High-strength mid-infrared wave-transparent calcium-aluminum ceramic and preparation method thereof

Abstract

This invention discloses a high-strength mid-infrared transparent calcium-aluminum ceramic, the main crystalline phases of which are CaAl2O4 and Ca. 12 Al 14 O 33 The crystal size is 30 nm-150 nm; it also contains a small amount of CaZr4O9 crystalline phase and an amorphous phase rich in SiO2; the preparation method includes the following steps: the raw materials are fully mixed according to the ratio and melted in a platinum crucible at a melting temperature of not less than 1450℃; after melting, the glass melt is poured into a forming mold for cooling, and then transferred to a muffle furnace for annealing. After annealing, it is cooled to room temperature with the furnace to obtain the precursor glass; a one-step heat treatment is adopted, the obtained precursor glass is added to a heat treatment furnace, and the temperature is raised to 900-1100℃ at a rate of not more than 10℃ / min, and the heat treatment time is not less than t(mm) / (0.15mm / h); through composition design and preparation process, this invention effectively expands the mid-infrared transmission band of calcium aluminum ceramics while ensuring a certain visible light transmittance, significantly improves the transmittance of the mid-infrared band, and improves the hardness and elastic modulus.

Description

Technical Field

[0001] This invention belongs to the field of ceramic materials technology, specifically relating to a calcium-aluminum ceramic and its preparation method. Background Technology

[0002] Calcium aluminate glass (CAG) has significant application value due to its excellent optical and mechanical properties and unique glass structure. CAG possesses a 6μm infrared cutoff edge, low optical loss, and high mechanical strength; however, it exhibits a severe hydroxyl absorption peak in the infrared band and has poor glass-forming ability, which seriously affects its preparation and application.

[0003] Transforming calcium aluminate glass into glass-ceramics or ceramics through composition design and heat treatment can improve its mechanical, thermal, and chemical stability. However, existing technologies still face several limitations. First, calcium aluminate glass typically has poor glass-forming ability and is prone to uncontrollable crystallization during casting. Therefore, a certain amount of glass network forging oxides (such as SiO2) and alkaline earth metal oxides (such as MgO and BaO) are usually introduced into the glass composition to improve its forming ability. However, the introduction of these oxides can easily lead to excessive glass phase residues in the glass-ceramics, reducing the transmittance of the sample after heat treatment. At the same time, various oxide crystalline phases are easily formed in the sample, which have significant differences in refractive index and coefficient of thermal expansion compared to the calcium aluminate crystalline phase, resulting in a decrease in the transmittance of the sample after heat treatment.

[0004] Secondly, for calcium aluminate glass, its microcrystalline glass, and ceramics, mid-infrared transmittance is mainly affected by hydroxyl absorption and microstructure. Reducing hydroxyl absorption and increasing mid-infrared transmittance typically requires dehydration of raw materials and glass melting in a vacuum or protective atmosphere, significantly increasing manufacturing costs. Simultaneously, the grain size, shape, and distribution of crystal phases formed in calcium aluminate microcrystalline glass or ceramics have a significant impact on their transmittance in the visible and infrared bands; controlling the grain size, shape, and distribution in calcium aluminate microcrystalline glass or ceramics can positively influence their transmittance. However, to date, calcium aluminate microcrystalline glass and ceramics exhibit low transmittance in the visible light band, a broad hydroxyl absorption peak with high absorption intensity in the infrared band, and a narrow mid-infrared transmittance. Summary of the Invention

[0005] To address the issues of low transmittance in the visible light band and narrow transmittance in the mid-infrared band of calcium aluminum microcrystalline glass and ceramics, this invention provides a calcium aluminum ceramic and its preparation method. Through composition design and preparation process, while ensuring a certain transmittance in the visible light band, the mid-infrared transmittance of calcium aluminum ceramic is effectively extended, significantly improving the transmittance in the mid-infrared band, while also improving hardness and elastic modulus.

[0006] To achieve the above objectives, the following technical solution is adopted:

[0007] A high-strength, mid-infrared transparent calcium-aluminum ceramic, with CaAl2O4 and Ca as its main crystalline phases. 12 Al 14 O 33 The grain size is 30nm-150nm; it also contains a small amount of CaZr4O9 crystalline phase and SiO2-rich amorphous phase.

