Li等[11]用化学镀法在聚苯乙烯(PS)微球表面沉积镍金属，制备出具有核壳结构的磁性镍微球Ni@MWCNTs，调控镍壳层的厚度可优化其吸波性能。微球镍壳厚度为45 nm的Ni-2@MWCNTs杂化体，在11.20 GHz频率处的最小反射损耗为-40.65 dB，RL < -10 dB的带宽为3.6 GHz。Gao等[12]用共沉淀法合成了球形Gd-Co铁氧体纳米颗粒，用聚合原硅酸四乙酯和葡萄糖依次包覆二氧化硅层和碳层，制备出具有三层核壳结构的Gd-Co ferrite@silica@carbon复合材料。厚度为2.5 mm的这种材料，在频率为9.93 GHz处吸波性能优异，最小反射损耗达到-46.85 dB，有效吸收带宽(Efficient absorption bandwidth, EAB)覆盖3.14 GHz。本文用电弧法制备Ni-TiN异质结构纳米颗粒，在其表面包覆高介电损耗的氮掺杂碳壳层制备具有多重异质结构的Ni-TiN@CN纳米复合材料，研究Ni-TiN异质核中Ni金属掺入量对Ni-TiN@CN纳米复合材料吸波性能的影响并揭示其机制。
1 实验方法
1.1 Ni-TiN纳米粉体和Ni-TiN@CN纳米复合材料的制备
实验用原料：纯度为99.99%的Ni金属棒和Ti金属棒。用直流电弧等离子体设备将质量分数分别为50%、40%、30%、20%和0的Ni和Ti金属原料熔炼，得到5种NiTi合金。阳极为NiTi合金，阴极为钨针。在电弧舱的真空度稍低于6.5 Pa时在舱体中通入15 kPa的氮气、5 kPa氢气和20 kPa氩气，然后点弧。电弧过程中的电流为90 A，电压为20~25 V，电弧时间为30 min。粉体沉降，通入40 kPa的氩气，然后静置钝化12 h，得到不同Ni金属含量的一系列黑色Ni-TiN纳米粉体。
用多巴胺自聚合热解法在Ni-TiN纳米粉体表面包覆氮掺杂碳层：在250 mL去离子水中加入300 mg三羟甲基氨基甲烷(Tris)、200 mg盐酸多巴胺和200 mg Ni-TiN纳米粉体，将其超声分散后置于35 ℃恒温水浴锅中机械搅拌8 h进行多巴胺自聚合反应。多巴胺自聚合反应完成后对液体进行离心分离，将产物用去离子水和无水乙醇交替充分洗涤(3次)，得到前驱体Ni-TiN@PDA。
将前驱体放入50 ℃真空干燥箱中干燥12 h，然后将干燥粉体置入管式炉中。在800 ℃流动氩气气氛中热处理2 h后得到Ni-TiN@CN纳米复合材料。制备流程如图1所示。为了研究Ni金属对粉体吸波性能的影响，Ni金属占总金属质量分数分别为50%，40%，30%，20%和0。其他条件不变，将所得纳米粉体分别记为：NTCN-1、NTCN-2、NTCN-3、NTCN-4和TCN。
图1
图1
Ni-TiN@CN纳米复合材料的制备流程
Fig.1
Schematic diagram of the Ni-TiN@CN nanocomposites
1.2 性能表征
用型号为D/Max 2200的X射线衍射仪(XRD)分析样品的晶体结构。用Jobin Yvon LabRam HR800型Raman光谱仪测试样品在100~2000 cm-1范围内的Raman光谱。用型号为Thermo Scientific K-Alpha的 X射线光电子能谱仪(XPS)测试样品表面的化学元素组成状态。用型号为Zeiss Ultra Plus的扫描电子显微镜(SEM)拍摄样品表面的形貌，用型号为JEOL-2010的透射电子显微镜(TEM)观察样品的形貌和微观结构。用型号为Agilent E5071C矢量网络分析仪(VNA)测试Ni-TiN@CN-石蜡复合物的电磁参数和电磁吸波性能。
2 结果和讨论
2.1 核壳结构Ni-TiN@CN纳米复合材料的结构和物相
图2a给出了纳米复合材料的XRD谱，在5个样品的谱中衍射角2θ分别为36.6°、42.6°、61.8°、74.0°和78.0°处的衍射峰，分别对应面心立方TiN的(111)、(200)、(220)、(311)和(222)晶面[13,14]。随着Ti金属在阳极合金中占比的降低，TiN的5个特征衍射峰的峰值强度逐渐降低。在NTCN-1~NTCN-4四个样品的XRD谱中2θ分别为44.6°、51.9°和76.6°处出现了Ni(111)、(200)和(220)晶面的衍射峰，表明Ni金属进入NTCN系列纳米复合材料[15]。同时，Ni特征衍射峰的强度随着Ni金属含量的提高而增强。同时，加入Ni金属元素制备的4个样品在27.5°也出现了衍射峰，对应g-C3N4的(002)晶面的层间堆积峰，表明存在外包CN层且结晶度较高[16,17]。
图2
图2
TCN、NTCN-1、NTCN-2、NTCN-3和NTCN-4纳米复合材料的XRD谱和Raman光谱
Fig. 2
