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1.
《Journal of the European Ceramic Society》2019,39(16):5174-5180
The effects of hot-pressing sintering on the phase composition, microstructure, thermal and electrical properties of AlN ceramics with CeO2–CeF3 additives were studied. During hot-pressing sintering, high pressure reduced the grain boundary phase CeAlO3 and decreased the concentration of oxygen in AlN ceramics. The hot-pressing sintered AlN samples had a much higher thermal conductivity of 191.9 W/m·K than pressureless sintered ones because of the great reduction of grain boundary phases and oxygen impurities in AlN ceramic. As the carbon content in hot-pressing sintered sample was very high, carbon contamination led to the decrease in electrical resistivity and changes in polarization mechanisms for AlN ceramics. The relaxation peak in the dielectric temperature spectrum with an activation energy of 0.64 eV for hot-pressing sintered samples was caused by electrons from free carbon at low temperature. Overall, hot-pressing sintering can effectively increase the thermal conductivity and change the electrical properties of AlN ceramics. 相似文献
2.
Microstructure,Thermal Conductivity,and Electrical Properties of In Situ Pressureless Densified SiC–BN Composites
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Yinsheng Li Jie Yin Haibo Wu Jingxian Zhang Jian Chen Yongjie Yan Xuejian Liu Zhengren Huang Dongliang Jiang 《Journal of the American Ceramic Society》2015,98(3):879-887
The microstructure, thermal conductivity, and electrical properties of pressureless densified SiC–BN composites prepared from in situ reaction of Si3N4, B4C, and C were systematically investigated, to achieve outstanding performance as substrate materials in electronic devices. The increasing BN content (0.25–8 wt%) in the composites resulted in finer microstructure, higher electrical resistivity, and lower dielectric constant and loss, at the expense of only slight degradation of thermal conductivity. The subsequently annealed composites showed more homogeneous microstructures with less crystal defects, further enhanced thermal conductivities and electrical resistivities, and reduced dielectric constants and losses, compared with the unannealed ones. The enhanced insulating performance, the weakened interface polarization, and the reduced current conduction loss were explained by the gradual equalization of dissolved B and N contents in SiC crystals and the consequent impurity compensation effect. The schottky contact between graphite and p‐type SiC grains presumably played a critical role in the formation of grain‐boundary barriers. The annealed composites doped with 8 wt% BN exhibited considerably high electrical resistivity (4.11 × 1011 Ω·cm) at 100 V/cm, low dielectric constant (16.50), and dielectric loss (0.127) at 1 MHz, good thermal conductivity [66.06 W·(m·K)?1] and relatively high strength (343 MPa) at room temperature. 相似文献
3.
《Journal of the European Ceramic Society》2022,42(10):4076-4085
The electrical, thermal, and mechanical properties of porous SiC ceramics with B4C-C additives were investigated as functions of C content and sintering temperature. The electrical resistivity of porous SiC ceramics decreased with increases in C content and sintering temperature. A minimal electrical resistivity of 4.6 × 10?2 Ω·cm was obtained in porous SiC ceramics with 1 wt% B4C and 10 wt% C. The thermal conductivity and flexural strength increased with increasing sintering temperature and showed maxima at 4 wt% C addition when sintered at 2000 °C and 2100 °C. The thermal conductivity and flexural strength of porous SiC ceramics can be tuned independently from the porosity by controlling C content and sintering temperature. Typical electrical resistivity, thermal conductivity, and flexural strength of porous SiC ceramics with 1 wt% B4C-4 wt% C sintered at 2100 °C were 1.3 × 10?1 Ω·cm, 76.0 W/(m·K), and 110.3 MPa, respectively. 相似文献
4.