[0008] This invention also provides a method for preparing the above-mentioned high-strength mid-infrared transparent calcium aluminum ceramic, comprising the following steps:

[0009] (1) Mix the raw materials thoroughly according to the proportions and melt them in a platinum crucible at a melting temperature of not less than 1450℃;

[0010] (2) After melting, the molten glass is poured into a molding mold to cool, and then transferred to a muffle furnace for annealing. After annealing, it is cooled to room temperature in the furnace to obtain the precursor glass.

[0011] (3) The precursor glass is subjected to one-step heat treatment. The glass is added to a heat treatment furnace and heated to 900-1100℃ at a rate of no more than 10℃ / min. The heat treatment time is no less than t / 0.15 hours, where t is the glass thickness in mm.

[0012] According to the above scheme, the raw material composition of the calcium-aluminum ceramic is designed as follows (molar percentage): CaO: 54-60%; Al2O3: 38-44%; SiO2: 1-5%; ZrO2: 1-5%; and 0.63≤Al2O3:CaO≤0.82, 2%≤ZrO2+SiO2≤6%. In a further optimized scheme, 0.68≤Al2O3:CaO≤0.78, 2%≤ZrO2+SiO2≤4%.

[0013] According to the above scheme, the preferred melting temperature in step (1) is 1500-1650℃, and the melting time is not less than 1 hour.

[0014] According to the above scheme, the annealing temperature in step (2) is 600-850℃ and the annealing time is not less than 1 hour.

[0015] According to the above scheme, the preferred heat treatment temperature in step (3) is 960-1100℃; the preferred heat treatment time is not less than t / 0.05 hours.

[0016] According to the above scheme, step (3) adopts a two-step heat treatment method. The first step is to raise the temperature to 860-960℃ at a rate of no more than 10℃ / min, and the heat treatment time is no less than 5 hours. The second step is to continue to raise the temperature to 960-1100℃, and the heat treatment time is no less than t / 0.15 hours, where t is the glass thickness in mm.

[0017] According to the above scheme, the calcium aluminum ceramic has a transmittance of more than 50% in the 550 nm band and a transmittance of more than 70% in the 3.5 μm-5 μm band, based on a thickness of 1 mm.

[0018] According to the above scheme, the Vickers hardness of the calcium aluminum ceramic is greater than 7 GPa and the elastic modulus is greater than 110 GPa.

[0019] To meet industrial production requirements and reduce energy consumption, transparent calcium aluminate ceramics require a precursor glass with a low melting point. According to the phase diagram, the ratio of CaO to Al₂O₃ should be close to the lowest eutectic point, with a molar ratio of Al₂O₃:CaO ≈ 0.56. The inventors discovered that this composition ratio easily produces an opaque crystalline layer after heat treatment and crystallization, affecting the transmittance of the prepared ceramic in the visible light band. To address this issue, this invention appropriately increases Al₂O₃ and reduces the CaO content, avoiding the formation of the opaque crystalline layer. Simultaneously, to further improve the glass-forming ability of calcium aluminate glass, this invention introduces small amounts of SiO₂ and ZrO₂ into the glass composition, enhancing the glass-forming ability and enabling the casting and forming of large-size glass. This invention also further optimizes the Al₂O₃ and CaO content to satisfy 0.63 ≤ Al₂O₃:CaO ≤ 0.82, thereby forming CaAl₂O₄ and Ca²⁺ after heat treatment. 12 Al 14 O 33 Two crystalline phases. The small amount of ZrO2 introduced in this invention forms small-sized CaZr4O9 grains with CaO during heat treatment; the small amount of SiO2 introduced forms a small-sized, SiO2-rich amorphous phase during heat treatment. These small-sized CaZr4O9 grains and the small-sized amorphous phase are dispersed in CaAl2O4 and Ca... 12 Al 14 O 33 At the grain boundaries of the two crystalline phases, the growth of CaAl2O4 and Ca is suppressed. 12 Al 14 O 33 The grains grow to a size of 30 nm-150 nm. The coexistence of polycrystalline and amorphous phases results in a uniform grain size distribution in the heat-treated ceramic, reducing scattering centers and significantly improving the transmittance of the ceramic in the visible light band; for example, the transmittance at 550 nm is higher than 50% for a 1 mm thick ceramic.

