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1.
AlN-Cu metal matrix composites containing AlN volume fractions between 0.1 and 0.5 were fabricated firstly by liquid phase sintering of AlN using Y2O3 as a sintering aid and then by hot pressing the powder mixtures of sintered AlN and Cu at 1050°C with a pressure of 40 MPa under flowing nitrogen. With Y2O3 additions of 1.5 to 10 wt%, the densification of AlN could be achieved by liquid phase sintering at 1900°C for 3 h and subsequently slow cooling. The sintered AlN showed a maximum thermal conductivity of 166 W/m/K at a Y2O3 level of 6 wt%. Dense AlN-Cu composites with AlN contents up to 40 vol% were achieved by hot pressing. The thermal conductivity and the coefficient of the thermal expansion (CTE) of the composites decreased with increasing AlN volume fractions, giving typical values of 235 W/m/K and 12.6 × 10–6/K at an AlN content of 40 vol%. 相似文献
2.
Chemical reactions to increase thermal conductivity by decreasing oxygen contents during AlN sintering with an Y2O3 additive in a reducing nitrogen atmosphere with carbon were investigated. They were: Al2O3 + N2 + 3CO ⇋ 2AlN + 3CO2, Al2Y4O9 + N2 + 3CO ⇋ 2AlN + 2Y2O3 + 3CO2 and Y2O3 + N2 + 3CO ⇋ 2YN + 3CO2. Some of the CO2 gas reduced to CO gas in the presence of carbon by a chemical reaction: CO2 + C ⇋ 2CO. These reactions were confirmed by examining oxygen contents, the grain boundary phases of the sintered AlN, and
the trapped CO and CO2 gases in the sintered bodies. These reducing reactions proceed with increasing sintering temperature and periods, and hence
the thermal conductivity is increased. 相似文献
3.
Rapid sintering of Yb2O3-added AlN was performed by applying the 28 GHz millimeter-wave heating method. It was found that full densification over 97%T.D. was attained by sintering at 1600°C for 20 min. The densification temperature was decreased by about 300°C, compared with those in the conventional method by an electric furnace. A high thermal conductivity over 180 W/(m · K) was obtained in the sample sintered at 1700°C for 40 min, even under non-reducing atmosphere. The main factor resulting in the rapid and low temperature sintering was attributed to efficient selective absorption of the millimeter-wave into Yb2O3 additive. 相似文献
4.
The effects of Y2O3 content, sintering time, sintering temperature, sintering pressure on thermal conductivity of AlN ceramics had been studied. X-ray diffraction (XRD), scanning electron microscope (SEM), laser conductometer and laser granularity dimension analysis measurer were respectively used to measure the phases, microstructure, thermal conductivity and particle size distribution of the samples. These studies reveal that the Y2O3 is an effective sintering addtive, and the best conditions of sintering are that the pressure is 5.15× 109 Pa, the temperature is 1700∘C and the sintering time is 115 min. Under these conditions, the sintered body has reasonable structure and its thermal conductivity is 200 w/(m⋅k). 相似文献
5.
《Materials Science & Technology》2013,29(2):513-517
AbstractDense aluminium nitride ceramics were prepared by spark plasma sintering at a lower sintering temperature of 1700°C with Y2O3, Sm2O3 and Dy2O3 as sintering additives respectively. The effects of three kinds of sintering additives on the phase composition, microstructure and thermal conductivity of AlN ceramics were investigated. The results showed that those sintering additives not only facilitated the densification via the liquid phase sintering mechanism, but also improved thermal conductivity by decreasing oxygen impurity. Sm2O3 could effectively improve thermal conductivity of AlN ceramics compared with Y2O3 and Dy2O3. Observation by scanning electron microscopy showed that AlN ceramics prepared by spark plasma sintering method manifested quite homogeneous microstructures, but AlN grain sizes and shapes and location of secondary phases varied with the sintering additives. The thermal conductivity of AlN ceramics was mainly affected by the additives through their effects on the growth of AlN grain and the location of secondary phases. 相似文献
6.
