An anoxic titanium dioxide conductive ceramic based on space charge effect reinforcement and a preparation method thereof

Abstract

The application relates to an anoxic titanium dioxide conductive ceramic based on space charge effect reinforcement and a preparation method thereof. The anoxic titanium dioxide conductive ceramic comprises an anoxic titanium dioxide TiO 2‑x matrix and M2O3 second-phase particles uniformly dispersed at grain boundaries of the anoxic titanium dioxide TiO 2‑x matrix; wherein a uniform M-Ti-O nanolayer is formed at the grain boundaries of the anoxic titanium dioxide TiO 2‑x matrix, and a jagged interlocking grain boundary is formed at the interface between the M2O3 second-phase particles and the anoxic titanium dioxide TiO 2‑x matrix. The application innovatively applies a space charge effect field commonly existing in a semiconductor ceramic to a conductive ceramic field for the first time, realizes synergistic enhancement of mechanical and electrical properties, and opens up a new idea for design of a high-performance conductive ceramic.

Description

Technical Field

[0001] This invention belongs to the field of conductive ceramic materials technology, and relates to an oxygen-deficient titanium dioxide conductive ceramic enhanced by space charge effect and its preparation method. Background Technology

[0002] TiO2 ceramics possess excellent dielectric and photocatalytic properties, but their intrinsic conductivity is low and their mechanical properties are generally poor, limiting their application in conductive functional components. Oxygen-deficient titanium dioxide (TiO2) can be formed through reduction treatment. 2-x It can introduce oxygen vacancies and Ti 3+ Self-doping can improve the electrical conductivity of ceramics to some extent. However, TiO2... 2-x Titanium oxide ceramics still suffer from the inherent defect of poor mechanical properties, making it difficult to meet the high reliability and high strength requirements of materials in applications such as semiconductor equipment carrier components and wastewater treatment electrodes.

[0003] In existing technologies, the addition of reinforcing phases or the use of grain refinement mechanisms can improve the performance of TiO₂ to some extent. 2-x While improving the mechanical properties of ceramics is important, adding reinforcing phases or employing grain refinement strategies often weakens the contribution of conductive grains in the matrix, sacrificing the overall electrical conductivity of the ceramic. Existing strategies struggle to simultaneously improve both mechanical and electrical properties.

[0004] Therefore, it is necessary to develop a method that can simultaneously and significantly improve TiO2. 2-x The new methods for studying the mechanical and electrical properties of conductive ceramics have significant application value. Summary of the Invention

[0005] To address the above problems, and to solve the existing TiO2... 2-x The present invention addresses the technical challenge of simultaneously achieving high mechanical strength and high electrical conductivity in conductive ceramics. It aims to provide a TiO₂-based material strengthened by the space charge effect. 2-x Conductive ceramics and their preparation methods.

[0006] On one hand, the present invention provides an oxygen-deficient titanium dioxide conductive ceramic enhanced by the space charge effect, wherein the oxygen-deficient titanium dioxide conductive ceramic comprises oxygen-deficient titanium dioxide (TiO₂). 2-x The matrix, and uniformly dispersed in oxygen-deficient titanium dioxide (TiO2). 2-x M2O3 second-phase particles at the grain boundaries of the matrix; wherein, in the oxygen-deficient titanium dioxide TiO 2-x A uniform M-Ti-O nanolayer is formed at the grain boundaries of the matrix, and the M2O3 second phase particles and the oxygen-deficient titanium dioxide TiO2 are interlayered. 2-x Serrated interlocking grain boundaries are formed at the interface of the matrix.

[0007] Preferably, the oxygen-deficient titanium dioxide (TiO2)2-x In the matrix, 0<x≤0.1.

[0008] Preferably, the M2O3 second-phase particles are trivalent metal oxides with a corundum-type crystal structure, selected from at least one of Al2O3, Ga2O3, In2O3, Fe2O3, V2O3, and Cr2O3, and more preferably Al2O3 or Ga2O3.

[0009] Preferably, in the oxygen-deficient titanium dioxide conductive ceramic, the M2O3 second phase particles account for 0.2 to 10 wt.% of the total mass of the oxygen-deficient titanium dioxide conductive ceramic, more preferably 0.5 to 3 wt.%.

[0010] Preferably, the thickness of the M-Ti-O nanolayer is 1–10 nm.

[0011] Preferably, the grain size of the oxygen-deficient titanium dioxide conductive ceramic is 0.5 to 5 µm.

[0012] Preferably, the oxygen-deficient titanium dioxide conductive ceramic has a flexural strength ≥250 MPa and a fracture toughness ≥3 MPa•m. 1 / 2 Electrical conductivity ≥ 0.02 S / cm.

[0013] On the other hand, the present invention provides a method for preparing the above-mentioned oxygen-deficient titanium dioxide conductive ceramic enhanced by space charge effect, comprising the following steps: (1) TiO2 powder and M2O3 powder are mixed, ball-milled, dried and sieved to obtain mixed powder; (2) The mixed powder is shaped and sintered to obtain the oxygen-deficient titanium dioxide conductive ceramic.

[0014] Preferably, in step (1), the mass ratio of TiO2 powder to M2O3 powder is (99.8-90):(0.2-10), and more preferably (99.5-97):(0.5-3).

[0015] Preferably, in step (1), the parameters of the ball milling include: a ball milling speed of 200-500 r / min, a ball milling time of 3-12 h, a ball milling medium of zirconia grinding balls, anhydrous ethanol as the solvent, and a mass ratio of mixed powder, anhydrous ethanol and zirconia grinding balls of 1:(1-3):(1-3).

