Distribution by Scientific Domains

Kinds of Lubricants

  • internal lubricant
  • oil lubricant

  • Selected Abstracts

    ORIGINAL ARTICLE: Safety Analysis of the Diaphragm in Combination with Lubricant or Acidifying Microbicide Gels: Effects on Markers of Inflammation and Innate Immunity in Cervicovaginal Fluid

    Deborah J. Anderson
    Objective, Diaphragms are being considered for use with vaginal microbicide gels to provide enhanced protection against sexually transmitted pathogens. The purpose of this study was to determine whether use of a diaphragm with microbicide or placebo gel causes cervicovaginal inflammation or perturbations in cervicovaginal immune defense. Method of study, Eighty-one non-pregnant women were randomized into three groups and instructed to use Milex® (CooperSurgical, Inc., Trumbull, CT, USA)diaphragms overnight for 14 days in combination with one of the two acid-buffering microbicide gels [ACIDFORMÔ (Instead Inc., La Jolla, CA, USA) or BufferGelÔ (BG; ReProtect Inc., Baltimore, Maryland)] or placebo gel (K-Y Jelly®; Personal Products Inc., Raritan, NJ, USA). Cervicovaginal lavages (CVLs) were performed prior to study entry and on days 8 and 16. Nine soluble mediators of vaginal inflammation or immune defense were measured in CVLs by Bio-Plex or ELISA. Results, Use of diaphragms with placebo or microbicide gel was not associated with increased levels of inflammation markers. Concentrations of secretory leukocyte protease inhibitor (SLPI) were markedly reduced in the BG group. Conclusion, Daily use of a diaphragm with placebo or acidifying microbicide gel did not cause cervicovaginal inflammation. However, diaphragm/BG use was associated with markedly reduced levels of SLPI, an important mediator of innate immune defense. Further studies are warranted to establish the safety of diaphragm/microbicide gel combinations. [source]

    Comparison of Topical Anesthetics and Lubricants Prior to Urethral Catheterization in Males: A Randomized Controlled Trial

    John Siderias DO
    Abstract Although male urethral catheterization in the emergency department (ED) is both common and painful, few studies have evaluated the use of topical anesthesia prior to catheterization. Objectives: To determine whether pretreatment of the urethra with topical lidocaine reduces the pain associated with urethral catheterization. Methods:This was a prospective, double-blind, randomized clinical trial of 36 alert, cooperative male adult patients requiring urethral catheterization, without allergies to the study medications or contraindications to their use, from a suburban university-based ED. Patients in the experimental group had topical lidocaine 2% gel injected in their urethras, whereas control patients received intraurethral lubrication only. Standardized catheterization with a no. 16 Foley was performed followed by pain assessment. The primary outcome measured was pain of catheterization on a 100-mm visual analog scale. Other outcomes included ease of insertion and procedural bleeding. Results: The authors evaluated 36 patients evenly distributed between study groups. Mean age was 62 years (range 22,85). Compared with controls, patients pretreated with lidocaine experienced significantly less pain of catheterization (38 ± 28 mm vs. 58 ± 30 mm; mean difference 20 mm; 95% confidence interval [95% CI] = 0.4 to 32; p = 0.04) and less pain of injection (23 ± 17 mm vs. 40 ± 25 mm; mean difference 17 mm; 95% CI = 3 to 32 mm; p = 0.02). There were no differences in the number of attempts and incidence of adverse events between the groups. Conclusions: Use of topical lidocaine gel reduces the pain associated with male urethral catheterization in comparison with topical lubricants only. [source]

    Effect of Internal Lubricants on Defects in Compacts Made from Spray-Dried Powders

    Sreeram Balasubramanian
    The role of internal lubricants in the closure of large intergranular pores during dry-pressing was investigated. Alumina was spray-dried with and without an internal lubricant to yield granules with similar characteristics other than lubricant effects. Green and sintered microstructures were evaluated at different compaction pressures. The defects were quantified by evaluating the fracture surface of ,90% dense sintered compacts. The samples that contained an internal lubricant had higher green densities and fewer defects at comparable compaction pressures. The internal lubricant did not cause any significant reduction in green strength or increase in springback. [source]

    A new focus on the Walther equation for lubricant viscosity determination

    M. Sánchez-Rubio
    Abstract Lubricants are widely used in industrial machinery in order to separate solid tribological surfaces and support high loads under severe conditions. In tribological contacts, viscosity plays an important role in the film-forming abilities of the lubricant, but this property is strongly dependent on temperature. Consequently, small variations in temperature cause appreciable variations in the viscosity of lubricating oils. For this reason it is of practical value to be able to predict viscosity changes with temperature. This paper presents a new focus on the Walther equation to determine the viscosity of commercial lubricants at different temperatures. This new approach provides very good correlation with experimental measurements. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Lubricants under high local pressure: Liquids act like solids

