Mechanical activation of trans-stilbene during wet grinding

The influence of process temperature on product particle size and solubility has been studied for wet grinding of trans-stilbene in ethanol. A positive effect of lowering the process temperature with respect to minimum product particle size was observed. Remarkably, the smallest product particle sizes x_50,3 < 1 μm were found for the lowest process temperature (251 K) at short process times (< 30 min) and moderate stressing conditions. In contrast, for the same stressing conditions at room temperature (293 K) particles of approximate size x_50,3 ≈ 8 μm are obtained.The product particle size is rather determined by the (temperature- and solvent-dependent) solid–liquid equilibrium, i.e. dissolution and precipitation phenomena, than by pure mechanical fracture. An increased solubility of stressed trans-stilbene with respect to the equilibrium solubility of the solid has been observed. By means of ¹H NMR spectroscopy and thermodynamic considerations it is shown that the solubility increase is neither due to an isomerisation of the solid nor due to size effects. In fact, mechanical activation leads to an increase in solubility of the stressed solid which was clearly proven by means of solubility studies at different temperatures. The van’t Hoff enthalpy of dissolution of the stressed solid decreased remarkably in comparison to the enthalpy of the non-stressed solid as shown by evaluation of van’t Hoff plots.     

Micromechanisms of fatigue crack growth in cast aluminium piston alloys

The fatigue crack growth behaviour in as-cast and hot isostatically pressed (HIP) model cast aluminium piston alloys with hypoeutectic Si compositions of 6.9 wt% and 0.67 wt% has been investigated. The HIP alloys showed slightly improved fatigue crack growth resistance. Analysis of the crack path profiles and fracture surfaces showed that the crack tends to avoid Si and intermetallic particles at low ΔK levels up to a mid-ΔK of ∼7 MPa√m. However, some particles do fail ahead of the crack tip to facilitate crack advance due to the interconnected microstructure of these alloys. At higher levels of ΔK, the crack increasingly seeks out Si and intermetallic particles up to a ΔK of ∼9 MPa√m after which the crack preferentially propagates through intermetallic particles in the 0.67 wt%Si alloy or Si and intermetallics in the 6.9 wt%Si alloys. It was also observed that crack interaction with intermetallics caused crack deflections that led to roughness-induced crack closure and possibly oxide-induced crack closure at low to mid-ΔK. However, crack closure appears unimportant at high ΔK due to the large crack openings and evidenced by the fast crack growth rates observed.     

A study on the effect of process parameters in stirred ball mill

An experimental study on the fine grinding of calcite powder (d₅₀ = 62.16 μm) using a 0.75 l laboratory stirred ball mill has been carried out. The effects of various operating factors, such as grinding time (min), stirrer speed (rpm), slurry density (wt.%) and ball filling ratio on fine grinding was studied under batch wet conditions using alumina balls, 95% purity with diameters 3.5–4.0 mm. A series of laboratory experiments using 2⁴ full factorial designs was conducted to determine the optimum grinding parameters. The test results showed that the stirrer speed and grinding time have strong effects on the grinding efficiency, based on the value of specific surface area (m²/g).     

Structure property relation of hybrid biocomposites based on jute,viscose and polypropylene: The effect of the fibre content and the length on the fracture toughness and the fatigue properties

In the present study, the extent of jute and viscose fibre breakage during the extrusion process on the fracture toughness and the fatigue properties was investigated. The composite materials were manufactured using direct long fibre thermoplastic (D-LFT) extrusion, followed by compression moulding. The fracture toughness (K_IC) and the fracture energy (G_IC) of the PP–J30 composites were significantly improved (133% and 514%, respectively) with the addition of 10 wt% viscose fibres, indicating hindered crack propagation. The addition of viscose fibres resulted in three times higher fatigue life compared with that of the unmodified jute composites. Further, with the addition of (2 wt%) MAPP, the PP–J30–V10 resulted in a higher average viscose fibre length of 8.1 mm, and the fracture toughness and fracture energy increased from 9.1 to 10.0 MPa m^1/2 and 28.9 to 31.2 kJ/m², respectively. Similarly, the fatigue life increased 51% compared with the PP–J30–V10, thus demonstrating the increased work energy due to hindrance of the propagation of cracks.     