[0016] Preferably, in step (1), the drying temperature is 50-80°C and the time is 6-24 h.

[0017] Preferably, in step (2), the molding method includes at least one of dry pressing and cold isostatic pressing; preferably, the pressure of dry pressing is 5 to 30 MPa and the holding time is 1 to 5 min; the pressure of cold isostatic pressing is 50 to 500 MPa and the holding time is 1 to 5 min.

[0018] Preferably, in step (2), the sintering atmosphere is a vacuum, an inert, or a reducing atmosphere; the sintering method includes atmospheric pressure sintering, hot pressing sintering, spark plasma sintering, or microwave sintering, preferably hot pressing sintering; more preferably, the sintering method is vacuum hot pressing sintering, and the vacuum hot pressing sintering process includes: heating to 500-700°C at a rate of 5-20°C / min under a vacuum of 0.1-100 Pa, while simultaneously increasing the pressure to 0.5-10 MPa; then heating to 1000-1150°C at a rate of 1-3°C / min, while simultaneously increasing the pressure to 15-50 MPa, and holding at the temperature and pressure for 0.5-3 h; then cooling to 600-800°C at a rate of 1-10°C / min, depressurizing to 0 MPa, and finally cooling with the furnace.

[0019] In this invention, a specially selected M2O3 reinforcing phase and an optimized sintering process are employed, cleverly utilizing TiO2. 2-x As an n-type semiconductor material, M is a space charge field induced by the Schottky barrier at the grain boundaries. Driven by this electric field, M... 3+ TiO2 diffuses orientedly along the grain boundaries and substitutes for it. 2-x Ti at grain boundaries 3+ This not only facilitated the formation of M-Ti-O nanolayers at grain boundaries, but also contributed to the formation of M2O3 / TiO2 nanolayers. 2-x The interface forms serrated interlocking grain boundaries. This unique microstructure significantly improves the mechanical properties of the ceramic through grain refinement, grain boundary strengthening, and crack deflection / bridging mechanisms. Furthermore, it reduces the Ti content at grain boundaries. 3+ By polarizing the subcenter and lowering the grain boundary barrier, the carrier mobility is effectively improved, thereby achieving a simultaneous increase in conductivity. Beneficial effects

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Significantly improved mechanical properties: The flexural strength of the oxygen-deficient titanium dioxide conductive ceramics provided by this invention can generally reach more than 400 MPa, and even exceed 500 MPa in some cases. Compared with the control group without the addition of M2O3 reinforcing phase, the flexural strength can be increased by more than 4 times, and the fracture toughness of the ceramics also exceeds 5 MPa•m. 1 / 2 This is significantly better than the publicly reported data of similar materials; (2) Simultaneous improvement of electrical properties: Using the preparation method provided by this invention, in TiO2... 2-xWhile significantly improving the mechanical properties of ceramics, the electrical conductivity is increased by more than 2 times, breaking the limitation of mutual constraints between the optimization of mechanical properties and electrical properties in existing technologies; (3) Mechanism and process innovation: This invention innovatively applies the space charge effect field, which is ubiquitous in semiconductor ceramics, to the field of conductive ceramics for the first time, achieving synergistic enhancement of its mechanical and electrical properties, and opening up new ideas for the design of high-performance conductive ceramics: the space charge field promotes M 3+ Ti at grain boundaries 3+ The substitution of M-Ti-O nanolayers hinders material transport at grain boundaries, refining the grains. Since MO bonds typically have higher bond strength than Ti-O bonds, the combination of grain refinement strengthening, grain boundary strengthening, and serrated grain boundary effects effectively improves the overall mechanical properties of the ceramics. 3+ Its electronegativity is typically lower than that of Ti. 3+ This effectively improves the carrier transport efficiency at grain boundaries, thereby enhancing the overall electrical properties of the ceramic. In terms of process, by utilizing the space charge effect field as a driving mechanism, high-melting-point M2O3 can be used to improve the ceramic microstructure and optimize various properties at relatively low sintering temperatures (typically 1200℃), thus significantly reducing the energy consumption and production cost of high-performance conductive ceramics. Attached Figure Description

[0021] Figure 1 SEM image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Comparative Example 1 of this invention. Figure 2 This is a SEM image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 4 of the present invention; Figure 3 EDS image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 6 of this invention; Figure 4 Line scan EDS image of the grain boundaries of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 6 of this invention; Figure 5 This is a TEM image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 6 of the present invention; Figure 6 TEM images of different locations of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 6 of the present invention; Figure 7 This is a TEM image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 9 of the present invention; Figure 8 This is a SEM image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 10 of the present invention; Figure 9 This is a SEM image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 11 of the present invention; Figure 10 Optical photographs of the oxygen-deficient titanium dioxide conductive ceramics prepared in Comparative Examples 1, 4, and 6 of this invention; Figure 11 EDS image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 2 of this invention; Figure 12 EDS image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 9 of this invention; Figure 13 EDS image of Ga element on a larger scale for the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 9 of the present invention. Detailed Implementation

[0022] To further illustrate the invention's content, features, and practical effects, the invention will be described in detail below with reference to embodiments. It should be noted that the modification methods of the invention are not limited to these specific implementation methods. Equivalent substitutions and modifications made by those skilled in the art based on their reading of the invention's content, without departing from the spirit and essence of the invention, are also within the scope of protection claimed by this invention.

