168 Matching Results

Search Results

Advanced search parameters have been applied.

Effects of solvents in improving boundary lubrication of steel by silicones

Description: Report presenting a study to establish the effect of solvents on boundary lubrication by silicones. Boundary-lubrication data were obtained which are considered substantiating evidence for a hypothesis that, in solutions of solvents blended with silicones, the silicones form a closely packed and oriented absorbed film on ferrous surfaces. Results regarding room-temperature lubrication experiments, elevated-temperature lubrication experiments, low-temperature physical behavior, and effect of conventional lubrication additive are provided.
Date: September 1952
Creator: Murray, S. F. & Johnson, Robert L.
Partner: UNT Libraries Government Documents Department

Desorption Kinetics of H2O from Cab-O-Sil-M-7D and Hi-Sil-233 Silica Particles

Description: Temperature programmed desorption (TPD) was performed at temperatures up to 850K on Cab-O-Sil-M-7D and Hi-Sil-233 silica particles. Physisorbed water molecules on both types of silica had activation energies in the range of 9-14.5 kcal/mol. However, the activation energies of desorption for chemisorbed water varied from {approx} 19 kcal/mol to > 59 kcal/mol for Cab-O-Sil-M-7D, and {approx} 23-37 kcal/mol for Hi-Sil-233. Our results suggest that physisorbed water can be effectively pumped away at room temperature (or preferably at 320 K) in a matter of hours. Chemisorbed water with high activation energies of desorption (>30 kcal/mol) will not escape the silica surfaces in 100 years even at 320 K, while a significant amount of the chemisorbed water with medium activation energies (19-26 kcal/mol) will leave the silica surfaces in that time span. Most of the chemisorbed water with activation energies < 30 kcal/mol can be pumped away in a matter of days in a good vacuum environment at 500 K. We had previously measured about 0.1-0.4 wt. % of water in M9787 polysiloxane formulations containing {approx} 21% Cab-O-Sil-M-7D and {approx} 4% Hi-Sil-233. Comparing present results with these formulations, we conclude that absorbed H{sub 2}O and Si-OH bonds on the silica surfaces are the major contributors to water outgassing from M97 series silicones.
Date: January 26, 2000
Creator: Dinh, L.; Balooch, M. & LeMay, J.D.
Partner: UNT Libraries Government Documents Department

ESP – Data from Restarted Life Tests of Various Silicone Materials - 2011

Description: Current funding has allowed the restart of testing of various silicone materials placed in Life Tests or Aging Studies from past efforts. Some of these materials have been in test since 1982, with no testing for approximately 10 years, until funding allowed the restart in FY97. This report will provide data on materials used in production and on experimental materials not used in production. Charts for the various materials at different thickness, compression, and temperature combinations illustrate trends for the load-bearing properties of the materials.
Date: December 31, 2011
Creator: Schneider, Jim
Partner: UNT Libraries Government Documents Department

H2O Outgassing from Silicones

Description: In this fiscal year, we have tested the H{sub 2}O outgassing model for TR55 against independent core tests performed at different temperatures by our collaborators at Y12. At higher temperature ({approx} 71 C), the model properly predicts moisture outgassing from TR55 over the entire experiment. At lower temperature ({approx} 42.5 C), the model correctly predicts long-term moisture outgassing. However, in short-term limit, a better fit with core tests might be expected when the diffusion effect of H{sub 2}O through the silicone matrix is included into the model in the near future. A lookup table for the moisture content as well as moisture outgassing kinetics for M9787 which have previously been heated to 460K for one day and then exposed to relevant low levels of moisture is also now available as a reference for engineers/technicians in the fields.
Date: November 9, 2004
Creator: Dinh, L N; Maxwell, R S; Schildbach, M A; Balazs, B & McLean II, W
Partner: UNT Libraries Government Documents Department

