New wear tests of tool materials for metal forming

Tribological phenomena, i.e. friction, tool wear and material pick-up to the tool, in metal forming processes are influenced by various factors. Therefore, in friction tests in the laboratory, these factors should be varied widely and independently and they should be measured easily. A new test method which has these features is described; the test parameters are the tool pressure, sliding speed, enlargement of the workpiece surface, length of contact between the tool and workpiece, sliding distance, contact angle and viscosity of the lubricant. Some results of the tests on tool wear are presented and discussed.     

Determination of the dissociation constant of molten Li2CO3/Na2CO3/K2CO3 using a stabilized zirconia oxide-ion indicator

An Li₂CO₃/Na₂CO₃/K₂CO₃ eutectic melt has been selected as an example of a molten-carbonate system and the suitability of a stabilized zirconia—air electrode as an oxide-ion concentration indicator for this melt has been confirmed.With this indicator, the dissociation constant of the reaction CO₃^2? (?) = CO₂(g) + O^2? (?) in this melt has been determined to be K_d = P_CO2 [O^2?] = 4.03 × 10^?3 Pa at 873 KReproducible measurements were obtained throughout the experiment and this method might find further application in the study of reactions related to the oxide ion in carbonate melts.     

Metal cation–acidic proton bifunctional catalyst for methane activation: conversion of CH4 in the presence of ethylene over metal cations-loaded H-ZSM-5

It has been investigated that ¹³CH₄ reacts with ethylene over metal cations such as indium cations-loaded H-ZSM-5 to form singly ¹³C-labeled propylene (¹³C¹²C₂H₆) and hydrogen at 673 K. The heterolytic dissociation of C---H bond in methane presumably proceeds by the reaction of methane with metal cations for the formation of CH₃^δ+ and metal hydride species, thus allowing the reaction of CH₃^δ+ with ethylene to form propylene and acidic protons. Metal cations are regenerated by the reaction of silver-hydride species with acidic protons, and hydrogen is simultaneously formed. Thus, bifunctionality of metal cations and acidic protons is essential for the activation of methane.     

Monitoring of corrosion fatigue cracking using harmonic analysis of current responses induced by cyclic stressing

The response of a current induced by sinusoidal stress within an elastic deformation was measured during corrosion fatigue tests to monitor the course of corrosion fatigue cracking and to evaluate corrosion fatigue damage. The test material was an iron bar subjected to a passive potential in borate buffer solution containing 5 mM NaCl. Harmonic analysis was used to analyze the current response and to extract valuable parameters that were associated with crack initiation and corrosion fatigue damage. The current response before crack initiation consisted of only the fundamental current without any harmonics. Higher harmonic amplitudes of the current response, especially the second and third harmonics, appeared and increased after crack initiation. In addition, the phase shift between the strain and the fundamental current response to the sinusoidal stress decreased from nearly 90° towards 0° as harmonic amplitudes of the current response increase. The results indicate that the amplitudes of the harmonic current response and the phase shift are the optimal parameters for detecting crack initiation and evaluating corrosion fatigue damage.     

Degradation mechanism of galvanized steel in wet-dry cyclic environment containing chloride ions

The wet-dry cyclic test of a galvanized steel (GI) and pure zinc (ZN), which simulates marine atmospheric environment, has been conducted to clarify the degradation mechanism of galvanized steel. The samples were exposed to alternate conditions of 1 h-immersion in a 0.05 M NaCl solution and 7 h-drying at 25 °C and 60%RH, and the corrosion was monitored for 10 days (30 cycles) using a two-electrode type probe. Simultaneously, the corrosion potential was measured every three cycles only during the immersed conditions. The reciprocal of polarization resistance R_p⁻¹ was taken as an index of the corrosion rate. Several sample plates of GI and ZN were exposed, together with the monitoring probes. They were removed from the test chamber at the end of 1st, 3rd, 9th, 18th, and 30th cycles of exposure and were analyzed for the corrosion products with XRD and laser Raman spectroscopy. Further, their cross sections were analyzed with FESEM-EDS. The FESEM photographs and elemental analysis of cross sections confirmed that the R_p⁻¹ value commences to decrease when the corrosion front reaches Zn-Fe alloy layers (boundary layers of zinc coating and steel substrate) due to localized nature of attack. A schematic model of degradation mechanism and the role of galvanic protection have been discussed.     

