PTC (Positive Temperature Coefficient) heating ceramic with high resistance value, high voltage resistance and high lift-drag ratio and preparation method thereof

Abstract

The invention relates to PTC (Positive Temperature Coefficient) ceramic, in particular to PTC heating ceramic with high resistance value, high voltage resistance and high lift-drag ratio and a preparation method thereof. The heating ceramic comprises a main material, a semiconducting element, an acceptor element, a sintering aid and a dispersing agent, the main materials comprise barium titanate and lead titanate; the semi-conductive element is formed by doping Nb2O5, La2O3, Sb2O3 and Nd2O3 or Y2O3, and the doping amount of the Nb2O5, the La2O3, the Sb2O3 and the The acceptor element is provided by MnO2 or Mn (NO3) 2; the sintering aid comprises BN (boron nitride), Li2CO3 and SiO2 (silicon dioxide). Through the effect of semiconductor elements, volatilization of PbO is fully inhibited, crystal grains are prevented from growing, and an internal structure with fine and uniform crystal grains is obtained, so that the aim of improving withstand voltage (greater than or equal to 1200V) and lift-drag ratio (2 * 103) is fulfilled. The resistance value of the ceramic chip is controlled to be 4-8 kiloohms by adjusting the dosage of the acceptor element and the sintering aid.

Description

Technical Field

[0001] The invention relates to a PTC ceramic, in particular to a PTC heating ceramic with high resistance, high withstand voltage and high lift-to-resistance ratio and a preparation method thereof. Background Art

[0002] PTC thermistor is a semiconductor ceramic whose resistance value increases with the increase of temperature. When the temperature exceeds its Curie temperature, the resistance value will increase stepwise. The principle of PTC heater is based on the constant temperature heating characteristics of PTC thermistor. When the PTC thermistor is powered on, its surface temperature will remain at a constant value. This temperature is only related to the Curie temperature of the PTC thermistor and the applied voltage, and has little to do with the ambient temperature, thus generating constant temperature heating.

[0003] New energy vehicles will generate high voltage when running and the vehicle will vibrate from time to time due to different road conditions. This is a great test for the comprehensive performance of PTC ceramic heaters. Ordinary PTC ceramic heaters cannot withstand it for a long time. Therefore, it is necessary to specially develop PTC ceramic heaters with long-term comprehensive performance, stable pressure resistance and high stability that meet the requirements of new energy vehicles.

[0004] BaTiO3 series PTC heating sheet is a classic PTC heating sheet. Its heating principle and the influence of various factors on its performance have been basically clarified. At present, the research on the formula of PTC for new energy vehicles has been very mature. Introducing donor impurities (semiconducting elements) into the material components can make BaTiO3 semiconducting. Semiconducting elements are divided into two categories: one is selected from Ba 2+ Similar radius, higher valence than Ba 2+ Replace Ba 2+ Position; a type of selection and Ti 4+ Similar radius, higher valence than Ti 4+ Elements replacing Ti 4+ By selecting two types of semiconducting elements and working together with the acceptor elements, the ceramic piece exhibits the PTC effect.

[0005] The smaller the grain size, the larger the grain boundary per unit thickness, and the smaller the effective voltage distributed on each grain boundary, thereby reducing the piezoresistance effect and improving the withstand voltage. However, if the grain size is uneven and there are some abnormally grown grains, a channel with low resistivity will be formed, and the withstand voltage will be reduced. PbTiO3, as a peak shifter, is indispensable in adjusting the Curie temperature point. However, due to Pb 2+ It is volatile at high temperatures, which will cause abnormal grain growth and reduce the withstand voltage. Summary of the invention

[0006] In order to solve the problem of reduced withstand voltage caused by abnormal grain growth, the present invention provides a PTC heating ceramic with high resistance, high withstand voltage and high lift-to-resistance ratio. The formula composition is optimized by selecting the type and addition amount of donor elements, so that the semiconducting elements can suppress the volatilization of Pb to the greatest extent, and the ball milling efficiency is maximized by introducing an efficient dispersant in the ball milling, and finally a fine and uniform grain structure is obtained, thereby improving its withstand voltage. The specific technical scheme is as follows:

[0007] A PTC heating ceramic with high resistance, high withstand voltage and high lift-to-drag ratio, comprising a main material, a semiconducting element, an acceptor element, a sintering aid and a dispersant; the main material comprises barium titanate and lead titanate; the semiconducting element is formed by doping Nb2O5, La2O3, Sb2O3 and Nd2O3 or Y2O3; the acceptor element is provided by MnO2 or Mn(NO3)2; the sintering aid comprises BN, Li2CO3 and SiO2.

