023] Beneficial effects of the present invention:

[0024] (1) Simple process: The preparation method of the present invention has a simple process and is easy to operate. Compared with the traditional process, it greatly reduces the complex processes and tedious links, significantly reduces the production difficulty and cost, and is easier to industrialize.

[0025] (2) High powder purity: The spontaneous combustion treatment process effectively removes organic residues in the gel to avoid the introduction of impurities; at the same time, the raw material ratio and reaction conditions are precisely controlled to ensure that the product has excellent chemical purity.

[0026] (3) Good particle size uniformity: In the hydrolysis and polymerization reactions, by utilizing the complexing effect of thiourea and combining with optimized reaction parameters, sub-micron powders were successfully prepared, which have a narrow particle size distribution and excellent dispersibility. This characteristic is crucial for the densification sintering of transparent ceramics and can significantly improve the light transmittance, mechanical strength, and optical properties of the materials.

[0027] (4) Strong controllability: By adjusting key parameters such as the raw material ratio, reaction temperature, and time, the directional design of the powder characteristics can be achieved, meeting the personalized requirements of different application scenarios for the properties of lanthanum calcium sulfide ceramics powders, with wide applicability. Description of the Drawings

[0028] Figure 1 XRD pattern of the lanthanum calcium sulfide precursor in Example 1 of the present invention

[0029] Figure 2 XRD pattern of the lanthanum calcium sulfide powder in Example 1 of the present invention.

[0030] Figure 3 SEM image of the lanthanum calcium sulfide precursor in Example 1 of the present invention Figure 4 SEM image of the lanthanum calcium sulfide powder in Example 1 of the present invention. Detailed Description of the Invention

[0031] The present invention will be further described below through specific examples in combination with, but it should not be understood as a limitation to the protection scope of the present invention. Those skilled in the art make some non-essential changes and adjustments based on the content of the above invention, which all fall within the protection scope of the present invention.

[0032] The following are the specific examples of the present invention:

[0033] Example 1

[0034] (1) Accurately weigh 2.3 mol of lanthanum nitrate hexahydrate and 1 mol of calcium nitrate tetrahydrate, mix them and dissolve in an appropriate amount of deionized water to make the molar concentration of metal ions reach 0.1 mol / L, obtaining a mixed solution A.

[0035] (2) Add 4.95 mol of thiourea solution to solution A to form a mixed solution. In this mixed solution, ensure that the total molar number of metal ions to thiourea is 1:1.5.

[0036] (3) Stir the mixed solution on a heating and stirring device at an appropriate speed for 2 hours to cause hydrolysis and polymerization reactions to form a white sol. Then place the sol in a drying oven at 70 °C until dehydration forms a dry gel.

[0037] (4) Put the dried gel into a muffle furnace, keep it at 800 °C for 1 hour, and then carry out spontaneous combustion treatment to obtain a white powdery lanthanum calcium sulfide precursor.

[0038] (5) Put the obtained precursor powder into an atmosphere furnace, keep it at 1250 °C for 4 hours under an H2S gas stream to obtain a yellow powdery lanthanum calcium sulfide powder.

[0039] From Figure 1 and Figure 2 the XRD patterns, it can be seen that lanthanum oxide and calcium oxide were obtained before sulfidation, and the lanthanum calcium sulfide product was obtained after sulfidation at 1250 °C for 2 h. Figure 3 This is the SEM image of the precursor powder obtained in Example 1 of the present invention. The particle size mainly concentrates in the sub-micron level. Such uniform and fine particle characteristics are beneficial for the subsequent sulfidation process. From Figure 3 it can be seen that the lanthanum calcium sulfide powder obtained in the present invention has a small and uniform particle size, which is beneficial for the subsequent sintering and densification of ceramics. After testing the purity of the lanthanum calcium sulfide powder, it reaches 99%, which is higher than that of other methods.

[0040] Example 2

[0041] (1) Accurately weigh 2.3 mol of lanthanum nitrate hexahydrate and 1 mol of calcium nitrate tetrahydrate, mix them and dissolve in an appropriate amount of deionized water to make the molar concentration of metal ions reach 0.1 mol / L to obtain a mixed solution A.

[0042] (2) Add 6.6 mol of thiourea solution to solution A, and the ratio of the total molar number of metal ions to citric acid is 1:2.

[0043] (3) Heat and stir the mixed solution for 4 hours. After forming a white transparent sol, place it in a drying oven at 90 °C to dehydrate and obtain a dried gel.

