Carbon-coated nanoparticles and their application in high performance polymer nanocomposites

Shrinking down into nanoscale, materials exhibit huge property advantages over their bulk form. New forms of carbon at nanoscale have occupied the prominent position in modern materials research. With a very long history accompanying our human civilisation, carbon as a wonder material has once again contributed to our technological advances, as evidenced by the discoveries and research attractions in the last a few decades. Research into fullerenes (C60, C70, etc.), carbon nanotubes (CNTs) and graphene has been continued raising, because of the numerous novel properties associated with these new carbon forms1-3. On top of their excellent electronical, physical and chemical properties, CNTs and graphene also exhibit excellent mechanical properties including ultra-high tensile strength, Young’s Modulus, as well as high thermal conductivities. Research into carbon has also promoted the flourish of many new non-carbon nanomaterials, and typical examples include the inorganic fullerene-like tungsten disulphide (IF-WS2) nanoparticles (NPs), numerous oxide NPs and nanowires that also exhibit various remarkable properties, such as high hardness and anti-oxidation stability. To combine the outstanding performances of both carbon and non-carbon nanomaterials by marrying nanoscale carbon with various metal oxide particles, which forms the backbone of my thesis by carrying out the intensive investigations. In my project it have further validated the advantages of the resulting new carbon-coated NPs in different polymeric matrix composites. The main findings are as follows: 1. A home-made rotary chemical vapour deposit (RCVD) system has been modified and this versatile facility has been applied successfully to produce different types of graphitic carbon-coated nanocomposite particles, from micro- down to nano-scale, including IF-WS2, TiO2, ZnO, Y2O3, Cr2O3, CeO2 and ZrO2 etc. The production can be up to 30 g/per batch, which is 10s times more than using a traditional static furnace, by avoiding severe agglomeration. 2. The resulting coating consists of a few layered graphitic carbon with lattice space 0.34 nm. The thickness of the coating is simply controllable between 1-5 nm, depending on the deposition time (10~60 min), precursor injection flow rate (1.2~2.4 ml/L) and heating temperature (700~900 oC). Furthermore, the oxide core of ZnO@C was removed by heating under the H2/Ar atmosphere, and have successfully generated nano- to micro-scale, hollow, closed, and all-carbon structures. 3. The commercial Nylon 12 is applied to fabricate the metal oxide polymer composite. Using ZnO@C-Nylon 12 composite as an example, at 2 wt% content, the composites have achieved with the ultimate tensile strength increased by 27% (from 47.9 to 59.6 MPa), In particular, at 4 wt% content, the ZnO@C showed an impressive improvement in thermal conductivity of nearly 50% (From 0.21 t0 0.31 W∙m-1∙K-1), comparing 16% improvement for ZnO-Nylon 12 composite. 4. Apart from investigations of nylon composite, intensive studies of the Poly ether ether ketone (PEEK), an important high performance engineering thermoplastics polymer, and its nanocomposites reinforced by IF-WS2 and IF-WS2@C have been carried out in this thesis. The IF-WS2/PEEK composites exhibited not only an improvements of 24% (From 77.6 to 96.7 MPa) in the tensile strength (2 wt%), but also showed an extraordinary increase in thermal conductivity by 190%, from 0.248 to 0.719 W∙m-1∙K-1 at 8 wt%, higher onset decomposing temperatures (54 oC) against the plain PEEK. 5. Moreover, owing to the better dispersal capacity of IF-WS2@C NPs, the ternary IF-WS2@C-PEEK nanocomposites produced in this thesis displayed impressive mechanical properties, increased by 51% (From 77.6 to 120.9 MPa, at 2 wt%), and extremely greater thermal conductivity, with 235% (From 0.248 to 0.831 W∙m-1∙K-1 at 8 wt%), and better stability than the comparison IF-WS2-PEEK composites. The parameters influencing the coating quality and thickness have also been investigated. Further, their interface studies based on the FTIR and XPS techniques have verified the formation of chemical bonding (C=S bonding and carbon π-π bonding), rather than physically bonded together. The successful application of the generic RCVD process can be further extended to the processing of many new particles for an ultrathin carbon coating. Considering the vast amount of literature focusing on carbon, the project further processing of carbon-coated materials in composites could easily be tailored to achieve desired surface contacts with different matrices and leading to the better desired performance, as verified in this thesis for the advanced binary and ternary composites. Finally, this research is expecting to expand the application potentials of PEEK-based nanocomposites in critical areas where thermal conductivity and thermal stability are important

Efficient Mobile Edge Computing for Mobile Internet of Thing in 5G Networks

We study the off-line efficient mobile edge computing (EMEC) problem for a joint computing to process a task both locally and remotely with the objective of minimizing the finishing time. When computing remotely, the time will include the communication and computing time. We first describe the time model, formulate EMEC, prove NP-completeness of EMEC, and show the lower bound. We then provide an integer linear programming (ILP) based algorithm to achieve the optimal solution and give results for small-scale cases. A fully polynomial-time approximation scheme (FPTAS), named Approximation Partition (AP), is provided through converting ILP to the subset sum problem. Numerical results show that both the total data length and the movement have great impact on the time for mobile edge computing. Numerical results also demonstrate that our AP algorithm obtain the finishing time, which is close to the optimal solution

Robustness on distributed coupling networks with multiple dependent links from finite functional components

