Preparation of high thermal conductivity spherical aluminum nitride fillers by water-based spray granulation
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摘要: 氮化铝（AlN）因具有优异的导热能力和电绝缘性，是热界面材料中导热填料的理想材料。本文首先对AlN粉末进行表面改性，提高了AlN粉体的抗水解能力，然后采用水基溶剂进行喷雾造粒，在浆料配置过程中对球磨时间、添加剂用量等工艺参数进行了优化，制备了球形度高的AlN生坯，最后经脱脂烧结，制备出具有低氧含量、高球形度及高导热性的AlN填料。研究表明，磷酸改性后的AlN粉体在16 h球磨过程中可保持良好的抗水解能力。粘结剂含量（质量分数）对喷雾造粒后的生坯形状有明显影响，采用2%PVB+2%PEG粘结剂制备的粉末具有良好的球形度与表面光滑程度。经过脱脂烧结，AlN陶瓷微球的热导率和抗弯强度分别达到171.2 W·m−1·K−1和340 MPa，具有良好的流动性。综上所述，水基喷雾造粒制备的球形AlN适合用作热界面材料的导热填料。Abstract: Aluminum nitride (AlN) is an ideal material for the thermally conductive fillers in thermal interface materials due to its excellent thermal conductivity and electrical insulation. The surface modification of the AlN powders was firstly carried out to improve the hydrolysis resistance of AlN powders in this paper, then the spray granulation was carried out using the water-based solvents. The process parameters, such as ball milling time and binder dosage, were optimized during the slurry configuration. The AlN spherical fillers with high sphericity were prepared. Finally, the AlN fillers with low oxygen content, high sphericity, and high thermal conductivity were fabricated by debinding and sintering. In the results, the phosphoric acid-modified AlN powders can maintain the good hydrolysis resistance after the ball milling for 16 h. The binder content (mass fraction) has the significant effect on the green shape after the spray granulation. The powders prepared with 2% PVB+2% PEG binders show the good sphericity and surface smoothness. After debinding and sintering, the thermal conductivity and flexural strength of the AlN ceramic microspheres reach 171.2 W·m−1·K−1 and 340 MPa, respectively, showing the good fluidity. In conclusion, the water-based spray granulation is suitable for the preparation of high thermal conductivity spherical aluminum nitride fillers.
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图 1 AlN粉体表面形貌（a）与粒度分布（b）
Figure 1. Surface morphology (a) and particle size distribution (b) of the raw AlN powders
图 2 AlN悬浮液pH值随时间变化规律
Figure 2. Relationship between the pH value of AlN suspension and time
图 3 不同球磨时间下AlN混合浆料氧质量分数变化情况
Figure 3. Relationship between the milling time and oxgen mass fraction of the AlN mixture slurry
图 4 不同研磨时间下600 ℃煅烧后AlN粉末氧质量分数增加值
Figure 4. Increase in the oxgen mass fraction of AlN powders after milling for different time calcining at 600 ℃
图 5 粘结剂对AlN浆料流变性能的影响
Figure 5. Influence of binders on the rheological properties of the AlN slurry
图 6 添加不同含量粘结剂的造粒粉显微形貌：（a）1%PVB+1%PEG；（b）2%PVB+2%PEG；（c）3%PVB+3%PEG
Figure 6. SEM images of the AlN granules added by binders in different content: (a) 1%PVB+1%PEG; (b) 2%PVB+2%PEG; (c) 3%PVB+3%PEG
图 7 选用2%PVA+2%PEG作为雾化造粒添加剂的AlN造粒粒度分布
Figure 7. Particle size distribution of the AlN granules using 2%PVA+2%PEG as binder
图 8 坯体空气中热失重分析曲线（10 ℃·min−1）
Figure 8. Thermogravimetric analysis curves of the green part in air (10 ℃·min−1)
图 10 脱脂烧结后AlN陶瓷微观组织形貌
Figure 10. Microstructure of the AlN ceramic after degreasing sintering
表 1 AlN原料粉末性能
Table 1. Performance of the raw AlN powders
D10 / μm D50 / μm D90 / μm 松装密度 / (g·cm−3) 振实密度/ (g·cm−3) 休止角 / (°) 0.51 1.15 3.53 0.29 0.43 45 
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表 2 选用2%PVA+2%PEG作为雾化造粒添加剂的AlN造粒粉末性能指标
Table 2. Performance of the AlN granules using 2%PVA+2%PEG as binder
D10 / μm D50 / μm D90 / μm 松装密度 / (g·cm−3) 振实密度 / (g·cm−3) 流动性 / (g·s−1) 休止角 / (°) 25.3 52.1 105.4 0.93 1.05 10 34
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表 3 脱脂烧结后AlN陶瓷性能
Table 3. Performance of the AlN ceramic after degreasing sintering
样品 热导率 / (W·m−1·K−1) 抗弯强度 / MPa 维氏硬度，HV0.1 AlN 171.2 340 980
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