Mechanical properties and microstructure of steel/iron slag blended mortar

This study aims to examine the mechanical properties and microstructures of steel/iron slag blended mortar (SISBM), which contains two by-products of the steel and iron industries: steel slag (basic oxygen furnace slag, BOFS) and iron slag (blast furnace slag, BFS). Test results indicate that steel slag will have effective hydration reactions with iron slag and contribute strength. The optimal mixing ratio of steel to iron slags was 3:7 (by weight), and the compressive strength was about 83.59% compared with that of ordinary Portland cement mortar (OPM). The strength development was similar to that of OPM and the strength increased as the curing period increased. The X-ray diffraction analysis results implied that the main products of hydration could be C–S–H, C–A–S–H, CaO–MgO–Al₂O₃–SiO₂, Fe_0.974O, and C₄AF. The scanning electron microscope images indicated that the distribution of Ca(OH)₂ and CaCO₃ increased as the inclusion of steel slag increased, perhaps resulting from insufficient reactions between BFS and Ca(OH)₂ and f-CaO due to excessive BOFS. In addition, the results indicated that the density of OPM was superior to that of SISBM. This may be the reason for lower strength of SISBM compared to OPM.     

The effect of nanoparticles on the adhesion of epoxy adhesive

In this investigation, the influence of different nanoparticles and surface roughness on the adhesion between epoxy adhesive and steel substrate was primarily investigated. The results of pull-off adhesion tests indicated that nano-Al₂O₃ of the three kinds of nanoparticles had the most influence on adhesion strength, which was the optimal additive for the epoxy adhesive to improve the adhesion strength. Also, it was found that modified by 2% nano-Al₂O₃, the strength multiplication on the surface abraded with silicon carbide paper of 150 grits (150#) was the highest, of three different surface roughness. So, as the results showed that modified by 2% nano-Al₂O₃, the adhesion strength of epoxy adhesive on the surface abraded with 150# was visibly improved by about 5 times. Transmission electron microscope (TEM) displayed nano-Al₂O₃ homogeneously dispersed in epoxy adhesive. Field emission scanning electronic microscope (FE-SEM) revealed that the surface morphology of steel well coincided with that of epoxy adhesive.     

Effect of grain-boundary crystallization on the high-temperature strength of silicon nitride

Si₃N₄ specimens having the composition 88.7 wt% Si₃N₄-4.9wt% SiO₂-6.4wt% Y₂O₃ (85.1 mol% Si₃N₄-11.1 mol% SiO₂-3.8mol% Y₂O₃) were sintered at 2140° C under 25 atm N₂ for 1 h and then subjected to a 5 h anneal at 1500° C. Crystallization of an amorphous grainboundary phase resulted in the formation of Y₂Si₂O₇. The short-time 1370° C strength of this material was compared with that of material of the same composition having no annealing treatment. No change in strength was noted. This is attributed to the refractory nature of the yttrium-rich grain-boundary phase (apparently identical in both glassy and crystalline phases) and the subsequent domination of the failure process by common processing flaws.Chemical analysis of the medium indicated 5.25 wt% O₂, 0.46 wt% C, 0.8 wt% Al, and expressed in p.p.m. 670 Ca, 30 Cu, 2000 Fe, <2 Ti, 370 Cr, 130 Mg, 90 Mn, <10 V, <20 Zr, 2000 Mo, 240 Ni, 130 Zn, <30 Pb, <60 Sn.     

Gas permeation properties of polyamide membrane prepared by interfacial polymerization

Interfacial polymerization technique has been widely employed to prepare reverse osmosis (RO) and nanofiltration (NF) membranes. The present study explores the possibility of preparing a polyamide membrane by interfacial polymerization and its utilization for the separation of CO₂ and H₂S from CH₄. A novel ultraporous substrate of polysulfone (PSF) was prepared by phase inversion technique from a solution containing 18% PSF and 4% propionic acid in dimethyl formamide (DMF) solvent. Thin film composite (TFC) polyamide membrane was synthesized on PSF substrate from the reaction between meta-phenylene diamine in an aqueous media and isophthaloyl chloride in hexane. The membrane prepared was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) to study intermolecular interactions, crystallinity, thermal stability and surface morphology, respectively. Gas permeabilities of pure CO₂, H₂S, CH₄, O₂, and N₂ gases were measured using the indigenously built permeation cell incorporated into a high-pressure gas separation manifold. At the feed pressure of 1 MPa, the membrane exhibited permeances of 15.2 GPU for CO₂ and 51.6 GPU for H₂S with selectivities of 14.4 and 49.1 for CO₂/CH₄ and H₂S/CH₄ systems, respectively. The observed N₂ permeance of 0.95 GPU was close to that of CH_4. The corresponding O₂ permeance was 5.13 GPU with a reasonably high O₂/N₂ selectivity of 5.4. The effect of feed pressure on polyamide membrane performance was examined. Further, molecular dynamics (MD) simulations were employed to compute the cohesive energy density (CED), solubility parameter (δ) and sorption of CO₂, H₂S, CH₄, O₂, and N₂ gases in polyamide membrane to corroborate theoretical study with experimentally determined gas transport properties.     