[0008] Preferably, the molar ratio of the main material is as follows: BaTiO3: 0.6-0.7 mol; PbTiO3: 0.3-0.4 mol.

[0009] Preferably, the molar ratio of the semiconducting elements is as follows: Nb2O5: 0.010-0.015% mol; La2O3: (0.05-x)-(0.06-x)% mol; Sb2O3: 0.01-0.03% mol; Nd2O3: x(0.001-0.0015)% mol, where x=0.001, 0.0011, 0.0012, 0.0013, 0.0014, 0.0015 or Y2O3: x(0.001-0.0015)% mol, where x=0.001, 0.0011, 0.0012, 0.0013, 0.0014, 0.0015.

[0010] Preferably, the mass percentage of the sintering aid in the main material is as follows: SiO2 content is 0.2-0.4wt%; BN content is 0.01-0.02wt%; Li2CO3 content is 0.01-0.02wt%.

[0011] Preferably, the mass fraction of Mn in the acceptor element is 0.02-0.04 wt% of the main material.

[0012] Preferably, the dispersant is of polycarboxylate ammonium type.

[0013] The dispersing aid is polycarboxylate ammonium type DSF8.

[0014] Furthermore, the particle size of the dispersant is 0.443 μm.

[0015] A method for preparing a PTC heating ceramic with high resistance, high withstand voltage and high lift-to-resistance ratio, which is used for preparing a PTC heating ceramic with high resistance, high withstand voltage and high lift-to-resistance ratio, is characterized in that it comprises the following steps:

[0016] Step 1, preparing the main material and the semiconducting element in proportion;

[0017] Step 2, the raw materials prepared in step 1 are placed in a ball mill at a material-water ratio of 1:1.2 for 24 hours, the slurry is poured out and placed in a sagger, the water is drained and placed in an electric furnace for pre-calcination at 1100° C. to obtain a pre-calcined synthetic material;

[0018] Step 3, adding sintering aids and acceptor elements according to mass percentage to the pre-sintered material in step 2, adding 0.2% to 0.25% dispersant of the mass of the main material according to the material-water ratio of 1:0.6 to improve the ball milling efficiency, and ball milling for 24 hours to obtain a slurry;

[0019] Step 4, granulating the slurry in step 3 by a spray granulator to obtain a powder with a particle size of 75 to 425 μm as a granulated material, and pressing the granulated material at a pressure of 10 to 20 MPa into a green blank of 115 mm×24 mm×2.4 mm;

[0020] Step 5: Place the green body in step 4 in a synthetic kiln and sinter at 1200-1300° C. to obtain a ceramic sheet, grind it according to the thickness requirement, spray aluminum electrodes, and obtain a PTC heating sheet.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The invention provides a PTC heating ceramic with high resistance, high withstand voltage and high lift-to-resistance ratio. The composition of the formula is optimized by selecting the type and addition amount of the donor element, so that the semiconductor element can suppress the Pb 2+ volatilization, thus avoiding abnormal grain growth. On the other hand, based on the traditional planetary ball milling, polycarboxylate ammonium dispersant is used instead of the original polypropionate ammonium dispersant, which improves the ball milling efficiency and reduces the grain size, and finally obtains a uniform and stable grain structure, thereby improving the pressure resistance of the PTC heating ceramic sheet, and also improving the temperature coefficient and lift-to-drag ratio of the heating ceramic sheet. The improved performance broadens the application field of this product. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention compares the voltage resistance of PTC heating ceramic sheets obtained by using polyacrylate ammonium dispersant and polycarboxylate ammonium dispersant respectively when BaTiO3 is 0.6 mol and PbTiO3 is 0.4 mol. DETAILED DESCRIPTION

[0024] The present invention will be further described with reference to the accompanying drawings.

[0025] Example 1

[0026] Preparation of PTC heating ceramics with high resistance, high withstand voltage and high lift-to-resistance ratio:

[0027] Step 1, weigh BaTiO36mol, PbTiO34mol respectively in a molar ratio of 6:4, weigh 0.014%molNb2O5, 0.0488%molLa2O3, 0.01%molSb2O3, 0.0012%molNd2O3 as semiconductor element providers in molar percentage, the material-water ratio is 1:1.2, and ball mill is placed in a ball mill for 24h. The slurry is inverted in a sagger, and the water is drained and pre-sintered at 1100℃ for synthesis.

