scholarly journals Transport Properties of One-Step Compression Molded Epoxy Nanocomposite Foams

Polymers ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 756 ◽  
Author(s):  
Mario Martin-Gallego ◽  
Emil Lopez-Hernandez ◽  
Javier Pinto ◽  
Miguel A. Rodriguez-Perez ◽  
Miguel A. Lopez-Manchado ◽  
...  
Keyword(s):  
Transport Properties ◽  
High Strength ◽  
Single Step ◽  
Environmental Stability ◽  
Syntactic Foams ◽  
Molding Process ◽  
Polymeric Microspheres ◽  
Nanocomposite Foams ◽  
One Step ◽  
Strength And Stiffness

Owing to their high strength and stiffness, thermal and environmental stability, lower shrinkage, and water resistance, epoxy resins have been the preferred matrix for the development of syntactic foams using hollow glass microspheres. Although these foams are exploited in multiple applications, one of their issues is the possibility of breakage of the glass hollow microspheres during processing. Here, we present a straightforward and single-step foaming protocol using expandable polymeric microspheres based on the well-established compression molding process. We demonstrate the viability of the protocol producing two sets of nanocomposite foams filled with carbon-based nanoparticles with improved transport properties.

scholarly journals 2D Rigid Benzoxazole-Linked Covalent Organic Framework Films with High-Strength, High-Modulus Mechanical Behavior

2020 ◽  
Author(s):  
Kristen Miller ◽  
Lawrence B. Alemany ◽  
Edwin L. Thomas ◽  
Eilaf Egap
Keyword(s):  
Mechanical Properties ◽  
High Strength ◽  
Single Step ◽  
Two Dimensions ◽  
Free Standing ◽  
Step Process ◽  
Axial Tensile ◽  
Solution Cast ◽  
One Step ◽  
Rigid Rod

<p>Two-dimensional (2D) benzoxazole-linked covalent organic frameworks (COFs) provide an opportunity to incorporate the strength and modulus of corresponding 1D rigid-rod polymers into multiple directions by extending covalent bonding into two dimensions while simultaneously reducing density. Thus far, this potential has been elusive because of the challenge of producing high-quality COF films, particularly those with irreversible, rigid benzazole linkages. The majority of COF syntheses use a single-step process approach where polymerization occurs faster than crystallization and typically result in a poorly ordered and insoluble powder. Here, we present a one-step synthesis and two-step process that allows the deposition of a uniform intermediate film via reversible, non-covalent interactions. This network then undergoes an annealing step that facilitates the irreversible conversion to 2D covalently-bonded polymer product. The resulting films are semi-crystalline with platelet-like crystals embedded in an amorphous matrix with sharp crystal-amorphous interfaces. By this approach, we achieve free-standing films for which we demonstrate the first example of mechanical testing of benzazole-linked COFs. These initial films have promising mechanical properties with an in-plane ultimate tensile strength of nearly 50 MPa and axial tensile and transverse compressive elastic moduli on the scale of several GPa. These mechanical properties already rival the performance of solution-cast films of 1D polybenzoxazole (PBO).<i></i></p>

scholarly journals 2D Rigid Benzoxazole-Linked Covalent Organic Framework Films with High-Strength, High-Modulus Mechanical Behavior

2020 ◽  
Author(s):  
Kristen Miller ◽  
Lawrence B. Alemany ◽  
Edwin L. Thomas ◽  
Eilaf Egap
Keyword(s):  
Mechanical Properties ◽  
High Strength ◽  
Single Step ◽  
Two Dimensions ◽  
Free Standing ◽  
Step Process ◽  
Axial Tensile ◽  
Solution Cast ◽  
One Step ◽  
Rigid Rod

