Thermal properties of organic and inorganic aerogels

1994 ◽  
Vol 9 (3) ◽  
pp. 731-738 ◽  
Author(s):  
Lawrence W. Hrubesh ◽  
Richard W. Pekala
Keyword(s):  
Thermal Conductivity ◽  
Pore Size ◽  
Average Pore Size ◽  
Sol Gel ◽  
Total Thermal Conductivity ◽  
Insulation Property ◽  
Average Pore ◽  
Thermal Insulating ◽  
Thermal Insulation Property ◽  
Infrared Extinction

Aerogels are open-cell foams that have already been shown to be among the best thermal insulating solid materials known. This paper examines the three major contributions to thermal transport through porous materials, solid, gaseous, and radiative, to identify how to reduce the thermal conductivity of air-filled aerogels. We found that significant improvements in the thermal insulation property of aerogels are possible by (i) employing materials with a low intrinsic solid conductivity, (ii) reducing the average pore size within aerogels, and (iii) affecting an increase of the infrared extinction in aerogels. Theoretically, polystyrene is the best of the organic materials and zirconia is the best inorganic material to use for the lowest achievable conductivity. Significant reduction of the thermal conductivity for all aerogel varieties is predicted with only a modest decrease of the average pore size. This might be achieved by modifying the sol-gel chemistry leading to aerogels. For example, a thermal resistance value of R = 20 per inch would be possible for an air-filled resorcinol-formaldehyde aerogel at a density of 156 kg/m3, if the average pore size was less than 35 nm. An equation is included which facilitates the calculation of the optimum density for the minimum total thermal conductivity, for all varieties of aerogels.

Synthesis, characterization, and photocatalytic activity of silver and zinc co-doped TiO2 nanoparticle for photodegradation of methyl orange dye in aqueous solution

2019 ◽  
Vol 97 (9) ◽  
pp. 642-650 ◽  
Author(s):  
Gabriel O. Oladipo ◽  
Akinola K. Akinlabi ◽  
Samson O. Alayande ◽  
Titus A.M. Msagati ◽  
Hlengilizwe H. Nyoni ◽  
...  
Keyword(s):  
Methyl Orange ◽  
Pore Size ◽  
Average Pore Size ◽  
Sol Gel ◽  
Average Crystallite Size ◽  
Rutile Phase ◽  
Absorption Bands ◽  
Average Pore ◽  
Methyl Orange Dye ◽  
Co Doped

In this study, TiO2 nanocrystals, 1 mol% Ag-doped TiO2, and 1 mol% Ag and 0.6 mol% Zn co-doped TiO2 powders were synthesized by the sol–gel route. Their photocatalytic activities on methyl orange dye under visible irradiation were investigated. The powders were characterized by X-ray diffraction (XRD), UV–visible spectroscopy (UV–vis), Brunauer–Emmett–Teller (BET), and Fourier transform infrared spectroscopy (FTIR). The XRD results revealed the presence of a rutile phase with an average crystallite size of 9 and 11 nm. The UV–vis spectra showed a red-shift towards a longer wavelength with the corresponding decrease in band gap from 2.9 to 2.5 eV. The BET surface areas of the nanoparticles ranged from 4.7 to 11.8 m2 g−1 with an average pore size between 18.9 and 56.6 nm. The Ag-doped TiO2 has the largest surface area of 11.8 m2 g−1, whereas the Ag–Zn co-doped TiO2 was found to have the highest pore size and volume. The absorption bands at 750–500 cm−1 were attributed to the –O–Ti–O– bond in the TiO2 lattice. The photocatalytic efficiency was highest at an optimum pH of 4.1 for Ag–Zn co-doped TiO2. The results confirmed that Ag-doped and Ag–Zn co-doped TiO2 were more effective than pure TiO2. The kinetic data were fitted into a pseudo first-order equation using a Langmuir–Hinshelwood kinetic model.

scholarly journals Sol–Gel Synthesis and Characterization of a Quaternary Bioglass for Bone Regeneration and Tissue Engineering