Effect of oxide addition on the sintering and high-temperature strength of Si3N4 containing Y2O3

The effect of oxide addition on the sintering behaviour and high-temperature strength of Si₃N₄ containing Y₂O₃ was studied at 0.1 to 30 MPa N₂ at 1600 to 2000° C. The addition of oxide, i.e. MgO, Al₂O₃, La₂O₃, or Nd₂O₃, was found to lower the densification temperature and increase the densification rate. The addition of Al₂O₃ or MgO reduced the strength of sintered materials at >1350° C. The addition of La₂O₃ or Nd₂O₃, on the other hand, did not affect high-temperature strength which remained equivalent to that of the material containing only Y₂O₃. These results indicate that the glassy phases in these systems are as refractory as that in the Si₃N₄-Y₂O₃.     

Micro-yield property of sub-micron Al2O3 particle reinforced 2024 aluminum matrix composite

The microstructure and micro-yield strength of sub-micron Al₂O₃ particle reinforced 2024Al composites and the effect of the thermal-cold cycling treatment on the microstructure and properties were studied. The results show that the dislocations are rare in the microstructure of the sub-micron Al₂O_3p/2024Al composite in the squeeze casting condition. Aging and thermal-cold cycling treatment does not change this phenomenon. The Al₂O₃ particles are fine, so the thermal misfit between particles and the matrix is very small during the temperature change, resulting in decreased dislocations. The tiny and uniformly dispersed S′ precipitates and sub-micron particles can effectively pin dislocations, therefore, the micro-yield strength of the composite increases. Depending on the condition of the thermal-cold cycling treatment after aging, both the size and distribution of the S′ precipitates in the composite change, and they have great effect on the micro-yield strength of the composite.     

Influence of heat treatment and spraying angle on cohesion strength of plasma sprayed deposits

Abstract

The influence of heat treatment and spraying angle on the cohesion strength of plasma sprayed deposits has been studied. Three coatings were selected: NiCr+Cr₂O₃, ZrO₂?1;O₃ (8 wt-%), and Mo. The substrate used was aferritic Cr steel. Heat treatments of 4 h were conducted after spraying in the temperature range 600–900° C and the spraying angle varied from 45 to 90° to the surface of the sample. The cohesion strength of the deposit was measured using tensile tests. For the Cr₂O₃ deposit, the cohesion tensile strength was found to increase strongly with the temperature of the heat treatment but was not influenced by spraying angle. For the ZrO₂?8Y₂O₃ coating neither the heat treatment nor the spraying angle affected the cohesion strength, whereas for the Mo coating, the cohesion strength increased with decreasing spraying angle and heat treatment had no effect.

MST/2012     

High Temperature Construction Materials on the Basis of Nanodisperse Silicon Nitride

Si₃N₄‐Al₂O₃‐Y₂O₃, Si₃N₄‐TiN and Si₃N₄‐AIN‐Al₂O₃‐Y₂O₃ (β‐sialon) nanopowders with the specific surface area of 60–70 m²/g and average particle size of 30–50 nm have been prepared by plasmachemical synthesis. By means of the hot pressing method at 1850°C compact materials with fine‐grained structure were prepared from this powders as well as from mixture of Si₃N₄‐Al₂O₃‐Y₂O₃ with the second phase (10 wt.% SiC‐Si₃N₄, ZrO₂, TiN nanopowder). Addition of the second phase to silicon nitride improves material strength.     

High-strength zirconium diboride-based ceramic composites consolidated by low-temperature hot pressing

Abstract

Two compositions of ZrB₂-based ceramic composites containing Si₃N₄, Al₂O₃ and Y₂O₃ have been hot-pressed at different temperatures between 1673 and 1773 K for 60 min in vacuum. The densification behavior of the composites was examined during the sintering process. The microstructures of the composites were characterized by scanning electron microscopy, and the crystalline phases were identified by x-ray diffraction. The effects of Al₂O₃ and Y₂O₃ additives on the densification behavior and flexural strength were assessed. A relative density of ～95% was obtained after sintering at 1723 K or higher temperatures. The microstructures of the composites consisted of (Zr,Y)B₂, α-Si₃N₄ and Y₃(Al,Si)₅O₁₂ phases. The room-temperature flexural strength increased with the amount of additives and approached 1 GPa.     

