Morphology Of Reaction Products Research Articles

Effect of cement composition and the storage conditions on the morphology of ASR products in concrete

AbstractUnder natural conditions, the alkali silica reaction (ASR) is a slow degradation process in concrete. Therefore, accelerated laboratory test methods are used to estimate the alkali‐reactivity of aggregates and concrete performance regarding a damaging ASR. In this study, concrete cubes were stored in a fog chamber at 40 °C/100% RH and at outdoor conditions in Munich climate for up to 9 years. Opaline sandstone/flint (25 vol.%) was used as reactive aggregate. 15 wt.% of OPC was replaced by fly ash and compared with the reference mix with 100 wt.% OPC. The cracks widths of the cubes were measured regularly. To investigate the effect of accelerating test conditions on the morphology of reaction products, the concrete microstructure, pore solution composition and ARS products formed under accelerated and field conditions were investigated. The present study shows that accelerated test methods consider only partial aspects of the complex mechanisms of ASR in concretes containing pozzolanic fly ash. Storage conditions have a direct effect on the morphology of the ASR products, the porosity and the pore solution composition of the concrete. When testing blended binders under accelerating conditions, opposing mechanisms are achieved and the chemical and physical processes can be changed significantly.

Synthesis of α-AlH3 by organic liquid reduction method and its hydrogen desorption performance

Aluminum hydride (AlH3) is considered to be a promising hydrogen storage material due to its moderate dehydrogenation temperature and high hydrogen desorption capacity. However, AlH3 has multiple crystal forms, and it is difficult to prepare a single crystalline, which restricted the development of this material. In this study, a new organic liquid reduction method was used to prepare pure α-AlH3. The synthesis process includes two steps: primary reduction reaction in ether and subsequent desolvation reaction in toluene. The effects of reaction conditions on product composition were discussed in detail. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were used to characterize the crystal structure and morphology of reaction products. Research results show that the final product is composed of α-AlH3 and γ-AlH3. The composition proportion of α-AlH3/γ-AlH3 can be adjusted by controlling reaction conditions. Through comparison and analysis, an optimal synthetic condition has been gained to obtain pure α-AlH3. The dehydrogenation performance of the obtained pure α-AlH3 were studied through thermal analysis methods. It is found that the α-AlH3 has a hydrogen desorption capacity of about 9.6 wt% below 200 °C. The dehydrogenation activation energy was also evaluated by using Kissinger and Friedman methods. This study provides a more simple and efficient method for synthesising pure α-AlH3, and also offers some reference for the future research of AlH3.

Experimental study on interface characteristics of liquid sodium-water vapor interaction in SWR

When the sodium-water boundary in the sodium-cooled fast reactor (SFR) fails, water vapor will enter the liquid sodium and cause the sodium water reaction (SWR) accident. SWR may lead to many serious consequences for power plant. Thus, it is a non-negligible factor to be considered in the design and operation of SFR. In this study, experiments on the interaction between liquid sodium and water vapor were carried out. The reaction phenomena, temperature of liquid sodium, morphology of reaction product and other characteristics of the chemical were summarized and analyzed in this paper. The experiment was conducted under different initial sodium temperatures (300–450 °C) and different mass fraction of water vapor (0.1–0.9 at 200 °C) conditions. Visualization scheme was used in this experiment and the reaction process was recorded by a high-speed camera. The results indicate that both mass fraction of water vapor and initial temperature of liquid sodium are important factors in the reaction process. The mass fraction of water vapor affects the actual reaction rate. The initial temperature determines the form of reaction products (liquid NaOH) on the surface of liquid sodium. For the experiments with initial temperature below 400 °C, the reaction products appear as bubbles and foams. While the initial experiment temperature exceeds 400 °C (including 400 °C), bubbles and foams gone, replaced by a thin film. By analyzing the conditions of bubble generation, the surface tension of liquid NaOH is an important cause, which can be affected by the temperature and bounding water molecules. Furthermore, according to the measurement results of sodium temperature, the reaction products in the form of a large concentration of foams have a strong blocking effect on mass transfer and greatly slow down the actual reaction rate. This research has important reference significance for the study of the mechanism of liquid sodium and water vapor reaction.