    M. H. MüserArticle first published online: 21 OCT 200
    Schmierstoff; Druck; plastisches Fliessen; Reibungsgesetz Abstract A lubricant layer solidifies when it is confined between two walls at large normal pressures. The atomic scale motion that occurs when the two confining surfaces slide past each other induces flow in the lubricant layer that is akin of plastic flow. This results in friction-velocity relationships similar to Coulomb's law of friction. Moreover, the lubricant layer does not necessarily melt, even when the two solids are in stick slip motion. In this paper, atomic-scale details of the plastic flow mechanism are investigated by means of molecular dynamics simulations. Schmierstoffe unter hohem lokalem Druck: Flüssigkeiten verhalten sich wie Feststoffe Eine molekular dünne Schicht Schmierstoff verfestigt sich, wenn sie zwischen zwei Festkörpern großen Drücken ausgesetzt ist. Die atomaren Bewegungsmechanismen, die in dem Schmierstofffilm auftreten, wenn die Festkörper gegeneinander verschoben werden, können als plastisches Fliessen verstanden werden. Dieser Mechanismus führt zu einer Kraft-Geschwindigkeitsrelation, die dem Coulomb'schen Reibungsgesetz ähnlich ist. Selbst wenn die beiden Wände in Stick-Slip Bewegung sind, verflüssigt sich der Schmiermittelfilm nicht automatisch. In dieser Arbeit werden die Details des angesprochenen plastischen Fliessens anhand von Molekular-Dynamik Simulationen im Detail untersucht. [source]

    Selective Capture of Water Using Microporous Adsorbents To Increase the Lifetime of Lubricants

    Eng-Poh Ng
    Abstract Long live lubricants: The selective capture of water from lubricants using nanosized microporous aluminophosphate (AEI) and aluminosilicate materials was studied. Nearly 98,% of the moisture was removed from the lubricating oil under ambient conditions, resulting in a significant improvement in the lubricating service lifetime. Moreover, both the lubricant and the microporous sorbents can be recovered and reused. The selective capture of water from lubricants using nanosized microporous aluminophosphate and aluminosilicate materials was studied with an aim to increase the lifetime of the lubricating mineral oil. The amount of water present in oxidized lubricating oil before and after treatment with microporous materials was studied by FTIR spectroscopy and determined quantitatively using the Karl Fischer titration method. Nanosized aluminophosphate revealed a high selectivity for water without adsorbing other additives, in contrast to nanosized aluminosilicates which also adsorb polar oxidation products and ionic additives. About 98,% of the initial moisture could be removed from the lubricating oil under ambient conditions, resulting in a significant improvement in the lubricating service lifetime. Moreover, no by-products are formed during the process and both the lubricant and the sorbents can be recovered and reused, thus the method is environmentally friendly. [source]

    Boiling heat transfer coefficient of R22 and an HFC/HC refrigerant mixture in a fin-and-tube evaporator of a window air conditioner

    M. Herbert Raj
    Abstract The commonly used refrigerant in unitary type air conditioners is R22 and its phase out schedule in developing countries is to commence from 2015. Many alternatives to R22 are found in published literature in which R407C has similar characteristics to those of R22 except for its zeotropic nature. However, R407C which is an HFC is made compatible with the mineral oil lubricant in the system compressor by the addition of 20% of HC. This HFC/HC mixture called the M20 refrigerant mixture is reported to be a retrofit refrigerant for R22. Though its latent heat value is greater than that of R22, its refrigerating capacity is lower when it is used to retrofit R22 window air conditioners. Hence, a heat transfer analysis was conducted in the evaporator of a room air conditioner, for practically realized heat flux conditions during standard performance testing. The tests were conducted as per the BIS and ASHRAE standards. Kattan,Thome,Favrat maps are used to confirm the flow patterns, which prevail inside the fin-and-tube evaporator in the tested operating conditions. It is revealed that the heat transfer coefficient/heat fluxes are poorer for M20 because of the lower mass flow rate and higher vapor fraction at the entry of the evaporator than that of R22 in the prevailing operating conditions. The heat transfer coefficients of the M20 refrigerant mixture under various test conditions are lower in the range of 14% to 56% than those of R22. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( DOI 10.1002/htj.20299 [source]

    Metal Corrosion and its Impact on Glass Tempering Furnace Design

    Peter Tiernan
    A reliable well-designed tempering furnace is considered to be the cornerstone of any modern glass-processing facility. This paper addresses a series of engineering anomalies encountered during the commissioning of such a glass-processing furnace. Following the installation of a furnace in a European facility, small black deposits were noticed on both the silica-fused rollers used to transport the glass through the hearth of the furnace and on the processed glass surface itself. EDAX and scanning electron microscopy investigations indicated conclusively that the deposits were primarily constituted of sodium sulfate and trace elements consistent with stainless steel (chromium, iron, and nickel). Traditionally, high-density glass fiber was used to insulate the roof walls and side walls of tempering furnaces; however, it was noticed in this particular case that rolled stainless steel sheeting (SS316) was used. Chemical and X-ray diffraction analyses were used to pinpoint the origin of the deposits. It was determined that poor material selection choices taken during the design stage of the furnace in question were at fault. The combination of stainless steel and sulfur dioxide (SO2 is used as a lubricant to prevent scuffing) at elevated temperatures (>650°C) generated droplets of sodium sulfate, which condensed due to the convectional flow of the heat currents within the oven. These droplets scorched the glass surface and destroyed the fused silica rollers. As a recommendation, the usage of stainless steel and other nonrefractory metals should be avoided in the design of any future glass tempering furnaces. [source]