[0028] Step 2: Weigh 2000 g of the pre-synthesized material, add sintering aids BN, Li2CO3, SiO2 and acceptor element Mn in proportion, with a material-water ratio of 1:0.6, add 4 g of polycarboxylate ammonium dispersant, and mill in a 5L ball mill for 24 hours to obtain a slurry.

[0029] Step 3, granulating the slurry through a spray granulator to obtain a powder with a particle size of 75 to 425 μm as a granulated material, and pressing the granulated material into a 115 mm×24 mm×2.4 mm green billet at a pressure of 15 MPa;

[0030] Step 4: Place the green blank in a synthetic kiln and sinter it at 1230° C. to obtain a ceramic sheet, grind it according to the thickness requirement, spray aluminum electrodes, and obtain a PTC heating sheet.

[0031] Step 5: Test the performance of the PTC chips. The average resistance is 4.5 kilo-ohms, the withstand voltage is 1230V, and the rise-to-resistance ratio is 2.3×10 3 .

[0032] Example 2

[0033] Step 1, weigh BaTiO37mol, PbTiO33mol respectively in a molar ratio of 7:3, weigh 0.015%molNb2O5, 0.0485%molLa2O3, 0.02%molSb2O3, 0.0015%molNd2O3 as semiconductor element providers in molar percentage, the material-water ratio is 1:1.2, and ball mill is used for 24h. The slurry is inverted in a sagger, and the water is drained and pre-sintered at 1100℃ for synthesis.

[0034] Step 2: Weigh 2000 g of the pre-synthesized material, add BN, Li2CO3, SiO2, and acceptor element Mn in proportion, with a material-water ratio of 1:0.6, add 4.5 g of polycarboxylate ammonium dispersant, and mill in a 5L ball mill for 24 hours to obtain a slurry.

[0035] Step 3, granulating the slurry through a spray granulator to obtain a powder with a particle size of 75 to 425 μm as a granulated material, and pressing the granulated material into a 115 mm×24 mm×2.4 mm green billet at a pressure of 15 MPa;

[0036] Step 4: Place the green blank in a synthetic kiln and sinter it at 1230° C. to obtain a ceramic sheet, grind it according to the thickness requirement, spray aluminum electrodes, and obtain a PTC heating sheet.

[0037] Step 5: Test the performance of the PTC chips. The average resistance is 4.2 kilo-ohms, the withstand voltage is 1250V, and the rise-to-resistance ratio is 4.8×10 3 .

[0038] Example 3

[0039] Step 1, weigh BaTiO38mol, PbTiO32mol respectively in a molar ratio of 8:2, weigh 0.013%molNb2O5, 0.0585%molLa2O3, 0.02%molSb2O3, 0.0015%molY2O3 as semiconductor element providers in molar percentage, the material-water ratio is 1:1.2, and ball mill is used for 24h. The slurry is inverted in a sagger, and the water is drained and pre-sintered at 1100℃ for synthesis.

[0040] Step 2: Weigh 2000 g of the pre-synthesized material, add BN, Li2CO3, SiO2, and acceptor element Mn in proportion, with a material-water ratio of 1:0.6, add 5 g of polycarboxylate ammonium dispersant, and mill in a 5L ball mill for 24 hours to obtain a slurry.

[0041] Step 3, granulating the slurry through a spray granulator to obtain a powder with a particle size of 75 to 425 μm as a granulated material, and pressing the granulated material into a 115 mm×24 mm×2.4 mm green billet at a pressure of 20 MPa;

[0042] Step 4: Place the green blank in a synthetic kiln and sinter it at 1230° C. to obtain a ceramic sheet, grind it according to the thickness requirement, spray aluminum electrodes, and obtain a PTC heating sheet.

[0043] Step 5: Test the performance of the PTC chips. The average resistance is 5.2 kilo-ohms, the withstand voltage is 1280V, and the rise-to-resistance ratio is 6.3×10 3 .

[0044] By optimizing the selection of semiconductor elements, compared with the current binary and ternary semiconductor formula systems, a quaternary formula system is selected. Through the action of semiconductor elements, the volatilization of PbO is fully suppressed, the grain growth is avoided, and a fine and uniform internal structure is obtained, thereby achieving improved withstand voltage (≥1200V) and lift-to-drag ratio (2×10 3 ) purpose.

