CN112573925B - 高性能电磁屏蔽NdB6/SiO2复相陶瓷材料及其制备方法 - Google Patents
高性能电磁屏蔽NdB6/SiO2复相陶瓷材料及其制备方法 Download PDFInfo
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Abstract
本发明涉及电磁屏蔽陶瓷技术领域，具体涉及一种高性能电磁屏蔽NdB6/SiO2复相陶瓷材料及其制备方法。所述的高性能电磁屏蔽NdB6/SiO2复相陶瓷材料的制备方法，先以三氧化二钕和碳化硼为原料，通过高温硼碳热还原反应合成六硼化铌粉末，再以六硼化钕粉末和二氧化硅为原料，经过混合、干燥，经高温热压烧结，制得高性能电磁屏蔽NdB6/SiO2复相陶瓷材料。本发明的高性能电磁屏蔽NdB6/SiO2复相陶瓷材料，既具有低密度、耐高温、耐腐蚀、抗氧化、导电、导热等综合性能，又具有优异的电磁屏蔽性能，应用范围广；本发明还提供其制备方法，原料成本低、工艺过程简单、设备要求低，适合大规模生产。
Description
技术领域
本发明涉及电磁屏蔽陶瓷技术领域，具体涉及一种高性能电磁屏蔽NdB6/SiO2复相陶瓷材料及其制备方法。
背景技术
随着电子通讯和远程控制设备在民用和军事领域的广泛应用，日益加剧电磁干扰不仅对人类的生存环境和人体健康产生影响，还可能影响电磁信号的传输及电子设备的正常工作。为了解决这个问题，必须采用电磁屏蔽材料通过有效吸收/或反射对电磁辐射进行屏蔽，防止电磁的泄露和干扰。传统的电磁屏蔽材料主要是金属材料，由于它们同时具有高磁导率和高介电常数，从而具有优异的电磁屏蔽效能。然而，由于金属材料比重大、耐磨性差和耐腐蚀性差等缺点，限制了它们在电磁屏蔽领域中的广泛应用。此外，金属材料的电磁屏蔽主要是靠反射机制实现的，存在电磁波二次污染的可能性。因此，需要发明不仅具有高电导率实现反射屏蔽还能够通过吸收电磁波实现屏蔽的新型材料，同时要求这类新型材料具有低密度、良好的力学、热学性能和抗腐蚀性能。
为了获得性能良好的电磁屏蔽效果，目前已开发了各种电磁屏蔽材料。文献1(Colloids Surf.A.571(2019)110–124)报道了Ni基电磁屏蔽涂层材料的制备及性能，文献2(Carbon 45 (2007)821–827)报道了碳基复合材料的电磁屏蔽性能，文献3(Adv.Mater.26(2014)5480–5487) 报道了纳米碳管增强树脂电磁屏蔽材料的制备和性能，文献4(Compos.Sci.Technol.159(2018) 240–250)报道了用铁氧体基电磁屏蔽材料的制备和性能，文献5(ACS Nano 14(2020) 5008–5016)报道了用二维迈克烯(MXene)作为电磁屏蔽材料的制备方法，文献6(J.Electron. Mater.25(1996)930–934)报道了用金属镍丝增强树脂复合材料作为电磁屏蔽材料的制备方法和性能。然而，上述材料存在高温或腐蚀环境中稳定性差，加工制备工艺复杂，原料成本高等缺点，因此，需要设计和寻找新的低密度、耐高温、抗氧化、耐腐蚀、导电、导热的新型电磁屏蔽材料。