<p>Two-dimensional (2D) benzoxazole-linked covalent organic frameworks (COFs) provide an opportunity to incorporate the strength and modulus of corresponding 1D rigid-rod polymers into multiple directions by extending covalent bonding into two dimensions while simultaneously reducing density. Thus far, this potential has been elusive because of the challenge of producing high-quality COF films, particularly those with irreversible, rigid benzazole linkages. The majority of COF syntheses use a single-step process approach where polymerization occurs faster than crystallization and typically result in a poorly ordered and insoluble powder. Here, we present a one-step synthesis and two-step process that allows the deposition of a uniform intermediate film via reversible, non-covalent interactions. This network then undergoes an annealing step that facilitates the irreversible conversion to 2D covalently-bonded polymer product. The resulting films are semi-crystalline with platelet-like crystals embedded in an amorphous matrix with sharp crystal-amorphous interfaces. By this approach, we achieve free-standing films for which we demonstrate the first example of mechanical testing of benzazole-linked COFs. These initial films have promising mechanical properties with an in-plane ultimate tensile strength of nearly 50 MPa and axial tensile and transverse compressive elastic moduli on the scale of several GPa. These mechanical properties already rival the performance of solution-cast films of 1D polybenzoxazole (PBO).<i></i></p>

Physical, Chemical, and Crystallographic Characterization of Anodic Coatings on High Strength Aluminum Base Alloys

1976 ◽  
Vol 34 ◽  
pp. 636-637
Author(s):  
R. E. Herfert ◽  
N. T. McDevitt
Keyword(s):  
Sulfuric Acid ◽  
Salt Spray ◽  
High Strength ◽  
Environmental Stability ◽  
Anodic Films ◽  
Sodium Dichromate ◽  
Corrosion Resistant ◽  
Aerospace Applications ◽  
Bond Strengths ◽  
Adhesive Bonded Joints

Durability of adhesive bonded joints in moisture and salt spray environments is essential to USAF aircraft. Structural bonding technology for aerospace applications has depended for many years on the preparation of aluminum surfaces by a sulfuric acid/sodium dichromate (FPL etch) treatment. Recently, specific thin film anodizing techniques, phosphoric acid, and chromic acid anodizing have been developed which not only provide good initial bond strengths but vastly improved environmental durability. These thin anodic films are in contrast to the commonly used thick anodic films such as the sulfuric acid or "hard" sulfuric acid anodic films which are highly corrosion resistant in themselves, but which do not provide good initial bond strengths, particularly in low temperature peel.The objective of this study was to determine the characteristics of anodic films on aluminum alloys that make them corrosion resistant. The chemical composition, physical morphology and structure, and mechanical properties of the thin oxide films were to be defined and correlated with the environmental stability of these surfaces in humidity and salt spray. It is anticipated that anodic film characteristics and corrosion resistance will vary with the anodizing processing conditions.

Synthesis of Polycycles and Oxacycles by Tandem Metathesis of endo–norbornene Derivatives

Synthesis ◽  
2021 ◽  
Author(s):  
Sambasivarao Kotha ◽  
Sunil Pulletikurti ◽  
Ambareen Fatma ◽  
gopal dhangar ◽  
gonna somu Naidu
Keyword(s):  
Natural Products ◽  
Metal Complex ◽  
Carbonyl Group ◽  
Single Step ◽  
Time Dependent ◽  
Computational Studies ◽  
Nmr Studies ◽  
Tricyclic Compounds ◽  
One Step ◽  
Norbornene Derivatives

Here, we have demonstrated that the presence of a carbonyl group at C7 position is preventing the olefin metathesis of endo-norbornene derivatives due to the complexation of the metal alkylidene. Time-dependent NMR studies showed the presence of new proton signals in the metal alkylidene region, which indicate the formation of metal complex with the carbonyl group of the substrate. These observations were further proved by ESI-MS analysis. Whereas, computational studies provided that the catalyst was interacting with the C7 carbonyl group and aligned perpendicular to that of norbornene olefin. Later, these endo-keto norbornene derivatives were reduced to hydroxyl derivatives diastereoselectively. Ring-rearrangement metathesis (RRM) of these hydroxyl derivatives, produced the [6/5/6], and [5/6/5] carbo-tricyclic cores of the natural products in one step. Whereas the RRM of O-allyl derivatives, delivered the oxa-tricyclic compounds in a single step with excellent yields.

scholarly journals Single Step 2-Port Device De-Embedding Algorithm for Fixture-DUT-Fixture Network Assembly

