High-performance thermistor and rapid preparation method thereof

Abstract

The invention belongs to the technical field of electronic functional material and component manufacturing, and particularly relates to a high-performance thermistor and a rapid preparation method thereof.The rapid preparation method comprises the steps that (MnCoFeNi) 3O4 is designed as a basic high-entropy ceramic component, La2O3 and Ce2O3 are cooperatively doped, and the thermal stability and the electrical performance of the material are effectively improved. A high-temperature hot pressed sintering-programmed cooling annealing integrated process is adopted, the temperature is rapidly increased to 1050-1200 DEG C at the speed of 90-120 DEG C / min, meanwhile, the pressure of 10-15 MPa is applied, heat preservation is conducted for 20-30 min, the temperature is slowly reduced to 750-850 DEG C, annealing is conducted, heat preservation is conducted for 2-3 h, powder forming and sintering are completed synchronously, and the production period is shortened. The obtained thermistor has high density (greater than 95%), the B value is between 3756 and 4201 K, the linearity of the resistivity logarithm-temperature reciprocal relation in a wide temperature range of-20 to 150 DEG C is good, and the resistance drift rate is lower than 1.5% after the thermistor is aged at 125 DEG C for 240 hours. The preparation efficiency is improved while the performance is guaranteed, and the method is suitable for the high-end fields of industrial measurement and control, medical electronics and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electronic functional materials and component manufacturing, and particularly relates to a high-performance thermistor and a rapid preparation method thereof. BACKGROUND

[0002] Negative temperature coefficient (NTC) thermistors are widely used in industrial measurement and control, medical electronics, automotive electronics and other fields due to their high sensitivity, fast response, small size, low cost and other advantages. Their traditional preparation relies on Mn-Ni-Co-Fe transition metal oxide systems and adopts a multi-step solid-phase reaction process of "dosing-ball milling-granulation-molding-sintering-electrode". This process route is long, high in energy consumption, and easy to introduce impurities, resulting in poor product consistency, insufficient stability, and difficulty in meeting the stringent requirements of high-end applications for performance and reliability.

[0003] To break through the bottleneck of traditional processes, researchers have explored new material systems and sintering technologies. In terms of material design, the concepts of high-entropy / middle-entropy ceramics are introduced to improve material stability. For example, Chinese invention application CN202510279783.X, a negative temperature coefficient middle-entropy thermistor material, preparation method and application, discloses (NiCoZnCu)Mn2O4 middle-entropy ceramic, which uses configuration entropy to stabilize the crystal phase, but the solid-phase diffusion of multiple components is difficult, which prolongs the reaction time and increases the risk of impurity phase formation. Chinese invention application CN202311131862.3, a thermistor material based on high-entropy concept and its preparation method, discloses (CoCrFeMgZn)3O4 high-entropy material which maintains high sensitivity, but has poor temperature stability and narrow effective temperature range. In terms of process optimization, Jin Xianjing et al. published, MnNiCuFe system material preparation by polymerization complex method and microwave sintering, electronic components and materials, 2009, 28 (08): 30-34, which uses microwave sintering to reduce the temperature, but uneven heating can cause local overheating of the product. Chinese invention application CN202310859284.2, a NTC thermistor and its preparation method, although the temperature range is widened by multi-component doping, the sensitivity and long-term stability are still not ideal. Chinese invention application CN202511120096.X, a preparation method of thermistor material, discloses that the B value is improved by complex doping, but at the cost of sacrificing the simplicity of the process, which is not conducive to large-scale production.

[0004] In summary, the prior art is caught in a dilemma: the pursuit of high performance (high B value, high stability) often requires complex material design and long sintering process, while the pursuit of high efficiency is usually at the expense of the uniformity of the microstructure and long-term stability of the material. This inherent contradiction between "performance" and "efficiency" is generally believed to be difficult to reconcile in the field. Therefore, there is an urgent need in the field for an innovative solution that can break through this technical prejudice and achieve high-efficiency preparation of NTC thermistors without sacrificing performance. SUMMARY