六硼化钕(NdB6)陶瓷具有高熔点、低密度、抗氧化、耐腐蚀、导电、导热和反铁磁性等优异的综合性能，是非常具有潜力的电磁屏蔽材料。文献7(Handbook of AdvancedCeramics and Composites,Springer,Cham,2019,pp.1-36)报道指出，由于六硼化钕(NdB6)的自扩散系数低，需要采用高温、高压的方法制备六硼化铌(NdB6)陶瓷。纯的六硼化钕(NdB6)陶瓷需要用高温热压烧结或放电等离子烧结等方法制备，制备温度高、成本高，并且电磁屏蔽性能不理想。
发明内容
本发明要解决的技术问题是提供一种高性能电磁屏蔽NdB6/SiO2复相陶瓷材料，既具有低密度、耐高温、耐腐蚀、抗氧化、导电、导热等综合性能，又具有优异的电磁屏蔽性能，应用范围广；本发明还提供其制备方法，其原料成本低、工艺过程简单、设备要求低，适合大规模生产。
本发明所述的高性能电磁屏蔽NdB6/SiO2复相陶瓷材料的制备方法，先以三氧化二钕 (Nd2O3)和碳化硼(B4C)为原料，通过高温硼碳热还原反应合成六硼化铌(NdB6)粉末，再以六硼化钕(NdB6)粉末和二氧化硅(SiO2)为原料，经过混合、干燥，经高温热压烧结，制得高性能电磁屏蔽NdB6/SiO2复相陶瓷材料。
具体地，所述的高性能电磁屏蔽NdB6/SiO2复相陶瓷材料的制备方法，包括以下步骤：
(1)合成六硼化钕(NdB6)粉体：将三氧化二钕(Nb2O3)和碳化硼(B4C)采用湿法混合后，进行真空干燥，然后通过高温硼碳热还原反应，合成六硼化钕(NdB6)粉体；
(2)制备NdB6/SiO2复相陶瓷：将六硼化钕(NdB6)和二氧化硅(SiO2)粉末采用湿法混合后，进行真空干燥，然后经高温热压烧结，制得高性能电磁屏蔽NdB6/SiO2复相陶瓷材料。
步骤(1)中，三氧化二钕(Nb2O3)和碳化硼(B4C)的摩尔比为Nb2O5:B4C＝1:3.1-3.4。
其中，三氧化二钕(Nd2O3)的纯度≥99.9wt％，粒度为1-5μm；碳化硼(B4C)的纯度≥98wt％，粒度为50-70μm。
步骤(1)中，湿法混合条件为：以玛瑙球和无水乙醇为混合介质，转速为80-150r/min，混合时间为8-24h。
步骤(1)中，真空干燥温度为25-50℃，干燥时间为8-48h。
步骤(1)中，高温硼碳热还原反应的气氛为真空，真空度为0.001-1Pa，反应温度为1400-1700℃，升温速率为10-20℃/min，反应时间为1-4h。在低真空度下，可降低反应温度。
步骤(2)中，以重量比计，NdB6/SiO2复相陶瓷的成分组成为NdB6:SiO2＝85-98:15-2。增加SiO2含量有利于降低烧结温度和保温时间，但同时会降低电导率，影响电磁屏蔽性能。
步骤(2)中，湿法混合条件为：以玛瑙球和无水乙醇为混合介质，转速为80-150r/min，混合时间为8-24h。
步骤(2)中，真空干燥温度为25-50℃，干燥时间为8-48h。
步骤(2)中，高温热压烧结的条件为：烧结温度1400-1650℃，压力20-30MPa，保温时间0.5-2h。
本发明所述的高性能电磁屏蔽NdB6/SiO2复相陶瓷材料，采用上述的制备方法制备得到。
本发明制备的高性能电磁屏蔽NdB6/SiO2复相陶瓷材料，既具有低密度、耐高温、耐腐蚀、抗氧化、导电、导热等综合性能又具有优异的电磁屏蔽性能，应用范围广，可以作为电磁屏蔽材料在5G手机、高性能计算机、高温微波通讯设备、银行密室、航空、航天、核工业、医疗设备的控制等领域应用。
本发明采用原位高温硼碳热还原反应制备六硼化铌(NdB6)粉体，当三氧化二钕(Nd2O3) 和碳化硼(B4C)的摩尔比为Nd2O3∶B4C＝1∶3.1-3.4混合时，加热过程中硼碳热还原反应如方程式(1)所示：
