Transport in Stochastic Fibrous Networks

2000 ◽  
Vol 123 (1) ◽  
pp. 12-19 ◽  
Author(s):  
X. Cheng ◽  
A. M. Sastry ◽  
B. E. Layton
Keyword(s):  
Volume Fraction ◽  
High Surface ◽  
High Surface Area ◽  
Statistical Technique ◽  
Porous Structures ◽  
Fibrous Materials ◽  
Aspect Ratios ◽  
And Performance ◽  
2D Network ◽  
Key Questions

Some fundamental issues concerning the design and performance of stochastic porous structures are examined, stemming from application of advanced fibrous electrode substrates in NiMH automotive cells. These electrodes must resist corrosion and local failures under hundreds of charge/discharge cycles. Such fibrous materials can be effectively used as substrates for chemical reactions because of their combinations of high surface area and high conductivity. Key questions concerning the relationships among connectivity and conductivity, scale and variability in material response are addressed. Two techniques are developed and compared for use in predicting these materials’ conductivity. The first approach uses a statistical technique in conjunction with an adaptation of classic micromechanical models. The second approach uses the statistical generation technique, followed by an exact calculation of 2D network conductivity. The two techniques are compared with one another and with classic results. Several important conclusions about the design of these materials are presented, including the importance of use of fibers with aspect ratios greater than at least 50, the weak effect of moderate alignment for unidirectional conductivity, and the weak power-law behavior of conductivity versus volume fraction over the range of possible behaviors.

Mechanical Design of Spicule-Reinforced Connective Tissue: Stiffness

1982 ◽  
Vol 98 (1) ◽  
pp. 239-267
Author(s):  
M.A. R. KOEHL
Keyword(s):  
Surface Area ◽  
Volume Fraction ◽  
High Surface ◽  
High Surface Area ◽  
Local Strain ◽  
High Volume ◽  
Tensile Behaviour ◽  
Connective Tissues ◽  
Aspect Ratios ◽  
Stiffening Effect

Many animals from different phyla have, embedded in their pliable connective tissues, small bits of stiff material known as spicules. The tensile behaviour of spicule-reinforced connective tissues from various cnidarians and sponges, as well as of model spiculated ‘tissues’, is here investigated in order to elucidate the effects on mechanical properties of spicule size and shape, and of their packing density and orientation within a tissue. The main conclusions are: 1. Spicules increase the stiffness of pliable connective tissues probably by mechanisms analogous to those by which filler particles stiffen deformable polymers-local strain amplification, and interference with molecular re-arrangement in response to a load. 2. The greater the volume fraction of spicules, the stiffer the tissue. 3. The greater the surface area of spicules per volume of tissue, the stiffer the tissue. Thus, a given volume of spicules of high surface-area-to-volumeratio (S/V) have a greater stiffening effect than does an equal volume of spicules of low S/V. Furthermore, a high volume fraction of large spicules in a tissue can have the same stiffening effect as a lower volume fraction of smaller spicules. 4. Spicules that are anisometric in shape have a greater stiffening effect parallel to their long axes. 5. Spicules with very high aspect ratios appear to act like reinforcing fibres-stress is transferred by shearing from the pliable matrix to the stiff fibres, which thus bear in tension part of the load on the composite. 6. Spicule-reinforced tissues exhibit stress-softening behaviour, which is more pronounced in heavily spiculated tissues.

scholarly journals Carbon-Based Catalysts for Biodiesel Production—A Review

2020 ◽  
Vol 10 (3) ◽  
pp. 918 ◽  
Author(s):  
Jack Clohessy ◽  
Witold Kwapinski
Keyword(s):  
Heterogeneous Catalysts ◽  
Catalyst Activity ◽  
High Surface ◽  
High Surface Area ◽  
Acid Catalyst ◽  
Biodiesel Production ◽  
Catalyst Characterization ◽  
Synthesis Methods ◽  
And Performance ◽  
Carbon Based