Investigations of Hellenistic Mortar from Umm Qais (Gadara), Jordan

Ancient mortars have been widely studied, in connection with both diagnosis and applications required for restoration. This study is primarily based on analyses of different mortar samples from a Hellenistic temple. The study was done by means of a polarizing microscope equipped for observations in transmitted and reflected light; and X-ray powder diffraction (XRD). Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy (SEM-EDS) were also used to confirm and supplement the microscopic data, and wet chemical analyses were performed on the acid filtrate for soluble oxides of Fe, Al, Ca, Mg, S, Na and K. Chemical and petrographic analysis were used to determine chemical composition and physical properties, which in turn provide an in-depth understanding of the structural behavior and durability characteristics as they relate to the composition. The results show that the plaster used was a lime-based mortar. The cementing binder was a lime (identified by spot test) with fossilized shell, very fine grain size quartz, and some other minerals as the aggregate. The EDS analysis showed the presence of calcium and a small proportion of magnesium; in addition, silicon, aluminum, potassium, and iron were detected. Possibly, the silicate compounds contributed to the hydraulic component. We found strong similarities among mortar samples used in the temple. Physical methods provided useful information on the mineralogical compounds and the surface structures of samples, allowing for the postulation of deterioration mechanisms and overall decay, including the identification and crystalline morphology of reaction products and salts. These results aid in both understanding the technology of historic mortars and planning the restoration of these mortars.

Strength enhancement and pore-size refinement in clinker-free CaO-activated GGBFS systems through substitution with gypsum

This study presents an improvement in the compressive strength of the clinker-free CaO-activated GGBFS system with the addition of gypsum. The compressive strength was primarily governed by the amount of ettringite, but more importantly, the morphology of reaction products (e.g., size, slenderness) is proposed as being a more dominant factor. The gypsum content at the best strength produced fine ettringite crystals and removed large pores that were around 100 μm in diameter, resulting in significant pore-size refinement. However, excessive addition reduced the strength and generated a large volume of detrimental pores with sizes of 0.03–0.4 μm, which were probably due to expansive cracking or large voids between the large sizes of re-precipitated gypsum crystals. The SEM images demonstrated that the fine ettringite crystals at the gypsum dosage of the best strength filled the pores effectively, which led to dense matrices; while the coarse crystals of gypsum or ettringite at the excessive addition level produced porous matrices.

Alkali Activation of AOD Stainless Steel Slag Under Steam Curing Conditions

Crystalline argon oxygen decarburization slag, in powdery form, was investigated for its hydration potential by alkali activation and curing at 80°C. Na‐silicate and K‐silicate of the same modulus were used as activators. Isothermal calorimetry at 80°C indicated exothermic reactions in the slag pastes. When the slag mortars were cured under steam at 80°C appreciable gain in compressive strength was measured. This was attributed to C–S–H which was detected in TG, FTIR, and 29Si NMR analyses. Upon hydration at 90 d, the amount of crystalline phases decreased, whereas the XRD amorphous content in the slag increased. Electron microscopy showed the formation of different morphologies of reaction products depending on the alkaline activator employed. Presence of reaction rims around the crystalline phases with a major presence of Ca, Si, and O in the reacted matrix was observed in elemental maps.

Preparation of Nano Melamine Phosphate and Its Application in Phenolic Foam

Nano melamine phosphate(NMP) flame retardant was synthesized using melamine and phosphoric acid as reagents by means of a solvothermal method. The prepared NMP was then characterized by means of Fourier transform infra-red spectroscopy, X-ray diffraction, and transmission electron microscopy. Effect of solvents, different kinds of surfactants(i.e. SDS, CTAB and NP), reaction temperature and time on the morphology of reaction product was investigated. It is found that the NMP can only be obtained by using benzene as a solvent. If distilled water and anhydrous ethanol were used as solvent, the particle size of the product is in micro scale. As reaction temperature or reaction time increases, the morphology of the products changes greatly. Moreover, types of surfactants have a great influence on the morphology of the products. Moreover, The polyethylene glycol toughened phenolic foam with addition of NMP exhibits a flexural strength 39% higher than that with addition of micro MP.

