Surface Pitting Research Articles

The effects of ball surface condition in the micro-scale abrasive wear test

The ball‐crater micro‐scale abrasive wear test can be applied to coated samples and small bulk samples. The surface condition of the ball influences the magnitude and the reproducibility of the measured wear coefficient. Use of a polished new ball in the test may give uncertain or anomalously low wear coefficients, particularly for relatively soft specimens. This effect is explained in terms of the ease of entrainment of abrasive particles into the contact area. Reproducible results are obtained with pre‐conditioned balls with slight surface pitting, and the use of such balls is recommended for routine testing.

Microscopic Behavior on the Protection of Polyacrylonitrile-Based Carbon Fibers from Thermal Oxidation

The surface of polyacrylonitrile-based carbon fiber was appropriately coated with dilute phosphoric acid to protect or retard its thermal oxidation occurring during an exposure to high temperatures above 600°C in air. Microscopic behavior on surface damage and size change in the uncoated and coated fibers was compared using thermogravimetric and scanning electron microscopic techniques. The result showed that the state of the carbon fiber surface was found to be remarkably improved by the coated phosphorous compound, minimizing the surface pitting, and size reduction of carbon fiber by high temperature oxidation. The microscopic evidence for the effective protection of carbon fiber from thermal oxidation also indicated that use of this technology may be positively considerable to other related materials.

A fracture mechanics model for the wear of gear flanks by pitting

A new model for determination the pitting resistance of gear teeth flanks is presented. The theory of short cracks is utilised for computational simulation of the fatigue process leading to pitting. The stress field in the contact area of meshing spur gears and functional relationship between the stress intensity factor and the crack length are determined by the finite element method using an equivalent model of two cylinders. The equivalent cylinders have the same radii as the curvature radii of gear teeth flanks in the inner point of a single teeth pair engagement, which represents the worst loading case. Based on computational results and with consideration of some particular material parameters the service life of gear flanks can then be determined from a number of stress cycles required for crack propagation from the initial to the critical crack length, when surface pitting can be expected. The model is applied to a real spur gear pair, which is also experimentally tested. The comparison of numerical and experimental results shows a good agreement. Further theoretical and experimental investigations are necessary to develop a reliable method for the estimation of gear life with a fracture mechanic model.

Uptake of fluoride into developing sheep teeth, following the 1995 volcanic eruption of Mt Ruapehu, New Zealand

In the southern Spring of 1995 (mid-October) the active volcano Mt Ruapehu in the central North Island of New Zealand erupted explosively, spreading up to 40 million m 3 of rhyolite tephra over thousands of km 2 of farmland during the lambing season. This ash contained a high concentration of soluble fluoride, and more than 2000 lactating ewes died of acute fluoride poisoning. To investigate the effects of this brief but acute dose on the teeth of grazing animals we examined the distributions of fluorine and calcium in the permanent incisor teeth of sheep which were one year old at the time. Where part of an incisor had been in the first (secretory) stage of calcification the erupted tooth disclosed surface pitting, a thin layer of enriched mineral across the enamel with as much as 1000 ppm F w/w, and a separate layer with ∼4000 ppm down the dentine. The part of an incisor which had attained the later (maturation) stage showed enriched layers only in the outer enamel and in the dentine. This study has demonstrated some important features of the calcification process, and the risk of fluoride toxicity to grazing animals.

Short fatigue crack growth due to contact loading

A numerical model for simulation of short fatigue crack growth due to normal and tangential contact loading is presented in this work. The model can be used for predictions of the service life of various contacting mechanical elements (gears, bearings, wheels, cams, etc.) in respect to the surface pitting. The simulation of short crack growth takes into account the modified BCS (Bilby, Cottrell and Swinden) model for simulation of dislocations motion along slip bands in the material. The stress field in the contact area and relationship between the stress intensity factor and the crack length are determined by the finite element method, where the virtual crack extension method (VCE) is used for determination of the stress intensity factor. On the basis of numerical results and with consideration of some particular material parameters, the number of stress cycles required for fatigue crack propagation from initial to the critical crack length can then easily be estimated. The developed model is applied to the real spur gear pair, which is also experimentally tested. The comparison of numerical and experimental results shows a good agreement and it can be concluded, that the developed model is appropriate for determination of service life of mechanical elements under contact loading.