Variation with added material in the effects of reactive mechanical grinding and hydriding–dehydriding cycling on the hydrogen-storage properties of Mg

Samples Mg–14Ni–6Fe₂O₃, Mg–14Ni–3Fe₂O₃–3Ti, and Mg–14Ni–2Fe₂O₃–2Ti–2Fe were prepared by reactive mechanical grinding, and their hydrogen storage properties were examined. The activated Mg–14Ni–2Fe₂O₃–2Ti–2Fe had the highest hydriding rate, absorbing 4.14 wt% H for 5 min, and 4.27 wt% H for 10 min, and 4.42 wt% H for 60 min at 573 K under 12 bar H₂. The activated Mg–14Ni–3Fe₂O₃–3Ti had the highest dehydriding rate, desorbing 3.81 wt% H for 20 min, 3.98 wt% H for 25 min, and 4.15 wt% H for 60 min. Mg–14Ni–6Fe₂O₃ dehydrided at n = 4 contained Mg, Mg₂Ni, MgO, and Mg(OH)₂. Mg(OH)₂ is considered to be formed by the reactions of MgH₂ or Mg with water vapor. The effects of reactive mechanical grinding and hydriding–dehydriding cycling are the creation of defects and cracks, and the reduction of Mg particle size. The addition of a larger amount of Ti and/or Fe has stronger effects of reactive mechanical grinding, whereas the addition of a larger amount of Fe₂O₃ has greater effects of hydriding–dehydriding cycling.     

Growing polystyrene chains from the surface of graphene layers via RAFT polymerization and the influence on their thermal properties

The polystyrene (PS) macromolecular chains were grafted on the surface of graphene layers by reversible addition-fragmentation chain transfer (RAFT) polymerization. In this procedure, a RAFT agent, 4-Cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl] pentanoic acid, was used to functionalize the thermal reduced graphene oxide (TRGO) to obtain the precursor (TRGO-RAFT). It can be calculated that the grafting density of PS/graphene (PRG) composites was about 0.18 chains per 100 carbons. Successful in-plain attachment of RAFT agent to TRGO and PS chain to TRGO-RAFT was shown an influence on the thermal property of the PRG composites. The thermal conductivity (λ) improved from 0.150 W m⁻¹ K⁻¹ of neat PS to 0.250 W m⁻¹ K⁻¹ of PRG composites with 10 wt% graphene sheets loading. The thermal property of PRG composites increased due to the homogeneous dispersion and ordered arrangement of graphene sheets in PS matrix and the formation of PRG composites.     

Damping behavior and acoustic performance of polyurethane/lead zirconate titanate ceramic composites

0–3 Type PU-based lead zirconate titanate ceramic (PZT) composites are prepared by in situ polymerization method, this PU/PZT composite material has excellent sound absorption property at low frequencies because of damping property and piezoelectric property. The dispersion of PZT particles in PU matrix, dielectric loss tangent (tan δ), dynamic storage modulus (E′), dynamic loss modulus (E″), and the acoustic absorption coefficient (α) of PU/PZT composites are studied by scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) and two-microphone impedance tube, respectively. The results indicate that the modified PZT particles dispersed well in PU matrix with the content of 30 wt%; the tan δ, E′ and E″ are 0.62, 3.75 GPa and 6.05 GPa, respectively, when the composite with 30 wt% of polarizing PZT; the acoustic absorption coefficient is found to increase with an increase of PZT content, and the average acoustic absorption coefficient is 0.32 at low frequencies from 125 to 500 Hz.     

Negative thermal expansion in silicalite-1 and zirconium silicalite-1 having MFI structure