[0005] The core inventive concept of the present application is to solve the contradiction between "efficiency" and "performance" through a specific "rapid hot-pressing sintering-programmed cooling annealing" process timing and (MnCoFeNi)3O4 high-entropy ceramic system and its rare earth doping. First, a rapid heating rate of 90~120℃ / min and a pressure of 10~15MPa are used to provide a large sintering driving force for the powder in a very short time, achieving rapid initial densification of the grains, which is the source of efficiency. However, this rapid sintering will induce lattice stress and a small amount of defects, and direct cooling will cause product cracking and damage to long-term stability. Therefore, the present application immediately connects "programmed cooling annealing" after the subsequent, slowly cools to 750~850℃ at 5℃ / min under constant pressure and holds, which on the one hand can effectively release the internal stress generated by the aforementioned rapid sintering; on the other hand, more importantly, it provides the best thermodynamic conditions for ceramic elements and trace rare earth ions to diffuse and occupy the octahedral vacancies in the spinel structure, thereby stabilizing the lattice and repairing defects. This close coupling of sintering and annealing parameters, as well as the functional synergy of high-entropy matrix and specific rare earth doping, is the fundamental reason for the coexistence of high density, wide temperature range, high B value, and aging resistance achieved by the present application.

[0006] To achieve the above object, the present application adopts the following technical solution: A rapid preparation method of high-performance thermistors, comprising the following steps: (1) mixing powder raw materials containing Mn, Co, Fe, Ni oxides and rare earth oxides, the Mn, Co, Fe, Ni oxide powders are used to constitute a (MnCoFeNi)3O4 high-entropy ceramic system, and the doping amount of rare earth oxides is 0.3~0.6wt%, the total mass of each component is 100%; (2) hot-pressing and sintering the mixed powder in a mold at the same time, wherein the sintering heating rate is 90~120℃ / min, the sintering temperature is 1050~1200℃, and the pressure is 10~15MPa; (3) programmed cooling annealing after sintering, the annealing temperature is 750~850℃; (4) Electrode preparation and packaging of the obtained ceramic body.

[0007] Specifically: (1) Component design and weighing: The component is screened by using the material genome method, and the composition and content of the (MnCoFeNi)3O4 high-entropy ceramic system are designed with the aid of first-principle calculation. The raw material powders are weighed according to the mass percentage, and the composition is: 23-27wt% Fe3O4, 25-27wt% Mn3O4, 23.4-26.4wt% Co3O4, 22-25wt% NiO, and 0.3-0.6wt% of nano Ce2O3 and / or La2O3, ensuring that the total mass of each component is 100%.

[0008] (2) Powder mixing: Put the weighed powder into the ball mill tank, add grinding balls at a ball-to-material ratio of 1:3, and alternately ball mill on a planetary ball mill at a speed of 300 rpm, supplemented by ultrasonic vibration at 20-30 kHz. The ball milling program is set as: forward rotation for 30 min → pause for 5 min → reverse rotation for 30 min, and then the mixed powder is taken out.

[0009] (3) Green compact forming and furnace loading: Laying 0.5-1mm thick graphite paper as a release layer in the graphite mold cavity, placing the lower punch, pouring the mixed powder and placing the upper punch in turn, and using a pre-press to pre-press the powder into a shape at a pressure of 1-2MPa. Then wrap the mold with an asbestos heat insulation layer, transfer it to a rapid hot-pressing sintering furnace, and apply a pressure of 10-15MPa and close the furnace door.

[0010] (4) Hot-pressing sintering and annealing: The temperature of the furnace is raised to 1050-1200℃ at a rate of 90-120℃ / min, and the pressure is maintained at 10-15MPa during this process. After reaching the sintering temperature, keep it for 20-30min; then reduce the temperature to 750-850℃ at a controlled rate of 5℃ / min, and anneal for 2-3h, finally remove the pressure and cool to room temperature with the furnace.

[0011] (5) Electrode preparation: After cutting and polishing the sintered compact, silver paste is used for double-sided screen printing, and then sintering at 700-800℃ for 5-10min to form the electrode.

[0012] (6) Packaging and forming: The ceramic sheet with electrode is cut into a 0.5×0.5mm chip, and then the lead wire is welded and packaged in sequence to obtain the finished thermistor product.

[0013] (7) Performance testing: The resistance was measured and the B value (material constant) was calculated in a constant temperature environment using a digital source meter; the microstructure and porosity were observed using a scanning electron microscope; the phase composition was analyzed using an X-ray diffractometer and a Raman spectrometer; the sample was placed in a constant temperature aging chamber at 125℃ for 240h and its resistance drift rate was measured to evaluate the aging performance.