Effect of atmosphere on pyrolysis of Nicalon

The pyrolytic behaviour of Nicalon under a N₂ atmosphere was investigated at temperatures from 1673 to 1973 K, and was compared with that under an Ar atmosphere. The pyrolytic rate was measured by thermogravimetry, and heat-treated Nicalon was examined by X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy and tensile testing. The pyrolytic rate was smaller in N₂ than in Ar. The nitrided case retarded the crystallization into -SiC and retained its high strength. The effectiveness of the nitrided case disappeared on heating in Ar. The strength was related to the size of the -SiC crystal in Nicalon.     

Gas permeation properties for organosilica membranes with different Si/C ratios and evaluation of microporous structures

Organosilica membranes were fabricated using bridged organoalkoxysilanes (bis(triethoxysilyl)methane (BTESM), bis(triethoxysilyl)ethane (BTESE), bis(triethoxysilyl)propane (BTESP), bis(trimethoxysilyl)hexane (BTMSH), bis(triethoxysilyl)benzene (BTESB), and bis(triethoxysilyl)octane (BTESO)) to produce highly permeable molecular sieving membranes. The effect of the organoalkoxysilanes on network pore size and microporous structure was evaluated by examining the molecular size and temperature dependence of gas permeance across a wide range of temperatures. Organosilica membranes showed H₂/N₂ and H₂/CH₄ permeance ratios that ranged from 10 to 150, corresponding to network pore size, and both H₂ selectivity decreased with an increase in the carbon number between 2 Si atoms. Organosilica membranes showed activated diffusion for He and H₂, and a slope of temperature dependence that increased approximate to the increase in the carbon number between 2 Si atoms. The relationship between activation energy and He/H₂ permeance ratio for SiO₂ and organosilica membranes suggested that the molecular sieving can dominate He and H₂ permeation properties via the rigid microporous structure, which was constructed by BTESM and BTESE. With increased in the carbon concentration in silica, polymer chain vibration in organic bridges, which is a kind of solution/diffusion mechanism, can dominate the permeation properties. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4491–4498, 2017     

Structural Characterization and Protein Adsorption Property of Hydroxyapatite Particles Modified With Zinc Ions

Zinc-containing hydroxyapatite particles (Zn/HAp) were prepared by an ion exchange reaction process involving hydroxyapatite (HAp) particles with aqueous solutions containing various amounts of zinc nitrate. The Zn²⁺ ion was partially substituted for the Ca²⁺ ion position in the HAp lattice, and hence, the obtained samples had changed little in crystallinity, particle size, and specific surface area. Adsorption of bovine serum albumin (BSA) and β₂-microglobulin (β₂-MG) in solutions containing both BSA and β₂-MG was examined. As the Zn²⁺ ion content in the apatites increased, the adsorbed amount of BSA was almost constant, whereas that of β₂-MG increased.     

Relations between the molecular aggregation state and ionic conductivity in photopolymerized crosslinking polymers with oligo(oxyethylene) chains

A mixture of a vinyl monomer and a crosslinking agent was photopolymerized to form a crosslinked polymer film. Methacrylate with pendant oligo(oxyethylene) chain and poly(ethylene glycol) dimethacrylate were used as the vinyl monomer and crosslinking agent, respectively. The ionic conductivity of the film increased with an increasing concentration of LiClO₄ and then decreased. The size of the quasicrystalline aggregation phase composed of pendant and crosslinking chains in the film decreased with an increasing concentration of LiClO₄. The amorphous pendant and crosslinking oxyethylene chains gave rise to increased segmental motion and conductivity. The dissolution was depressed for a decrease in the ionic conductivity at a high LiClO₄ concentration at which the interactions among ions became stronger and the crystal phase of LiClO₄ was formed. The amount of the dissolution of the aggregation phase increased with an increasing crosslinking agent concentration. The quasicrystalline aggregation phase became larger with an increasing length of the pendant chains, and an increase in the size of the aggregation phase resulted in a decrease in the ionic conductivity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1272–1277, 2002