Ng Of Material Research Articles

Friction and Wear Studies Using Taguchi Method: Application to the Characterization of Carbon‐Silicon Carbide Tribological Couples of Automotive Water Pump Seals

An experimental design based on the Taguchi method has been applied to optimize the use of a dynamic sealing element of water pump of automotives combustion engines. A carbon primary ring and a silicon carbide mating ring set up this dynamic sealing element. The aim of this work was to experimentally determine the crossed influence of the primary ring variant, the normal load, the surrounding, the mating ring finishing, and the rotational frequency on the dynamic friction coefficient and on the wear of carbon primary ring‐silicon carbide mating ring tribological couples. The coefficient of dynamic friction and the wear depend on the design factors. They are also functions of theinteractions between these experimental factors, from the implementation of an experimental design. The results obtained allow the optimal functioning condition to be determined and the best friction couple to be used for a given dynamic sealing application.

Mechanical seal with thermally stable mating ring

Mechanical seal with thermally stable mating ring

Sulfur isotope ratio measurements of individual sulfate particles by NanoSIMS

The sulfur isotopic compositions of barite (BaSO 4), anhydrite (CaSO 4), gypsum (CaSO 4·2H 2O), mascagnite ((NH 4) 2SO 4), thenardite (Na 2SO 4), boetite (K 2SO 4), epsomite (MgSO 4·7H 2O), magnesium sulfate (MgSO 4· xH 2O) and cysteine (an amino acid) were determined with a Cameca NanoSIMS 50 ion microprobe employing a Cs + primary ion beam and measuring negative secondary ions. This ion microprobe permits the analysis of sulfur isotope ratios in sulfates on 0.001–0.5 ng of sample material, enabling the analysis of individual S-bearing particles with diameters as small as 500 nm. The grain-to-grain reproducibility of measurements is typically 5‰ (1 σ) for micron-sized grains, <5‰ for submicron-sized grains down to roughly 500 nm, and <2‰ for polished thin sections and ultra microtome sections which were studied for comparison. The role of chemical composition (matrix effect) and sample preparation technique on the instrumental mass fractionation (IMF) of the 34S/ 32S ratio in the NanoSIMS has been investigated for different sulfates and one amino acid. The IMF varies by ∼15‰ between the standards studied here, underlining the importance of a good understanding of the matrix-specific IMF correction in order to get precise S isotope data for very small samples such as aerosol particles. A good correlation between IMF and ionic radius of the cations in sulfates was found, permitting inference of IMF corrections for sulfates for which no isotope standards are available.

Mechanical seal with single-piece, perforated mating ring

Mechanical seal with single-piece, perforated mating ring

Numerical Simulations of the Flow Field Around the Rings of Mechanical Seals

The flow inside a seal chamber as induced by the influx of the flush fluid and the rotation of the primary ring is analyzed. The 3-D flow characteristic around the mating ring and the rotating ring are predicted by solving the Navier-Stokes equations in cylindrical coordinates. For this purpose, the pressure correction method was used in conjunction with the SIMPLE algorithm. A series of numerical solutions is presented that show the flow mechanism within the gap between the rings and the gland. The implication of the flow characteristic on the cooling of the rings is discussed.

Key Role of Conserved Histidines in Recombinant Mouse β-Carotene 15,15′-Monooxygenase-1 Activity

Alignment of sequences of vertebrate beta-carotene 15,15'-monooxygenase-1 (BCMO1) and related oxygenases revealed four perfectly conserved histidines and five acidic residues (His172, His237, His308, His514, Asp52, Glu140, Glu314, Glu405, and Glu457 in mouse BCMO1). Because BCMO1 activity is iron-dependent, we propose that these residues participate in iron coordination and therefore are essential for catalytic activity. To test this hypothesis, we produced mutant forms of mouse BCMO1 by replacing the conserved histidines and acidic residues as well as four histidines and one glutamate non-conserved in the overall family with alanines by site-directed mutagenesis. Our in vitro and in vivo data showed that mutation of any of the four conserved histidines and Glu405 caused total loss of activity. However, mutations of non-conserved histidines or any of the other conserved acidic residues produced impaired although enzymatically active proteins, with a decrease in activity mostly due to changes in V(max). The iron bound to protein was determined by inductively coupled plasma atomic emission spectrometry. Bound iron was much lower in preparations of inactive mutants than in the wild-type protein. Therefore, the conserved histidines and Glu405 are absolutely required for the catalytic mechanism of BCMO1. Because the mutant proteins are impaired in iron binding, these residues are concluded to coordinate iron required for catalytic activity. These data are discussed in the context of the predicted structure for the related eubacterial apocarotenal oxygenase.

