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1

Effects of different grain size of expanded perlite aggregate and content of silica aerogel on the characteristics of lightweight cementitious composite

Vashchuk Andrii, Ślosarczyk Agnieszka

Physicochemical Problems of Mineral Processing

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2023

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Vol. 59, iss. 4

art. no. 174338

EN

In this research, an attempt was made to investigate effects of expanded perlite aggregate grain size on consistency, density, compressive strength, thermal conductivity and microstructure of 15 different composite mixes with silica aerogel. As for the samples preparation, expanded perlite aggregate of 5 different groups based on grain size, were used for sample preparation, then partially replaced by volume for 20% and 40% of hydrophobic silica aerogel particles. The results showed, that density of the samples varied between 0.35 g/cm3 and 1.5 g/cm3, flexural strength varied between 3.4 MPa and 7.4 MPa, compressive strength was in the range between 12.3 MPa and 55 MPa, thermal conductivity coefficient was in the range between 0.130 W/mK and 0.190 W/mK. Scanning electron microscopy showed that expanded perlite aggregates and silica aerogel particles are capable of being mixed and formed homogenous mixture. Nevertheless, microscope images indicated weaker adhesion of silica aerogel particles at interfacial zone as compared with expanded perlite aggregate particles. Results revealed, that both of the factors: grain size of expanded perlite aggregate particles silica aerogel content influenced the density, compressive strength and thermal conductivity. The study also indicated feasibility of expanded perlite aggregate and silica aerogel for achieving homogeneous mixture of the lightweight cementitious composites. Study demonstrated that using different size fractions of expanded perlite aggregate affects differently physical, mechanical and thermal characteristics of the lightweight cementitious composite with silica aerogel.

2

Thermal Behavior of Aerogel-Embedded Nonwovens in Cross Airflow

Xiong Xiaoman, Venkataraman Mohanapriya, Jašíková Darina, Yang Tao, Mishra Rajesh, Militký Jiří, Petrů Michal

Autex Research Journal

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2021

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Vol. 21, no. 1

115--124

EN

Thermal performance of aerogel-embedded polyester/polyethylene nonwoven fabrics in cross airflow was experimentally studied by using a laboratory-built dynamic heat transfer measuring device in which the fabric could be applied on a heating rod. Experiments were performed with different airflow velocities and heating conditions. The temperature–time histories of different materials were collected and compared. The temperature difference and convective heat transfer coefficient under continuous heating were analyzed and discussed. Results showed that under preheated conditions, the aerogel-embedded nonwoven fabrics had very small decrease in temperature and good ability to prevent against heat loss in cross flow. As for the continuous heating conditions, the heat transfer rate of each material showed an increasing trend with increase in the Reynolds number. The aerogel-treated nonwoven fabric with the least fabric thickness and aerogel content delivered a significantly increased heat transfer rate at higher Reynolds number. Thicker fabrics with higher aerogel content could provide better insulation ability in cross flow.

3

Study on the Thermal Insulation Performance of PAN Pre-Oxidised Fibre Felts

Zhao Xiaoming, Liu Yuanjun, Liang Tenglong

Fibres & Textiles in Eastern Europe

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2020

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Vol. 28, no. 3 (141)

27--37

EN

In this paper, an orthogonal experiment of 3 factors and 3 levels was firstly designed to prepare PAN pre-oxidised fibre felts with good thermal insulation properties; the range method was used to analyse the result of the orthogonal experiment, and finally the tensile properties and thermal stability were tested. Finally, pre-oxidised fibre felt composites for the coating of silica aerogel were prepared using the coating process to compound silica aerogel on re-oxidised fibre felts. Firstly, the influence of the content of silica aerogel on the heat insulation performance of the coated composite materials was analysed, and then a test of the coefficient of thermal conductivity, an experiment on the back temperature, and characterisations of the tensile properties and thermal stability of the composite coating of pre-oxidised fibre felt composites of the coating of silica aerogel were carried out. Results showed that through analysis of the orthogonal experiment, we can state that the best preparation process of pre-oxidised fibre needled felts was as follows: needle number – 2, needle depth – 8 mm, and needle frequency – 140 times/min. The transverse tensile strength of PAN pre-oxidised fibre needled felts prepared by crossly webbing of PAN pre-oxidised fibres was superior to the longitudinal tensile strength; thermogravimetric analysis showed that the pre-oxidised fibre needled felts had excellent thermal stability. The coefficient of thermal conductivity of the aerogel coating of the composites firstly decreased and then increased with an increase in the content of aerogel. Coated composites had the lowest coefficient of thermal conductivity when the aerogel content was 4% wt. At temperatures of 100 °C, 150 °C and 200 °C, the heating rate of the transient-state back temperature and the steady-state average temperature were both the lowest when the aerogel content was 6% wt.

