500 research outputs found
Particle formation in a laser-heated aerosol reactor. Application to silicon and silicon nitride synthesis
No full textApplied Science
Possible techniques for particle size analysis in a SiH4-NH3 flame
No full textRecent interest in high temperature structural ceramics has led to the development of chemical vapour phase techniques for the formation of a variety of high quality ceramic powders. Silicon nitride, Si3N4, is one of the most promising materials of these structural ceramics, because of its high temperature strength, thermal shock resistance and corrosion resistance. Si3N4 powders have been prepared by several techniques such as direct nitridation of silicon, decomposition of silicon diimide and vapour phase synthesis. Although, relatively small particles can be produced by using vapour phase synthesis initiated by convective heat [Lit.1], smaller and less agglomerated powders have been prepared using a sophisticated technique, Laser-Chemical Vapour phase Precipitation (L-CVP), developed by Haggerty and Danforth [Lit.2]. Characteristic of this laser-driven gas phase process is a well defined reaction zone which should facilitate a considerable degree of control over composition, size and size distribution of the produced powders. This report gives the results of a literature study performed to investigate the possible techniques for particle size analyses in this reaction zone. The aim of this research is to get a better understanding of the processes taking place in this zone. This particle size analysis is to be performed in a flame of SiH4 and NH3 which is used in the production of Si3N4. The ideal technique measures a particle size distribution in-situ, in the submicron range, is cheap, easy to handle, fast and does not influence our process. The second chapter handles on techniques which use a form of light to determine the psd and are non-intrusive. The third chapter deals with techniques which require sampling, and some possible ways of sampling are reported. Chapter 4 deals with techniques which do not belong to the first two groups. Since thermophoresis can become an important phenomenon in our setup the last chapter deals with this phenomenon.Applied SciencesProcess TechnologyParticle technology and Risk managemen
Het Actieve Kool proces van Bergbau Forschung voor het simultane verwijdering van SO2 en NOx uit rookgassen
No full textDocument(en) uit de collectie Chemische Procestechnologie.DelftChemTechApplied Science
The synthesis of Si3N4 using a laser-heated reactor
No full textIt was proved that in the newly developed reactor it is possible to produce Si and Si3N4 powders. The yield varied between 0.2 and 2 g. In 1 hour the theoretical yield (100 % SiH4 conversion, 100 sccm) is 13.7 g Si3N4. It could not be determined whether this low yield was due to low SiH4 conversion or to a low Electrostatic precipitator efficiency. The produced powders were analysed by means of TEM-photography, BET-surface determination and a N-content determination…Applied SciencesParticle Technolog
Modellering van de oplosbaarheid van een zout in gemengde oplosmiddelen
No full textHet doel van deze scriptie is een overzicht te geven van de methoden die een beschrijving geven van de oplosbaarheid van een zout in gemengde oplosmiddelen, of die daar eventueel voor gebruikt zouden kunnen worden. Het eerste deel behandelt de verschillende semi-empirische modellen voor de beschrijving van de oplosbaarheid van een zout in gemengde oplosmiddelen; het tweede deel beschrijft de verschillende modellen voor de activiteitscoefficienten van ionen in gemengde oplosmiddelen, waaruit op verschillende manieren de oplosbaarheid bepaald kan worden. Het literatuuronderzoek gebeurde aan de hand van enkele bron-artikelen en een search in Chemical Abstracts, vanaf 1968. Aan de hand van de gevonden artikelen werd verder teruggezocht. De conclusies zijn dat de semi-empirische modellen zich niet lenen voor nauwkeurige beschrijving van de oplosbaarheden, zelfs het beste model, het solventing out model van Alfassi, is slechts in een beperkt gebied toepasbaar en niet erg nauwkeurig. De modellen voor de activiteiten van de ionen lijken beter geschikt maar ook gelijk veel ingewikkelder; er moeten waarschijnlijk data regressie methoden op toegepast worden. Er moet dan wel een verband gelegd worden tussen activiteit en oplosbaarheid. Als er binaire (vloeistof-zout en vloeistof-vloeistof) vloeistof-damp gegevens beschikbaar zijn, is het Schuberth model het eenvoudigst. Voor het NRTL en UNIQUAC model is de dielectrische constante van het solvent nodig; verder moet voor het NRTL model nog een geschikte ion-ion interactie term gevonden worden.Applied Science
Thermal analysis of the Wire and Arc Additive Manufacturing process using the F.E. method
No full textIn this research, a thermal analysis of the wire and arc additive manufacturing process is presented based on the F.E. method. An important quality of the F.E. model that is presented in this research is to describe the temperature field that is experienced by the deposited material in the wire and arc additive manufacturing process. In contrast to the traditional method of monitoring the substrate temperature, the F.E. model allows to describe the temperature field that is experienced by the deposited material constituting both the multilayer weld deposit and the component. Accordingly, the F.E. model is capable to describe the effect of the locally attained temperature field on the microstructure of the deposited material constituting the multilayer weld deposit in terms of the thermal characteristics including the temperature distribution, the locally attained temperature values, the cooling rates and the temperature gradients throughout the component. Two cooling methods are proposed to control the heat dissipation from the component to the environment based on the application of an interlayer waiting time and immersing the component into a cooling medium. The results show a significant effect of the cooling methods on the temperature field that is experienced by the material constituting both the multilayer weld deposit and the component. Indicating that the cooling methods that are proposed in this research are effective to control the microstructure and the temperature field that is experienced by the component in the wire and arc additive manufacturing process. The resulting microstructure is characterised in terms of the microstructural morphology and the microstructural constituents, using optical microscopy based on the average grain size and the distribution of alloying elements throughout the material constituting the multilayer weld deposit. In addition, the average grain size and the distribution of the alloying elements throughout the material are evaluated in terms of the hardness values.Materials Science and Engineerin
Thermodynamic Calculations on the Chemical Vapor-Deposition of Silicon-Nitride and Silicon from Silane and Chlorinated Silanes
No full textPRESENCE AS CYBER-IMMERSION AND INFANTILE LIFEWORLD TRANSITION FACTOR F.E. VASILYUK'S TYPOLOGY
No full textАвтор статьи анализирует психологические аспекты "виртуализации" человека и его бытия в контексте типологии жизненных миров Ф.Е. Василюка. Выдвигается гипотеза о сущностной близости пребывания человека в виртуальном пространстве и нахождения в инфантильном жизненном мире. Автор полагает, что ключевую роль в процессах киберпогружения и перехода в инфантильный жизненный мир может играть нахождение в "состоянии присутствия" как субъективного переживания пребывания в иллюзорном мире, альтернативном реальности.The author analyses psychological aspects of "virtualization" in terms of F.E. Vasilyuk's lifeworlds' typology. The author states that being in the cyberspace is similar to existence in the infantile lifeworld and that the "presence" phenomenon may serve as the key mechanism to cyber-immersion and "slipping" into the infantile lifeworld.111-11
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