[0014] The present invention also discloses a thermistor prepared by the above method.

[0015] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the synergistic breakthroughs in performance, efficiency and consistency: Performance Improvement and Balancing: As shown in Table 3, Examples 1-6 of this invention, while maintaining a wide resistance-temperature linear range and a high B value (3756.02 ~ 4201.04 K), successfully controlled the resistance drift rate after aging at 125℃ for 240 h to the level of 1.13%~1.46%. More importantly, Comparative Example 1 (without rare earth doping) demonstrates that, apart from the synergistic system of this invention, although the B value is high (4343.08 K), the aging performance deteriorates sharply (4.03%); while Comparative Examples 3 and 5 (excessive doping) and Figure 3 The XRD results show that deviating from the doping range of this invention will damage the phase structure, leading to severe degradation of the B value. This demonstrates that this invention achieves an optimal balance between high sensitivity and high stability within a single spinel phase structure.

[0016] (2) Improved preparation efficiency: Due to the adoption of the integrated hot pressing molding and sintering process, the traditional process of granulation, separate molding and long sintering is eliminated, and the heating rate is increased to 90~120℃ / min, which shortens the total production cycle by more than 50%.

[0017] (3) High product consistency and yield: The collaborative process has a wide window and good repeatability. The yield of the prepared 0.5×0.5mm microchip is stable at over 98%, and the density is greater than 95%, which is suitable for large-scale production. Attached Figure Description

[0018] Figure 1 The DSC diagram of the high-entropy ceramic powder system in Comparative Example 1 is shown. Figure 2 SEM image of the thermistor prepared in Example 1; Figure 3 The XRD pattern of the thermistor prepared in Example 1; Figure 4 The XRD pattern of the thermistor prepared for Comparative Example 3; Figure 5 This is a graph showing the relationship between the logarithm of resistivity and the reciprocal of temperature for the product in Example 1. Detailed Implementation

[0019] This invention provides a high-performance thermistor with the chemical formula (MnCoFeNi)3O4, co-doped with Ce and La. Its raw materials are analytical grade Fe3O4, Mn3O4, Co3O4, NiO, Ce2O3, and La2O3 powders, which are NTC thermistors that meet the requirements of low cost, environmental protection, high thermal sensitivity, and high stability.

[0020] Using a materials genome approach, Fe, Mn, Ni, and Co with similar atomic radii were screened as basic components to construct a stable high-entropy system. Simulations were performed using the VASP software package, combined with PAW pseudopotentials and GGA functionals, on three supercell models: FCC, BCT, and FCO. When the four elements are combined in a molar ratio close to 1:1:1:1, the system's lattice constant is approximately 8.15 Å, and the formation energy is as low as approximately -700 kJ / mol. This composition can form a structurally stable single spinel phase with high thermodynamic properties. Introducing trace amounts of Ce₂O₃ and La₂O₃ for doping modification into the aforementioned high-entropy matrix allows rare earth ions to preferentially occupy octahedral sites in the spinel structure, effectively improving the material's thermal stability. The compositional design synergistically utilizes the high-entropy effect and slow diffusion effect to suppress elemental segregation, ensuring long-term phase stability. Meanwhile, the strong lattice distortion significantly enhances scattering during carrier migration, making the resistance extremely sensitive to temperature changes, thus successfully achieving a balance between high thermodynamic performance and high stability.

[0021] The determination of the rapid heating rate (90~120℃ / min) and the hot-pressing sintering temperature range (1050~1200℃) is based on a comprehensive result of theoretical analysis and experimental verification. Differential thermal analysis (DSC) experiments were conducted using the powder composition of Comparative Example 1, and the test analysis results are as follows: Figure 1 As shown, the (MnCoFeNi)3O4 high-entropy ceramic powder exhibits a significant endothermic phase transition peak around 1070℃, therefore the theoretical lower limit of the sintering temperature is set at 1050℃. Temperature gradient experiments conducted under hot-pressing conditions of 10~15MPa confirmed that when the temperature is below 1050℃, insufficient densification and crystallinity lead to deterioration of electrical properties. When the heating rate exceeds 120℃ / min and the temperature exceeds 1200℃, overheating is difficult to control, easily leading to defects such as abnormal grain growth and elemental segregation. Therefore, while ensuring production efficiency and avoiding overheating, a rapid heating rate of 90~120℃ / min and a sintering temperature of 1050~1200℃ are key windows for ensuring high density and a single-phase structure. This temperature range works closely with the subsequent programmed cooling annealing process to jointly ensure excellent comprehensive performance of the product, achieving high B-value and low aging drift rate while improving preparation efficiency.