Modified Atmosphere Packaging Minimizes Increases in Putrescine and Abscisic Acid Levels Caused by Chilling Injury in Pepper Fruit

Bell pepper fruit (Capsicum annuum L. cv. Lamuyo) at two stages of maturity, mature green (MG) and mature red (MR), were stored at 2 and 10 °C to investigate physiological changes resulting from chilling injury. The MG fruit showed evidence of chilling injury (surface pitting) when stored at 2 °C, while MR fruit were unaffected by cold. At the same time, differences in the evolution of plant regulators were detected: In chilling-sensitive MG peppers, ethylene evolution and levels of 1-aminocyclopropane-1-carboxylic acid (ACC), putrescine (Put), and abscisic acid (ABA) rose significantly during storage, while in MG fruits stored at 10 °C and MR fruit stored at both 2 and 10 °C the values were low and no changes were observed. Spermidine (Spmd) content remained low in fruits at both maturity stages and at both temperatures. Chilling injury was reduced in MG fruits stored at 2 °C when modified atmosphere packaging (MAP) was used, particularly with the less permeable film. MAP also led to less pronounced inc...

Reactive ion etching of diamond as a means of enhancing chemically-assisted mechanical polishing efficiency

Abstract Diamond, due to its unique combination of excellent thermal, electrical and mechanical properties, is a candidate material for MCM thermal management. However, because of inherent limitations in its growth, some degree of post-deposition surface finishing is usually required. This paper describes the results of reactive ion etching (RIE) of polycrystalline diamond films in an oxygen plasma. The etching procedure was characterized in terms of etch rate and impact on the surface morphology of the diamond and its potential as a pretreatment for the chemically-assisted mechanical polishing (CAMP) of diamond films. Diamond films deposited by both DC arcjet chemical vapor deposition (CVD) and microwave plasma CVD (MPCVD) were used in this work. The etch rate is shown to increase with increasing RF power, chamber pressure and a restricted range of oxygen flow rate. At low pressures, etching occurs primarily in the grain boundary regions, whereas, at high pressures, microchannels are formed near the tips of individual crystallites. Etching at low powers produces uniform surface pitting and columnar structures over the entire surface. Etching also causes all films to darken in color. The degree of darkening increases with increasing etch rate and etch time. Etch rates are in the range of 50–100 nm/min for the DC arcjet films and 50–60 nm/min for the MPCVD films. Etching reduced the average surface roughness by approximately 50%.

Vitamin E as an antioxidant for poly(etherurethane urea): in vivo studies. Student Research Award in the Doctoral Degree Candidate Category, Fifth World Biomaterials Congress (22nd Annual Meeting of the Society for Biomaterials), Toronto, Canada, May 29-June 2, 1996.

Poly(etherurethane) elastomers are useful materials in medical devices because of their mechanical properties and biocompatibility. However, it is necessary to stabilize these elastomers against the oxidation of their ether soft segments. Synthetic antioxidants such as Santowhite and Irganox are often satisfactory; however, particularly for biomedical applications, it was of interest to test the natural antioxidant vitamin E in poly(etherurethane urea) (PEUU) elastomers in vivo. The alpha-tocopherol form of vitamin E was added to PEUU at 5% by weight. Biaxially strained PEUU specimens with and without vitamin E were tested in vivo in the cage implant system. The influence of vitamin E on PEUU biostability was analyzed by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and scanning electron microscopic (SEM) characterization of the PEUU surface. ATR-FTIR results showed that vitamin E prevented chemical degradation of the PEUU surface up to 5 weeks implantation, and at 10 weeks 82% of the ether remained. In contrast, without an antioxidant, only 18% of the ether remained after 10 weeks. No surface pitting or cracking was observed by SEM on PEUU with vitamin E; PEUU without antioxidant ruptured owing to extensive pitting and cracking. It was concluded that the antioxidant properties of vitamin E prevented oxidation of strained PEUU elastomers in vivo. The influence of vitamin E on PEUU biocompatibility was characterized by exudate leukocyte counts, density of leukocytes adherent to the PEUU, and morphology of adherent leukocytes. These results indicated decreased leukocyte counts in the exudate and less active adherent cells on the PEUU with vitamin E compared to PEUU without antioxidant. A proposed cell-polymer feedback system demonstrates how vitamin E improves both biostability and biocompatibility of PEUU elastomers in vivo.