Yusen Duan Jingxian Zhang Xiaoguang Li Hainan Bai Pavol Sajgalik Dongliang Jiang 《International Journal of Applied Ceramic Technology》2019,16(4):1399-1406
Silicon nitride ceramics were pressureless sintered at low temperature using ternary sintering additives (TiO2, MgO and Y2O3), and the effects of sintering aids on thermal conductivity and mechanical properties were studied. TiO2–Y2O3–MgO sintering additives will react with the surface silica present on the silicon nitride particles to form a low melting temperature liquid phase which allows liquid phase sintering to occur and densification of the Si3N4. The highest flexural strength was 791(±20) MPa with 12 wt% additives sintered at 1780°C for 2 hours, comparable to the samples prepared by gas pressure sintering. Fracture toughness of all the specimens was higher than 7.2 MPa·m1/2 as the sintering temperature was increased to 1810°C. Thermal conductivity was improved by prolonging the dwelling time and adopting the annealing process. The highest thermal conductivity of 74 W/(m∙K) was achieved with 9 wt% sintering additives sintered at 1810°C with 4 hours holding followed by postannealing. 相似文献
5.
Yuelei Bai Xinxin Qi Xiaodong He Guangping Song Yongting Zheng Bingbing Hao Hang Yin Jin Gao Andrew Ian Duff 《Journal of the American Ceramic Society》2020,103(10):5837-5851
The elastic, magnetic, electrical, and thermodynamic properties of bulk polycrystalline Fe2AlB2 are reported, with further theoretical insights provided through first-principles calculations. DFT simulations, along with an appropriate empirical method to treat magnetic contributions, reproduce well the experimental heat capacity, phonon thermal conductivity, and thermal expansion. The shear, Young's and bulk moduli all decrease linearly from 107.7, 264.5, and 162.4 GPa at 298 K to 91.4, 227.7, and 149.6 GPa at 1273 K, respectively, while the Poisson's ratio shows a weak dependence on temperature, hovering around 0.23-0.26. The mechanical damping, Q−1, is found to be a weak function of temperature up to 973 K, but above this temperature increases sharply, peaking at a specific temperature that becomes higher with increasing resonant frequency. The phonon contribution plays a dominant role in the measured heat capacity from 4.2 to 1000 K, while the magnetic contribution becomes significant around the Curie temperature (301 K). The electronic contribution increases with temperature above 100 K. Furthermore, the standard enthalpy, entropy, and Gibbs free energy are calculated as 16.60 kJ/mol, 92.92 J/(mol·K) and −11.09 kJ/mol, respectively. The thermal conductivity increases linearly with increasing temperature from RT to 1173 K, up to around 13.0 W/(m·K) at 1323 K after hovering at around 7.8 W/(m·K) in the low-temperature range. The electrons play a dominant role in heat conduction, while the phonons contribute only a little to the thermal conductivity. The dilatometric coefficient of thermal expansion of Fe2AlB2 is measured as 13.5 × 10−6 K−1 in the temperature range RT-1348 K. 相似文献
6.
7.
《Ceramics International》2022,48(15):21700-21708
A two-step method, combined with cold isostatic pressing, was used to prepare CeO2-doped ZrP2O7 ceramics, and their microstructure, mechanical properties, thermal conductivities, and dielectric properties were determined. It was found that CeO2 doping could increase the Zr–P and P–O bond lengths, which in turn decreased the thermal conductivity of the ZrP2O7 matrix. Doping with 12 wt% CeO2 simultaneously reduced the sintering temperature and improved the mechanical properties of the ZrP2O7 ceramics, while retaining its low thermal conductivity and good dielectric properties. The maximum cold modulus of rupture of a sample at 1250 °C was 75.91 MPa, which met most conditions for use at room temperature. A COMSOL model was used to predict the thermal conductivity, based on the microstructure, with a relatively high degree of accuracy. The thermal conductivity of the CeO2-doped samples was lower than 1.083 W/(m·K). The dielectric constant was in the range of 5.93–6.52 at 20–40 GHz, and the dielectric loss was less than 4 × 10?3. The ZrP2O7-doped ceramics have potential for application in millimetre wave technology, satellite communication, and vehicle radar fields, because they can meet the high thermal insulation requirements for these applications. 相似文献
8.
