High-conductivity zinc oxide linear resistance ceramic with extremely low resistance-temperature coefficient and preparation method of high-conductivity zinc oxide linear resistance ceramic

Abstract

The invention belongs to the technical field of functional ceramic materials, and particularly relates to a high-conductivity zinc oxide linear resistance ceramic with an extremely low resistance-temperature coefficient and a preparation method of the high-conductivity zinc oxide linear resistance ceramic. Aiming at the problems of high temperature resistance coefficient and the like of the existing zinc oxide linear resistor component material, the invention provides the zinc oxide linear resistor ceramic material which comprises a zinc oxide main phase and an additive phase, the additive phase comprises the following components: TiO2, MgO, ZrO2 and A2O3, wherein A is Al or Ga; the total molar weight of the zinc oxide linear resistor ceramic material is 100 mol%, the molar percentage content of the zinc oxide main phase is 86 mol%-99.75 mol%, and the content of the additive phase is 0.25 mol%-14 mol%. In the invention, the zinc oxide linear resistance ceramic has an extremely low positive temperature resistance coefficient which is 8.02 * 10 <-5 > / DEG C and is two orders of magnitude lower than that of metal and other ZnO resistance ceramics.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional ceramic materials, and in particular relates to a high-conductivity zinc oxide linear resistor ceramic material with an extremely low temperature resistance coefficient and a preparation method thereof. Background Art

[0002] Highly conductive zinc oxide linear resistors, as a new type of metal oxide ceramic linear resistance device, have attracted much attention due to their corrosion resistance, ability to operate in extremely harsh environments, small size, resistance to high-energy pulse absorption and high current density. They are high-performance resistance devices developed in recent years.

[0003] Generally speaking, the conductive properties of oxide ceramics are semiconductor properties, that is, the conductivity is low and the resistivity usually decreases with increasing temperature (that is, the temperature coefficient is negative). When the current is overloaded or the power is on for a long time, the resistor made of materials with a negative temperature coefficient will heat up and the resistance will decrease, causing the current to continue to increase and the circuit to collapse easily; at the same time, the resistor with a small absolute value of the temperature coefficient makes the electronic circuit have small circuit fluctuations when the temperature changes. Therefore, the temperature coefficient of resistance (TCR) of the material is positive and the value is small, which is of great significance in practical applications. There is little research on zinc oxide linear resistor materials internationally. The conventional basic composition of zinc oxide linear resistors is the Zn-Mg-Ti-Al system. China Patent No. 101905972.A uses spark plasma sintering technology to increase the conductivity of aluminum-doped zinc oxide ceramics to 6×10 4 S·m -1 However, this sintering technology is expensive and not conducive to industrial production. Chinese patent number CN104478430A reported that ZnO was doped with MgO, Al2O3, La2O3, Si2O3 and Fe2O3 to adjust its conductivity, and its maximum conductivity was only 17.2S·m -1 The best resistance temperature coefficient is only 2.25×10 -3 / ℃, and it is doped with many elements and has a complex composition. Chinese patent authorization number ZL201510672210.X obtains a low-resistance metal oxide ceramic material by sintering in this system under atmosphere control, but the temperature resistance coefficient is only 1.49×10 -3 / ℃. Metal resistor materials with good electrical conductivity, such as gold and silver, have a temperature resistance coefficient of 3.24×10 -3 / ℃ and 3.8×10 -3 / ℃. Summary of the Invention

[0004] In view of the problems of high temperature resistance coefficient in existing zinc oxide linear resistor component materials, the purpose of the present invention is to provide a high-conductivity zinc oxide linear resistor ceramic material with low temperature resistance coefficient and a preparation method thereof.

[0005] In one aspect, the present invention provides a zinc oxide linear resistor ceramic material, comprising: a zinc oxide main phase and an additive phase; the additive phase comprises TiO2, MgO, ZrO2 and A2O3, wherein A is Al or Ga; Taking the total molar amount of the zinc oxide linear resistor ceramic material as 100 mol%, the molar percentage of the zinc oxide main phase is 86 mol% to 99.75 mol%, and the content of the additive phase is 0.25 mol% to 14 mol%.

[0006] In the present invention, the additives are composed of A2O3 (A is Al or Ga), MgO, ZrO2 and TiO2, wherein Al2O3 and Ga2O3 act as donor impurities to provide free electrons to the zinc oxide lattice and increase the carrier concentration inside the material, and MgO acts as a catalytic agent to improve the carrier concentration inside the material. 2+ As Zn 2+ The same valence doping is beneficial to improve the sintering density and improve the temperature coefficient of resistance. ZrO2 is helpful for the refinement of ceramics. 4+ By using Zn 2+ The reaction forms spinel phase Zn2TiO4, which is used to control the grain size of zinc oxide ceramics.