[0022] The technical solution of the present invention will be further described below with reference to specific embodiments. The equipment models used in the embodiments and comparative examples are shown in Table 1 below; other similar equipment may also be selected. The mass composition of the oxides in the embodiments and comparative examples of the present invention is shown in Table 2 below.

[0023] Table 1. Preparation and testing equipment used in the embodiments of the present invention.

[0024] Table 2. Oxide mass composition (wt%) in each embodiment and comparative example

[0025] Example 1 Weigh the powder raw materials as described in Table 2 above, totaling 500g, and place them in a ball mill jar, mixing them at a ball-to-material ratio of 1:3. Mix in a planetary ball mill at 300r / min with 20kHz ultrasonic vibration, using a "forward rotation 30min—pause 5min—reverse rotation 30min" mode. After mixing, load the powder into a mold lined with graphite paper, pre-pressing it with 1MPa pressure for initial shaping. Wrap the pressed blank with asbestos and transfer it to a hot-pressing sintering furnace, applying 10MPa pressure, heating at 90℃ / min to 1050℃, holding for 30min, then cooling at 5℃ / min to 850℃, holding for 2h, and finally depressurizing and cooling with the furnace. The resulting sintered blank is sliced ​​and polished, then double-sided electrodes are printed using silver paste, sintered at 700℃ for 10min to produce a 0.5×0.5mm chip, with leads soldered and encapsulated to obtain the finished thermistor. Example 2

[0026] Weigh the powder raw materials as described in Table 2 above, totaling 500g, and place them in a ball mill jar, mixing them at a ball-to-material ratio of 1:3. Mix in a planetary ball mill at 300r / min with 25kHz ultrasonic vibration, using a "forward rotation 30min—pause 5min—reverse rotation 30min" mode. After mixing, the powder is placed into a mold lined with graphite paper and pre-pressed with 2MPa pressure for initial shaping. The pressed blank is then wrapped with asbestos and transferred to a hot-press sintering furnace, where 15MPa pressure is applied, and the temperature is increased to 1200℃ at 120℃ / min, held for 20min, then cooled to 750℃ at 5℃ / min, held for 3h, and finally depressurized and cooled with the furnace. The resulting sintered blank is sliced ​​and polished, then double-sided electrodes are printed using silver paste, sintered at 800℃ for 5min to produce a 0.5×0.5mm chip, leads are soldered and encapsulated to obtain the finished thermistor. Example 3

[0027] Weigh the powder raw materials as described in Table 2 above, totaling 500g, and place them in a ball mill jar, mixing them at a ball-to-material ratio of 1:3. Mix in a planetary ball mill at 300r / min with 30kHz ultrasonic vibration, using a "forward rotation 30min—pause 5min—reverse rotation 30min" mode. After mixing, the powder is placed into a mold lined with graphite paper and pre-pressed with 2MPa pressure for initial shaping. The pressed blank is then wrapped with asbestos and transferred to a hot-press sintering furnace, where 10MPa pressure is applied, and the temperature is increased to 1050℃ at 120℃ / min, held for 20min, then cooled to 750℃ at 5℃ / min, held for 3h, and finally depressurized and cooled with the furnace. The resulting sintered blank is sliced ​​and polished, then double-sided electrodes are printed using silver paste, sintered at 700℃ for 10min to produce a 0.5×0.5mm chip, leads are soldered and encapsulated to obtain the finished thermistor. Example 4