In situ high temperature X-ray diffraction (HTXRD) studies on monoclinic silicalite-1 (S-1, silica polymorph of ZSM-5) and an orthorhombic metallosilicate molecular sieve, zirconium silicalite-1 (ZrS-1) with MFI structure (Si/Zr = 50) have been carried out using a laboratory X-ray diffractometer with an Anton Parr HTK 1600 attachment. While the structure of the S-1 collapsed at 1123 K forming α-cristobalite. S-1 and ZrS-1 showed a complex thermal expansion behavior in the temperature range 298–1023 K, ZrS-1 was stable. Powder X-ray diffraction (PXRD) data taken in this region have shown strong negative lattice thermal expansion coefficient, α_V = −6.75 × 10⁻⁶ and −17.92 × 10⁻⁶ K⁻¹ in the temperature range 298–1023 K⁻¹ for S-1 and ZrS-1 samples, respectively. The thermal expansion behavior of S-1 and ZrS-1 is anisotropic, with the relative strength of contraction along a axis is more than that along b and c axes. Three different thermal expansion regions could be identified in the overall temperature range (298–1023 K) studied, corroborating with the three steps of weight loss in the TG curve of ZrS-1 sample. While the region between 298 and 423 K, displays positive thermal expansion coefficient with α_V = 2.647 × 10⁻⁶ and 4.24 × 10⁻⁶ K⁻¹, the second region between 423 and 873 K shows strong negative thermal expansion (NTE) coefficient α_V = −7.602 × 10⁻⁶ and −15.04 × 10⁻⁶ K⁻¹, respectively, for S-1 and ZrS-1 samples. The region between 873 and 1023 K, shows a very strong NTE coefficient with α_V = −12.08 × 10⁻⁶ and −45.622 × 10⁻⁶ K⁻¹ for S-1 and ZrS-1, respectively, which is the highest in the whole temperature range studied. NTE seen over a temperature range 298–1023 K could be associated with transverse vibrations of bridging oxygen atoms in the structure which results in an apparent shortening of the Si–O distances.     

Evaluation of residual stress relaxation and its effect on fatigue strength of AISI 316L stainless steel ground surfaces: Experimental and numerical approaches

This paper is aimed at evaluating the residual stress relaxation and its effect on the fatigue strength of AISI 316L steel ground surfaces in comparison to electro-polished surfaces. An experimental evaluation was performed using 3-point and 4-point bending fatigue tests at R_σ = 0.1 on two sets of notched specimens finished by electro-polishing and grinding. The residual stress fields were measured at the notch root of specimens, before and after fatigue tests, by means of the X-ray diffraction technique. It was found a degradation of about −35% for the 4-point bending fatigue limit at 2 × 10⁶ cycles of the ground specimens in comparison to the electro-polished ones. This degradation is associated with a slight relaxation of the grinding residual stresses which remain significant tensile stresses at the stabilized state. While under the 3-point bending test, these residual stresses relax completely and provoke a noticeable increase of the fatigue limit estimated at about 50% in comparison to the 4-point bending fatigue test. The numerical evaluation of residual stress relaxation was carried out by FE analyses of the cyclic hardening behaviour of the ground layer. The isotropic and nonlinear kinematic model proposed by Chaboche was used and calibrated for the base material and the ground layer. The results show that residual stresses relax to a stabilized state characterized by elastic-shakedown response. This stabilization is occurred after the first cycle of the 4-point bending test corresponding to the higher stress concentration (K_t-4p = 1.66), while it requires many cycles under the 3-point bending test corresponding to the lower stress concentration (K_t-3p = 1.54). The incorporation of stabilized residual stress values into the Dang Van’s criterion has permitted to predict with an acceptable accuracy the fatigue limits under both bending modes.     

An innovative process to fabricate copper/diamond composite films for thermal management applications

Diamond dispersed copper matrix (Cu/D) composite films with strong interfacial bonding were produced by tape casting and hot pressing without carbide forming additives. The tape casting process offers an original solution to obtain laminated materials with accurate thickness control, smooth surface finish, material net-shaping, scalability, and low cost. This study presents an innovative process of copper submicronic particles deposition onto diamond reinforcements prior to densification by hot pressing. Copper particles act as chemical bonding agents between the copper matrix and the diamond reinforcements during hot pressing, thus offering an alternative solution to traditionnal carbide-forming materials in order to get efficient interfacial bonding and heat-transfer in Cu/D composites. It allows high thermal performances with low content of diamond, thus enhancing the cost-effectiveness of the materials. Microstructural study of composites by scanning electron microscopy (SEM) was correlated with thermal conductivity and thermal expansion coefficient measurements. The as-fabricated films exhibit a thermal conductivity of 455 W m^?1 K^?1 associated to a coefficient of thermal expansion of 12 × 10^?6 °C^?1 and a density of 6.6 g cm^?3 with a diamond volume fraction of 40%, which represents a strong enhancement relative to pure copper properties (λ_Cu = 400 W m^?1 K^?1, α_Cu = 17 × 10^?6 °C^?1, ρ_Cu = 8.95 g cm^?3). The as-fabricated composite films might be useful as heat-spreading layers for thermal management of power electronic modules.     