In recent years, a new class of superior heterogeneous acid catalyst for biodiesel production has emerged. These catalysts offer advantages over their predecessors such as high surface area, elevated acid site density, enhanced catalyst activity, good operation stability and relevant economic affordability in an environmentally friendly frame. This review was concerned with carbon-based solid acid (CBAS) catalysts derived from both carbohydrate and pyrolysis products. A series of CBASs with various origins such as D-glucose, sucrose, starch, cellulose and vegetable oil asphalt, converted to char and sulphonated, have been explored as potential heterogeneous catalysts. Catalyst preparation and synthesis methods were briefly summarized. Catalyst characterization and performance for biofuels related reactions were elucidated, identifying potential research applications. Three catalysts in particular were identified as having potential for industrial application and requiring further research.

scholarly journals Synthesis, Characterization and Performance of Low-Cost Unconventional Adsorbents Derived from Waste Materials

2020 ◽  
Vol 10 (6) ◽  
pp. 7243-7256 ◽  
Keyword(s):  
Adsorption Mechanism ◽  
Low Cost ◽  
High Surface ◽  
High Surface Area ◽  
Kinetic Studies ◽  
Maximum Adsorption Capacity ◽  
Batch Experiments ◽  
Adsorbate Concentration ◽  
Optimum Ph ◽  
And Performance

Adsorption of the solute on solid is an equilibrium operation. The nature of adsorbent affects the efficiency of the operation. High surface area per unit volume is the essential attribute of a good adsorbent. Isotherm and kinetic studies are carried out to understand the adsorption mechanism. Many investigators have carried out batch experiments to study the effect of various parameters like initial adsorbate concentration, pH, particle size, and adsorbent dose. The use of adsorbents derived from low-cost materials makes this operation acceptable in industries. Regeneration of adsorbent can reduce the problem of disposal of used adsorbent material. Optimum values of affecting parameters can be determined from batch experiments. The isotherm and kinetic constants can be determined from batch experiments. These investigations give us an idea about the nature of adsorbent, maximum adsorption capacity, the order of adsorption, and optimum pH. This review sheds light on investigations on adsorbents derived from unconventional adsorbents and their characterization and performance evaluation.

Cationic Cellulose Nanocrystals: Synthesis, Characterization and Cytotoxicity Studies

2015 ◽  
Vol 1718 ◽  
pp. 91-96 ◽  
Author(s):  
Rajesh Sunasee ◽  
Usha D. Hemraz ◽  
Karina Ckless ◽  
James S. Burdick ◽  
Yaman Boluk
Keyword(s):  
Cellulose Nanocrystals ◽  
Low Cost ◽  
High Surface ◽  
High Surface Area ◽  
Cationic Polymers ◽  
Mcf7 Cells ◽  
Aspect Ratios ◽  
Cytotoxicity Studies ◽  
Cytotoxicity Effects ◽  
Surface Modified

ABSTRACTCellulose nanocrystals (CNCs) have emerged as a new class of renewable material for various applications due to their remarkable properties and commercialization prospect. The relative low density, expected low cost, non-toxic character, uniform nanosize distribution, high aspect ratios, high surface area, thermal properties and high modulus of elasticity make CNCs attractive nanomaterials that recently prompted the industrial production of CNCs in North America. Surface functionalization of CNCs continues to be an exciting area of research for the design of novel CNC-based materials. In this work, we report the synthesis, characterization and cytotoxicity studies of novel cationic surface modified CNC derivatives. The negative surface of CNC was rendered positive after grafting with cationic polymers via surface-initiated living radical polymerization method. The modified CNCs were characterized by both spectroscopic and microscopic techniques. Their cytotoxicity effects were evaluated using MTT assay in two cell lines such as mouse macrophages (J774.A1) and human breast cancer (MCF7). Preliminary studies indicated that only one of the modified CNCs caused significant decrease in J774.A1 cell viability (50%), at the highest concentration tested (100 µg/mL). However this concentration is well above of what would be applicable for biomedical purposes. MCF7 cells were not affected by any of the cationic CNCs at any concentration. A detailed cytotoxicity study is currently underway to fully understand the interaction of these cationic CNCs with the biological systems for possible bio-inspired applications.