[0028] Weigh the powder raw materials as described in Table 2 above, totaling 500g, and place them in a ball mill jar, mixing them at a ball-to-material ratio of 1:3. Mix in a planetary ball mill at 300r / min with 30kHz ultrasonic vibration, using a "forward rotation 30min—pause 5min—reverse rotation 30min" mode. After mixing, the powder is placed into a mold lined with graphite paper and pre-pressed with 2MPa pressure for initial shaping. The pressed blank is then wrapped with asbestos and transferred to a hot-press sintering furnace, where 15MPa pressure is applied, and the temperature is increased to 1200℃ at 120℃ / min, held for 20min, then cooled to 750℃ at 5℃ / min, held for 3h, and finally depressurized and cooled with the furnace. The resulting sintered blank is sliced ​​and polished, then electrodes are printed on both sides using silver paste, sintered at 800℃ for 5min to produce a 0.5×0.5mm chip, leads are soldered and encapsulated to obtain the finished thermistor. Example 5

[0029] Weigh the powder raw materials as described in Table 2 above, totaling 500g, and place them in a ball mill jar, mixing them at a ball-to-material ratio of 1:3. Mix in a planetary ball mill at 300r / min with 30kHz ultrasonic vibration, using a "forward rotation 30min—pause 5min—reverse rotation 30min" mode. After mixing, the powder is placed into a mold lined with graphite paper and pre-pressed with 2MPa pressure for initial shaping. The pressed blank is then wrapped with asbestos and transferred to a hot-press sintering furnace, where 15MPa pressure is applied, and the temperature is increased to 1100℃ at 110℃ / min, held for 25min, then cooled to 800℃ at 5℃ / min, held for 3h, and finally depressurized and cooled with the furnace. The resulting sintered blank is sliced ​​and polished, then double-sided electrodes are printed using silver paste, sintered at 800℃ for 8min to produce a 0.5×0.5mm chip, leads are soldered and encapsulated to obtain the finished thermistor. Example 6

[0030] Weigh the powder raw materials as described in Table 2 above, totaling 500g, and place them in a ball mill jar, mixing them at a ball-to-material ratio of 1:3. Mix in a planetary ball mill at 300r / min with 30kHz ultrasonic vibration, using a "forward rotation 30min—pause 5min—reverse rotation 30min" mode. After mixing, the powder is placed into a mold lined with graphite paper and pre-pressed with 2MPa pressure for initial shaping. The pressed blank is then wrapped with asbestos and transferred to a hot-press sintering furnace, where 15MPa pressure is applied, and the temperature is raised to 1150℃ at 110℃ / min, held for 25min, then cooled to 800℃ at 5℃ / min, held for 3h, and finally depressurized and cooled with the furnace. The resulting sintered blank is sliced ​​and polished, then double-sided electrodes are printed using silver paste, sintered at 800℃ for 10min to produce a 0.5×0.5mm chip, leads are soldered and encapsulated to obtain the finished thermistor. Comparative Examples 1-6

[0031] The powder raw materials were weighed as described in Table 2 above, and the thermistors were prepared using the same method as in Example 1. The matrix of Comparative Example 6 was a non-high-entropy ceramic composition.

[0032] The purpose of Examples 1 and 2 is to study the performance of thermistors doped with Ce alone; the purpose of Examples 3 and 4 is to study the performance of thermistors doped with La alone; and the purpose of Examples 5 and 6 is to study the performance of thermistors co-doped with Ce and La. The purpose of Comparative Example 1 is to study the performance of high-entropy ceramic thermistors without rare-earth oxide doping; the purpose of Comparative Examples 2 to 5 is to study the performance of thermistors doped with La and Ce at very low and very high contents; and the purpose of Comparative Example 6 is to study the performance of thermistors doped with La and Ce in non-high-entropy ceramic systems.

[0033] The thermistor samples prepared in Examples 1-6 and Comparative Examples 1-6 were subjected to microstructure, phase composition, and performance testing and analysis. The microstructure (grain size, porosity) was observed using a scanning electron microscope. The micromorphology of the sample in Example 1 is shown below. Figure 2 As shown. From Figure 2 It can be seen that the thermosensitive ceramic body has a fine and uniform structure with extremely low porosity, and the density of the sample was measured to be 97.5%. Phase analysis was performed using X-ray diffraction. Figure 3 The image shows the XRD pattern of the sample from Example 1. Combined with Raman spectroscopy analysis, it shows a complete spinel structure when an appropriate amount of rare earth elements are added. Figure 4The XRD pattern of sample 3 is shown. When excessive rare earth doping occurs, a distinct perovskite impurity phase peak appears. Electrical performance parameters were measured using a digital source meter in a constant-temperature oil bath environment. Aging performance was assessed by measuring resistance and calculating drift rate after continuous holding at 125℃ for 240 hours in a constant-temperature aging chamber. The measured data were processed into a logarithm-temperature inverse relationship curve, revealing a good linear relationship between -20℃ and 150℃ (temperatures 253-423K) (as shown in the curve of Example 1). Figure 5 (As shown in the figure). The performance of the obtained thermistors is shown in Table 3 below.

