Synthesis of nano-alumina and their effect on structure, mechanical and thermal properties of geopolymer (original) (raw)
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Deleted Journal, 2024
Influence of various types of nano powder on the physico-mechanical properties of geopolymer materials has been studied, in addition to studying their firing stability up to 1000 °C. Alumino-silicate materials used are kaolin, fired kaolin and lime stone. Materials prepared at water/binder ratios of 0.40; whereas the used equal volume of activator 5 M sodium hydroxide with liquid sodium silicate. Nano-kaolin admixed with Nano-powder as a partial replacement from metakaolin material. The control mixes incorporating either 7% Nano-glass or 5% Nano-silica fume. Nano-kaolin was partially replaced Nano-glass powder and Nano-silica fume. It is possible to use the mixes containing limestone and nano materials to solve the problem of using heat curing, thermal energy consumption and pollution by reducing the MK used for MK-geopolymer cement. Results indicated an enhancement in the physico-mechanical properties of mix incorporating 1: 6% and 2:3% of NK:N-glass and NK:N-silica fume, respectively. Firing of hardened geopolymer resulted in high thermal resistance up to 700 °C then exposed to decrease up to 1000 °C. However, no micro-cracks were noticed up to 800 °C for all samples as recorded by visual examination of the fired samples, while micro-cracks were recorded for hardened composites at 1000 °C.
MECHANICAL PROPERTIES OF METAKAOLIN MODIFIED GEOPOLYMER AND THE EFFECT OF SI/AL RATIO
The environmental impact of the production of cement has left the construction industry with little choice but to develop an alternative material. Geopolymer synthesis has promising potential in that direction. Alkali activation of aluminosilicate raw material produces geopolymer. Flyash is a widely used precursor in geopolymer. Flyash (FA) based geopolymer is porous and hence less durable. Metakaolin is rich in aluminosilicate (52% of Sio2, 46% ofAl 2O3)and has a smaller particle size (2 µm) and high specific area (20 m 2/g)compared to flyash.Metakaolin (MK) based geopolymers are expected to give higher strength and less porous than FA based geopolymer. This research aims to investigate the use of MK as a precursor in geopolymer synthesis as a replacement for FA in various percentagesto utilize the advantages of MK over FA. MK based concrete cured at different temperaturesand various solid/ liquid ratio is tested for compressive strength. Experimental investigation of FA-MK based geopolymer in this research is found to have to have 11% to 65% less compressive strength compared to FA based geopolymer when replaced by 10% to 40% of MK. Lesser strength is attributed to the Si/Al ratio of the MK precursor.
MICROSTRUCTURE AND MICROCHEMISTRY OF FULLY-REACTED GEOPOLYMERS AND GEOPOLYMER MATRIX COMPOSITES
Geopolymers (GPs) may be thought of as a type of chemically bonded ceramic, more specifically, as "alkali-bonded ceramics" or "ABCs". They are a class of cementitious materials that do not depend on the presence of calcium. Geopolymers are amorphous, gel-like ceramics that are formed by the mixing of alkali-silicate solutions with aluminosilicate minerals or glasses. Two processing routes for the thermal conversion of potassium-based geopolymers into ceramics were carried out for this study. A low water content GP, having a molar composition of K 2 O • Al 2 O 3 • 4 SiO 2 • 7.5 H 2 O and reinforced with amorphous 500 nm silica spheres, was thermally converted into crystalline leucite of the same dehydrated composition, by heating above 900 o C. Upon thermal conversion the dehydrated GP exhibited macroscopic cracking. The microstructure consisted of a glazed surface covered with spherical voids, caused by entrapped air. Ceramic powders derived by crushing GPs having a molar composition of K 2 O • Al 2 O 3 • 4 SiO 2 • 7.5 H 2 O were die-pressed into pellets and sintered at 1200 o C into leucite. The resulting pellets exhibited no cracking upon conversion into leucite. SEM analysis also showed a similar glazed surface. The interior of the sample was compromised of ~3 µm size phases, which according to XRD were leucite grains, dispersed in an intergranular, amorphous phase. TEM of the amorphous matrix phase showed a stable amorphous phase having a remnant, typical geopolymer, microstructural texture. Selected area diffraction patterns of the continuous matrix phase suggested that it was generally amorphous, with numerous incipient nanocrystals of leucite forming. Further in-depth TEM studies are warranted.