[0007] Preferably, the composition content of the additive phase includes: A2O3 is 0.05mol% to 3mol%, MgO is 0.1mol% to 5mol%, TiO2 is 0.1mol% to 5mol%, and ZrO2 is 0 to 1mol%.

[0008] Preferably, the resistivity of the zinc oxide linear resistor ceramic material is 9.61×10 -6 Ω·m~7.00×10 -4 Ω·m.

[0009] Preferably, the conductivity of the zinc oxide linear resistor ceramic material at room temperature to 275°C is 1.43×10 3 S·m -1 ~1.04×10 4 S·m -1 The conductivity of the zinc oxide linear resistor ceramic material changes by no more than 2.005% between room temperature and 275°C.

[0010] Preferably, the forward temperature coefficient of the zinc oxide linear resistor ceramic material is 1.58×10 -5 ~8.02×10 -5 / ℃.

[0011] In another aspect, the present invention provides a method for preparing a zinc oxide linear resistor ceramic material, comprising: (1) mixing TiO2 powder, MgO powder, ZrO2 powder and A2O3 powder to obtain raw material powder; (2) The raw material powder is subjected to calcination, granulation, compression molding, debinding and vacuum sintering to obtain the zinc oxide linear resistor ceramic material.

[0012] In the present invention, the sintering of the high-conductivity zinc oxide linear resistor ceramic material is carried out under vacuum. Vacuum sintering can reduce the content of oxygen adsorbed at the grain boundaries, prevent the rapid growth of ZnO grains, increase the diffusion rate of the donor element Al or Ga at the grain boundaries, and allow it to diffuse into the grains, thereby increasing the solid solubility of the Al or Ga element in the grains, increasing the donor concentration inside the material, increasing the carrier concentration, and improving the electrical conductivity. The extremely low temperature coefficient of resistance (TCR) of ZnO-based ceramics prepared by vacuum sintering is due to the carrier concentration (~10 19 cm -3 ) is higher than the commonly reported carrier concentration of ZnO-based ceramics, but lower than the electron concentration of conductive metals. Therefore, free electrons are not easily subject to mutual collision and scattering during transmission under an electric field, thereby reducing the electrical conductivity. As the temperature rises, the number of free electrons that increases due to thermal excitation and the number of free electrons that are lost due to intensified thermal motion reach a dynamic balance, ultimately resulting in the vacuum-sintered ZnO-based ceramics exhibiting an extremely low temperature resistivity in the macroscopic range of 0-350°C.

[0013] Preferably, in step (1), the mixing method is ball milling; the rotation speed of the ball milling is 200 to 600 rpm, and the time is 3 to 12 hours; preferably, after ball milling, the raw material powder is obtained by drying.

[0014] Preferably, in step (2): the calcination temperature is 400-800°C, and the holding time is 3-8 hours; The binder used in the granulation is a polyvinyl alcohol solution; the concentration of the polyvinyl alcohol solution is 5-10 wt%; the amount of polyvinyl alcohol added is 5-10 wt% of the total mass of the raw material powder.

[0015] Preferably, in step (2): the pressing pressure is 75-200 MPa, and the holding time is 5-30 s; the debinding parameters include: debinding under air; temperature is 400-600°C; holding time is 3-4 hours; preferably the heating rate is 1°C / min;.

[0016] Preferably, in step (2): the parameters of the vacuum sintering include: vacuum degree of 1kPa to 10kPa; temperature of 1100 to 1400°C; holding time of 1 to 4 hours; preferably, the heating rate of the vacuum sintering is 1 to 10°C / min.

[0017] Beneficial effects of the present invention: In the present invention, the high-conductivity zinc oxide linear resistor ceramic is prepared by vacuum sintering, which has an extremely low positive resistance temperature coefficient of 8.02×10 -5 / ℃, which is two orders of magnitude lower than that of metals and other ZnO resistive ceramics. 4 S·m -1 , density is as high as 95.00%; The synthesis method proposed by the invention has simple process, low composition, few doping elements, low cost, and can prepare high-performance zinc oxide linear resistor components. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The conductivity of the ZnO linear resistor ceramic obtained in Example 1 changes with temperature; Figure 2 The volt-ampere characteristic curve of the ZnO linear resistor ceramic obtained in Example 1; Figure 3 The volt-ampere characteristic curve of the ZnO linear resistor ceramic obtained in Example 1; Figure 4 The conductivity of the ZnO linear resistor ceramic obtained in Example 2 changes with temperature; Figure 5 The curve showing the change of conductivity of the ZnO linear resistor ceramic obtained in Example 3 with temperature. DETAILED DESCRIPTION

[0019] The present invention is further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, rather than to limit the present invention.