[0020] Hydroxyl groups and free water in glass exhibit strong and broad absorption bands in the mid-infrared band, significantly reducing the transmittance of glass in this band and narrowing its transmission range. The Ca formed in ceramics in this invention... 12 Al 14 O33 The crystalline phase can accommodate a large number of hydroxyl groups, which occupy Ca²⁺ and other groups. 12 Al 14 O 33 The lattice sites in the crystal phase provide uniform absorption at a fixed wavelength; the broadband absorption in the mid-infrared band of the original glass is transformed into narrowband absorption in the ceramic, thereby expanding the transmission band of the ceramic in the mid-infrared band and significantly improving the transmittance in the mid-infrared band. The mid-infrared transparent ceramic of this invention has a hydroxyl absorption in the mid-infrared band at -3547 cm⁻¹. -1 At this location, the absorption peak half-width at half-maximum is less than 90 cm. -1 It is much smaller than the width of the hydroxyl absorption band in glass (830 cm). -1 The ceramic has a transmittance of more than 70% in the 3.5μm-5μm band (based on a thickness of 1 mm).

[0021] This invention generates high-strength CaAl2O4 and Ca in the sample through glass composition design and heat treatment. 12 Al 14 O 33 The crystalline phase, and further suppressed by small-sized CaZr4O9 grains dispersed at the grain boundaries of the above two crystalline phases and the amorphous phase, inhibited the growth of CaAl2O4 and Ca. 12 Al 14 O 33 Excessive growth of the crystal phase results in ceramics with more uniform grain size, which improves the hardness and modulus of the ceramics. The Vickers hardness is greater than 7 GPa and the elastic modulus is greater than 110 GPa.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The introduction of small amounts of SiO2 and ZrO2 not only enhances the glass-forming ability of the precursor, enabling the casting and forming of large-size glass, but also allows for the formation of dispersed silicon-containing amorphous phases and zirconium-containing crystalline phases during heat treatment. This is beneficial for the main crystalline phases (CaAl2O4, Ca...). 12 Al 14 O 33 The growth of the ceramic is inhibited, resulting in smaller and more uniform grain size, which improves the transmittance of the ceramic in the visible light band.

[0024] By achieving high crystallinity, the broad absorption peaks of hydroxyl groups and other groups commonly found in calcium aluminate glass are eliminated. The hydroxyl groups originally present in the glass network then enter the Ca... 12 Al 14 O 33The crystal lattice structure narrows the full width at half maximum (FWHM) of the absorption peak, achieving high transmittance in the mid-infrared band over a wider wavelength range. Compared to existing methods for eliminating or reducing the hydroxyl absorption peak in calcium aluminate glass, such as melting in a nitrogen atmosphere or adding fluorides to the raw materials, the method provided by this invention is lower in cost, simpler to operate, and easier to apply on a large scale.

[0025] This invention transforms calcium aluminate glass into calcium aluminate ceramics through a rational composition design and a heat treatment crystallization method, significantly improving mechanical properties. Attached Figure Description

[0026] Figure 1 The ceramic powder obtained in Example 1 and CaAl2O4, Ca 12 Al 14 O 33 X-ray diffraction comparison diagram of standard cards.

[0027] Figure 2 The transmittance curves of the precursor glass and the ceramic obtained after heat treatment in Example 1 are shown in the range of 250 nm to 2000 nm (all test samples are 1 mm).

[0028] Figure 3 The transmittance curves of the precursor glass and the ceramic obtained after heat treatment in Example 1 are shown in the range of 2μm-7μm (all test samples are 1 mm).

[0029] Figure 4 The morphology of the ceramic obtained in Example 1 is shown under a transmission electron microscope.