Nd2O3+3B4C＝2NdB6+3CO (1)
反应自由能随温度和一氧化碳(CO)分压的变化如图1所示，从图1可以看出，随着一氧化碳(CO)分压的降低，反应温度逐渐降低，因此，在低真空即低一氧化碳(CO)分压下可以用较低的温度合成六硼化钕(NdB6)粉体。
Nd2O3和B4C混合无加热反应过程中样品的重量变化、重量变化率如图2所示，从图2可以看出，在600℃之前有两个失重峰，温度分别是270℃和386℃，对应的是Nd2O3的水化产物Nd(OH)3逐步分解成NdOOH和Nd2O3。高温区分别在1304℃和1365℃有两个吸热峰，对应的是硼碳热还原反应的中间产物Nd2CO5和NdBO3的还原：
Nd2CO5(s)＝Nd2O3(s)+CO2(g) (2)
4NdBO3+5B4C+7C＝4NdB6+12CO(g) (3)
上述反应(2)和反应(3)的失重分别是11.6％和28.7％，所以1365℃的失重率明显的比1304℃大。基于图2的热分析结果，三氧化二钕(Nd2O3)和碳化硼(B4C)合成六硼化钕(NdB6) 的反应可以表示为：
4Nd2O3(s)+7B4C(s)＝4NdB6(s)+4NdBO3(s)+7C(s) (4)
4NdBO3(s)+7C(s)+5B4C(s)＝4NdB6(s)+12CO(g) (5)
为了验证上述反应过程，将三氧化二钕(Nd2O3)和碳化硼(B4C)的摩尔比按 Nd2O3∶B4C＝1∶3.1混合、干燥、加热，X-射线分析表明硼碳热还原反应的产物与反应(1)-(5) 描述的一致，如图3所示。
本发明利用原位高温硼碳热还原反应制备六硼化钕(NdB6)粉体，关键是控制原料的比例、硼碳热还原反应的温度和CO分压，使得硼碳热还原反应在较低的温度进行。具体方法是适当增加B4C的含量，即将三氧化二钕(Nd2O3)和碳化硼(B4C)的摩尔比控制在 Nd2O3∶B4C＝1∶3.1-3.4的范围，同时通过控制真空度降低CO的分压，使硼碳热还原反应能在较低的温度进行。
本发明采用粘滞流度热压烧结的方法制备NdB6/SiO2复相陶瓷材料，其原理是二氧化硅 (SiO2)在高温发生软化，促进热压烧结，特别是在1550℃二氧化硅(SiO2)的粘度迅速降低，使高温热压可以在较低的温度进行，降低烧结温度，避免晶粒长大。采用粘滞流度热压烧结方法制备的NdB6/SiO2复相陶瓷与高温放电等离子烧结方法制备得到的NdB6/SiO2复相陶瓷相比，样品的晶粒明显减小、晶粒尺寸仅仅是高温放电等离子烧结方法制备得到的材料的四分之一左右，此外，还具有成分容易控制、致密度高、气孔率低、电导率高、电磁屏蔽性能好等特点。
与现有技术相比，本发明有以下有益效果：
(1)本发明从三氧化二钕(Nd2O3)和碳化硼(B4C)原料出发，经过高温硼碳热还原反应制备六硼化钕(NdB6)粉末，然后通过高温粘滞流度热压烧结的方法制备NdB6/SiO2复相陶瓷材料，将六硼化钕(NdB6)与二氧化硅(SiO2)有机结合，既通过二氧化硅(SiO2)的粘滞流动降低材料的制备温度，又降低了材料的密度，同时提高电磁屏蔽性能，且原料成本低、工艺过程简单、设备要求低，适合大规模生产；
(2)本发明的设备要求低，粉末反应条件和块体材料制备条件温和，工艺过程简单，制备的NdB6/SiO2复相陶瓷晶粒尺寸小、气孔率低、二氧化硅(SiO2)分布均匀、材料的电导率高，制备的NdB6/SiO2复相陶瓷材料具有优异的电磁屏蔽性能；