XRD patterns (a) and Raman spectra (b) of TCN, NTCN-1, NTCN-2, NTCN-3 and NTCN-4 nanocomposites
图2b给出了5种样品的Raman光谱，在谱中100~750 cm-1均出现了非计量TiN x 的特征峰，分别位于156、208、400和600 cm-1，且其强度随着Ti元素含量的降低而减弱。无缺陷的面心立方TiN晶体不存在一阶Raman散射，因此Raman谱峰的出现也证实用直流电弧等离子体法制备的粉体均为非计量TiN x，其内部有缺陷[18]。同时，Raman光谱谱中1350和1580 cm-1处的两个特征峰分别对应石墨碳的D带和G带，证实外包层为石墨碳层。石墨碳的D带与石墨碳中的缺陷相关，表征了石墨碳的无序化程度，而G带则与材料中有序石墨碳结构相关[19]。为了评估纳米复合材料中石墨碳的有序和无序程度，计算了Raman光谱中石墨碳的D带与G带的峰强之比(ID/IG)。5个样品的ID/IG峰强比值分别为0.99、0.92、0.94、0.95和0.90，表明随着Ni金属含量的提高外包覆C层的无序度有所波动。
图3a、e给出了TiN@CN和Ni-TiN@CN样品的XPS全谱，可见TiN@CN样品表面主要由Ti、N、C和O四种元素组成，而Ni-TiN@CN样品表面主要由Ti、Ni、N、C和O五种元素组成。图3b、f分别给出了两种样品的Ti 2p高分辨光电子能谱，其中拟合曲线峰位于455.68，458.87，461.39和464.57 eV，都对应非化学计量TiN x，证明TiN内部有缺陷，这也是用电弧制备的TiN基纳米复合材料具有吸波性能的主要原因之一[20]。此外，位于457.07 eV的拟合峰对应Ti-N键，证明样品中有少量的面心立方TiN。而位于462.78 eV的拟合峰对应Ti-O键，表明样品轻度氧化。
图3
图3
TCN和NTCN-3纳米复合材料的X射线光电子能谱
Fig.3
XPS spectra of TCN (a-d) and NTCN-3 (e-i) nanocomposites (a, e) survey, (b, f) Ti 2p, (c, g) N 1s, (d, h) C 1s, (i) Ni 2p
图3c、g分别给出了两种样品的N 1s高分辨光电子能谱，其中位于396.44 eV的拟合曲线峰对应Ti-N键，而位于397.66，399.04和401.10 eV的3个拟合峰则分别对应吡啶氮、吡咯氮和石墨氮。这表明，样品的外壳层是多巴胺热解后形成的氮掺杂石墨碳壳层，因掺杂N也出现缺陷[21]。图3d、h分别给出了两种样品的C 1s高分辨光电子能谱，结合能为284.83、286.23和288.72 eV的拟合峰分别对应C-C、C-N和C=N键。这也表明，N原子已经掺杂进入了纳米复合材料外表所包覆的石墨碳层中，并且外包的氮掺杂碳层来源于聚多巴胺的热解[22]。图3i给出了Ni-TiN@CN样品的Ni 2p高分辨光电子能谱，表明其表面的Ni元素主要以Ni单质和微氧化的Ni离子形式存在。此外，位于861.68和879.92 eV的两个拟合峰分别对应Ni元素的卫星峰[23]。
2.2 纳米复合材料的微观结构
图4
图4
纳米复合材料的SEM照片
Fig.4
SEM images of nanocomposites (a) TCN, (b) NTCN-1, (c) NTCN-2, (d) NTCN-3, (e) NTCN-4
图5给出了TCN和NTCN-3样品的TEM和HRTEM图像。从图5a可以看出，TiN@CN样品中TiN的形态是清晰的立方体，根据HRTEM图中还能测出其内核的晶面间距为0.215 nm，与面心立方TiN的(200)晶面对应。从对应的元素分布图像也可看出，TiN@CN中有Ti、C、N三种元素，表明TiN颗粒包覆了氮掺杂碳的外壳。图5b给出了NTCN-3样品的TEM照片，可确认样品的核芯是表面附着了镍球的面心立方Ni-TiN纳米颗粒，外层是CN壳层。根据HRTEM图测出晶面间距分别为0.216和0.218 nm，分别对应面心立方TiN的(200)晶面和Ni的(002)晶面，也证实内核有Ni和面心立方TiN。另外，对比两种样品TiN的晶面间距发现，加入Ni金属使TiN的晶面间距增大了0.001 nm，原因是Ni原子进入面心立方TiN的晶格导致TiN的晶格膨胀[24]。其原因是，在电弧形核过程中Ni原子和TiN纳米颗粒之间产生了复杂的相互作用，使Ni原子替代了晶格中不同位点的原子。这种原子替代在NTCN系列样品中产生了缺陷并改变局域电子的分布，从而提高了纳米复合材料的电磁吸波性。图5c给出了TCN样品的前驱体TiN的TEM图像，可见用直流电弧等离子体法制备的TiN纳米颗粒是边缘清晰的立方体。图5d给出了NTCN-3样品的前驱体Ni-TiN纳米颗粒的TEM照片，可见在立方体TiN纳米颗粒外表面的半球形Ni原子。这表明，在用直流电弧法制备过程中Ni进入TiN晶格中生成了Ni-TiN纳米复合材料的异质核。
