Mechanical properties of roller compacted concrete containing rice husk ash with original and recycled asphalt pavement material

This study focused on the effects of rice husk ash (RHA) on the mechanical properties of roller compacted concrete (RCC) designed with original and reclaimed asphalt pavement (RAP) materials. The RCC mixes were produced by partial substitution of cement with RHA at varying amounts of 3% and 5%. Four aggregate combinations including the mix with original aggregate, coarse RAP + fine original aggregate, coarse original aggregate + fine RAP and total RAP were considered. The main experimental design consisted of the compressive strength and three points bending tests. Bending test was used to measure the modulus of rupture, material’s energy absorbency and analyse the fatigue response of RCC mixes. All tests were performed after 7, 28 and 120 days curing except the fatigue test that performed on 120 days specimens. Adding RHA resulted in higher optimum moisture content (OMC) and lower maximum dry density. Furthermore, adding RAP with different dimensions reduced the OMC and maximum dry density. The material’s flexibility improved upon replacing 3% cement by RHA. However, the energy absorbency reduced by increasing the RHA content to 5%. The fatigue life of RCC mixes containing RAP material was lower than the conventional one. Furthermore, replacing the coarse aggregate by RAP led to higher fatigue life than the fine aggregate. There was a strong relationship (R² > 0.90) between the energy absorbency and fatigue response of RCC mixes. At higher stress ratios of 0.72, the mix with higher energy absorbency behaved better under repeated loadings. Besides, a reverse relationship was found between the fatigue life and material porosity. Adding 3% RHA reduced the porosity especially after 120 days curing and improved the fatigue resistance. However, the addition of RHA to 5% resulted in higher porosities and lower fatigue lives.     

Low-firing of BiSbO4 microwave dielectric ceramic with V2O5–CuO addition

Effects of 1.0 wt.% V₂O₅–CuO mixture addition on the sintering behavior, phase composition and microwave dielectric properties of BiSbO₄ ceramics have been investigated. BiSbO₄ ceramics can be well densified below temperature about 930 °C with 1.0 wt.% V₂O₅–CuO mixtures addition with different ratios of CuO to V₂O₅. The formation of BiVO₄ phase and substitution of Cu²⁺ can explain the decrease of sintering temperature. Dense BiSbO₄ ceramics sintered at 930 °C for 2 h exhibited good microwave dielectric properties with permittivity between 19 and 20.5, Qf values between 19,000 and 40,000 GHz and temperature coefficient of resonant frequency shifting between ?71.5 ppm °C^?1 and ?77.8 ppm °C^?1. BiSbO₄ ceramics could be a candidate for microwave application and low temperature co-fired ceramics technology.     

Optimum manufacturing parameters for compressed lumber from oil palm (Elaeis guineensis) trunks: Respond surface approach

The objective of this investigation was to evaluate optimum manufacturing parameters to produce compressed lumber from oil palm (Elaeis guineensis) trunks. Experimental samples were made using steaming time, pressure, pressure time and temperature ranging from 2 to 4 h, from 5 to 12 MPa, from 20 min to 60 min and from 100 °C to 200 °C, respectively. Compression and recovery ratios of the specimens were determined employing Response Surface Methodology (RSM) approach within the scope of Central Composite Design (CCD) computer program. Experimental and calculated values were compared to each other. Based on the results of the work, the specimens steamed for 2 h before they were compressed using a pressure of 11.16 MPa at a temperature of 200 °C for 60 min resulted in optimum conditions. Measured and calculated compression and recovery ratios of the samples showed 0.70 and 0.83 correlation coefficient values, respectively.     

