L’étude de la précipitation de la silice amorphe à partir de TétraEthylOrtoSilicate (TEOS) et d’eau, selon le procédé Stöber, a permis de quantifier la cinétique de réaction par spectroscopie Infra Rouge à Transformée de Fourrier. Nous avons montré que la croissance des particules se fait par agrégation des nuclei, qui sont formés tout au long de la réaction. La transposition de ce procédé en microémulsion eau-dans-huile a permis de synthétiser des nanoparticules de silice de tailles contrôlées. L’hydrolyse du TEOS est ici dix fois plus faible qu’en phase homogène. Lors de l’ajout du TEOS à la microémulsion, on observe une coalescence des gouttelettes accompagnée d’échanges inter-micellaires. Ce phénomène a pu être décrit par un noyau d’agrégation qui dépend des concentrations en tensioactif et en TEOS non hydrolysé. L’étude de ce procédé en macroémulsion a montré l’effet déstabilisateur de l’éthanol et la nécessité de stabiliser l’émulsion pour synthétiser des particules sphériques / The study of the precipitation of amorphous silica starting from Tetraethoxysilane (TEOS) and water according to the Stöber process, made it possible to quantify the kinetics of the reaction by Fourier-Transform Infrared spectroscopy. We demonstrated that the particles grow by aggregation of the nuclei, which are formed throughout the reaction.The transposition of this process in water-in-oil microemulsion made it possible to synthesize silica nanoparticules with controlled sizes. The hydrolysis of the TEOS is here ten times weaker than in homogeneous phase. When we add the TEOS to the microemulsion, we observe a coalescence of the droplets accompanied by inter-micellar exchanges. This coalescence is well described by a core of aggregation which depends on the concentrations of the surfactant and the non-hydrolysed TEOS. The study of this process in macroemulsions showed the destabilizing effect of ethanol and the need for stabilizing the emulsion to synthesize spherical particles

Solid-state batteries are gaining a lot of attention in the commecial sector today. Development of the solid state electrolytes is an important part in making commercially viable solid-state batteries. While many solid-state electrolytes are struggling with low ionic conductivity, some have shown comparatively high conductivities that can be engineered to perform better to be implemented for consumer market. Silica based solid composite electrolytes (SCEs) are one of the materials that are of huge interest as solid-state electrolytes. As a continuation of the previous research into the silica based SCE’s, the current work focuses on the study of SCEs based on the commercially available mesoporous silica (MPS) of different pore sizes and nanosized silica powder (SNP). Ionic Liquid electrolyte (ILE) based on Li-TFSI and BMP-TFSI mixture was used to prepare composities under different humidity conditions. The effect of the extent of -OH group functionalization of silica, determined by FTIR on treated and untreated powders, on ionic conductivity was also evaluated. Obtained composities were evaluated with electrochemical impedance spectroscopy (EIS) and analysed with TGA to establish correlations based on particle size and pore characteristics of MPS powder. Camparison with SNP was also made in anticipation to draw correlations with MPS. It was found that the pore size and pore volume change have more impact on the conductivity compared to surafce area of commercially obtained MPS and an unexplored pheonomenon was observed in case of SNP based SCE’s. Glovebox (GB) samples at relative humidity (RH)-0.005% have higher conductivity than dryroom samples at RH-0.5%. These findings can be used for a future reference in evaluating commercial MPS based composites as solid-state electrolytes. / Solid-state-batterier får stor uppmärksamhet i den kommersiella sektorn idag. Utveckling av fasta elektrolyter är en viktig del för att göra kommersiellt gångbara solid state-batterier. Medan många fasta elektrolyter kämpar med låg jonledningsförmåga, har vissa visat jämförelsevis höga ledningsförmåga som kan konstrueras för att prestera bättre för att implementeras för konsumentmarknaden. Kiselbaserade fasta kompositelektrolyter (SCE) är ett av de material som är av stort intresse som fasta elektrolyter. Som en fortsättning på den tidigare forskningen om de kiselbaserade SCE:erna fokuserar det nuvarande arbetet på studiet av SCE:er baserade på den kommersiellt tillgängliga mesoporösa kiseldioxiden (MPS) av olika porstorlekar och nanosized kiseldioxidpulver (SNP). Jonisk flytande elektrolyt (ILE) baserad på Li-TFSI och BMP-TFSI-blandning användes för att framställa kompositer under olika luftfuktighetsförhållanden. Effekten av omfattningen av -OH-gruppfunktionalisering av kiseldioxid, bestämd med FTIR på behandlade och obehandlade pulver, på jonkonduktiviteten utvärderades också. Erhållna sammansättningar utvärderades med elektrokemisk impedansspektroskopi (EIS) och analyserades med TGA för att fastställa korrelationer baserat på partikelstorlek och poregenskaper hos MPS-pulver. Kamparison med SNP gjordes också i väntan på att dra korrelationer med MPS. Det visade sig att porstorleken och porvolymsförändringen har mer inverkan på konduktiviteten jämfört med ytan för kommersiellt erhållen MPS och ett outforskat fenomen observerades i fallet med SNP-baserade SCE. Handskbox (GB) prover vid relativ fuktighet (RH)-0,005 % har högre konduktivitet än torrrumsprover vid RH-0,5 %. Dessa resultat kan användas för en framtida referens vid utvärdering av kommersiella MPS-baserade kompositer som fasta elektrolyter.

