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Quadruple-Cation Wide-Bandgap Perovskite Solar Cells with Enhanced Thermal Stability Enabled by Vacuum Deposition
No full textVacuum processing of multicomponent perovskites is not
straightforward, because the number of precursors is in principle limited by
the number of available thermal sources. Herein, we present a process which
allows increasing the complexity of the formulation of vacuum-deposited lead
halide perovskite films by multisource deposition and premixing both inorganic
and organic components. We apply it to the preparation of wide-bandgap
CsMAFA triple-cation perovskite solar cells, which are found to be efficient but
not thermally stable. With the aim of stabilizing the perovskite phase, we add
guanidinium (GA+) to the material formulation and obtained CsMAFAGA
quadruple-cation perovskite films with enhanced thermal stability, as observed by
X-ray diffraction and rationalized by microstructural analysis. The corresponding solar cells showed similar performance with
improved thermal stability. This work paves the way toward the vacuum processing of complex perovskite formulations, with
important implications not only for photovoltaics but also for other fields of application
Influence of different types of fibers on flexural tensile strength
No full textThe paper presents the influence of the application of different types of fibers in
concrete beams on the flexural tensile strength. All concrete beams were made of
the same component materials and composition, except for the amount of fiber,
which is varied. After hardening, the height of the concrete beams in the central
part was reduced to 125 mm by cutting. The measurement of flexural tensile
strength by was performed according to SRPS EN 14651. Based on the test
results, depending on the type, shape, quantity and distribution of fibers, the
values of ultimate and residual strengths were analyzed
Grejna ploča za merenje toplotne provodljivosti građevinskih materijala
No full textTehničko rešenje predstavlja poboljšanu konstrukciju zaštićene grejne ploče (hotguarded plate) za merenje toplotne provodljivosti termoizolacionih materijala
postavljanjem ispitnog uzorka iznad i ispod grejne ploče (standardna simetrična
ispitna konfiguracija). Merenje toplotne provodljivosti vrši se u skladu sa
standardom SRPS U.A2.020.
Ovim rešenjem toplotna provodljivost se proračunava na osnovu vrednosti
izmerenog toplotnog fluksa korišćenjem dva tanka toplotna fluksmetra na toploj
i hladnoj strani ispitivanih uzoraka. Prednost korišćenja fluksmetara na grejnoj i
rashladnoj ploči u odnosu na uobičajen metod za određivanje toplotne
provodljivosti (hot-guarded plate) je u periodu dostizanja stacionarnog stanja koji
je znatno kraći. Na taj način bi se ostvarila sva zahtevana merenja toplotne
provodljivsti termoizolacionih materijala usled povećane potražnje za ovakvom
vrstom ispitivanja u Republici Srbiji.
Kod metoda merenja sa toplotnim fluksmetrima, uobičajeno je da se koristi jedan
fluksmetar na zaštićenoj grejnoj ploči. Kod ovog tehničkog rešenja koriste se dva
toplotna fluksmetra na površini uzorka. Na taj način se precizno može utvrditi
srednja vrednost toplotnog fluksa kroz ispitivani uzorak tj. srednji toplotni fluks
kroz sam uzorak je tačnije određen. Fluksmetri za ovakvu vrstu merenja su
odabrani sa velikom mernom površinom da bi se dobile što merodavnije
vrednosti raspodele toplotnog fluksa po mernoj površi, pri čemu uobičajeno
korišćenje znatno manjih toplotnih fluksmetara.
Novi koncept grejne ploče ne odgovara uobičajenim grejnim pločama koje su
opisane u standardima. Specifičnost ovog dizajna ploče je u smanjenom
toplotnom prekidu – prostor između unutrašnje zaštićene (hot) i spoljašnje
zaštitne (guard) ploče koje zajedno čine predmet ovog tehničkog rešenja.
Veličinom toplotnog prekida od 1 mm popunjenog dvokomponentnim
termoizolacionim lepkom, određena je i minimalna dozvoljena debljina uzorka.
Na taj način je omogućeno merenje tanjih termoizolacija, tj. povećan je merni
opseg samog uređaja pri ovakvom načinu izrade grejne ploče.
Dodatna prednost u pogledu konstrukcije toplotnog prekida je u formiranju
stepenika čija je osnovna svrha formiranje jednodelne konstrukcije koja se sastoji
od zaštićene (hot) i spoljašnje zaštitne (guard) ploče. Uobičajeno se ovakve ploče
izrađuju iz više segmenata dok je specifičnost ove konstrukcije da se sastoji iz
jednog dela.
Temperaturska razlika između dve ploče se kontroliše korišćenjem termoparova
u diferencijalnom spoju koji su raspoređeni po obimu kontakta dve ploče.
Merenjem naponskog signala za praćenje temperaturne razlike između pomenute
dve ploče mogu se proceniti lateralni gubici između zaštićene i zaštitne ploče i
izmereni naponski signal se može koristiti u svrhe upravljanja.