PL

W artykule zaprojektowano ortogonalny eksperyment z 3 czynnikami i 3 poziomami w celu przygotowania wstępnie utlenionych filców PAN o dobrych właściwościach termoizolacyjnych; do analizy wyników eksperymentu ortogonalnego zastosowano metodę zakresu, a na koniec przetestowano właściwości rozciągania i stabilność termiczną. Najpierw przeanalizowano wpływ zawartości aerożelu krzemionkowego na właściwości izolacji cieplnej powleczonych materiałów kompozytowych, a następnie wykonano test współczynnika przewodności cieplnej, przeanalizowano też charakterystykę właściwości rozciągania i stabilności termicznej powłoki kompozytowej wstępnie utlenionych kompozytów filcowych. Wyniki pokazały, że poprzez analizę eksperymentu ortogonalnego można stwierdzić, że najlepszy proces przygotowania filców igłowanych charakteryzuje się następującymi parametrami: liczba igły – 2, głębokość igły – 8 mm i częstotliwość igły – 140 razy/min. Wytrzymałość poprzeczna na rozciąganie igłowanych filców z włókien PAN była lepsza niż wytrzymałość na rozciąganie wzdłużne; analiza termograwimetryczna wykazała, że igłowane filce z wstępnie utlenionego włókna miały doskonałą stabilność termiczną. Współczynnik przewodności cieplnej powłoki aerożelowej kompozytów najpierw zmniejszył się, a następnie wzrósł wraz ze wzrostem zawartości aerożelu. Powlekane kompozyty miały najniższy współczynnik przewodności cieplnej, gdy zawartość aerożelu wynosiła 4% wag. W temperaturach 100, 150 i 200 °C szybkość ogrzewania i średnia temperatura w stanie ustalonym były najniższe, gdy zawartość aerożelu wynosiła 6% wag.

4

Application of Silica Aerogel in Composites Protecting Against Thermal Radiation

Krzemińska Sylwia, Cieślak Małgorzata, Kamińska Irena, Nejman Alicja

Autex Research Journal

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2020

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Vol. 20, no. 3

274--287

EN

Aerogels are characterized by excellent insulation properties and a good resistance to high and low temperatures. The objective of this study was to investigate the effects of silica aerogel on thermal properties of textile–polymer composites. Aerogel was applied in protective clothing fabric to improve its heat resistance. The composites were produced by coating a fabric made of meta-aramid (polyamide–imide) yarns with a dispersion of polychloroprene latex and synthetic resins or an acrylic–styrene dispersion with aerogel (100–700 μm particle size). The composites were subjected to thermal radiation (20 kW/m2) and their thermal properties were determined by thermogravimetry/derivative thermogravimetry (TG/DTG). Scanning electron microscopy/X-ray energy dispersive spectroscopy (SEM/EDS) was used to characterize the microstructure and study the elemental composition of materials. The thermal conductivity and resistance of composites were measured with an Alambeta apparatus. The tests indicated an increase in resistance to thermal radiation by approximately 15–25%. In TG/DTG analysis, the initial temperature for an unmodified fabric was 423.3°C. After modification, it decreased to 361.8° and 365.3°C for composites with 7 and 14% of aerogel, respectively. SEM images revealed a reduction in aerogel particle size.

5

Fabrication of Agar-Silica Aerogel Nanocomposite Films

Lee Min-Jin, Jung Hyun-Ah, Lee Kyong-Jin, Hwang Haejin

Archives of Metallurgy and Materials

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2019

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Vol. 64, iss. 3

851--855

EN

In this study, agar-based nanocomposite films containing ultra-porous silica aerogel particles were fabricated by gel casting using an aqueous agar/silica aerogel slurry. The silica aerogel particles did not show significant agglomeration and were homogeneously distributed in the agar matrix. Transmission electron microscopy observations demonstrated that the silica aerogel particles had a mesoporous microstructure and their pores were not incorporated into the agar polymer molecules. The thermal conductivities of the agar and agar/5wt.% silica aerogel nanocomposite films were 0.36 and 0.20 W·m-1·K-1, respectively. The transmittance of the agar films did not decrease upon the addition of silica aerogel particles into them. This can be attributed to the anti-reflection effect of silica aerogel particles.