[0030] Figure 5 The images shown are high-resolution transmission electron microscopy images and fast Fourier transform diagrams of the black small particles in the ceramic obtained in Example 1.

[0031] Figure 6 The image shows the energy dispersive spectroscopy (EDS) spectrum of a selected region of the ceramic obtained in Example 1 under a transmission electron microscope.

[0032] Figure 7 The XRD pattern of the ceramic obtained in Comparative Example 1 is shown (the diffraction peaks marked with "*" in the figure are diffraction peaks of heterocrystalline phases). Detailed Implementation

[0033] The following embodiments and comparative examples further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0034] A specific embodiment provides a method for preparing high-strength mid-infrared transparent calcium-aluminum ceramics, including the following steps:

[0035] The raw materials are thoroughly mixed according to the specified ratio and then melted in a platinum crucible. The melting temperature is not lower than 1450℃, preferably within the range of 1500-1650℃. The melting time is not less than 1 hour. During the melting process, the high-temperature glass can be stirred appropriately to improve the uniformity of the molten glass.

[0036] After melting, the molten glass is poured into a forming mold to cool and then transferred to a muffle furnace for annealing. The preferred annealing temperature range is 600-850℃, and the annealing time is not less than 1 hour. After annealing, the power to the annealing furnace is turned off, and the precursor glass is allowed to cool down with the furnace. After the temperature drops to room temperature, the precursor glass is obtained.

[0037] To prepare calcium aluminate ceramics, the obtained precursor is shaped and then placed in a heat treatment furnace for heat treatment. A one-step or two-step heat treatment method can be used; based on the characteristics of surface crystallization in calcium aluminate glass and to reduce production costs, a one-step heat treatment method is preferred. When using a one-step heat treatment method, the heat treatment temperature range is 900-1100℃, preferably 960-1100℃; the heating rate of the heat treatment furnace is no greater than 10℃ / min; the heat treatment time is selected according to the sample thickness, and the heat treatment time is not less than t(mm) / (0.15mm / h), preferably not less than t(mm) / (0.05mm / h), where t is the glass thickness (mm). When using a two-step heat treatment method, the first heat treatment temperature range is 860-960℃, and the heat treatment time is not less than 5 hours; the second heat treatment temperature range is 960-1100℃, and the heat treatment time is the same as the one-step heat treatment time.

[0038] In a specific embodiment, the raw material composition of the calcium-aluminum ceramic is designed as follows (molar percentage): CaO: 54-60%; Al2O3: 38-44%; SiO2: 1-5%; ZrO2: 1-5%; and 0.63≤Al2O3:CaO≤0.82, 2%≤ZrO2+SiO2≤6%. The raw materials used include, but are not limited to, CaCO3, Ca(OH)2, Al2O3, Al(OH)3, SiO2, ZrO2, etc., and the purity of the raw materials is not less than 99.9%. CaO is introduced via CaCO3 or Ca(OH)2, Al2O3 via Al2O3 or Al(OH)3, SiO2 via chemically synthesized SiO2 or high-purity quartz sand, and ZrO2 via chemically synthesized ZrO2. The SiO2, ZrO2, Al2O3, and CaO can also be introduced in the form of compounds such as CaSiO3, CaZrO3, and CaAl2O4. Unless otherwise specified, all other raw materials and equipment involved in the specific embodiments are commercially available.

[0039] Example 1

[0040] The raw materials for CaO are CaCO3 (99.9%); the raw materials for Al2O3 are Al(OH)3 (99.9%); the raw materials for SiO2 are SiO2 (99.9%); and the raw materials for ZrO2 are ZrO2 (99.9%).

[0041] The raw materials were thoroughly mixed according to the specified ratio and melted in a platinum crucible at a temperature of 1600℃ for 2 hours. During the melting process, the high-temperature glass could be stirred appropriately to improve the uniformity of the molten glass. After melting, the molten glass was poured into a forming mold to cool and then transferred to a muffle furnace for annealing at 750℃ for 5 hours. After annealing, the power to the annealing furnace was turned off, and the precursor glass was allowed to cool down with the furnace. Once the temperature dropped to room temperature, the precursor glass was obtained.