Chemical weathering rates of a soil chronosequence on granitic alluvium: I. Quantification of mineralogical and surface area changes and calculation of primary silicate reaction rates

Mineral weathering rates are determined for a series of soils ranging in age from 0.2–3000 Ky developed on alluvial terraces near Merced in the Central Valley of California. Mineralogical and elemental abundances exhibit time-dependent trends documenting the chemical evolution of granitic sand to residual kaolinite and quartz. Mineral losses with time occur in the order: hornblende > plagioclase > K-feldspar. Maximum volume decreases of >50% occur in the older soils. BET surface areas of the bulk soils increase with age, as do specific surface areas of aluminosilicate mineral fractions such as plagioclase, which increases from 0.4–1.5 m 2 g −1 over 600 Ky. Quartz surface areas are lower and change less with time (0.11–0.23 m 2 g −1). BET surface areas correspond to increasing external surface roughness (λ = 10–600) and relatively constant internal surface area (≈ 1.3 m 2 g −1). SEM observations confirm both surface pitting and development of internal porosity. A numerical model describes aluminosilicate dissolution rates as a function of changes in residual mineral abundance, grain size distributions, and mineral surface areas with time. A simple geometric treatment, assuming spherical grains and no surface roughness, predicts average dissolution rates (plagioclase, 10 −17.4; K-feldspar, 10 −17.8; and hornblende, 10 −17.5 mol cm −1 s −1) that are constant with time and comparable to previous estimates of soil weathering. Average rates, based on BET surface area measurements and variable surface roughnesses, are much slower (plagioclase, 10 −19.9; K-feldspar, 10 −20.5; and hornblende 10 −20.1 mol cm −2 s −1). Rates for individual soil horizons decrease by a factor of 10 1.5 over 3000 Ky indicating that the surface reactivities of minerals decrease as the physical surface areas increase. Rate constants based on BET estimates for the Merced soils are factors of 10 3–104 slower than reported experimental dissolution rates determined from freshly prepared silicates with low surface roughness (λ < 10). This study demonstrates that the utility of experimental rate constants to predict weathering in soils is limited without consideration of variable surface areas and processes that control the evolution of surface reactivity with time.

The Surface Degradation of Glass Within RPL Dosemeters

Phosphate glass within radiophotoluminescent dosemeters can suffer from a brown discoloration. Typical RPL signal fading is normally 3-4% per year but brown glasses have shown an average loss of 9.24 ± 0.84% per year which can be reduced to 3.96% ± 0.36% by acid cleaning. Similar cleaning of glasses stored in a desiccator raised the signal loss to 4.2 ± 0.6% from 3.12 ± 0.24% per year. Rutherford back scattering (RBS) has shown that the front surface had a 100 to 200nm film rich in silver while, across the rear face, silver appeared to migrate locally. In contrast, surfaces of glasses stored in a desiccator were all of the same composition. Scanning electron microscopy has shown that the front surface of brown glass is partly covered with small pits, approximately 2 μm in diameter. On the rear surface pitting is confined to areas near to a silver rich dendritic growth.

Analysis of the effects of surface pitting and wear on the vibration of a gear transmission system

A comprehensive procedure to simulate and analyse the vibrations in a gear transmission system with surface pitting, wear, and partial tooth fracture of the gear teeth is presented. An analytical model was developed where the effects of surface pitting and wear of the gear tooth were simulated by phase and magnitude changes in the gear mesh stiffness. Changes in the gear mesh stiffness were incorporated into each gear-shaft model during the global dynamic simulation of the system. The overall dynamics of the system were evaluated by solving for the transient dynamics of each shaft system simultaneously with the vibration of the gearbox structure. In order to reduce the number of degrees-of-freedom in the system, a modal synthesis procedure was used in the global transient dynamic analysis of the overall transmission ststem. An FFT procedure was used to transform the averaged time signal into the frequency domain for signature analysis. In addition, the Wigner-Ville distribution was also introduced to examine the gear vibration in the joint time-frequency domain for vibration pattern recognition. Experimental results obtained from a gear fatigue test rig at NASA Lewis Research Center were used to evaluate the analytical model.

Structural and compositional alteration of tooth enamel in hereditary epidermolysis bullosa.

Epidermolysis bullosa (EB) is a group of conditions characterized by basement membrane and cellular defects that result in skin fragility and variable extra-cutaneous involvement. The teeth can be severely affected with marked enamel malformations. The purpose of this study was to characterize the structure and composition of teeth from individuals representing the major EB groups (EB simplex, dystrophic EB and junctional EB). Teeth were examined from 28 individuals with EB and 10 healthy people unaffected by EB. Teeth from individuals with junctional EB had marked enamel hypoplasia with varying abnormalities in the enamel structure. Minor structural defects of enamel, including areas of surface pitting, were seen in the other EB types. Although there was a slight reduction (approximately 10%) in the enamel mineral content in several dystrophic EB and junctional EB teeth, the mean mineral content was similar for all EB enamel types and normal enamel. This study shows that while individuals with junctional EB have marked alteration of the enamel structure, the composition may be normal to only mildly altered. Laminin-5, the molecular defect in junctional EB, is associated primarily with alteration in the amount and/or structure of enamel while the mineralization process appears relatively intact. The marked enamel hypoplasia in this EB type suggests that laminin-5 plays an important role in the secretory phase of enamel development.