    Paste extrusion control and its influence on pore size properties of PTFE membranes

    Radium Huang
    Abstract Polytetrafluoroethylene (PTFE) is a remarkable membrane material. Owing to its high-melting point, PTFE fine powder cannot be processed using conventional melting processing methods. Instead, techniques such as paste extrusion, rolling, and sintering have to be employed. Each processing step has an important influence on the final pore size quality within the membrane. In this paper, a PID controller (proportional-integral-derivative controller) was used to improve the properties of PTFE paste during the extrusion process and the quality of the PTFE membrane. A range of lubricant content (18, 20, and 22 wt%) was used to monitor the pressure drop at different extrusion speeds (0.5, 1, and 2 mm/s) and reduction ratios (RR = 26.47, 47.06, 80.06). It was found that a higher lubricant content and a higher reduction ratio resulted in a lower pressure drop. It was also found that a higher stretching temperature tends to result in larger pore size and broader pore size distribution at the same stretching rate. At a monitored and controlled constant low-extrusion speed, the porosity of PTFE membrane was increased from 38% to 55% and the mean pore size was decreased from 0.22 to 0.15 ,m because of less migration and more uniform distribution of lubricant during extrusion. Properties and the associated property uniformity of the PTFE extrudate affect the subsequent membrane-forming process and the final pore size and size distribution significantly. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 26:163,172, 2007; Published online in Wiley InterScience ( DOI 10.1002/adv.20099 [source]

    Thermoplastic silicone elastomer lubricant in extrusion of polypropylene wood flour composites

    Velichko Hristov
    Abstract A possibility of using a thermoplastic silicone elastomer (TPSE) for reduction of surface defects in the extrusion of wood-filled metallocene polypropylene (mPP) has been investigated in this work. A capillary rheometer and a single-screw extruder have been utilized to study the effect of the additive on the extrudate distortions. Maleated syndiotactic metallocene polypropylene was also used as an adhesion promoter in mPP/wood flour composites. At loadings of 50 wt% wood flour in the mPP, the extrudates come out of the die with significant tearing and surface roughness. The surface rupture mechanism is similar to that of sharkskin in neat polymers; however, the defect is much more exaggerated in the case of wood fiber-filled composites. It was found that TPSE at low concentrations (1 wt%) was able to reduce or even completely eliminate extrudate surface tearing. Increasing the extrusion speed yielded better results. Addition of a coupling agent also provides improvement in the extrudate appearance. © 2007 Wiley Periodicals, Inc. Adv Polym Techn 26:100,108, 2007; Published online in Wiley InterScience ( DOI 10.1002/adv.20090 [source]

    Effects of epoxidized sunflower oil on the mechanical and dynamical analysis of the plasticized poly(vinyl chloride)

    Badra Bouchareb
    Abstract Epoxidized soybean oil (ESBO), is one of the most commonly used epoxides because of its typical combined roles as a plasticizer and heat stabilizer. In this study, a novel plasticizer of poly(vinyl chloride) (PVC) resins, epoxidized sunflower oil (ESO), was synthesized, and its performance was evaluated. ESO was designed to act as a coplasticizer and a heat stabilizer like ESBO. ESO is used as organic coplasticizer for plasticized PVC containing Ca and Zn stearates as primary stabilizers and stearic acid as lubricant. Di-(2-ethylhexyl) phthalate (DEHP), a conventional plasticizer for PVC, was partially replaced by ESO. Mechanical properties (tensile and shore D hardness) were investigated. The performance of ESO to ESB0 (20 g) for comparison, indicated that ESO could be used as secondary plasticizer for PVC in combination with DEHP. All mechanical and dynamical properties of plasticized PVC sheets varied with the oxirane oxygen of the ESO. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Disposition and pharmacokinetics of a lubricant contaminant, 2,6-di- tert -butyl 4-nitrophenol, in grafted human skin