Characterization of Reaction Products on the Surface of Li/Air Battery Electrodes

Recently, the Li/air batteries have received a lot of attention as an alternative of lithium ion batteries (LIB), since they provide higher energy density than LIB. The Li/air batteries are composed of air electrode, separator, electrolyte, and anode electrode. Among them air electrode plays a key role because the capacity and cycle life of the Li/air batteries are highly dependent on the air electrode. Therefore many studies have focused on the development of air electrode with enhanced electrochemical performances. During the discharge, lithium ions and oxygen dissolved in electrolyte have a reaction on the surface of air electrode and forms reaction products like Li2O2. Interestingly, it has been reported that the morphology of the reaction products can affect the electrochemical property of the Li/air cell such as cyclic performance and overpotential [1, 2]. Our study gives importance to characterize the morphology of reaction products. To achieve the image of morphologies on the surface of air electrode, we have composed the air electrode on the nickel grid for TEM and manufactured cell. After test of cell using the grid, we could take the TEM images of reaction products. In addition, it is observed that morphologies have difference according to several conditions like the presence of a catalyst or the rate of discharge/charge. It is expected that observation of morphologies in our approach could signpost for development of enhanced air electrode for Li/air batteries.Reference[1] Y. Shao-Horn, B. M. Gallant, R. R. Mitchell, D. G. Kwabi, J. Zhou, L.Zuin, C. V. Thompson, J.Phys. Chem. C 2012, 116, 20800-20805[2] Y. shao-Horn, B. M. Gallant, D. G. Kwabi, R. R. Mitchell, J. Zhou, C. V. Thompson, Energy Environ. Sci. DOI: 10.1039/c3ee40998h

Synthesis and Characterization of Nano Melamine Phosphate

nanomelamine phosphate (NMP) flame retardant was synthesized by means of a solvothermal method, and was characterized by Fourier transform infra-red spectroscopy, X-ray diffraction, and scanning electron microscopy. Effects of reaction temperature and reaction time on the morphology of reaction products were investigated. It was observed that the morphology of the products changes greatly as reaction temperature or reaction time changes.

Interfacial microstructure and fracture behavior of laser welded–brazed Mg alloys to Zn-coated steel

Laser lap welding–brazing of AZ31B Mg alloy to Zn-coated dual phase 980 steel using Mg-based filler was performed. The microstructures at the brazed side were characterized. Fracture behavior was then investigated by in situ scanning electron microscopy observation. The results indicated that heterogeneous reaction layers formed along the interface between the seam and the steel, which had a significant influence on the fracture behavior. Thick and diverse morphologies of reaction products were observed at the seam head and the seam root, where the crack initiated during in situ tensile test. The crack from the seam head then propagated along the Mg-Zn reaction layer/the original Fe-Al phase smoothly due to their weak bonding. When the crack propagated to the direct laser irradiation zone, the newly formed Fe-Al phase at the interface played a positive role in inhibiting the crack propagation, making the crack deflect into the seam zone. Owing to this, the joint strength was ultimately enhanced to 200 N/mm. While the crack from the seam root just propagated into the seam and contributed little to the failure of joint.

Preparation of (Ca+M) (M=Mg, Yb, Sr) Co-Doped α-SiAlON Powders by Combustion Synthesis

In this paper, α-SiAlON powders co-doped with (Ca+M) (M=Mg, Yb, Sr) were prepared by combustion synthesis. The effect of Ca incorporation on the phase composition and grain morphology of reaction products was discussed. The experimental results showed that Ca incorporation promoted the growth of rod-like α-SiAlON crystals in (Ca+Mg) and (Ca+Yb) systems. For (Ca+Sr) system, the addition of Ca assisted Sr into α-SiAlON crystal lattice and increased the relative content of α-SiAlON in reaction product.