Electronics ◽  
2021 ◽  
Vol 10 (11) ◽  
pp. 1275
Author(s):  
Simone Scafati ◽  
Enza Pellegrino ◽  
Francesco de Paulis ◽  
Carlo Olivieri ◽  
James Drewniak ◽  
...  
Keyword(s):  
Standard Technique ◽  
Single Step ◽  
Scattering Parameters ◽  
Linear Set ◽  
S Parameter ◽  
Parameter Conversion ◽  
Before And After ◽  
One Step ◽  
Typical Measurement

The de-embedding of measurement fixtures is relevant for an accurate experimental characterization of radio frequency and digital electronic devices. The standard technique consists in removing the effects of the measurement fixtures by the calculation of the transfer scattering parameters (T-parameters) from the available measured (or simulated) global scattering parameters (S-parameters). The standard de-embedding is achieved by a multiple steps process, involving the S-to-T and subsequent T-to-S parameter conversion. In a typical measurement setup, two fixtures are usually placed before and after the device under test (DUT) allowing the connection of the device to the calibrated vector network analyzer coaxial ports. An alternative method is proposed in this paper: it is based on the newly developed multi-network cascading algorithm. The matrices involved in the fixture-DUT-fixture cascading gives rise to a non-linear set of equations that is in one step analytically solved in closed form, obtaining a unique solution. The method is shown to be effective and at least as accurate as the standard multi-step de-embedding one.

Low-temperature processed inorganic perovskites for flexible detectors with a broadband photoresponse

Nanoscale ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 2871-2877 ◽  
Author(s):  
Ting Zhang ◽  
Feng Wang ◽  
Peng Zhang ◽  
Yafei Wang ◽  
Hao Chen ◽  
...  
Keyword(s):  
Low Temperature ◽  
Visible Light ◽  
Environmental Stability ◽  
Step Method ◽  
Broadband Spectrum ◽  
One Step ◽  
Spectrum Response

The flexible perovskite photodetector, fabricated by a modified one-step method, showed a broadband spectrum response from blind ultraviolet to visible light, and exhibited excellent mechanical flexibility and improved environmental stability.

scholarly journals Materials for Automotive Lightweighting

2019 ◽  
Vol 49 (1) ◽  
pp. 327-359 ◽  
Author(s):  
Alan Taub ◽  
Emmanuel De Moor ◽  
Alan Luo ◽  
David K. Matlock ◽  
John G. Speer ◽  
...  
Keyword(s):  
Galvanic Corrosion ◽  
Low Carbon Steel ◽  
High Strength Steels ◽  
High Strength ◽  
Low Carbon ◽  
New Materials ◽  
Specific Strength ◽  
Advanced High Strength Steels ◽  
Strength And Stiffness ◽  
The Cost

Reducing the weight of automobiles is a major contributor to increased fuel economy. The baseline materials for vehicle construction, low-carbon steel and cast iron, are being replaced by materials with higher specific strength and stiffness: advanced high-strength steels, aluminum, magnesium, and polymer composites. The key challenge is to reduce the cost of manufacturing structures with these new materials. Maximizing the weight reduction requires optimized designs utilizing multimaterials in various forms. This use of mixed materials presents additional challenges in joining and preventing galvanic corrosion.

scholarly journals Computational and experimental investigations of one-step conversion of poly(carbonate)s into value-added poly(aryl ether sulfone)s

2016 ◽  
Vol 113 (28) ◽  
pp. 7722-7726 ◽  
Author(s):  
Gavin O. Jones ◽  
Alexander Yuen ◽  
Rudy J. Wojtecki ◽  
James L. Hedrick ◽  
Jeannette M. García
Keyword(s):  
High Performance ◽  
Density Functional ◽  
Value Added ◽  
Single Step ◽  
Nucleophilic Attack ◽  
Experimental Investigations ◽  
Aryl Ether ◽  
One Step ◽  
Poly Carbonate

