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Showing papers in "Journal of Materials Science in 2007"


Journal ArticleDOI
TL;DR: A brief history and review of geopolymer technology is presented with the aim of introducing the technology and the vast categories of materials that may be synthesized by alkali activation of aluminosilicates as mentioned in this paper.
Abstract: A brief history and review of geopolymer technology is presented with the aim of introducing the technology and the vast categories of materials that may be synthesized by alkali-activation of aluminosilicates. The fundamental chemical and structural characteristics of geopolymers derived from metakaolin, fly ash and slag are explored in terms of the effects of raw material selection on the properties of geopolymer composites. It is shown that the raw materials and processing conditions are critical in determining the setting behavior, workability and chemical and physical properties of geopolymeric products. The structural and chemical characteristics that are common to all geopolymeric materials are presented, as well as those that are determined by the specific interactions occurring in different systems, providing the ability for tailored design of geopolymers to specific applications in terms of both technical and commercial requirements.

3,302 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present the work carried out on the chemical reaction, the source materials, and the factor affecting geopolymerization, and demonstrate that certain mix compositions and reaction conditions such as Al2O3/SiO2, alkali concentration, curing temperature with curing time, water/solid ratio and pH significantly influences the formation and properties of a geopolymers.
Abstract: Geopolymerization is a developing field of research for utilizing solid waste and by-products. It provides a mature and cost-effective solution to many problems where hazardous residue has to be treated and stored under critical environmental conditions. Geopolymer involves the silicates and aluminates of by-products to undergo process of geopolymerization. It is environmentally friendly and need moderate energy to produce. This review presents the work carried out on the chemical reaction, the source materials, and the factor affecting geopolymerization. Literature demonstrates that certain mix compositions and reaction conditions such as Al2O3/SiO2, alkali concentration, curing temperature with curing time, water/solid ratio and pH significantly influences the formation and properties of a geopolymer. It is utilized to manufacture precast structures and non-structural elements, concrete pavements, concrete products and immobilization of toxic metal bearing waste that are resistant to heat and aggressive environment. Geopolymers gain 70% of the final strength in first 3–4 h of curing.

1,078 citations


Journal ArticleDOI
TL;DR: In this article, the durability of AAFA pastes in aggressive environments was evaluated in a number of aggressive environments (deionized water, seawater, sodium sulphate and acidic solutions) and with respect to alkali-silica reaction-induced expansion.
Abstract: The study described in the present paper addresses the durability of alkali-activated fly ash (AAFA) cement under different conditions: specifically, cement performance is measured in a number of aggressive environments (deionized water, ASTM seawater, sodium sulphate and acidic solutions) and with respect to alkali–silica reaction-induced expansion. The chief parameters studied are: weight loss, compressive strength, variations in volume, presence of the products of degradation and microstructural changes. The results show that AAFA pastes perform satisfactorily in aggressive environments and that degradation in these materials is distinctly different from such processes in OPC paste. These mortars are also compliant with the 16-day expansion limit stipulated in ASTM standard C1260-94 on potential alkali–silica reactivity.

494 citations


Journal ArticleDOI
TL;DR: In this article, the effect of nominal Si/Al on the processes and mechanisms of thermal shrinkage and weight loss throughout constant heating of Na-geopolymers was explored by use of dilatometry, thermogravimetry, nitrogen porosimetry and use of different constant heating rates.
Abstract: The thermal shrinkage and weight loss of a systematic series of geopolymers with nominal composition of NaAlO2(SiO2) z · 5.5H2O (1.15 ≤ z ≤ 2.15) made by activation of metakaolin with sodium silicate solutions are presented. The thermal behaviour of Na-geopolymers are varied, but may be categorised into four regions of behaviour exhibited by all specimens. This investigation explores the effect of nominal Si/Al on the processes and mechanisms of thermal shrinkage and weight loss throughout constant heating of Na-geopolymer. The overall thermal shrinkage of Na-geopolymer increases with increasing nominal Si/Al, with the onset temperature of structural densification occurring at lower temperature with increasing Si/Al. Thermal shrinkage is observed to result from capillary strain, dehydroxylation and viscous sintering in different temperature regions, and is explored by use of dilatometry, thermogravimetry, nitrogen porosimetry and use of different constant heating rates.