Preparation and characterization of a titanium bonding porcelain

The titanium bonding porcelain was synthesized through normal melting-derived route using borate–silicate system. The porcelain was characterized by thermal expansion, X-ray diffraction, scanning electron microscope and cytotoxicity tests. The results of X-ray diffraction showed that the main phase of the bonding porcelain was SnO₂. The SnO₂ microcrystals precipitated from the glass matrix when the SnO₂ content was increased. The thermal expansion coefficient of bonding porcelains decreased with the increasing concentration of SiO₂. The thermal expansion coefficient of bonding porcelains first decreased slightly with the increasing of B₂O₃ concentration (from 0 wt% to 10 wt%) and then increased to about 9.4 × 10^? 6/°C(from 10 wt% to 12 wt%). As an intermediate, B₂O₃ can act as both network formers and modifiers, depending on the relationship between the concentration of basic oxides and intermediates. The Vickers hardness of bonding porcelains increased with the increase of SnO₂ concentration. When SnO₂ concentration was 6 wt%, only Si and Sn elements attended the reaction between titanium and porcelain and mainly adhesive fracture was found at Ti-porcelain interface. When SnO₂ concentration was 12 wt%, failure of the titanium–porcelain predominantly occurred in the bonding porcelain and mainly cohesive fracture was found at Ti-porcelain interface. The methyl thiazolyl tetrazolium assay results demonstrated that the cytotoxicity of the titanium porcelain was ranked as 0.     

Effect of grinding conditions on mechanochemical grafting of poly(1-vinyl-2-pyrrolidone) onto quartz particles

Grinding of quartz in an aqueous solution of 1-vinyl-2-pyrrolidone (VP) in a stirred media mill results in grafting of poly(1-vinyl-2-pyrrolidone) (PVP) onto the quartz particles as proven by FTIR-spectroscopy. The grinding kinetics, the particle size of the final product and the amount of PVP grafted onto the silica particles depend on grinding conditions like VP and quartz concentration, pH and size of grinding media. The grinding kinetics becomes slower in the presence of VP due to the damping effect of the forming PVP chains. The final particle size, however, is almost independent on VP concentration. The amount of PVP grafted onto the silica particles ground for 12 h increases with growing VP concentration because the amount of adsorbed VP and the polymerization rate increase with growing VP concentration.The primary particle size and the kinetics of particle breakage do not depend on the pH-value of the dispersing medium, whereas the degree of agglomeration of the particles decreases with increasing pH-value of the medium. Under alkaline conditions, however, less PVP is grafted onto the quartz particles than under neutral or strong acidic conditions. The reasons for these effects are pH-dependent interactions between the grafted PVP chains and the surface hydroxyl groups on the quartz particles. If the quartz concentration in the suspension decreases the grinding kinetics becomes much faster because the specific energy input increases with decreasing particle concentration if the other process parameters are kept constant. For a very low quartz concentration (1 wt.%), however, after 7 h of grinding the particle size measured by dynamic light scattering starts to increase with grinding time. SEM investigations reveal that grinding of 1 wt.% quartz in aqueous VP solution for longer than 7 h results in the formation of plate-like particles.     

Studies of photorefractive fields of MnO and Fe2O3 co-doped near stoichiometric LiNbO3 crystals

In this paper, photorefractive field properties of MnO and Fe₂O₃ co-doped near stoichiometric LiNbO₃ (nSLN) crystals were studied. The nSLN crystals co-doped with 0.005 wt% Fe₂O₃ and MnO at the concentration of 0, 0.003 wt%, 0.005 wt%, and 0.010 wt%, respectively, have been grown by the top seeded solution growth (TSSG) method by adding K₂O flux to Li₂O–Nb₂O₅ solution. Their IR spectra showed that the crystals were near stoichiometric. In the two-wave coupling experiments of the crystals, from the measured maximum diffraction efficiency and the incidence angles between the reference and signal beams, the maximum saturation field E_q, photovoltaic field E_ph, diffusion field E_d and space charge field E_sc of the crystals were calculated by iterative method for the first time.     