    Lynn K. Pershing
    Abstract Disposition and uptake/elimination profiles of topical 2,6-di- t -butyl, 4-nitrophenol (DBNP), the nitrated metabolite of an antioxidant additive of lubricant and hydraulic fluids was quantified in human skin grafted on athymic mice after a single topical 75 µg dose in corn oil. DBNP was quantified throughout the stratum corneum (SC), epidermis (E) and dermis (D) in punch biopsies collected from treated skin 0.5, 1, 2, 4, 8 and 24 h after application. SC samples were harvested from the treated skin with 20 adhesive discs. E and D were generated from the biopsy using a manual sectioning method. Detectable DBNP concentrations were measured in all skin compartments at all time points investigated. The Cmax of DBNP in SC was 1663 ± 602 µg cm,3, and ,30 and ,300 fold greater than the Cmax for E and D, respectively. Tmax occurred at 1.0, 0.5 and 1.0 in the SC, E and D, respectively. Over a 24 h interval (AUC0,24 h) there was 52 and 520 fold more DBNP in the SC than E and D, respectively. The elimination half-life of DBNP was 11 h from the SC and 9 h from both E and D. Thus, DBNP was quickly absorbed into the outermost layer of skin and established a steep concentration profile through human skin. The data are consistent with the vast majority of DBNP remaining on the surface (77%) or within human skin (15%) in vivo with only 0.2% of the DBNP dose quantified in the systemic blood circulation. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    The effect of surface treatments on the fretting behavior of Ti-6Al-4V alloy

    Matteo Dalmiglio
    Abstract Stem modularity in total hip replacement introduces an additional taper joint between Ti-6Al-4V stem components with the potential for fretting corrosion processes. One possible way to reduce the susceptibility of the Ti-6Al-4V/Ti-6Al-4V interface to fretting is the surface modification of the Ti-6Al-4V alloy. Among the tested, industrially available surface treatments, a combination of two deep anodic spark deposition treatments followed by barrel polishing resulted in a four times lower material release with respect to untreated, machined fretting pad surfaces. The fretting release has been quantified by means of radiotracers introduced in the alloy surface by proton irradiation. In a simple sphere on flat geometry, the semispherical fretting pads were pressed against flat, dog-bone shaped Ti-6Al-4V fatigue samples cyclically loaded at 4 Hz. In this way a cyclic displacement amplitude along the surfaces of 20 ,m has been achieved. A further simplification consisted in the use of deionized water as lubricant. A comparison of the radiotracer results with an electrochemical material characterization after selected treatments by potentiostatic tests of modular stems in 0.9% NaCl at 40°C for 10 days confirmed the benefit of deep anodic spark deposition and subsequent barrel polishing for improving the fretting behavior of Ti-6Al-4V. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source]

    Wear in molded tibial inserts: Knee simulator study of H1900 and GUR1050 polyethylenes

    Riichiro Tsukamoto
    Abstract Hi-fax 1900Ô tibial inserts were used in the IB-1 total knee replacement (TKR) beginning 1978, soon followed by the AGC design. Such direct compression molded (DCM) inserts was relatively immune to oxidation. Unfortunately the Hi-fax 1900Ô resin (H1900) was taken off the market in year 2004. As an alternate, GUR1050 was introduced in the VanguardÔ TKR. However there appeared to be little or no wear comparisons of molded inserts. Therefore the study aim was to compare wear performance of GUR1050 to the historical H1900. The hypothesis was that Hi-fax and GUR1050 would show comparable wear performance. The VanguardÔ was a posterior-cruciate sacrificing design (Biomet Inc.). All tibial inserts were sterilized by gamma-radiation (3.2 Mrad) under argon. A 6-channel, displacement,controlled knee simulator was used with serum lubricant (protein concentration 20 mg/mL). Wear assessments were by gravimetric methods and linear regression techniques. The gross weight-loss trends over 2.5 Mc duration demonstrated excellent linear behavior with good agreement between TKR sets (<±10%). Fluid sorption artifacts in control represented less than 5% of gross wear magnitudes. Thus suitable corrections could be made in determining net wear. The H1900 and GUR1050inserts demonstrated net wear-rates of 3.6 and 3.4 mm3/Mc, respectively. This difference was not found to be statistically significant. This wear study demonstrated that GUR1050 inserts were indistinguishable from the Hi-fax 1900 in terms of laboratory wear performance, proving our hypothesis. Given the excellent clinical history of DCM Hi-fax 1900, the GUR1050 should be an ideal candidate for TKR. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source]