图5
图5
样品的TEM和HRTEM照片
Fig.5
TEM images and HRTEM images of the samples (a) TCN, (b) NTCN-3, (c) TiN, (d) Ni-TiN
2.3 电磁参数和吸波性能
为了研究Ni金属的加入对Ni-TiN@CN纳米复合材料电磁性能的影响，在2~18 GHz频率范围测试了5种样品的电磁参数(复介电常数和复磁导率)，并根据传输线理论模拟计算了纳米复合材料的电磁吸波性能。复介电常数和复磁导率的实部(ε′和µ′)分别表征材料对电场能和磁场能的储存，而虚部(ε″和µ″)则分别表征材料对电场能和磁场能的损耗[25]。
图6
图6
纳米复合材料的复介电常数与频率的关系
Fig.6
Complex permittivity versus frequency for nanocomposites (a) real part of relative complex permittivity, (b) imaginary part of the relative complex permittivity
为了研究磁性元素Ni的加入对Ni-TiN@CN异质结构纳米复合材料磁性能的影响，画出了磁导率随频率变化的曲线，如图7所示。从图7可以看出，TCN样品有一定的磁存储性能[28]，加入磁性金属Ni使NTCN复合材料的磁导率实部弛豫峰发生改变，在8、12.6和16.2 GHz三个频率出现弛豫峰，源于Ni金属产生了复杂的磁相互作用；在外加电磁场的作用下Ni和TiN之间产生了界面耦合和磁矩重排，从而改变了体系的磁弛豫行为。图7b中TCN样品的磁导率虚部出现了负值，是纳米TiN材料的高导电性和氮掺杂碳的高导电性碳石墨网络所致。与TCN样品相比，4个NTCN纳米复合材料的磁导率虚部均提高并出现了相似的磁损耗性能和多重磁共振，且在3~4 GHz、11~12 GHz和16.5~17.5 GHz频率范围出现了明显的共振弛豫峰。对比3个共振弛豫峰的位置发现，随着Ni金属的添加共振峰向高频方向移动。其原因是，Ni金属的添加使磁晶各向异性增强，导致磁化强度提高和磁矩偏转时能量耗散增大[29]。NTCN纳米复合材料的磁损耗源于自然共振、交换共振以及涡流损耗。在1~18 GHz范围内，频率为3~4 GHz的共振峰归因于NTCN纳米复合材料的自然共振。其余两处出现的共振峰源于交换共振和涡流损耗。Ni-TiN@CN纳米复合材料的磁损耗源于磁性Ni纳米粒子的加入、非化学计量TiN x 的弱磁性以及材料的结构缺陷产生的局部磁有序。介电常数和磁导率的变化趋势表明，改变Ni金属的加入量可调控异质NTCN纳米复合材料的电磁性能。
图7
图7
纳米复合材料的磁导率与频率的关系
Fig.7
Complex permeability versus frequency for nanocomposites (a) real part of relative complex permeability, (b) imaginary part of the relative complex permeability
为了研究Ni含量对Ni-TiN@CN纳米复合材料吸波性能的影响，根据传输线理论
模拟计算了样品的反射损耗[30]
其中Zin为输入阻抗，Zo为自由空间的阻抗，f为电磁波频率，d为匹配厚度，c为电磁波在自由空间的速度，µr和εr分别为材料的复磁导率和复介电常数。
图8
如图8a~c所示，TCN样品在频率为3.95 GHz处的反射损耗最小(-29.90 dB)，但是对应的涂层厚度较大(为5.2 mm)。与TCN样品相比，NTCN-1、NTCN-2、NTCN-3和NTCN-4四个样品的微波吸收特性优异。如图8d~f所示，匹配厚度为2.3 mm的样品NTCN-1的最小反射损耗达到了-39.8 dB。对应厚度为2.3 mm时，其有效吸收带宽为4.94 GHz(7.01~11.95 GHz)。在选定的厚度范围内，综合有效吸收带宽约为14.5 GHz。这个结果表明，NTCN-1的微波吸收性能良好和阻抗匹配厚度较小。在图8g~i中，NTCN-2样品在厚度0.8 mm处的反射损耗低于-10 dB，有效吸收带宽为4.23 GHz，覆盖范围为13.09~17.32 GHz。在选定的厚度范围内，其综合有效吸带宽度约为14.7 GHz。与NTCN-1样品对比，虽然NTCN-2样品的最佳反射损耗数值减小，但是有效吸收带宽略有增加且匹配厚度较小。NTCN-3的微波吸收性能比NTCN-1和NTCN-2的更好。