Sugar response of boronic acid-substituted azobenzene dye-modified polymer

We synthesized a boronic acid-appended azobenzene dye (BA) and attached it to poly(ethyleneimine) (polyBA) for studying its sugar response. The addition of d-glucose induced a significant change in the UV–visible absorption spectra of the polyBA solution. The binding constants for d-glucose (K_glu) and d-fructose (K_fru) were calculated to be 54 M^? 1 and 110 M^? 1, respectively. The selectivity for d-glucose was higher in polyBA as compared with that of monomeric BA (K_glu = 1.2 M^? 1, K_fru = 17 M^? 1). We also fabricated multilayered films composed of polyBA and polyanions {poly(vinyl sulfate) (PVS), carboxymethylcellulose (CMC)} using a layer-by-layer deposition technique. In (PVS/polyBA)₁₀ films, the affinity for d-glucose was relatively low (K_glu = 1.7 M^? 1, K_fru = 28 M^? 1). In contrast, (CMC/polyBA)₅ films showed a high affinity for d-glucose (K_glu = 18 M^? 1, K_fru = 42 M^? 1). The loosely packed structure of the (CMC/polyBA)₅ film and the suitable chemical structures of CMC probably led to a high affinity for d-glucose.     

Thermal and rheological properties of highly concentrated PET composites with ferrite nanoparticles

Ferrite nanoparticles were introduced into poly(ethylene terephthalate) (PET) in a melt state at 270 °C upto 20 wt%, and the thermal and rheological properties of the nanocomposites were investigated. The introduction of ferrite nanoparticles increased a little the crystallization temperature (T_c) of PET by ca. 3 °C, while it had little effect on the melting temperature (T_m). In addition, it increased both heat of crystallization (ΔH_c) and heat of fusion (ΔH_m) with ferrite content. PET nanocomposites with ferrite 5 wt% and above exhibited an increased thermal stability and a two-stage degradation. The dynamic viscosity of PET nanocomposites was increased with ferrite content. However, ferrite loading of 5 wt% and above produced a high degree of shear thinning leading to even lower viscosity in a high frequency range than that of pure PET. The nanocomposites gave a non-zero positive value of yield stress, which was notably increased particularly from 5 wt% loading. In the Cole–Cole plot, at contents 1 wt% and above, ferrite nanoparticles caused the deviation from the master curve and a reduced slope. In addition, the relaxation time was increased with ferrite content and an increasing degree was more notable at a lower frequency.     

Influence of defects on fatigue strength and failure mechanisms in the VHCF-region for quenched and tempered steel and nodular cast iron

Investigations are presented in this paper on quenched and tempered steel 42CrMoS4 from two batches, with two different tensile strengths (R_m = 1100 MPa, 1350 MPa) but with similar microstructure, and a nodular cast iron EN-GJS-900-2 (R_m = 930 MPa). Fatigue tests with smooth (K_t = 1) and notched (K_t = 1.75) specimens were performed at R = −1 and R = 0 up to the number of cycles N = 2·10⁹ in order to determine the fatigue strength behaviour and failure mechanisms, especially in the VHCF-region. Failure in smooth specimens often initiated at material defects such as oxides in the quenched and tempered steel and shrinkage holes in the nodular cast iron. Firstly, a fatigue strength analysis was performed that did not consider these defects. A possibility of analysis of experimental data including VHCF-results has been discussed. Next, a linear elastic fracture mechanics analysis was performed in order to describe the defect behaviour, assuming that the defects act like cracks. The results showed that there are lower limit or threshold values of the stress intensity factor range ΔK for crack propagation in both materials. Analysis of defects and defect distribution in run-out specimens confirmed this conclusion. From the comparison of the results with an S–N curve from the design code FKM-Guideline Analytical strength assessment of components, recommendations for design and assessment of components have been derived.     

