Monodisperse ZnO Micro and Nanoparticles Obtained by Micro Segmented Flow Synthesis

Mikro- und Nanopartikel aus Zinkoxyd (ZnO) besitzen bemerkenswerte Eigenschaften für Applikationen im Bereich der Elektronik, Optik und Photonic. Als ein Halbleitermaterial mit großer Bandlücke ist ZnO ebenfalls für die Entwicklung von Sensoren, Light Emitting Diodes (LEDs) und Solarzellen von hohem Interesse. Die Herstellung definierter Materialien mit einheitlicher Morphologie und enger Partikel-Größenverteilung ist hierzu eine wichtige Voraussetzung. Verschiedene Verfahren zur Herstellung entsprechender Partikel sind in der Vergangenheit untersucht worden. Die tropfenbasierte Mikrofluidik bietet die Möglichkeit einer exzellenten Reaktionskontrolle durch die Verwendung eines Tropfens als Reaktionsgefäß. Kurze Mischzeiten, hohe Heiz-/Kühlraten sowie eine definierte Verweilzeit ermöglichen so neben stöchiometrischen Parametern eine exakte Reaktionsführung. Ziel der hier vorliegenden Dissertationsschrift ist die Untersuchung der ZnO-Präzipitation in entsprechenden mikrofluidischen Systemen sowie die Charakterisierung der hergestellten Materialien.ZnO micro and nanoparticles have attracted considerable interest because of their remarkable performance in electronics, optics and photonics. As a wide band gap semiconductor material, ZnO is also a potential candidate for various applications including gas sensing, light emitting devices and solar cells. Although some technologies have been developed to produce well-defined ZnO particles of different shapes and sizes, ZnO particles prepared by micro segmented flow synthesis have been rarely reported. The aim of this work was to develop a microfluidic system based on the micro segmented flow method and to test whether the microfluidic components are suitable for the generation and investigation of ZnO particles with improved homogeneity.In order to optimize the experimental conditions, ZnO particles were first synthesized in batch. The optimized batch conditions were then adapted to two microfluidic arrangements for continuous synthesis of ZnO particles below 100°C. The set-ups included computer-controlled syringe pumps, T-injectors, PTFE tubings and PTFE knot mixers in a thermostat water bath. The ZnO particles were obtained under strong alkaline conditions at elevated temperature in aqueous solution and DMSO solution. Needle-like, flower-like and compact ZnO particles were obtained. In nearly all cases, a strong effect of the flow conditions on the homogeneity of the formed particles was observed. The higher quality of the particles can be attributed to the fast mixing and enhanced heat transfer caused by segment-internal convection.In addition, two other microfluidic set-ups were developed to control the ZnO formation reaction at temperature up to 150°C. A static micromixer was used for mixing the reactants at room temperature. The formation of segmented flow was realized by injection of the reaction mixture into a carrier stream. The particle growth took place in PTFE tube coils inside a thermostat, which allowed to heat up to 150°C. By using this set-up, flower-like, star-like, and spherical ZnO particles were successfully synthesized. The shape and size of the formed particles were strongly dependent on the reactant concentration and the molar ratio of NaOH/Zn(Ac)2. The total residence time for preparation of these particles was only 9.3s, which is very short compared to the most conventional methods.The effect of the solvent on the formation of ZnO particle has also been investigated using this microfluidic set-up. Two different experimental conditions were applied to prepare ZnO particles, where Zn(Ac)2 and NaOH in ethylene glycol (EG) were mixed with water or water/EG mixing solvent to achieve different water contents in the final mixture solution. The formation of homogeneous particles was characterized by SEM and TEM. A stronger dependence of the particle size and shape on the water content was observed. Furthermore, the water content can be used for tuning the optical absorption spectra of the formed ZnO particles. Besides the ZnO microparticles, ZnO nanoparticles with an average diameter around 4-5nm have been synthesized using Zn(Ac)2 and LiOH in ethanol. The prepared nanoparticles exhibited green and blue emission under excitation at 325nm. In order to understand the size-dependent optical properties of ZnO nanoparticles, extended X-ray absorption fine structure (EXAFS) spectroscopy was applied to study their local structure properties and compared with that of ZnO flower-like microparticles. The EXAFS measurements revealed higher vacancies and a higher degree of structural disorders in the nanoparticles than the microparticles. These disorders and vacancies could contribute to the blue shift of the visible emission from ZnO nanopartilces.Due to the potential applications of semiconductor-metal composite particles in diverse areas, the flower-like ZnO microparticles obtained by micro segmented flow synthesis were used to fabricate ZnO/4-MBA/Au composite particles using a simple strategy. The formed composite particles were very homogeneous in shape and size. The surface coverage of Au nanoparticles on ZnO/4-MBA particles can be adjusted by changing the molar ratio of ZnO/4-MBA to Au. In order to study the interaction of 4-MBA molecules with ZnO and Au particles, Raman spectra of ZnO/4-MBA and ZnO/4-MBA/Au particles were analysed.In summary, the segmented flow technique is suitable to generate ZnO particles with controlled size and morphology. Compared to most conventional methods, this technique offers several advantages, and it provides a new insight into material synthesis under environmentally friendly conditions