[0034] Table 3 Performance test results of Examples 1-6 and Comparative Examples 1-6

[0035] Combining the data from Examples 1-6 and Comparative Examples 1-6, it can be seen that the material constant (B) of Comparative Example 1 is... 25 / 50 The highest value was 4343.08 K, indicating that this (MnCoFeNi)3O4 high-entropy ceramic, by utilizing lattice distortion and high-entropy effects, can achieve high sensitivity while maintaining lattice structure stability. However, its aging performance is poor, with a resistivity drift rate as high as 4.03%. With increasing La and Ce doping amounts, the material constant decreases, but the aging resistivity drift rate also decreases, indicating that while maintaining high sensitivity, the material's stability is enhanced, and its temperature characteristics are relatively more stable. However, if the doping amount is too low, the aging resistivity drift rate remains high; while excessive doping significantly weakens the material's high sensitivity characteristics.

[0036] The performance of Comparative Example 6 deteriorated across the board (B value as low as 3517.21 K, aging rate as high as 5.35%), fundamentally due to its composition being a traditional Mn-based, non-high-entropy system. This system cannot form the strong lattice distortion and slow diffusion effects characteristic of high-entropy systems, and its electrical properties and structural stability are inherently far lower than those of high-entropy systems. In contrast, Examples 1-6, while maintaining high material constants (3756.02~4201.04 K) for high sensitivity, successfully controlled the resistivity drift within an extremely low range of 1.13%~1.46%. This indicates that the material systems represented by the examples successfully solved the problem of balancing high sensitivity and high stability in Comparative Example 6, achieving performance optimization and balance. This comparison powerfully demonstrates that the high-entropy ceramic substrate of this invention is an essential foundation for achieving high performance, and its combination with rare earth doping and subsequent rapid sintering-processed annealing produces a synergistic enhancement effect.

Claims

1. A rapid fabrication method for a high-performance thermistor, characterized in that, Includes the following steps: (1) Powder raw materials containing oxides of Mn, Co, Fe, Ni and rare earth oxides are mixed, wherein the oxide powders of Mn, Co, Fe and Ni are used to form a (MnCoFeNi)3O4 high-entropy ceramic system, and the amount of rare earth oxides is 0.3~0.6wt%, and the total mass of each component is 100%; (2) The mixed powder is simultaneously hot-pressed and sintered in a mold, wherein the sintering heating rate is 90~120℃ / min, the sintering temperature is 1050~1200℃, and the pressure is 10~15MPa; (3) After sintering, perform programmed cooling annealing at a temperature of 750~850℃; (4) Electrode preparation and encapsulation of the obtained ceramic body.

2. The rapid fabrication method for a high-performance thermistor according to claim 1, characterized in that, The rare earth oxides are Ce2O3 and / or La2O3.

3. The rapid fabrication method of a high-performance thermistor according to claim 1, characterized in that, The oxide has the following mass percentage composition: 23~27wt% Fe3O4, 25~27wt% Mn3O4, 23.4~26.4wt% Co3O4, and 22~25wt% NiO.

4. The rapid fabrication method for a high-performance thermistor according to claim 1, characterized in that, The powder was mixed using an alternating ball milling process, supplemented by ultrasonic vibration at 20-30 kHz.

5. The rapid fabrication method for a high-performance thermistor according to claim 1, characterized in that, The programmed cooling annealing involves reducing the temperature from the sintering temperature to the annealing temperature at a rate of 5°C / min, and then holding the temperature at the annealing temperature for 2-3 hours.

6. The rapid fabrication method for a high-performance thermistor according to claim 1, characterized in that, The electrode is prepared by screen printing silver paste and sintering it at 700-800℃ for 5-10 minutes.

7. A thermistor prepared by a rapid preparation method for a high-performance thermistor according to any one of claims 1-6.

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