从图8j~l可见，NTCN-3样品的吸波性能优异，在频率为6.78 GHz处匹配厚度为2.5 mm时最小反射损耗达到了-48.97 dB。厚度为0.8 mm时，其有效吸收带宽为3.52 GHz (12.89~16.41 GHz)。值得注意的是，NTCN-3低于-20 dB的吸收宽度覆盖了4.87~7.63 GHz和10.44~12.67 GHz。NTCN-4样品的最小反射损耗降低和有效吸波带宽减小。从图8m~o可见，NTCN-4样品涂层厚度为1.2 mm时最佳反射损耗值为-31.37 dB，对应频率为10.2 GHz；而厚度为1.3 mm时，其有效吸收带宽为3.48 GHz (7.95~11.43 GHz)。上述结果表明，加入适量的Ni金属可在复合材料内部形成多重异质结构，从而使纳米复合材料的电磁吸波性能显著提高。但是，引入过量的Ni金属反而使NTCN材料的吸波性能降低。因此，必须控制Ni金属的加入量以优化Ni-TiN@CN纳米复合材料吸波性能。
2.4 损耗机制、衰减常数和阻抗匹配
分析了NTCN纳米复合材料的介电损耗和磁损耗特性以研究引入磁性Ni金属的影响。在微波频段，介电损耗主要来源于极化损耗和电导损耗。基于Debye驰豫理论，在电磁波作用下纳米复合材料发生极化驰豫，介电常数实部ε′和虚部ε″的关系为[32]
其中εs为静态介电常数，ε∞ 为光频介电常数。5种纳米复合材料的Cole-Cole曲线如图9所示。可以看出，5个样品的曲线中有多个Cole-Cole半圆。这意味着，在外加电磁波作用下样品发生了多个极化弛豫过程。曲线不是非标准的半圆而是近似半圆的曲线，证明样品的极化弛豫为非理想的极化弛豫[33]。从图9a可见，TCN样品中的Cole-Cole半圆曲线数量较少(2个)且杂乱和交叠。引入Ni金属的4个NTCN样品均呈现清晰的半圆形状(4个)，如图9b~e所示。这表明，NTCN样品的极化弛豫过程比TCN样品的多。对比图9b~e可见，添加磁性元素Ni制备的4种样品其Cole-Cole曲线图也包含多个不规则半圆，证明也存在多个极化弛豫过程。极化弛豫，源于纳米复合材料内由缺陷引入的偶极子极化和多异质界面产生的界面极化等。此外，添加磁性元素Ni的4种样品的Cole-Cole半圆半径明显增加，表明Ni的加入使复合材料内出现了多个异质界面，如：Ni-TiN, Ni-CN, TiN-CN及CN-CN等。在异质界面处出现的电荷堆积产生了大量电偶极子，增强了界面处的电子和偶极子的极化弛豫过程，使纳米复合材料的极化弛豫损耗显著增强，提高了其对电磁波的衰减性能[34]。因此，弛豫过程的增加源于NTCN纳米复合材料内由氮掺杂碳引入的缺陷偶极子极化、Ni-TiN@CN中多重异质界面产生的界面极化以及Ni-TiN@CN中本征偶极子的极化等。
图9
图9
纳米复合材料的Cole-Cole半圆
Fig.9
Cole-Cole semicircles plots for the nanocomposites (a) TCN, (b) NTCN-1, (c) NTCN-2, (d) NTCN-3, (e) NTCN-4
曲线的尾部均表现为长尾直线的形式，意味着在电磁波作用下样品内部存在显著的电导损失[35]。随着Ni金属含量的提高，从NTCN-4至NTCN-1样品的Cole-Cole半圆中尾部直线的长度逐渐减小，表明电导损耗逐渐降低[36]。4个NTCN样品的电导损失源于TiN的高导电性、磁性金属元素Ni的引入以及外包覆的氮掺杂碳壳层等在样品中形成的密集连续的导电网络，为电子提供了更多的迁移和跳跃路径而使电磁波衰减。此外，纳米复合材料中的非计量TiN x 中的空位缺陷、立方体TiN表面附着的Ni原子以及纳米胶囊表面的氮掺杂碳层引入的缺陷导致C结构变形，都作为材料的跳跃中心在微波范围内产生介电弛豫损耗。这表明，NTCN-3样品的多重极化损耗以及合适的电导损耗能力的协调产生了良好的介电损耗性能。
除了介电弛豫损耗，纳米复合材料的磁损耗也对吸波性能有重要的影响。在2~18 GHz频段范围，磁损耗主要源于涡流损耗和铁磁共振(自然共振和交换共振)。涡流损耗可用涡流损耗系数[37]
表示，其中μ0为真空中的磁导率，σ为材料的电导率，d为材料的厚度。
图10a给出了涡流损耗系数C0随频率的变化。在12~18 GHz，涡流损耗系数为0.01~0.05，表明磁损耗以涡流损耗为主。在2~8 GHz，随着Ni金属掺入量的增加涡流损耗系数先增大后减小。低频率的磁损耗主要源于自然共振，是NTCN纳米复合材料中的磁性颗粒在外加电磁场的作用下高速磁旋转产生的能量损耗。Ni-TiN@CN纳米复合材料的磁损耗，主要归因于磁性元素Ni掺入核壳材料的核中构建了多重异质结构，发生了自然共振而使其磁损耗提高。
图10
图10
