(Et3Si)2Se as a precursor for atomic layer deposition: growth analysis of thermoelectric Bi2Se3

An atomic layer deposition (ALD) process was developed for an important thermoelectric material Bi2Se3utilizing dechlorosilylation reactions between BiCl3and (Et3Si)2Se precursors.</p

Large-area approach to evaluate DC electro-thermal ageing behavior of BOPP thin films for capacitor insulation systems

A large-area electro-thermal ageing test setup was developed and utilized to age several laboratory-scale biaxially oriented polypropylene (BOPP)–hydrophobic silica nanocomposite films. The films were aged in test capacitors with self-healing metallized film electrodes, which enabled the ageing test to continue beyond the first breakdowns. Eight different films were aged for 1000 hours under 100 V/µm DC stress at 75 °C, and large-area DC breakdown measurements, dielectric spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and dielectric spectroscopy were used to detect localized and bulk degradation after the ageing period. The effects of antioxidant contents, different PP grades and compounder screw speed were evaluated. Material characterization indicates no bulk degradation had occurred during ageing, which was associated with moderate temperature stress and inert nitrogen atmosphere. On the other hand, low-field breakdowns (weak points) were observed in all but two of the aged materials, indicating that ageing was dominated by localized degradation which may have introduced new breakdown mechanisms. Weak points were also measured in a similarly aged commercial capacitor-grade BOPP film aged at a lower field, supporting this conclusion. The importance of long-term characterization in material development is demonstrated, and it is shown that long-term properties of the evaluated nanocomposites were at least on the same level compared to neat BOPP films.acceptedVersionPeer reviewe

Silica-Polypropylene Nanocomposites for Film Capacitors:Structure–Property Studies and the Role of Biaxial Stretching Conditions

Biaxial-stretching-induced morphology development and dielectric properties of hydrophobic fumed silica-BOPP nanocomposite films were investigated. The precursor (cast) film morphology, pre-heating as well as biaxial stretchingtemperature and stretch ratio were found to profoundly affect the silica-BOPP film bulk morphology, surface texture and the formation of particle/agglomerate-induced cavitation upon biaxial stretching. Isothermal high-field conductivity and thermally stimulated depolarization current measurements indicated decreasing high-field/high-temperature conductivityand modification of trap density of states upon incorporation of nanosilica in comparison to neat BOPP. Large-area DC dielectric strength is, however, sensitive to thermal/mechanical stresses upon biaxial stretching, hence necessitating careful optimization of the nanocomposite formulation and processing

Biaxially oriented silica–polypropylene nanocomposites for HVDC film capacitors : morphology-dielectric property relationships, and critical evaluation of the current progress and limitations

Dielectric polymer nanocomposites are considered as one of the most promising insulation material candidates for future capacitive energy storage applications, providing tailorability of charge trapping and transport properties at the nanometric level which is a key for increased dielectric performance of biaxially oriented polypropylene (BOPP) for metallized film capacitors in high-voltage direct current (HVDC) applications. In this study, a comprehensive investigation of morphology and dielectric performance of pilot-scale BOPP nanocomposites with hexamethyldisilazane (HMDS)-treated hydrophobic fumed silica nanoparticles was carried out, providing critical perspectives on the performance and challenges of PNCs for thin film capacitors also in a broader context. In non-oriented cast films, incorporation of nanosilica modified the crystallization kinetics and α/β-crystalline spherulitic morphology of polypropylene and reduced the accumulation of space charge under a DC electric field. The nanocomposites exhibited promising dispersion characteristics in the nano-scale, however, the low amount of micron-sized agglomerates inherently present in commercial fumed silica persisted in the compounds which can become critical for thin film applications. Subsequently, biaxial-stretching-induced morphology development and dielectric properties of silica-BOPP nanocomposites were evaluated, highlighting the role of precursor morphology and film processing in the silica-BOPP film morphology, defects and dielectric performance. Charge trapping and transport properties of silica-BOPP films were investigated by isothermal and thermally stimulated techniques under high DC electro-thermal stresses, indicating profound modification of the trap density of states brought about by nanosilica. This resulted in more homogeneous space charge distribution and reduced temperature- and field dependent DC conductivity at 100 °C in comparison to neat BOPP under moderate field stresses (<200 V μm−1), while simultaneously maintaining low dielectric loss. However, the localized weak points caused by silica agglomerates still remain a challenge for the structural homogeneity and dielectric breakdown performance of thin BOPP films under extreme-field stress, hence emphasizing the need for further advancements in the agglomerate and PNC film morphology control to provide high-reliability nanodielectric capacitor thin films for practical HVDC film capacitor applications.publishedVersionPeer reviewe

