Yuko Hibi

Tribochemical wear of silicon nitride in water, n-alcohols and their mixtures☆

Abstract In order to evaluate the lubrication compatibility of Si 3 N 4 with n -alcohols, sliding experiments were conducted in which Si 3 N 4 specimens were reciprocated against each other in deionized water, purified n -alcohols of carbon number, nC , from 1 to 10, water-methanol and methanol-nonanol. The specimens were tested at a low constant speed of 2.4 mm s −1 and at a load of 9.8 N using a reciprocating ball-on-block machine. The results showed that both the friction and the wear were significantly higher in water than in the n -alcohols. The friction coefficient was 0.78 in water, 0.14 in the n -alcohols for nC ⩽ 4 and 0.09 for 5 ⩽ nC ⩽ 10. Wear in the n -alcohols was minimal: it decreased with an increase of nC for nC ⩽ 4 and was very small for nC ⩾ 5. In methanol, even small concentrations of water degraded both the friction and the wear characteristics. Scanning electron microscopy (SEM) revealed the formation of a tribochemical film as thick as 1 μm on surfaces worn in the lower alcohols. The observation also indicated that formation, delamination and dissolution of the film may occur at the sliding interface. The mechanism proposed is that wear of Si 3 N 4 and lower alcohols occurs by a tribochemical reaction in which siloxane is formed and removed by esterification of oxidized surfaces of Si 3 N 4 .

EXCIMER LASER ASSISTED CHEMICAL MACHINING OF SIC CERAMIC

A highly effective method of machining ceramic has been newly developed using a krypton fluoride (KrF) excimer laser with a 248 nm wavelength. The laser was irradiated on SiC in water to form a soft hydrous oxide layer by photochemical reaction. The softened layer was then cut with a diamond tool to form a mirror surface finish. The optimum conditions were found for both high machining rate and better surface integrity of SiC.

Global Interference: The Effect of Exposure Duration That is Substituted for Spatial Frequency

In this study, participants were required to identify hierarchically structured patterns that appeared at either global or local level. Paquet and Merikle (1984 Canadian Journal of Psychology 381 45–53) showed that global interference is affected by exposure duration in the processing of a hierarchical structure. They showed that only global-to-local interference occurred at short exposure durations. In contrast, global-to-local as well as local-to-global interference was observed at long exposure durations. They suggested that the effect of exposure duration with global interference depends on the high-spatial-frequency versus low-spatial-frequency channel. In the present study, exposure duration (short or long) was varied randomly from trial to trial (experiment 1), or held constant (experiment 2). In experiment 1, global-to-local interference occurred at both short and long exposure durations, even though the same physical properties existed as in experiment 2. In experiment 2, both global-to-local and local-to-global interference occurred at only long exposure durations, in line with the results reported by Paquet and Merikle. This suggests that the effect of exposure duration on global interference is explained not only by spatial-frequency channels, but also by attentional shift.

Lubrication of Si3N4 and Al2O3 in water with and without addition of silane coupling agents in the range of 0.05-0.10 mol/l

To improve water lubrication of ceramics at a lower sliding velocity, the effect of the addition of silane coupling agents was investigated. Si3N4 and Al2O3 were slid against themselves in water with and without the addition of silane coupling agents in amounts ranging from 0.05 to 0.10 mol/l. Silane coupling agents containing one or more amino groups were effective in reducing the friction of Si3N4 and Al2O3 in water. Si3N4 also showed significant wear reduction but not Al2O3. However, the addition of a silane coupling agent containing an epoxy group increased both friction and wear of Si3N4. Improved lubricative characteristics of Si3N4 in water and in silane coupling agent solutions were obtained when Si3N4 contained smaller amounts of sintering additives. The adsorption behaviour of a silane coupling agent on ceramics was examined using both Fourier transform infrared spectroscopy and thin layer chromatography to clarify the interaction between the silane coupling agent and the ceramics. The role of polysiloxane film formation on ceramics is discussed to demonstrate the lubrication properties of ceramics.

Age differences in dimension weighting on visual feature search

Two experiments examined age‐difference effects in visual feature search for two types of prior information (knowledge about target‐defining features and intertrial transition of target‐defining features). In Experiment 1, younger participants had shorter reaction times searching for a target in blocks where the target was defined by a single feature dimension compared to where the target was defined across dimensions (within‐dimension facilitation; WDF). However, WDF was not found in older participants. Intertrial facilitation (ITF), a dimension‐based carryover effect in consecutive trials, was observed both for young and older participants. Experiment 2 provided participants with probabilistic knowledge about target‐defining features. Again, young participants showed a facilitatory effect related to this knowledge, but this effect was reduced in older participants. However, intertrial facilitation was observed for young and older adults to the same degree. These results are not consistent with general age‐related decrement in the maintenance of dimension weighting, but support a dual mechanism of dimension weighting (Kumada, 2001). The results suggest that knowledge‐based control of dimension weighting declined with ageing, but involuntary shift of dimension weighting by intertrial transition of target‐defining features is maintained in ageing.

Friction and Wear Properties of the Siliconized, Chromized and Borochromized Steel Substrates

In this study, the friction and wear properties of the siliconized, chromized and borochromized SS 400 steel/Si3N4 tribopairs were investigated in ethyl alcohol at 298 K. The surface of the siliconized plate specimens mainly consisted of Fe3Si, while the surfaces of the chromized and borochromized steel plate specimens were mainly composed of Fe-Cr alloy and Cr2B phases, respectively. The borochromized specimens exhibited the highest microvickers hardness of all the plate specimens. Also, it was found that both the chromized and borochromized steel specimens exhibited friction coefficients as low as 0.2 in ethyl alcohol, and that the friction coefficients of the siliconized steel specimens were slightly lower than those of the non-coated steel specimens.

Friction and Wear Properties of Fe7Mo6-Based Alloy under the Lubrication of Ethyl-Alcohol

In this study, the friction and wear properties of Fe-Mo type alloy disk specimens were investigated against ASTM 52100 steel balls under the lubrication of ethyl-alcohol using a reciprocating Optimol SRV tribometer. It was found that the Fe7Mo6-based alloy disk specimens with a composition of Fe-42at% Mo exhibited more stable and lower friction coefficients than the Fe and Mo disk specimens.In addition, the friction coefficients of Mo disk specimens rapidly increased 1.8 ks after starting their friction tests, while the friction coefficients of Mo disk specimens were rapidly reduced 2.4 ks after starting their friction tests.