6

Performance of silica aerogels modified with amino functional groups in PB(II) and CD(II) removal from aqueous solutions

Faghihian H., Nourmoradi H., Shokouhi M.

Polish Journal of Chemical Technology

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2012

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Vol. 14, nr 1

50-56

EN

The adsorption behavior of Pb(II) and Cd(II) ions in aqueous solutions on silica aerogels modified with amino propyl triethoxysilane was investigated as a function of pH, contact time, adsorbate concentration and adsorbent dose. It was found that maximum adsorption of Pb(II) and Cd(II) ions occurs at pH 6.0 and pH 8.0, respectively. The optimum contact time to obtain equilibrium adsorption with the modified silica aerogel was experimentally found to be around 48h. Adsorption isotherms clearly indicated that the adsorption behavior of metals ions on the modified silica aerogels is fitted well with both the Langmuir and Freundlich isotherms. The maximum adsorption capacities of Pb(II) and Cd(II) on modified silica aerogel were found to be 45.45mg/g and 35.71mg/g, respectively. The results indicated that silica aerogels modified with amino functional groups can be used as an efficient adsorbent in the removal of metal ions such as Pb(II) and Cd(II) from aqueous solutions.

7

Wpływ aerożelu na właściwości wulkanizatów kauczuku butadienowo-akrylonitrylowego (NBR)

Magryta J.

Polimery

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2012

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T. 57, nr 2

117-123

PL

Zbadano wpływ dodatku handlowego aerożelu krzemionkowego na właściwości mechaniczne wulkanizatów kauczuku butadienowo-akrylonitrylowego (NBR). Sporządzono dwie serie mieszanek kauczukowych (NBR 1 i NBR 2) napełnionych krzemionką i aerożelem w ilości, odpowiednio, 70 lub 76 cz. mas. napełniacza na 100 cz. mas. kauczuku, przy czym mieszanka NBR 1 zawierała ponadto żywicę nowolakową (50 phr). Aerożel wprowadzano do mieszanek kauczukowych w typowy sposób, stosowany w przemyśle gumowym. Mimo bardzo dużej w porównaniu z krzemionką powierzchni właściwej aerożelu uzyskane wzmocnienie wulkanizatów było znacznie mniejsze od oczekiwanego. Obserwowano niewielkie zmiany twardości i wytrzymałości na rozciąganie, a charakter tych zmian zależał od obecności żywicy nowolakowej w mieszance kauczukowej. Zastąpienie krzemionki aerożelem powodowało wzrost elastyczności przy odbiciu oraz zmniejszenie kąta stratności. Zmiany modułu dynamicznego były stosunkowo niewielkie i również zależne od obecności żywicy nowolakowej w mieszance. Porównywalne wartości gęstości wulkanizatów badanych mieszanek kauczukowych z udziałem aerożelu lub krzemionki mogą świadczyć o tym, że część porowatej struktury aerożelu uległa zniszczeniu w trakcie procesu przygotowania mieszanek kauczukowych i próbek wulkanizatów.

EN

The effect of the addition of commercial silica aerogel (Table 1) on the mechanical properties of peroxide cured acrylonitrile-butadiene rubber (NBR) was studied. Two series of rubber compounds (NBR 1 and NBR 2) were prepared, filled respectively with silica (70 phr) and aerogel (76 phr), additionally NBR 1 contained novolak resin (50 phr). The aerogel was introduced into the rubber compound in a manner typical for fillers in rubber industry. In spite of the very large surface area of the aerogel in comparison with the silica, the reinforcing effect was significantly weaker than expected. Slight changes in the hardness and tensile strength were observed, the character of these changes was dependent on the presence of novolak resin in the rubber compound (Table 2, 3, Fig. 1). The replacement of silica by aerogel resulted in the increased impact resilience and decreased loss angle in the simple shear dynamic tests as a function of the shear amplitude (Figs. 4, 5) or the aerogel content (Figs. 8, 9). Changes in the dynamic modulus were relatively minor and dependent on the presence of novolak resin in the rubber compound (Figs. 6, 7, 10, 11). The comparable density values for the vulcanizates with the silica and the aerogel may indicate that a part of the porous structure of the aerogel was destroyed during the preparation of rubber compounds and vulcanizates.