纳米复合材料的C0曲线和衰减系数
Fig.10
C0 curves (a) and the attenuation constant (b) for the nanocomposites
为了进一步明确NTCN纳米复合材料强反射损耗的来源，可计算其衰减系数[38]
如图10b所示，TCN和NTCN复合纳米材料的衰减系数相近，表明其对电磁波的衰减能力相近。加入磁性元素Ni后，衰减系数α随着Ni金属质量的增加呈先增大后减小的趋势。在2~18 GHz内NTCN-3样品的衰减系数均最大，表明其强反射损耗源于强衰减系数。
除了衰减系数，阻抗匹配特性也是表征材料吸波性能的重要参数。良好的阻抗匹配意味着，在交界面处绝大部分电磁波都能进入吸波材料内部。可用|Δ|函数[19]
表征材料的阻抗匹配性能。其中f为电磁波频率，d为吸波材料的匹配厚度。
其中δe为介电损耗角，δm为磁损耗角。
本文用|Δ|≤ 0.4作为判断样品阻抗匹配性能良好的标准，并定义样品的有效阻抗匹配面积(|Δ|≤ 0.4)与总面积之比为β。根据计算结果，画出了|Δ|函数的二维分布图并计算了各样品的匹配比β值，如图11所示。TCN样品的β值为45.48%，NTCN-4样品的β值为43.31%，NTCN-3样品在2~10 GHz频率范围内的阻抗匹配较好，其匹配β值达到了66.25%。随着Ni元素含量的提高，阻抗匹配性能明显降低。结果表明，NTCN-3样品的衰减能力较强和阻抗匹配最佳。
图11
图11
纳米复合材料的阻抗匹配
Fig.11
Impedance matching of the nanocomposites (a) TCN, (b) NTCN-1, (c) NTCN-2, (d) NTCN-3, (e) NTCN-4
随着匹配厚度的增大Ni-TiN@CN样品的最小反射损耗峰向低频方向移动，对此可根据四分之一波长理论解释。事实上，除了材料介质本身的介电损耗和磁损耗，自身结构满足特定几何尺寸的Ni-TiN@CN，也通过多重反射和散射对电磁波产生结构损耗，使入射电磁波在吸收剂表面就被反射的概率大大降低。为了验证这一点，根据
模拟计算了NTCN-3样品的匹配厚度和匹配频率，结果如图12所示。式中取n等于1。图中的上半部分为样品的实际厚度，下半部分则是基于理论计算出的匹配厚度。从图12可见，在选定的厚度下tm(以绿星标记)几乎均位于λ/4理论曲线处，表明最小反射损耗对应的实际厚度与理论计算的厚度在大多数情况下一致。结果表明，Ni-TiN@CN最佳吸收峰符合λ/4匹配模型，其内部确实发生了干涉相消现象。这说明，磁性金属Ni的加入使NTCN材料内形成了一种多级结构。这种结构为电磁波传递提供多级通道，显著提高了入射电磁波在材料内的多重反射和散射的可能性，延长了电磁波与材料相互作用的时间，增强了Ni-TiN@CN对电磁波的吸收。
图12
图12
NTCN-3的最小反射损耗对应的频率位点与λ/4曲线的关系
Fig.12
The frequency versus λ/4 curves for the minimum reflection loss of NTCN-3
上述结果表明，磁性金属Ni的加入使NTCN材料内部构建了异质结构、丰富了磁损耗和介电损耗的作用机制和优化了材料的阻抗匹配能力，实现了良好的吸波特性。电介质损耗和磁损耗的协同均衡是使Ni-TiN@CN复合材料具有高效微波吸收性能的关键因素，其优异的微波吸收性能可归因于：(1)异质结构形成的三维导电网络提供了显著的电导损耗；(2) 丰富的多异质界面引入诱导的界面极化，产生明显的极化弛豫损耗；(3) 磁性Ni纳米粒子及非化学计量TiN x 引入的磁损耗；(4) 优化的阻抗匹配及出色的电磁波衰减能力。
3 结论
(1) 将直流电弧等离子体法与多巴胺原位自聚合热解法结合可制备具有核壳结构的Ni-TiN@CN纳米复合材料，在TiN中掺入适量的Ni金属构建的Ni-TiN@CN多重异质结构，可调控纳米复合材料吸波性能。
(2) Ni-TiN@CN纳米复合材料的内核为TiN立方体表面附着了Ni球，外壳为氮掺杂碳层，尺寸为30~200 nm。
(3) Ni金属质量占比为30%的纳米复合材料NTCN-3电磁吸波性能最佳。磁性元素的引入、多重异质结构的构建使Ni-TiN@CN材料具有丰富的界面极化、缺陷偶极子极化、增强的电导损耗和优异的磁损耗性能。
(4) Ni-TiN@CN纳米复合材料具有优化的阻抗匹配特性和高的衰减系数。多重损耗机制的协调作用，使Ni-TiN@CN纳米复合材料的电磁波吸收性能优异。
参考文献
Efficient ferrite/Co/porous carbon microwave absorbing material based on ferrite@metal-organic framework
[J].