《Ceramics International》2023,49(15):24948-24959
Aluminum nitride ceramics were prepared by aqueous gelcasting method and pressureless sintering technique in N2 atmosphere using Y2O3 as sintering additives with nontoxic curdlan as gel system. The solidification mechanism of curdlan was studied. The effects of curdlan content and solid content on the microstructure, relative density and flexural strength of green bodies were investigated. The influences of Y2O3 content and sintering soaking time on the microstructure and properties of sintered bodies were also studied. The results show that, as the temperature increases to 80 °C, the ceramic powders solidify through three-dimensional gel networks of curdlan during gelling process. The green bodies can be successfully fabricated through aqueous gelcasting method with modified powder as original materials. Suitable curdlan content and solid content contribute to fabricating green body with uniform microstructures and high flexural strength. The relative density and flexural strength of sintered bodies enhance as the Y2O3 content and soaking time increase. The flexural strength and thermal conductivity are about 107.5∼172.3 MPa and 75.2∼112.5 W/(m·K), respectively. The sintered body with 4 wt% Y2O3 soaking for 3 h exhibits the highest thermal conductivity because of appropriate relative density, uniform microstructure and reasonable intergranular phase distribution. The mechanical property and thermal conductivity of sintered bodies can be improved by optimizing the gelcasting process parameter, Y2O3 content, and soaking time. The nontoxic gelling system will have wide application for aqueous gelcasting ceramic with complex shape. 相似文献
9.
《Ceramics International》2023,49(5):7861-7870
Glass/ceramic composites applied in the field of low-temperature co-fired ceramics (LTCC) were successfully prepared at 670–710 °C by using waste soda-lime glass (WG) as a binder and natural volcanic ash as a ceramic raw material. Based on the theories of suppression and supplementary network effects, alkaline-earth metal ions (R2+, R = Mg, Ca, Sr, and Ba) and B2O3 were applied to improve the dielectric properties of WG and composites, respectively. The influence of R2+ on the crystal phase evolution, microstructure, mechanical, dielectric, and thermal properties of WG-volcanic ash-based composites were systematically investigated. By doping 2.5 wt% Ba2+ to the environment-friendly LTCC composites, physical properties i.e., εr of 4.86 at 1 MHz, tan δ of 6.32 × 10?3, coefficient of thermal expansion of 8.72 × 10?6/°C, and thermal conductivity of 1.04 W/(m·K) are obtained. It is worth mentioning that the environment-friendly LTCC composite uses WG with a low glass transition temperature to reduce the sintering temperature and a tiny amount of a modifier to adjust the dielectric performance instead of synthesizing specific crystals by adding lots of chemical reagents. These, in turn, do not only have the potential to be used in the LTCC packaging technology but also have significance for sustainable development. Additionally, because of good chemical compatibility between aluminum and the composites, the environment-friendly LTCC composites with ultra-low sintering temperature have the potential ability to lower the cost of LTCC packaging materials. 相似文献
10.
Mingsheng Ma Zhifu Liu Yongxiang Li Yuping Zeng Dongxu Yao 《Journal of the European Ceramic Society》2013,33(4):833-839
The effects of β-Si3N4 whiskers on the thermal conductivity of low-temperature sintered borosilicate glass–AlN composites were systematically investigated. The thermal conductivity of borosilicate glass–AlN ceramic composite was increased from 11.9 to 18.8 W/m K by incorporating 14 vol% β-Si3N4 whiskers, and high flexural strength up to 226 MPa were achieved along with low relative dielectric constant of 6.5 and dielectric loss of 0.16% at 1 MHz. Microstructure characterization and percolation model analysis indicated that thermal percolation network formation in the ceramic composites led to the high thermal conductivity. The crystallization of the borosilicate microcrystal glass also contributed to the enhancement of thermal conductivity. Such ceramic composites with low sintering temperature and high thermal conductivity might be a promising material for electronic packaging applications. 相似文献
11.