[0020] The present invention utilizes a conventional solid-phase method to synthesize zinc oxide linear resistor ceramics. Specifically, ZnO is the primary ingredient, and TiO2, MgO, ZrO2, and A2O3 (where A is Al or Ga) are added as additives. The raw materials are first mixed (for example, by ball milling followed by drying), and then calcined, granulated, pressed, debinded, and vacuum sintered to produce a highly conductive zinc oxide linear resistor ceramic with an extremely low temperature resistivity.

[0021] In an optional embodiment, the mixing method is ball milling, the rotation speed of the ball milling can be 200 to 600 revolutions per minute, and the time can be 3 to 12 hours.

[0022] In an optional embodiment, the temperature of the high-temperature calcined powder may be 400-800° C., and the holding time may be 3-8 hours.

[0023] In an optional embodiment, a binder is added to the composite powder for granulation before compression molding. The binder is a polyvinyl alcohol solution with a concentration of 10 wt % and the amount of solution added can be 5-10 wt % of the total mass of the raw material powder. During the compression process, the pressure can be 75-200 MPa and the holding time can be 5-30 seconds.

[0024] In an optional embodiment, the pressed green body is debonded and vacuum sintered. During sintering, the vacuum degree in the furnace is always 1 kPa-10 kPa, and the ceramic green body is heated from room temperature to 1100-1400°C at a rate of 1-10°C / min, held at that temperature for 1-4 hours, and then cooled in the furnace.

[0025] Compared with existing technologies, this invention uses Al and Ga as donor elements for trace doping and vacuum sintering to produce a highly conductive zinc oxide linear resistor. While maintaining material density, it achieves high conductivity and a low forward temperature coefficient of resistance. This also significantly broadens the resistivity adjustment range of the zinc oxide linear resistor, resulting in a metal-like conductive ceramic material. The vacuum-sintered sample has an extremely low positive temperature coefficient of resistance, with a resistivity variation of 8.02×10-1 over a wide temperature range from room temperature to 300°C. -5 / ℃, and the conductivity is 1.04×10 4 S·m -1 The synthesis method proposed in the present invention has simple process, few doping elements in the composition, no toxic elements, is green and environmentally friendly, low cost, and has both practicality and broad application prospects.

[0026] The following examples are further given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the scope of protection of the present invention. The specific process parameters and the like in the following examples are only examples within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, and are not limited to the specific numerical values ​​exemplified below.

[0027] Example 1 The composition of this embodiment is as follows: ZnO (98.2%), MgO (1%), TiO2 (0.5%), ZrO2 (0%), Ga2O3 (0.3%), and the distribution ratio of each group is a molar fraction ratio.

[0028] The above materials are placed together in a nylon jar and wet-milled in a planetary ball mill using zirconium oxide balls or stainless steel balls with water as the medium at a rotation speed of 350 rpm, a material-ball ratio of 3:1, and ball milling for 6 hours. The ground slurry is dried at 120°C, then passed through a 40-mesh sieve and calcined at 600°C for 30 minutes to obtain a zinc oxide composite powder. The calcined zinc oxide composite powder is then passed through a 40-mesh sieve, 10 wt% of a binder (PVA, content is 5 wt%) is added, and granulation is performed. The particle size of the powder after granulation is controlled to be between 40 and 120 mesh. The granulated powder is pressed with a pressure of 150 MPa and maintained for 10 seconds. The thickness of the pressed green body is about 1.5 mm and the diameter is about 12 mm. The binder is removed after molding. The sample after debinding is cold isostatically pressed and then vacuum sintered. The ceramic green body is heated from room temperature to 1200°C at a rate of 5°C / min, kept warm for 3 hours, and then cooled with the furnace. The vacuum degree in the furnace is always maintained to obtain a dense ZnO ceramic material.

[0029] The high-conductivity zinc oxide linear resistor ceramic in Example 1 has a conductivity of 1.04×10 4 S·m -1 , and has an extremely low forward temperature coefficient of 8.02×10 -5 / ℃, with metal-like properties and excellent resistance temperature stability.