Radiation damage on SiPMs for space applications
[J].
Chromosomal damage, gene expression and alternative transcription in human lymphocytes exposed to mixed ionizing radiation as encountered in space
[J].
Astronauts travelling in space will be exposed to mixed beams of particle radiation and photons. Exposure limits that correspond to defined cancer risk are calculated by multiplying absorbed doses by a radiation-type specific quality factor that reflects the biological effectiveness of the particle without considering possible interaction with photons. We have shown previously that alpha radiation and X-rays may interact resulting in synergistic DNA damage responses in human peripheral blood lymphocytes but the level of intra-individual variability was high. In order to assess the variability and validate the synergism, blood from two male donors was drawn at 9 time points during 3 seasons of the year and exposed to 0-2 Gy of X-rays, alpha particles or 1:1 mixture of both (half the dose each). DNA damage response was quantified by chromosomal aberrations and by mRNA levels of 3 radiation-responsive genes FDXR, CDKN1A and MDM2 measured 24 h post exposure. The quality of response in terms of differential expression of alternative transcripts was assessed by using two primer pairs per gene. A consistently higher than expected effect of mixed beams was found in both donors for chromosomal aberrations and gene expression with some seasonal variability for the latter. No synergy was detected for alternative transcription.© 2024. The Author(s).
Effects of Ce Zn co-substitution on structure, magnetic and microwave absorption properties of nickel ferrite nanoparticles
[J].
Tunable magnetic coupling and dipole polarization of core-shell Magnéli Ti4O7 ceramic/magnetic metal possessing broadband microwave absorption properties
[J].
Energy absorption performances of silicon carbide particles during microwave heating process
[J].
A superior microwave absorption material: Ni2+-Zr4+ Co-Doped barium ferrite ceramics with large reflection loss and broad bandwidth
[J].
Enhancing absorption dominated microwave shielding in Co@C-PVDF nanocomposites through improved magnetization and graphitization of the Co@C-nanoparticles
[J].Using composites of polyvinylidene fluoride (PVDF) and carbon nanostructures embedded with Co-nanoparticles we demonstrate that electromagnetic shielding effectiveness depends strongly on the graphitic carbon concentration and the magnetic properties of Co-particles. Cobalt nanoparticles encapsulated by graphitic carbon embedded in an amorphous carbon-matrix were synthesized by a one-pot pyrolysis method at two different synthesis temperatures, TS = 800 °C (Co-800) and 1000 °C (Co-1000). We demonstrate that TS plays an important role in determining the structure, morphology and magnetic properties of the carbonaceous matrix, the graphite layer and the Co nanoparticles. Higher amounts of graphitic carbon and high saturation magnetization were observed for the Co-1000 sample than that for the Co-800 sample. We observed that the electromagnetic interference (EMI) shielding behavior of the PVDF-Co-1000 nanocomposite shows higher shielding effectiveness than that of the PVDF-Co-800 specimen. A more inhomogeneous dielectric medium in the PVDF-Co-1000 composite results in higher dielectric loss and impedance mismatch. A direct correlation between the shielding effectiveness with dielectric permittivity and magnetic permeability is demonstrated. The synergy between the multiple reflections at the interfaces and absorption of the microwave radiation in the conducting species confirms that a higher degree of graphitization and highly magnetic particles in nanocomposites are effectively superior for EMI shielding of microwave radiation.
One-step fabrication of N-doped CNTs encapsulating M nanoparticles (M = Fe, Co, Ni) for efficient microwave absorption
[J].