Hydrothermal Synthesis, Characterization and Electrocatalytic Activity of La<sub>0.8</sub>Sr<sub>0.2</sub>MnO<sub>3</sub> Nanocubes for Oxygen Reduction Reaction

The La0.8Sr0.2MnO3 nanocubes have been synthesized by simple precipitation followed by hydrothermal process. The as-obtained nanocubes were characterized by SEM, TEM, EDS, XRD and ICP-AA. The SEM and TEM images clearly showed cube type morphology of reaction product. The XRD pattern gave evidence for the phase purity and high crystallinity of the La0.8Sr0.2MnO3 nanocubes. The ICP-AA analysis along with EDS confirms the stoichiometry of the product. Electrochemical activity for oxygen reduction reaction was carried out in 1 M KOH. The oxygen reduction current measured by cyclic voltametry showed six times higher value for nanocubes than that of bulk catalysts of same composition.

Corrosion behaviour of CoW0·013C0·001 in aqueous acidic sulphate solutions containing sodium lauryl sulphate and sodium citrate

The corrosion behaviour of the CoWxCy binder alloy has been shown to be the key factor in the chemical stability of hardmetals of the WC–Co type. The anodic oxidation of the CoW0·013C0·001 alloy was studied in 0·1M H2SO4 with and without additions of 20 mM sodium lauryl sulphate or 20 mM tri-sodium citrate which were intended to act as organic corrosion inhibitors. In this investigation, use was made of linear sweep voltammetry, chronoamperometry, and ac impedance measurements (which can convey additional information on anodic activation processes occurring during corrosion). The reaction product morphology and composition were studied by scanning electron microscopy and energy dispersive spectroscopy. The inhibiting effects of the organic additives on the pseudo-passivating mechanisms were described. The precipitation of layers of corrosion products with different protective effectiveness was assessed and correlated with the electrochemical kinetics and with the morphological and chemical characteristics brought about by the presence of the organics. Sodium citrate proved more effective than sodium lauryl sulphate in inhibiting corrosion in the test conditions used in the present study.

Surface Preparation of Aluminum Nitride for Metallization: Effect of Temperature on Surface Reactivity

The current aqueous cleaning step in the surface preparation of aluminum nitride (AlN) prior to metallization causes performance and reliability issues for the substrates used for microelectronic packaging due to surface reactions. These issues limit the use of AlN and its replacing of BeO, an environmentally hazardous material currently used. The aim of this investigation was to determine the effects of different solutions on the surface of AlN substrates under varying conditions at times up to 2419.2 ks (28 days). Concentration of the solutions, temperature, and immersion time were varied for the AlN samples in the solutions. Both elevated temperatures (50°C and 90°C) and low temperatures (5°C) were investigated. Four general types of behavior were observed: minor changes in average surface roughness and microstructure, linear change in average surface roughness and pitted grains, nonlinear change in average surface roughness and product formation on AlN surface, and miscellaneous change in average surface roughness with surface product formation. The surface roughening kinetics were very complex due to changes in both the reaction product morphology and reaction mechanism with temperature, solvent, and pH for a specific solvent. Minor changes in average surface roughness and microstructure were observed for HCl pH = 5 , H 2 SO 4 pH = 5 , NaOH pH = 8 , NaOH pH = 10 , NaOH pH = 12 , deionized water and Alfred tap water at 5°C, HCl pH = 3 and oleic acid at 50°C and citric acid and oleic acid at 90°C. Linear changes in average surface roughness and pitted grains were observed for HCl pH = 2 and H 2 SO 4 pH = 3 at 50°C and HCl pH = 2 , H 2 SO 4 pH = 3 , and deionized water at 90°C. Non-linear change in average surface roughness and product formation on AlN surface was observed for HCl pH = 5 , NaOH pH = 8 and Alfred tap water at 50°C and HCl pH = 5 and H 2 SO 4 pH = 2 at 90°C. Miscellaneous changes in average surface roughness with surface product formation were observed for H 2 SO 4 pH = 2 , H 2 SO 4 pH = 5 , NaOH pH = 10 , NaOH pH = 12 , citric acid, Micro-90 and deionized water at 50 °C and HCl pH = 3 , H 2 SO 4 pH = 5 , NaOH pH = 8 , NaOH pH = 10 , NaOH pH = 12 , Micro-90 and Alfred tap water at 90°C.

