scholarly journals Microstructure Evolution Mechanism of Geopolymers with Exposure to High-Temperature Environment

Crystals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1062
Author(s):  
Yuanen Lu ◽  
Na Cui ◽  
Yougong Xian ◽  
Jiaqing Liu ◽  
Chao Xing ◽  
...  
Keyword(s):  
Microstructure Evolution ◽  
Crystallization Process ◽  
Glassy Phase ◽  
Heating Temperature ◽  
Average Pore Size ◽  
Cementitious Materials ◽  
Molar Ratio ◽  
Binder Phase ◽  
Average Pore ◽  
Average Size

The investigation on geopolymers has intrigued broad interests in the past decades, due to the requirements for the recycling of aluminosilicate solid wastes, such as red mud, slags, sludges and demolished concrete. Previous studies have demonstrated the feasibility of reusing this Aluminosilicate as a resource to prepare cementitious materials and indicated their promising properties at ambient temperature. However, when this material was exposed to high temperatures, especially above 1000 °C, the microstructure evolution mechanisms were not systematically investigated. In this study, the microstructural evolution process of metakaolin-based K geopolymer (molar ratio of K:Al:Si was 1:1:4) is investigated. The crystalized leucite originated from the geopolymer precursor was detected above 1000 °C. The SEM results indicate that the microstructure of the geopolymer before heating was composed of non-reacted metakaolin with a typical layered structure and reacted amorphous binder phase. As the geopolymer heated to 1000 °C, the microstructure of the geopolymer changed to a porous structure with an average pore size from 10 to 30 μm. When the heating temperature reached 1100 °C, the pores started to close along with the leucite crystallization process. As the heating temperature reached 1200 °C, most of the pores were closed. The TEM results show that the microstructure of the geopolymer, after being heated to 1400 °C, was composed of an amorphous glassy phase and crystallized leucite phase. The crystallized leucite grains originated from the nano-sized crystal nuclei, with an average size of 2–3 nm. The TEM-EDS results indicate that the chemical composition of the glassy phase was complicated. It varied from area to area because of the movement and uneven distribution of K.

PHOTOCATALYTIC REMOVAL OF PHENOL OVER MESOPOROUS ZnO/TiO2 COMPOSITES

2018 ◽  
Vol 80 (2) ◽  
Author(s):  
Klinsmann Cheong Lee Khang ◽  
Mohd Hayrie Mohd Hatta ◽  
Siew Ling Lee ◽  
Leny Yuliati
Keyword(s):  
Pore Size ◽  
Uv Light ◽  
Average Pore Size ◽  
Anatase Tio2 ◽  
Light Irradiation ◽  
Molar Ratio ◽  
Average Pore ◽  
Uv Light Irradiation ◽  
Photocatalytic Removal ◽  
Mesoporous Zno

A series of mesoporous ZnO/TiO2 composites were successfully synthesized using cetyltrimethylammonium bromide surfactant. The composites of different Zn:Ti molar ratios (0.5:1, 0.75:1, and 1:1) were prepared by impregnating ZnO onto mesoporous TiO2. XRD results verified co-existence of both anatase TiO2 and hexagonal wurtzite ZnO in the ZnO/TiO2 composites. Based on the Tauc plots, all the composites showed almost the same band gap energy of approximately 3.21 eV. The fourier transform infrared spectroscopy results successful covering of ZnO on the surface of the TiO2 as the hydrophilicity property of TiO2 decreased remarkably with the loading of ZnO in the composites. N2 adsorption-desorption isotherms of the samples exhibited type-IV isotherm with a hysteresis loop. The Barrett-Joyner-Halenda pore size distribution revealed that the average pore size of the composites was around 3.6 nm, indicating the formation of mesopores dominantly in the samples. The photocatalytic removal of phenol over the samples under UV light irradiation after 3 h decreased in the order: ZnO/TiO2 composites > anatase TiO2 (with surfactant) > anatase TiO2 (without surfactant) > ZnO. The composite with Zn:Ti molar ratio of 0.75:1 has achieved the highest photocatalytic activity of 36.5% in the removal of phenol under UV light irradiation for 3 h.

scholarly journals Evaluation of dolomite as catalyst in the transesterification reaction using palm oil (RBD)

DYNA ◽  
2019 ◽  
Vol 86 (209) ◽  
pp. 180-187
Author(s):  
Stephanie Alexa Ñústez Castaño ◽  
Duvan Oswaldo Villamizar Castro ◽  
Edgar Mauricio Vargas Solano
Keyword(s):  
Palm Oil ◽  
Batch Reactor ◽  
Methyl Esters ◽  
Average Pore Size ◽  
Molar Ratio ◽  
Reaction Conditions ◽  
Average Pore ◽  
X Ray ◽  
Rbd Palm Oil ◽  
Methyl Ester Content