Architectural Modifications for Flexible Supercapacitor Performance Optimization

We have developed material and architectural alternatives for flexible supercapacitors and investigated their effect on practical performance. The substrate alternatives include paperboard as well as various polyethylene terephthalate (PET) films and laminates, with aqueous NaCl electrolyte used in all devices. In all the supercapacitors, activated carbon is used as the active layer and graphite ink as the current collector, with various aluminium or copper structures applied to enhance the current collectors’ conductivity. The capacitance of the supercapacitors was between 0.05 F and 0.58 F and their equivalent series resistance (ESR) was from <1 Ω to 14 Ω, depending mainly on the current collector structure. Furthermore, leakage current and self- discharge rates were defined and compared for the various architectures. The barrier properties of the supercapacitor encapsulation have a clear correlation with leakage current, as was clearly shown by the lower leakage in devices with an aluminium barrier layer. A cycle life test showed that after 40000 charge-discharge cycles the capacitance decreases by less than 10%.acceptedVersionPeer reviewe

Biomassan tuotanto pelloilla ja soilla sekä käyttö energian tuotantoon - 501

Teknologian kehittämiskeskus, Energiateknologian tutkimusohjelma 1993-1998Vo

Biomassan tuotanto pelloilla ja soilla sekä käyttö energian tuotantoon

Teknologian kehittämiskeskus, Energiateknologian tutkimusohjelma 1993 - 1998Vo

Ruokohelven viljely ja korjuu energian tuotantoa varten

Ruokohelpi on monivuotinen heinäkasvi, jota on viljelty rehuksi. Tässä julkaisussa kuvataan ruokohelven viljely- ja korjuutekniikka energian tuotantoa varten. Ruokohelpi kylvetään puhtaana kasvustona Etelä-Suomessa viimeistään kesäkuun viimeisellä viikolla, pohjoisempana aikaisemmin. Typpilannoitukseksi kylvön yhteydessä riittää 40 kg/ha ja satovuosina 50-100 kg/ha maalajista ja multavuudesta riippuen. Fosfori- ja kaliumlannoitus tehdään maan viljavuusanalyysin perusteella. Länsi-Suomessa parhaiten menestyvät lajikkeet Palaton, Lara, Vantage ja Venture, Pohjois-Suomessa lisäksi Barphal 050 -lajike. Kun ruokohelven biomassa korjataan keväällä kuloheinänä, kylvöjen väli voi olla yli 10 vuotta. Ensimmäisen satovuoden jälkeen kuiva-ainesato on 6-8 t/ha. Ruokohelpi niitetään aikaisin keväällä matalaan sänkeen ja paalataan mahdollisimman tiukkoihin paaleihin pyörö- tai suurkanttipaalaimella. Paalit kuljetetaan aumalle erillisellä traktorilla/kuormaajalla tai traktori-perävaunu -yhdistelmällä. Paalausta tehostetaan leveän niittokoneen tekemällä karheella. Paalit säilyvät pilaantumatta, kun ne varastoidaan aumaan ja peitetään. Myös ruokohelven irtokorjuumenetelmää on kehitetty. Viljelyn lopettamisen jälkeen ruokohelpikasvusto hävitetään glyfosaatilla ja kynnetään syksyllä. Kahtena seuraavana vuonna viljellään kevätviljaa. Ruokohelven siemensato vaihtelee riippuen kasvuston iästä. Siementuotantokokeissa ensimmäisinä vuosina satoa saatiin enimmillään noin 300 kg/ha. Neljän vuoden keskimääräinen siemensato oli noin 100 kg/ha. Siemensadon paras korjuuaika on 15 päivää kukinnan päättymisestä. Keväällä korjattu ruokohelpi soveltuu seospolttoon sekoitettuna turpeeseen, hakkeeseen tai kuoren ja purun seokseen. Konekustannukset lannoitteiden ohella ovat merkittävimmät kustannuserät ruokohelven viljelyssä. Jos ruokohelven energiasisältö hinnoitellaan energiaturpeen mukaan, ruokohelpi pärjää hyvin kannattavuusvertailussa rehuohran viljelyn kanssa