397 citations


Journal ArticleDOI
TL;DR: A review of electrospray methods and devices, including liquid metal ion sources, used for thin film deposition can be found in this article, where the authors show that the performance of the charged spray on an object is usually higher than that for uncharged droplets, and that it can be applied to many processes in industry and in scientific instruments manufacturing.
Abstract: Electrospraying utilises electrical forces for liquid atomisation. Droplets obtained by this method are highly charged to a fraction of the Rayleigh limit. The advantage of electrospraying is that the droplets can be extremely small, down to the order of 10’s nanometres, and the charge and size of the droplets can be controlled to some extent be electrical means. Motion of the charged droplets can be controlled by electric field. The deposition efficiency of the charged spray on an object is usually higher than that for uncharged droplets. Electrospray is, or potentially can be applied to many processes in industry and in scientific instruments manufacturing. The paper reviews electrospray methods and devices, including liquid metal ion sources, used for thin film deposition. This technique is applied in modern material technologies, microelectronics, micromachining, and nanotechnology.

375 citations


Journal ArticleDOI
TL;DR: In this article, the electrical properties of carbon-based conductive polymer composites are discussed and special emphasis is placed on the percolation phenomenon, the factors that affect the Percolation threshold as well as related theoretical research work.
Abstract: Composite material has attracted increasingly remarked interest over the last few decades and set it apart in its own class due to its distinct properties. World annual production is over 10 million tonnes and the market has in recent years been growing at 5–10% per annum. Among these materials, one subgroup, conductive polymer composite, has figured out and its importance is increasing in years to come. When used as conductive material, it possesses the merits of light weight, ease of manufacturing and chemical resistance. This review focuses on the electrical properties of carbon based conductive polymer composites. Special emphases are placed on the percolation phenomenon, the factors that affect the percolation threshold as well as related theoretical research work. Then mechanisms of electric conduction and factors influencing conductive properties are addressed.

341 citations


Journal ArticleDOI
TL;DR: In this paper, the initial geopolymeric reaction processes governing dissolution of solid aluminosilicate particles in alkali solutions have been investigated using conventional experimental techniques, and the data analysed by speciation predictions of the partial charge model (PCM).
Abstract: Initial geopolymeric reaction processes governing dissolution of solid aluminosilicate particles in alkali solutions have been investigated using conventional experimental techniques, and the data analysed by speciation predictions of the partial charge model (PCM). For metakaolin powders activated with 5.0 M NaOH, solid-state nuclear magnetic resonance (NMR) spectra disclose the existence of monomeric [Al(OH)4]− species after two hours of dissolution, consistent with PCM predictions. However, no equivalent monomeric silicate species were observed for 5.0–10.0 M NaOH activator solutions characteristic of systems with nominal Si/Al ≤ 1. The apparent absence of monomeric silicate species suggest rapid condensation of silicate units with [Al(OH)4]− to generate aluminosilicate species, as indicated by the evolution of the shoulder at around −87 ppm in the 29Si NMR spectra. Of the two possible stable silicate species [SiO2(OH)2]2− and [SiO(OH)3]−, the latter appears most likely to condense with [Al(OH)4]− to produce aluminosilicate oligomers, from which larger oligomers subsequently form through further condensation with [Al(OH)4]− leading to a gradual build up of aluminosilicate networks and a lowering of system alkalinity. This dissolution and hydrolysis sequence at the early stages of synthesis suggests a reaction path wholly consistent with predictions of the partial charge model.