[0023] First, this invention provides an oxygen-deficient titanium dioxide conductive ceramic enhanced by the space charge effect, wherein the oxygen-deficient titanium dioxide conductive ceramic comprises oxygen-deficient titanium dioxide (TiO₂). 2-x The matrix, and uniformly dispersed in oxygen-deficient titanium dioxide (TiO2). 2-x M2O3 second-phase particles at the grain boundaries of the matrix; wherein, in TiO 2-x / TiO 2-x A uniform M-Ti-O nanolayer is formed at the grain boundaries, in M2O3 / TiO 2-x Serrated interlocking grain boundaries are formed at the interface. Specifically, in the oxygen-deficient titanium dioxide conductive ceramic, TiO₂… 2-x Driven by the space charge field at the grain boundary, M in M2O3 3+ Directional migration and partial substitution of Ti towards grain boundaries 3+ This results in the formation of M-Ti-O nanolayers with a thickness of 1–10 nm at the grain boundaries; simultaneously, M 3+ The continuous dissolution of M2O3 causes the volume of M2O3 to shrink, promoting the M2O3 / TiO2 ratio. 2-x Grain boundaries migrate into the interior of M2O3 grains, and this uneven dissolution further induces the formation of serrated interlocking grain boundaries at the interface. The oxygen-deficient titanium dioxide conductive ceramic exhibits a flexural strength ≥250 MPa and a fracture toughness ≥3 MPa•m. 1 / 2 Electrical conductivity ≥ 0.02 S / cm.

[0024] In an optional embodiment, the oxygen-deficient titanium dioxide (TiO₂) 2-xIn the matrix, 0 < x ≤ 0.1. The oxygen-deficient titanium dioxide (TiO₂) 2-x The substrate is a semiconductor ceramic material with a significant built-in potential field, which is sufficient to trigger the nanoscale space charge effect.

[0025] In an optional embodiment, the M2O3 second phase particles are trivalent metal oxides with a corundum-type crystal structure similar to Ti2O3, selected from at least one of Al2O3, Ga2O3, In2O3, Fe2O3, V2O3, and Cr2O3, preferably Al2O3 or Ga2O3.

[0026] In an optional embodiment, the M2O3 second-phase particles in the oxygen-deficient titanium dioxide conductive ceramic account for 0.2–10 wt.% of the total mass of the oxygen-deficient titanium dioxide conductive ceramic, preferably 0.5–3 wt.%. If the content of M2O3 second-phase particles is too low, the M-Ti-O nanolayer and the M2O3 reinforcing phase cannot be sufficiently and uniformly distributed throughout the ceramic matrix to achieve reliable overall strengthening of the ceramic, thus degrading the ceramic performance.

[0027] In this invention, TiO2 is reduced by using a vacuum or other reducing environment, causing some lattice oxygen to detach and making TiO2 oxygen-deficient, i.e., TiO2. 2-x In TiO 2-x In this process, due to the difference between the material interface environment and the bulk environment, a space charge field spontaneously forms throughout the material. This invention creatively introduces a space charge field composed of TiO₂... 2-x Space charge field-driven, capable of completing Ti 3+ The substituted M2O3 second phase (reinforcing phase). From a thermodynamic perspective, it is superior to Ti. 3+ The weakly electronegative isovalent state M 3+ All ions have the potential to undergo diffusion substitution; from a kinetic perspective, considering M... 3+ With Ti 3+ Due to the differences in ionic radii and the structural compatibility of the local lattice before and after substitution, the present invention preferably uses M. 3+ For Al 3+ or Ga 3+ M 3+ The process of TiO2 will be completed under the drive of space charge forces within the material. 2-x Ti enriched at grain boundaries 3+ Substitution, thus in TiO 2-x / TiO 2-x M-Ti-O nanolayers are formed at the grain boundaries; simultaneously, M 3+ The directional dissolution process from M2O3 is directional and also promotes the dissolution of TiO2. 2-x Serrated grain boundaries are formed at the M2O3 grain boundaries. Regarding mechanical properties, on the one hand, the heterogeneous element M at the grain boundaries... 3+The presence of O hinders the transport of Ti and O at the grain boundaries, and together with the M2O3 reinforcing phase particles, it reduces the growth rate of ceramic grains through pinning and anchoring, thereby refining the ceramic grains and giving the material fine-grained strengthening. On the other hand, the M2O3 bond usually has a higher bond energy than the Ti-O bond, and is more resistant to atomic-level fracture, thus directly strengthening the grain boundary's resistance to damage and giving the material a grain boundary strengthening effect. In addition, TiO 2-x The serrated grain boundaries at / M2O3 form a strong mechanically interlocked structure, which also strengthens the material's grain boundaries. Regarding electrical properties, TiO2... 2-x Ti in this oxygen vacancy enrichment region on the grain surface 3+ Not entirely acting as a carrier provider, Ti first ionizes under a certain degree of external electric field. 3+ The resulting change in electric potential field will cause unionized Ti 3+ The ionization energy is increased several times, and the unionized Ti 3+ The electrons they carry strongly couple with the surrounding lattice to form localized small polarons, which will manifest as negatively charged localized states on a larger scale. These negatively charged localized states can influence electrons attempting to cross grain boundaries, either increasing the probability of electron collisions, scattering migrating free carriers and reducing their mobility, or trapping and replacing migrating electrons, hindering their continuous transport and reducing their mean free path. 3+ Substituting part of Ti at the grain boundaries 3+ Subsequently, the Ti at the grain boundaries, which act as polarization centers, was directly reduced. 3+ The number of carriers reduces the associated scattering and trapping effects, promotes charge redistribution at grain boundaries, lowers the grain boundary barrier, and makes it easier for electrons to cross grain boundaries, thus significantly optimizing the carrier migration rate of the ceramic. When the increase in mobility is sufficient to offset the effect of the decrease in carrier concentration, the overall conductivity of the ceramic is improved.