[0042] To prepare calcium-aluminate ceramics, the obtained precursor was shaped to obtain a 1 mm thick glass block, which was then placed in a heat treatment furnace for one-step heat treatment. The heating rate of the heat treatment furnace was 5 °C / min, the heat treatment temperature was 980 °C, and the time was 14 h.

[0043] Figure 1 Powder X-ray diffraction pattern of transparent ceramic after one-step heat treatment in Example 1, and the concentrations of CaAl2O4 and Ca. 12 Al 14 O 33 X-ray diffraction comparison diagram of standard card. Example 1 mainly precipitates the above two types of crystals.

[0044] Figure 2 The transmittance curves for the precursor glass and the transparent ceramic after one-step heat treatment in Example 1 are shown in the 250 nm-2000 nm range, with a thickness of 1 mm. Although the transmittance is low in the short wavelength range, it can reach nearly 90% in the long wavelength range.

[0045] Figure 3 The transmittance curves for the precursor glass and the transparent ceramic after one-step heat treatment in Example 1 (2μm-7μm) are shown, with a thickness of 1 mm. It can be seen that the transparent ceramic obtained from the heat treatment in Example 1 not only has high transmittance in the near-infrared and mid-infrared bands, but also exhibits a significantly narrower hydroxyl absorption peak compared to calcium aluminate glass. The narrowed absorption peak of the transparent ceramic in the mid-infrared band is located at 2.82 μm, and there are also weak absorption peaks at 2.28 μm, 2.70 μm, and 2.89 μm. These characteristic absorption peaks are related to Ca... 12 Al 14 O 33 This indicates that hydroxyl groups have entered the crystal lattice.

[0046] Figure 4The image shows the morphology of the ceramic after one-step heat treatment in Example 1 under a transmission electron microscope. The main crystalline phase (CaAl2O4, Ca) is visible. 12 Al 14 O 33 They are uniform in size and closely packed.

[0047] Figure 5 This is a high-resolution transmission electron microscope (TEM) image and fast Fourier transform (FFT) diagram of the black particles in the ceramic after one-step heat treatment in Example 1. The interplanar spacing and interplanar angles closely match those of CaZr4O9, confirming that... Figure 3 The dispersed black particles are zirconium-containing crystalline phases (CaZr4O9).

[0048] Figure 6 This is the energy dispersive spectroscopy (EDS) spectrum of a selected region of the ceramic after one-step heat treatment in Example 1. The elemental distribution shows enrichment of silicon and zirconium in some small regions. No crystallization was detected in the silicon-rich regions, while the zirconium-rich regions showed... Figure 5 The corresponding CaZr4O9 phase indicates that, in addition to the main crystalline phase (CaAl2O4, Ca...), the ceramic also contains other phases. 12 Al 14 O 33 In addition, there are tiny and dispersed silicon-containing amorphous phases and zirconium-containing crystalline phases.

[0049] Example 2

[0050] The raw materials for CaO are Ca(OH)2 (99.9%); the raw materials for Al2O3 are Al2O3 (99.9%); the raw materials for SiO2 are SiO2 (99.9%); and the raw materials for ZrO2 are ZrO2 (99.9%).

[0051] The raw materials were thoroughly mixed according to the specified ratio and melted in a platinum crucible at a temperature of 1500℃ for 4 hours. During the melting process, the high-temperature glass could be stirred appropriately to improve the homogeneity of the molten glass. After melting, the molten glass was poured into a forming mold to cool and then transferred to a muffle furnace for annealing at 700℃ for 3 hours. After annealing, the power to the annealing furnace was turned off, allowing the precursor glass to cool down with the furnace. Once the temperature reached room temperature, the precursor glass was obtained.

[0052] To prepare calcium-aluminate ceramics, the obtained precursor was shaped to obtain a 3 mm thick glass block, which was then placed in a heat treatment furnace for one-step heat treatment. The heating rate of the heat treatment furnace was 2℃ / min, the heat treatment temperature was 980℃, and the time was 20 h.