Instead of Y2O3 powders, yittrium isopropoxide (YIP) was used as a sintering additive to sinter high thermal conductivity polycrystalline aluminum nitride (AlN). The reasons for using sintering additive in sol-gel form are due to the fact that the particle sizes are uniform in the nano scale and also they promote a better coating of AlN grains, being more effective during sintering process. The binder burn out was carried in two different atmospheres, N2 (N2 BBO) and air (air BBO). The thermal conductivity of dense polycrystalline aluminum nitride samples with the addition of Y2O3 (YIP formulation) ranging from 1.0 to 10.0 wt% with N2 BBO and air BBO was measured by the laser-flash technique. The results of measured thermal conductivity exhibited higher values than those reported for samples of same yttria formulation (Y2O3 powder) and sintered conditions. 相似文献
7.
CaO-Y2O3添加剂对AlN陶瓷显微结构及性能的影响 总被引:4,自引:0,他引:4
研究了掺杂CaO-Y2O3热压烧结和常压烧结AlN陶瓷的性能和显微结构.结果表明:热压烧结AlN陶瓷的第二相为Y3Al5O12,常压烧结AlN陶瓷的第二相为Y3Al5O12和Ca3Y2O6;热压烧结AlN的第二相体积百分数和晶格氧含量均低于常压烧结;热压烧结AlN陶瓷的微观结构良好,其热导率达到200W/m·K. 相似文献
8.
Spark plasma sintering (SPS) is a newly developed technique that enables poorly sinterable aluminum nitride (AlN) powder to be fully densified. It is addressed that pure AlN sintered by SPS has relatively low thermal conductivity. In this work, SPS of AlN ceramic was carried out with Y2O3, Sm2O3 and Li2O as sintering aids. Effects of additives on AlN densification, microstructure and properties were investigated. Addition of sintering aids accelerated the densification, lowered AlN sintering temperature and was advantageous to improve properties of AlN ceramic. Thermal conductivity and strength were found to be greatly improved with the present of Sm2O3 as sintering additive, with a thermal conductivity value about 131 Wm−1K−1 and bending strength about 330 MPa for the 2 wt% Sm2O3-doped AlN sample SPS at 1,780 °C for 5 min. XRD measurement revealed that additives had no obvious effect on the AlN lattice parameters. Observation by SEM showed that AlN ceramics prepared by SPS method manifested quite homogeneous microstructure. However, AlN grain sizes and shapes, location of secondary phases varied with the additives. The thermal conductivity of AlN ceramics was mainly affected by the additives through their effects on the growth of AlN grain and the location of liquid phases. 相似文献
9.
F. Y. C. Boey L. Sun X. Song K. A. Khor 《Journal of Materials Science: Materials in Electronics》1999,10(5-6):455-459
Increasing demand for higher performance dielectric material for multi-layer ceramics packaging has led to the use of the AlN system due to its very high thermal conductivity and coefficient of expansion compatibility with silicon. This paper reports on a novel process method used to produce an AlN/Al2O3 composite powder system which can be subsequently tape cast as a dielectric substrate. The mixture of both Al2O3 and AlN was first mechanically alloyed and then spray-dried to obtain a suitable agglomerated powder that was subsequently plasma-sprayed, resulting in a fine micrometer level integrated composite powder. The two main criteria used to ascertain the optimal process parameters during plasma spraying were a high gamma/alpha Al2O3 phase ratio, which ensured that all the Al2O3 phase had melted during plasma spraying, and a minimal reduction in the AlN/Al2O3 ratio to ensure minimal change in the AlN during processing. For the plasma-sprayed composite powders, fully sintered ceramic tapes were produced attaining>99.0% of the theoretical density after sintering at 1650°C for 6 h, which yielded a thermal conductivity value of 32.0 W m–1 K–1. 相似文献
10.
AlN and graphite disks were successfully joined using a polymer plasticized ceramic tape as the interlayer by spark plasma sintering (SPS). The tape contains either composite powders of AlN and graphite or AlN powders without graphite. Both tapes contained 5 mass% Y2O3 as the sintering aid of AlN. The joining was carried out at 1700–1900 °C and 30 MPa for 5 min. No other reaction phase except for Al2Y4O9 was identified in the joints. The maximum tensile strength of the joints was obtained when the AlN–graphite composite interlayer tape was used. The joining mechanism is attributed not to the chemical bonding, but to the physical bonding of the Al2Y4O9 phase, which is solidified from the molten Al–Y–O squeezing into the porous graphite under pressure during SPS. 相似文献
11.