[0030] Example 2 The composition of the zinc oxide linear resistor ceramic in Example 2 is as follows: ZnO (98.1%), MgO (1%), TiO2 (0.75%), ZrO2 (0.1%), and Ga2O3 (0.05%). The proportions of each component are all molar ratios. The experimental conditions were the same as those in Example 1. The zinc oxide high-conductivity linear resistor ceramic in Example 2 had a conductivity of 3.39×10 3 S·m -1 , and has an extremely low forward temperature coefficient of 3.60×10 -5 / ℃, with metal-like properties and excellent resistance temperature stability.

[0031] Example 3 The composition of the zinc oxide linear resistor ceramic in Example 3 is as follows: ZnO (91.8%), MgO (5%), TiO2 (0.1%), ZrO2 (0.1%), and Ga2O3 (3%). The proportions of each component are expressed in mole fractions. The experimental conditions were the same as those in Example 1. The zinc oxide high-conductivity linear resistor ceramic in Example 3 had a conductivity of 1.52×10 3 S·m -1 , and has an extremely low forward temperature coefficient of 1.79×10 -5 / ℃, with metal-like properties and excellent resistance temperature stability.

[0032] Examples 4-9 The compositions of the zinc oxide linear resistor ceramics in Examples 4-9 are shown in Table 1.

[0033] Comparative Examples 1-3 The compositions of the zinc oxide linear resistor ceramics in Comparative Examples 1-3 are shown in Table 1.

[0034] Table 1 shows the composition and performance parameters of zinc oxide linear resistor ceramics: ZnO MgO <![CDATA[TiO2]]> <![CDATA[ZrO2]]> <![CDATA[Ga2O3]]> <![CDATA[Conductivity (S·m -1 )]]> Forward temperature coefficient ( / ℃) Example 1 98.2％ 1％ 0.5％ 0％ 0.3％ <![CDATA[1.04×10 4 ]]> <![CDATA[8.02×10 -5 ]]> Example 2 98.1％ 1％ 0.75％ 0.1％ 0.05％ <![CDATA[3.39×10 3 ]]> <![CDATA[3.60×10 -5 ]]> Example 3 91.8％ 5％ 0.1％ 0.1％ 3％ <![CDATA[1.52×10 3 ]]> <![CDATA[1.79×10 -5 ]]> Example 4 91.9％ 5％ 0.1％ 0％ 3％ <![CDATA[1.43×10 3 ]]> <![CDATA[2.05×10 -5 ]]> Example 5 91.8％ 5％ 0.1％ 0.1％ <![CDATA[Al2O3 / 3%]]> <![CDATA[3.43×10 3 ]]> <![CDATA[5.68×10 -3 ]]> Example 6 94.75％ 5％ 0.1％ 0.1％ 0.05％ <![CDATA[3.02×10 3 ]]> <![CDATA[1.92×10 -5 ]]> Example 7 94.5％ 5％ 0.1％ 0.1％ 0.3％ <![CDATA[4.31×10 3 ]]> <![CDATA[7.35×10 -5 ]]> Example 8 93.8％ 5％ 0.1％ 0.1％ 1％ <![CDATA[2.80×10 3 ]]> <![CDATA[4.60×10 -5 ]]> Example 9 92.8％ 5％ 0.1％ 0.1％ 2％ <![CDATA[2.96×10 3 ]]> <![CDATA[3.96×10 -5 ]]> Comparative Example 1 94.8％ 5％ 0.1％ 0.1％ 0％ <![CDATA[2.02×10 3 ]]> <![CDATA[2.93×10 -3 ]]> Comparative Example 2 90.8％ 5％ 0.1％ 0.1％ 4％ <![CDATA[1.86×10 3 ]]> <![CDATA[1.58×10 -5 ]]> Comparative Example 3 91.9％ 5％ 0.1％ 0％ <![CDATA[Al2O3 / 3%]]> <![CDATA[6.59×10 3 ]]> <![CDATA[8.29×10 -3 ]]> .

[0035] Figure 1 The conductivity curve of Example 1 is a graph showing the change in conductivity with temperature. The sample was cut into small strips of 2mm×1mm×8mm and tested using the four-terminal method in a hotspot test system. The vacuum-sintered sample 1 has an extremely low positive temperature coefficient of resistance of 8.02×10 -5 / ℃, and the conductivity at room temperature is 1.04×10 4 S·m -1 .