[0053] Example 3

[0054] The raw materials for CaO are Ca(OH)2 (99.9%) and CaSiO3 (99.9%); the raw materials for Al2O3 are Al2O3 (99.9%); the raw materials for SiO2 are CaSiO3 (99.9%); and the raw materials for ZrO2 are ZrO2 (99.9%).

[0055] The raw materials were thoroughly mixed according to the specified ratio and melted in a platinum crucible at a temperature of 1650°C for 1 hour. During the melting process, the high-temperature glass could be stirred appropriately to improve the uniformity of the molten glass. After melting, the molten glass was poured into a forming mold to cool and then transferred to a muffle furnace for annealing at 850°C for 2 hours. After annealing, the power to the annealing furnace was turned off, allowing the precursor glass to cool down with the furnace. Once the temperature reached room temperature, the precursor glass was obtained.

[0056] To prepare calcium-aluminate ceramics, the obtained precursor was shaped to obtain a 5 mm thick glass block, which was then placed in a heat treatment furnace for one-step heat treatment. The heating rate of the heat treatment furnace was 10 °C / min, the heat treatment temperature was 960 °C, and the time was 60 h.

[0057] Example 4

[0058] The raw materials for CaO are CaCO3 (99.9%) and CaZrO3 (99.9%); the raw materials for Al2O3 are Al(OH)3 (99.9%); the raw materials for SiO2 are SiO2 (99.9%); and the raw materials for ZrO2 are CaZrO3 (99.9%).

[0059] The raw materials were thoroughly mixed according to the specified ratio and melted in a platinum crucible at a temperature of 1550℃ for 2 hours. During the melting process, the high-temperature glass could be stirred appropriately to improve the uniformity of the molten glass. After melting, the molten glass was poured into a forming mold to cool and then transferred to a muffle furnace for annealing at 800℃ for 2 hours. After annealing, the power to the annealing furnace was turned off, allowing the precursor glass to cool down with the furnace. Once the temperature reached room temperature, the precursor glass was obtained.

[0060] To prepare calcium-aluminate ceramics, the obtained precursor was shaped to obtain a 4 mm thick glass block, which was then placed in a heat treatment furnace for one-step heat treatment. The heating rate of the heat treatment furnace was 8 °C / min, the heat treatment temperature was 1000 °C, and the time was 80 h.

[0061] Example 5

[0062] The raw materials for CaO are CaCO3 (99.9%) and CaAl2O4 (99.9%); the raw materials for Al2O3 are Al(OH)3 (99.9%) and CaAl2O4 (99.9%); the raw materials for SiO2 are SiO2 (99.9%); and the raw materials for ZrO2 are ZrO2 (99.9%).

[0063] The raw materials were thoroughly mixed according to the specified ratio and melted in a platinum crucible at a temperature of 1630°C for 3 hours. During the melting process, the high-temperature glass could be stirred appropriately to improve the uniformity of the molten glass. After melting, the molten glass was poured into a forming mold to cool and then transferred to a muffle furnace for annealing at 750°C for 2 hours. After annealing, the power to the annealing furnace was turned off, and the precursor glass was allowed to cool down with the furnace. Once the temperature dropped to room temperature, the precursor glass was obtained.

[0064] To prepare calcium-aluminate ceramics, the obtained precursor was shaped to obtain a 4 mm thick glass block, which was then placed in a heat treatment furnace for a two-step heat treatment. The heating rate of the heat treatment furnace was 8℃ / min. The first heat treatment temperature was 920℃ and the time was 5 h. The second heat treatment temperature was 1000℃ and the time was 50 h.

[0065] The main process parameters and product performance characterization of Examples 1-5 are shown in Table 1.

[0066] Table 1

[0067]

[0068] Comparative Example 1

[0069] The raw materials for CaO are Ca(OH)2 (99.9%); the raw materials for Al2O3 are Al2O3 (99.9%); the raw materials for SiO2 are SiO2 (99.9%); and the raw materials for ZrO2 are ZrO2 (99.9%).