    The antioxidant capacity of saliva

    M. Battino
    Abstract Background/aims: Saliva, a heterogeneous fluid comprising proteins, glycoproteins, electrolytes, small organic molecules and compounds transported from the blood, constantly bathes the teeth and oral mucosa. It acts as a cleansing solution, an ion reservoir, a lubricant and a buffer. In addition to its other host-protective properties, saliva could constitute a first line of defence against free radical-mediated oxidative stress, since the process of mastication and digestion of ingested foods promotes a variety of reactions, including lipid peroxidation. Moreover, during gingival inflammation, gingival crevicular fluid flow increases the change of saliva composition with products from the inflammatory response; this, in turn, could have some rôle in controlling and/or modulating oxidative damages in the oral cavity. This is the reason why the antioxidant capacity of saliva has led to increasing interest, and the development of techniques suitable for saliva antioxidant evaluation. Materials and Methods: Here, we review the current peer-reviewed literature concerning the nature and characteristics of free radicals, reactive oxygen species, oxidants, pro-oxidants and antioxidants in saliva, especially pro-oxidant and antioxidant features, as well as current methods for assessing the antioxidant capacity of saliva. Results and Conclusions: In the last decade, several methods have been developed for assaying the antioxidant activity of saliva, indicating an increasing interest of researchers and clinicians. Unfortunately, systematic studies of saliva are still lacking, even in healthy populations. Zusammenfassung Hintergrund/Zielsetzung: Der Speichel, eine heterogene Flüssigkeit bestehend aus Proteinen, Glykoproteinen, Elektrolyten, kleinen organischen Molekülen und Bestandteilen aus dem Blut, umspült andauernd Zähne und Mundschleimhäute. Er wirkt als Reinigungslösung, Reservoir für Ionen, als Schmiermittel und als Puffer. Zusätzlich zu seinen anderen Abwehreigenschaften könnte der Speichel eine erste Verteidigungslinie gegen durch freie Radikal verursachten oxidativen Stress sein, da der Prozess der Nahrungszerkleinerung und -verdauung eine Vielzahl von Reaktionen auslöst einschließlich der Lipidperoxidation. Darüber hinaus erhöht sich während gingivaler Entzündung der Sulkusflüssigkeitsfluss und verändert die Zusammensetzung des Speichels durch Produkte der Entzündungsreaktion. Dies könnte eine Rolle bei der Kontrolle und/oder Beeinflussung oxidativer Schäden in der Mundhöhle spielen. Dies sind die Gründe dafür, warum die antioxidative Kapazität des Speichels zu einem wachsenden Interesse und zur Entwicklung von Techniken geführt hat, die die Bestimmung der antioxidativen Kapazität des Speichels erlauben. Material und Methoden: In diesem Übersichtsartikel wird die akutelle Literatur hinsichtlich der Natur und Charakteristika freier Radikale, reaktiver Sauerstoffarten, Oxidantien, Prooxidantien und Antioxidantien im Speichel, insbesondere Eigenschaften der Pro- und Antioxidantien sowie aktuelle Methoden zur Bestimmung der antioxidative Kapazität des Speichels, dargestellt. Ergebnisse/Schlussfolgerungen: Während des vergangenen Jahrzehnts wurden mehrere Methoden für die Bestimmung der antioxidativen Kapazität des Speichels entwickelt, was für ein wachsendes wissenschaftliches und klinisches Interesse spricht. Unglücklicherweise fehlen noch systematische Studien zum Speichel selbst für gesunde Kollektive. Résumé Origine/but: La salive, fluide hétérogène constitué de protéines, de glycoprotéines, d'électrolytes, de petites molécules organiques et de composés transportés du sang, baigne constamment les dents et les muqueuses buccales. Elle agit comme une solution nettoyante, comme réservoir d'ions, comme lubrifiant et comme tampon. En plus de ces propriétés protectrices pour l'hôte, la salive pourrait constituer une première ligne de défense contre le stress oxydatif dû aux radicaux libres puisque le processus de mastication et de digestion des nourritures ingérées induit une variété de réactions, telle la peroxidation des lipides. De plus, pendant l'inflammation gingivale, le flux gingival sulculaire augmente et altère la compositon de la salive par les produits de la réponse inflammatoire. Cela, à son tour, pourrait avoir un rôle dans le contrôle ou la modulation des dommages oxydatifs dans la cavité buccale. C'est la raison pour laquelle la capacité antioxydant de la salive a connu un intérêt croissant et le développement de techniques fiables pour l'évaluation des antioxydants salivaires. Matériaux et méthodes: Ici, nous passons en revue de façon concise la littérature actuelle concernant la nature et les caractéristiques des radicaux libres, des espèces réactives à l'oxygène, des oxydants, des pro-oxydants et des antioxydants dans la salive, particulièrement les caractéristiques pro-oxydante et antioxydante et les méthodes actuelles de mise en évidence des capacités antioxydantes de la salive. Résultats et conclusions: Lors de la dernière décade, plusieurs méthodes ont été développées pour tester l'activité antioxydante de la salive, ce qui prouve un intérêt grandissant des chercheurs et des cliniciens. Malheureusement, des études systématiques sur la salive manquent même pour les populations saines. [source]

    Solution theory model for thermophysical properties of refrigerant/lubricant mixtures