CO2 decomposition with mangano-wüstite

Mn(II)-ferrite (Mn_0.97Fe_2.02O_4.00) prepared by the wet method was reduced in a hydrogen at 300°C to form highly reactive mangano-wüstite ((Fe_0.67, Mn_0.32)O) for CO₂ decomposition. Approximately 23% CO₂ injected (3.40 mmol) was decomposed to CO by the mangano-wüstite (3.22 g) in the initial stage of the reaction in a batch system at 400°C. 88% CO was further decomposed to carbon. Approximately 58% CO₂ injected was reversibly adsorbed on the surface and the remaining 12% was unchanged after 200 h reaction. The mangano-wüstite was concurrently transformed to Mn(II)-bearing ferrite (Mn_0.23Fe_2.77O_4.00) and manganeserich mangano-wüstite ((Fe_0.60, Mn_0.40)O). The higher CO₂ decomposition capacity for this mangano-wüstite than that for oxygen-deficient Mn(II)-ferrite is discussed in detail, based on electron hopping and movement of ions in the bulk.     

High-strength zirconium diboride-based ceramic composites consolidated by low-temperature hot pressing

Two compositions of ZrB₂-based ceramic composites containing Si₃N₄, Al₂O₃ and Y₂O₃ have been hot-pressed at different temperatures between 1673 and 1773 K for 60 min in vacuum. The densification behavior of the composites was examined during the sintering process. The microstructures of the composites were characterized by scanning electron microscopy, and the crystalline phases were identified by x-ray diffraction. The effects of Al₂O₃ and Y₂O₃ additives on the densification behavior and flexural strength were assessed. A relative density of ∼95% was obtained after sintering at 1723 K or higher temperatures. The microstructures of the composites consisted of (Zr,Y)B₂, α-Si₃N₄ and Y₃(Al,Si)₅O₁₂ phases. The room-temperature flexural strength increased with the amount of additives and approached 1 GPa.     

Synthesis of nanocrystalline M50 steel powders by cryomilling

The present paper reports on a study of the synthesis of nanocrystalline high speed tool steel M50 powders (4.5% Mo, 4.0% Cr, 1.0% V, 0.8% C, balance Fe) by cryogenic high energy ball milling (cryomilling). Pre-alloyed M50 steel is spray atomized, and subsequently cryomilled in liquid nitrogen for 25 hours. Elemental Al powder is added prior to cryomilling to promote the formation of nanoscale Al₂O₃ and AlN dispersoids to improve the thermal stability of the nanocrystalline M50 steel. High resolution transmission electron microscopy (HRTEM) reveals the formation of various carbides (V₈C₇, Fe₃C, and FeC), oxides (Al₂O₃, MoO₃, and V₃O₇), and a nitride phase (AlN) during cryomilling. Following one hour of heat treatment at 1373 K (0.77 T_m), an average grain size of 70 nm was retained for the M50 steel powders.     

Pressureless sintering of Si3N4 with Y2O2 and Al2O3

Pressureless sintering of Si₃N₄ with Y₂O₃ and Al₂O₃ as additives was carried out at 1750°C in N₂ atmosphere. Si₃N₄ materials which had more than 92% relative density were obtained with 20wt% addition of additives. The flexural strength of as-sintered materials containing 5 to 8.6wt% Al₂O₃ and 15 to 11.4wt% Y₂O₃ was in the range of 480 to 560 MPa at room temperature. The glassy grain-boundary phase of as-sintered materials crystallized to 3Y₂O₃ · 5Al₂O₃ (YAG), Y₂O₃ · SiO₂ (YS), Y₂O₃ · 2SiO₂ (Y2S) and 10Y₂O₃ · 9SiO₂ sd Si₃N₄ (NA) by heat-treatment at 1250° C for 3 days. A specimen containing 15wt% Y₂O₃ and 5wt% Al₂O₃ sintered at 1750° C for 4 h was heat-treated at 1250° C for 3 days to precipitate YAG and YS. The nitrogen concentration of the grain-boundary glassy phase of the specimen was found to be very high, and therefore the flexural strength of the crystallized specimen scarcely decreased at elevated temperatures (the flexural strength of this specimen is 390 MPa at room temperature and 360 MPa at 1300° C). Resistance to oxidation at 1200° C of the specimen was good as well as the flexural strength, compared with that of as-sintered materials.     