330 citations


Journal ArticleDOI
TL;DR: A brief overview of the field of structural nanocrystalline materials can be found in this article, where the major processing methods for production of bulk nanocrystine materials are reviewed.
Abstract: This paper presents a brief overview of the field of structural nanocrystalline materials. These are materials in either bulk, coating, or thin film form whose function is for structural applications. The major processing methods for production of bulk nanocrystalline materials are reviewed. These methods include inert gas condensation, chemical reaction methods, electrodeposition, mechanical attrition, and severe plastic deformation. The stability of the nanocrystalline microstructure is discussed in terms of strategies for retardation of grain growth. Selected mechanical properties of nanocrystalline materials are described; specifically strength and ductility. Corrosion resistance is briefly addressed. Examples of present or potential applications for structural nanocrystalline materials are given.

323 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present a critical review on the experimental results and theories associated with the strain rate sensitivity of UFG/NC metals with different lattice structures, and the influences on some constitutive responses.
Abstract: Mounting evidence is pointing to some emerging novel behaviors of metals with ultrafine-grain (UFG) and/or nanocrystalline (NC) microstructures. One such novel behavior is related to the thermodynamic and kinetic aspects of plastic response in the UFG/NC regime. Two inter-related parameters, viz., the strain rate sensitivity (SRS) and the activation volumes of plastic deformation, are used as fingerprints for the thermodynamics and kinetics of plastic deformation. Changes of these parameters with grain size may indicate transition of plastic deformation mechanisms. Therefore, investigations of these phenomena may bring out new strategies for ingenious design and synthesis of UFG/NC materials with desirable properties. In this article, we present a critical review on the experimental results and theories associated with the SRS of UFG/NC metals with different lattice structures, and the influences on some constitutive responses.

309 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of calcium and its content on the structure formation, hardening, and performance of fly ash based geopolymeric binder was investigated, and the results were compared to the type and composition of reaction product, which was detected by 29Si NMR spectroscopy and X-ray diffraction.
Abstract: The influence of calcium and its content on the structure formation, hardening, and performance of fly ash based geopolymeric binder was the objective of our investigation. Calcium hydroxide was added to fly ash in different amounts. Since it is known that the formed structure determines certain properties of the material, the coherence between different types and various ratios of the reaction products on thermal properties such as strength after thermal treatment up to 1,100 °C, thermal resistance under load, creep in compression, and axial dilation were investigated. The results were compared to the type and composition of the reaction product, which was detected, for example, by 29Si NMR spectroscopy and X-ray diffraction. Along with calcium containing zeolitic phases, the calcium built C–S–H-phases using the silicon from the fly ash, both of which crystallize or convert into new phases at elevated temperatures.

290 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the influence of fabrication conditions on the performance of magnetorheological elastomers (MR Elastomers) such as matrix type, external magnetic flux density, and temperature, plasticizer and iron particles.
Abstract: Magnetorheological Elastomers (MR Elastomers or MREs) are a kind of novel smart material, whose mechanical, electrical, magnetic properties are controllable under applied magnetic fields. They have attracted increasing attentions and broad application prospects. But conventional MREs are limited to wide applications because their MR effects and mechanical performances are not high enough. This paper aims to optimize the fabrication method and to fabricate good natural rubber based MREs with high modulus by investigating the influences of a variety of fabrication conditions on the MREs performances, such as matrix type, external magnetic flux density, and temperature, plasticizer and iron particles. Among these factors, the content of iron particles plays a most important contribution in shear modulus. When the iron particle weight fraction is 80% and the external magnetic flux density is 1 T, the field-induced increment of shear modulus reaches 3.6 MPa, and the relative MR effect is 133%. If the iron weight fraction increases to 90%, the field-induced increment of shear modulus is 4.5 MPa. This result has exceeded the best report in the literatures researching the MREs on the same kind of matrix. The dynamic performances of MREs were also experimentally characterized by using a modified Dynamic Mechanical Analyzer (DMA) system. The effects of strain amplitude and driving frequency on viscoelastic properties of MREs were analyzed.