[0028] The following is an exemplary description of the preparation method of oxygen-deficient titanium dioxide conductive ceramics enhanced by space charge effect provided by the present invention.

[0029] TiO2 powder and M2O3 powder are mixed, ball-milled, dried and sieved to obtain mixed powder.

[0030] In an optional embodiment, the mass ratio of TiO2 powder to M2O3 powder is (99.8–90):(0.2–10). Within this mass ratio range, the M2O3 reinforcing phase can be used efficiently to strengthen the titanium oxide-based ceramic. If this mass ratio is too small, i.e., the M2O3 powder content is too high, the sintering process for the titanium oxide ceramic matrix will not be able to completely densify the M2O3, thereby introducing voids and defects into the matrix. In addition, excessive M2O3 will also weaken the intrinsic properties of the titanium oxide matrix, thus significantly reducing the mechanical and electrical properties of the ceramic.

[0031] In an optional embodiment, the ball milling parameters include: a ball milling speed of 200–500 r / min, a ball milling time of 3–12 h, a ball milling medium of zirconia grinding balls, anhydrous ethanol as the solvent, and a mass ratio of the mixed powder, anhydrous ethanol, and zirconia grinding balls of 1:(1–3):(1–3). The drying temperature is 50–80°C, and the drying time is 6–24 h.

[0032] The mixed powder is shaped and sintered to obtain the oxygen-deficient titanium dioxide conductive ceramic.

[0033] In an optional embodiment, the molding method includes at least one of hot pressing, dry pressing, and cold isostatic pressing. The dry pressing pressure is 5–30 MPa, and the holding time is 1–5 min. The cold isostatic pressing pressure is 50–500 MPa, and the holding time is 1–5 min.

[0034] In an optional embodiment, the sintering atmosphere is a vacuum, inert, or reducing atmosphere to appropriately reduce TiO2 to TiO2. 2-x The sintering methods include atmospheric pressure sintering, hot pressing sintering, spark plasma sintering, or microwave sintering, with hot pressing sintering being preferred. When formulating the sintering regime, the amount of M in the ceramic at sintering temperatures above 600℃ should be fully considered. 3+To mitigate the diffusion process and the potential phase transformation of TiO2, a process strategy of appropriately reducing the heating rate or extending the holding time is adopted. Taking vacuum hot pressing sintering as an example, the vacuum hot pressing sintering process includes: heating to 500–700°C at a rate of 5–20°C / min under a vacuum of 0.1–100 Pa, while simultaneously increasing the pressure to 0.5–10 MPa; then heating to 1000–1150°C at a rate of 1–3°C / min, while simultaneously increasing the pressure to 25–50 MPa, and holding at that temperature and pressure for 0.5–3 h; then cooling to 600–800°C at a rate of 1–10°C / min, depressurizing to 0 MPa, and finally cooling with the furnace. Under the above sintering regime, high-density, high-strength, high-toughness, and conductive ceramics can be obtained. If this sintering process is not adopted, the residual pores in the finished material caused by rapid densification during the middle stage of sintering will have an adverse effect on the mechanical and electrical properties of ceramics, such as strength, toughness, and electrical conductivity, under the influence of stress concentration and void formation mechanisms.

[0035] The core driving force of this invention is TiO2. 2-x The space charge field at the grain boundaries is induced by the Schottky barrier. During sintering in a vacuum or reducing atmosphere, TiO2 is reduced to oxygen-deficient TiO2. 2-x (0<x≤0.1), the grain boundaries are positively charged due to the enrichment of donor defects such as oxygen vacancies, while a negatively charged space charge layer is formed on both sides of the grain boundaries. Driven by the above space charge field, the evolution of ceramic microstructure can be divided into three key steps: (1) M 3+ Along the grain boundary, M migrates and substitutes in a directional manner, driven by space charge forces, in the M2O3 second-phase particles. 3+ Ions along TiO 2-x Ti diffuses directionally across grain boundaries, migrates to the grain boundaries, and partially substituted for and enriches therein. 3+ Because of M 3+ Its electronegativity is typically lower than that of Ti. 3+ This substitution is thermodynamically advantageous; (2) the formation of M-Ti-O nanolayers. M 3+ In TiO 2-x / TiO 2-x Ti substitution at grain boundaries 3+ Then, together with the surrounding Ti and O atoms, a uniform M-Ti-O nanolayer with a thickness of 1 to 10 nm is formed at the grain boundary; (3) Formation of serrated interlocking grain boundaries. M 3+ The continuous, directional dissolution from M₂O₃ grains causes volume shrinkage of the M₂O₃ grains. This uneven dissolution process promotes the growth of TiO₂. 2-x The M2O3 interface (phase boundary) migrates into the interior of the M2O3 grains, eventually inducing the formation of serrated interlocking grain boundaries at the phase boundary. This is a strongly mechanically interlocked structure.

[0036] In this invention, TiO2-x The ceramic matrix phase, the M2O3 reinforcing phase, and a specific sintering process are all indispensable. TiO 2-x The matrix provides a usable space charge field environment; M2O3 utilizes TiO2 2-x The inherent space charge field completed the process of TiO 2-x Partial Ti in the crystal lattice 3+ Substitution strengthens the matrix material; specific sintering regimes were optimized for the phase transformation behavior and characteristics of each sintering stage of titanium oxide sintering, improving the microstructure of the ceramic. TiO 2-x The combination of the ceramic matrix phase, the M2O3 reinforcing phase, and a specific sintering process jointly achieves TiO2 reinforced based on the space charge effect. 2-x Preparation of conductive ceramics.

