The effect of carboxymethyl cellulose swelling on the stability of natural graphite particulates in an aqueous medium for lithium ion battery anodes

The effect of carboxymethyl cellulose (CMC) swelling on the stability and chemical properties of a natural graphite suspension in an aqueous medium was investigated. Suspensions prepared at different pH were characterized according to swelling behavior, rheology, green microstructural observation, and measurement of the pore size. A correlation was found between dispersion stability and electrochemical performance. It was found that the swelling of CMC was a critical factor influencing the stability of graphite suspensions. This was evidenced by observations of the green microstructures and changes noted in sedimentation behaviors. Electrochemical experiments using a Li/organic electrolyte/natural graphite anode half-cell and 750 mAh-class lithium ion cells exhibited an initial discharge capacity above 340 mAh g⁻¹ and an improved charge-discharge efficiency.     

Crack formation in MLCCs depending on position with and without post-heat treatment

The crack formation behavior and mechanical properties, hardness (H), modulus (E), and fracture toughness (K _IC), at each plane of BaTiO₃ based multilayer ceramic capacitors (MLCCs) have been investigated and estimated using a nanoindentation technique, including effects of the post-heat treatment and the external electrode on the crack formation and mechanical properties. The crack length in each plane, length (x plane) and width (y plane) planes, has been measured for MLCCs with and without the post-heat treatment, as a function of the distance from the internal electrode. H and E values are 11.5–12.0 GPa and 175–190 GPa, respectively, independent of the plane and the post-heat treatment. The crack length in the x plane is smaller than that in the y plane, which is gradually increased as the indentation position is far away from the internal electrode. The external electrode affects the crack formation in regions near to the internal electrode, showing small crack length till 20 μm from the internal electrode. K _IC values in the x plane are larger than those in the y plane. The external electrode affects only the K _IC values in the x plane within the error range, without effect of the post-heat treatment.     

Ultimate shear strength of plate elements with pit corrosion wastage

The aim of the present paper is to investigate the ultimate strength characteristics of steel plate elements with pit corrosion wastage and under in-plane shear loads. A series of the ANSYS nonlinear finite element analyses for plate elements under in-plane shear loads are carried out, varying the degree of pit corrosion intensity and the plate geometric properties. Closed-form design formulae for the ultimate strength of pitted plates under edge shear, which are essentially needed for the ultimate limit state based risk or reliability assessment of corroded structures, are derived by the regression analysis of the computed results. The insights developed from the present study will be very useful for damage tolerant design of plated structures with pit corrosion wastage.     

Reaction of hexamethylene diisocyanate with poly(vinyl alcohol) films for biomedical applications

The objective of this work was to obtain primary amine groups on the surface of poly(vinyl alcohol) films by means of a reaction with hexamethylene diisocyanate. The reaction was run in such a way as to minimize the internal crosslinking by employing a large excess of hexamethylene diisocyanate in toluene and then hydrolyzing the unreacted isocyanate endgroup to primary amine. After dialyzing out the adsorbed hexamethylenediamine from the aqueous solution of reacted poly(vinyl alcohol), the extent of covalent bonding of hexamethylene diisocyanate onto the polymer was determined by measuring aminohexyl content through a fluorescence assay. This assay is based on the reaction of fluorescamine, 4-phenylspiro[furan-2(3H)-1′-phthalan]-3,3′-dione, with a primary amine to yield a fluorophor which will emit a strong fluorescence at 475–490 nm when excited at 390 nm. Analyses show a range of 1.1 × 10^?10?3.6 × 10^?10 mole of amines per cm² of reacted poly(vinyl alcohol) film. When assuming 47% as degree of crystallinity approximated by IR spectroscopy for these polymer films, the availability of hydroxyl groups in amorphous region was estimated to be 3.7 × 10^?10 mole/cm². The extent of reaction based on available hydroxyl groups was then in the range of 31–97%. The primary amine groups attached by this method can now be exploited for binding biomolecules such as heparin (anticoagulant) or fibrinolytic enzymes in an attempt to achieve biocompatible materials.     

