A wide-temperature-range, high-negative-thermal-expansion phosphate ceramic material and its sintering and bonding method

Abstract

This invention discloses a wide-temperature-range, high-negative thermal expansion phosphate ceramic material and its sintering method, belonging to the field of inorganic non-metallic materials technology. It uses NH4H2PO4, Fe2O3, V2O5, and Mg(OH)2 as raw materials, and follows the target product Fe... x Mg 2‑x P 2‑y V y O 7+δ Raw materials were weighed according to the stoichiometric molar ratio, ground and mixed evenly, pre-calcined at 800-1000℃ for 2-5 h, ground and mixed evenly again, and then sintered directly or after tableting at 1000-1150℃ for 2-7 h to obtain the target product. This invention uses Fe... 3+ Ions partially replace Mg in Mg2P2O7 2+ Ions, further V 5+ Ion partial substitution of P 5+ Fe, a phosphate ceramic material with huge negative thermal expansion over a wide temperature range, was prepared by ion-solid phase method. x Mg 2‑x P2O 7+δ and Fe 0.05 Mg 1.95 P 2‑y V y O 7+0.025 The coefficient of thermal expansion is -82.7 × 10⁻⁶. ‑6 ℃ ‑1 ~ -345.4×10 ‑6 ℃ ‑1 The temperature range ΔT is 16℃~37℃, which realizes the adjustment of temperature range and thermal expansion coefficient. The process is simple, low-cost, and suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic materials, and specifically relates to a wide-temperature-range giant negative thermal expansion phosphate ceramic material and its sintering synthesis method. Background Technology

[0002] Most materials in nature exhibit significant thermal expansion and contraction (positive thermal expansion), and materials with a large positive thermal expansion coefficient have a clear advantage in applications such as thermometers. However, thermal stress easily arises between materials with significantly different thermal expansion coefficients. Even within the same material, differences in thermal expansion coefficients due to temperature variations can generate thermal stress. This is particularly problematic for precision devices within confined spaces, where repeated thermal cycling accumulates thermal stress that is difficult to release. When the accumulated thermal stress exceeds the material's binding force, it releases through the formation of microcracks. As these cracks enlarge, parts of the material detach from the overall structure, leading to complete device failure. Reducing thermal stress is crucial for improving the thermal stability of devices. While negative thermal expansion materials have been discovered, and combining positive and negative thermal expansion materials can reduce the positive thermal expansion coefficient—essentially compensating for positive thermal expansion—currently discovered negative thermal expansion materials typically have a small negative thermal expansion coefficient (e.g., zirconium tungstate, with its strong thermal shrinkage properties, has a negative thermal expansion coefficient of -8.1 × 10⁻⁶). -6 ℃ -1 The coefficient of thermal expansion of aluminum is 23.5 × 10⁻⁶. -6 ℃ -1 If we want to increase the thermal expansion compensation effect of negative thermal expansion materials (one-third of the total), we can only increase the proportion of negative thermal expansion materials. However, this makes the negative thermal expansion materials, which constitute the majority of the material, actually reduce the performance of the original positive thermal expansion devices. For example, in our previous research on positive thermal expansion metal aluminum and negative thermal expansion material Zr2P2WO... 12 Its coefficient of thermal shrinkage is -2.3 × 10⁻⁶ -6 ℃ -1 One example is the composite material (Al-Zr2P2WO3, a metal-based ceramic material with a controllable coefficient of thermal expansion). 12 The sintering method (ZL201110283736.0) is mentioned. Therefore, it is urgent to improve the thermal shrinkage coefficient of negative thermal expansion materials to enhance their thermal compensation effect.

[0003] Current reports indicate that Mg₂P₂O₇ exhibits a large negative thermal expansion coefficient of -57.6 × 10⁻⁶ during the α→β phase transformation. -6 ℃ -1(It has 2.5 times the coefficient of thermal expansion of aluminum), and the temperature range is 14℃ (64~78℃) (Yige Du, et al. Optimized negative thermal expansion property in low-cost Mg2P2O7-based bulk material, Results in Physics 35 (2022) 105415). The substitution of P-site isovalent ions with V significantly increases its negative thermal expansion coefficient, reaching 127.5 × 10⁻⁶. -6 ℃ -1 However, the temperature range increases to 31℃ (9~40℃); by substituting Cu ions at the Mg sites, its negative thermal expansion coefficient actually decreases to -28.4 × 10⁻⁶. -6 ℃ -1 Although the temperature range is significantly increased to 100℃ (-113~-13℃), this report indicates that isovalent ion substitution only moderately adjusts the crystal structure and phase transition. The negative thermal expansion effect is still a phase transition and cannot add new negative thermal expansion effects. In other words, it cannot superimpose more negative thermal expansion effects to achieve a significant increase in both the negative thermal expansion coefficient and the temperature range.

