Shulyak Vladimir A, Morozov Nikolai S, Ivanov Andrei V, Gracheva Alexandra V, Chebotarev Sergei N, Avdeev Viktor V
Department of Chemistry, Lomonosov Moscow State University, 119234 Moscow, Russia.
Nanomaterials (Basel). 2024 Mar 19;14(6):540. doi: 10.3390/nano14060540.
The physical and mechanical properties and structural condition of flexible graphite foils produced by processing natural graphite with nitric acid, hydrolysis, thermal expansion of graphite and subsequent rolling were studied. The processes of obtaining materials and changing their characteristics has been thoroughly described and demonstrated. The structural transformations of graphite in the manufacture of foils were studied by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). A decrease in the average size of the coherent scattering regions (CSR) of nanocrystallites was revealed during the transition from natural graphite to thermally expanded graphite from 57.3 nm to 20.5 nm at a temperature of 900 °C. The rolling pressure ranged from 0.05 MPa to 72.5 MPa. The thickness of the flexible graphite foils varied from 0.11 mm to 0.75 mm, the density-from 0.70 to 1.75 g/cm. It was shown that with an increase in density within these limits, the compressibility of the graphite foil decreased from 65% to 9%, the recoverability increased from 5% to 60%, and the resiliency decreased from 10% to 6%, which is explained by the structural features of nanocrystallites. The properties' anisotropy of graphite foils was studied. The tensile strength increased with increasing density from 3.0 MPa (ρ = 0.7 g/cm) to 14.0 MPa (ρ = 1.75 g/cm) both in the rolling direction L and across T. At the same time, the anisotropy of physical and mechanical properties increased with an increase in density along L and T to 12% with absolute values of 14.0 MPa against 12.5 MPa at a thickness of 200 μm. Expressed anisotropy was observed along L and T when studying the misorientation angles of nanocrystallites: at ρ = 0.7 g/cm, it was from 13.4° to 14.4° (up to 5% at the same thickness); at ρ = 1.3 g/cm-from 11.0° to 12.8° (up to 7%); at ρ = 1.75 g/cm-from 10.9° to 12.4° (up to 11%). It was found that in graphite foils, there was an increase in the coherent scattering regions in nanocrystallites with an increase in density from 24.8 nm to 49.6 nm. The observed effect can be explained by the coagulation of nanocrystallites by enhancing the Van der Waals interaction between the surface planes of coaxial nanocrystallites, which is accompanied by an increase in microstrains. The results obtained can help discover the mechanism of deformation of porous graphite foils. The obtained results can help discover the deformation mechanism of porous graphite foils. We assume that this will help predict the material behavior under industrial operating conditions of products based flexible graphite foils.
研究了通过用硝酸处理天然石墨、水解、石墨热膨胀以及随后的轧制所制备的柔性石墨箔的物理和机械性能以及结构状况。对获得材料及其特性变化的过程进行了详尽的描述和展示。通过X射线衍射分析（XRD）和透射电子显微镜（TEM）研究了箔材制造过程中石墨的结构转变。在900℃温度下，从天然石墨转变为热膨胀石墨时，发现纳米微晶的相干散射区域（CSR）平均尺寸从57.3nm减小到20.5nm。轧制压力范围为0.05MPa至72.5MPa。柔性石墨箔的厚度从0.11mm变化到0.75mm，密度从0.70g/cm³到1.75g/cm³。结果表明，在这些限制范围内，随着密度增加，石墨箔的压缩率从65%降至9%，恢复率从5%增至60%，弹性从10%降至6%，这可由纳米微晶的结构特征来解释。研究了石墨箔的性能各向异性。在轧制方向L和横向T上，拉伸强度均随密度增加而提高，从3.0MPa（ρ = 0.7g/cm³）增至14.0MPa（ρ = 1.75g/cm³）。同时，物理和机械性能的各向异性随着密度沿L和T方向增加至12%，在200μm厚度下，绝对值分别为14.0MPa和12.5MPa。在研究纳米微晶的取向差角时，沿L和T方向观察到明显的各向异性：在ρ = 0.7g/cm³时，为13.4°至14.4°（相同厚度下高达5%）；在ρ = 1.3g/cm³时，为11.0°至12.8°（高达7%）；在ρ = 1.75g/cm³时，为10.9°至12.4°（高达11%）。发现随着密度从24.8nm增加到49.6nm，石墨箔中纳米微晶的相干散射区域增大。观察到的这种效应可以通过增强同轴纳米微晶表面平面之间的范德华相互作用使纳米微晶凝聚来解释，这伴随着微观应变的增加。所得结果有助于揭示多孔石墨箔的变形机制。我们认为这将有助于预测基于柔性石墨箔的产品在工业运行条件下的材料行为。