Residual durability of the surface layer of ShKh15 bearing steel

On the basis of a model used to compute the residual durability of rolling surfaces in the framework of linear fracture mechanics, we estimate the durability of ShKh15 bearing steel under the conditions of prevailing influence of lubrication. To obtain experimental data necessary for computation, we performed the tests on cyclic fatigue crack-growth resistance of steel both in the as-received state and after the standard procedure of heat treatment and constructed the corresponding kinetic diagrams of fatigue fracture. Numerical analysis enabled us to establish some regularities of the process of surface pitting induced by lubricated rolling contact.

Reaction of enzymes with starch granules: kinetics and products of the reaction with glucoamylase

The reaction of glucoamylase with starch granules from seven botanical sources (waxy maize, maize, barley, tapioca, amylomaize-7, shoti, and potato) and with four potato starches modified with acid in four types of alcohols (methanol, ethanol, 2-propanol, and 1-butanol) were studied using three concentrations of enzyme (2, 20, and 200 units mL −1). The kinetics of the formation of d-glucose were followed over 32 h for the three enzyme concentrations. The starches showed a wide degree of variance in their susceptibility to enzyme hydrolysis. They divided into three groups: waxy maize starch was the most susceptible being converted into 50, 95, and 98% d-glucose in 32 h for the three concentrations of enzyme, respectively; an intermediate group (barley, maize, and tapioca starches) was converted into 10–15, 60, and 75–80% d-glucose in 32 h for the three concentrations of enzyme, respectively; and the third and least susceptible group (amylomaize-7, shoti, and potato starches) was converted into 2–8, 9–16, and 13–21% d-glucose in 32 h for the three concentrations of enzyme, respectively. The percent conversion for the modified potato starches was proportional to the amount of enzyme and the degree of modification. The 100X (200 U mL −1) amount of enzyme gave 13, 17, 21 and 27% d-glucose in 32 h for potato starch modified in the four alcohols, respectively. The number and size of the granules were determined over 32 h of reaction using 10X (20 U mL −1) enzyme for waxy maize starch and 100X enzyme for the other starches. The number of granules for waxy maize, barley, maize, and tapioca starches significantly increased in the first part of the reaction and then decreased; this was paralleled by a decrease of 40–50% in the size of the granules. The number and size of the potato and shoti starch granules did not change very significantly and the number and size of amylomaize-7 starch granules decreased slightly but steadily to about 25% of the number and size of the native granules. The morphologies of the granules during reaction were studied by scanning electron microscopy. Extensive conversion into 50% d-glucose for the starches in the first two groups showed the classical “Swiss cheese” shell structure with many deep holes into the granules. The least susceptible starches in the third group did not show much change in morphology, except for some minor surface pitting.

Modified-atmosphere Packaging of `Sweetheart' Cherries

Kilogram quantities of `Sweetheart' cherries were stored in HDPE perforated bags (1993, 50.8 μ thickness, OTR = 750 ml·m–2·day–1) or in nonperforated bags (1994, 11 μ thickness, OTR = 5196 ml·m–2·day–1) at 0C. Samples were removed at 1, 2, 4, and 6 weeks of storage and evaluated for fruit and sensory quality. Bag atmospheres after 6 weeks of storage were 10% CO2 and 4.6% O2 for the perforated bags and 3.5% CO2 and 6.6% O2 for the nonperforated bags. Fruit brightness, firmness, and titratable acidity declined during storage. Skin color tended to be redder with the longer storage periods. Sensory evaluation in 1993 showed a decline in overall appearance and flavor with time, but texture and juiciness did not change. Acceptability remained high for the first 4 weeks of storage but dropped at week 6. Surface pitting was noticeable at weeks 4 and 6, particularly from stem bruising.