High voltage rotating machines play a significant role in generation and use of electrical energy as the demand for power continues to increase. However, one of the main causes for down times in high voltage rotating machines is related to problems with the winding insulation. The utilities want to reduce costs through longer maintenance intervals and a higher lifetime of the machines. These demands create a challenge for the producers of winding insulations, the manufacturers of high voltage rotating machines and the utilities to develop new insulation materials which can improve the life of the equipment and reduce the maintenance cost. The advent of nanotechnology in recent times has heralded a new era in materials technology by creating opportunities to significantly enhance the properties of existing conventional materials. Polymer nanocomposites belong to one such class of materials that exhibit unique combinations of physical, mechanical and thermal properties which are advantageous as compared to the traditional polymers or their composites. Even though they show tremendous promise for dielectric/electrical insulation applications, there are no studies relating to the long term performance as well as life estimation of the nanocomposites. Considering this, an attempt is made to generate an understanding on the feasibility of these nanocomposites for electrical insulation applications. An epoxy based nanocomposite system is chosen for this study along with alumina (Al2O3) and silica (SiO2) as the nanofillers. The first and the foremost requirement for studies on polymer nanocomposites is to achieve a uniform dispersion of nanoparticles in the polymer matrix, as nanoparticles are known to agglomerate and form large particle sizes. A laboratory based direct dispersion method is used to process epoxy nanocomposites in order to get well dispersed samples. A detailed microscopy analysis of the filler dispersion using Scanning Electron Microscope (SEM) has been carried out to check the dispersion of the nanofiller in the polymer. An attempt is made to characterize and analyze the interaction dynamics at the interface regions in the epoxy nanocomposite by glass transition temperature (Tg) measurements and Fourier transform infrared (FTIR) spectroscopy studies. The values of Tg for the nanocomposites studied decreases at 0.1 wt% filler loading and then starts to increase gradually with increase in filler loading. This Tg variation suggests that there is certainly an interaction between the epoxy chains and the nanoparticles. Also no new chemical bonds were observed in the spectra of epoxy nanocomposite as compared to unfilled epoxy. But changes were observed in the peak intensity and width of the –OH band in the spectrum of epoxy nanocomposite. This change was due to the formation of the hydrogen bonding between the epoxy and the nanofiller. The thermal conductivity of the epoxy alumina and the epoxy silica nanocomposites increased even with the addition of 0.1 wt% of the filler. This increase in thermal conductivity is one of the factors that make these nanocomposites a better option for electrical insulation applications. The dielectric properties of epoxy nanocomposites obtained in this investigation also reveal few interesting behaviors which are found to be unique and advantageous as compared to similar properties of unfilled materials. It is observed that the addition of fillers of certain loadings of nanoparticles to epoxy results in the nanocomposite permittivity value to be lower than that of the unfilled epoxy over the entire range of frequencies [10-2-106 Hz] considered in this study. This reduction has been attributed to the inhibition of polymer chain mobility caused by the addition of the nanoparticles. The tan values are almost the same or lower as compared to the unfilled epoxy for the different filler loadings considered. This behavior is probably due to the influence of the interface as the strong bonding at the interface will make the interface very stable with fewer defects apart from acting as charge trapping centres. From a practical application point of view, the surface discharge resistant characteristics of the materials are very important and this property has also been evaluated. The resistance to surface discharge is measured in the form of roughness on the surface of the material caused by the discharges. A significant enhancement in the discharge resistance has been observed for nanocomposites as compared to unfilled epoxy/ microcomposites, especially at longer exposure durations. The partial discharge (PD) measurements were carried out at regular intervals of time and it is observed that the PD magnitude reduced with discharge duration in the case of epoxy alumina nanocomposites. An attempt was made to understand the chemical changes on the surface by conducting the FTIR studies on the aged surface. For all electrical insulation applications, materials having higher values of dielectric strengths are always desired and necessary. So AC breakdown studies have also been conducted. The AC breakdown strength shows a decreasing trend up to a certain filler loading and then an increase at 5 wt% filler loading for epoxy alumina nanocomposites. It has been also observed that the type of filler as well as the thickness of the filler influences the breakdown strength. The AC dielectric strength of microcomposites are observed to be lower than the nanocomposites. Extensive research by long term aging studies and life estimation are needed before these new nanocomposites can be put into useful service. So long term aging studies under combined electrical and thermal stresses have been carried out on unfilled epoxy and epoxy alumina nanocomposite samples of filler loading 5 wt%. The important dielectric parameters like pemittivity, tan  and volume resistivity were measured before and after aging to understand the performance of the material under study. The leakage current was measured at regular intervals and tan  values were calculated with duration of aging. It was observed that the tan  values increased drastically for unfilled epoxy for the aging duration considered as compared to epoxy alumina nanocomposites. The life estimation of unfilled epoxy as well as epoxy nanocomposites were also performed by subjecting the samples to different stress levels of 6 kV/mm, 7 kV/mm and 8 kV/mm at 60 oC. It is observed that the epoxy alumina nanocomposite has an enhanced life which is nine times the life of the unfilled epoxy. These results obtained for the nanocomposites enable us to design a better material with improved dielectric strength, dielectric properties, thermal conductivity, resistance to surface discharge degradation and enhanced life without sacrificing the flexibility in the end product and the ease of processing. Dry type transformers and stator winding insulation need to be cast with the above material developed and tested before practically implementing these in the actual application.