R. Fu K. Chen S. Agathopoulos M. C. Ferro D. U. Tulyaganov J. M. F. Ferreira 《Journal of Materials Science》2005,40(9-10):2425-2429
In the process of low-temperature sintering of AlN ceramics, the reaction of the sintering aids YF3 and CaF2 with superficial Al2O3, inherently contained in AlN lattice, results in formation of liquid phase. Nevertheless, the uniformly dispersed liquid phase is prone to migrate from the bulk to the surface of the samples, opposing densification. The analysis of the experimental results indicates that fresh liquid phase can continuously arrive from the bulk to the surface due to chemical reactions and crystallization which occur at the surface as well as wettalibilty and capillarity phenomena. The surface is depleted of liquid phase since the latter is consumed due crystallization and carbothermal reduction reactions with the elements of the atmosphere of the furnace N2 and C, resulting in formation of a dense layer of crystals of Al2Y4O9, CaYAl3O7 and Y2O3, grown perpendicularly to the surface. The chemical and structural features of this newly formed crystalline surface layer generate a significant difference of the wetting regimes and the capillary forces between the surface and the bulk, favouring pumping of the liquid from the bulk to the surface. 相似文献
12.
Yi-Quan Wu Yu-Feng Zhang Xiao-Xian Huang Bao-Shun Li Jing-Kun Guo 《Journal of Materials Science》2001,36(17):4195-4199
Al2O3/25 vol% LaAl11O18 composites were prepared by pressureless sintering at 1550°C with composite powders obtained by copercipiated method using La(NO3) · 6H2O and Al(NO3)3 · 9H2O as starting materials. The enhanced reactive activity of Al2O3 and chemically homogeneous mixing of the constituents made LaAl11O18 phase to be formed at low temperature in composite powders. AlF3 additive was used to reduce the transformation temperature of transition alumina. The LaAl11O18 grains in the composite powder obtained at 1500°C showed rodlike morphology distributed homogeneously in Al2O3 powder. The samples sintered at 1550°C for 4 h with CAS (CaO-Al2O3-SiO2) sintering aid can obtain a high relative density. The effects of the sintering time on the grain growth of Al2O3 and the fracture toughness of the composites were studied and the results showed that LaAl11O18 grains reduced the growth of Al2O3 grains and the rodlike grains increased the fracture toughness. The improvement in fracture toughness of the composites was mainly attributed to the mechanism of crack deflection. 相似文献
13.
The thermal conductivity of β- and α-BaB2O4 single crystals has been measured at temperatures from 50 to 300 K by a steady-state axial flow technique. The 300-K thermal
conductivity of the β-polymorph along and across its c axis is 1.64 ± 0.08 and 1.24 ± 0.06 W/(m K), respectively, and that of the α-polymorph along its c axis is 1.65 ± 0.08 W/(m K). Swirls and twin boundaries have an insignificant effect on the thermal conductivity of α-BaB2O4 crystals. The heat capacity of α-BaB2O4 measured in the range 56–300 K using adiabatic calorimetry differs little from that of the β-polymorph. 相似文献
14.
《Advanced Powder Technology》2014,25(1):450-456
Y-doped ultrafine AlN powders were synthesized by a carbothermal reduction nitridation (CRN) route from precursors of Al2O3, C and Y2O3 prepared by a sol–gel low temperature combustion technology. The Y dopant reacted with alumina and thus forming yttrium aluminate of AlYO3, Al3Y5O12 and Al2Y4O9, which formed a liquid at about 1400 °C and promoted the transformation of Al2O3 to AlN and the growth of AlN particles. Compared with the conventional solid CRN process, Y dopant reduced the synthesis temperature by 150 °C, and Al2O3 transformed to AlN completely at 1450 °C. The content of Y dopant had little effect on the synthesis temperature of AlN whereas it influenced the phase of Y compounds in the products. As the Y/Al molar ratio was in the range of 0.007648–0.022944, the particle sizes of Y-doped AlN powders synthesized at 1450 °C were 150–300 nm. 相似文献
15.