The rapid advancement of technology underscores the critical importance of robustness in complex network systems. This paper presents a framework for investigating the structural robustness of interconnected network models. This paper presents a framework for investigating the structural robustness of interconnected network models. In this context, we define functional nodes within interconnected networks as those belonging to clusters of size greater than or equal to $s$ in the local network, while maintaining at least $M$ significant dependency links. This model presents precise analytical expressions for the cascading failure process, the proportion of functional nodes in the stable state, and a methodology for calculating the critical threshold. The findings reveal an abrupt phase transition behavior in the system following the initial failure. Additionally, we observe that the system necessitates higher internal connection densities to avert collapse, especially when more effective support links are required. These results are validated through simulations using both Poisson and power-law network models, which align closely with the theoretical outcomes. The method proposed in this study can assist decision-makers in designing more resilient reality-dependent systems and formulating optimal protection strategies

Vacuum Microwave Sources of Electromagnetic Radiation

This chapter contains new simulation results concerning the physical foundations of how microwave tubes operate based on Cherenkov’s mechanism of radiation (interaction with slow electromagnetic wave) and some experimental results connected with improving the output characteristics of the magnetrons (a mm band surface wave magnetron and a magnetron with two RF outputs of energy), as well as results of computer modeling of a 320-GHz band traveling wave tube (TWT). The results of analytical calculations and computer modeling, a phase bunching process in the mm band surface wave magnetron, are considered. It is shown that the process of phase focusing has two features associated with a concentration of RF wave energy close to the vanes of an anode block and higher electron hub of a space charge as compared to the classical magnetrons. The features and examples of practical application of the magnetron with two RF outputs of energy are presented. It is shown that the main advantage of the magnetrons is its extended functionalities (for example, possibility of frequency tuning including electronic tuning of a frequency from a pulse to pulse). The presented materials will be of interest not only for starting researchers but also for those who have microwave tube experience

燃料電池用酸素還元反応の白金触媒量低減化に関する研究

Polymer electrolyte membrane fuel cell (PEMFC) is recognized as one of the most effective, environmental-friendly, and futuristic technologies for clean energy. However, the low conversion efficiency of the oxygen reduction reaction (ORR) catalysts hindered its further practical application. Because a commercial and efficient ORR catalyst, Pt nanoparticles loaded on the carbon (XC-72) cannot meet the demand for widespread application due to its excessive cost, poor durability, and fast poisoning during the reaction. Identifying plausible solutions to these problems is still a challenge. In this thesis, we focused on the development of the novel efficient catalysts for ORR with ultra-low Pt loading amount and Pt-free materials. In order to further improve catalytic activity, we also synthesized a new 2-D material Nb2C to replace the carbon support of the catalyst. In chapter 1, the fundamental theory and the structure of fuel cells were briefly described. The theoretical analyses of the ORR process were also introduced. Furthermore, the recent development of the ORR catalysts was summarized. Finally, we exhibited the issues of ORR catalysts and the purposes in this thesis. In chapter 2, the reagents and instruments used in this work were summarized. We also introduced the preparation methods of the working electrode and the characterizations. Finally, the electrochemical measurements and analyses, such as the cyclic voltammetry (CV) and the linear sweep voltammetry (LSV) were presented. In chapter 3, the synthesis procedure for PtM (M: Fe, Co, Ni) alloy samples through a simple method under the mild conditions was described. In detail, the transition metals were doped into the Pt nanoplate crystals to form PtM (M: Fe, Co, Ni) alloys. The physical characterizations proved that the PtFe alloy has a well-defined, homogeneous, and ultra-small particle size morphology. We found that the morphology contributes the higher catalytic activity. Finally, the PtM (M: Fe, Co, Ni) alloys are used as the ORR catalyst, and they show the excellent catalytic activity and stability both in the acidic and alkaline medium. In chapter 4, 3 kinds of Pt-free catalysts were successfully designed and synthesized. A metal-organic framework (MOF) was used as a precursor. The influences of the carbonization temperature and the ratios of the two transition metals were studied in terms of the ORR performance. Meanwhile, the synergistic effect of the dual transition metals was considered to have a positive impact on improving the electrocatalytic activity. The electrochemistry analyses displayed that FCPA-900 shows the best ORR catalytic activities, because of the larger specific surface area and the better-defined amorphous carbon structure. In chapter 5, firstly, in order to obtain a 2-D MAX Nb2AlC under a mild condition, we studied on the influence of target materials under the different conditions, such as reaction method, type of molten salts flux, reaction temperature, and reaction time. The synthesis temperature of the MAX Nb2AlC was successfully decreased from 1600oC to 1000oC by using the molten salt assisted solid-state reaction. The reaction mechanism of the Nb2AlC was also investigated, and the effect of the NaCl flux on Nb2AlC synthesis was confirmed. Secondly, the multilayer 2-D MXene Nb2C material was obtained by etching the MAX Nb2AlC. Finally, the ORR catalytic activity of the Pt nanoparticles loaded on the multilayer 2-D MXene Nb2C was studied. The results of the electrochemical measurements show that the 2-D MXene Nb2C is an excellent support material to replace carbon for the Pt loading catalyst. In chapter 6, the general conclusions and prospects were presented. The electrochemical performance of the obtained Pt-based and Pt-free catalysts for the ORR was summarized. Further studies need to focus on improving the stability, promoting the efficiency, and developing new high-performance ORR catalysts.九州工業大学博士学位論文 学位記番号：生工博甲第325号 学位授与年月日：平成30年9月21日1 Background|2 Experimental section for electrode preparation, physic characteristic, and data analysis|3 PtM (M: Fe, Co, Ni) alloys as the ORR electrocatalysts with the facile operating conditions|4 Temperature-dependence of electrocatalytic activity for dual transition metals embedded in P-doped porous carbon used as ORR catalyst|5 2-D material MXene Nb2C synthesized by the molten salt method at the low temperature as the catalytic support to enhance the oxygen reduction reaction九州工業大学平成30年

燃料電池用酸素還元反応の白金触媒量低減化に関する研究

九州工業大学博士学位論文（要旨）学位記番号：生工博甲第325号 学位授与年月日：平成30年9月21