Control of degradation rate of bioabsorbable magnesium by anodization and steam treatment

The control of degradation rate of bioabsorbable magnesium devices is crucial for their biomedical applications. In this study, the influence of anodizing voltages and autoclaving on the degradation behavior of anodized pure magnesium was examined by immersion tests in a culture medium for 14 d. The anodization and autoclaving varied the morphology of surface film. Porous films were formed at 7 V and 100 V, and non-porous films were formed at 2 V and 20 V. The microscopic appearance of the anodized films did not change by autoclaving. The degradation rate on Day 1 was the highest and subsequently decreased to a quasi-steady state within the initial 3–5 d. The 7 V- and 100 V-anodized specimens showed the highest and the lowest quasi-steady degradation rate, respectively. The autoclaving significantly retarded the degradation of the anodized specimens. These facts revealed that anodization and autoclaving are useful for the control of the degradation rate of magnesium and its alloys. The porous anodized films showed local corrosion, whereas the non-porous anodized film formed at 20 V did not show apparent local corrosion. The local corrosion was prevented by autoclaving. These results suggest that the occurrence of local corrosion depends on the porous morphology of surface film.     

Mechanical properties of reactive powder concrete containing high volumes of ground granulated blast furnace slag

The mechanical properties (flexural strength, compressive strength, toughness and fracture energy) of steel microfiber reinforced reactive powder concrete (RPC) were investigated under different curing conditions (standard, autoclave and steam curing). Portland cement was replaced with ground granulated blast furnace slag (GGBFS) at 20%, 40% and 60%. Sintered bauxite, granite and quartz were used as aggregates in different series. The compressive strength of high volume GGBFS RPC was over 250 MPa after autoclaving. When an external pressure was applied during setting and hardening stages, compressive strength reached up to 400 MPa. The amount of silica fume can be decreased with increasing amount of GGBFS. SEM micrographs revealed the tobermorite after autoclave curing.     

Physical and mechanical characterization of Fiber-Reinforced Aerated Concrete (FRAC)

Fiber-Reinforced Aerated Concrete (FRAC) is a novel lightweight aerated concrete that includes internal reinforcement with short polymeric fibers. The autoclaving process is eliminated from the production of FRAC and curing is performed at room temperature. Several instrumented experiments were performed to characterize FRAC blocks for their physical and mechanical properties. This work includes the study of pore-structure at micro-scale and macro-scale; the variations of density and compressive strength within a block; compressive, flexural and tensile properties; impact resistance; and thermal conductivity. Furthermore, the effect of fiber content on the mechanical characteristics of FRAC was studied at three volume fractions and compared to plain Autoclaved Aerated Concrete (AAC). The instrumented experimental results for the highest fiber content FRAC indicated compressive strength of approximately 3 MPa, flexural strength of 0.56 MPa, flexural toughness of more than 25 N m, and thermal conductivity of 0.15 W/K m.     

Effects of sintering process on preparing iron-based friction material directly from vanadium-bearing titanomagnetite concentrates

In order to optimize an innovative two-stage process for preparing an iron-based friction material directly from vanadium-bearing titanomagnetite concentrates, this paper focuses on the effects of sintering process on the microstructures and properties of an iron-based friction material. On one hand, the samples were sintered at 900 °C, 950 °C, and 1000 °C for 3 h respectively; On the other hand, the samples were sintered at 1000 °C for 1 h, 2 h, 3 h, and 4 h respectively. As a result, after the samples were sintered at above 950 °C for more than 3 h, a lot of laminated microstructures appear in these samples owing to the formation of a large number of pearlites. Besides, the density, the hardness, and the friction coefficient of this material are positively correlated to the sintering temperature or the sintering time, and the wear rate of this material is negatively related to the sintering temperature or the sintering time. This study can contribute to the attainment of much clearer insight into the effects of sintering process and lay the foundation of practical application of this innovative two-stage process.     