[0045] By adjusting the dosage of the acceptor element and the sintering aid, the resistance value of the ceramic sheet can be controlled within 4-8 kilo-ohms.

[0046] The technical principle of the present invention is described above in conjunction with specific embodiments. These descriptions are only for explaining the principle of the present invention and cannot be interpreted as limiting the protection scope of the present invention in any way. Based on the explanations herein, those skilled in the art can associate other specific implementations of the present invention without paying creative labor, and these methods will fall within the protection scope of the claims of the present invention.

Claims

1. A PTC heating ceramic with high resistance, high withstand voltage and high lift-to-resistance ratio, characterized in that: It includes main material, semiconducting element, acceptor element, sintering aid and dispersant; The main materials include barium titanate and lead titanate; The semiconducting element is doped with Nb2O5, La2O3, Sb2O3 and Nd2O3 or Y2O3; The acceptor element is provided by MnO2 or Mn(NO3)2; The sintering aids include BN, Li2CO3, and SiO2.

2. A PTC heating ceramic with high resistance, high withstand voltage and high lift-to-drag ratio according to claim 1, characterized in that: The molar ratio of the main ingredients is as follows: BaTiO3: 0.6~0.7mol; PbTiO3: 0.3~0.4mol.

3. The PTC heating ceramic with high resistance, high withstand voltage and high lift-to-drag ratio according to claim 1, characterized in that: The molar ratio of the semiconducting element is as follows: Nb2O5: 0.010~0.015%mol; La2O3: (0.05-x)~(0.06-x)%mol; Sb2O3: 0.01~0.03%mol; Nd2O3: x (0.001-0.0015) % mol, where x = 0.001, 0.0011, 0.0012, 0.0013, 0.0014, 0.0015 or Y2O3: x (0.001-0.0015)% mol, where x = 0.001, 0.0011, 0.0012, 0.0013, 0.0014, 0.0015.

4. The PTC heating ceramic with high resistance, high withstand voltage and high lift-to-drag ratio according to claim 1, characterized in that: The mass percentage of the sintering aid in the main material is as follows: SiO2 content is 0.2-0.4wt%; BN content is 0.01-0.02wt%; The amount of Li2CO3 is 0.01 to 0.02 wt%.

5. The PTC heating ceramic with high resistance, high withstand voltage and high lift-to-drag ratio according to claim 1, characterized in that: The mass fraction of Mn in the acceptor element is 0.02-0.04 wt % of the main material.

6. The PTC heating ceramic with high resistance, high withstand voltage and high lift-to-resistance ratio according to claim 1, characterized in that: The dispersant is of polycarboxylate ammonium type.

7. A PTC heating ceramic with high resistance, high withstand voltage and high lift-to-resistance ratio according to claim 6, characterized in that: The particle size of the dispersant is 0.443 μm.

8. A method for preparing a PTC heating ceramic with high resistance, high withstand voltage and high lift-to-resistance ratio, used for preparing a PTC heating ceramic with high resistance, high withstand voltage and high lift-to-resistance ratio as claimed in claim 1, characterized in that: The steps include: Step 1, preparing the main material and the semiconducting element in proportion; Step 2, the raw materials prepared in step 1 are placed in a ball mill at a material-water ratio of 1:1.2 for 24 hours, the slurry is poured out and placed in a sagger, the water is drained, and the slurry is placed in an electric furnace at 1100° C. for pre-calcination to obtain a pre-calcined synthetic material; Step 3, adding sintering aids and acceptor elements according to mass percentage to the pre-sintered material in step 2, adding 0.2% to 0.25% dispersant of the mass of the main material according to the material-water ratio of 1:0.6 to improve the ball milling efficiency, and ball milling for 24 hours to obtain a slurry; Step 4, granulating the slurry in step 3 by a spray granulator to obtain a powder with a particle size of 75 to 425 μm as a granulated material, and pressing the granulated material at a pressure of 10 to 20 MPa into a green blank of 115 mm×24 mm×2.4 mm; Step 5: Place the green body in step 4 in a synthetic kiln and sinter at 1200-1300° C. to obtain a ceramic sheet, grind it according to the thickness requirement, spray aluminum electrodes, and obtain a PTC heating sheet.

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