[0070] The raw materials were thoroughly mixed according to the specified ratio and melted in a platinum crucible at a temperature of 1600℃ for 2 hours. During the melting process, the high-temperature glass could be stirred appropriately to improve the uniformity of the molten glass. After melting, the molten glass was poured into a forming mold to cool and then transferred to a muffle furnace for annealing at 700℃ for 3 hours. After annealing, the power to the annealing furnace was turned off, allowing the precursor glass to cool down with the furnace. Once the temperature reached room temperature, the precursor glass was obtained.

[0071] To prepare calcium-aluminate ceramics, the obtained precursor was shaped to obtain a 1 mm thick glass block, which was then placed in a heat treatment furnace for one-step heat treatment. The heating rate of the heat treatment furnace was 5 °C / min, the heat treatment temperature was 1100 °C, and the time was 12 h.

[0072] The composition is approximately Al2O3:CaO = 0.77, ZrO2 + SiO2 = 8 mol%. After heat treatment, impurity phases appeared in the sample, and the visible light band showed devitrification, while the mid-infrared band also had low transmittance. Figure 7 The powder X-ray diffraction pattern of the ceramic after one-step heat treatment in Comparative Example 1 and the concentrations of CaAl2O4 and Ca... 12 Al 14 O 33 The X-ray diffraction comparison diagrams of the standard card show that, in addition to the two crystals mentioned above, other impurities are also present in Comparative Example 1.

[0073] Comparative Example 2

[0074] The raw materials for CaO are Ca(OH)2 (99.9%); the raw materials for Al2O3 are Al2O3 (99.9%); the raw materials for SiO2 are SiO2 (99.9%); and the raw materials for ZrO2 are ZrO2 (99.9%).

[0075] The raw materials were thoroughly mixed according to the specified ratio and melted in a platinum crucible at a temperature of 1600℃ for 4 hours. During the melting process, the high-temperature glass could be stirred appropriately to improve the homogeneity of the molten glass. After melting, the molten glass was poured into a forming mold to cool and then transferred to a muffle furnace for annealing at 750℃ for 3 hours. After annealing, the power to the annealing furnace was turned off, allowing the precursor glass to cool down with the furnace. Once the temperature reached room temperature, the precursor glass was obtained.

[0076] To prepare calcium-aluminate ceramics, the obtained precursor was shaped to obtain a 1 mm thick glass block, which was then placed in a heat treatment furnace for one-step heat treatment. The heating rate of the heat treatment furnace was 5 °C / min, the heat treatment temperature was 1000 °C, and the time was 20 h.

[0077] The composition is Al2O3:CaO = 0.6, ZrO2+SiO2 = 4%. After heat treatment, an opaque crystalline layer will appear on the surface, affecting light transmission.

[0078] Comparative Example 3

[0079] The raw materials for CaO are Ca(OH)2 (99.9%); the raw materials for Al2O3 are Al2O3 (99.9%); the raw materials for SiO2 are SiO2 (99.9%); and the raw materials for ZrO2 are ZrO2 (99.9%).

[0080] The raw materials were thoroughly mixed according to the specified ratio and melted in a platinum crucible at a temperature of 1630°C for 4 hours. During the melting process, the high-temperature glass could be stirred appropriately to improve the homogeneity of the molten glass. After melting, the molten glass was poured into a forming mold to cool and then transferred to a muffle furnace for annealing at 600°C for 3 hours. After annealing, the power to the annealing furnace was turned off, allowing the precursor glass to cool down with the furnace. Once the temperature reached room temperature, the precursor glass was obtained.

[0081] The composition is approximately Al2O3:CaO = 0.88, and ZrO2+SiO2 = 4%. At this point, the precursor glass is completely detransmitted in the visible light band, with low transmittance in the infrared band.

[0082] Comparative Example 4

[0083] The raw materials for CaO are Ca(OH)2 (99.9%); the raw materials for Al2O3 are Al2O3 (99.9%); the raw materials for SiO2 are SiO2 (99.9%); and the raw materials for ZrO2 are ZrO2 (99.9%).