Monitoring 3D Printer Performance using Internet of Things (IoT) Application

Most of the current desktop 3D printers are built based on open-source designs from online communities. The largest group of open-source 3D printers is the Self-Replicating Rapid Prototype (RepRap) 3D printers. A RepRap 3D printer needs to connect to a computer or a microprocessor to feed G Code and provide interface for users to control the 3D printer. However, local computer is a relatively expensive solution comparing to the cost of a RepRap 3D printer; while the microprocessor has much less computing capability comparing to a normal computer, and cannot handle computing-intensive jobs like slicing 3D objects or generating G Code. An alternate solution is to use the internet of things (IoT) application to control and monitor 3D printers. IoT is the network of physical devices, vehicles, buildings and other items, allowing objects to be sensed and controlled remotely across existing network. IoT and 3D printing are two important new technologies, which progressively impact a lot of areas of the industries and also our everyday life. Students need to be introduced to these technologies, and get ready for future career opportunities. A multidisciplinary student project is developed to provide students access to both 3D printer and IoT platform, and also learn to collaborate with engineers from other disciplines to solve complex engineering problems. The objective of the project is to design and develop an IoT application to remote monitor the performance of a RepRap 3D printer including the printing progress and the temperatures of the heated bed and hot end. Major tasks involved in the project are: to inspect and upgrade the current 3D printer to avoid any possible compliance issues between the 3D printer and the hardware components or software tools for the IoT application; to connect the 3D printer to the Raspberry Pi microprocessor; and to design and develop the IoT application. The methods and algorithms of connecting a 3D printer to an IoT application is reported, and the IoT application interface and workflow will be presented in the results section. As a pilot study, this project provides first-hand data on the requirements of time and resources to introduce IoT to undergraduate students

Remediation of Copper Contaminated Kaolin by Electrokinetics Coupled with Permeable Reactive Barrier

AbstractElectrokinetics is an in situ soil remediation technique by which the flow direction of the pollutants can be controlled and the soil with low permeability can be treated. In this study, the remediation of copper contaminated kaolin by electrokinetic process coupled with activated carbon permeable reactive barrier (PRB) was investigated. The experimental results showed that the integration of PRB with electrokinetics successfully removed copper from kaolin with pH control of the catholyte. The average removal rate reached the highest of 96.60% when the initial Cu2+ concentration was 2000mg/kg. Compared to the electrokinetic process without PRB, the application of the coupled system could reduce the pollution of the electrolyte

Three-dimensional canine displacement patterns in response to translation and controlled tipping retraction strategies

OBJECTIVE: To validate whether applying a well-defined initial three-dimensional (3D) load can create consistently expected tooth movement in patients. MATERIALS AND METHODS: Twenty-one patients who needed bilateral canine retraction to close extraction space were selected for this split-mouth clinical trial. After initial alignment and leveling, two canines in each patient were randomly assigned to receive either translation (TR) or controlled tipping (CT) load. The load was delivered by segmental T-loops designed to give specific initial moment/force ratios to the canines in each treatment interval (TI), verified with an orthodontic force tester. Maxillary dental casts were made before canine retraction and after each TI. The casts were digitized with a 3D laser scanner. The digital models were superimposed on the palatal rugae region. The 3D canine displacements and the displacement patterns in terms of TR, CT, and torque were calculated for each TI. RESULTS: The method can reliably detect a TR displacement greater than 0.3 mm and a rotation greater than 1.5°. Ninety-two TIs had displacements that were greater than 0.3 mm and were used for further analysis. Most displacements were oriented within ±45° from the distal direction. The displacement pattern in terms of TR or CT was not uniquely controlled by the initial moment/force ratio. CONCLUSIONS: The initial load system is not the only key factor controlling tooth movement. Using a segmental T-loop with a well-controlled load system, large variations in canine displacement can be expected clinically

Extreme enrichment in atmospheric 15N15N.