Jet mill grinding of portland cement,limestone, and fly ash: Impact on particle size,hydration rate,and strength

While the majority of commercial ordinary portland cement (OPC) is ground using a ball mill or a vertical roller mill, other industries have shown that jet mill grinding can be an alternative approach for grinding materials. This paper investigates the potential application of jet mill grinding for two systems. The first system is a blend of OPC and 15% limestone, and the second system is a blend of OPC and 40% fly ash. It was observed that when jet mill grinding is used, the average particle size of the powders is decreased to approximately 4 μm or less with a narrower particle size distribution than that achieved using ball milling. In addition to evaluating the size and shape of the particles obtained from the jet mill grinding process, this paper focuses on evaluating, using isothermal calorimetry, the effect these changes in particle size and distribution have on the extent and rate of hydration as well as their effect on the compressive strength of cement pastes or mortars.This study also investigated differences between inter-grinding and blending separately ground materials to form an OPC/limestone mixture. Both inter-ground and separately ground OPC/limestone mortars demonstrated an accelerated hydration at early ages accompanied by an increase in early age strength. This appears to be primarily due to the increased surface area of the finer particles that provides more available surface for the hydration reaction. The inter-grinding appeared to be more effective than grinding the materials separately because an improved graded particle size distribution was obtained. The inter-ground OPC/limestone mixture shows accelerated initial hydration at water to powder ratios (w/p, where powder = cement + limestone) of 0.50 and 0.35 when compared with the samples before grinding. At the lower w/p of 0.35, the OPC/limestone mixture appears much more efficient. In the OPC/fly ash mixture, jet mill grinding also accelerates the rate of hydration and strength development.     

Severity of disability related to road traffic crashes in the Spanish adult population

BackgroundThe severity of disability related to road traffic crashes has been little studied, despite the significant health and socio-economic impacts that determine victims’ quality of life.ObjectiveTo estimate the consequences of road traffic crashes on the severity of disability, in terms of individuals’ capacity to execute activities and perform tasks in their current environment, using aids.MethodsCross-sectional study conducted on community-dwelling participants in the “2008 National Survey of Disability”, with data on 91,846 households having 20,425 disabled persons, 443 of whom had disability due to road traffic crashes. We measured severity using two indicators, i.e., the Capacity (CSI) and Performance (PSI) Severity Indices.ResultsThe highest proportion of disability was mild (CSI = 70.5%; PSI = 80.8%), while 7.6% (CSI) and 4.9% (PSI) was severe/complete respectively. The moderate/severe disability rate was 0.6 per thousand on the CSI, decreasing to 0.4 per thousand on the PSI. No differences were observed by age or sex. Moderate/severely disabled persons had a fourfold higher probability of being retired or unfit for work. Mental and nervous system impairments were more closely related to moderate/severe/complete problems of capacity and performance (p < 0.001), disability for carrying out general tasks and demands, and interpersonal interactions and relationships (p < 0.001). Being permanently bedridden (p < 0.001), receiving aids (p < 0.001), family support (p < 0.05) and moving home (p < 0.05) increased with an increase in the level of severity.ConclusionRoad traffic crashes mainly cause mild disability. Moderate/severe disability is associated with lower work capacity, greater functional dependence, and increased need of aids, moving home and family support.     

High-precision CTE measurement of hybrid C/SiC composite for cryogenic space telescopes

This paper presents highly precise measurements of thermal expansion of a “hybrid” carbon-fiber reinforced silicon carbide composite, HB-Cesic® – a trademark of ECM, in the temperature region of ～310–10 K. Whilst C/SiC composites have been considered to be promising for the mirrors and other structures of space-borne cryogenic telescopes, the anisotropic thermal expansion has been a potential disadvantage of this material. HB-Cesic® is a newly developed composite using a mixture of different types of chopped, short carbon-fiber, in which one of the important aims of the development was to reduce the anisotropy. The measurements indicate that the anisotropy was much reduced down to 4% as a result of hybridization. The thermal expansion data obtained are presented as functions of temperature using eighth-order polynomials separately for the horizontal (XY-) and vertical (Z-) directions of the fabrication process. The average CTEs and their dispersion (1σ) in the range 293–10 K derived from the data for the XY- and Z-directions were 0.805 ± 0.003 × 10^?6 K^?1 and 0.837 ± 0.001 × 10^?6 K^?1, respectively. The absolute accuracy and the reproducibility of the present measurements are suggested to be better than 0.01 × 10^?6 K^?1 and 0.001 × 10^?6 K^?1, respectively. The residual anisotropy of the thermal expansion was consistent with our previous speculation regarding carbon-fiber, in which the residual anisotropy tended to lie mainly in the horizontal plane.