[0037] This invention utilizes the space charge effect to drive M 3+ Ti substitution along grain boundaries 3+ Grain boundary pinning, grain refinement, and enhanced grain boundary bonding can be achieved at lower sintering temperatures, while reducing Ti at grain boundaries. 3+ The polarization center enhances carrier mobility, thereby significantly improving both the mechanical and electrical properties of the ceramic. The ceramic of this invention exhibits a flexural strength exceeding 250 MPa and a fracture toughness exceeding 3 MPa·m. 1 / 2 With a conductivity of over 0.02 S / cm, it is suitable for high-performance conductive ceramic applications such as semiconductor equipment components and wastewater treatment electrodes.

[0038] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0039] Comparative Example 1 (without M2O3 added, vacuum hot pressing sintering) (1) Preparation of ceramic powder. Anatase TiO2 powder was placed in a ball mill jar and ball milled at a mass ratio of 2:3:3 for TiO2 powder, anhydrous ethanol and zirconium oxide grinding balls at 300 r / min for 12 h to obtain ceramic slurry. The ceramic slurry was placed in an oven and dried at 80℃ for 12 h to obtain ceramic powder. (2) Molding and sintering. The ceramic powder was dry-pressed at 20 MPa for 3 min to obtain a ceramic blank. The ceramic blank was placed in a graphite mold and vacuum hot-pressed for sintering. The sintering process included: heating to 600℃ at a rate of 5℃ / min under a vacuum of 30 Pa, while simultaneously increasing the pressure to 1 MPa; then heating to 1050℃ at a rate of 2.5℃ / min, while simultaneously increasing the pressure to 30 MPa, and holding at 1050℃ and 30 MPa for 2 h; finally cooling to 800℃ at a rate of 5℃ / min, and linearly reducing the pressure to 0 MPa to obtain titanium dioxide conductive ceramic.

[0040] Comparative Example 1 yields a TiO2 without space charge effect enhancement. 2-x Conductive ceramic with a flexural strength of 67 MPa and a fracture toughness of 2.4 MPa•m. 1 / 2 Its electrical conductivity is 1.3 S / cm.

[0041] Examples 1-3 (with Al2O3 reinforcing phase added, vacuum hot pressing sintering) (1) Preparation of mixed powder. Anatase TiO2 powder and Al2O3 powder were mixed according to the proportions in Table 1 and placed in a ball mill jar. The mass ratio of ceramic powder, anhydrous ethanol and zirconium oxide grinding balls was 1:3:3. The ball milling speed was 300 r / min and the ball milling was performed for 12 h to obtain a ceramic slurry. The ceramic slurry was placed in an oven and dried at 80℃ for 12 h to obtain mixed powder. (2) Molding and sintering. The mixed powder was dry-pressed at 30 MPa for 1 min to obtain a ceramic green body; the ceramic green body was placed in a graphite mold for vacuum hot pressing sintering. The sintering process included: heating to 600℃ at a rate of 5℃ / min under a vacuum of 30 Pa, while simultaneously increasing the pressure to 2 MPa; then heating to 1050℃ at a rate of 2.5℃ / min, while simultaneously increasing the pressure to 30 MPa, and holding at 1050℃ and 30 MPa for 2 h; finally cooling to 800℃ at a rate of 5℃ / min, and linearly reducing the pressure to 0 MPa to obtain oxygen-deficient titanium dioxide conductive ceramic (TiO2). 2-x (x=0.04). The difference between Examples 1-3 is the different contents of TiO2 powder and Al2O3 powder. Please refer to Table 1 for details. Table 1 lists the raw material ratios of Examples 1-3.

[0042] Table 1: .

[0043] Examples 1-3 yielded TiO2 enhanced based on space charge effect. 2-x The mechanical and electrical properties of conductive ceramics are shown in Table 2.

[0044] Table 2: .

[0045] Examples 4-7 (with Al2O3 reinforcing phase and M2O3 added, vacuum hot pressing sintering) (1) Preparation of mixed powder. Anatase TiO2 powder and Al2O3 powder were mixed in the proportions shown in Table 3 and placed in a ball mill jar. The mass ratio of ceramic powder, anhydrous ethanol and zirconium oxide grinding balls was 2:3:3. The ball milling speed was 300 r / min and the mixture was ball milled for 12 h to obtain a ceramic slurry. The ceramic slurry was placed in an oven and dried at 80℃ for 12 h to obtain the mixed powder. (2) Molding and sintering. The mixed powder was dry-pressed at 20 MPa for 3 min to obtain a ceramic green body; the ceramic green body was placed in a graphite mold for vacuum hot pressing sintering. The sintering process included: heating to 600℃ at a rate of 5℃ / min under a vacuum of 30 Pa, while simultaneously increasing the pressure to 1 MPa; then heating to 1050℃ at a rate of 2.5℃ / min, while simultaneously increasing the pressure to 30 MPa, and holding at 1050℃ and 30 MPa for 2 h; finally cooling to 800℃ at a rate of 5℃ / min, and linearly reducing the pressure to 0 MPa to obtain oxygen-deficient titanium dioxide conductive ceramic (TiO2). 2-x (x=0.04). The difference between Examples 4-7 is the different contents of TiO2 powder and Al2O3 powder. Please refer to Table 3 for details. Table 3 lists the raw material ratios of Examples 4-7.

[0046] Table 3: .

[0047] Examples 4-7 yielded TiO2 enhanced based on space charge effect. 2-x The mechanical and electrical properties of conductive ceramics are shown in Table 4.

[0048] Table 4: .