Computational Fluid Dynamics Simulation of a Tubular Aerosol Reactor for Solar Thermal ZnO Decomposition

2007 ◽  
Author(s):  
Christopher Perkins ◽  
Alan W. Weimer
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Surface ◽  
High Surface Area ◽  
Dynamics Simulation ◽  
Base Case ◽  
Reactor Wall ◽  
Conductive Heat ◽  
Sensitive Material ◽  
Aspect Ratios

Computational fluid dynamics simulations were performed to model solar ZnO dissociation in a tubular aerosol reactor at ultra-high temperatures (1900 K–2300 K). Reactor aspect ratios ranged between 0.15 and 0.45, with the smallest ratio base case corresponding to a reactor diameter of .02286 m. Gas flowrates were set such that the Ar:ZnO ratio was greater than 3:1 and the system residence time was below 2 s. The system was found to exhibit highly laminar flow in all cases (Re ∼ 10), but gas velocity profiles did not seriously affect temperature profiles. Particle heating was nearly instantaneous, a result of the high radiation heat flux from the wall. There was essentially no difference between gas and particle temperatures due to the high surface area for conductive heat exchange between the phases. Calculation of ZnO conversion showed that significant conversions (>90%) could be attained for residence times typical of rapid aerosol processing. Particle sizes larger than 1 μm negatively affected conversion, but sizes of 10 μm still gave acceptable conversion levels. Simulation of reaction of product oxygen with the reactor wall showed that a reactor constructed of an oxidation-sensitive material would not be a viable choice for a high temperature solar reactor.

Shape tailored Ni3(NO3)2(OH)4 nano-flakes simulating 3-D bouquet-like structures for supercapacitors: exploring the effect of electrolytes on stability and performance

RSC Advances ◽  
2014 ◽  
Vol 4 (74) ◽  
pp. 39378-39385 ◽  
Author(s):  
Jickson Joseph ◽  
Ranjusha Rajagopalan ◽  
S. S. Anoop ◽  
V. Amruthalakshmi ◽  
Amrutha Ajay ◽  
...  
Keyword(s):  
Surface Area ◽  
Nickel Hydroxide ◽  
High Surface ◽  
High Surface Area ◽  
And Performance ◽  
Supercapacitor Applications

3-D bouquets of nickel hydroxide nitrate were processed into high surface area electrodes for supercapacitor applications.

A Stereolithography-Based Sugar Foaming Method for Porous Strucutre Fabrication

2016 ◽  
Author(s):  
Xuan Song ◽  
Zhuofeng Zhang ◽  
Zeyu Chen ◽  
Yong Chen
Keyword(s):  
Porous Structure ◽  
High Surface ◽  
High Surface Area ◽  
Porous Polymer ◽  
Solid Loading ◽  
Porous Structures ◽  
Large Area ◽  
Foaming Agent ◽  
Stress Transmission ◽  
Limited Accuracy

Porous structure has wide application in industry, thanks to some of its special properties such as low density, low thermal conductivity, high surface area and efficient stress transmission. Both templating and foaming agent methods are used to fabricate porous structures. However, these methods can only produce simple geometries. In recent years, many research studies have been done to use additive manufacturing (AM), e.g. stereolithography (SLA), in the fabrication of porous structure, but the porosity that can be achieved is relatively small due to their limited accuracy in building micro-scale features on a large area. This paper presents a projection based SLA process to fabricate porous polymer structures using sugar as the foaming agent. With a solid loading of 50wt% of the sugar in the resin, the method can achieve a porosity over 50%. This method can be used to increase the porosity achieved by current SLA methods by over 100%.