Electrochemical scanning tunneling microscopy study of the electrochemical behavior of naked and n-alkanethiol-modified Au(111) surfaces in F−- and CN−-containing electrolyte solutions

We report an electrochemical scanning tunneling microscopy (ECSTM) study of CN−- and F−-induced etching of naked and n-alkanethiol-modified Au(111) surfaces. We use electrochemical methods to activate or deactivate etching of the Au surface, and we monitor changes in surface topography simultaneously using STM. In F−-containing electrolytes we have observed that the STM tip can induce surface–atom diffusion in the electrochemical environment thereby enhancing surface pitting, island growth, and step edge movement. At potentials more negative than −150 mV (vs Ag/AgCl) the tip selectively removes Au atoms from surface defects and enhances growth on terraces. Similarly, we have found that the STM tip can profoundly alter the CN−-induced dissolution rate of Au. On naked Au surfaces held at extreme negative potentials, no CN− etching of the surface occurs. However, at slightly more positive potentials the surface is homogeneously etched. At intermediate potentials the area under the scanning STM tip is selectively etched at positive tip biases, but at slightly more negative biases etching proceeds less rapidly in the scanned region. Finally, when the Au(111) surface is modified with a single self-assembled monolayer (SAM) of organomercaptan molecules, surface etching processes are dramatically attenuated regardless of the substrate potential or tip bias.

`Eureka' Lemon Chilling Injury

In accordance with the currently approved Australian citrus disinfestation protocol for export to Japan, degreened `Eureka' lemons [Citrus limon (L.) Burm.] were cold-stored for 2 weeks at 1C. Following cold treatment, fruit were stored at 5C for 3 weeks, then transferred to 20C for an additional week to simulate transportation and handling. Fruit harvested early in the season were more susceptible to chilling injury than fruit harvested later, with 62% having lesions &gt;1 cm2 after 2 weeks at 1C. Most of the chilling injury occurred after subsequent storage (at 5C) rather than immediately after the 1C treatment. Injury was different from surface pitting or oleocellosis, manifesting as large uniform surface lesions 2 to 3 cm in diameter that rapidly discolored following storage at 20C. Although the oil glands were flattened, the collenchyma layer immediately above the oil gland remained intact. Cellular discoloration was localized around the oil gland, possibly indicating a lateral release of oil gland contents. Nondegreened late-season fruit developed substantially lower levels of chilling injury.

Surface area of aqueous sodium hydroxide hydrolyzed high‐speed spun poly(ethylene terephthalate) fibers

AbstractThe specific surface area (SSA) of delustered undrawn and drawn high‐speed spun PET fibers hydrolyzed in aqueous NaOH was measured using three methods: (1) geometric, based on fiber diameter; (2) gas adsorption using N2 and the BET equation; and (3) adsorption of a nonionic surfactant. Increasing the spinning speed had little effect on the SSA of the untreated fibers, while drawing resulted in considerably larger SSA. For the hydrolyzed fibers, both adsorption methods resulted in larger SSAs than that predicted geometrically due to surface pitting. After hydrolysis, the higher spinning speed resulted in a greater increase in SSA over the untreated sample, whereas the increase in SSA was less for the drawn fibers compared to the undrawn. The kinetics of hydrolysis are also discussed. © 1995 John Wiley &amp; Sons, Inc.

Pattern of enzyme hydrolysis in raw sago starch: effects of processing history

Hydrolysis patterns of five batches of sago starch were studied by using Novo Nordisk and Sigma α-amylases and glucoamylases. Native sago starch was a poor substrate to the enzymes and the hydrolysis patterns were surface erosion, pitting and crevassing. After incubation with pH 3·5 acetate buffer at 60 °C for 2 h, the hydrolysis pattern was different: a single deep round hole developed regardless of the batch or enzyme(s) used. This step also significantly increased the degree of hydrolysis. Granule size distribution results indicated that at about 67% hydrolysis, treated granule residues were the same mean size as native granules while untreated granule residues had two major size populations. DSC results suggested that amorphous regions of the untreated granule were preferentially hydrolysed, however, upon pretreatment regions within the granule were more uniform towards enzymes' action.

Surface Treatment of Carbon Fibers Using Low Temperature Plasma

Abstract Low temperature plasma treatment experiments were conducted on AS4 and AU4 type fibers in the presence of air, argon and nitrogen to study their effects on the resulting fiber-matrix adhesion in the composites fabricated with the fibers. Optimum conditions for the introduction of maximum surface oxygen and nitrogen functional groups on AS4 and AU4 fiber surfaces were derived. X-ray photelectron spectroscopy was performed on the fiber surfaces to determine the effect of plasma treatment on the amount and types of surface functional groups introduced. Scanning electron microscopy was performed on the fiber surfaces and the amount of surface etching and pitting was correlated to the plasma treatment conditions. Transverse tensile specimens were fabricated from treated fibers representing a few plasma treatment conditions, and their transverse tensile strengths were measured experimentally. An attempt was made to determine the effects of factors such as amount of chemical groups on the fiber surfaces...