Ion microprobe measurement of strontium isotopes in calcium carbonate with application to salmon otoliths

The ion microprobe has the capability to generate high resolution, high precision isotopic measurements, but analysis of the isotopic composition of strontium, as measured by the 87Sr/ 86Sr ratio, has been hindered by isobaric interferences. Here we report the first high precision measurements of 87Sr/ 86Sr by ion microprobe in calcium carbonate samples with moderate Sr concentrations. We use the high mass resolving power (7000 to 9000 M.R.P.) of the SHRIMP-RG ion microprobe in combination with its high transmission to reduce the number of interfering species while maintaining sufficiently high count rates for precise isotopic measurements. The isobaric interferences are characterized by peak modeling and repeated analyses of standards. We demonstrate that by sample-standard bracketing, 87Sr/ 86Sr ratios can be measured in inorganic and biogenic carbonates with Sr concentrations between 400 and 1500 ppm with ∼2‰ external precision (2σ) for a single analysis, and subpermil external precision with repeated analyses. Explicit correction for isobaric interferences (peak-stripping) is found to be less accurate and precise than sample-standard bracketing. Spatial resolution is ∼25 μm laterally and 2 μm deep for a single analysis, consuming on the order of 2 ng of material. The method is tested on otoliths from salmon to demonstrate its accuracy and utility. In these growth-banded aragonitic structures, one-week temporal resolution can be achieved. The analytical method should be applicable to other calcium carbonate samples with similar Sr concentrations.

Real-time NASBA for Detection of Strawberry Vein Banding Virus

An assay for the detection of Strawberry vein banding virus (SVBV) in Fragaria spp. based on nucleic acid sequence based amplification (NASBA) and real-time detection using molecular beacons (real-time NASBA) is described. This assay was compared both with biological indexing, the current method for certification of SVBV, and a newly optimised PCR-based detection method. Performance of the assay was tested on three SVBV isolates in Fragaria indicator plants and 317 field strawberries from five European countries. The assay was shown to be SVBV-specific, testing negative for other common aphid-borne strawberry viruses. The virus was detected in purified total RNA preparations diluted a millionfold, which is an amount equivalent to ∼1 ng of fresh material. The real-time NASBA method developed here offers the potential of a fast, sensitive and reliable approach for the routine diagnosis of strawberry stock material.

A Laser Surface Textured Hydrostatic Mechanical Seal

A mechanical seal subjected to laser surface texturing over an annular portion of one of its mating rings is theoretically and experimentally investigated. The partial surface texturing provides a mechanism for hydrostatic pressure build up in the sealing dam similar to that of a radial step or face coning. Optimization of the surface texturing parameters to obtain maximum hydrostatic pressure effect is performed on a theoretical model. A test rig that allows friction torque and temperature measurements in a back-to-back double seal arrangement is used to validate the surface texturing effect. It is found that optimally textured seals generate substantially less friction and heat. Moreover, a simple unbalanced seal, limited in its pressure capacity, can be easily transformed by surface texturing to an equivalent balanced seal with much higher pressure capability. Presented at the 57th Annual Meeting Houston, Texas May 19–23, 2002

Sampling and Analysis of Particulate Matter by Glow Discharge Atomic Emission and Mass Spectrometries

The direct introduction of particulate matter into glow discharge atomic emission and mass spectrometry sources through a particle beam/momentum separator apparatus is described. Vacuum action through a narrow (0.0625 in. i.d.) stainless steel tube allows the introduction of discrete samples of NIST SRM 1648 urban particulate matter (UPM) and caffeine in powder form. Introduction of "ambient" airborne particulate matter is also possible. Particles passing through the aerodynamic momentum separator impinge on the heated (∼200-250 °C) inner surface of the glow discharge plasma volume and are flash-vaporized. The resultant atoms/molecules are subjected to excitation/ionization collisions within the low-pressure (0.5-5 Torr of He or Ar) plasma, producing characteristic photon emission and/or signature ionic species. In this way, atomic emission and mass spectrometry identification of particle constituents is possible. Basic design aspects of the apparatus are presented, and demonstrations of atomic emission detection of the constituents in the NIST SRM illustrate the general characteristics of the approach. Transient atomic emission signals are captured for the introduction of preweighed, discrete samples, with the integrated areas used to construct analytical response curves. Limits of detection using this relatively simple atomic emission system are on the order of tens of nanograms for sample masses of ∼50 μg. Mass spectrometric monitoring of introduced caffeine particles and a mixture of polycyclic aromatic hydrocarbons (PAHs) illustrates the ability of the glow discharge plasma to produce high-quality, library (electron impact) searchable mass spectra of molecular species while also yielding isotopic identification of elemental components of the UPM. Limits of detection for Fe in the NIST SRM are on the order of 175 ng of material, equivalent to ∼7 ng of analyte Fe. It is believed that the small size, low power consumption, ease of operation, and multimode sampling capabilities (AES/MS) of the particle beam-glow discharge (PB-GD) apparatus hold promise for applications in continuous monitoring and discrete particle sampling.