[0036] Figure 2 and Figure 3 This is the volt-ampere characteristic curve of Example 1. The sample size is a 1mm small disc with a diameter of Φ10, and the double-sided silver electrode is tested. Figure 2 The test results are based on Keithley 2400 under 0-1A DC current. The results show that the linear resistance of the ZnO linear resistor is excellent, with a resistance of 0.948Ω. Figure 3 The test was conducted using a BS1009 steep-slope lightning current dual-wave tester under a 1 / 10μs pulse lightning current wave. The vacuum-sintered sample achieved a nonlinear coefficient of 1.048 and maintained good linearity and stable resistivity even under high current shocks.

[0037] Figure 4 The conductivity of Example 2 changes with temperature. The vacuum sintered sample 2 has an extremely low positive temperature resistance coefficient of 3.6×10 -5 / ℃, and the conductivity at room temperature is 3.39×10 3 S·m -1 .

[0038] Figure 5 The conductivity of Example 3 changes with temperature. The vacuum sintered sample 3 has an extremely low positive temperature resistance coefficient of 1.79×10 -5 / ℃, and the conductivity at room temperature is 1.52×10 3 S·m -1 .

Claims

1. A zinc oxide linear resistor ceramic material, characterized in that: include: A zinc oxide main phase and an additive phase; the additive phase comprises TiO2, MgO, ZrO2 and A2O3, wherein A is Al or Ga; Taking the total molar amount of the zinc oxide linear resistor ceramic material as 100 mol%, the molar percentage of the zinc oxide main phase is 86 mol% to 99.75 mol%, and the content of the additive phase is 0.25 mol% to 14 mol%.

2. The zinc oxide linear resistor ceramic material according to claim 1, characterized in that: The composition and content of the additive phase include: A2O3 is 0.05 mol% to 3 mol%, MgO is 0.1 mol% to 5 mol%, TiO2 is 0.1 mol% to 5 mol%, and ZrO2 is 0 to 1 mol%.

3. The zinc oxide linear resistor ceramic material according to claim 1 or 2, characterized in that: The resistivity of the zinc oxide linear resistor ceramic material is 9.61×10 -6 Ω·m~7.00×10 -4 Ω·m.

4. The zinc oxide linear resistor ceramic material according to claim 1 or 2, characterized in that: The conductivity of the zinc oxide linear resistor ceramic material at room temperature to 275°C is 1.43×10 3 S·m -1 ~1.04×10 4 S·m -1 The conductivity of the zinc oxide linear resistor ceramic material changes by no more than 2.005% between room temperature and 275°C.

5. The zinc oxide linear resistor ceramic material according to claim 1 or 2, characterized in that: The forward temperature coefficient of the zinc oxide linear resistor ceramic material is 1.58×10 -5 / ℃~8.02×10 -5 / ℃.

6. A method for preparing the zinc oxide linear resistor ceramic material according to any one of claims 1 to 5, characterized in that: include: (1) mixing TiO2 powder, MgO powder, ZrO2 powder and A2O3 powder to obtain raw material powder; (2) The raw material powder is subjected to calcination, granulation, compression molding, debinding and vacuum sintering to obtain the zinc oxide linear resistor ceramic material.

7. The preparation method according to claim 6, characterized in that In step (1), the mixing method is ball milling; the rotation speed of the ball milling is 200 to 600 rpm, and the time is 3 to 12 hours; preferably, after ball milling, the raw material powder is obtained by drying.

8. The preparation method according to claim 6 or 7, characterized in that In step (2), the calcination temperature is 400-800° C. and the holding time is 3-8 hours; The binder used in the granulation is a polyvinyl alcohol solution; the concentration of the polyvinyl alcohol solution is 5-10 wt%; the amount of polyvinyl alcohol added is 5-10 wt% of the total mass of the raw material powder.

9. The preparation method according to any one of claims 6 to 8, characterized in that In step (2): the compression molding pressure is 75 to 200 MPa, and the holding time is 5 to 30 seconds; The debinding parameters include: debinding under air; temperature of 400-600° C.; holding time of 3-4 hours; preferably, heating rate of 1° C. / min;.

10. The preparation method according to any one of claims 6 to 9, characterized in that In step (2): the parameters of the vacuum sintering include: vacuum degree of 1kPa to 10kPa; temperature of 1100 to 1400°C; holding time of 1 to 4 hours; preferably, the heating rate of the vacuum sintering is 1 to 10°C / min.

Images