Journal ArticleDOI
TL;DR: In this paper, the authors present the results of experimental study and analysis on the behaviour and the strength of reinforced geopolymer concrete slender columns and demonstrate that the design provisions contained in the current standards and codes can be used to design reinforced fly ash-based concrete columns.
Abstract: The objectives of this paper are to present the results of experimental study and analysis on the behaviour and the strength of reinforced geopolymer concrete slender columns. The experimental work involved testing of twelve columns under axial load and uniaxial bending in single curvature mode. The compressive strength of concrete for the first group of six columns was about 40 MPa, whereas concrete with a compressive strength of about 60 MPa was used in the other six columns. The other variables of the test program were longitudinal reinforcement ratio and load eccentricity. The test results gathered included the load carrying capacity, the load-deflection characteristics, and the failure modes of the columns. The analytical work involved the calculation of ultimate strength of test columns using the methods currently available in the literature. A simplified stability analysis is used to calculate the strength of columns. In addition, the design provisions contained in the Australian Standard AS3600 and the American Concrete Institute Building Code ACI318-02 are used to calculate the strength of geopolymer concrete columns. This paper demonstrates that the design provisions contained in the current standards and codes can be used to design reinforced fly ash-based geopolymer concrete columns.

Journal ArticleDOI
TL;DR: In this paper, the authors compared the behavior of nanoscale silica/cross-linked low density polyethylene nanocomposites with several silica surface treatments and found that a reduction in the mobility in nanocom composites as well as a change in the defect size may be key to explaining the improvement in the properties.
Abstract: The incorporation of silica nanoparticles into polyethylene has been shown to increase the breakdown strength significantly compared to composites with micron scale fillers. Additionally, the voltage endurance of the nanocomposites is two orders of magnitude higher than that of the base polymer. The most significant difference between micron-scale and nano-scale fillers is the large interfacial area in nanocomposites. Because the interfacial region (interaction zone) is likely to be pivotal in controlling properties, this paper compares the behavior of nanoscale silica/cross-linked low density polyethylene nanocomposites with several silica surface treatments. In addition to breakdown strength and voltage endurance, dielectric spectroscopy, absorption current measurements, and thermally stimulated current determinations (TSC) were performed to elucidate the role of the interface. It was found that a reduction in the mobility in nanocomposites as well as a change in the defect size may be key to explaining the improvement in the properties.

Journal ArticleDOI
TL;DR: In this article, the effects of the initial particle size, hot pressing time, and hot pressing temperature on the final grain size and morphology were examined for ZrB2 containing 30 volume percent SiC particulates.
Abstract: Structure–property relations were examined for ZrB2 containing 30 volume percent SiC particulates. Two grades of ZrB2 with initial particle sizes of 2 and 6 μm were used. Billets of ZrB2–SiC were produced by hot pressing at 1850, 1950 or 2050 °C for 45 min. In addition, the material prepared from ZrB2 with an initial particle size of 2 μm was hot pressed at 2050 °C for 90 and 180 min. Microstructures and mechanical properties were characterized to determine the effects of the initial particle size, hot pressing time, and hot pressing temperature on the final grain size and morphology. The average grain size of the ZrB2 phase ranged from 2.2 to 4.7 μm. Similarly, the average grain size of the SiC phase ranged from 1.2 to 2.7 μm. Hardness and modulus of elasticity were not affected by the processing conditions with average values of 22 and 505 GPa, respectively. However, flexural strength decreased as grain size increased from a maximum of ∼1050 MPa for the finest grain sizes to ∼700 MPa for the largest grain sizes. Analysis suggested that the strength of ZrB2–SiC was limited by the size of the SiC inclusions in the ZrB2 matrix.

Journal ArticleDOI
TL;DR: An overview of recent activities in this evolving area of Ti-TiB composites, covering processing, properties and potential applications, can be found in this paper, where the authors also provide an overview of the TiBw in-situ whisker reinforcements.
Abstract: Although titanium (Ti) alloys possess desirable properties such as specific strength, corrosion resistance and low density, their low specific stiffness and wear resistance have restricted their widespread application. Recently, composite strategies have provided means for overcoming these limitations. Titanium boride (TiBw) in-situ whisker reinforcements are currently recognized as one of the most compatible and effective reinforcements for Ti. This paper provides an overview of recent activities in this evolving area of Ti–TiB composites, covering processing, properties and potential applications.