[0049] As shown in Tables 1-4, Comparative Example 1 and Examples 1-7 used the same vacuum hot pressing sintering process and regime, but Examples 1-7 added an appropriate amount of Al2O3. Because Al... 3+ TiO, along with Ti and O, forms an Al-Ti-O nanolayer at the grain boundaries, along with serrated grain boundaries at specific locations, significantly enhancing the mechanical and electrical properties of the ceramic. Furthermore, with increasing Al2O3 content, TiO2O3... 2-xThe mechanical and electrical properties of conductive ceramics generally show a trend of first increasing and then decreasing. This is because during the performance improvement period, the strengthening mechanism of the ceramic dominates, and the strengthening mechanism gradually strengthens with the increase of the reinforcing phase content. When the amount of reinforcing phase added exceeds the threshold, incomplete densification leads to residual porosity, the conductive pathway begins to be physically blocked, and the thermal expansion coefficient mismatch between the reinforcing phase and the matrix causes the ceramic performance to decline. The optimal M2O3 addition amount is between 0.5% and 3 wt.% for the ceramic to achieve the best overall performance.

[0050] Example 8 (Al2O3 reinforcing phase added, vacuum atmospheric pressure sintering) The preparation process of the oxygen-deficient titanium dioxide conductive ceramic in Example 8 is the same as in Example 5, except that in step (2), the forming method is dry pressing + cold isostatic pressing, and the sintering method is atmospheric pressure sintering. The mixed powder was dry-pressed at 20 MPa for 3 min to obtain a ceramic green body. The green body was then cold-isostatically pressed at 200 MPa for 3 min, and then sintered at atmospheric pressure in a vacuum environment in a vacuum furnace. The sintering process included: heating to 600℃ at a rate of 5℃ / min under a vacuum of 30 Pa; then heating to 1150℃ at a rate of 2.5℃ / min and holding for 6 h; then cooling to 800℃ at a rate of 5℃ / min, and finally cooling with the furnace to obtain oxygen-deficient titanium dioxide conductive ceramic (TiO₂). 2-x (0 < x ≤ 0.1)).

[0051] This embodiment 8 yields a TiO2 material that has been simply enhanced by the space charge effect. 2-x Conductive ceramic with a flexural strength of 215 MPa and a fracture toughness of 3.7 MPa•m. 1 / 2 The material's electrical conductivity is 0.02 S / cm. It can be seen that, compared to Comparative Example 3, the electrical conductivity of TiO₂ is significantly higher. 2-x The addition of M2O3 significantly improves the performance of ceramics. This is because TiO2 has virtually no space charge field that affects atomic redistribution, so the strengthening effect of M2O3 on TiO2 is not limited. In Example 8, all conditions for heteroatomic substitution strengthening using the space charge effect are met, resulting in a prominent strengthening effect. However, compared to the hot-pressed sintered sample of Example 5, the sample obtained in Example 8 has lower density and relatively weaker performance. This is because hot-pressing is more conducive to the densification process of ceramics, and the addition of hot-pressing pressure as an additional sintering driving force is more helpful in achieving the preparation of high-strength, high-toughness, and high-conductivity titanium oxide conductive ceramics.

[0052] Examples 9-12 (Ga2O3 reinforcing phase added, vacuum hot pressing sintering) (1) Preparation of mixed powder. Anatase TiO2 powder and Ga2O3 powder were mixed according to the proportions in Table 5 and placed in a ball mill jar. The mass ratio of ceramic powder, anhydrous ethanol and zirconium oxide grinding balls was 2:3:3. The ball milling speed was 300 r / min and the ball milling was performed for 12 h to obtain a ceramic slurry. The ceramic slurry was placed in an oven and dried at 80℃ for 12 h to obtain mixed powder. (2) Molding and sintering. The ceramic powder was dry-pressed at 20 MPa for 3 min to obtain a ceramic green body; the ceramic green body was placed in a graphite mold for vacuum hot pressing sintering. The sintering process included: heating to 600℃ at a rate of 5℃ / min under a vacuum of 10 Pa, while simultaneously increasing the pressure to 1 MPa; then heating to 1050℃ at a rate of 2.5℃ / min, while simultaneously increasing the pressure to 30 MPa, and holding at 1050℃ and 30 MPa for 2 h; finally cooling to 800℃ at a rate of 5℃ / min, and linearly reducing the pressure to 0 MPa to obtain oxygen-deficient titanium dioxide conductive ceramic (TiO2). 2-x (x=0.05). The difference between Examples 9-12 is the different contents of TiO2 powder and Ga2O3 powder. For details, please refer to Table 5. Table 5 lists the raw material ratios of Examples 9-12.

[0053] Table 5: .

[0054] Examples 9-12 yielded TiO2 enhanced based on space charge effect. 2-x The mechanical and electrical properties of conductive ceramics are shown in Table 6.

[0055] Table 6: .

[0056] As shown in Table 6, Comparative Examples 1 and 9-12 used the same vacuum hot pressing sintering process and regime, but Examples 9-12 added an appropriate amount of Ga2O3, because Ga... 3+ Together with Ti and O at grain boundaries, Ga-Ti-O nanolayers and serrated grain boundaries at specific locations are formed, significantly enhancing the mechanical and electrical properties of the ceramic. Furthermore, the more significant optimization of the ceramic's mechanical properties after adding Ga2O3 is also related to the rod-shaped crystals promoted by Ga2O3.