A Sythetic Study of a Cyclic Siloxydiyne and its Iron Carbonyl Complex

Description: The synthetic studies include the synthesis of the cyclic siloxydiyne, 3,3,5,5,8,8,10,10-octamethyl-4,9-dioxa-3,5,8,10-tetrasilacyclodeca-1,6- diyne [VI] and its novel iron carbonyl complex. In the preparation of [VI] by HBr promoted condensation of bis (methoxydimethylsilyl) acetylene, a minor product, a cyclic trimer was always formed along with the major product [VI]. No evidence of an equilibrium between the trimerization product and the dimerization product was found. Compound [VI] can react with iron carbonyl reagents to produce a novel binuclear iron complex of trimethylenemethane [VII] in very low yield either in a thermal or photo-reaction. The key step proposed by us in the formation of [VII] is a I,2-silyl shift in a complexed bis (silyl) acetylene to form a vinylidene intermediate. Experiments aimed at isolating this intermediate were not successful.
Date: December 1989
Creator: Chi, Xiang-yong
Partner: UNT Libraries

Desorption Kinetics of H2O, H2, CO, and CO2 from Silica Reinforced Polysiloxane

Description: We performed temperature programmed desorption up to 500K on silica-reinforced polysiloxane in both solid and foamed forms (M9787 and M9750 respectively). Our data show that H{sub 2}O was the dominant desorbing species in both forms of silicone (on the order of 100 {micro}g of physisorbed water and 900 {micro}g of chemisorbed water per gram of polymer), which are expected to be very hydrophilic when dehydrated. Detailed studies of the TPD spectra of H{sub 2}O from the silicones and from the fumed silica fillers suggest that H{sub 2}O molecules preferentially adsorbed on the surface of silica particles contained in the silicones with activation energies of desorption of 15 {+-} 3 kcal/mol and 50 {+-} 10 kcal/mol. There was strong evidence of H{sub 2} desorption below 400K from the silicones. The equivalent concentration of H{sub 2} in the silicones was 0.44 {micro}g of H{sub 2} per gram of silicone. Other species desorbing from the silicones were CO, and CO{sub 2} with concentrations on the order of 2.5 {micro}g, and 1.6 {micro}g per gram of silicone and activation energies of desorption of 10 {+-} 2 kcal/mol and 9.5 {+-} 1.5 kcal/mol, respectively.
Date: August 11, 1999
Creator: Dinh, L. & Balooch, M.
Partner: UNT Libraries Government Documents Department

Diffuse reflectance FTIR of stains on grit blasted metals

Description: Diffuse reflectance mid-infrared Fourier transform (DRIFT) spectroscopy has been applied to the detection of oil contamination on grit-blasted metals. The object of this application is to detect and discriminate between silicone and hydrocarbon oil contamination at levels approaching 10 mg/m{sup 2}. A portable FTIR spectrometer with dedicated diffuse reflectance optics was developed for this purpose. Using translation devices positioned by instructions from the spectrometer operating system, images of macroscopic substrates were produced with millimeter spatial resolution. The pixels that comprise an image are each a full mid-infrared spectrum with excellent signal-to-noise, each determined as individual files and uniquely saved to disc. Reduced spectra amplitudes, based on peak height, area, or other chemometric techniques, mapped as a function of the spatial coordinates of the pixel are used to display the image. This paper demonstrates the application of the technique to the analysis of stains on grit-blasted metals, including the calibration of the method, the inspection of substrates, and the migration of oil contamination.
Date: August 9, 1997
Creator: Powell, G.L.; Hallman, R.L. Jr. & Cox, R.L.
Partner: UNT Libraries Government Documents Department

Fillers and potting compounds. Quarterly report, October--December, 1971

Description: The work this period concentrated on packaging RTV silicone fluids in a commercial purchased package-bag. The samples will be stored for a period of six months at ambient temperature. Because of the rigid film of the Bipax Bag, it is doubtful that this method of packaging silicones will develop into an acceptable process. To enhance this process, a more pliable bag should be incorporated into the packaging system.
Date: December 31, 1972
Creator: Montague, J.L.
Partner: UNT Libraries Government Documents Department

