Anisotropic PDMS/Alumina/Carbon Fiber Composites with a High Thermal Conductivity and an Electromagnetic Interference Shielding Performance

The development of polymer-based composites with a high thermal conductivity and electromagnetic interference (EMI) shielding performance is crucial to the application of polymer-based composites in electronic equipment. Herein, a novel strategy combining ice-templated assembly and stress-induced orientation was proposed to prepare polydimethylsiloxane (PDMS)/alumina/carbon fiber (CF) composites. CF in the composites exhibited a highly oriented structure in the horizontal direction. Alumina was connected to the CF, promoting the formation of thermal conductive pathways in both the horizontal and vertical directions. As the CF content was 27.5 vol% and the alumina content was 14.0 vol%, the PDMS/alumina/CF composite had high thermal conductivities in the horizontal and vertical directions, which were 8.44 and 2.34 W/(m·K), respectively. The thermal conductivity in the horizontal direction was 40.2 times higher than that of PDMS and 5.0 times higher than that of the composite with a randomly distributed filler. The significant enhancement of the thermal conductivity was attributed to the oriented structure of the CF and the bridging effect of alumina. The PDMS/alumina/CF composite exhibited an excellent EMI shielding effectiveness of 40.8 dB which was 2.4 times higher than that of the composite with a randomly distributed filler. The PDMS/alumina/CF composite also exhibited a low reflectivity of the electromagnetic waves. This work could provide a guide for the research of polymer-based composites with a high thermal conductivity and an EMI shielding performance.     

Effect of Two-Step Sintering on Properties of Alumina Ceramics Containing Waste Alumina Powder

This study aims to evaluate the recycling potential of solid waste alumina powder (WAP) by utilization of the two-step sintering (TSS) process. For the study, WAP was collected as an industrial scrap after the machining process for the formation of green alumina compacts. The alumina samples were prepared according to the slip casting method by preparing suspensions containing commercial alumina with 0.8 μm average particle size and by adding up to 20 dwb. % (i.e., expressed on a dry weight basis) of WAP with 3.4 μm average particle size. The samples were sintered at optimized TSS conditions and compared with conventional one-step sintering (OSS) by conducting morphological analyses. The average grain size (AGS) was determined from the obtained field emission scanning electron microscopy (FESEM) images, while the sample porosity was calculated based on apparent densities. The obtained micrographs after TSS implementation revealed a partially textured microstructure. Furthermore, a comparison of the mechanical properties of alumina samples lacking or containing 20 dwb. % of WAP obtained after sintering is presented. The indentation fracture toughness (~3.2 MPa m^1/2) and Vickers hardness data (~14.5 GPa) showed a positive effect of adding WAP to alumina samples. The slightly improved mechanical properties of ceramic samples containing waste alumina are a consequence of lower porosity, which is due to the remaining sintering additives in WAP. The collected results demonstrate the possibility of using TSS for sintering ceramic materials that contain WAP.     

3-D Surface Morphological Characterization of CAD/CAM Milled Dental Zirconia: An In Vitro Study of the Effect of Post-Fabrication Processes

Objective: To investigate the effect on zirconia surface of the post-fabrication surface treatments on the morphological characteristics and mechanical properties of CAD/CAM milled dental zirconia specimens as well as to identify the critical parameters in the measurement of oral retention under in vitro circumstances. Method: The zirconia specimens (N = 20, n = 4) were subjected to CAD/CAM milling and divided into five groups. The specifications were: Group G1—sintered; Group G2—sintered followed by a polishing process; Group G3—sintered followed by polishing and sandblasting with alumina particles Al₂O₃ (110 µm); Group G4—sintered followed by sandblasting; Group G5—sintered followed by sandblasting with polishing as the end process. All the groups were subjected to Fretting wear tests, 3-D surface roughness measurements, and Vickers’s Micro hardness tests. Investigation of the phase transformation using XRD, and surface feature examination using SEM were also carried out. Additionally, one-way ANOVA, Tukey, and Pearson correlations were statistically analysed. Results: The fabrication processes had a significant effect on the performance of zirconia specimens in all the groups (p > 0.05). Specimens that underwent polishing as the last process exhibited lower surface roughness. The monoclinic phase of zirconia was observed in all the specimens before and after wear except for those in the G2 and G5 groups, where polishing was the end process. In G5, the post-wear surface properties revealed lower surface roughness and hardness. Further, the SEM and 3-D topography show grooves as seen by the dale void volume (Vvv) values; shallow valley depth (Svk); micro craters; and wear track. Conclusion: Specimens in G5 that were subjected to multistep post-fabrication process, namely sandblasting followed by polishing, yielded better results when compared to those in the other groups (G1, G2, G3, and G4). G5 with an interlayer of alumina is recommended for clinical applications due to its enhanced surface properties, mechanical properties, and low wear.     