In this study, the catalytic activity of dolomite was evaluated for the transesterification of Colombian RBD palm oil with methanol, carried out in a batch reactor at 333,15K and 600rpm. The activated dolomites (calcined at 1073.15K for 2h) were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), Hammett indicators method, and quantification of the surface area, average pore size and average pore volume BET. The influence of reaction variables such as catalyst amount (%wt /wt) and methanol / palm oil molar ratio (mole/mole) was investigated. Under the suitable reaction conditions, the amount of calcined dolomite equal to 4% (wt /wt) based on the weight of oil, the methanol-oil molar ratio equal to 9:1, and the reaction time = 1h, the methyl ester content of 82.67% of fatty acid methyl esters (FAME) can be achieved.

Small-angle neutron scattering characterization of processing/microstructure relationships in the sintering of crystalline and glassy ceramics

1991 ◽  
Vol 6 (12) ◽  
pp. 2706-2715 ◽  
Author(s):  
G.G. Long ◽  
S. Krueger ◽  
R.A. Gerhardt ◽  
R.A. Page
Keyword(s):  
Neutron Scattering ◽  
Microstructure Evolution ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Average Pore Size ◽  
Unit Surface Area ◽  
Average Pore ◽  
Sintering Mechanisms ◽  
Alpha Alumina

Small-angle neutron scattering measurements were used to examine the pore microstructure evolution of glassy silica and polycrystalline alpha-alumina as a function of sintering. It was shown that the two major sintering mechanisms, viscous flow and surface and volume diffusion, lead to very different microstructure evolution signatures in terms of the average pore size as a function of density. However, with respect to topology, the evolution of the porosity per unit surface area as a function of density is remarkably similar in the two systems.

Synthesis and Characterization of YCrxAl1-xO3 Particles by a Reverse Micelle Processing

2017 ◽  
Vol 47 ◽  
pp. 54-59 ◽  
Author(s):  
Dae Han Lee ◽  
Ji Young Ock ◽  
Jeong Hoon Son ◽  
Dong Sik Bae
Keyword(s):  
Reverse Micelle ◽  
Heating Temperature ◽  
Molar Ratio ◽  
Synthesis And Characterization ◽  
X Ray Diffraction ◽  
Inorganic Pigment ◽  
X Ray ◽  
Heat Treated ◽  
Average Size

YCrxAl1-xO3 nanoparticles were synthesized by a reverse micelle processing for inorganic pigment. Y(NO3)2·6H2O, Cr (NO3)2·6H2O and Al (NO3)3·9H2O are used for precursors in order to synthesis YCrxAl1-xO3 nanoparticles. The aqueous solution consists of mixing the molar ratio of Y/Cr/Al at 1:x:1-x and heat treated at 900~1300°C for 2h. The average size and distribution of synthesized YCrxAl1-xO3 powders was in the range of 10-20nm and narrow, respectively. The average size of the synthesized YCrxAl1-xO3 powders increased with increasing water to surfactant molar ratio and heating temperature. The crystallinity of synthesized YCrxAl1-xO3 powder increased with increasing heating temperature. The synthesized YCrxAl1-xO3 powders were characterized by X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM) and color spectrophotometer. The properties of the synthesized powders were affected by such variables as molar ratio, heating temperature etc.

scholarly journals Sol-Gel Processed Cobalt-Doped Methylated Silica Membranes Calcined under N2 Atmosphere: Microstructure and Hydrogen Perm-Selectivity

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4188
Author(s):  
Lunwei Wang ◽  
Jing Yang ◽  
Ruihua Mu ◽  
Yingming Guo ◽  
Haiyun Hou
Keyword(s):  
Average Pore Size ◽  
Sol Gel ◽  
Total Pore Volume ◽  
Molar Ratio ◽  
Average Pore ◽  
Silica Membranes ◽  
Physical Chemical ◽  
N2 Atmosphere ◽  
Coating Method ◽  
Gel Technique