(3)本发明的NdB6/SiO2复相陶瓷材料应用范围广，可以作为通讯设备、医疗器械、银行系统主机以及航天、航空、核工业控制设备的电磁屏蔽材料应用。
附图说明
图1是以三氧化二钕(Nd2O3)和碳化硼(B4C)原料按反应式(1)硼碳热还原反应合成六硼化钕(NdB6)粉末的自由能变化(ΔG)随温度和CO分压的变化图；
图2是以三氧化二钕(Nd2O3)和碳化硼(B4C)原料合成六硼化钕(NdB6)粉末，当原料比例为Nd2O3:B4C＝1:3.1时加热过程中的热重(TG)和热重变化速率(DTG)曲线；
图3是以三氧化二钕(Nd2O3)和碳化硼(B4C)原料合成六硼化钕(NdB6)粉末，当原料比例 Nd2O3:B4C＝1:3.1时加热过程中的物相变化的X-射线衍射谱；
图4是实施例1制备的NdB6/SiO2复相陶瓷的显微结构和晶粒尺寸(b、d、f)与对比例1制备的NdB6/SiO2复相陶瓷的显微结构和晶粒尺寸(a、c、e)对比；
图5是实施例3制备的NdB6/SiO2复相陶瓷(b)与对比例1制备的NdB6/SiO2复相陶瓷(a)的电磁屏蔽性能对比。
具体实施方式
下面结合实施例详述本发明。
实施例1
(1)合成六硼化钕(NdB6)粉末：将原料三氧化二钕(Nd2O3)和碳化硼(B4C)按照摩尔比 Nd2O3:B4C＝1:3.1称重，置于玛瑙混料罐中，以玛瑙球和无水乙醇为介质在混料机上混合，混料机的转速为80r/min，混合时间为24h；然后将混合均匀的原料置于真空烘箱中进行干燥处理，干燥温度为30℃，干燥时间为48h；将干燥后的三氧化二钕(Nd2O3)和碳化硼(B4C)粉末置于石墨坩埚中，放入高温真空炉中，以15℃/min的速率加热到1650℃，常压下保温1h，进行硼碳热还原反应合成六硼化钕(NdB6)粉末，其平均颗粒尺寸为2.25μm。
(2)制备NdB6/SiO2复相陶瓷：将六硼化钕(NdB6)粉和二氧化硅(SiO2)粉按照重量比 NdB6:SiO2＝95:5称重，以玛瑙球和无水乙醇为混合介质，转速为90r/min，混合时间为24h，经50℃、8h干燥后，置入石墨模具中，然后加热到1550℃，在25MPa下热压烧结保温1h，制备得到NdB6/SiO2复相陶瓷材料，其显微结构如图4(b、d、f)所示。
实施例2
(1)合成六硼化钕(NdB6)粉末：将原料三氧化二钕(Nd2O3)和碳化硼(B4C)按照摩尔比 Nd2O3:B4C＝1:3.2称重，置于玛瑙混料罐中，以玛瑙球和无水乙醇为介质在混料机上混合，混料机的转速为100r/min，混合时间为12h；然后将混合均匀的原料置于真空烘箱中进行干燥处理，干燥温度为50℃，干燥时间为10h；将干燥后的三氧化二铌(Nd2O3)和碳化硼(B4C) 粉末置于石墨坩埚中，放入高温真空炉中，以15℃/min的速率加热到1550℃，真空度1Pa 下保温2h，进行硼碳热还原反应合成六硼化钕(NdB6)粉末，其平均颗粒尺寸为1.86μm。
(2)制备NdB6/SiO2复相陶瓷：将六硼化钕(NdB6)粉和二氧化硅(SiO2)粉按照重量比 NdB6:SiO2＝90:10称重，以玛瑙球和无水乙醇为混合介质，转速为100r/min，混合时间为12h，经50℃、12h干燥后，置入石墨模具中，然后加热到1600℃，在20MPa下热压烧结保温1h，制备得到NdB6/SiO2复相陶瓷材料。