[0004] The substitution of heterovalent ions, due to their differences in valence state and ionic radius, inevitably introduces charge imbalance and greater lattice distortion. For divalent Mg in Mg₂P₂O₇... 2+ There are no reports of using trivalent ions as substitutes. Related research will provide useful insights for exploring how to improve negative thermal expansion performance by superimposing two or more negative thermal expansion effects.

[0005] Therefore, this application provides a method using heterovalent Fe ions. 3+ Replacement of Mg in Mg2P2O7 2+ Ions, and further increase the V of isovalent ions. 5+ Replace P 5+ A wide-temperature-range giant negative thermal expansion phosphate ceramic material was prepared. This wide-temperature-range giant negative thermal expansion material was prepared by a solid-state method, which is suitable for industrial production and is of great significance for the promotion and application of negative expansion materials. Summary of the Invention

[0006] The purpose of this invention is to design a wide-temperature-range, high-negative-thermal-expansion phosphate ceramic material and its sintering and synthesis method.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A wide-temperature-range, high-negative thermal expansion phosphate ceramic material, the structural formula of which is Fe x Mg 2-x P 2-yV y O 7+δ , x =0.01~0.1, δ= x / 2, y =0 or x =0.05, y =0.03~0.05.

[0009] Preferably, the ceramic material has the structural formula Fe. 0.01 Mg 1.99 P2O 7+0.005 Fe 0.05 Mg 1.99 P2O 7+0.025 Fe 0.1 Mg 1.99 P2O 7+0.05 Fe 0.05 Mg 1.95 P 1.97 V 0.03 O 7+0.025 or Fe 0.05 Mg 1.95 P 1.95 V 0.05 O 7+0.025 .

[0010] Furthermore, the coefficient of thermal expansion of the ceramic material is -82.7 × 10⁻⁶. -6 ℃ -1 ~-345.4×10 -6 ℃ -1 The temperature range ΔT is 16℃~37℃.

[0011] The above-mentioned sintering method for wide-temperature-range giant negative thermal expansion phosphate ceramic materials uses NH4H2PO4, Fe2O3, V2O5, and Mg(OH)2 as raw materials, according to the target product Fe x Mg 2-x P 2-y V y O 7+δ ( x =0.01~0.1, δ= x / 2, y =0 or x =0.05, y The raw materials were weighed in a stoichiometric molar ratio of 0.03~0.05, ground and mixed evenly, and then solid-state sintered to obtain the target product.

[0012] Furthermore, solid-state sintering refers to first directly or pressing the material into a cylinder and then pre-sintering it at 800~1000℃ for 2~5 h; then grinding and mixing it evenly, and then directly or pressing it into a sheet and sintering it at 1000~1150℃ for 2~7 h.

[0013] The beneficial effects of this invention are:

[0014] 1. This invention uses NH4H2PO4, Fe2O3, and Mg(OH)2 as raw materials to prepare a novel wide-temperature-range giant negative thermal expansion phosphate ceramic material Fe 0.05 Mg 1.95 P2O 7+0.025 (-100.9×10 -6 ℃ -1 (35~70℃, ΔT=35℃), Fe 0.05 Mg 1.95 P 1.95 V 0.05 O 7+0.025 (-345.4×10 -6 ℃ -1 (45~69℃, ΔT=24℃), their negative thermal expansion coefficients are 1.7 and 5.7 times that of Mg2P2O7, respectively, and the temperature range expansion is 1.8 and 1.2 times that of Mg2P2O7, respectively.

[0015] 2. This invention uses solid-state sintering, which is simple, low-cost, and suitable for industrial production. Attached Figure Description

[0016] Figure 1 The X-ray diffraction (XRD) pattern of Mg2P2O7 synthesized in Example 1;

[0017] Figure 2 Fe synthesized in Example 2 0.01 Mg 1.99 P2O 7+0.005 XRD patterns;

[0018] Figure 3 Fe synthesized in Example 3 0.05 Mg 1.95 P2O 7+0.025 XRD patterns;

[0019] Figure 4 Fe prepared in Example 4 0.1 Mg 1.9 P2O 7+0.05 XRD patterns;

[0020] Figure 5 Fe prepared in Example 5 0.05 Mg 1.95 P 1.97 V 0.03 O 7+0.025 XRD patterns;

[0021] Figure 6Fe prepared in Example 5 0.05 Mg 1.95 P 1.95 V 0.05 O 7+0.025 XRD patterns;

[0022] Figure 7 The curves show the relative length of the ceramic products prepared in Examples 1-4 as a function of temperature.