Journal ArticleDOI
TL;DR: In this paper, experiments were performed on blended cements containing 30% Portland cement clinker and 70% fly ash, where powdery material was mixed with deionised water for normal hydration, and with two different alkaline solutions for normal alkaline activation.
Abstract: In the present paper, experiments were performed on blended cements containing 30% Portland cement clinker and 70% fly ash. The powdery material was mixed with deionised water for “normal” hydration, and with two different alkaline solutions for “normal” alkaline activation. The mechanical strength developed by this highly blended cement differed significantly depending on the hydrating solution used. XRD, FTIR and 29Si MAS-NMR characterisation studies were conducted to obtain information on the complex structural nature of the hardened matrices, which in all cases consisted of a mixture of amorphous gels (C-S-H + N-A-S-H gel). These highly blended cements are able to comply with the specifications defined in the European Standard EN-197-1:2000.

Journal ArticleDOI
TL;DR: PA6 filled with 2 wt% nanosilver is an effective antimicrobial material for long-term applications and was shown to be active against Escherichia coli whereas the pure PA6 did not show any antimicrobial efficacy.
Abstract: Elemental silver nanoparticles were generated in polyamide 6 (PA6) by the thermal reduction of silver ions during the melt processing of a PA6/silver acetate mixture. The silver ion release from PA6 filled with 2 wt% nanosilver obeys a zero-order rate law for at least 100 days. During this time about 17 μg silver per day, per litre immersion liquid and per cm2 sample surface are released. The PA6/Ag-nanocomposite was shown to be active against Escherichia coli whereas the pure PA6 did not show any antimicrobial efficacy. Immersion of a nanocomposite containing 2 wt% silver in water for 100 days does not reduce its antimicrobial efficacy against Escherichia coli. Thus PA6 filled with 2 wt% nanosilver is an effective antimicrobial material for long-term applications.

Journal ArticleDOI
TL;DR: Blast furnace slag and metakaolin were blended together and the combination activated by sodium hydroxide solution as mentioned in this paper, and the boundary mixtures were set by the activation of the pure slags and pure metakaol powders.
Abstract: Blast furnace slag and metakaolin were blended together and the combination activated by sodium hydroxide solution. The boundary mixtures were set by the activation of the pure slag and pure metakaolin powders. The type and quantity of the reaction products in the alkaline activated blended binders was determined. It is discussed whether both raw materials react separately and are unaffected by each other or if there is a chemical interaction. The discussion bases on extensive investigations with 29Si and 27Al nuclear magnetic resonance spectroscopy compared with X-ray diffraction and thermal analysis (DTA/TG). Additionally, the strength performance will be presented and related to structure, composition and the amount of the reaction products.

Journal ArticleDOI
TL;DR: In this paper, the authors examined various reports of superplasticity in ultrafine-grained materials and showed that these materials exhibit many characteristics similar to conventional super-plastic alloys.
Abstract: Ultrafine-grained materials are attractive for achieving superplastic elongations provided the grains are reasonably stable at elevated temperatures. Since the strain rate in superplasticity varies inversely with the grain size raised to a power of two, a reduction in grain size to the submicrometer level leads to the occurrence of superplastic flow within the region of high strain rate superplasticity at strain rates >10−2 s−1. This paper tabulates and examines the various reports of superplasticity in ultrafine-grained materials. It is shown that these materials exhibit many characteristics similar to conventional superplastic alloys including strain rates that are consistent with the standard model for superplastic flow and the development of internal cavitation during the flow process.