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4515
Author(s):  
Ricardo Bento ◽  
Anuraag Gaddam ◽  
José M. F. Ferreira
Keyword(s):  
Tissue Engineering ◽  
Bone Regeneration ◽  
Pore Size ◽  
Average Pore Size ◽  
Glass Structure ◽  
Sol Gel ◽  
Atomic Scale ◽  
Average Pore ◽  
Hydrolysis And Condensation ◽  
Sol Gel Synthesis

Sol–gel synthesis using inorganic and/or organic precursors that undergo hydrolysis and condensation at room temperature is a very attractive and less energetic method for preparing bioactive glass (BG) compositions, as an alternative to the melt-quenching process. When properly conducted, sol–gel synthesis might result in amorphous structures, with all of the components intimately mixed at the atomic scale. Moreover, developing new and better performing materials for bone tissue engineering is a growing concern, as the aging of the world’s population leads to lower bone density and osteoporosis. This work describes the sol–gel synthesis of a novel quaternary silicate-based BG with the composition 60 SiO2–34 CaO–4 MgO–2 P2O5 (mol%), which was prepared using acidified distilled water as a single solvent. By controlling the kinetics of the hydrolysis and condensation steps, an amorphous glass structure could be obtained. The XRD results of samples calcined within the temperature range of 600–900 °C demonstrated that the amorphous nature was maintained until 800 °C, followed by partial crystallization at 900 °C. The specific surface area—an important factor in osteoconduction—was also evaluated over different temperatures, ranging from 160.6 ± 0.8 m2/g at 600 °C to 2.2 ± 0.1 m2/g at 900 °C, accompanied by consistent changes in average pore size and pore size distribution. The immersion of the BG particles in simulated body fluid (SBF) led to the formation of an extensive apatite layer on its surface. These overall results indicate that the proposed material is very promising for biomedical applications in bone regeneration and tissue engineering.

Nanoporous TiO2/SiO2 Composite Prepared by a Combined Sol-Gel and Hybrid Method

2008 ◽  
Vol 368-372 ◽  
pp. 1497-1499 ◽  
Author(s):  
Wen Yuan Xu ◽  
Lu Bin Wei ◽  
Ming Biao Luo
Keyword(s):  
Phase Composition ◽  
Pore Size ◽  
Hybrid Method ◽  
Average Pore Size ◽  
Sol Gel ◽  
Molar Ratio ◽  
Tetrabutyl Titanate ◽  
Average Pore ◽  
Silica Nanocomposites ◽  
Surface Areas

Titania-silica nanocomposites with different TiO2/SiO2 compositions have been prepared by a sol-gel and hybrid method from tetraethylorthosilicate (TEOS) and tetrabutyl titanate(TBT) and β-Cyclodextrin as a pore-forming template. Drying and calcining of the hybrid xerogel can lead to the formation of nanoporous particles with surface areas in the range of 298-418 m2/g. The effect of the β-cyclodextrin concentration, the molar ratio of TiO2/SiO2 and the calcining temperature on the phase composition and structural properties of TiO2/SiO2 composites were also investigated. The results show that an increase in β-cyclodextrin concentration can lead to a decrease of the surface area and an increase of average pore size, which can be controlled by the amount of β- cyclodextrin in the hybrid sol.

scholarly journals Incorporation of Polymers into Calcined Clays as Improved Thermal Insulating Materials for Construction

2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
Serina Ng ◽  
Bjørn Petter Jelle
Keyword(s):  
Thermal Conductivity ◽  
Thermal Insulation ◽  
Insulation Property ◽  
One Pot ◽  
Calcined Clay ◽  
Thermal Insulating ◽  
Thermal Insulation Property ◽  
Clay Layers ◽  
Thermally Conducting ◽  
Cementing Material

Calcined clay is a Type Q supplementary cementing material according to EN197-1:2000. It possesses lower thermal conductivity than cement. To further improve its thermal insulation property, polymer-calcined clay complexes (PCCs) were produced in a one-pot synthesis. Two contrasting polymers, polystyrene (PS) and polyethylene glycol (PEG), were employed. The hydrophilicity of the polymers influenced the thermal conductivity of PCC. Hydrophilic PEG entrapped more water molecules on clay layers than the hydrophobic PS, making PEG-PCC more thermally conducting than PS-PCC. Contaminants in calcined clays played a role in affecting the overall thermal conductivity. PCC can improve thermal insulation properties for future construction applications.