Investigation of the effect of rice husk derived Si/SiC on the morphology and thermal stability of carbon composite aerogels

Highly porous carbon aerogels were prepared by pyrolyzing the novolac–silica aerogels. The silica phase was extracted from rice husk ash (RHA). The polymer aerogel was synthesized via the novel method of sol–gel polymerization in solvent vapor-saturated atmosphere. This method removes the need for supercritical drying and reduces the shrinkage of aerogels during drying stage and also has much lower process time compared to the conventional sol–gel method. In the next step, polymer composite aerogels become carbon/silica and carbon/silica/silicon carbide composites in pyrolysis (800 °C) and carbothermal reduction (1500 °C) stages, respectively. The characterization of the prepared composite aerogels was performed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses, respectively. Thermal and mechanical properties of the samples were investigated by differential scanning calorimetry (DSC) and compressive strength analysis. The resultant composite aerogels show a nanostructure with high porosity (above 82%) and low density (below 0.3 g cm^− 3). Si mapping images showed the good distribution of silica phase throughout the carbon matrix. Also the rate of oxidation for carbon composites decreased by silica incorporation and oxidation temperature increased about 20% by adding RHA silica. Compressive strength of composite samples increased about 25% by increasing RHA silica phase content.     

Effect of phase transformation and intermetallic compounds on the microstructure and tensile strength properties of diffusion-bonded joints between Ti–6Al–4V and AISI 304L

The occurrence of a phase transformation and the effect of intermetallic compounds on the microstructure and tensile strength properties of diffusion-bonded (DB) joints between Ti–6Al–4V and AISI 304L were studied in the temperature range of 875–950 °C with an interval of 25 °C, a bonding time of 60 min and pressures of 4 MPa and 8 MPa. A maximum tensile strength of 242.6 MPa, was observed for diffusion-bonded joints that were processed at a temperature of 900 °C, bonded for 60 min at a pressure of 4 MPa and annealed for 2 h at 750 °C. Optical microscopy and scanning electron microscopy (SEM) were used to examine the grain growth and the fine details of the interface structure. Energy dispersive X-ray analysis (EDAX) and X-ray diffraction analysis (XRD) revealed the existence of intermetallic compounds and corroborated the phase transformation.     

Comparative study of seeding methods; dip-coating,rubbing and EPD,in SAPO-34 thin film fabrication

Seeding methods; including rubbing, dip-coating and electro-phoretic deposition (EPD) were comparatively implemented for silicoalumino phosphate-34 (SAPO-34) thin film fabrication via secondary growth. The size of surface particles and thicknesses of fabricated layers were characterized by Scanning Electron Microscopy. The so-called properties were analyzed and modified to achieve a fairly defect free surface coverage and thin layers with finest particles. One-step dip-coating method provided well-distributed seeds on the support surface with a very poor coverage. Rubbing and EPD methods preferentially provided defect free and uniform surface coverage, however the grown particles from EPD method were bigger than those from rubbing method. It was revealed that in situ (no seeding) crystallization and one-step dip-coating method failed to produce defect free qualified membranes whereas EPD and rubbing methods caused continuous and defect free SAPO-34 membrane layers. To control synthesis parameters in the secondary growth crystallization, two important parameters were studied; crystallization time at three levels of 12, 24 and 48 h and crystallization temperature at three levels of 458, 473, and 488 K were simultaneously examined with the aforesaid seeding methods. Significant effects of crystallization temperature and time were observed on the formed layer qualities. The fabricated membrane by rubbing method during 24 h crystallization time at 473 K temperature was tested under equimolar gas mixture of hydrogen–methane at 293 K with pressure drops ranging from 1 to 6 bar. At one bar pressure drop, H₂ was enriched up to 84.2 mol% in the permeate side with the permeance of 6 × 10⁻⁸ mol/(m² s Pa).     

Influence of air annealing temperature and time on the optical properties of Yb:YAG single crystal grown by HDS method