Journal ArticleDOI
TL;DR: In this paper, a liquid-form nano-montmorillonite particle with a planar diameter of about 100nm was incorporated into the Portland cement paste at five different dosages and analyzed at four different ages to identify the nanosizing effects on material properties of such cement-based composite.
Abstract: The nano-montmorillonite, which has characteristics of high aspect ratio and interaction between polymer chains and dispersed nanolayers, has been widely used in the development of new reinforced nanocomposite polymers to improve their mechanical properties. Since a potential pozzolanic reaction may occur between Portland cement paste and high amount of silicon dioxide (SiO2) in nano-montmorillonite, the effects of introduction of montmorillonite to Portland cement-based material on the improvement of matrix properties of cement paste is of great interest in the construction industry. In this study, a liquid-form of nano-montmorillonite particle with a planar diameter of about 100 nm were incorporated into the Portland cement paste at five different dosages and analyzed at four different ages to identify the nanosizing effects on material properties of such cement-based composite. Experimental results show that the composite with 0.60% and 0.40% of added nano-montmorillonite by weight of cement have the optimum compressive strength and permeability coefficient, respectively, in which the increase of compressive strength is about 13.24%, and the decrease of permeability coefficient about 49.95%. Microstructural properties through the analyses of XRD, DSC, NMR, and MIP also indicate that the microstructures of cement paste with nano-montmorillonite contain more dense solid material and more stable bonding framework.

Journal ArticleDOI
TL;DR: In this paper, the leaching behavior of six aluminosilicate industrial minerals and byproducts (kaolin, metakaolin, fly ash, natural pozzolana from Milos, zeolite and furnace slag) in alkaline solutions is investigated, the variables studied are the kind of alkali metal (K, Na), the concentration of the alkaline solution (25, 5 and 10 M), and the time of dissolution (5, 10 and 24 h).
Abstract: In this work, the leaching behaviour of six aluminosilicate industrial minerals and by-products (kaolin, metakaolin, fly ash, natural pozzolana from Milos, zeolite and furnace slag) in alkaline solutions is investigated The variables studied are the kind of alkali metal (K, Na), the concentration of the alkaline solution (25, 5 and 10 M) and the time of dissolution (5, 10 and 24 h) The solid residue after the leaching was examined by means of XRD and FTIR As it is concluded, the leaching ability of Al and Si is according to the following descending order: Metakaolin > Zeolite > Slag > Fly Ash > Pozzolana > Kaolin The extent of dissolution is higher in NaOH than in KOH solutions, especially when the most reactive materials are concerned Finally, Si and Al seem to have a synchronized leaching behaviour in both alkaline solutions

Journal ArticleDOI
TL;DR: In this article, more than 50% construction and demolition (CD) and (ii) the deformation and permeability of RAC can be enhanced when adopting TSMA, on top of the previously verified strength improvement.
Abstract: As more than 50% construction and demolition (CD and (ii) the deformation and permeability of RAC can be enhanced when adopting TSMA. Therefore, it demonstrates that TSMA can help to improve the durability of RAC, on top of the previously verified strength improvement, and thus opening up wider applications of RAC.

Journal ArticleDOI
TL;DR: In this article, reaction models are proposed to quantify the hydration products and to determine the composition of C-S-H from alkali-activated slags (AAS) from slag hydration.
Abstract: Reaction models are proposed to quantify the hydration products and to determine the composition of C–S–H from alkali-activated slags (AAS). Products of the slag hydration are first summarized from observations in literature. The main hydration products include C–S–H, hydrotalcite, hydrogarnet, AFm phases (C4AH13 and C2ASH8) and ettringite. Then, three stoichiometric reaction models are established correlating the mineral composition of slag (the glass part) with the hydration products. Using the proposed models, quantities of hydration products and composition of C–S–H are determined. The models are validated with a number of experimental investigations reported in literature, yielding good agreement, i.e., these models can successfully predict the hydration reaction of AAS. The models are furthermore applied to calculate the retained water in the hydration products of AAS in different hydration states and a general hydration equation of AAS is derived. As an illustration to one of the model applications, chemical shrinkage of the AAS cement paste in different hydration states are predicted. The chemical shrinkage of AAS is shown to be remarkably higher than OPC. Furthermore, phase distribution in the hardened AAS paste and the porosity are calculated.