The response of SiC fibres to vacuum plasma spraying and vacuum hot pressing during the fabrication of titanium matrix composites

Vacuum plasma spraying (VPS) and vacuum hot pressing (VHP) have been used to fabricate Ti-6Al-4V matrix composite material reinforced longitudinally with DERA Sigma C coated SiC 1140+ fibres. VPS of Ti-6Al-4V onto Sigma 1140+ SiC fibres caused no fibre/matrix interfacial reaction. During VHP a fibre/matrix reaction occurred, producing a mixture of fine (< 50 nm) TiCx (x </= 1) adjacent to the fibre coating and coarse-grained (0.3-0.5 &mgr;m) equiaxed TiCx adjacent to the Ti matrix. A decrease in C concentration with increasing distance from the C coating is proposed, and is consistent with the evidence presented. A similar thickness and morphology of reaction product arose from conventional foil-fibre foil processing, but the matrix coated fibre/hot isostatic pressing process led to a slightly thicker reaction layer. The TiCx reaction product acted as a diffusion barrier, inhibiting further reaction more effectively than in experiments on earlier SiC fibres having a C coating. Surface damage was shown to be a factor in lowering 1140+ SiC fibre failure stress. Surface damage to 1140+ fibres resulted from both VPS and VHP, the former causing a slight reduction in mean ultimate tensile strength (UTS), and a large reduction in the bend strain to failure Weibull modulus. This damage was caused by both fibre winding and by deposition of metal during VPS, giving rise to coating flaws, and is not in itself considered to be a major problem. Surface damage increased after VHP, reducing the mean UTS and tensile Weibull modulus, and the mean bend strain to failure. This damage arose from bending and flattening of the rough monotapes, and from the fibre/matrix reaction caused by thermal exposure. The level of damage to 1140+ SiC fibre from VHP was reduced by modification of the process path. Increasing the VHP temperature and lowering the pressure ramp rate reduced fibre damage sufficiently to enable a macroscopic composite UTS of 95% of the theoretical maximum to be achieved.

Strength and Microstructure of Brazed Alumina‐Silicon Carbide Ceramic‐Matrix Composites

Alumina‐silicon carbide whisker (Al2O3‐SiCw) composite pieces were brazed under high vacuum with Ag‐Cu‐based active braze alloys. Joined specimens exhibit mean fracture strengths of 480 MPa (4.5 wt% titanium in braze) and 591 MPa (2.0 wt% titanium in braze) in four‐point bend tests; these strengths are 78%−96% of the measured strength of the composite. The interfacial phases have been identified, by using transmission electron microscopy and electron probe microanalysis, as being Ti3(Cu,Al,Si)3O, Ti5Si3, TiC, and γ‐TiO, and the relative locations of the interfacial phases are described. The high strengths are believed to result from both good wetting behavior under high vacuum and the composite nature of the reaction product morphology.

Neutron scattering studies of hydrating cement pastes

The progress of the hydration reactions of tricalcium silicate (C 3S) has been followed using quasielastic neutron scattering (QNS) at an energy resolution of 60 μeV and a momentum transfer of q = 1 A ̊ −1 . The degree of reaction in the hydrating cement paste is inferred from the fraction of water that is chemically bound to the cement reaction products and the known stoichiometry of C 3S hydration. Three different water-to-cement ratios were studied in this experiment: W/C = 0.7, 0.5 and 0.3. The results of an Avrami-model analysis of the first 15 h of the reaction are consistent with three types of C 3SH 2O reaction product morphology and growth mechanisms: (i) a plate-type product phase from either phase boundary growth with no nucleation; (ii) diffusion-limited growth with constant nucleation; or (iii) a needle-type product phase with phase boundary growth and constant nucleation. Analysis of the later-time diffusion-limited portion of the reaction provides apparent diffusion constants for the migration of water through the C 3S hydration products. These data indicate that the diffusion constants vary approximately exponentially over the range of water-to-cement values studied.

