Improvement of aramid fiber III reinforced bismaleimide composite interfacial adhesion by oxygen plasma treatment

Domestic Aramid Fiber III (DAF III) was modified by oxygen plasma treatment. The effects of oxygen plasma treatment power on fiber surface and DAF III reinforced bismaleimides (BMI) composite interfacial properties were investigated, respectively. The fiber surface characteristics were analyzed by X-ray photoelectron spectroscopy, Scanning Electron Microscopy, Atomic Force Microscopy and Dynamic Contact Angles Analysis, respectively. The results showed that oxygen plasma treatment introduced new oxygen containing groups such as C=O and –COO on to the fiber surfaces, changed the fiber surface morphologies and enhanced surface roughness by oxidative reactions and plasma etching. Finally, the fiber surface wettability was effectively improved. The total free energy increased from 49.8 to 71.7 mJ/m2 at maximum with 300 W oxygen plasma treatment. The composite interlaminar shear strength (ILSS) was evaluated by short beam shear measurement. The ILSS value increased from 49.3 to 59.8 MPa (by 21.3%) within 300 W plasma treatment.     

Combined effects of high pressure and sodium hydrogen carbonate treatment on beef: improvement of texture and color

We investigated the effect of combined high pressure and sodium hydrogen carbonate (NaHCO₃) treatment on the physical properties and color of silverside Australian beef. Meat samples were pressurized at 100–500 MPa and the water content, weight reduction, rupture stress, and meat color were determined. The water content of meat treated with NaHCO₃ and high pressure (300 MPa) reached a maximum of 70.1%. Weight reduction tended to decrease with high pressure treatment at 300 MPa. Meats treated with NaHCO₃ and high pressure at 400 MPa showed a>50% decrease in hardness. Whitening of the meat was reduced by the combined high pressure and NaHCO₃ treatment. Therefore, the combined high pressure and NaHCO₃ treatment is effective for improvement of beef quality.     

Void formation in Nickel during high temperature proton irradiation

Pure Ni foils, doped with He from 0 to 28 appm, were irradiated with protons at temperatures in the range 0.3–0.6 T_m (T_m = melting point in °K) and void formation was studied. The influence of He doping, irradiation temperature and alloying were investigated. For constant He content and proton fluence, void number density and swelling are maximum at about 400°C, while the void size increases with temperature. Most voids are octahedral in shape with no sign of truncation. Helium is required to nucleate voids, and lowering the stacking fault energy by alloying suppresses void formation completely. Present results suggest that void nucleation is inhomogeneous. Some implications of these findings are discussed.     

Generation of microcellular poly(methyl methacrylate) by compressed gases

Abstract

Generation of microcellular poly(methy1 methacrylate) (PMMA) was studied in CO₂ and N₂O at pressures from 2 to 15MPa at three temperatures, 293.2K, 308.2K, and 323.2 K. The average diameter d and average number density N of voids generated by a rapid expansion of compressed gases in PMMA were measured by use of an optical microscope. Effects of gases, temperature, and pressure on the d and N values were examined. Even at pressure below glass transition pressure of PMMA with both gases, voids of diameter being as small as those found at high pressure, 15MPa, were obtained at each temperature. However, the void density of PMMA at lower pressure by both gases was not so good as those obtained at high pressures.     

Effects of pressure and temperature on the survival rate of adherent A-172 cells

Preservation of cells under high pressure is an important alternative to cryopreservation. We studied the effect of temperature (4, 25, 37°C) and pressure (0.1–350 MPa) on the survival rate of A-172 glioblastoma cells. The survival rate was not changed by brief (10 min) pressurization of up to 150 MPa, but the survival rate began to decrease from 150 MPa, and most of the A-172 cells died when treated with over 200 MPa. Lengthy pressurization (4 days) at lower pressure (upto 20.1 MPa) without medium exchange showed complex results. The survival rate of cells preserved at 25°C showed two maxima at 1.6 and 20.1 MPa. After preservation, cells adhered and proliferated in the same way as normal cells when cultured at 37°C in a CO₂ incubator. The other two temperatures, 4° and 37°C, showed no maximum survival rate. Therefore, a high survival rate can be maintained with high pressure treatment.     