Journal ArticleDOI
TL;DR: In this article, the microstructure of joints between an Al-alloy and a zinc coated ferritic steel sheet manufactured by the so-called CMT joining method is investigated.
Abstract: The microstructure of joints between an Al-alloy and a zinc coated ferritic steel sheet manufactured by the so-called CMT joining method is investigated. The joint consists of a weld between the Al-alloy and Al 99.8 filler and a brazing of the filler to the zinc coated steel. The morphology, the structure and the defects of the intermetallic phases that developed at the interface between the steel and the Al 99.8 filler are characterised using scanning and transmission electron microscopy. The intermetallic phase seam is only about 2.3 μm thick and consists of trapezoidal nearly equiaxial Fe2Al5 grains surrounded by finger-like remains of the steel and mostly elliptical FeAl3 grains extending into the Al 99.8 filler material. Both the Fe2Al5 and the FeAl3 grains contain crystal defects.

Journal ArticleDOI
TL;DR: In this article, the reaction kinetics and mechanism of geopolymers are studied and a characteristic time for the setting of the reaction mixture is derived from isothermal Dynamic Mechanical Analysis experiments.
Abstract: The reaction kinetics and mechanism of geopolymers are studied. The dissolved silicate concentration decreases from the beginning of the reaction. A characteristic time ‘t 0,vit’ for the setting of the reaction mixture is derived from isothermal Dynamic Mechanical Analysis experiments. ‘t 0,vit’ increases with SiO2/R2O but goes through a minimum for increasing water content. The reaction is slower for K compared to Na-silicate based systems. 29Si and 27Al solution NMR are used to probe the molecular changes. 27Al NMR and FTIR reveal that an ‘intermediate aluminosilicate species’ (IAS) is formed from the start of the reaction. The concentration decrease of OH− during low-temperature reaction is related to the formation of IAS. The rate law of this process seems to be obeyed by a total reaction order of 5/3, with a partial order of 1 for OH− and 0 for Na+ in the silicate solution. During first heating after polymerization water is lost leading to a distortion of the Al environment. According to XRD, no crystallization occurs below 900 °C. However, between 950 and 1100 °C a crystallization exotherm of nepheline is observed with DSC for a geopolymer with SiO2/Na2O = 1.4. Neither T g of the amorphous geopolymer, nor the shrinkage and expansion around T g during first heating, cause a measurable heat effect.

Journal ArticleDOI
TL;DR: In this article, the feasibility of geopolymer synthesis from low Ca electric arc ferronickel slags was investigated through a 23 factorial design and the experimental results and the variance analysis have shown that only aging period has a statistically very significant and positive effect on the final compressive strength while the effect of other factors as well as of their interactions were either less significant or negligible.
Abstract: The present experimental study investigates the feasibility of geopolymer synthesis from low Ca electric arc ferronickel slags. Additives used include kaolinite, sodium silicate, sodium hydroxide and water. The effect of the main factors considered (heating temperature, heating time and aging period) as well as of their interactions on the final compressive strength of the geopolymers produced was studied through a 23 factorial design. The experimental results and the variance analysis have shown that only aging period has a statistically very significant and positive effect on the final compressive strength while the effect of the other factors as well as of their interactions were either less significant or negligible. Identification of new phases formed in order to elucidate geopolymerisation mechanisms was carried out by XRD and FTIR. Sodalite, maghemite, thermonatrite, trona and calcite are the major phases identified. The structural integrity of the produced geopolymers was studied by subjecting them to accelerated freeze–thaw cycles. Finally, the durability of the produced geopolymers when immersed in various aquatic and acidic solutions was investigated.