8 at.% Yb:YAG plate single crystal with the dimension of 170 mm × 150 mm × 30 mm was grown in vacuum by Horizontal Directional Solidification method. Aimed at blue-green color centers, annealing treatments of 15 mm × 15 mm × 1 mm samples from 900 °C to 1400 °C for 5 h and at 900 °C from 5 h to 40 h in air were conducted. The absorption spectra, emission spectra, fluorescence lifetime and X-ray photoelectron spectroscopy of samples under different annealing conditions were measured at room temperature, respectively. Annealing at above 1000 °C for 5 h or at 900 °C for 40 h made the blue-green color centers disappear and the samples turned to transparent. Absorption coefficients decreased in the 300 nm–800 nm wavelength range, emission intensities increased and emission bands broadened around 486 nm and 1029 nm with increasing temperature up to 1200 °C, then varied inversely. These values decreased or increased monotonically with increasing annealing time at 900 °C. The maximal increases of fluorescence lifetime were 62.3% and 64.7%, respectively. The calculated emission cross section of 1200 °C for 5 h was up to 4.4 × 10⁻²⁰ cm². In X-ray photoelectron spectroscopy, the concentrations of oxygen vacancies reduced from 1.28% down to absence by annealing. These experiments show that color centers are detrimental to the optical properties of HDS-Yb:YAG laser crystal and optimal annealing treatments should be conducted.     

The mechanical,transport and thermal properties of mortar and concrete containing waste cork

This study examines the impact of cork used as sand replacement or stone replacement on the plastic, mechanical, transport, microstructural and thermal properties of mortar and concrete. Mix design variables include the percentage of cork, cork size, and the cork blend. Key findings from this study revealed that: (i) The greatest early age (days 3 and 7) cube strengths were achieved by 24 h moisture saturation of the cork followed by draining it prior to use in concrete. Heat exposure of 50 °C or 100 °C resulted in detrimental effects on cube strength gain. (ii) Finer cork sizes were most beneficial to achieve optimum mechanical, and transport properties however high permeability values indicate that concrete-cork composites considered in this study may be vulnerable to poor durability performance. (iii) Greater percentages of cork as sand or stone replacement had the greatest impact on thermal resistance. (iv) Blending multiple cork sizes to achieve a greater size distribution of cork granules used as sand or stone replacement did not yield notable beneficial results.     

Magnetic and catalytic properties of cubic copper ferrite nanopowders synthesized from secondary resources

Cubic copper ferrite CuFe₂O₄ nanopowders have been synthesized via a hydrothermal route using industrial wastes. The synthesis conditions were systematically studied using statistical design (Box–Behnken Program) and the optimum conditions were determined. The results revealed that single phase of cubic copper ferrite powders can be obtained at different temperatures from 100 to 200 °C for times from 12 to 36 h with pH values 8–12. The crystallite size of the produced powders was in the range between 24.6 and 51.5 nm. The produced copper ferrite powders were appeared as a homogeneous pseudo-cubic-like structure. A high saturation magnetization (M_s 83.7 emu/g) was achieved at hydrothermal temperature 200 °C for 24 h and pH 8. Photocatalytic degradation of the methylene blue dye using copper ferrite powders produced at different conditions was investigated. A good catalytic efficiency was 95.9% at hydrothermal temperature 200 °C for hydrothermal time 24 h at pH 12 due to high surface area (118.4 m²/g).     

Structural and microstructural characterizations of nanocrystalline hydroxyapatite synthesized by mechanical alloying

Single phase nanocrystalline hydroxyapatite (HAp) powder has been synthesized by mechanical alloying the stoichiometric mixture of CaCO₃ and CaHPO₄ powders in open air at room temperature, for the first time, within 2 h of milling. Nanocrystalline hexagonal single crystals are obtained by sintering of 2 h milled sample at 500 °C. Structural and microstructural properties of as-milled and sintered powders are revealed from both the X-ray line profile analysis and transmission electron microscopy. Shape and lattice strain of nanocrystalline HAp particles are found to be anisotropic in nature. Particle size of HAp powder remains almost invariant up to 10 h of milling and there is no significant growth of nanocrystalline HAp particles after sintering at 500 °C for 3 h. Changes in lattice volume and some primary bond lengths of as-milled and sintered are critically measured, which indicate that lattice imperfections introduced into the HAp lattice during ball milling have been reduced partially after sintering the powder at elevated temperatures. We could achieve ~ 96.7% of theoretical density of HAp within 3 h by sintering the pellet of nanocrystalline powder at a lower temperature of 1000 °C. Vickers microhardness (VHN) of the uni-axially pressed (6.86 MPa) pellet of nanocrystalline HAp is 4.5 GPa at 100 gm load which is close to the VHN of bulk HAp sintered at higher temperature. The strain-hardening index (n) of the sintered pellet is found to be > 2, indicating a further increase in microhardness value at higher load.     