Effect of high pressure on cod (Gadus morhua) desalting

The effect of high pressure on salt and water diffusion in the desalting process of cod was studied. Under pressure, up to 300 MPa, the osmotic equilibrium is reached much faster, compared to desalting at atmospheric pressure. Water (D _ew) and salt (D _es) effective diffusion coefficients reached a maximum at 200 MPa, increasing 500- and 160-fold, respectively, compared with desalting at atmospheric pressure. Increasing pressure up to 300 MPa causes a reduction in both effective diffusion coefficients, although they were still about 70-fold higher than at atmospheric pressure. Up to 200 MPa, a linear correlation was found between D _ew and D _es and pressure. However, the total diffused amounts of water and salt, when the osmotic equilibrium was reached, were lower under pressure. At atmospheric pressure cod water content increased 1.65-fold, but under pressure the increment was on average 1.25-fold, while salt content decreased to 0.51-fold the initial value at atmospheric pressure and to around 0.75-fold under pressure.     

Vapor Pressure Assisted Void Growth and Cracking of Polymeric Films and Interfaces

Pores and cavities form at filler particle-polymer matrix interfaces, at polymer film-silicon substrate interfaces as well as in molding compounds of IC packages. Moisture diffuses to these voids. During reflow soldering, surface mount plastic encapsulated devices are exposed to temperatures between 210 to 260°C. At these temperatures, the condensed moisture vaporizes. The rapidly expanding water vapor can create internal pressures within the voids that reach 3–6 MPa. These levels are comparable to the yield strengths of epoxy molding compounds and epoxy adhesives, whose glass transition temperatures T _g range between 150 to 300°C. Under the combined action of thermal stress and high vapor pressure (relative to the yield strength at T _g), both pre-existing and newly nucleated voids grow rapidly and coalesce. In extreme situations, vapor pressure alone could drive voids to grow and coalesce unstably causing film rupture, film-substrate interface delamination and cracking of the plastic package.Vapor pressure effects on void growth have been incorporated into Gurson's porous material model and a cohesive law. Crack growth resistance-curve calculations using these models show that high vapor pressure combined with high porosity bring about severe reduction in the fracture toughness. In some cases, high vapor pressure accelerates void growth and coalescence resulting in brittle-like interface delamination. Vapor pressure also contributes a strong tensile mode component to an otherwise shear dominated interface loading. An example of vapor pressure related IC package failure, known as popcorn cracking, is discussed.     

A molecular dynamics investigation of the micro-mechanism for vacancy formation between Ag3Sn and βSn under electromigration

In this paper, the vacancy formation at the interface between different grains (Ag₃Sn and βSn) induced by electromigration was investigated from the perspective of atom diffusion. To explain the micro-mechanism of void formation near the interface, the diffusion coefficient was specifically studied here via molecular dynamics (MD) simulation. By comparing the atom diffusion rates of atoms in βSn and Ag₃Sn, a significant difference could be observed when the temperature is up to 400 K. The Sn atoms in βSn have a higher diffusion coefficient (8E ? 9 cm²/s) than atoms in Ag₃Sn (4E ? 9 cm²/s), which indicated that the void would be prone to appear in βSn near the interface. Moreover, the effect of grain size and pressure on atom diffusivity was studied. Results show that the atom diffusivity depends heavily on the grain size of Ag₃Sn. When the thickness of Ag₃Sn is increased from 4 to 12 nm, this difference is significant when the temperature is only 375 K. On the other hand, the atom diffusion character of Ag₃Sn and βSn changes substantially under constant pressure. The difference of the atom diffusion rate would be inhibited by pressure perpendicular to the interface, which indicated voids have less possibility to appear herein.     

Possibility of Campylobacter jejuni inactivation in smoked salmon by high-pressure treatment

The sterile samples of cold-smoked salmon were placed in polyamide–polyethylene pouches and inoculated with three-strain composite of Campylobacter jejuni (inoculum ca 10⁷ CFU g^?1). The inoculated samples were sealed under vacuum and subjected to 200, 300 and 400 MPa of hydrostatic pressure for 0, 5, 10 and 15 min. The number of surviving C. jejuni per gram was determined by the 10-fold dilution method followed by plating on Karmali agar. D ₁₀ values were calculated. This work has shown that for reducing C. jejuni in cold-smoked salmon by 6 log units, the application of 200 MPa for 64.26 min or 300 MPa for 17.10 min or 400 MPa for less than 5 min is needed. Applying such parameters of high-pressure processing should not change significantly the organoleptic properties of the product.     

Effect of high hydrostatic pressure on seed germination,microbial quality,anatomy–morphology and physiological characteristics of garden cress (Lepidium sativum) seedlings

High hydrostatic pressure is a non-thermal food processing technology that is found to increase the percentage of germination, decrease the germination time and improve the microbial quality of seeds. In this study, pressures of 100–400 MPa for 10 min at 30°C are used to compare the percentage of germination, the microbial quality of seeds, chlorophyll a and b, and total phenolic compounds concentrations in seedlings, and the anatomy–morphology characteristics of garden cress. Enhanced reductions of total aerobic mesophilic bacteria, total and fecal coliforms, and yeast and mould populations in seeds were observed, especially at 300 MPa. In addition, the percentage of germination, chlorophyll content and phenolic compounds concentrations, fresh and dry weights, and hypocotyl lengths of the seedlings are higher than those of all samples, where the percentage of germination is equal to controls but higher than other samples, and radicula length is lower than controls but higher than others.     