Characterization of TiO2 Film Prepared by Sol-Gel Method Using Ti(OC4H9)4

2011 ◽  
Vol 298 ◽  
pp. 249-252 ◽  
Author(s):  
Li Li Yang ◽  
Jia Wei Bai ◽  
Wen Jie Zhang
Keyword(s):  
Pore Size ◽  
Tio2 Film ◽  
Average Pore Size ◽  
Sol Gel ◽  
Total Pore Volume ◽  
Source Surface ◽  
Average Pore ◽  
Tio2 Particles ◽  
Sol Gel Process

TiO2 film was dip-coated on glass substrate by a sol-gel process. Ti(OC4H9)4 was used as the titanium source. Surface morphology, crystallite phase, UV-Vis transmittance spectrum and pore size distribution of TiO2 powder prepared under the same conditions of the film were investigated. Surface of TiO2 film is fairly smooth with very slight roughness. No obvious hole or pore is found on the surface of the film. The strongest diffraction peak situated at 2θ=25.3o is the characteristic of anatase TiO2. The absorption edge of the TiO2 film is around 350 nm, while the transmittance fluctuates between 50% and 90%. The average pore size of the TiO2 particles calculated by BJH method is 23 nm. The total pore volume and specific surface area are 0.16 ml/g and 27 m2/g, respectively.

Porous Silica Nanomaterial Derived from Organic Waste Rice Husk as Highly Potential Drug Delivery Material

2019 ◽  
Vol 964 ◽  
pp. 88-96
Author(s):  
Hariyati Purwaningsih ◽  
Slamet Raharjo ◽  
Vania Mitha Pratiwi ◽  
Diah Susanti ◽  
Agung Purniawan
Keyword(s):  
Mesoporous Silica ◽  
Pore Size ◽  
Surface Area ◽  
Hydrothermal Treatment ◽  
Rice Husk ◽  
Average Pore Size ◽  
Sol Gel ◽  
Average Pore ◽  
Hydrothermal Temperature ◽  
Mcm 41

Rice became the main product of agriculture in agrarian countries including Indonesia. Rice husk is a waste of rice as one of the largest silica producers. Silica from rice husks can be used as a source of silica in the manufacture of sodium silicate as an alternative to the formation of mesoporous silica at a low price. In this research, the characterization of mesoporous silica nanoparticle (MSN) MCM-41 from rice husk (rice husk) with sol-gel method followed by hydrothermal treatment. Silica extraction was performed by titrating sodium silica using HCl method until the gel was formed. The mesoporous synthesis was performed with the addition of CTAB. The titration is then carried out using a solution of acetic acid. XRD shows silica with an amorphous structure. The FTIR results show that extraction silica and MSN MCM-41 contain pure silica displayed with Si-O-Si functional groups in the sample. The SEM results show MSN MCM-41 images such as a coral-like structure of agglomerated silica and the higher temperature hydrothermal treatment then it would be the more large size of particles. The material has a hexagonal pore structure such as a honeycomb as characteristic of MCM-41 with a pore size of 2.535 nm which includes mesoporous material. The result of nitrogen adsorption-desorption isotherms shows lower hydrothermal temperature will increase the specific surface area and decrease average pore size, where the best result with surface area value is 825.365 m2/gr and average pore size is 6.10426 nm obtained from process hydrothermal at 85°C.