Effect of heat treatment on the tribological properties of Al–Cu–Mg/nanoSiC composites

In this study, the effect of heat treatment on the tribological properties of Al–Cu–Mg alloy reinforced with 4 wt.% SiC particles with 650 nm average particle size has been investigated. The age hardening process consists of solution treatment at 540 °C for 6 h, followed by water quenching and ageing at different temperatures of 175, 200 and 225 °C with soaking times of 3, 6 and 9 h. Hardness measurements were applied to monitor the precipitation effect and the aged samples were then subjected to wear tests under dry sliding conditions against steel and alumina counterfaces. The results showed that the reinforced material exhibits an enhanced ageing response compared to the unreinforced material in the same heat treatment conditions. The rate of ageing increases with increasing temperature; however, ageing at 200 and 225 °C for more than 6 h resulted in over-ageing. The best combinations for the enhanced tribological properties for the composite material were selected as 6 h ageing at 225 °C. The precipitation effect for this alloy can be enhanced by the small addition of SiC nanoparticles. Having a small amount of nanoSiC particles with fine precipitates inside the matrix further increases the hardness and wear properties.     

Effects of hot water pre-extraction on surface properties of bagasse soda pulp

In this work, the effects of hot water pre-extraction of depithed bagasse on the soda pulping and surface properties were studied. The conditions of hot water pre-extraction were: maximum temperature 170 °C, heat-up time 90 min, time at maximum temperature 10 min, and solid to liquor ratio (S:L) 1:8. Consequently, the pre-extracted and un-extracted bagasse chips were subjected to soda pulping at 160 °C for 1 h with 11, 14 and 17% active alkali charge and an S:L of 1:5. The results showed that the hot water pre-extraction increased bagasse surface texture porosity by hemicellulose degradation. Therefore, the delignification was faster for pulping of pre-extracted samples. At a certain charge of alkali, pre-extracted samples showed higher screened yield and lower Kappa number. For instance, at 17% alkali charge, pre-extracted bagasse gave 11.3% higher pulp yield compared with the un-extracted ones. Inverse gas chromatography (IGC) results showed that the hot water pre-extraction changed the active sites on the bagasse surface, decreasing the dispersive energy and the basicity character, and affected the particle morphology. The pulping process decreased the hydrophobicity and the basicity of the bagasse surface. The surfaces of un-extracted and pre-extracted bagasse pulps had similar properties but different morphology. The pulps present higher surface area and permeability with more reactive capacity.     

Optimizing conditions for preparation of MnOx/RHA catalyst particle for the catalytic oxidation of NO

Rice husk ash (RHA) was utilized as support to synthesize MnOx/RHA catalyst by incipient wetness impregnation. In order to detailedly investigate the influence of preparation variables on the catalytic activity of MnOx/RHA for NO oxidation, the quadratic regression orthogonal rotation design (QRROD) was employed. An empirical model was developed to correlate preparation variables with the conversion of NO to NO₂. The surface species and morphology of the catalyst were also analyzed by SEM and XRD, respectively. It was found that most of MnOx supported on RHA were granular with micron-size and in the form of amorphous phase. The preparation variables except for calcination time (x₂) had significant effect on the catalytic activity of MnOx/RHA. The model could accurately describe the relationship between the preparation variables and NO conversion through the analysis of variance (ANOVA) and the comparison of experimental results and predicted results. The particles size of MnOx was increased from 0.1 to 1.0 μm, as the calcination temperature was raised from 200 to 800 °C, and the fraction of crystal MnOx also increased. The surface structure of RHA was markedly affected by incineration temperature. With incineration temperature increasing, the surface structure becomes compacter.     