[0044] (4) Put the dried gel into a muffle furnace, keep it at 800 °C for 1 hour and then carry out spontaneous combustion treatment to obtain a lanthanum calcium sulfide precursor.

[0045] (5) Put the obtained precursor powder into an atmosphere furnace, keep it at 1250 °C for 2 hours under an H2S gas stream to obtain a yellow powdery lanthanum calcium sulfide powder.

[0046] Example 3

[0047] (1) Accurately weigh 2.7 mol of lanthanum nitrate hexahydrate and 1 mol of calcium nitrate tetrahydrate, mix them and dissolve in an appropriate amount of deionized water to make the molar concentration of metal ions reach 0.2 mol / L to obtain a mixed solution A.

[0048] (2) Add 6.6 mol of thiourea solution to Solution A, where the ratio of the total molar amount of metal ions to thiourea is 1:2.

[0049] (3) Heat and stir the mixture for 2 hours. After a white sol is formed, place it in a drying oven at 90 °C for dehydration to obtain a dried gel.

[0050] (4) Put the dried gel into a muffle furnace, perform self-ignition treatment after holding at 800 °C for 1 hour to obtain a lanthanum calcium sulfide precursor.

[0051] (5) Put the obtained precursor powder into an atmosphere furnace, hold at 1100 °C for 4 hours under an H2S gas flow to obtain a yellow powdery lanthanum calcium sulfide powder.

[0052] It can be seen from the above examples that the method of the present invention can stably prepare high-quality lanthanum calcium sulfide ceramic nanopowders, and the process parameters can be adjusted according to actual needs to meet different application requirements.

Claims

1. A lanthanum calcium sulfide transparent ceramic powder with wide spectral transmittance and a preparation method thereof, characterized in that, The preparation method comprises the following steps: S1: Preparation of raw material solution The lanthanum and calcium nitrate raw materials were accurately weighed, dissolved in deionized water according to a preset molar ratio, and the total metal ion concentration was controlled within a predetermined range to prepare solution A. S2: Complexing agent addition Add thiourea aqueous solution dropwise to solution A to obtain a uniform mixed solution. The molar ratio of the total molar number of metal ions to thiourea in the system is controlled to be 1:1-1:

5. S3: Sol-Gel Transformation The mixed solution is continuously stirred and heated at a constant temperature. By controlling the hydrolysis and polymerization processes, the solution gradually transforms into a white sol. The sol is then transferred to a constant temperature drying oven and dehydrated to form a dry block gel. S4: Preparation of precursors by self-combustion method The gel is placed in a muffle furnace and kept at a set temperature. After the gel undergoes a self-ignition reaction, a white submicron-sized lanthanum calcium sulfide precursor powder is obtained. S5: Sulfurization The precursor powder is evenly spread in a crucible, placed in an atmosphere furnace, and subjected to a sulfurization reaction in a sulfur-containing atmosphere to finally obtain high-purity lanthanum calcium sulfide powder.

2. The lanthanum calcium sulfide transparent ceramic powder with a wide spectral transmittance and its preparation method according to claim 1, characterized in that, In the first step, the nitrates containing La and Ca are lanthanum nitrate hexahydrate and calcium nitrate tetrahydrate respectively, the molar ratio of La / Ca is 2.0-10.0, and the molar concentration of the metal ions is 0.1-1.0 mol / L.

3. A lanthanum calcium sulfide transparent ceramic powder with a wide spectral transmittance and a preparation method thereof according to claim 1, characterized in that, In the second step, the ratio of the total molar number of the metal ions to the thiourea is 1:1-5.

4. A lanthanum calcium sulfide transparent ceramic powder with a wide spectral transmittance and a preparation method thereof according to claim 1, characterized in that, In the third step, the mixture is heated for 2-6 hours to obtain a transparent colloid. The oven drying temperature is 60-90° C. and the drying time is 6-24 hours.

5. A lanthanum calcium sulfide transparent ceramic powder with a wide spectral transmittance and a preparation method thereof according to claim 1, characterized in that, In the fourth step, the temperature of the muffle furnace is 500-900° C., and the holding time is 0.5-3 h.

6. A lanthanum calcium sulfide transparent ceramic powder with a wide spectral transmittance and a preparation method thereof according to claim 1, characterized in that, In the fifth step, the sulfur-containing atmosphere is one or more of hydrogen sulfide, carbon disulfide, hydrogen, and nitrogen. The sulfurization time is 1-9 hours and the sulfurization temperature is 800-1300°C.

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