Systematic in vitro nanotoxicity study on anodic alumina nanotubes with engineered aspect ratio: Understanding nanotoxicity by a nanomaterial model

Here, we report a detailed and systematic approach for studying the in vitro nanotoxicity study of high aspect ratio (HAR) nanomaterials using anodic alumina nanotubes (AANTs) as a nanomaterial model. AANTs with bio-inert properties and tailored aspect ratios ranging from 7.8 to 63.3 were synthesized by an electrochemical pulse anodization process. Cytotoxicity studies were conducted with RAW 264.7 mouse macrophage cells and MDA-MB 231-TXSA human breast cancer cells through several toxicity parameters, including cell viability and morphology, pro-inflammatory response, mitochondrial depolarization, lysosomal membrane permeabilization (LMP), induction of autophagy and endoplasmic reticulum (ER) stress. The resulting toxicity patterns were cell-type dependent and strongly related with AANTs dose, length of time, and importantly the AR of AANTs. Long AANTs triggered enhanced cell death, morphological changes, tumor necrosis factor α (TNF-α) release, LMP and ER stress than short AANTs. The toxic AR window of AANTs was determined to be 7.8, which is shorter than that of other previously reported HAR nanomaterials. This toxic AR window provides a promising opportunity to control the nanotoxicity of HAR nanomaterials for their advanced drug delivery application.     

高效液相色谱法测定烟道沥青烟中苯并[a]芘

本文用玻璃纤维滤料在烟道外部(<50℃)采集颗粒物,超声波法提取,碱性氧化铝净化样品,高效液相色谱分离,荧光检测器检测烟道气中苯并[a]芘,检测下限为2pg,平均回收率为104.6％,合并变异系数为6.5％。     

不透明牙本质瓷的厚度对In-Ceram渗透铝瓷基底复合颜色影响的实验研究

目的:研究VidadurAlpha饰瓷中不透明牙本质瓷的厚度对In-Ceram渗透铝瓷复合颜色的影响。方法:分别制作四种颜色渗透铝瓷基底AL1、AL2、AL3、AL4,厚度为0.5mm。在渗透铝瓷基底表面分别构筑与其相对应的A1、A3、B4、C4的不透明牙本质瓷,厚度分别为0.1mm、0.2mm、0.3mm、0.4mm、0.5mm五种。用MINOLTACR-321型测色仪在标准白背景下测色,记录数值,进行比较、分析。结果:①复合颜色随不透明牙本质瓷厚度的增加,四种试件的明度值L呈下降趋势;②饱和度在一定的厚度范围内无显著性差异(P>0.05);③不透明牙本质瓷厚度在0.2～0.4mm时,色相角无明显变化(P>0.05)。结论:不透明牙本质瓷厚度变化对调节修复体最终的颜色有一定的影响。     

不同全瓷材料修复不同程度变色前牙的效果对比

目的 比较不同全瓷材料对根管治疗后不同程度变色前牙的修复效果.方法 选择根管治疗后前牙变色患者83例(102颗牙),将患牙按牙体变色的程度不同分为轻度变色牙46颗、中度变色牙33颗、重度变色牙23颗.用IPSe-max铸瓷制作全瓷冠修复轻度变色牙18颗、中度变色牙9颗、重度变色牙3颗;用Vita In-ceram渗透氧化铝陶瓷制作全瓷冠修复轻度变色牙14颗、中度变色牙11颗、重度变色牙7颗;用Lava氧化锆陶瓷制作全瓷冠修复轻度变色牙14颗、中度变色牙13颗、重度变色牙13颗.通过Crystaleye比色仪分别对修复体和天然邻牙进行测色,计算总色差△E值,并对全瓷冠与天然邻牙的颜色匹配度进行牙冠颜色评分(CCS).结果 IPS e-max铸瓷修复的轻度变色牙、中度变色牙及重度变色牙,其△E值依次升高(P＜0.05),而另外2种材料的△E值在不同程度变色牙组中比较,差异均无统计学意义(P＞0.05).在轻、中度变色牙组中,3种材料CCS比较,差异均无统计学意义(P＞0.05);在重度变色牙组中,Vita In-ceram、Lava氧化锆材料的CCS优于IPS e-max铸瓷(P＜0.05).结论 IPS e-max铸瓷对中、重度变色牙的修复效果较差,而Vita In-ceram渗透氧化铝陶瓷和Lava氧化锆陶瓷对于轻、中、重度变色前牙均有较好的修复效果.     

全瓷固定桥的研究进展

尽管受脆性、抗弯强度和断裂韧性等材料性能的影响,全瓷固定桥目前尚未成为常规的固定修复手段,但其临床应用和研究报道越来越多,并显示出良好的应用前景。本文对硅酸盐陶瓷、玻璃渗透氧化铝陶瓷和氧化锆陶瓷全瓷桥材料的基础研究和临床研究进行了综述。