《Journal of the European Ceramic Society》2023,43(9):3998-4007
Because they have a high application potential in the thermal management of insulation environments, high-quality hexagonal boron nitride (h-BN)-based multiphase ceramics have been highly desired. However, so far, their synthesis is still full of challenges. Here, a kind of boron nitride nanosheets (BNNSs)/glass (GS) composite ceramics was prepared by a pressureless sintering method at a lower temperature of 900 °C. Due to a tightly bonded interaction between BNNSs and GS, the formed BNNSs/GS ceramics exhibit excellent multifunction performance. They have an outstanding compressive strength in the range of 19 ∼ 64 MPa and Vickers hardness ranging from 50 to 179 HV. For the BNNSs/GS ceramics with BNNS’s filling fraction of 90 wt%, their maximum side-surface TC values are 12.01 ± 0.18 W m−1 K−1 at 25 °C and 13.64 ± 0.37 W m−1 K−1 at 300 °C, respectively. In the ultra-high frequency range of 26.5 ∼ 40 GHz, the dielectric constant values of the BNNSs/GS ceramics are primarily between 2 and 3, and the corresponding loss tangent values are < 0.3. In addition, based on the remarkable integrity of their structure, these BNNSs/GS ceramics exhibit outstanding thermal-shock stability and prominent thermal management capacity during lots of heating/cooling-testing cycles. Therefore, we believe this kind of BNNSs/GS ceramic system will have great application potential in the new-generation thermal management and/or insulation packaging fields. 相似文献
12.
Zhiqiang Feng Xiaohong Liu Jiaming Liu Xi Chen Bifang Chen Liyan Liang 《Polymer Engineering and Science》2023,63(3):932-942
A composite was prepared by in-situ polymerization of liquid crystal epoxy (LCE4) with a low dielectric and high thermal conductivity boron nitride (BN) filler, which the filler (f-BN) was surface-functionalized by γ-glycidoxypropyltrimethoxysilane (KH560) and aminopropylisobutyl polyhedral oligomeric silsesquioxane (NH2-POSS). The surface-functionalized BN was more uniformly dispersed in LCE4, which improved the interfacial compatibility between inorganic and organic phases. Compared with pure LCE4, KH560, and NH2-POSS modified f-BN/LCE4 composites exhibited a higher glass transition temperature, better thermal stability, and higher thermal conductivity. For example, when the f-BN content reached 30 wt%, the energy storage modulus of the composite increased to 2580 MPa, and the glass transition temperature was 103°C. The thermal conductivity of this 30 wt% f-BN composite was 0.48 W m−1 K−1, 128.6% higher than that of pure LCE4. In addition, thermal stability, low hygroscopicity, and dielectric properties of the composites were characterized and analyzed to explore the application prospects of f-BN/LCE4 composites in electronic packaging and in high-performance microelectronic devices. 相似文献
13.
Liangliang Wu Feng Xiang Wenlong Liu Rong Ma Hong Wang 《Ceramics International》2018,44(14):16594-16598
High thermal conductivity and low dielectric constant are the more and more important properties for high-frequency substrate materials to enhance their heat radiation and reduce signal delay. In this work, a series of BN-SiO2 composite ceramics for high frequency application were successfully synthesized by hot-pressing sintering method. And their structures, thermal and dielectric properties were systematically studied. According to the results, the excellent thermal conductivity with low dielectric constant and low dielectric loss has been obtained in the BN-SiO2 ceramic. Compared to the pure SiO2, the sample with 50?wt% BN addition sintered at 1650?℃ exhibited excellent physical properties, including a high thermal conductivity of 6.75?W/m?K which is almost five times higher than that of pure SiO2 and a low dielectric constant of 3.73. The achieved high thermal conductivity and appropriate dielectric property of the BN-SiO2 composite ceramic make it a promising candidate for high-frequency substrate application. 相似文献
14.