Analytical and Experimental Investigation of Laser-Textured Mechanical Seal Faces

An analytical model is developed to predict the relation between the opening force and operating conditions in a mechanical seal with laser textured microsurface structure in the form of micropores. The model is valid for any desired shape of the micropores. An optimization is performed for spherical shape micropores evenly distributed on one of the mating rings face to maximize the opening force and fluid film stiffness. Results of a parametric study are presented showing the effect of the main design parameters on the seal performance. Some results of an experimental investigation with water-lubricated seal rings are also shown and compared with the theoretical model. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, October 26–28, 1998

Fluid Temperature and Film Coefficient Prediction and Measurement in Mechanical Face Seals—Experimental Results

Experiments were run where the temperature of the sealed fluid was measured in a seal chamber in a plane moving in the radial and axial directions. Temperatures within the nonrotating mating ring were also measured. Tests were run at various speeds, flush flow rates, and flush flow directions in water and oil. Details of the experimental apparatus, procedure, operating conditions, and the test results are summarized in the paper. The experimental results confirm the computational fluid dynamics (CFD) predicted results made based on the model presented in the previous paper entitled 'Fluid Temperature and Film Coefficient Prediction and Measurement in Mechanical Face Seals–Theoretical Results” in most respects. Several important conclusions were reached. For flush flow-cooled seals, the fluid temperature surrounding the seal is nearly uniform with small increases occurring only very near to the seal interface. The heat generated by the seal interface and by viscous dissipation in the sealed fluid is taken up by the fluid flow almost immediately upon entry of the flush fluid. Both experiments and modeling show the strong effect of flush flow rate on seal temperatures. Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

Metallization of poly(4-methyl-1-pentene) microcellular foam

Low density microcellular foam from poly(4-methyl-1-pentene) (PMP) has been metallized by laser-induced chemical vapor deposition (LICVD). KrF excimer laser radiation (248 nm) was used to photolytically decompose molybdenum hexacarbonyl with and without a buffer gas. Metal oxycarbide deposits 100 μm in diameter were formed. The microstructure of the PMP foam was unaltered. The deposition was confirmed to be 100 μm using scanning electron microscopy and energy dispersive x-ray spectroscopy. X-ray fluorescence was used to determine that approximately 80 ng of material was deposited.

Improved measurement of stable isotope ratios in gas chromatography/mass spectrometry using the microwave-powered chemical reaction interface for mass spectrometry

The microwave-powered chemical reaction interface for mass spectrometry (CRIMS) has been successfully used for selective detection of analytes labeled with 13C, 15N and D following capillary gas chromatography separation with good analytical characteristics in biological applications. In this study we evaluated how an advanced data system coupled to a quadrupole mass analyzer could improve precision and sensitivity of stable isotope ratio measurements for 13C and 15N. The enrichments of 13C and 15N are determined by monitoring CO2 (m/z 44 and 45) and NO (m/z 30 and 31). These small molecules are produced from the analyte in the chemical reaction interface in the presence of SO2 as a reactant gas. Using caffeine and its 13C1, 15N2-labeled analog for these quantitative studies, we have found that the Vector 2 system improves overall precision (RSD = 0.6% for both carbon and nitrogen) and sensitivity of stable isotope measurements by at least a factor of two compared to the Vector 1 system, and by more than an order of magnitude compared to our older results. With the optimum system we are now able to measure an atom% enrichment of 0.0044 for 15N and 0.015 for 13C in caffeine in the presence of 300 ng of unlabeled material. This is more than half way between isotopic detection limits of conventional gas chromatography/mass spectrometry and the state-of-the-art, which is a gas chromatograph coupled to a chemical combustor and a dual-collector isotope ratio mass spectrometer.