[0023] Figure 8 The curves showing the relative length of the ceramic products prepared in Examples 1, 3, 5, and 6 as a function of temperature are shown. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] Example 1

[0026] A sintering method for a negative thermal expansion phosphate ceramic material Mg2P2O7 is described below: Using NH4H2PO4 and Mg(OH)2 as raw materials, the raw materials are weighed according to the stoichiometric molar ratio of Mg:P = 1:1. The raw materials are ground in a mortar for approximately 2 hours, and then pressed into cylinders with a diameter of 10 mm and a height of 5 mm under a uniaxial pressing machine at a pressure of 3 tons. The cylinders are then placed in a muffle furnace and pre-sintered at 1000℃ for 2 hours at a heating rate of 5℃ / min, followed by natural cooling to room temperature in air. Afterward, the cylinders are ground for another 2 hours, pressed again under a pressure of 200 MPa, and sintered at 1150℃ for 7 hours at the same heating rate, followed by natural cooling to room temperature in air. XRD patterns and phase analysis of the product are shown below. Figure 1 The XRD results, compared with the PDF card of standard Mg2P2O7, showed that a single phase was formed.

[0027] Example 2

[0028] A wide-temperature-range negative thermal expansion phosphate ceramic material Fe 0.01 Mg 1.99 P2O 7+0.005 The sintering method differs from Example 1 in that it uses NH4H2PO4, Fe2O3, and Mg(OH)2 as raw materials, and the raw materials are selected according to the target product Fe. 0.01 Mg 1.99 P2O 7+0.005 The raw materials were weighed with a stoichiometric molar ratio of Fe:Mg:P = 0.01:1.99:2.0. The XRD pattern and phase analysis of the product are shown below. Figure 2 The XRD results, compared with the PDF card of standard Mg2P2O7, showed that a single phase was formed.

[0029] Example 3

[0030] A wide-temperature-range negative thermal expansion phosphate ceramic material Fe 0.05 Mg 1.99 P2O 7+0.025 The sintering method differs from Example 1 in that it uses NH4H2PO4, Fe2O3, and Mg(OH)2 as raw materials, and the raw materials are selected according to the target product Fe. 0.05 Mg 1.95 P2O 7+0.025 The raw materials were weighed with a stoichiometric molar ratio of Fe:Mg:P = 0.05:1.95:2.0. The XRD pattern and phase analysis of the product are shown below. Figure 3 The XRD results, compared with the PDF card of standard Mg2P2O7, showed that a single phase was formed.

[0031] Example 4

[0032] A wide-temperature-range negative thermal expansion phosphate ceramic material Fe 0.1 Mg 1.99 P2O 7+0.05 The sintering method differs from Example 1 in that it uses NH4H2PO4, Fe2O3, and Mg(OH)2 as raw materials, and the raw materials are selected according to the target product Fe. 0.1 Mg 1.9 P2O 7+0.05 The raw materials were weighed with a stoichiometric molar ratio of Fe:Mg:P = 0.1:1.9:2.0. The XRD pattern and phase analysis of the product are shown below. Figure 4 The XRD results, compared with the PDF card of standard Mg2P2O7, showed that a single phase was formed.

[0033] Example 5

[0034] A giant negative thermal expansion phosphate ceramic material Fe 0.05 Mg 1.95 P 1.97 V 0.03 O 7+0.025 The sintering method differs from Example 3 in that it uses NH4H2PO4, Fe2O3, V2O5, and Mg(OH)2 as raw materials, and the raw materials are selected according to the target product Fe. 0.05 Mg 1.95 P 1.97 V 0.03 O 7+0.025 The raw materials were weighed with a stoichiometric molar ratio of Fe:Mg:P:V = 0.05:1.95:1.97:0.03. The XRD pattern and phase analysis of the product are shown below. Figure 5 The XRD results, compared with the PDF card of standard Mg2P2O7, showed that a single phase was formed.