Work of Adhesion Measurements of Silicone Networks Using Contract Mechanics

Description: Work of adhesion (Wa) measurements are being studied for several types of polymer/metal combinations in order to obtain a better understanding of the adhesive failure mechanisms for systems containing encapsulated and bonded components. A primary concern is whether studies of model systems can be extended to systems of technological interest. One study performed in our laboratory involved the determination of Wa between silicone (PDMS) and Al surfaces in order to establish potential adhesive failure mechanisms. Our initial work with PDMS was based on Dow Corning 170 Sylgard. PDMS hemispheres were synthesized following the procedure outlined by Chaudhury and Whitesides where the filler was stripped from the commercial silicone by centrifuging. Wa between PDMS surfaces was determined using the JKR method. Our results for the Wa of PDMS were in agreement with those reported by Chaudhury and Whitesides. However, further JKR studies using these PDMS hemispheres on flat Al surfaces were fraught with difficulty. We could not discriminate hydrogen-bonding effects between Al{sub 2}O{sub 3} and hydroxyl groups in the PDMS and other possible bonding mechanisms. It was suggested that commercial systems contain inhibitors and additives that interfere with understanding the PMDS/Al interface. Therefore, the current study uses pure PDMS networks synthesized in our lab. Also, two contact mechanics methods were deployed to measure the Wa--JKR method using two hemispheres and a LEFM method using a cylinder containing a circumferential crack. This paper contains a description of the synthesis of the PDMS used for these studies and the determination of Wa between PDMS surfaces using the JKR method, contact angle measurements, and a LEFM method that consists of a cylinder containing a circumferential crack.
Date: April 21, 1999
Creator: Benkoski, J.; Emerson, J.A.; Miller, G.V. & Pearson, R.A.
Partner: UNT Libraries Government Documents Department

Evaluation of the metal/adhesive interfaces in the MC2370 fire set

Description: Several analysis methods have been applied to evaluate the structure and composition of the electrode/adhesive interfaces i previously fielded M2370 Fire Sets. A method of interfacial fracture at cryogenic temperatures as been employed to expose regions of these interfaces at multiple levels in a SFE stack. Electron microscopy shows that bond failure induced by the fracture is predominantly adhesive with an equal probability of failure of the Au and Cu interfaces. Some evidence for cohesive, indicative of a possible microstructure related to electrical breakdown. Pinhole-free larger regions of adhesive also exist which may explain the observed high resistance in impedance measurements.
Date: October 1, 1997
Creator: Zavadil, K.R.
Partner: UNT Libraries Government Documents Department

Adhesives, fillers and potting compounds. Second progress report, December 1, 1967--April 1, 1968

Description: Progress in the development program whose immediate purpose is to reduce set time of a silicone compound is described. Data are presented showing that a formulation of a current RTV silicone rubber with dibutyltin diacetate has a profitably lower set time than the same rubber in the present formulation which uses dibutyltin dilaurate, without increase in probability of either reversion or penalty to other weapons components. Time to set sufficiently to allow the next assembly step is 2 to 4 hours, compared to the 16 to 24 hours presently allowed or the 8 to 12 hours minimum attainable with the present formulation. The reduction is of the magnitude set as a goal, the attainment of which would increase production capacity enough to reduce the amount of new construction planned to accommodate weapons assembly programs.
Date: 1968
Creator: Lichte, H. W. & Akst, I. B.
Partner: UNT Libraries Government Documents Department

Assessment of surface contamination with contact mechanics

Description: The authors are particularly interested in the work of adhesion measurements as a means to facilitate the understanding of the adhesive failure mechanisms for systems containing encapsulated and bonded components. Of the several issues under investigation, one is the effect of organic contamination on the adhesive strength for several types of polymer/metal interface combinations. The specific question that the authors are trying to address is at what level of contamination does adhesive strength decrease. The use of contact mechanics, the JKR method, is a good approach for studying this question. Another approach being studied is the use of interracial fracture mechanics. The model contaminant is hexadecane--non-polar, medium molecular weight hydrocarbon fluid. They choose hexadecane because it replicates typical machining fluids, is nonreactive with Al surfaces, and should not dissolve readily into the adhesive systems of interest. The application of a uniform, controllable and reproducible hexadecane layer on Al surfaces has proven to be difficult. A primary concern is whether studies of model systems can be extended to systems of technological interest. The JKR theory is a continuum mechanics model of contact between two solid spheres that was developed by Johnson, Kendall and Roberts. The JKR theory is an extension of Hertzian contact theory and attributes the additional increase in the contact area between a soft elastomeric hemisphere to adhesive forces between the two surfaces. The JKR theory allows a direct estimate of the surface free energy of interface as well as the work of adhesion (Wa) between solids. Early studies performed in this laboratory involved the determination of Wa between silicone (PDMS) and Al surfaces in order to establish the potential adhesive failure mechanisms. However, the JKR studies using commercial based PDMS [poly(dimethylsiloxane)] was fraught with difficulty that were attributed to the additives used in commercial PDMS systems. The authors ...
Date: February 21, 2000
Partner: UNT Libraries Government Documents Department