It is estimated that ∼2.7 million tons poly(carbonate)s (PCs) are produced annually worldwide. In 2008, retailers pulled products from store shelves after reports of bisphenol A (BPA) leaching from baby bottles, reusable drink bottles, and other retail products. Since PCs are not typically recycled, a need for the repurposing of the PC waste has arisen. We report the one-step synthesis of poly(aryl ether sulfone)s (PSUs) from the depolymerization of PCs and in situ polycondensation with bis(aryl fluorides) in the presence of carbonate salts. PSUs are high-performance engineering thermoplastics that are commonly used for reverse osmosis and water purification membranes, medical equipment, as well as high temperature applications. PSUs generated through this cascade approach were isolated in high purity and yield with the expected thermal properties and represent a procedure for direct conversion of one class of polymer to another in a single step. Computational investigations performed with density functional theory predict that the carbonate salt plays two important catalytic roles in this reaction: it decomposes the PCs by nucleophilic attack, and in the subsequent polyether formation process, it promotes the reaction of phenolate dimers formed in situ with the aryl fluorides present. We envision repurposing poly(BPA carbonate) for the production of value-added polymers.

Recent Advances in Development and Processing of Titanium Aluminide Alloys

2000 ◽  
Vol 646 ◽  
Author(s):  
Fritz Appel ◽  
Helmut Clemens ◽  
Michael Oehring
Keyword(s):  
High Temperature ◽  
Titanium Aluminide ◽  
Titanium Aluminides ◽  
Environmental Stability ◽  
Physical Metallurgy ◽  
Specific Strength ◽  
Wide Range ◽  
Structural Applications ◽  
Strength And Stiffness ◽  
Nickel Base

ABSTRACTIntermetallic titanium aluminides are one of the few classes of emerging materials that have the potential to be used in demanding high-temperature structural applications whenever specific strength and stiffness are of major concern. However, in order to effectively replace the heavier nickel-base superalloys currently in use, titanium aluminides must combine a wide range of mechanical property capabilities. Advanced alloy designs are tailored for strength, toughness, creep resistance, and environmental stability. Some of these concerns are addressed in the present paper through specific comments on the physical metallurgy and technology of gamma TiAl-base alloys. Particular emphasis is placed on recent developments of TiAl alloys with enhanced high-temperature capability.

Effects of finite-rate chemistry and detailed transport on the instability of jet diffusion flames

2014 ◽  
Vol 745 ◽  
pp. 647-681 ◽  
Author(s):  
Yee Chee See ◽  
Matthias Ihme
Keyword(s):  
Transport Properties ◽  
Diffusion Flames ◽  
Diffusive Transport ◽  
Mean Flow ◽  
Stability Behaviour ◽  
Jet Diffusion Flames ◽  
One Step ◽  
The Mean ◽  
Modelling Assumptions ◽  
The Stability

AbstractLocal linear stability analysis has been shown to provide valuable information about the response of jet diffusion flames to flow-field perturbations. However, this analysis commonly relies on several modelling assumptions about the mean flow prescription, the thermo-viscous-diffusive transport properties, and the complexity and representation of the chemical reaction mechanisms. In this work, the effects of these modelling assumptions on the stability behaviour of a jet diffusion flame are systematically investigated. A flamelet formulation is combined with linear stability theory to fully account for the effects of complex transport properties and the detailed reaction chemistry on the perturbation dynamics. The model is applied to a methane–air jet diffusion flame that was experimentally investigated by Füriet al.(Proc. Combust. Inst., vol. 29, 2002, pp. 1653–1661). Detailed simulations are performed to obtain mean flow quantities, about which the stability analysis is performed. Simulation results show that the growth rate of the inviscid instability mode is insensitive to the representation of the transport properties at low frequencies, and exhibits a stronger dependence on the mean flow representation. The effects of the complexity of the reaction chemistry on the stability behaviour are investigated in the context of an adiabatic jet flame configuration. Comparisons with a detailed chemical-kinetics model show that the use of a one-step chemistry representation in combination with a simplified viscous-diffusive transport model can affect the mean flow representation and heat release location, thereby modifying the instability behaviour. This is attributed to the shift in the flame structure predicted by the one-step chemistry model, and is further exacerbated by the representation of the transport properties. A pinch-point analysis is performed to investigate the stability behaviour; it is shown that the shear-layer instability is convectively unstable, while the outer buoyancy-driven instability mode transitions from absolutely to convectively unstable in the nozzle near field, and this transition point is dependent on the Froude number.

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