Three-dimensional structure of polystyrene colloidal crystal by synchrotron radiation X-ray phase-contrast computed tomography

Colloidal crystal with long-range ordered structure has attracted great attention for their applications in various fields. Although perfect colloidal crystals have been achieved by some fabrications for utilization, little is known about their exact structures and internal defects. In this study, we use synchrotron radiation (SR) phase-contrast computed tomography (CT) to noninvasively access the internal structure of polystyrene (PS) colloidal crystals in three dimensions (3D). The phase-attenuation duality Paganin algorithm phase retrieval was employed to achieve a satisfactory contrast and outline of the spheres. After CT reconstruction, the positions of individual PS particles and structural defects are identified in three dimensions, and the local crystal structure is revealed. Further quantitative analysis of the void system in colloidal crystal illustrates that single voids can be mostly attributed to tetrahedron void of sphere close packing, but the interconnected voids with large volume induce a sphere volume fraction of 59.39 % that reflects a metastable glass behavior of colloidal crystal arrangement. The void orientation result reveals that the 3D close-packing difficulty mainly lies in the stacking of interlayer.     

Effect of one-dimensional diffusion on void nucleation

Nucleation of voids via the stochastic accumulation of vacancies is considered when one-dimensionally migrating self-interstitials are present. A system instability signaling a non-equilibrium phase transition is found to occur when the mean free path of the one-dimensionally moving self-interstitials becomes comparable with the average distance between the voids at a sufficiently high void-number density. At this point, due to the exponential dependence of void nucleation probability on the net vacancy flux, the nucleation of voids is much more favored at the void lattice positions. At the same time, voids initially nucleated at positions where neighboring voids are non-aligned will shrink away. The shrinkage of non-aligned voids is caused entirely by the stochastic fluctuations in point-defect fluxes received by the voids. These two processes leave the aligned voids to form a regular lattice. The formation of the void lattice in this way can be accomplished at a void swelling of below 1%, in agreement with experimental observation. PACS 61.80.Az; 61.72.Cc; 05.65.+b     

Investigation of the design of a metal-lined fully wrapped composite vessel under high internal pressure

In this study, a Type III composite pressure vessel (ISO 11439:2000) loaded with high internal pressure is investigated in terms of the effect of the orientation of the element coordinate system while simulating the continuous variation of the fibre angle, the effect of symmetric and non-symmetric composite wall stacking sequences, and lastly, a stacking sequence evaluation for reducing the cylindrical section-end cap transition region stress concentration. The research was performed using an Ansys^® model with 2.9 l volume, 6061 T6 aluminium liner/Kevlar^® 49-Epoxy vessel material, and a service internal pressure loading of 22 MPa. The results show that symmetric stacking sequences give higher burst pressures by up to 15%. Stacking sequence evaluations provided a further 7% pressure-carrying capacity as well as reduced stress concentration in the transition region. Finally, the Type III vessel under consideration provides a 45% lighter construction as compared with an all metal (Type I) vessel.     

Synthesis of graphene/nickel oxide composite with improved electrochemical performance in capacitors

A novel reduced graphene oxide/NiO nanosheet composite (r-GO/NiO) (ca. 75 % NiO in weight) was synthesized by a facile two-step method, where the NiO nanosheets were decorated with some voids. The composite was characterized by using X-ray diffraction, transmission electron microscopy, thermal gravimetric analysis, and Raman spectroscopy. The electrochemical properties of the composite were investigated by cyclic voltammetry, galvanostatic charge, and discharge measurements. The results show that the r-GO/NiO composite exhibits a stable average specific capacitance of ca. 1,139 F g^?1 (at 0.5 A g^?1) during 1,000 charge–discharge cycles, suggesting that the r-GO/NiO composite is a potential supercapacitor material. The main correlation between the electrochemical performance and the structure of the materials was studied, and the formation process of the composite was also discussed.     