Synthesis and characterization of xTiO2(1 − x)α-Fe2O3 magnetic ceramic nanostructure system

Rutile-doped hematite xTiO₂(1 ? x)α-Fe₂O₃ (x = 0.0–1.0) nanostructures were synthesized using mechanochemical activation by ball milling. Their complex structural, magnetic and thermal properties were characterized by X-ray diffraction, Mössbauer spectroscopy and simultaneous DSC–TGA. XRD patterns yielded the dependence of lattice parameters and grain size as a function of ball milling time. For the molar concentrations x = 0.1 and 0.3, the Mössbauer spectra were fitted with one, two, three or four sextets, corresponding to the degree of Ti ion substitution of Fe ions in hematite lattice. After 12 h of ball milling, the completion of Ti ion substitution of Fe ions in hematite lattice occurs for x = 0.1 and 0.3. For x = 0.5 and 0.7, Mössbauer spectra fitting required sextets and a quadrupole-split doublet, representing Fe ions substituting Ti ions in the rutile lattice. The completion of Fe ion substitution of Ti ions in rutile lattice was not observed, as indicated by XRD patterns and Mössbauer spectra for these two molar concentrations. Simultaneous DSC–TGA measurements revealed that the mechanochemical activation by ball milling has a strong effect on the thermal behavior of this nanostructure system. The enthalpy dropped dramatically after 2 h of milling time, indicating the strong solid–solid interactions between TiO₂ and α-Fe₂O₃ after ball milling. The change in weight loss of hematite was caused by the decrease of grain size and ion substitutions between Fe and Ti after mechanochemical activation.     

Studies on phase formation,microstructure development and elastic properties of reduced NiO–8YSZ anode supported bi-layer half-cell structures of solid oxide fuel cells

Half-cell structures of solid oxide fuel cells (SOFCs) with a thin and dense electrolyte layer of 8YSZ supported by a thick and porous NiO–8YSZ anode precursor structure were reduced in a gas mixture of 5% H₂–95% Ar at 800 °C for selected time periods in order to fabricate cermets with desired microstructure and composition, and to study their effects on the elastic properties at ambient and reactive atmospheres. It appears that 2 h of exposure to the reducing conditions is enough to reduce ～80% of NiO with an enhanced porosity value of 35%. The Ni–8YSZ cermet phase formation in the anode was analyzed with X-ray diffraction (XRD) in correlation with its microstructure. The elastic properties were determined after the reduction, at room and elevated temperatures using the impulse excitation technique. At room temperature the decrease in the Young's modulus was about 44% (after 8 h of reduction) and can be attributed mainly to the changes in the microstructure, particularly the increase in porosity from ～12% to 37%. Young's moduli of the as-received precursor and reduced anodes were evaluated as a function of temperature in air and reducing atmosphere. The results were explained in correlation to the initial porosity, composition and oxidation of Ni at the elevated temperatures.     

Preparation and properties of porous Ti–10Mo alloy by selective laser sintering

In this study, porous Ti–10Mo alloy was prepared from a mixture of titanium, molybdenum and epoxy resin powders by selective laser sintering preforming, debinding and sintering at 1200 °C under a pure argon atmosphere. The influence of sintering process on the porous, microstructural and mechanical properties of the porous alloy was discussed. The results indicate that the pore characteristic parameters and mechanical properties mainly depend on the holding time at 1200 °C, except that the maximum strain keeps at about 45%. The matrix microstructure is dominated by α phase with a small quantity of β phase at room temperature. As the holding time lengthens from 2 to 6 h, the average pore size and the porosity decrease from 180 to 50 μm and from 70 to 40%, respectively. Meanwhile, the Young's modulus and the compressive yield strength increase in the ranges of 10–20 GPa and 180–260 MPa, respectively. Both the porous structure and the mechanical properties of the porous Ti–10Mo alloy can be adjusted to match with those of natural bone.