[0057] Comparative Example 2 (without adding Al2O3 reinforcing phase, and sintered under normal pressure in an air environment) The preparation process of the titanium dioxide conductive ceramic in Comparative Example 2 is the same as that in Example 5, except that: in step (1), Al2O3 powder is not added; in step (2), the forming method is dry pressing + cold isostatic pressing, and the sintering method is atmospheric pressure sintering in air environment. The mixed powder was dry-pressed at 20 MPa for 3 min to obtain a ceramic green body. The ceramic green body was then cold-isostatically pressed at 200 MPa for 3 min, and then placed in a muffle furnace for atmospheric pressure sintering in air. The sintering process included: heating to 600℃ at a rate of 5℃ / min; then heating to 1150℃ at a rate of 2.5℃ / min and holding for 6 h; then cooling to 800℃ at a rate of 5℃ / min, and finally cooling in the furnace to obtain titanium dioxide conductive ceramic.

[0058] Comparative Example 2 yielded a TiO2 conductive ceramic without space charge effect strengthening, exhibiting a flexural strength of 77 MPa and a fracture toughness of 1.6 MPa•m. 1 / 2 Conductivity <10 -5 S / cm. It can be seen that, under the conditions of Comparative Example 2, the mechanical and electrical properties of TiO2 ceramics without any reinforcing phase are at a low level.

[0059] Comparative Example 3 (Al2O3 reinforcing phase added, and sintered under normal pressure in air environment) The preparation process of the titanium dioxide conductive ceramic in Comparative Example 3 is the same as that in Example 2, except that in step (2), the forming method is dry pressing + cold isostatic pressing, and the sintering method is atmospheric pressure sintering in an air environment. The mixed powder was dry-pressed at 20 MPa for 3 min to obtain a ceramic green body. The ceramic green body was then cold-isostatically pressed at 200 MPa for 3 min, and then placed in a muffle furnace for atmospheric pressure sintering in air. The sintering process included: heating to 600℃ at a rate of 5℃ / min; then heating to 1150℃ at a rate of 2.5℃ / min and holding for 6 h; then cooling to 800℃ at a rate of 5℃ / min, and finally cooling in the furnace to obtain titanium dioxide conductive ceramic.

[0060] Comparative Example 3 yielded a TiO2 conductive ceramic without space charge effect strengthening, exhibiting a flexural strength of 174 MPa and a fracture toughness of 2.3 MPa•m. 1 / 2 Conductivity <10 -5 S / cm. It can be seen that although Al2O3 was added as a reinforcing phase in Comparative Example 3, the TiO2 sintered in air was not sufficiently oxygen-deficient, and an effective space charge field could not be formed in the material to promote grain boundary substitution, resulting in poor ceramic performance.

[0061] Figure 1 This is a SEM image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Comparative Example 1 of this invention. As can be seen from the figure, the titanium oxide ceramics that are not strengthened by the space charge effect are prone to abnormal grain growth (grain size of 27µm), which degrades the ceramic microstructure.

[0062] Figure 2 This is a SEM image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 4 of the present invention. As can be seen from the figure, after adding Al2O3 and carrying out the same molding and preparation process as Comparative Example 1, the ceramic grains are refined (grain size is 2µm), and the microstructure is improved.

[0063] Figure 3 This is an EDS image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 6 of the present invention. As can be seen from the image, in TiO₂… 2-x Introducing an appropriate amount of Al2O3 into the ceramic forms a uniformly thick Al-Ti-O nanolayer.

[0064] Figure 4 This is a line-scan EDS image of the grain boundaries of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 6 of this invention. As can be seen from the image, in TiO₂… 2-x When an appropriate amount of Al2O3 is introduced into the ceramic, a uniform Al-Ti-O nanolayer is formed at different locations throughout the material.

[0065] Figure 5 This is a TEM image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 6 of the present invention. As can be seen from the image, the addition of an appropriate amount of Al2O3 to TiO2... 2-x In ceramics, in TiO 2-x At the Al2O3 grain boundary, serrated interlocking grain boundaries were formed.

[0066] Figure 6 The oxygen-deficient titanium dioxide conductive ceramic prepared in Example 6 of this invention is based on TiO2. 2-x TEM images of different locations on the Al2O3 grain boundaries. The images show that the addition of an appropriate amount of Al2O3 to TiO2... 2-x In ceramics, in TiO 2-x At the Al2O3 grain boundary, serrated interlocking grain boundaries were formed.

[0067] Figure 7 This is a TEM image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 9 of the present invention. As can be seen from the image, the addition of an appropriate amount of Ga2O3 to TiO2... 2-x In ceramics, in TiO 2-x At the / Ga2O3 grain boundary, serrated interlocking grain boundaries are formed.

[0068] Figure 8 This is a SEM image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 10 of the present invention. As shown in the image, the addition of an appropriate amount of Ga2O3 to TiO2... 2-x The ceramic grains are refined (average grain size is 1.7µm). Under the influence of metal elements and hot pressing sintering process, some texture phenomenon also appears. The grains are interlocked and interwoven at the micron scale, resulting in excellent microstructure.

[0069] Figure 9 This is a SEM image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 11 of the present invention. As shown in the image, the addition of an appropriate amount of Ga2O3 to TiO2... 2-x The ceramic grains are refined (average grain size is 1.4µm). Under the influence of metal elements and hot pressing sintering process, some texture phenomenon also appears. The grains are interlocked and interwoven at the micron scale, resulting in excellent microstructure.

[0070] Figure 10 These are optical photographs of the oxygen-deficient titanium dioxide conductive ceramics prepared in Comparative Examples 1, 4, and 6 of this invention. As can be seen from the figures, M2O3 enhances the performance relative to TiO2. 2-x The improvement of the ceramic fracture mode has a significant impact. In Comparative Example 1, the ceramic fracture surface is parallel to the direction of force on a macroscopic scale and the fracture path is relatively short. In Examples 4 and 6, the ceramic fracture surfaces are tortuous and the fracture paths are relatively long. Moreover, the ceramics are smooth and rounded on the fracture surface, which further illustrates that the ceramic grain size is small and the fracture mode is excellent.