Study on Environmental Materials with Pore Size and Photocatalytic Activity of Porous TiO2-Al2O3 Photocatalyst

2013 ◽  
Vol 700 ◽  
pp. 67-70 ◽  
Author(s):  
Rui Ma ◽  
Wen Jie Zhang
Keyword(s):  
Methyl Orange ◽  
Photocatalytic Degradation ◽  
Pore Size ◽  
Pore Volume ◽  
Average Pore Size ◽  
Sol Gel ◽  
Total Pore Volume ◽  
Degradation Process ◽  
Order Kinetic ◽  
Average Pore

A novel porous TiO2-Al2O3 composite as a kind of environmental material was prepared by sol-gel method. The pore size distribution is not even in the whole pore size range. When pore size is 7.049 nm, the maximum pore volume of the material is 0.06627 cm3·g-1. The average pore size for the material is 14.56 nm and the total pore volume is 0.3945 cm3·g-1, as calculated from BJH method. Photocatalytic degradation of methyl orange can be regarded as following first order kinetic reaction. After 90 min of reaction, methyl orange degradation on the material was 77.0% and the total dye decoloration rate was 95.1%, containing both adsorption and photocatalytic degradation. The intensities of both peaks in visible and UV regions decreased sharply during photocatalytic degradation process.

Sol-Gel Processing of Low Dielectric Constant Nanoporous Silica Thin Films

2001 ◽  
Vol 703 ◽  
Author(s):  
Deok-Yang Kim ◽  
Henry Du ◽  
Suhas Bhandarkar ◽  
David W. Johnson
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Average Pore Size ◽  
Sol Gel ◽  
Porous Silica ◽  
Dielectric Constants ◽  
Gelling Agent ◽  
Porous Films ◽  
Average Pore

ABSTRACTTetramethyl ammonium silicate (TMAS) is known as a structuring agent in zeolite synthesis. We report its first use to prepare porous silica films for low k dielectric applications in microelectronics. A solution of TMAS 18.7 wt. % was spin coated on silicon substrates with a 3000 Å thick thermal oxide. The spin coated films were subsequently heat-treated at 450°C to obtain porous silica. The use of TMAS solution without gelation led to films of only moderate porosity value of 10%. The addition of methyl lactate, a gelling agent, significantly increased film porosity and improved the pore size distribution. For example, 50% porosity and uniform pore size distribution (average pore size ∼ 40 Å) has been achieved. Dielectric constants (k) of our porous films are as low as 2.5.

Sol–gel synthesis of mesoporous spherical zirconia

RSC Advances ◽  
2015 ◽  
Vol 5 (127) ◽  
pp. 104629-104634 ◽  
Author(s):  
Yulei Chang ◽  
Chen Wang ◽  
Tongxiang Liang ◽  
Chunsong Zhao ◽  
Xi Luo ◽  
...  
Keyword(s):  
Pore Size ◽  
Surface Area ◽  
Average Pore Size ◽  
Sol Gel ◽  
Sodium Dodecyl ◽  
Sodium Dodecyl Sulfonate ◽  
Average Pore ◽  
Gel Method ◽  
Sol Gel Method ◽  
Sol Gel Synthesis

Mesoporous spherical zirconia (ZrO2) with a surface area of 113 m2g−1and average pore size of 5.0 nm is prepared by a sol–gel method with ZrOCl2·8H2O precursors and Sodium Dodecyl Sulfonate (SDS) templates with subsequent annealing at 500 °C in air.

The pore morphology of fluoride catalyzed xerogels

1989 ◽  
Vol 4 (3) ◽  
pp. 693-697 ◽  
Author(s):  
J-B. Chan ◽  
D-W. Hua ◽  
R. Winter ◽  
J. Jonas
Keyword(s):  
Pore Size ◽  
Heating Temperature ◽  
Average Pore Size ◽  
Sol Gel ◽  
Fluoride Concentration ◽  
Silica Gels ◽  
Fluoride Anion ◽  
Average Pore ◽  
Host Materials ◽  
Wide Range

The fluoride anion has been shown to be one of the most effective catalysts in accelerating the polycondensation of alkoxide-derived silica gels. A detailed pore analysis study has been employed to investigate the effect of NaF on the pore structure of the resulting xerogels and its evolution during thermal heat treatment up to 800 °C. Addition of NaF to tetramethylorthosilicate-sols leads to an increase in average pore size, and the pore size distribution becomes narrower. By changing the fluoride concentration and the heating temperature, the surface properties of the xerogels can be tuned over a wide range. The possible application of the F− anion catalyzed sol gel process to prepare porous host materials for the studies of fluids in restricted geometries is also discussed.

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