Inverse Opal Nanoassemblies: Novel Architectures for Gas Sensors The SnO2:Zn Case

2006 ◽  
Vol 915 ◽  
Author(s):  
Alessandra Sutti ◽  
Gianluca Calestani ◽  
Chiara Dionigi ◽  
Camilla Baratto ◽  
Matteo Ferroni ◽  
...  
Keyword(s):  
Gas Sensing ◽  
Electrical Response ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Electrical Characterization ◽  
Inverse Opal ◽  
Porous Structures ◽  
Transmission Electron ◽  
20 Nm

AbstractA novel technique is here presented, based on inverse opal metal oxide structures for the production of high quality macro and meso-porous structures for gas sensing. Taking advantage of a sol-gel templated approach, different mixed semiconducting oxides with high surface area, commonly used in chemical sensing application, were synthesized. In this work we report the comparison between SnO2 and SnO2:Zn. As witnessed by Scanning and Transmission Electron Microscopy (SEM and TEM) analyses and by Powder x-ray Diffraction (PXRD), highly ordered meso-porous structures were formed with oxide crystalline size never exceeding 20 nm. The filled templates, in form of thick films, were bound to allumina substrate with Pt interdigitated contacts and Pt heater, through in situ calcination,in order to perform standard electrical characterization. Pollutant gases like CO and NO2 and methanol, as interfering gas, were used for the targeted electrical gas tests. All samples showed low detection limits towards both reducing and oxidizing species in low temperature measurements. Moreover, the addiction of high molar percentages of Zn(II) affected the behaviour of electrical response improving the selectivity of the proposed system.

EDTA-Directed Synthesis of Highly Active Porous Titania with Bicrystalline Framework

2007 ◽  
Vol 7 (12) ◽  
pp. 4339-4345 ◽  
Author(s):  
Yun Liu ◽  
Chun-Yan Liu ◽  
Zhi-Ying Zhang
Keyword(s):  
Organic Molecules ◽  
High Surface ◽  
Hydrothermal Process ◽  
High Surface Area ◽  
Porous Structures ◽  
Sodium Salts ◽  
Highly Active ◽  
Porous Titania ◽  
Directed Synthesis ◽  
Facile Hydrothermal Process

Porous titania with bicrystalline (anatase and rutile) framework was successfully synthesized by a facile hydrothermal process using inexpensive and nontoxic organic molecules, EDTA (ethylenediamine-tetra-acetic acid) or its sodium salts as a template, which could be removed from porous titania by the extraction with sodium hydroxide aqueous solution and then easily recovered by acidification. XRD investigation suggested that the ratio of anatase to rutile could be readily tuned by employing different sodium salts of EDTA. All of as-prepared porous titania showed higher activities than the commercial photocatalyst P25 for the degradation of methyl orange (MO), because of the high surface area, bicrystalline phase composition and bimodal porous structures.

scholarly journals An Overview of the Design of Chitosan-Based Fiber Composite Materials

2021 ◽  
Vol 5 (6) ◽  
pp. 160
Author(s):  
Chen Xue ◽  
Lee D. Wilson
Keyword(s):  
Composite Materials ◽  
Food Packaging ◽  
Fiber Composite ◽  
High Surface ◽  
High Surface Area ◽  
Fibrous Materials ◽  
Structure Property ◽  
Structure Property Relationships ◽  
Chitosan Composite ◽  
Fiber Composite Materials

Chitosan composite fibrous materials continue to generate significant interest for wastewater treatment, food packaging, and biomedical applications. This relates to the relatively high surface area and porosity of such fibrous chitosan materials that synergize with their unique physicochemical properties. Various methods are involved in the preparation of chitosan composite fibrous materials, which include the modification of the biopolymer that serve to alter the solubility of chitosan, along with post-treatment of the composite materials to improve the water stability or to achieve tailored functional properties. Two promising methods to produce such composite fibrous materials involve freeze-drying and electrospinning. Future developments of such composite fibrous materials demands an understanding of the various modes of preparation and methods of structural characterization of such materials. This review contributes to an understanding of the structure–property relationships of composite fibrous materials that contain chitosan, along with an overview of recent advancements concerning their preparation.

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