Load-Induced Reduction of Real Contact Area in Carbon Face Seals Operating Under Boundary Lubrication Conditions

The topography of carbon seal faces tends to distort under compression, resulting in an increase in the real mechanical contact area between the seal faces. This reduces the effective area between the seal faces subjected to full hydraulic pressures, and consequently increases the mechanical contact forces. The electrical resistance in the junction between the carbon seal face and a lapped steel mating ring was used to estimate the real contact area between the two materials. The estimated reduced contact area was then utilized to compute mechanical contact forces. The computed values were cross-checked against mechanical contact forces derived from torque measurements. Finally, a semi-empirical algorithm is presented, allowing the effect of an increased mechanical contact area to be computed for a typical carbon insert with a modulus of elasticity in the range of 2 × 1010 N/M2.

A Study of the Relationship Between Sealing Performance and Surface Condition of Mechanical Face Seals

The relationship between topography of the sealing surfaces of mechanical face seals and their sealing characteristics was experimentally and theoretically evaluated. As a result of testing and analysis, it is evident that the micro-streaks formed on the sealing surface of the mating ring by the polishing process had a remarkable influence on the sealing performance.

Tribological Behavior of SiC‐Whisker/Al2O3 Composites against Carburized 8620 Steel in Lubricated Sliding

Mineral oil lubricated sliding tests of Sic‐whisker (SiCw,)/A1203 composites and monolithic alumina against carburized 8620 steel were conducted on a cylinder‐on‐cylinder machine. The wear rate of the composites was one or two orders of magnitude less than that of pure alumina. Hot‐pressed 25 wt% SiCw,/A1203 composite had a lower wear rate than sintered and HIPed 7.5 wt% SiC/Al2O3 composite under the same conditions. The weight loss of the steel mating ring against the 25 wt% SiCw, composite was a factor of four lower than against the 7.5 wt% SiCw, composite, but the former was a factor of 50 to 60 less than that against pure alumina. The composites showed lower friction coefficients than alumina during the run‐in stage. The friction coefficients decreased with initial wear. The steady‐state friction coefficient decreased with increasing load up to 500 N for hot‐pressed 25 wt% SiC,/Al203 composite. Further, SEM observation showed much less microfracture in composites than in alumina. EDAX analysis revealed less Fe transfer from the steel ring to the composites than to pure alumina. Wear by microfracture and by adhesion in composites was suggested to be suppressed by SIC whiskers. This in turn reduced wear of the steel because of the generation of fewer hard particles.

A Study of the Relationship Between Frictional Characteristics and Surface Condition of Mechanical Face Seals

This paper deals with the sealing characteristics of mechanical face seals from the viewpoint of rubbing surface conditions. The relationship between topography of the sealing surface of the mechanical face seal and the frictional, wear and sealing characteristics were experimentally evaluated. As a result of testing, it became clear that the radius of curvature of the asperity in profiles of roughness curve of the mating ring surface on the mechanical face seal has a remarkable effect on the friction and wear characteristics of mechanical face seals.

A spatial and temporal probe for laser-generated plumes based on density gradients

A new universal detector is reported for transient atomization events such as the laser-generated plume. A probe laser beam interrogates the density gradients, which can be monitored as a deflection of the beam in far field. A simple model is used to explain the observations. Both the shape and the magnitudes of the experimental signals are in good agreement with the predictions. As little as 1 ng of material vaporized off a silicon wafer can be detected. The technique provides insight into the laser vaporization process, because both spatial and temporal information can be derived for individual events.

Rapid diagnosis of rabies infection by means of a dot hybridization assay.

Dot hybridization was used to detect specific rabies RNA in brains, either from experimental infection in mouse or from brain material to be processed for routine diagnosis. 32P cDNA probes were employed to identify minute amounts of specific viral RNA. Purified RNA was obtained after phenol extraction. The RNA was fixed on nylon membranes and hybridized with a pool of M13 inserts complementary to 200-400 nucleotides of each rabies gene and mRNA. Hybridized, labelled probes were detected by autoradiography. There was strong cross-hybridization between fixed rabies and street rabies virus RNA, which enable the detection of field strains for diagnosis purpose using a fixed rabies (PV strain) cDNA. A positive response was obtained with as little as 80 ng of brain RNA material from a fixed rabies-infected mouse. Detection of viral RNA was still specific 1 week after death, the brain material being left at room temperature. A total correlation was found when the samples were examined in parallel using a fluorescent rabies-specific antibody and by virus isolation on murine neuroblastoma cells. These data show that the use of rabies-specific cDNA probes in a dot-blot hybridization assay has great potential for the diagnosis of rabies.