实施例3
(1)合成六硼化钕(NdB6)粉末：将原料三氧化二钕(Nd2O3)和碳化硼(B4C)按照摩尔比 Nd2O3:B4C＝1:3.3称重，置于玛瑙混料罐中，以玛瑙球和无水乙醇为介质在混料机上混合，混料机的转速为120r/min，混合时间为15h；然后将混合均匀的原料置于真空烘箱中进行干燥处理，干燥温度为45℃，干燥时间为12h；将干燥后的三氧化二铌(Nd2O3)和碳化硼(B4C) 粉末置于石墨坩埚中，放入高温真空炉中，以10℃/min的速率加热到1500℃，真空度0.1Pa 下保温3h，进行硼碳热还原反应合成六硼化钕(NdB6)粉末，其平均颗粒尺寸为1.45μm。
(2)制备NdB6/SiO2复相陶瓷：将六硼化钕(NdB6)粉和二氧化硅(SiO2)粉按照重量比NdB6:SiO2＝94:6称重，以玛瑙球和无水乙醇为混合介质，转速为120r/min，混合时间为15h，经45℃、15h干燥后，置入石墨模具中，然后加热到1550℃，在30MPa下热压烧结保温0.5h，制备得到NdB6/SiO2复相陶瓷材料，其在18-27GHz范围内的屏蔽效率如图5(b)所示。
对比例1
(1)合成六硼化钕(NdB6)粉末：将原料三氧化二钕(Nd2O3)和碳化硼(B4C)按照摩尔比 Nd2O3:B4C＝1:3.3称重，置于玛瑙混料罐中，以玛瑙球和无水乙醇为介质在混料机上混合，混料机的转速为120r/min，混合时间为15h；然后将混合均匀的原料置于真空烘箱中进行干燥处理，干燥温度为45℃，干燥时间为12h；将干燥后的三氧化二铌(Nd2O3)和碳化硼(B4C) 粉末置于石墨坩埚中，放入高温真空炉中，以10℃/min的速率加热到1500℃，真空度0.1Pa 下保温3h，进行硼碳热还原反应合成六硼化钕(NdB6)粉末，其平均颗粒尺寸为1.45μm。
(2)制备NdB6/SiO2复相陶瓷：将六硼化钕(NdB6)粉和二氧化硅(SiO2)粉按照重量比 NdB6:SiO2＝94:6称重，以玛瑙球和无水乙醇为混合介质，转速为150r/min，混合时间为10h，经40℃、15h干燥后，置入高强钢模具中，经100MPa干压成型后获得六硼化钕(NdB6)/二氧化硅(SiO2)复相陶瓷生坯，将生坯放入真空碳管炉中，然后加热到1680℃，保温3h，制备得到的NdB6/SiO2复相陶瓷材料。
对比例2
(1)合成六硼化钕(NdB6)粉末：将原料三氧化二钕(Nd2O3)和碳化硼(B4C)按照摩尔比 Nd2O3:B4C＝1:3.3称重，置于玛瑙混料罐中，以玛瑙球和无水乙醇为介质在混料机上混合，混料机的转速为120r/min，混合时间为15h；然后将混合均匀的原料置于真空烘箱中进行干燥处理，干燥温度为45℃，干燥时间为12h；将干燥后的三氧化二铌(Nd2O3)和碳化硼(B4C) 粉末置于石墨坩埚中，放入高温真空炉中，以10℃/min的速率加热到1500℃，真空度0.1Pa 下保温3h，进行硼碳热还原反应合成六硼化钕(NdB6)粉末，其平均颗粒尺寸为1.45μm。