Synthesis, characterization and photoluminescence properties of (Gd0.99,Pr0.01)2O2S sub-microphosphor by homogeneous precipitation method

Homogeneous precipitation method for synthesizing (Gd_0.99,Pr_0.01)₂O₂S sub-microphosphor was developed, using the commercially available Gd₂O₃, Pr₆O₁₁, H₂SO₄ and (NH₂)₂CO (urea) as the starting materials. It was found that the as-synthesized precursor is mainly composed of (Gd_0.99,Pr_0.01)₂(OH)₂(CO₃)(SO₄)·nH₂O. Pure quasi-spherical shaped (Gd_0.99,Pr_0.01)₂O₂S particles can be synthesized by calcining the precursor at a temperature higher than 700 °C for 1 h in flowing hydrogen. The (Gd_0.99,Pr_0.01)₂O₂S particles have a narrow size distribution with a mean grain size of about 300-400 nm. Photoluminescence spectra of (Gd_0.99,Pr_0.01)₂O₂S under 303 nm UV excitation show a green emission at 515 nm as the most prominent peak, which corresponds to the ³P₀ → ³H₄ transition of Pr³⁺ ions. Decay study reveals that the ³P₀ → ³H₄ transition of Pr³⁺ ions in Gd₂O₂S host lattice has a single exponential decay behavior.     

Preparation,characterisation and catalytic property of ultrafine Ce–La–Mn mixed oxides

Using cerium carbonate, lanthanum oxide and manganese nitrate as raw materials, ultrafine particles of Ce–La–Mn mixed oxides were prepared by the sol–gel method combined with supercritical drying technology. The prepared materials were characterised by thermo-gravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscope. The catalytic properties of ultrafine Ce–La–Mn mixed oxides were tested by the reaction ‘2CO?+?2NO?=?2CO₂?+?N₂’. The key aim was to examine the effect of supercritical fluid drying technology and Ce-doping on the crystal structure, morphology and catalytic activity of ultrafine Ce–La–Mn mixed oxides. The results show that at 260°C, Ce–La–Mn mixed oxides are brown loose flocculent powders with good dispersibility. The particles are spherical about 10?nm in size. The main crystal components are CeO₂, MnO, La₅O₇NO₃ and La(OH)₂NO₃. After thermal treating at 850°C, Ce–La–Mn mixed oxides were made up of plenty of quasi-global grains smaller than 20?nm; the main crystal components of the Ce–La–Mn mixed oxides are LaMnO_{3+ λ} , La₂O₃ and CeO₂; heat treatment can enhance the crystallinity of the materials. Cerium-doped mixtures just exist as crystal CeO₂, which contributes to the crystallisation of Ce–La–Mn mixed oxides in the process of supercritical fluid drying at 260°C, enhancing the catalytic activity of ultrafine Ce–La–Mn mixed oxides which are thermal treated at 850°C.     

Development of light composite materials with low coefficients of thermal expansion

Abstract

Composite materials based on aluminium are used in different fields where weight, thermal expansion, and thermal stability are key requirements. The aim of the present study was to develop a universal method and scientific approach for evaluating the design of lightweight, Al matrix composites with low coefficients of thermal expansion (CTE) and high dimensional stability, and to produce such composites using the vacuum plasma spray (VPS)process. The methodology is general and could be applied to other composite systems. The VPS-produced Al and Al alloy 6061 based composites were reinforced with a variety of ceramic particles including Si₃N₄, B₄C, TiB₂, and 3Al₂O₃.2SiO₂. These composites have low CTE values ((12–13)×10^-6 K^-1), similar to that of steel, and high dimensional stability (capable of keeping dimensions stable with changes in temperature). They have low porosity (98–99%dense) and a uniform distribution of the strengthening particles. Hot rolling of the VPS-formed composites, followed by heat treatment, resulted in a significant improvement in the mechanical properties. Deformed and heat treated 6061 based composites, containing 20 wt-%TiB₂ and 40 wt-%3Al₂O₃?2SiO₂, showed excellent mechanical properties (ultimate tensile strength 210–250 MPa, elongation >4%).     