8

Optically transparent and structurally sound silica aerogels: insights from a process study

Athmuri K., Marinov V.

Advances in Materials Science

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2012

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Vol. 12, nr 1(31)

5-16

EN

Aerogels are internally nanostructured materials characterized with a plethora of unique properties. Monoliths with high optical transparency made of silica aerogels were some of the first and still one of the most important classes of aerogels. Experiments and theory indicate that optical transparency and structural integrity of silica aerogels are negatively correlated. Other than optimal combination of processing conditions during aerogel fabrication can result in either highly transparent but cracked or in crack-free but less transparent and even opaque aerogels monoliths. Results are presented from the study of the relationship between the properties of single-step tetramethoxysilane (TMOS) base-catalyzed silica aerogels and the processing conditions, both at the alcogel preparation step and during the supercritical liquid CO2 drying process. Crack-free aerogel monoliths with good optical transparency were obtained with TMOS:methanol (MeOH) molar ratios of 1:16 and TMOS:ammonia (NH4OH) molar ratios of 1:0.05, CO2-MeOH exchange rates of about 1.25 ml/min, and autoclave decompression rates of 70 KPa/min. Adding glycerol in the sol-gel stage had a positive effect on the aerogel monolithicity but, even without glycerol, crack-free silica aerogels can be obtained by reducing the depressurization rate of the autoclave. A strict control and careful selection of the aerogel’s processing conditions within the set of parameters identified will enable the fabrication of structurally sound silica aerogels with good optical properties essential for a number of applications.

9

Nanostructure of some porous materials studied by SAXS.

Pająk L., Jarzębski A.B., Mrowiec-Białoń J., Bierska B.

Archiwum Nauki o Materiałach

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2001

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T. 22, nr 2

107-114

PL

Struktura większości materiałów porowatych jest zazwyczaj złożona. Porowatość materiałów (część objętości materiału zajmowana przez pory) może się zmieniać w szerokim zakresie, osiągając w aerożelach nawet wielkość powyżej 99%. W ostatnim dwudziestoleciu osiągnięto znaczący postep w opisie złożonych, nieuporządkowanych struktur materiałów porowatych poprzez wprowadzenie geometrii fraktalnej. Obecnie przyjmuje się, że modele fraktalne struktury por lepiej opisują rzeczywistą strukturę aniżeli klasyczne, proste modele. Metoda małokątowego rozpraszania promieni rentgenowskich (SAXS) jest szczególnie użyteczna w badaniach materiałów porowatych, niejednorodnych w skali 10-1000 angstremów. Badania struktury wybranych materiałów porowatych wykonano dla aerożeli o szkielecie zbudowanym z SiO2 i ZrO2, żelu krzemionkowego, krzemionki pirogenicznej, szkła porowatego, elektroosadzanego metalu i różnych materiałów węglowych. Natężenie małokątowego rozpraszania analizowano głównie na podstawie prawa potęgowego rozpraszania. Podano przykłady materiałów porowatych o strukturze typu fraktali masowych, powierzchniowych i porowych. Wyznaczono odpowiednio wartości masowych, powierzchniowych i porowych (Dm, Ds i Dp) wymiarów fraktalnych.

EN

The structure of most porous materials is quite complex. The porosity of materials (total volume fraction of material occupied by pores) can vary in a very broad range, from much less than 1% up to more than 99% in the case of aerogels. In the last two decades the characterisation of the complex, disordered structure of porous materials has made a milestone progress owing to the use of fractal geometry. At present it is generally accepted that the fractal models of pore structure describe the real structure better than the classical models which assume the existence of macro-, meso- and micropores of simple geometry. The small-angle X-ray scattering (SAXS) method is specially useful in the studies of porous materials in the length scale 10-1000 angstroms. The SAXS studies were performed on dry, porous materials like silica and zirconia aerogels, conventional silica gel, fumed silica, porous glass, electrodeposited metal and different carbonaceous materials. The scattering intensities I(q) were tested mainly in terms of power-law equation . The examples of porous materials with mass, surface and pore fractal morphology are given. Mass surface and pore fractal dimensions (Dm, Ds and Dp) were estimated, respectively.