Investigation of the impact of cleaning on the adhesive bond and the process implications

Description: While surface cleaning is the most common process step in DOE manufacturing operations, the link between a successful adhesive bond and the surface clean performed before adhesion is not well understood. An innovative approach that combines computer modeling expertise, fracture mechanics understanding, and cleaning experience to address how to achieve a good adhesive bond is discussed here to develop a capability that would result in reduced cleaning development time and testing, improved bonds, improved manufacturability, and even an understanding that leads to improved aging. A simulation modeling technique, polymer reference interaction site model applied near wall (Wall PRISM), provided the capability to include contaminants on the surface. Calculations determined an approximately 8% reduction in the work of adhesion for 1% by weight of ethanol contamination on the structure of a silicone adhesive near a surface. The demonstration of repeatable coatings and quantitative analysis of the surface for deposition of controlled amounts of contamination (hexadecane and mineral oil) was based on three deposition methods. The effect of the cleaning process used on interfacial toughness was determined. The measured interfacial toughness of samples with a Brulin cleaned sandblasted aluminum surface was found to be {approximately} 15% greater than that with a TCE cleaned aluminum surface. The sensitivity of measured fracture toughness to various test conditions determined that both interfacial toughness and interface corner toughness depended strongly on surface roughness. The work of adhesion value for silicone/silicone interface was determined by a contact mechanics technique known as the JKR method. Correlation with fracture data has allowed a better understanding between interfacial fracture parameters and surface energy.
Date: May 1, 2000
Partner: UNT Libraries Government Documents Department

Identification of silicone oil/PETN interaction. Quarterly report, January--March 1971

Description: Infrared and UV spectra have been obtained on oils pressed from GE5601 silicone rubber. A method for depositing oil on PETN has also been investigated. In order to determine if the oil was evenly deposited on the PETN, an analytical method was developed for determining the concentration of oil on PETN.
Date: September 1, 1997
Creator: Faubion, B.D.
Partner: UNT Libraries Government Documents Department

Application & testing of high temperature materials for solenoid coils

Description: Sandia National Laboratories has designed and proven-in two new Solenoid coils for a highly-reliable electromechanical switch. Mil-Spec Magnetics Inc., Walnut CA manufactured the coils. The new design utilizes two new materials: Liquid Crystal Polymer (Vectra C130) for the bobbin and Thermal Barrier Silicone (VI-SIL V-658) for the encapsulant. The use of these two new materials solved most of the manufacturing problems inherent in the old Sandia design. The coils are easier to precision wind and more robust for handling, testing, and storage. The coils have some unique weapon related safety requirements. The most severe of these requirements is the 400{degrees}C, 1600 V test. The coils must not, and did not, produce any outgassing products to affect the voltage breakdown between contacts in the switch at these temperatures and voltages. Actual coils in switches were tested under these conditions. This paper covers the prove-in of this new coil design.
Date: August 1, 1997
Creator: Sanchez, R.O.; Archer, W.E. & Zich, J.L.
Partner: UNT Libraries Government Documents Department