Grejači zaštićene i zaštitne ploče su ukopani u materijal grejne ploče i napravljeni
su korišćenjem žice za izradu termoparova K tipa. Grejači su vezani na standardni
priključak za termoparove tipa K, koji je fiksiran za grejnu ploču. Preko fiksiranih
priključaka ostvareno je napajanje grejača naponskim dvokanalnim nezavisnim
izvorom. Korišćene su rashladne ploče koje su hlađene korišćem automatzovanog
rashladnog kupatila sa propisanom površinskom fluktuacijom temperature
rashladne površi od 0,1°C.
Validacija grejne ploče je izvršena učešćem u međulaboratorijskom poređenju
Energy dispersive X-ray fluorescence in the investigation of the composition of historical mortars
No full textThe influence of mineral composition on the plastic properties of clay soil
No full textThe paper presents the results of testing the influence of mineralogical composition on the physical and mechanical properties of clayey soil, i.e. Atteberg consistency limits. The tests were conducted on samples of highly plastic clay soil with a high content of clay component in the granulometric composition (CF>80%). The results show that the liquid limit (LL) and the plasticity index (PI) increase with the increased content of clay minerals. High content of clay fraction, high values of Atteberg's consistency limits, analysis of colloidal activity, mineralogical and chemical analyzes showed that these are bentonite type clays containing montmorillonite and kaolinite minerals
Determination of ductile-to-brittle transition temperature of NIOMOL 490K steel welded joints
Get PDFThis paper is devoted to the ductile–brittle transition behavior of high strength low alloyed structural steel NIOMOL 490K. This steel grade is designed for welded pressure vessels exposed to dynamic loads, operating at temperatures below zero, and that is why it must have acceptable toughness. Due to its importance for the safety assessment of pressure vessels, a characterization of this steel with Charpy V-notch test in range of temperature between-60 ⁰C and +60 ⁰C was undertaken. Ductile-to-brittle transition temperature curves were generated in the present study by using instrumented Charpy pendulum impact test on V-notch specimens. Notches were located in the parent material, heat-affected zone and weld metal. The nil-ductility temperature and tensile properties in temperature range from -60 ⁰C to +60 ⁰C are presented in this paper. We used different test temperatures to better understand ductile-to brittle transition response than just use either Charpy energy or other related ductility criteria
Alkali-activated geopolymerization of a low illitic raw clay and waste brick mixture. An alternative to traditional ceramics
No full textGeopolymerization was investigated as an alternative to traditional ceramic products by developing a more sustainable approach that avoids thermal treatment. The study presents the first known alkali-activation of the raw clay and waste clay brick mixture using the solid to liquid ratios of 2.33 and 2.78. Several experimental sets were prepared to harden under varying conditions (2–4 days drying in 60 °C–70 °C and 3 h steam-curing). Non-activated and activated samples were analyzed for their physical and chemical properties after 14, 21, and 28 days. The tile-shaped specimens exhibited better initial drying behavior than the cubes and produced stronger materials with fewer cracks. Pre-curing in steam conditions induced higher flexural strength (13.7 MPa) and water absorption (13.13%) for the geopolymer tiles. The highest Si/Al molar ratio in the amorphous portion of 5.78 induced the best flexural strength. The geopolymerization process showed microstructural changes associated with the appearance of fibrous Na-zeolite nanocrystals. The degree of geopolymerization and zeolite formation was enhanced by steam-curing, but the microstructural stress and heterogeneity induced by the reactions resulted in higher water absorption. Ongoing reactions of amorphization in the bulk material and further crystallization at the surface are documented after 6 months of curing. This first detailed study reveals that the production of geopolymer ceramics from brick waste is possible, but further optimization of the activating solution and curing parameters is required
European and national assessment procedure for the fire performance of facades
Get PDFInnovative construction systems, increasing use of combustible material in facades, less and less space between buildings, increased energy requirements; the transformation of facades in response to these changes requires the involvement of fire safety experts. nts at Grenfell Tower,
London and The Address in Dubai have demonstrated, use of combustible façade elements and lack of-quick time, primarily through the façade. We need to learn from these disasters. Other
incidents prove that the use of nonsuppression.
In the past years EU experts are working on development of common method for assessment of the fire performance of façade systems. The classification system should be transparent and should fit within the framework of existing national regulations. The common assessment method should be applicable to the wide range of façades systems available in the market including glazed façades, green façades and other emerging technologies.
There is a progress in developing legislation on façade fire safety in non-EU countries, due to
emerging fire safety problems and harmonization of regulation with EU. Fire safety of facades in
Serbia is defined through several rulebooks and standards, which significantly improved requirements.
This paper presents the comparative analysis of legislation on facade fire safety in Serbia and other European countries