    AICHE JOURNAL, Issue 12 2009
    Albeiro Restrepo
    Abstract A general model for predicting the thermophysical properties of refrigerant/lubricant mixtures has been developed based on applicable theory for the excess Gibbs energy of nonideal solutions. In our approach, flexible thermodynamic forms are chosen to describe the properties of both the gas and liquid phases of refrigerant/lubricant mixtures. After an extensive study of models for describing nonideal liquid effects, the Wohl [3]-suffix equations, which have been extensively used in the analysis of hydrocarbon mixtures, have been developed into a general form applicable to mixtures where one component is a polyolester or alkylbenzene lubricant. We have developed a nonideal solution computer code, based on the Wohl model that predicts dew point or bubble point conditions over a wide range of composition and temperature and includes the calculation of the enthalpy and entropy of refrigerant/lubricant mixtures. Our present analysis includes the thermodynamic properties of an ideal solution mixture and the corrections due to nonideal solution behavior. These nonideal solution corrections are based on analysis of the excess Gibbs energy of the mixture. We find that these nonideal solution corrections are small (<4%) for most refrigerant/lubricant mixtures, except at very low temperatures. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

    Occlusal contact area (OCA) wear of two new composite restoratives

    A. U. J. Yap
    The occlusal contact area wear resistance of two new composite restoratives (Z250 and P60) was investigated and compared with two existing materials (Silux and Z100) using a reciprocal compression-sliding test apparatus. Six wear specimens were made for each material and subjected to wear testing at 20 MPa with artificial saliva as lubricant. Wear depth (,m) was measured using profilometry every 20 000 cycles up to 120 000 cycles. Results were analysed using ANOVA/Scheffe's test (P < 0·05) and Pearson's correlation. The effects of cyclic loading on wear and counter-body loss were material dependent. Silux had the lowest wear at all cyclic intervals. At 20 000 and 40 000 cycles, Silux had significantly less wear than all the other composites evaluated, and Z100 had significantly less wear than Z250 and P60. After 60 000 cycles, significant differences in wear was observed only between Silux and the other composites. Correlation between number of cycles and wear/counter-body loss, and between wear and counter-body were significant and positive. The microfilled composite Silux had significantly better OCA wear resistance than the minifilled composites Z100, Z250 and P60. [source]

    The presence and distribution of lubricin in the caprine intervertebral disc

    Kristy M. Shine
    Abstract Lubricin is a large, multifunctional glycoprotein that is known to play a role as a boundary lubricant in diarthrodial joint articulation. The hypothesis of this study was that lubricin is present in the intervertebral disc in a distribution consistent with serving to facilitate interlamellar tribology. The objectives were to: (1) determine the distribution of lubricin in the normal caprine disc; and (2) investigate the synthesis of lubricin by caprine annulus fibrosus (AF) and nucleus pulposus (NP) cells in vitro, using immunohistochemical methods. Caprine lumbar intervertebral discs from five levels and four animals were studied. Positive staining revealed the presence of the lubricin in the outer AF of nearly all samples. No staining was present in the inner AF or the NP. Within the outer AF, lubricin was prominent in the layers separating lamellae and in the extracellular matrix of the lamellae. Some of the AF cells within the lubricin-positive regions demonstrated intracellular lubricin staining, suggesting that these cells may be synthesizing the lubricin protein observed. Immunohistochemistry performed on monolayer cultures of primary AF and NP cells demonstrated intracellular lubricin staining in both cell types. Thus, lubricin is selectively present in the outer caprine intervertebral disc AF, and its distribution suggests that it may play a role in interlamellar tribology. Cells from both the annulus and nucleus were found capable of synthesizing lubricin in vitro, suggesting that these cells may be a potential source of the glycoprotein under some conditions. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1398,1406, 2008 [source]

    Phospholipid composition of articular cartilage boundary lubricant

    A. V. Sarma
    The mechanism of lubrication in normal human joints depends on loading and velocity conditions. Boundary lubrication, a mechanism in which layers of molecules separate opposing surfaces, occurs under severe loading. This study was aimed at characterizing the phospholipid composition of the adsorbed molecular layer on the surface of normal cartilage that performs as a boundary lubricant. The different types of phospholipid adsorbed onto the surface of cartilage were isolated by extraction and identified by chromatography on silica gel paper and mass spectroscopy. The main phospholipid classes identified were quantified by a phosphate assay. Gas chromatography and electrospray ionization mass spectrometry were used to further characterize the fatty acyl chains in each major phospholipid component and to identify the molecular species present. Phosphatidylcholine (41%), phosphatidylethanolamine (27%) and sphingomyelin (32%) were the major components of the lipid layer on the normal cartilage surface. For each lipid type, a mixture of fatty acids was detected, with a higher percentage of unsaturated species compared to saturated species. The most abundant fatty acid observed with all three lipid types was oleic acid (C18:1). Additional work to further quantify the molecular species using electrospray ionization mass spectrometry is recommended. © 2001 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source]

    Functionalization of multiwalled carbon nanotube via surface reversible addition fragmentation chain transfer polymerization and as lubricant additives