[0084] The raw materials were thoroughly mixed according to the specified ratio and melted in a platinum crucible at a temperature of 1600℃ for 2 hours. During the melting process, the high-temperature glass could be stirred appropriately to improve the uniformity of the molten glass. After melting, the molten glass was poured into a forming mold to cool and then transferred to a muffle furnace for annealing at 750℃ for 5 hours. After annealing, the power to the annealing furnace was turned off, allowing the precursor glass to cool down with the furnace. Once the temperature reached room temperature, the precursor glass was obtained.

[0085] To prepare calcium-aluminate ceramics, the obtained precursor was shaped to obtain a 1 mm thick glass block, which was then placed in a heat treatment furnace for one-step heat treatment. The heating rate of the heat treatment furnace was 5 °C / min, the heat treatment temperature was 980 °C, and the time was 16 h.

[0086] The composition is approximately Al2O3:CaO = 0.71, and ZrO2+SiO2 = 8%. After heat treatment, the sample exhibits devitrification and distortion in the visible light band.

[0087] The main process parameters and product performance characterization of Comparative Examples 1-4 are shown in Table 2.

[0088] Table 2

[0089]

Claims

1. A high-strength mid-infrared transparent calcium-aluminum ceramic, characterized in that... The main crystal phase is CaAl2O4 and Ca 12 Al 14 O 33 , the grain size is 30 nm-150 nm; meanwhile, a small amount of CaZr4O9 crystal phase and amorphous phase rich in SiO2 are also contained; The raw material composition of the calcium-aluminum ceramic is designed as follows (in molar percentage): CaO: 54-60%; Al2O3: 38-44%; SiO2: 1-5%; ZrO2: 1-5%; and 0.63≤Al2O3:CaO≤0.82, 2%≤ZrO2+SiO2≤6%.

2. The preparation method of the high-strength mid-infrared transparent calcium aluminum ceramic according to claim 1, characterized in that... Includes the following steps: (1) Mix the raw materials thoroughly according to the proportions and melt them in a platinum crucible at a melting temperature of not less than 1450℃; (2) After melting, the molten glass is poured into a molding mold to cool, and then transferred to a muffle furnace for annealing. After annealing, it is cooled to room temperature in the furnace to obtain the precursor glass. (3) The precursor glass is subjected to one-step heat treatment. The glass is added to a heat treatment furnace and heated to 900-1100℃ at a rate of no more than 10℃ / min. The heat treatment time is no less than t / 0.15 hours, where t is the glass thickness in mm.

3. The preparation method of high-strength mid-infrared transparent calcium-aluminum ceramic as described in claim 2, characterized in that... 0.68≤Al2O3:CaO≤0.78, 2%≤ZrO2+SiO2≤4%.

4. The preparation method of high-strength mid-infrared transparent calcium-aluminum ceramic as described in claim 2, characterized in that... In step (1), the melting temperature is 1500-1650℃ and the melting time is no less than 1 hour.

5. The preparation method of high-strength mid-infrared transparent calcium aluminum ceramic as described in claim 2, characterized in that... In step (2), the annealing temperature is 600-850℃ and the annealing time is not less than 1 hour.

6. The preparation method of high-strength mid-infrared transparent calcium aluminum ceramic as described in claim 2, characterized in that... In step (3), the heat treatment temperature is 960-1100℃ and the heat treatment time is not less than t / 0.05 hours.

7. The preparation method of high-strength mid-infrared transparent calcium aluminum ceramic as described in claim 2, characterized in that... Step (3) adopts a two-step heat treatment method. In the first step, the temperature is increased to 860-960℃ at a rate of no more than 10℃ / min, and the heat treatment time is no less than 5 hours. In the second step, the temperature is increased to 960-1100℃, and the heat treatment time is no less than t / 0.15 hours, where t is the glass thickness in mm.

8. The preparation method of high-strength mid-infrared transparent calcium aluminum ceramic as described in claim 2, characterized in that... The calcium-aluminate ceramic has a transmittance of greater than 50% in the 550 nm band and greater than 70% in the 3.5 μm-5 μm band, based on a thickness of 1 mm.

9. The preparation method of high-strength mid-infrared transparent calcium-aluminum ceramic as described in claim 2, characterized in that... The calcium-aluminate ceramic has a Vickers hardness greater than 7 GPa and an elastic modulus greater than 110 GPa.

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