An investigation on the microwave absorption properties of Co-Al-Ti substituted barium hexaferrite-MWCNT nanocomposites
[J].
Effect of nickel shell thickness of Ni-microsphere on microwave absorption properties of Ni-microsphere@MWCNTs hybrids
[J].
Preparation and microwave absorption properties of Gd-Co ferrite@silica@carbon multilayer core-shell structure composites
[J].
TiN-based materials for multispectral electromagnetic wave absorption
[J].
Facile preparation and properties of cubic TiN@CN nanocapsules as electrode materials for supercapacitors and as microwave absorbers
[J].
Effect of pulse current density on microstructure and wear property of Ni-TiN nanocoatings deposited via pulse electrodeposition
[J].
Preparation of phosphorus-doped graphitic carbon nitride and its application in lithium-sulfur batteries
[J].
磷掺杂石墨相氮化碳的制备及其在锂硫电池中的应用
[J].
Fabrication of TiN/Carbon nanofibers by electrospinning and their electromagnetic wave absorption properties
[J].
Raman scattering investigation of nanocrystalline δ-TiN x synthesized by solid-state reaction
[J].
Bimetallic MOF@wood-derived hierarchical porous carbon composites for efficient microwave absorption
[J].
A complete and self-consistent evaluation of XPS spectra of TiN
[J].
Tailoring of N-doped graphite coated cobalt nanoparticles via arc discharge enables the high microwave absorption
[J].
Co@N-doped double-shell hollow carbon via self-templating-polymerization strategy for microwave absorption
[J].
LiO x -modification of Ni and Co3O4 surfaces: an XPS, LEIS and LEED study
[J].
Structure and properties of TiAlLaN films deposited at various bias voltages
[J].
Hollow beaded Fe3C/N-doped carbon fibers toward broadband microwave absorption
[J].
Tailoring conductive network nanostructures of ZIF-derived cobalt-decorated N-doped graphene/carbon nanotubes for microwave absorption applications
[J].
Preparation and microwave absorption properties of NiCo@C(N)/NC nanocomposites
[J].Nanocomposites NiCo@C(N)/NC were fabricated by a two-step method, that is, NiCo@C(N) nanocapsules were first prepared by arc-discharge technique, next dopamine (DA) was self-polymerized on NiCo@C(N) surface, which then were subjected to post-heat treatment. The study focuses on the effect of the dopamine content on the microwave absorption performance of the nanocomposites. The acquired nanocomposites NiCo@C(N)/NC were characterized by means of X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and vector network analyzer in terms of their phase composition, microstructure, and electromagnetic properties etc. The results show that the NiCo@C(N)/NC nanocomposites possess excellent wave-absorbing properties when the mass ratio of NiCo@C(N) to DA is 1∶2. Accordingly, the optimal reflection loss is -38.87 dB at a thickness of 3.17 mm and a frequency of 6.61 GHz. It achieves an effective absorption bandwidth of 4.93 GHz when the coating is matched to a thickness of 1.67 mm. The NiCo@C(N)/NC nanocomposites exhibit excellent wave absorbing performance due to the heterogeneous structure of N-doped carbon, defective induced dipole polarization, and the formation of a conductive network, all of which contribute to its high dielectric loss capability. Also, the appropriate amount of N-doped graphitic carbon can effectively improve the electromagnetic synergy effect between the NiCo core and the nitrogen-doped carbon double-shell, thus optimize the impedance matching of the nanocomposites.
NiCo@C(N)/NC纳米复合物的制备及其吸波性能
[J].采用电弧放电法和多巴胺原位自聚合热解法制备NiCo@C(N)/NC纳米复合物，使用X射线衍射、拉曼光谱、X射线电子能谱、透射电子显微镜和矢量网络分析仪等手段表征其物相组成、微观结构和电磁特性，研究了多巴胺含量对这种纳米复合物吸波性能的影响。结果表明，NiCo@C(N)与多巴胺质量比为1∶2的NiCo@C(N)/NC纳米复合物具有优异的吸波性能，在厚度为3.17 mm、频率6.61 GHz时其最佳反射损耗达到-38.87 dB。NiCo@C(N)/NC纳米复合物的匹配厚度为1.67 mm时，其有效吸收带宽达到4.93 GHz。NiCo@C(N)/NC纳米复合物的优异吸波性能，主要源于其双壳层氮掺杂碳构成的异质结构多界面极化、缺陷偶极子极化及形成的导电网络增强了介电响应能力。同时，适量的N掺杂石墨碳含量能调制纳米复合物的电磁参数，改善NiCo核和氮掺杂碳双壳层的电磁损耗协同作用和优化纳米复合物的阻抗匹配。
Room-temperature ferromagnetism evolution in nanostructured titanium nitride superconductors—the influence of structural defects
[J].