Modelling a modified atmosphere packaging system for fresh scallops (Argopecten purpuratus)

Seafood is a highly perishable food, which has a relative short shelf‐life. Modified atmosphere packaging (MAP) is a system that offers a way of extending the shelf‐life of seafood products, maintaining quality and inhibiting bacterial growth. The objective of this research was to study and determine the optimal conditions for packaging scallops in a modified atmosphere system, which includes CO₂/O₂/N₂ mixture, headspace:food ratio and storage temperature, utilizing an integrated mathematical model for MAP systems with its respective experimental validation. For validation purposes, two experiments were conducted, using gas mixtures of: (a) 45% CO₂/10% O₂/45% N₂; and (b) 60% CO₂/10% O₂/30% N₂. In addition, two experiments, at 6°C and 20°C, were conducted to obtain the shelf‐life model, utilizing the following gas mixtures: 30% CO₂/10% O₂/60% N₂; 45% CO₂/10% O₂/45% N₂; 60% CO₂/10% O₂/30% N₂; and 75% CO₂/10% O₂/15% N₂. Gas mixtures with CO₂ concentrations between 30% and 70% and different headspace:food ratios were tested during simulations. The optimal conditions for scallop storage were a 60% CO₂/10% O₂/30% N₂ gas mixture and a headspace:food ratio of 2:1. With these conditions, a simulated shelf‐life of 21 days was obtained. Optimal conditions consider maximum shelf‐life, an adequate film collapse criterion, and time to reach the pseudo‐equilibrium condition. The predictive mathematical model, coupled with experimental studies for specific products, can be efficiently utilized to evaluate packaging alternatives (size, material and selected thickness) for different temperatures and initial gas concentration scenarios of MAP products. Copyright © 2006 John Wiley & Sons, Ltd.     

Desulphurization of grain-oriented silicon iron during heat treatment in vacuum

The kinetics of desulphurization has been studied in 0.35 mm thick grain-oriented 3% silicon iron strips with various contents of sulphur (0.007, 0.020 and 0.060% S) and of manganese (0.11 and 0.31% Mn) in vacuum at pressures of 1330 Pa (10 Torr) and 0.0122 Pa (10^?4 Torr), at temperatures of 1150 and 1200°C. The specimens were examined without a coating and, after a previous oxidation, coated with a layer of MgO suspension with and without the addition of 7% Cr₂O₃ and of 0.5% CaO. It was proved that in the course of the vacuum heat treatment of transformer sheets the application of high vacuum is favourable for steel refining. The state of the surface has a considerable influence on the desulphurizing process; an addition of Cr₂O₃ and of CaO to the coating based on the MgO suspension retards the desulphurization process, while without that addition to the MgO suspension the desulphurization process proceeds as of uncoated strips.     

Synthesis of polypyrrole coated manganese nanowires and their application in hydrogen peroxide detection

This study focuses on the synthesis and application of polypyrrole coated manganese nanowires (Mn/PPy NWs) as an enzyme-less sensor for the detection of hydrogen peroxide (H₂O₂). The X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) results confirm a core–shell structure with the Mn nanowires encapsulated by the PPy. An electrochemical sensor based on the Mn/PPy NWs for amperometric determination of H₂O₂ is prepared. The electrochemical behaviour of H₂O₂ is investigated by cyclic voltammetry with the use of modified glassy carbon electrode (GCE) with Mn/PPy NWs film. The modified glassy carbon electrode (GCE) with Mn/PPy NWs shows enhanced amperometric response for the detection of H₂O₂. This is due to the high available surface area of Mn/PPy NWs which can provide a suitable area for the reaction of H₂O₂. The detection limit and limit of quantification (S/N = 3) for two linear segments (low and high concentration of H₂O₂) are estimated to be 2.12 μmol L⁻¹, 7.07 μmol L⁻¹ and 22.3 μmol L⁻¹, 74.5 μmol L⁻¹, respectively. In addition, the sensitivity for these two linear segments is 0.4762 μA mM⁻¹ and 0.0452 μA mM⁻¹ respectively.     

Effects of sintering aids on the microstructure and mechanical properties of laminated Si3N4/BN ceramics

Laminated Si₃N₄/BN ceramics with two types of sintering aids, MgO–Y₂O₃–Al₂O₃ (MYA) and La₂O₃–Y₂O₃–Al₂O₃ (LYA), were fabricated through roll compaction and hot-pressing. Sintering aids influence evidently the microstructure and mechanical properties of laminated Si₃N₄/BN ceramics. In comparison with La₂O₃–Y₂O₃–Al₂O₃, MgO–Y₂O₃–Al₂O₃ sintering aid is easier to form a glassy phase with lower viscosity and lower eutectic temperature, which is much easier to migrate into BN interlayers. This results in the denser interlayer microstructure and good bending strength of laminated Si₃N₄/BN ceramics at room temperature, but poor work of fracture (WOF) at room temperature, low strength and work of fracture at elevated temperature. In addition, the LYA sintering aid is good for forming elongated and interlocked β-Si₃N₄ grains and beneficial to the mechanical properties of the laminated Si₃N₄/BN ceramics.