[0071] Figure 11 This is an EDS image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 2 of this invention. As can be seen from the image, adding a small amount of Al₂O₃ is sufficient to... 2-x TiO in ceramics 2-x / TiO 2-x An Al-Ti-O nanolayer is formed at the grain boundaries.

[0072] Figure 12 This is an EDS image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 9 of the present invention. As can be seen from the image, in TiO₂… 2-x Introducing an appropriate amount of Ga2O3 into ceramics can improve TiO2 content. 2-x / TiO 2-x Ga-Ti-O nanolayers are formed at the grain boundaries.

[0073] Figure 13 This is a larger-scale EDS image of the oxygen-deficient titanium dioxide conductive ceramic prepared in Example 9 of this invention, focusing on Ga. As can be seen from the image, in TiO₂… 2-x Introducing an appropriate amount of Ga2O3 into ceramics can improve TiO2 content. 2-x / TiO 2-x Ga-Ti-O nanolayers are formed at the grain boundaries.

[0074] The above description represents only some preferred embodiments of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content and spirit of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A space charge effect-enhanced oxygen-deficient titanium dioxide conductive ceramic, characterized in that, The oxygen-deficient titanium dioxide conductive ceramic includes oxygen-deficient titanium dioxide (TiO₂). 2-x The matrix, and uniformly dispersed in oxygen-deficient titanium dioxide (TiO2). 2-x M2O3 second-phase particles at the grain boundaries of the matrix; wherein, in the oxygen-deficient titanium dioxide TiO 2-x A uniform M-Ti-O nanolayer is formed at the grain boundaries of the matrix, and the M2O3 second phase particles and the oxygen-deficient titanium dioxide TiO2 are interlayered. 2-x Serrated interlocking grain boundaries are formed at the interface of the matrix.

2. The oxygen-deficient titanium dioxide conductive ceramic enhanced by space charge effect according to claim 1, characterized in that, The oxygen-deficient titanium dioxide (TiO) 2-x In the matrix, 0 < x ≤ 0.1; the thickness of the M-Ti-O nanolayer is 1 to 10 nm.

3. The oxygen-deficient titanium dioxide conductive ceramic enhanced by space charge effect according to claim 1 or 2, characterized in that, The M2O3 second-phase particles are trivalent metal oxides with a corundum-type crystal structure, selected from at least one of Al2O3, Ga2O3, In2O3, Fe2O3, V2O3, and Cr2O3, preferably Al2O3 or Ga2O3.

4. The oxygen-deficient titanium dioxide conductive ceramic enhanced by space charge effect according to any one of claims 1-3, characterized in that, In the oxygen-deficient titanium dioxide conductive ceramic, the M2O3 second phase particles account for 0.2 to 10 wt.% of the total mass of the oxygen-deficient titanium dioxide conductive ceramic, preferably 0.5 to 3 wt.%.

5. The oxygen-deficient titanium dioxide conductive ceramic enhanced by space charge effect according to any one of claims 1-4, characterized in that, The grain size of the oxygen-deficient titanium dioxide conductive ceramic is 0.5–5 µm; The oxygen-deficient titanium dioxide conductive ceramic has a flexural strength ≥250 MPa and a fracture toughness ≥3 MPa•m. 1 / 2 Electrical conductivity ≥ 0.02 S / cm.

6. A method for preparing oxygen-deficient titanium dioxide conductive ceramics based on space charge effect enhancement according to any one of claims 1-5, characterized in that, Includes the following steps: (1) TiO2 powder and M2O3 powder are mixed, ball-milled, dried and sieved to obtain mixed powder; (2) The mixed powder is shaped and sintered to obtain the oxygen-deficient titanium dioxide conductive ceramic.

7. The preparation method according to claim 6, characterized in that, In step (1), the mass ratio of TiO2 powder to M2O3 powder is (99.8-90):(0.2-10).

8. The preparation method according to claim 6 or 7, characterized in that, In step (1), the parameters of the ball milling include: a ball milling speed of 200-500 r / min, a ball milling time of 3-12 h, a ball milling medium of zirconia grinding balls, anhydrous ethanol as the solvent, and a mass ratio of mixed powder, anhydrous ethanol and zirconia grinding balls of 1:(1-3):(1-3). The drying temperature is 50–80°C, and the time is 6–24 h.

9. The preparation method according to any one of claims 6-8, characterized in that, In step (2), the molding method includes at least one of dry pressing and cold isostatic pressing. Preferably, the pressure of dry pressing is 5-30 MPa and the holding time is 1-5 min; the pressure of cold isostatic pressing is 50-500 MPa and the holding time is 1-5 min.

10. The preparation method according to any one of claims 6-9, characterized in that, In step (2), the sintering atmosphere is a vacuum, an inert, or a reducing atmosphere; the sintering method includes atmospheric pressure sintering, hot pressing sintering, spark plasma sintering, or microwave sintering, preferably hot pressing sintering; more preferably, the sintering method is vacuum hot pressing sintering, and the vacuum hot pressing sintering process includes: heating to 500-700°C at a rate of 5-20°C / min under a vacuum of 0.1-100 Pa, while simultaneously increasing the pressure to 0.5-10 MPa; then heating to 1000-1150°C at a rate of 1-3°C / min, while simultaneously increasing the pressure to 15-50 MPa, and holding at the temperature and pressure for 0.5-3 h; then cooling to 600-800°C at a rate of 1-10°C / min, depressurizing to 0 MPa, and finally cooling with the furnace.

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