Thermal behaviour of inorganic geopolymers and composites derived from sodium polysialate
Materials Research Bulletin, 2003
Inorganic polymers based on alumina and silica polysialate units were synthesised at room temperature from metakaolinite and sodium silicate in a highly alkaline medium, followed by curing and drying at 65 8C. When properly cured, these polymers exhibit remarkable thermal stability; after losing their hydration water at about 200 8C, they retain their X-ray-amorphous tetrahedral Al and Si network up to the onset of melting at 1300 8C. A small amount of mullite and corundum formed at 1200±1300 8C may result from the presence of a trace of unreacted metakaolinite. Similar experiments with poorly-curing formulations containing higher Na and Si contents show that their unpolymerised components form crystalline nepheline (NaAlSiO 4 ) at 800 8C, prior to melting at about 1100 8C.
Construction and Building Materials, 2019
This paper explored reported the effect of sewage sludge ash (SSA) on the mechanical and microstructural properties of geopolymers based on metakaolin (MK) involving two different SiO2/Na2O molar ratios (0.8 and 1.6), two temperature curing conditions (25°C and 65°C) and various ages of curing (1, 3, 7, 14, 28, 90 or 180 days). The geopolymers tests were characterized performed using different techniques: as X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and compressive strength of mortars. Tests were performed for both high (65°C) and room (25°C) temperature curing conditions lasting for 1, 3, 7, 14, 28, 90 or 180 days. The geopolymeric samples were activated using sodium hydroxide and sodium silicate solutions using two different SiO2/Na2O molar ratios (0.8 and 1.6). The compressive strength tests showed that the replacement of MK by SSA in 10 wt.% when cured at 25 °C with the highest SiO2/Na2O molar ratio reaches similar compressive strengths after 14 days of curing compared to the samples with only MK, which reached a maximum compressive strength of 50.8 MPa at 180 days. The FTIR analyses carried out in the geopolymer pastes with SSA (10 wt.% of SSA and 90 wt.% of MK) showed a formation of N-AS -H gels in the samples cured at 25 °C. The microstructural studies by XRD, TGA and SEM pointed out the formation of a crystalline phase as Na P-type zeolite in MK/SSA based-geopolymer pastes cured at 65 °C, which explained the loss of compressive strength of the samples cured at high temperature. However, the SSA retarded the crystallization process in the MK basedgeopolymer.
Effect of molar ratios on strength, microstructure & embodied energy of metakaolin geopolymer
2021
In this study, twenty-five geopolymer (GP) mixes were prepared by varying the alkaline solids to Metakaolin (MK) and sodium silicate to NaOH ratios from 0.1 to 0.5 and 0.2 to 1.0, respectively, thus giving a wide range of molar ratios of silica to alumina, sodium oxide to alumina and water to sodium oxide. The compressive strength of these GP mixes was determined for four curing schemes involving oven curing at 100oC for 24 h and three ambient curing with the curing ages of 3, 14, and 28 days. The test results revealed that for the manufacture of GP binder for structural applications of strength up to 90 MPa, the molar ratio of silica to alumina should be greater than 2.3, sodium oxide to alumina should be between 0.6 to 1.2, and water to sodium oxide should not exceed 12. The compressive strength of ambient cured GP mortar gets stabilized at 28 days of ambient curing. Experimental findings were also corroborated by GP microstructure analysis. The embodied energy of MK-based GP mort...
Assessment of important parameters involved in the synthesis of geopolymer composites: A review
Construction and Building Materials, 2020
h i g h l i g h t s An updated and comprehensive review of geopolymer composites with critical parametric assessment. Review paper based on more than 300 research papers spanning over more than 26 years. Microstructure analysis of geopolymer composites presented in simplified form. Evaluation of important parameters involved in geopolymer synthesis. Evaluation based on impact on fresh, mechanical, durability properties and thermal resistance. Consolidation of data base detailing geopolymer mix proportioning, impact of particle size distribution, additives & curing regimes. Identification and elaboration of research gap.
Review on Current Geopolymer as a Coating Material
A world towards the concept of sustainable development and environment with low greenhouse gas emissions, zero waste and low energy consumption is an important endeavor. Geopolymer is an aluminosilicate materials occurred by dissolve it in highly alkaline solution then transform into tridimensional tecto-aluminosilicate materials. As an inorganic material, geopolymer has a potential in fire resistant and protective coating for different surfaces including metal and concrete due to their superior mechanical, chemical and thermal resistance properties. With an additional engineering design, in curing and sintering temperature, Si:Al ratio as well as additives used will improve the geopolymer coating properties. The present paper outlines briefly the potential of geopolymer as a coating material to bring the world towards a better future with a reduced carbon footprint.