Labile protein-methyl ester: comparison between chemically and enzymatically synthesized

The rate of hydrolysis of protein-methyl ester, the enzymatic product of S-adenosylmethionine: protein-carboxyl methyltransferase (EC.2.1.1.24) acting on oxidized ribonuclease, was measured at pH 7.1 and 8.6 at 37 degrees C. The half-life of the hydrolysis of the ester is 25 min at pH 7.1, and 4 min at 8.6. The rate of hydrolysis of the enzymatically formed esters at pH 7.0, in 0.1 M phosphate buffer, was about 25 times faster than that of esters formed chemically by reaction with methanol in HCl. The lability of the enzymatically synthesized protein-methyl ester suggests that the esterification is specific to sites such that ionization of neighboring amino acid side chains enhances the rate of the hydrolysis.     

Solder reflow process induced residual warpage measurement and its influence on reliability of flip-chip electronic packages

To meet the future needs of high pin count and high performance, package size of flip-chip devices is constrained to become larger. In addition, to fulfill the environment issues, lead free solders will be replacing lead contained eutectic (Sn/37Pb) in near future. Thus, in this work, the effect of residual warpage and consequent residual stress on the reliability of large flip-chip using lead free solder is examined. Several effective experimental approaches to accurately measure residual warpage, using Moiré interferometry, shadow Moiré, and image processing schemes, are introduced. Moreover, geometric, process, and material parameters affecting the residual warpage during reflow process are discussed and some modifications are suggested. Finally, it is verified that it is crucial to accurately quantify and control the residual warpage in order to guarantee the overall reliability of flip-chip packages regardless of presence of underfill.     

Effect of equal channel angular pressing on structure and mechanical properties of a low carbon steel

Experiments were conducted on a plain low carbon steel with an initial grain size of ~ 30μm to investigate the changes of microstructure and mechanical properties by repetitive equal channel angular pressings. Under the pressing conditions of giving a strain of ~ 1 and rotating samples 180° between each pass, the yield strength significantly increases from 310 to 750 MPa after single pass, and it reaches 1050 MPa after 12 passes. The increment of yield strength gradually decreases as the number of passes increases. The examination of microstructure by transmission electron microscopy shows that ferrite consists of parallel bands of elongated subgrains having a width of 0.3 μm and a length of 2 μm after a single pass. The subgrains are further divided by boundaries with low angle misorientation on subsequent passages. Low angle boundaries turn to high angle boundaries without noticeable grain refinement as the number of pass increases. In addition, lamellar cementites in pearlite are broken up into fragments within a pearlite colony. Analyses of structural and mechanical changes in a plain low carbon steel by equal channel angular pressing indicate that the strength enhancement is mainly due to the grain refinement of ferrite.     

Development of three-dimensional memory die stack packages usingpolymer insulated sidewall technique

A newly designed three dimensional (3-D) memory die stack package has been established, and the prototype of the 3-D package using mechanical dies has been successfully demonstrated. Fabrication processes of the 3-D package consist of: (1) wafer cutting into die segments; (2) die passivation including sidewall insulation; (3) via opening on the original I/O pads; (4) I/O redistribution from center pads to sidewall; (5) bare die stacking using polymer adhesive; (6) sidewall interconnection; and (7) solder balls attachment. There are several significant improvements in this new 3-D package design compared with the current 3-D package concept. The unique feature of this newly developed package is the sidewall insulation of dies prior to the I/O redistribution of dies, which produces (1) better chip-to-wafer yields and (2) significant process simplification during subsequent fabrication steps. According to this design, 100% of die yields on a conventional wafer design can be obtained without any neighboring die losses which usually occur during the I/O redistribution processes of conventional 3-D package design. Furthermore, the new 3-D package design can simplify the following processes such as I/O redistribution, sidewall insulation, sidewall interconnection, and package formation. It is proven that the mechanical integrity of the prototype 3-D stacked package meets requirements of the JEDEC Level III and 85°C/85% test