The research on electromagnetic wave absorption performances of multi-shell nickel matrix composites
[D].
多壳层镍基复合材料的电磁波吸收性能研究
[D].
Anionic MOF derived Bimetallic Ni x Co y @Nano-porous carbon composites toward strong and efficient electromagnetic wave absorption
[J].
Controlled fabrication of ramie plant derived magnetic helical/chiral porous carbon fibers (Ni@CNTs@HPCFs) for highly efficient microwave absorption performance and EAB across a broad temperature range
[J].
Bead-like cobalt nanoparticles coated with dielectric SiO2 and carbon shells for high-performance microwave absorber
[J].
High-temperature oxidation-resistant ZrN0.4B0.6/SiC nanohybrid for enhanced microwave absorption
[J].
Microstructure design of magnetic-dielectric MCHS@Co@CNTs composites with tunable conductive loss for high-performance microwave absorption
[J].
Microwave absorption performance of encapsulated magnetic particles with Nitrogen-doped Carbon nanotubes Fe3O4@NCNTs
[J].
氮掺杂碳纳米管原位封装磁性粒子异质结构(Fe3O4@NCNTs)及其轻质宽频吸波性能
[J].用一步热解工艺制备氮掺杂碳纳米管原位封装金属粒子异质结构(Fe<sub>3</sub>O<sub>4</sub>@NCNTs)，使用粉末X射线衍射(XRD)、拉曼光谱、扫描电镜(SEM)和透射电镜(TEM)等手段表征其结构和物相组成，基于同轴法测试其电磁参数并用Matlab模拟反射损耗。结果表明：煅烧温度和原料比例对氮元素掺杂磁功能化碳纳米管复合材料的微波吸收性能有重要的影响。当原料比例(金属盐/碳源)为2∶1时，煅烧温度为750℃、低填充量为10%的复合材料具有最优异的吸波性能，其最小反射损耗(RL<sub>min</sub>)为-57.7 dB，匹配厚度为2.0 mm时，有效吸收带宽(EAB)达到6.4 GHz。
Nitrogen-enriched, double-shelled carbon/layered double hydroxide hollow microspheres for excellent electrochemical performance
[J].A unique, double-shelled, hollow, carbon-based composite with enriched nitrogen has been prepared through a facile and versatile synthetic strategy. The hierarchical composite employs the nitrogen-enriched carbon hollow sphere as an interior shell and intercrossed Ni/Al layered double hydroxide (LDH) nanosheets as an exterior shell. The obtained N-C@LDH hollow microspheres (HMS) have high nitrogen enrichment, large specific surface area (337 m(2) g(-1)), and uniform and open mesoporous structure. Taking advantage of these characteristics, the composite exhibits obviously superior capacitive behavior, including high specific capacitance, excellent rate capability and good cycling stability, compared with nitrogen-free carbon@LDH composite and hollow LDH without carbon shell. The composite displays high specific capacitance of 1711.51 F g(-1) at a current density of 1 A g(-1). In particular, the high specific capacitance can be kept to 997.3 F g(-1) at a high current density of 10 A g(-1), which still retains 94.97% of the initial specific capacitance after 500 cycles at this high current density. This N-enriched, hollow carbon/LDH composite can be expected to be a promising electrode material for electrochemical capacitors due to its high electrochemical performance.
Encapsulated prussian blue analogs derived nanocubes with tunable yolk-shell structure enabling highly efficient microwave absorption
[J].
Synergistic regulation of dielectric-magnetic dual-loss and triple heterointerface polarization via magnetic MXene for high-performance electromagnetic wave absorption
[J].The single dielectric/magnetic loss mechanism and invalid polarization loss are the crucial issues which limit the exploitation of multi-component electromagnetic wave (EMW) absorption materials, especially Ti3C2Tx MXene based absorption materials. In this work, a series of loosely packed accordion-like 3D NiCo/CeO2/Ti3C2Tx with tunable and high-efficient EMW absorption were fabricated by introducing self-assembled NiCo alloys on the surface of Ti3C2Tx and subsequent anchoring of CeO2. On the one hand, the magnetic NiCo particles and highly conductive Ti3C2Tx achieved the dielectric-magnetic dual-loss. On the other hand, the triple interfacial polarization among NiCo/CeO2/Ti3C2Tx further enhanced the relaxation loss. In addition, the effects of cerium ions on tuning the compositional structure, electromagnetic parameters and impedance behavior of the composites are explored. The NiCo/CeO2/Ti3C2Tx-0.1 performed a wide absorption bandwidth of 6.32 GHz at 1.9 mm, as well as, the minimum reflection loss value of -42.48 dB at 2.0 mm. This work putted forward a new synergistic regulation strategy of dielectric-magnetic dual-loss and triple heterointerface polarization via magnetic MXene for high-performance EMW absorption, which may shed new light on the fabrication of multiple-component synergistic loss absorption materials.