    Xiaowei Pei
    Abstract Polymer-grafted multiwalled carbon nanotube (MWCNT) hybrid composite which possess a hard backbone of MWCNT and a soft shell of brush-like polystyrene (PSt) were synthesized. The reversible addition fragmentation chain transfer (RAFT) agents were successfully immobilized onto the surface of MWCNT first, and PSt chains were subsequently grafted from sidewall of MWCNT via RAFT polymerization. Chemical structure of resulting product and the quantities of grafted polymer were determined by Fourier transform infrared, thermal gravimetric analysis, nuclear magnetic resonance, and X-ray photoelectron spectra. Transmission electron microscopy and field emission scanning electron microscopy images clearly indicate that the nanotubes were coated with a polymer layer. Furthermore, the functionalized MWCNT as additives was added to base lubricant and the tribological property of resultant MWCNT lubricant was investigated with four-ball machines. The results indicate that the functionalization led to an improvement in the dispersion of MWCNT and as additives it amended the tribological property of base lubricant. The mechanism of the significant improvements on the tribological properties of the functionalized MWCNT as additives was discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3014,3023, 2008 [source]

    Nonaqueous Aluminum Nitride Extrusion: I, Die-Entry Flow Behavior

    John F. Jr. Wight
    Simultaneous orifice and capillary rheometry at 160°C was used to determine flow parameters of aluminum nitride extrudates plasticized with a polyethylene,mineral-oil binder. Data were analyzed using the Benbow model for square-entry ram extrusion. Variables included the powder concentration, polymer molecular weight and concentration, and lubricant concentration. Die-entry rheology was explained in terms of the mean interparticle separation, polymer spatial requirements, and lubricant adsorption. Particles and polymer were observed to not pack independently. The yield stress of the body increased rapidly as the solids loading approached the critical volume limit of extrudability. An increase in polymer molecular weight or partial decrease of adsorbed lubricant increased the yield stress of the body and produced a satisfactory extrudate. [source]

    Effect of Internal Lubricants on Defects in Compacts Made from Spray-Dried Powders

    Sreeram Balasubramanian
    The role of internal lubricants in the closure of large intergranular pores during dry-pressing was investigated. Alumina was spray-dried with and without an internal lubricant to yield granules with similar characteristics other than lubricant effects. Green and sintered microstructures were evaluated at different compaction pressures. The defects were quantified by evaluating the fracture surface of ,90% dense sintered compacts. The samples that contained an internal lubricant had higher green densities and fewer defects at comparable compaction pressures. The internal lubricant did not cause any significant reduction in green strength or increase in springback. [source]

    Lubrication mechanism of poly(vinyl chloride) compounds: Changes upon PVC fusion (gelation)

    James W. Summers
    Poly(vinyl chloride) (PVC) compounds perform best with adequate metal lubrication and polymer-to-polymer lubrication of PVC primary particle flow units. Much of the mechanism for the lubrication of PVC has been elucidated over the years. One point has not been completely understood, which is the "lubricant failure" at higher processing temperatures where the compound is known to become less ductile. This result is contrary to what might be expected with better PVC fusion (gelation). This article discusses the mechanism involved, which is lubricant inversion, where the lubricant goes from the continuous phase, as a surfactant coating all the PVC primary particle flow units at lower melt temperatures, to become the discontinuous phase at higher melt temperatures. J. VINYL. ADDIT. TECHNOL., 11:57,62, 2005. © 2005 Society of Plastics Engineers [source]

    Improvement of thermooxidative stability of non-edible vegetable oils of Indian origin for biodegradable lubricant application

    P. V. Joseph
    Abstract For environmental reasons, as well as the dwindling source of petroleum, a new class of environmentally acceptable and renewable lubricants based on vegetable oils is available. Even though vegetable oils possess excellent lubricant-related properties, there are some concerns about using it as lubricant base oil. Still, unmodified and modified varieties of soybean, rapeseed, sunflower and canola oils have been in use in the USA and Europe. In India, with the shortage of edible oil, alternate sources of vegetable oils stocks are being explored. With this aim, a comprehensive study has been conducted earlier in the authors' laboratory. In this study, numerous options of non-edible vegetable oil sources were explored, and a few potential vegetable oils were studied in the laboratory. It was found that even though the oils performed much better in comparison with other vegetable oils, it still required improvement in thermooxidative stability. Therefore, in the later part of the study, different options were explored to improve thermooxidative stability. With a background on the initial studies of the authors as described above, the present paper deals with the studies on improvement of these non-edible candidate vegetable oils of Indian origin for lubricant by treating with selected antioxidants for applying them in lubricants. Copyright © 2010 John Wiley & Sons, Ltd. [source]

    Interaction of fomblin® lubricant with surface nitrided and/or coated bearing (M50) steel