《Ceramics International》2022,48(22):33571-33579
The construction of high thermal conductivity polymer composites by the orientation of fillers is of great significance in electronic devices. Herein, a novel strategy to prepare boron nitride-Ni nanoparticles/epoxy resin composites (hmBN-Ni/EP) through the synergistic effect of magnetic field and hot-pressing on the orientation of BN-Ni fillers has been reported. hmBN-Ni/EP composites have better BN orientation in the in-plane direction than other BN-based/EP composites obtained by hot-pressing or magnetic field orientation only. The thermal conductivity of hmBN-Ni/EP reached 2.42 W m?1 K?1 at 30 wt% BN-Ni loading, which was 1145% higher than pure EP. The enhancement of thermal conductivity of hmBN-Ni/EP was attributed to the high in-plane orientation of BN-Ni through the synergistic effect of magnetic field orientation and hot-pressing. Meanwhile, the as-prepared hmBN-Ni/EP composites showed good insulation and mechanical properties which were facilitated to its industrial application in electronic packaging. This work provided a new strategy for better orientation of BN-Based fillers in polymer matrix by combining the magnetic field orientation and hot-pressing. 相似文献
15.
《Ceramics International》2020,46(7):9103-9108
ZrO2 fiberboards with ultra-low densities (0.34–0.40 g/cm3) were fabricated using biomorphic ZrO2 hollow fibers, which have a lower density and better thermal insulation than traditional ZrO2 solid fibers. The effects of sol binder content, sintering temperature, and proportion of solid fibers on the density, microstructure, compressive strength, linear shrinkage, and thermal conductivity of lightweight ZrO2 fiberboards were investigated. The results showed that the hollow features of biomorphic ZrO2 fibers were successfully maintained after they were made into ZrO2 fiberboards, which made them less dense and thermally conductive. The best conditions were found to be a sol binder content of 30 vol%, sintering temperature of 1400 °C, and 20 wt% sintered solid fibers to balance thermal insulation and compressive strength. The results show that the density and thermal conductivity of lightweight ZrO2 fiberboard gives it obvious advantages as a heat-insulating ceramic. Specifically, when the sintering temperature was 1400 °C, the sample had an ultra-low density of 0.34–0.40 g/cm3, a thermal conductivity of 0.101–0.116 W/(m·K) (at 500 °C), a compressive strength of 0.05–0.24 MPa, and a linear shrinkage of 9.4–13%. 相似文献
16.
Carbon nanotube/graphene oxide‐added CaO‐B2O3‐SiO2 glass/Al2O3 composite as substrate for chip‐type supercapacitor
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Tae‐Ho Lee Sung‐Hoon Cho Tae‐Gon Lee Hyo Tae Kim In‐Kyu You Sahn Nahm 《Journal of the American Ceramic Society》2018,101(7):3156-3167
A CaO‐B2O3‐SiO2 (CBS) glass/40 wt% Al2O3 composite sintered at 900°C exhibited a dense microstructure with a low porosity of 0.21%. This composite contained Al2O3 and anorthite phases, but pure glass sintered at 900°C has small quantities of wollastonite and diopside phases. This composite was measured to have a high bending strength of 323 MPa and thermal conductivity of 3.75 W/(mK). The thermal conductivity increased when the composite was annealed at 850°C after sintering at 900°C, because of the increase in the amount of the anorthite phase. 0.25 wt% graphene oxide and 0.75 wt% multi‐wall carbon nanotubes were added to the CBS/40 wt% Al2O3 composite to further enhance the thermal conductivity and bending strength. The specimen sintered at 900°C and subsequently annealed at 850°C exhibited a large bending strength of 420 MPa and thermal conductivity of 5.51 W/(mK), indicating that it would be a highly effective substrate for a chip‐type supercapacitor. 相似文献
17.