辐照材料的肿胀理论(Ⅰ)——中性尾闾

本文从反应扩散方程出发,研究在辐照条件下,微洞和位错(无应力场)周围点缺陷的分布情况。对含有点缺陷复合项的定态的反应扩散方程,给出了一种近似求解的方法并分别得到了微洞和位错吸收点缺陷的汇强度。从所得结果与前人略去复合项的结果比较可知,微洞较大时,复合项对汇强度的影响变得重要;对于位错,当点缺陷产生率较大时,考虑了复合项后所得的汇强度可达前人结果的1.5倍以上。 关键词：     

Effect of explosive contact and non-contact shock-processing on structure, microstructure and mechanical characteristics of aluminum

Contact and non-contact techniques are used to obtain monoliths of micro-sized aluminum powder under explosive shock loading. The measurement technique involves instrumented detonics to determine the velocity of detonation and compaction of powder in a single-shot experiment. The compacted specimens were examined for crystallographic, micro-strain, particle size, microstructure, mechanical strength, microhardness and density variations. Results indicate that non-contact technique gives rise to uniform thick compacts with negligible change in particle size, micro-strain, microhardness and microstructure with lower density. Whereas the compacts obtained by contact arrangement are accompanied by a substantial change in these parameters with higher density. Compacts of uniform density greater than 98 % theoretical value have been obtained by using explosive mixture of detonation velocity of 4.2 km/s. The compacted specimens possess micro-strain 2.8×10^?3, microhardness (60±2)H _v, tensile strength of 112 MPa and compressive strength of 116 MPa with elongation up to 6.4 %. Fracture/void free compacts obtained by contact arrangement have tremendous use in materials science and technology.     

Fabrication of Poly-l-lactide Biomaterials with High Mechanical Properties Using Fiber Oriented Pressing

A new technique of dilute solution spinning to obtain poly-l-lactide (PLLA) fiber was presented. PLLA materials were fabricated by using fiber oriented pressing and the effects of pressing pressure and temperature on the mechanical properties and weight average molecular mass of PLLA were investigated. Good oriented fibers with porous structure (0.1 ～ 1 μm) were obtained by a dilute solution spinning method. Bending and shearing strength of PLLA samples first increase and then decrease with the increase of pressing temperature and pressure. The bending strength, shearing strength, and bending modulus reach 238.8 ± 6.5 MPa, 127.5 ± 3.5 MPa and 3.25 ± 0.25 GPa, respectively, if the pressing temperature is 185°C and the pressure is 130 MPa. These values are greater than conventional pressing methods. In addition, the decrease in weight average molecular mass (19.5%) that results from using oriented pressing is lower than that seen (30.0%) by using the conventional pressing method.     

Biological interface study of HA/ZrO2 graded composite in a dog lumbar vertebra bone defect model

This study compared bony fusion in autologous bone grafting with HA/ZrO₂ graded composite in terms of mineral depositions, histological characteristics, and biomechanical properties of bonding interface. Twenty-four beagle dogs were established four places of bone defect in two adjacent lumbar vertebral bodies (L4 and L5) and were successively implanted with HA/ZrO₂ graded composite (group A), HA/ZrO₂ unilayer composite (group B), pure ZrO₂ (group C), and pure HA (group D). After operation, lumbar vertebral specimens were respectively harvested per time at week 6, 12, and 16. Then, the bony fusion interface was evaluated by fluorescence microscope and computer image analysis system to measure mineral apposition rates (MAR). Histological analysis of specimen was used to determine bone bonding rates (BBR) and possible foreign body reactions associated with each groups. And interface bonding force between implant and autogenous bone was quantified with biomechanical push-out test. Compared with other groups, group A led to significantly higher MAR from week 6 to 12 (p < 0.05). Histologically, new bony tissue and hyaline cartilage were seen around the HA/ZrO₂ graded composite, accompanied by mild chronic inflammation. And the BBR of HA/ZrO₂ graded composite were the highest (p < 0.05), while reaching (90.3 ± 3.8) % at week 16. Moreover, the biomechanical push-out tests revealed that the maximum interface shear strength of group A was respectively (2.64 ± 0.16) MPa, (2.95 ± 0.19) MPa, and (3.45 ± 0.23) MPa at week 6, 12, and 16, which all possessed significantly statistical differences with other three groups (p < 0.05).     

On the thermal expansion of CNT/Cu composites for electronic packaging applications

Carbon nanotubes (CNTs) exhibit both excellent high thermal conductivity and low coefficient of thermal expansion (CTE), which are an ideal reinforcement in composite materials for high performance electronic packaging applications. In the present study, CNT/Cu composites containing CNTs varying from 0 vol.% to 15 vol.% are prepared, and their CTE behavior is studied in detail. The results indicate that the CTE of 0–10 vol.% CNT/Cu composites is significantly decreased with increasing CNT content. However, as the CNT content increases to 15 vol.%, the decrease in CTE of the composites is pronouncedly reduced. Possible mechanisms are discussed in combination with CTE model predictions.