Synthesis of NiAl/Al 2O 3 composites via in-situ reduction of precursor oxides

Preliminary results show that the deliberate additions of precursor oxides to NiAl to generate Al{sub 2}O{sub 3} via in-situ reduction by aluminum is feasible. The reaction with SiO{sub 2} results in an aggregate morphology whereas reaction with TiO{sub 2} results in a more continuous morphology of the product phases in the reaction zone. This difference in microstructural characteristics may be related to the volume change associated with the respective reactions. The silicon and titanium released during the reaction dissolve into the NiAl matrix and an understanding of the phase equilibria in the respective ternary systems is essential to determine the effects of these elements on the stability of the matrix. Further work is in progress to (1) identify the probable reaction sequences involved in the displacement reactions of NiAl with SiO{sub 2} or TiO{sub 2} and determine the relative influences of factors affecting the reaction product morphologies, (2) to understand the influence of volume change on the characteristics of the displacement reaction by extending the reaction to other potential precursor oxides (e.g. nickel oxide, iron oxide, etc.) that involve different volume changes in their transformation to Al{sub 2}O{sub 3} and (3) to extend the reaction scheme to other potential aluminidesmore » such as those containing titanium and iron.« less

Interfacial reaction and adhesion between SiC and thin sputtered cobalt films

Thin sputtered nickel films grown on SiC were annealed in an Ar/4 vol % H2 atmosphere at temperatures between 550 to 1450 °C for various times. The reactivity and the reaction-product morphology were characterized using optical microscopy, surface profilometry, X-ray diffraction, scanning electron microscopy and electron probe microanalysis. The reaction with the formation of silicides and carbon was observed to first occur above 650 °C. Above 750 °C, as the reaction proceeded, the initially formed Ni3Si2 layer was converted to Ni2Si and carbon precipitates were observed within this zone. The thin nickel film reacted completely with SiC after annealing at 950 °C for 2 h. The thermodynamically stable Ni2Si is the only observed silicide in the reaction zone up to 1050 °C. Above 1250 °C, carbon precipitated preferentially on the outer surface of the reaction zone and crystallized as graphite. The relative adhesive strength of the reaction layers was qualitatively compared using the scratch test method. At temperatures between 850 to 1050 °C the relatively higher critical load values of 20–33 N for SiC/Ni couples are formed.

Thin film Ti⧸6H-SiC interfacial reaction: high spatial resolution electron microscopy study

The structure and chemistry of thin Ti films on Si-terminated vicinal (0001) α-SiC substrates was investigated by high-resolution imaging and high-spatial-resolution nanospectroscopy. The Ti was deposited on in-situ cleaned SiC substrates under UHV conditions by evaporation; subsequent post-deposition heat treatments were also performed under UHV conditions. Examination of as-deposited interfaces showed that Ti deposited epitaxially with basal plane/close-packed direction alignment on the substrate. No reaction zone was visible and the interface was chemically sharp. Lattice misfit was accomodated by interface dislocations. Post-deposition heat treatment at 700°C caused formation of Ti 5Si 3 and TiC reaction products at the Ti/SiC interface. The reaction product morphology was complex and dependent on reaction time. For short times (≈ 20 min) parabolic rate kinetics were obeyed, but for longer times (≈ 60 min) formation of Ti 5Si 3 dominated and the rate decreased. HREM image contrast of SiC, Ti 5Si 3 and TiC varied with position near the interfaces. Preliminary theoretical calculations indicated these apparent changes in structure resulted from local changes in orientation and thickness.