Journal ArticleDOI
TL;DR: In this paper, the authors reported the first study on ultra-high straining of h.c.p. metals by the accumulative roll-bonding (ARB) process up to 8 cycles (equivalent strain of 6.4).
Abstract: Commercial purity titanium was deformed by accumulative roll-bonding (ARB) process up to 8 cycles (equivalent strain of 6.4) at ambient temperature. This is the first study on ultra-high straining of h.c.p. metals by the ARB process. The microstructure of the ARB-processed specimens showed two kinds of characteristic ultrafine microstructures. One was the lamellar boundary structure elongated along RD, which has been also reported in the ARB-processed cubic metals. The lamellar boundary spacing decreased with increasing ARB strain and reached about 80 nm after 5 ARB cycles. The other microstructure was the equiaxed grains having mean grain size of 80–100 nm. Such a fine and equiaxed grain structure has not yet been reported in the as-ARB-processed materials before. The fraction of the equiaxed grains increased as the ARB process proceeded, and 90% of the specimen was filled with the equiaxed grains after 8 ARB cycles. As the number of the ARB process increased, the tensile strength increased and the total elongation decreased gradually. After 6 ARB cycles, the specimen exhibited almost the same mechanical properties as that of commercial Ti-6Al-4V alloy.

Journal ArticleDOI
TL;DR: In this paper, the authors used Fourier Transform infrared (FT-IR) spectroscopy to study the hydrolysis and condensation reactions of γ-APS molecules in different acid content aqueous solution.
Abstract: The hydrolysis and condensation reactions of γ-APS have been studied in different acid content aqueous solution by using Fourier Transform infrared (FT-IR) spectroscopy. The hydrolysis of γ-APS under the studied conditions can be followed by the increase of the ethanol band located at 882 cm−1 and the decrease of the band due to the ρ(CH3) of γ-APS molecules located at 959 cm−1. Hydrolysis reaction is faster by increasing both H2O and acid concentrations, and it is completed when 3 moles of H2O per mole of γ-APS are used. The increase of the vibrational band located at 1146 cm−1 shows that condensation of the hydrolysed γ-APS molecules take place forming linear chains in poorly cross-linked structures. Besides, both 8-membered cyclic siloxane formations and poorly cross-linked structures are formed and increase as the water and acid content are increased. On the other hand, highly connected cross-linked structures do not appear due to the steric hindrance of the non-hydrolysable aminopropyl group. The silanol band shows that hydrolysis is faster than condensation except for samples with the lowest H2O content.

Journal ArticleDOI
TL;DR: In this paper, the introduction of nano-silica particles into an epoxy polymer has increased both the initial toughness, as measured by the fracture toughness, KIc, and also significantly improved the cyclic-fatigue behaviour of the epoxy polyamide polymer.
Abstract: The introduction of nano-silica particles into an epoxy polymer has increased both the initial toughness, as measured by the fracture toughness, KIc, and also significantly improved the cyclic-fatigue behaviour of the epoxy polymer. Thus, the significant increases recorded in the values of the range of applied stress-intensity factor at threshold, ΔKth, from the cyclic-fatigue tests for the nano-silica modified materials are very noteworthy, since these increases are accompanied by significant improvements being recorded in the initial toughness.

Journal ArticleDOI
TL;DR: In this paper, the effect of milling time on the particle size, morphology and CNT dispersions was investigated, and the results showed that particle size and morphology vary with milling times and carbon nanotubes content.
Abstract: One of the major obstacles to the effective use of carbon nanotubes as reinforcements in metal matrix composites is their agglomeration and poor distribution/dispersion within the metallic matrix. In the present work, we use mechanical alloying (MA) to mechanically mix CNT (2 and 5 wt.%) with Al powders. These powders would be used as precursors for subsequent consolidation to generate bulk CNT-Al composites. Hence controlling the initial powder characteristics prior to high temperature consolidation is important. Up to 48 h of milling was employed to investigate the effect of milling time on the particle size, morphology and CNT dispersions. The results show that particle size and morphology vary with milling time and CNT content. Also the addition of process control agents such as methanol can aid in controlling the powder characteristics.