《Ceramics International》2017,43(15):12109-12119
In this work, we present novel hexagonal boron nitride (h-BN)/poly(arylene ether nitrile) nanocomposites with high dielectric permittivity and thermal conductivity. For this purpose, the interfacial adhesion and orientation of nanofillers are the two key factors that need to be considered. Firstly, iron oxide was attached onto the surface of h-BN to obtain magnetically responsive property, which would realize the orientation of h-BN by applying an external magnetic field during the preparation process of PEN composites. Secondly, the magnetic h-BN was further modified by mussel-inspired method with dopamine and secondary functional monomer (KH550). It was found that the alignment of h-BN and improvement of interfacial adhesion resulted in the interesting properties of PEN composites. With addition of 30 wt% modified h-BN, the dielectric permittivity of PEN composites was increased from 3.2 of neat PEN to 16.4 (increased by 413%), and the low dielectric loss was remained. Meanwhile, the thermal conductivity was enhanced to 0.662 W/m K (increased by 140%) at the same loading content. In addition, the resulting h-BN/PEN nanocomposites maintained high mechanical strength and thermal stability even the nanofillers loading content reached 30 wt%. Therefore, the dielectric and thermally conductive h-BN/PEN composites with high mechanical strength and thermal stability have big advantages in the area of energy storage devices. 相似文献
18.
《Ceramics International》2020,46(17):27175-27183
The fabrication of silicon nitride (Si3N4) ceramics with a high thermal conductivity was investigated by pressureless sintering at 1800 °C for 4 h in a nitrogen atmosphere with MgO and Y2O3 as sintering additives. The phase compositions, relative densities, microstructures, and thermal conductivities of the obtained Si3N4 ceramics were investigated systemically. It was found that at the optimal MgO/Y2O3 ratio of 3/6, the relative density and thermal conductivity of the obtained Si3N4 ceramic doped with 9 wt% sintering aids reached 98.2% and 71.51 W/(m·K), respectively. EDS element mapping showed the distributions of yttrium, magnesium and oxygen elements. The Si3N4 ceramics containing rod-like grains and grain boundaries were fabricated by focused ion beam technique. TEM observations revealed that magnesium existed as an amorphous phase and that yttrium produced a new secondary phase. 相似文献
19.
Mechanical and dielectric properties of reduced graphene oxide nanosheets/alumina composite ceramics
《Ceramics International》2020,46(12):19731-19737
Reduced graphene oxide (rGO) nanosheets/alumina (Al2O3) composite ceramics were fabricated by hot-pressing sintering. The density, porosity, microhardness, flexural strength and complex permittivity were investigated to study their mechanical and dielectric properties. The results revealed that the rGO nanosheets were uniformly distributed in the Al2O3 matrix and that the composite ceramics were highly dense at 3.67–3.99 g/cm3. Due to low rGO hardness and elevated porosity, the microhardness exhibits a decreasing trend as the rGO content increases. The flexural strength first increased and then decreased with the escalation of rGO content, and the highest strength of 313.75 MPa was obtained at 3 wt%, increasing by 37.61% relative to that of the hot-pressing sintered Al2O3 ceramic. Owing to the enhanced interfacial polarization, dipole polarization, polarization relaxation loss and conductance loss, the real part and imaginary part of complex permittivity increase from 10.40 to 52.73 and from 0.08 to 28.86 as the rGO content rose from 0 wt% to 4 wt%, respectively. 相似文献
20.
《Ceramics International》2017,43(11):8284-8288
The silicon nitride ceramics with a beneficial combination of low dielectric losses and improved physical properties was fabricated by cold isostatic pressing and pressureless sintering. The fine grain microstructure, three-phase composition based on the β-SiAlON, the small amount of the glass phase and relatively small porosity promote a unique combination of a low thermal conductivity 14.51 W m−1 K−1 and low dielectric loss 1.4·10−3. A novel method is proposed to overcome the main drawbacks of the commercial and high-cost technologies. 相似文献