    A. K. Rai
    Abstract High-temperature perfluoropolalkylether lubricants including Fomblin® are susceptible to degradation and cause corrosion in the presence of ferrous metals such as M50 bearing steel. This paper describes the effect of surface treatment (nitriding), coating chemistry and architecture in preventing corrosion/oxidation of M50 steel and thermo-oxidative degradation of Fomblin® fluid. Specifically, Cr-CrN multilayered coating architecture was used with and without a nitrided steel surface. The oxidation/corrosion tests were conducted by immersing the nitrided and/or coated M50 coupons in Fomblin® fluid in an oxidative environment at 270°C for 24,h and compared with untreated/uncoated coupons. It is shown that a considerable lessening of the corrosion of the steel and degradation of the Fomblin® fluid can be achieved by nitriding alone. Nitriding in combination with the multilayered Cr-CrN coating exhibited the best protection. The results are discussed in relation to the literature data. Copyright © 2009 John Wiley and Sons, Ltd. [source]

    Tribological performances of heterocyclic-containing ether and/or thioether as additives in the synthetic diester

    Peipei Liang
    Abstract The load-carrying capacity, wear and friction properties of 2-octoxyl methylthio-benzothiazole (DEOY) and 2-dodecylthio methylthio-benzothiazole (DEMB) added to a synthetic lubricant (diester) were evaluated using a four-ball test machine. The results indicate that the two compounds added to the diester possess good load-carrying capacities and excellent anti-wear and friction reduction properties. The thermal stability of the two compounds under nitrogen atmosphere was investigated by thermogravimetric analysis (TGA). It was found that the compounds DEOY and DEMB possess excellent thermal stability. The surface topography of the rubbed surface was investigated with scanning electron microscopy, the elemental chemical nature of the anti-wear films generated on steel counterface were investigated with X-ray photoelectron spectroscopy. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Separation of a sphere from a flat in the presence of couple stress fluids

    Abdallah A. Elsharkawy
    Abstract A mathematical model for couple stress fluid is presented to analyse the separation flow of a fully flooded sphere from a flat under the condition of constant load. Assuming the lubricant between the sphere and the flat to contain additives, the couple stress effect, presented by the characteristic length of the additives, has been considered to account for the non-Newtonian behaviour. In addition, the effect of the sphere inertia on accelerating the separation process has been considered. Compared with the Newtonian fluid case, the results of the numerical solution indicated that the separation time increases with increasing the characteristic length of the additives. It was also found that the additive characteristic length has negligible effect on the thickness of the lubricant film at the separation point. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Experimental investigation of transient and thermal effects on lubricated non-conformal contacts

    R. Bassani
    Abstract In this work, thermal and transient effects on non-conformal lubricated contacts are investigated through experimental analyses. Experiments between a ball and a plane surface of a disc are described. Friction coefficients and film thicknesses are measured (the film thickness only for the glass-on-steel contact). A paraffin base mineral oil is used as a lubricant. First experiments are carried out under steady-state conditions. To include effects due to different thermal properties of contacting materials, a steel-on-steel and a glass-on-steel contact with different slide-to-roll ratios are tested. If the contacting materials have different thermal properties, as in the case of a glass-on-steel contact, thermal effects like the temperature,viscosity wedge action could clearly be shown. It is found that the friction coefficients are influenced by the slide-to-roll ratio and the thermal properties of the contacting materials. Under transient conditions, the entraining velocity is varied with a sinusoidal law. Squeeze effects explain ,loops' of friction and film thickness found also in previous works. The formation of friction loops is related to the measured film thickness differences. However, also under non-steady-state conditions, thermal effects, like the temperature,viscosity wedge action, influence the friction coefficients. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Characterisation of lubricants on ball bearings by FT-IR using an integrating sphere

    K.W. Street
    Abstract Fourier transform-infrared reflectance microspectroscopy has been used extensively for the examination of coatings on non-planar surfaces such as ball bearings. While this technique offers considerable advantages, practical application has many drawbacks, some of which are easily overcome by the use of integrating sphere technology. This paper described the use of an integrating sphere for the quantification of thin layers of lubricant on the surface of ball bearings and the parameters that require optimisation in order to obtain reliable data. Several applications of the technique were discussed including determination of lubricant load on 12.7mm steel ball bearings and the examination of degraded lubricant on post-mortem specimens. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Experimental evaluation of friction between contacting discs for the simulation of gear contact

    J. Kleemola
    Abstract Instant gear contact can be simulated with contacting discs, which provides steady operating conditions and eliminates most of the dynamics and manufacturing tolerances involved in real gears, resulting in an accurately controlled contact condition. A high-pressure twin-disc test device was developed, where loading and rolling velocity can be varied continuously. It is equipped with disc bulk temperature, mean contact resistance and friction moment measurements. The test discs were grinded transversal to the disc rolling direction with proper crowning corresponding to the real gear flank properties. The test device was applied by studying the friction behaviour against the slide-to-roll ratio at different contact pressures, rolling velocities and surface roughness. The measurements were performed using mineral base oil in the range of operation conditions often used in industrial gears. In general, the measured friction coefficient behaviour correlates with earlier published results and is logical with measured bulk temperature and mean contact resistance. The limiting shear stress of the lubricant has an essential role in friction behaviour. Copyright © 2006 John Wiley & Sons, Ltd. [source]