Fine-grained and transparent polycrystalline ruby ceramics (Cr2O3-doped Al2O3) were successfully prepared by spark plasma sintering (SPS). The effect of Cr2O3 concentration on the grain size, hardness, fracture toughness and thermal conductivity of ruby ceramics was investigated systematically. For 0.05 wt.% Cr2O3, high in-line transmittance of 85% at 2000 nm can be reached, further increase of Cr2O3 concentration leads to the decrease in transmittance. High hardness of 23.95-25.05 GPa can be achieved due to the fine grain size in all ruby ceramics. The fracture toughness of 1.9-2.29 MPa m1/2 indicates that no improvement in fracture toughness over pure Al2O3 can be obtained by Cr2O3 doping in these submicron grained ruby ceramics. High thermal conductivity of 28-29.8 W/(m K) at room temperature, close to that of single crystal sapphire, can be achieved. The change in grain size for different Cr2O3 concentrations is the major reason for the change in mechanical and thermal properties, but not for the change in optical properties. 相似文献
16.
WEI-GUO MIAO YIN WU HE-PING ZHOU 《Journal of Materials Science: Materials in Electronics》1997,8(4):233-238
A process for low temperature co-fired AlN multilayer substrates is introduced. Some key factors about this technology are
delineated and discussed. A two-step burnout process may solve the contradiction between tungsten oxidation and carbon removal.
Sintering with additives appears to improve densification at low temperature. DyN was found as a second phase in AlN ceramics,
which suggests that Dy2O3 efficiently removes oxygen from the AlN lattice. The microstructure of AlN ceramics is ideal for achieving high thermal conductivity.
Analysis of the AlN-W interface showed there were no second phases, but there was probably an intricate interlocking structure
between the grains of tungsten and AlN. Co-firing at 1650°C for 4 h produced an AlN multilayer substrate with a thermal conductivity
of up to 130 W m−1 K−1.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Photothermal reflectance microscopy was applied to the analysis of local thermal diffusivity on tape-cast AlN ceramics. The materials were obtained from three different commercial powders, two sintering temperatures (1750 and 1800 °C), and 3 wt % Y2O3 sintering aid. Owing to the high spatial resolution of the technique (30 m in the present case), measurements in different positions on the sample surface were carried out. In this way a study of the homogeneity of thermal properties was performed. 相似文献
18.
《Materials Letters》2005,59(19-20):2601-2604
Porous sialon ceramics have been cost-effectively prepared by pressureless sintering from a mixture of elongated SHS β-sialon powders with an α-sialon precursor composition composed of α-Si3N4, AlN, Y2O3 and Al2O3. The obtained porous sialon ceramics exhibited low shrinkage and homogeneous pore size distribution. The results of X-ray diffraction and scanning electron microscopy showed that a uniform microstructure with elongated and intermingled β-SiAlON grains, which were strongly connected by α-SiAlON phase, has been obtained. 相似文献
19.
W. A. Groen P. F. Van Hal M. J. Kraan N. Sweegers G. De With 《Journal of Materials Science》1995,30(19):4775-4780
The synthesis of Al28C6O21N6 powder (ALCON), starting from the binary compounds is described. The powder is resistant to oxidation in air up to 760°C. From the prepared powder, fully dense ceramics have successfully been prepared using hot pressing. The as-prepared ceramics had a thermal conductivity of 20 W m–1 K–1. Experiments showed that it is also possible to prepare ALCON ceramics by reactive hot-pressing, starting from Al2O3, AlN and Al4C3. Further optimization is expected to raise the thermal conductivity significantly. The strength, about 300 MPa, is similar to that of AlN. The thermal expansion coefficient of 4.8 × 10–6K–1 closely matches that of silicon, making application of ALCON ceramics as heat sinks an interesting possibility. 相似文献
20.
The influence of the molar ratio of Al2O3 to Y2O3 (i.e. MAl2O3/MY2O3) on sintering densification, microstructure and the mechanical properties of a SiC–Al2O3–Y2O3 ceramic composite were studied. It was shown that the optimal value of MAl2O3/MY2O3 was 3/2, not 5/3, which is customarily considered the optimal molar ratio for the formation of YAG (Y3Al5O12) phase. When MAl2O3/MY2O3 is 5/3, materials existed in two phases of YAG and very little YAM phases. The sintering mechanism of the solid phase occurred at 1850 °C. When MAl2O3/MY2O3 was 3/2, materials existed in the two phases YAG (Y3Al5O12) and YAM (Y4Al2O9). The formation of the low melting point eutectic liquid phase (YAG + YAM) increased sintering densification. Flexure strength, hardness and relative density were all higher. 相似文献