(2)制备NdB6/SiO2复相陶瓷：将六硼化钕(NdB6)粉和二氧化硅(SiO2)粉按照重量比 NdB6:SiO2＝94:6称重，以玛瑙球和无水乙醇为混合介质，转速为150r/min，混合时间为10h，经40℃、15h干燥后，置入石墨模具中，然后以100℃/分钟的速率加热到1900℃，在30MPa 下放电等离子烧结保温20min，制备得到NdB6/SiO2复相陶瓷材料，由于放电等离子烧结温度高，造成SiO2在放电等离子烧结过程中流出，制备得到的NdB6/SiO2复相陶瓷材料中剩余 SiO2的含量为3.4％。其显微结构如图4(a、c、e)所示，在18-27GHz范围内的屏蔽效率如图5(a)所示。
将实施例1-4和对比例1制备的NdB6/SiO2复相陶瓷材料进行性能测试，其中电导率采用北京精仪的BEST-300C四探针电阻仪测试，热导率采用德过耐驰的LFA467激光热导仪测试，强度和断裂韧性用美国MTS-CriterioC45.105电子万能试验机测试，硬度用上海泰明的 HXD-2000TMC硬度计测试，电磁屏蔽性能用美国安捷伦公司的Agilent N5244A网络矢量仪测试，样品尺寸为11.0mm×4.0mm×3.0mm，获得的散射参数S转化成总电磁屏蔽效率(SET), 吸收损耗(SEA)和反射损耗(SER)。
测试结果如表1和图5所示。
表1实施例1-4和对比例1制备的NdB6/SiO2复相陶瓷材料的性能指标
结合表1和图4可以看出，本发明采用粘滞流度热压烧结方法制备的NdB6/SiO2复相陶瓷材料和对比例1采用高温放电等离子烧结制备的NdB6/SiO2复相陶瓷材料相比，致密度相当但晶粒尺寸明显减小，平均晶粒尺寸为3.87μm(远低于对比例1的13.28μm)；结合表1和图5可以看出，本发明采用粘滞流度热压烧结方法制备的NdB6/SiO2复相陶瓷材料和对比例1采用高温放电等离子烧结制备的NdB6/SiO2复相陶瓷材料相比，在18-27GHz范围内的屏蔽效率大大提高。
Claims (3)
1.一种高性能电磁屏蔽NdB6/SiO2复相陶瓷材料的制备方法，其特征在于：包括以下步骤：
（1）合成六硼化钕粉体：将三氧化二钕和碳化硼采用湿法混合后，进行真空干燥，然后通过高温硼碳热还原反应，合成六硼化钕粉体；
（2）制备NdB6/SiO2复相陶瓷：将六硼化钕和二氧化硅粉末采用湿法混合后，进行真空干燥，然后经高温热压烧结，制得高性能电磁屏蔽NdB6/SiO2复相陶瓷材料；
步骤（1）中，三氧化二钕和碳化硼的摩尔比为Nd2O3:B4C=1:3.1-3.4；
步骤（1）中，三氧化二钕的纯度≥99.9wt%，粒度为1-5μm；碳化硼的纯度≥98wt%，粒度为50-70μm；
步骤（1）中，高温硼碳热还原反应的气氛为真空，真空度为0.001-1Pa，反应温度为1400-1700℃，升温速率为10-20℃/min，反应时间为1-4h；
步骤（2）中，高温热压烧结的条件为：烧结温度1400-1650℃，压力20-30MPa，保温时间0.5-2h；
步骤（1）和步骤（2）中，真空干燥温度均为25-50℃，干燥时间均为8-48h；
步骤（2）中，以重量比计，NdB6/SiO2复相陶瓷的成分组成为NdB6:SiO2=85-98:15-2。
2.根据权利要求1所述的高性能电磁屏蔽NdB6/SiO2复相陶瓷材料的制备方法，其特征在于：步骤（1）和步骤（2）中，湿法混合条件均为：以玛瑙球和无水乙醇为混合介质，转速为80-150r/min，混合时间为8-24h。
3.一种根据权利要求1或2所述的制备方法制备得到的高性能电磁屏蔽NdB6/SiO2复相陶瓷材料。
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