Numerical Simulation for Exploring the Effect of Viscosity on Single-screw Extrusion Process of Propellant

AbstractSingle-screw extrusion process of propellant has the characteristics of multiple accidents, complicated rheological parameters and difficult measurement of real-time conditions, however, the process details can be reproduced by simulation conveniently and intuitively. In this paper, the POLYFLOW simulation platform was used to model and analyze the single-screw extrusion process of propellant through the application of Finite Element Analysis on extrusion of plastic. The distributions and changes of viscosity in extrusion process, which were taken as the starting point to study the threshold and distribution of pressure, temperature and other sensitive parameters, were obtained. The simulation shows that the risk at the screw edge is higher because of severe mixing and plasticizing process, and the viscous heating is up to 1.4×105 W · m-3. Parameters under different speed conditions were studied as well, which provide guidance for the coordination of security and economy in production

Growth-in-place deployment of in-plane silicon nanowires

International audienceUp-scaling silicon nanowire (SiNW)-based functionalities requires a reliable strategy to precisely position and integrate individual nanowires. We here propose an all-in-situ approach to fabricate self-positioned/aligned SiNW, via an in-plane solid-liquid-solid growth mode. Prototype field effect transistors, fabricated out of in-plane SiNWs using a simple bottom-gate configuration, demonstrate a hole mobility of 228 cm2/V s and on/off ratio >103. Further insight into the intrinsic doping and structural properties of these structures was obtained by laser-assisted 3 dimensional atom probe tomography and high resolution transmission electron microscopy characterizations. The results could provide a solid basis to deploy the SiNW functionalities in a cost-effective way

Atomic scale investigation of silicon nanowires and nanoclusters

In this study, we have performed nanoscale characterization of Si-clusters and Si-nanowires with a laser-assisted tomographic atom probe. Intrinsic and p-type silicon nanowires (SiNWs) are elaborated by chemical vapor deposition method using gold as catalyst, silane as silicon precursor, and diborane as dopant reactant. The concentration and distribution of impurity (gold) and dopant (boron) in SiNW are investigated and discussed. Silicon nanoclusters are produced by thermal annealing of silicon-rich silicon oxide and silica multilayers. In this process, atom probe tomography (APT) provides accurate information on the silicon nanoparticles and the chemistry of the nanolayers

Modélisation de la croissance des nanofils de Si et métrologie à l'échelle atomique de la composition des nanofils

Si nanowires (NWs) are the typical one-dimensional nanomaterials and attract lots of interest in recent years due to their good properties and their wide range of possible applications. As far as their applications are considered, it is important to control their growth as well as their doping. Therefore, the aim of this thesis is devoted to the modeling the growth of Si NWs and the atomic scale metrology of Si NW composition In the first part of this work, we study the NW growth rate (length) as well as the morphology such as tapering. Several models are proposed owing to different nature of NWs synthesized via different methods: Chemical Vapor Deposition (CVD) and Molecular Beam Epitaxy (MBE). Different growth rate tendencies are found depending on the synthesis methods. A good fit is found between the modeling and the experimental data. The influence of experimental conditions on NW morphology is also investigated in this part. The aim of the second part of this thesis is devoted to the metrology of impurities (catalyst and dopant) in Si NWs using the Atom Probe Tomography (APT). This technique allows analysis at the atomic scale in real space with a three-dimensional analysis. Several types of Si NWs synthesized via different approaches such as etching, Vapor-Liquid-Solid (VLS) mechanism and Solid-Liquid-Solid (SLS) mechanism with different growth catalysts (Au, In and Sn) are investigated. The residing of catalyst atoms in Si NWs is found to be a rather general phenomenon and it is related to the catalyst types and growth mechanisms. The dopant concentration and distribution in Si NW produced by etching is unchanged. As far as the doped Si NWs via VLS mechanism are concerned, a formation of NW core-shell structure with an under-doped core surrounded by an over-doped shell is found whatever the NW morphology and dopant type. A NW sidewall diffusion-based model is proposed to reproduce experimental data and give a possible incorporation pathway for dopant into NW.Les nanofils de silicium (Si) sont des nano-objets à une dimension. Ils font l'objet de beaucoup d'intérêt ces dernières années en raison de leurs bonnes propriétés et leur grand potentiel d'applications. Pour ces applications, il est important de parfaitement contrôler la croissance de ces objets ainsi que leurs dopages. Dans ce contexte, l'objectif de ce travail de thèse est la modélisation de la croissance des nanofils de Si et la métrologie à l'échelle atomique de la composition des nanofils. Dans la première partie de ce travail, nous avons étudié le taux de croissance (longueur) ainsi que l'évolution de la morphologie des nanofils, en particulier l'effet d'effilage. Plusieurs modèles sont proposés selon la nature des nanofils synthétisés via différentes méthodes d'élaboration: Dépôt Chimique en phase Vapeur et Epitaxie par Jets Moléculaires. Les taux de croissance varient selon les méthodes de synthèse. Le modèle reproduit fidèlement les données expérimentales. L'influence des conditions expérimentales sur la morphologie des nanofils est également étudiée dans cette partie. L'objectif de la seconde partie de ce travail est la métrologie des impuretés (catalyseur et dopant) dans les nanofils de Si. Cette étude est réalisée à l'aide de la technique de Sonde Atomique Tomographique (SAT). Cette technique permet une analyse à l'échelle atomique, dans l'espace réel et en trois dimensions de l'objet analysé. Des nanofils synthétisés par différentes techniques telles : la gravure chimique, la méthode Vapeur-Liquide-Solide (VLS) et la méthode Solide-Liquide-Solide (SLS), en utilisant différents catalyseurs de croissance tels Au, In et Sn, sont étudiés. La présence d'atomes des catalyseurs dans les nanofils se trouve être un phénomène général. Un travail sur la métrologie des dopants a également été réalisé. La concentration des dopants et leurs distributions dans les nanofils synthétisé par gravure chimique est inchangée. En revanche, dans les nanofils de Si dopés via un mécanisme de croissance VLS, une structure cœur-coquille avec un cœur sous-dopé et une coquille sur-dopée est observée. Ceci est retrouvé quelque soit la morphologie du nanofil et la nature chimique du dopant. Un modèle basé sur la diffusion latéral (via la surface du nanofil) des dopants est proposé afin de reproduire les profils expérimentaux observés et aussi préciser une voie d'incorporation possible des dopants