Molecular nitrogen (N2) comprises three-quarters of Earth's atmosphere and significant portions of other planetary atmospheres. We report a 19 per mil (‰) excess of 15N15N in air relative to a random distribution of nitrogen isotopes, an enrichment that is 10 times larger than what isotopic equilibration in the atmosphere allows. Biological experiments show that the main sources and sinks of N2 yield much smaller proportions of 15N15N in N2. Electrical discharge experiments, however, establish 15N15N excesses of up to +23‰. We argue that 15N15N accumulates in the atmosphere because of gas-phase chemistry in the thermosphere (>100 km altitude) on time scales comparable to those of biological cycling. The atmospheric 15N15N excess therefore reflects a planetary-scale balance of biogeochemical and atmospheric nitrogen chemistry, one that may also exist on other planets

Comparison of movement rate with different initial moment-to-force ratios

Introduction: The objective of this clinical prospective study was to evaluate the effect of the two treatment strategies, translation or controlled tipping followed by root correction, on canine retraction efficiency, specifically canine movement rate. Methods: Twenty-one patients who needed bilateral maxillary canine retraction to close extraction space as part of their treatment plan were selected for this study. Segmental T-loops designed for controlled tipping or for translation were applied randomly to each side. Two digital maxillary dental casts (taken pre- and post-treatment) were used to measure the tooth displacements of each patient. The coordinate system located at the center of canine crown on the pre-treatment model with the three axes defined in the mesial-distal (M-D), buccal-lingual (B-L), and occlusal-gingival (O-G) directions was used to express the six tooth displacement components. The movement rates on the occlusal plane and in the M-D direction were computed. Movement rates were calculated by dividing the M-D displacements or the resultant displacement on the occlusal plane with the corresponding treatment time. Results: T-loops for controlled tipping moved canines faster (33.3% on occlusal plane and 38.5% in the M-D direction) than T-loops for translation. The differences are statistically significant (p = 0.041 on the occlusal plane and 0.020 in the M-D direction). Conclusion: 1. Moment-to-force ratio (M/F) impacts on the canine movement rate in a maxillary canine retraction treatment with segmented T-loop mechanism. 2. Within the neighborhood of the ratio for translation, lower M/F moves canine faster than higher M/F both on occlusal plane and in the M-D direction

Hounsfield unit change in root and alveolar bone during canine retraction

INTRODUCTION: The objective of this study was to determine the Hounsfield unit (HU) changes in the alveolar bone and root surfaces during controlled canine retractions. METHODS: Eighteen maxillary canine retraction patients were selected for this split-mouth design clinical trial. The canines in each patient were randomly assigned to receive either translation or controlled tipping treatment. Pretreatment and posttreatment cone-beam computed tomography scans of each patient were used to determine tooth movement direction and HU changes. The alveolar bone and root surface were divided into 108 divisions, respectively. The HUs in each division were measured. Mixed-model analysis of variance was applied to test the HU change distribution at the P <0.05 significance level. RESULTS: The HU changes varied with the directions relative to the canine movement. The HU reductions occurred at the root surfaces. Larger reductions occurred in the divisions that were perpendicular to the moving direction. However, HUs decreased in the alveolar bone in the moving direction. The highest HU reduction was at the coronal level. CONCLUSIONS: HU reduction occurs on the root surface in the direction perpendicular to tooth movement and in the alveolar bone in the direction of tooth movement when a canine is retracted

Muon radiography experiments on the subway overburden structure detection

Muon radiography is an innovative and non-destructive technique for internal density structure imaging, based on measuring the attenuation of cosmic-ray muons after they penetrate the target. Due to the strong penetration ability of muons, the detection range of muon radiography can reach the order of hundreds of meters or even kilometers. Using a portable muon detector composed of plastic scintillators and silicon photomultipliers, we performed a short-duration(1h) flux scanning experiment of the overburden above the platform and tunnel of the Xiaoying West Road subway station under construction. With the observation direction facing up, the detector is placed on the north side of the track and moved eastward from the platform section inside the station to the tunnel section. The scanning length is 264m and a total of 21 locations are observed. By comparing the observed and predicted values of the muon survival ratio at different locations, the experiment accurately detects the jump in thickness at the interface of the platform section and tunnel section. Furthermore, unknown anomalies caused by random placed light brick piles and side passage mouth above the observation locations are detected and confirmed later. This experiment verifies the feasibility of using natural muons to quickly detect abnormal structures of the overburden of tunnel, and shows that muon radiography has broad application prospects in tunnel safety and other similar aspects.Comment: 30 pages, 10 figure