Crystallization Behavior of M97 Series Silicone Cushions

Description: M97 series siloxanes are poly(dimethyl-diphenyl) siloxanes that are reinforced through a mixture of precipitated and fumed silica fillers which are blended in through the addition of a short chain polydimethylsiloxane processing aid. M97 silicones exhibit crystallization at -80.25 C by thermal (modulated differential scanning calorimetry) and mechanical (dynamic mechanical analysis) techniques. Isothermal dynamic mechanical analysis experiments illustrated that crystallization occurred over a 1.8 hour period in silica-filled systems and 2.8 hours in unfilled systems. The onset of crystallization typically occurred after a 30 minute incubation/nucleation period. {gamma}-radiation caused the crystallization rate to decrease proportionally with dosage, but did not decrease the amount of crystallization that ultimately occurred. Irradiation in vacuum resulted in slower overall crystallization rates compared to air irradiation due to increased crosslinking of the polymer matrix under vacuum. Modulated differential scanning calorimetry contrasted the crystallization and melting behavior of pure PDMS versus the M97 base polymer and helped determine which component of the composite was the origin of the crystallization phenomena.
Date: September 7, 2000
Creator: Chien, A.; DeTeresa, S.; Cohenour, R.; Schnieder, J.; LeMay, J. & Balazs, B.
Partner: UNT Libraries Government Documents Department

Bridged polysilsesquioxane xerogels: A molecular based approach for the preparation of porous hybrid organic-inorganic materials

Description: Bridged polysilsesquioxanes represent an interesting family of hybrid organic-inorganic composite materials. It has been shown that manipulation of the organic bridging component offers the potential for the synthesis of a variety of materials with a range of surface areas and porosities. In addition, incorporation of a heteroatom within the bridging organic component allows for further chemical transformation of the polysilsesquioxane material.
Date: June 1, 1995
Creator: Small, J.H.; Shea, K.J. & Loy, D.A.
Partner: UNT Libraries Government Documents Department

Commercial synthesis of M97KVB gum, a precursor to cellular silicone cushions. Part I

Description: The technology for producing an LLNL-developed polymer, L97KVB, has been transferred to a commercial speciality silicones manufacturer, McGhan-NuSil Corporation. Workers there have demonstrated both on a small scale and on a 200 lb. scale that they can produce a polymer which meets our analytical specifications and which will also perform satisfactorily in our load deflection and compression set tests.
Date: May 14, 1982
Creator: Riley, M.O.; Kolb, J.R. & Jessop, E.S.
Partner: UNT Libraries Government Documents Department

Evaluation Of Automated Low-Field Nuclear Magnetic Resonance (NMR) Relaxometry For Analysis Of Silicone Polymers

Description: Screening studies and Design of Experiments (DoE) were performed to evaluate measurement variation of a new, non-destructive Nuclear Magnetic Resonance (NMR) test system designed to assess age-induced degradation of Outer Pressure Pads (OPP). The test method and results from 54,275 measurements are described. A reduction in measurement error was obtained after metal support struts were replaced with plastic support struts adjacent to the front position of the test chamber. However, remaining interference and a lack of detecting any age-related degradation prevent the use of the NMR system as a non-destructive surveillance test for OPPs. A cursory evaluation of the system with cellular silicone samples obtained more uniform results with increased error as measurements approached the sample’s edge.
Date: October 2, 2009
Creator: Wilson, M. H.
Partner: UNT Libraries Government Documents Department

Synthesis and characterization of a new silicone multiblock polymer

Description: The Lawrence Livermore National Laboratory (LLNL) has an active interest in the synthesis of new polysiloxanes as base polymers for cellular silicone materials. These elastomers have properties uniquely suited to very specific engineering requirements. While the polymers which we have prepared via random equilibrium of various cyclic tetrasiloxanes have adequate properties for certain applications, there is evidence to suggest that alternating block polysiloxanes prepared via condensation-polymerization techniques have properties more suited to our end uses as flexible foam materials (cushions). The synthetic sequence developed to prepare these materials involves reactions of functionally terminated (silylamino and silanol) polysiloxane oligomers to produce alternating multiblock (ABAB...) materials of high molecular weight. Dialkylamines are condensation byproducts in this reaction. The analysis and characterization of these multiblock polymers is reported.
Date: May 10, 1982
Creator: Riley, M.O.; Kolb, J.R. & Jessop, E.S.
Partner: UNT Libraries Government Documents Department