Modélisation de la croissance des nanofils de Si et métrologie à l'échelle atomique de la composition des nanofils

Si nanowires (NWs) are the typical one-dimensional nanomaterials and attract lots of interest in recent years due to their good properties and their wide range of possible applications. As far as their applications are considered, it is important to control their growth as well as their doping. Therefore, the aim of this thesis is devoted to the modeling the growth of Si NWs and the atomic scale metrology of Si NW composition In the first part of this work, we study the NW growth rate (length) as well as the morphology such as tapering. Several models are proposed owing to different nature of NWs synthesized via different methods: Chemical Vapor Deposition (CVD) and Molecular Beam Epitaxy (MBE). Different growth rate tendencies are found depending on the synthesis methods. A good fit is found between the modeling and the experimental data. The influence of experimental conditions on NW morphology is also investigated in this part. The aim of the second part of this thesis is devoted to the metrology of impurities (catalyst and dopant) in Si NWs using the Atom Probe Tomography (APT). This technique allows analysis at the atomic scale in real space with a three-dimensional analysis. Several types of Si NWs synthesized via different approaches such as etching, Vapor-Liquid-Solid (VLS) mechanism and Solid-Liquid-Solid (SLS) mechanism with different growth catalysts (Au, In and Sn) are investigated. The residing of catalyst atoms in Si NWs is found to be a rather general phenomenon and it is related to the catalyst types and growth mechanisms. The dopant concentration and distribution in Si NW produced by etching is unchanged. As far as the doped Si NWs via VLS mechanism are concerned, a formation of NW core-shell structure with an under-doped core surrounded by an over-doped shell is found whatever the NW morphology and dopant type. A NW sidewall diffusion-based model is proposed to reproduce experimental data and give a possible incorporation pathway for dopant into NW.Les nanofils de silicium (Si) sont des nano-objets à une dimension. Ils font l'objet de beaucoup d'intérêt ces dernières années en raison de leurs bonnes propriétés et leur grand potentiel d'applications. Pour ces applications, il est important de parfaitement contrôler la croissance de ces objets ainsi que leurs dopages. Dans ce contexte, l'objectif de ce travail de thèse est la modélisation de la croissance des nanofils de Si et la métrologie à l'échelle atomique de la composition des nanofils. Dans la première partie de ce travail, nous avons étudié le taux de croissance (longueur) ainsi que l'évolution de la morphologie des nanofils, en particulier l'effet d'effilage. Plusieurs modèles sont proposés selon la nature des nanofils synthétisés via différentes méthodes d'élaboration: Dépôt Chimique en phase Vapeur et Epitaxie par Jets Moléculaires. Les taux de croissance varient selon les méthodes de synthèse. Le modèle reproduit fidèlement les données expérimentales. L'influence des conditions expérimentales sur la morphologie des nanofils est également étudiée dans cette partie. L'objectif de la seconde partie de ce travail est la métrologie des impuretés (catalyseur et dopant) dans les nanofils de Si. Cette étude est réalisée à l'aide de la technique de Sonde Atomique Tomographique (SAT). Cette technique permet une analyse à l'échelle atomique, dans l'espace réel et en trois dimensions de l'objet analysé. Des nanofils synthétisés par différentes techniques telles : la gravure chimique, la méthode Vapeur-Liquide-Solide (VLS) et la méthode Solide-Liquide-Solide (SLS), en utilisant différents catalyseurs de croissance tels Au, In et Sn, sont étudiés. La présence d'atomes des catalyseurs dans les nanofils se trouve être un phénomène général. Un travail sur la métrologie des dopants a également été réalisé. La concentration des dopants et leurs distributions dans les nanofils synthétisé par gravure chimique est inchangée. En revanche, dans les nanofils de Si dopés via un mécanisme de croissance VLS, une structure cœur-coquille avec un cœur sous-dopé et une coquille sur-dopée est observée. Ceci est retrouvé quelque soit la morphologie du nanofil et la nature chimique du dopant. Un modèle basé sur la diffusion latéral (via la surface du nanofil) des dopants est proposé afin de reproduire les profils expérimentaux observés et aussi préciser une voie d'incorporation possible des dopants