Methyl-modified, cobalt-doped silica (Co/MSiO2) materials were synthesized by sol-gel technique calcined in N2 atmospheres, and membranes were made thereof by coating method. The effects of Co/Si molar ratio (nCo) on the physical-chemical constructions of Co/MSiO2 materials and microstructures of Co/MSiO2 membranes were systematically investigated. The gas permeance performance and hydrothermal stability of Co/MSiO2 membranes were also tested. The results show that the cobalt element in Co/MSiO2 material calcined at 400 °C exists not only as Si–O–Co bond but also as Co3O4 and CoO crystals. The introduction of metallic cobalt and methyl can enlarge the total pore volume and average pore size of the SiO2 membrane. The activation energy (Ea) values of H2, CO2, and N2 for Co/MSiO2 membranes are less than those for MSiO2 membranes. When operating at a pressure difference of 0.2 MPa and 200 °C compared with MSiO2 membrane, the permeances of H2, CO2, and N2 for Co/MSiO2 membrane with nCo = 0.08 increased by 1.17, 0.70, and 0.83 times, respectively, and the perm-selectivities of H2/CO2 and H2/N2 increased by 27.66% and 18.53%, respectively. After being steamed and thermally regenerated, the change of H2 permeance and H2 perm-selectivities for Co/MSiO2 membrane is much smaller than those for MSiO2 membrane.

scholarly journals Synthesis and mechanism of aluminum silicate mesoporous materials by F108 template

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Zhijun Ma ◽  
Jing Gao ◽  
Xingyuan Weng ◽  
Shuai Yang ◽  
Kai Peng
Keyword(s):  
Pore Size ◽  
Sodium Hydroxide ◽  
Surface Area ◽  
Mesoporous Materials ◽  
Pore Volume ◽  
Average Pore Size ◽  
Molar Ratio ◽  
Aluminum Silicate ◽  
Synthetic Material ◽  
Average Pore

Abstract Aluminosilicate mesoporous materials were synthesized using F108 template (polyethylene glycol-polypropylene glycolpolyethylene glycol) at a concentration of 0.034 g/ml and the molar ratio of Al2O3 to SiO2 was 0.09. The products were then characterized using nitrogen adsorption/desorption tests, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The effects of various crystallization temperatures as well as sodium hydroxide concentrations on the average diameter, pore volume, surface area, and morphology of the synthetic material were analyzed. Results showed that a sodium hydroxide concentration of 11 mol/L and a crystallization temperature of 130 °C produced a synthetic material with regular pore size and homogeneous arrangement including a specific surface area of 137.62 m2/g, an average pore volume of 0.27 cm3/g, along with an average pore size of 15.33 nm.

scholarly journals Synthesis and Characterization of Fe3O4@SiO2@mesoporous-SiO2 Materials

2021 ◽  
Author(s):  
Shuiping LI
Keyword(s):  
Average Pore Size ◽  
Average Particle Size ◽  
Molar Ratio ◽  
Synthesis Process ◽  
Template Method ◽  
Average Particle ◽  
Step Method ◽  
Average Pore ◽  
Thermal Synthesis ◽  
Mesoporous Sio2

In this work, a magnetic Fe3O4@SiO2@mesoporous-SiO2 (F@S@m-S) material was successfully prepared by a three-step method: firstly, Fe3O4 particles were synthesized through hydro-thermal synthesis process; secondly, Fe3O4@SiO2 materials were fabricated via a template method using tetraethyl orthosilicate (TEOS) as silicon sources and cetyltrimethylammonium chloride (CTAC) as templates; lastly, F@S@m-S materials were prepared through a template method as well. The influence of TEOS/CTAC molar ratio on the morphology and mesostructure was investigated. The product was characterized by Fourier-transform Infrared Spectroscopy (FT-IR), small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), transmission electron microscope (TEM), and N2 adsorption-desorption. The results demonstrated that F@S@m-S materials have a well spherical morphology and a typical mesostructure. The increase of TEOS/CTAC molar ratio can improve the mesostructure and crystal form of F@S@m-S materials. The average particle size, specific surface area, average pore size and pore volume of F@[email protected] materials are 130 nm, 77.1 m2/g, 9.2 nm and 0.1668 cm2/g, respectively.

Structural Characterization of MMT Modified by Acrylamide

2011 ◽  
Vol 689 ◽  
pp. 425-431
Author(s):  
Zeng Zhi Zhang ◽  
Dan Dan Ma
Keyword(s):  
Pore Size ◽  
Lamellar Structure ◽  
Heating Temperature ◽  
Average Pore Size ◽  
Lamellar Spacing ◽  
Treatment Temperature ◽  
Carbonization Temperature ◽  
Average Pore ◽  
Heating Treatment