[0035] Example 6

[0036] A wide-temperature-range giant negative thermal expansion phosphate ceramic material Fe 0.05 Mg 1.95 P 1.95 V 0.05 O 7+0.025 The sintering method differs from Example 3 in that it uses NH4H2PO4, Fe2O3, V2O5, and Mg(OH)2 as raw materials, and the raw materials are selected according to the target product Fe. 0.05 Mg 1.95 P 1.95 V 0.05 O 7+0.025 The raw materials were weighed according to the stoichiometric molar ratio of Fe:Mg:P:V = 0.05:1.95:1.95:0.05. The XRD pattern and phase analysis of the product are shown below. Figure 6 The XRD results, compared with the PDF card of standard Mg2P2O7, showed that a single phase was formed.

[0037] Thermal expansion coefficient test:

[0038] Figure 7 These are the relative length curves of the ceramic products prepared in Examples 1, 2, 3, and 4 as a function of temperature. The comparison shows that the introduction of Fe significantly increases the absolute value of the negative thermal expansion coefficient, shifts the onset temperature of negative thermal expansion to lower temperatures, and broadens the temperature range. (Mg2P2O7, Fe) 0.01 Mg 1.99 P2O 7+0.005 Fe 0.05 Mg 1.95 P2O 7+0.025 Fe 0.1 Mg 1.9 P2O 7+0.05 The coefficients of thermal expansion are -61.0×10⁻⁶. -6 ℃ -1 (60~80℃, ΔT=20℃), -119.3×10 -6 ℃ -1 (55~77℃, ΔT=22℃), -100.9×10 -6 ℃ -1 (35~70℃, ΔT=35℃), -82.7×10 -6 ℃ -1 (26~63℃, ΔT=37℃).

[0039] Figure 8 These are the curves showing the relative length of the ceramic products prepared in Examples 1, 3, 5, and 6 as a function of temperature. The comparison shows that introducing V on top of Fe significantly increases the absolute value of the negative thermal expansion coefficient, and the starting temperature for negative thermal expansion shifts to lower temperatures; however, the widening of the temperature range is not obvious or even narrows. Fe0.05 Mg 1.95 P 1.97 V 0.03 O 7+0.025 Its negative coefficient of thermal expansion is -342.5 × 10⁻⁶. -6 ℃ -1 (54~70℃, ΔT=16℃), reaching 5.6 times the negative thermal expansion coefficient of Mg2P2O7, but the temperature range narrows by 4℃; Fe 0.05 Mg 1.95 P 1.95 V 0.05 O 7+0.025 Its negative coefficient of thermal expansion is -345.4 × 10⁻⁶. -6 ℃ -1 (45~69℃, ΔT=24℃), reaching 5.7 times the negative thermal expansion coefficient of Mg2P2O7, and the temperature range is widened by 1.2 times.

Claims

1. A wide-temperature-range, high-negative-thermal-expansion phosphate ceramic material, characterized in that: The structural formula of the ceramic material is Fe x Mg 2- x P 2-y V y O 7+δ , x =0.01~0.1, δ= x / 2, y =0 or x =0.05, δ= x / 2, y =0.03~0.

05.

2. The wide-temperature-range giant negative thermal expansion phosphate ceramic material according to claim 1, characterized in that: The structural formula of the ceramic material is Fe 0.01 Mg 1.99 P2O 7+0.005 Fe 0.05 Mg 1.99 P2O 7+0.025 Fe 0.1 Mg 1.99 P2O 7+0.05 Fe 0.05 Mg 1.95 P 1.97 V 0.03 O 7+0.025 or Fe 0.05 Mg 1.95 P 1.95 V 0.05 O 7+0.025 .

3. The wide-temperature-range giant negative thermal expansion phosphate ceramic material according to claim 1 or 2, characterized in that: The coefficient of thermal expansion of the ceramic material is -82.7 × 10⁻⁶. -6 ℃ -1 ~-345.4×10 -6 ℃ -1 The temperature range ΔT is 16℃~37℃.

4. The sintering and forming method of the wide-temperature-range giant negative thermal expansion phosphate ceramic material according to any one of claims 1 to 3, characterized in that: Using NH4H2PO4, Fe2O3, V2O5, and Mg(OH)2 as raw materials, according to the target product Fe x Mg 2-x P 2-y V y O 7+δ The raw materials are weighed according to the stoichiometric molar ratio, ground and mixed evenly, and then solid-state sintered to obtain the target product.

5. The sintering and forming method according to claim 4, characterized in that: Solid-state sintering refers to the process of first directly or pressing the material into a cylinder and then pre-sintering it at 800~1000℃ for 2~5 h; then grinding and mixing it evenly, and then directly or pressing it into a tablet and sintering it at 1000~1150℃ for 2~7 h.

6. The sintering and forming method according to claim 5, characterized in that: The heating rate during pre-sintering or sintering is 2~10 ℃ / min.

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