Development of Adiabatic Criterion for Runaway Detection and Safe Operating Condition Designing in Semibatch Reactors

To prevent the occurrence of thermal runaway accidents in semibatch reactors (SBRs), it is desirable and practicable to develop criteria that can distinguish between the safe and runaway operating regions. In this article a new safety criterion, namely, the adiabatic criterion, has been developed for SBRs in which liquid homogeneous as well as liquid–liquid heterogeneous reactions with arbitrary reaction orders occur. It states that an SBR is operated in the potential runaway situation if the value of the adiabatic criterion exceeds zero at a segment of the reaction path. Numerical results show that the adiabatic criterion is more conservative than the two other criteria (divergence criterion and target temperature criterion). However, the adiabatic criterion is not suitable to reactions with autocatalytic behaviors. Also knowledge of activation energies and reaction enthalpies is necessary to utilize the adiabatic criterion

Study on the thermal decomposition kinetics of DNTF

3,4-Dinitrofurazanylfuroxan (DNTF) is a representative of the third-generation energetic materials with complex thermal decomposition behavior. Understanding thermal decomposition process of DNTF is of great significance for the safety of its production, storage and use. In this paper, the dynamic differential scanning calorimetry (DSC) test is carried out to study its thermal decomposition characteristics. The quench and reheat experiments and isothermal tests were performed to determine the types of decomposition reactions. A four-step consecutive reaction model, A→B→C→D→E, where each step is an N-order reaction was established for the decomposition process. The established kinetic models were verified by 250°C isothermal test

A Novel Wireless 3D Localization Method Supported by WSN

In many applications, the location information should be necessary. This paper propose a cheap multi-plane 3D localization solution, which based on the existing 2D localization system, a perpendicular 2D plane is added to achieve 3D localization. The algorithm is intended for applications which require information of the height, but remain less sensitive to the location accuracy. At the same time, this paper also introduces symmetrical double-sided two-way ranging (SDS-TWR) and dynamic power consumption intensity searching algorithm into localization system, which can effectively lessen the influence of time synchronization and ease internet traffic congestion of wireless localization network

Impacts of Thermal Inertia Factor on Adiabatic Decomposition of 40% Mass Content DCP in Ethyl Benzene

To reduce the fire and explosion accident of dicumyl peroxide (DCP) in experiment and production, the thermal hazards of DCP and 40% mass content DCP in ethyl benzene (40% DCP) have been studied by the differential scanning calorimeter (DSC) and the accelerating rate calorimeter (ARC) in this paper. DSC experiment showed that ethyl benzene has no effect on the characteristic parameters of thermal decomposition of DCP, such as the temperature of the exothermic peak (Tpeak) and the decomposition energy (Ea), and the thermal decomposition reaction of 40% DCP followed the one-step reaction principle. ARC experiment showed that with the increase of inertia factor (Φ), the measured initial decomposition temperature (Ton) would be higher and the caculated Ea and pre-exponential factor (A) would be greater. It was also proved that after modification of Φ, TD24 was relatively consistent near Ton, but different at higher temperatures. Fisher's correction method was used to verify the necessity of consistency between experimental conditions and prediction conditions