Carbon pillared MMT was prepared from Na-MMT modified by acrylamide. The structural behavior of the MMT and AM/modified MMT were characterized by TG-DTA and DSC. The analysis of modified MMT showed that: the lamellar structure of carbon pillared MMT increases clearly with the carbonization temperature. In the experiment temperature range, the higher the heating temperature, the more significantly carbonization properties of MMT exhibited, and the more apertures of Pillared MMT developed. In the test MMT lamellar spacing of the carbide change with the heating treatment temperature, d001 value of the MMT augmented to the largest when carbonization temperature reach 200°C; the average pore size of treated MMT was larger than untreated MMT, the pore size became the largest average at 400 °C.

scholarly journals Effect of K/Al Molar Ratio on the Thermo-Mechanical Properties of Metakaolinite-Based Geopolymer Composites

Polymers ◽  
2021 ◽  
Vol 13 (21) ◽  
pp. 3754
Author(s):  
Jan Kohout ◽  
Petr Koutník ◽  
Pavlína Hájková ◽  
Eliška Kohoutová ◽  
Aleš Soukup
Keyword(s):  
Mechanical Properties ◽  
Pore Size ◽  
Average Pore Size ◽  
Local Maximum ◽  
Raw Material ◽  
Molar Ratio ◽  
Average Pore ◽  
Thermal Dilatation ◽  
Compressive And Flexural Strengths ◽  
Geopolymer Composites

A metakaolinite-based geopolymer binder was prepared by using calcined claystone as the main raw material and potassium as the alkaline activator. Chamotte was added (65 vol%) to form geopolymer composites. Potassium hydroxide (KOH) was used to adjust the molar ratio of K/Al and the effect of K/Al on thermo-mechanical properties of geopolymer composites was investigated. This study aimed to analyze the effect of K/Al ratio and exposure to high temperatures (up to 1200 °C) on the compressive and flexural strengths, phase composition, pore size distribution, and thermal dilatation. With an increasing K/Al ratio, the crystallization temperature of the new phases (leucite and kalsilite) decreased. Increasing content of K/Al led to a decline in the onset temperature of the major shrinkage. The average pore size slightly increased with increasing K/Al ratio at laboratory temperature. Mechanical properties of geopolymer composites showed degradation with the increase of the K/Al ratio. The exception was the local maximum at a K/Al ratio equal to one. The results showed that the compressive strength decreases with increasing temperature. For thermal applications above 600 °C, it is better to use samples with lower K/Al ratios (0.55 or 0.70).

scholarly journals Development of Biodegradable Polymer Blends Based on Chitosan and Polylactide and Study of Their Properties

Materials ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 4900
Author(s):  
Ivan Lednev ◽  
Evgeniia Salomatina ◽  
Svetlana Ilyina ◽  
Sergey Zaitsev ◽  
Roman Kovylin ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Elastic Modulus ◽  
Average Pore Size ◽  
Weight Ratio ◽  
Cellular Adhesion ◽  
Ammonium Bicarbonate ◽  
Molar Ratio ◽  
Average Pore ◽  
Composite Surface

Composite materials of various compositions based on chitosan and polylactide were obtained in the form of films or porous bulk samples. Preliminarily, poly-D,L-lactide was synthesized by ring-opening polymerization of lactide in the presence of Ti(OiPr)4. Polylactide obtained at components molar ratio [lactide]:[Ti(OiPr)4] = 3:1 had the best molecular weight characteristics at a high product yield. Film composition with the weight ratio chitosan-polylactide 50:50 wt. % was characterized by high mechanical properties. The value of the tensile strength of the film was 72 MPa with a deformation of 10% and an elastic modulus of 40 GPa, which is higher than the tensile strength of native chitosan by ~three times. The observed effect is a consequence of the fact that the chitosan-polylactide composite has an amorphous structure in contrast to the native chitosan, which is proved by X-ray phase analysis. An increase in the elastic modulus of the composite in the range of 20–60 °C in contrast to polylactide was found by dynamic mechanical analysis. The observed effect is apparently caused by the formation of hydrogen bonds between functional groups of chitosan and polylactide which is possible through an increase in polylactide segments mobility when its glass transition temperature is reached. The composite material is biocompatible and characterized by high cellular adhesion of fibroblasts (line hTERT BJ-5ta). Their growth on the composite surface was 2.4 times more active than on native chitosan. Bulk porous samples of the composition with the weight ratio chitosan-polylactide 50:50 wt. % were synthesized by original method in ammonium bicarbonate presence. Samples were characterized by a porosity of 82.4% and an average pore size of 100 microns. The biodegradability of such material and absence of inflammatory processes were proven in vivo by the blood parameters of experimental animals. Thus, materials with the weight ratio chitosan-polylactide 50:50 wt. % are promising for potential use in regenerative medicine.

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