Polyimide-Silica Hybrid Aerogels with High Mechanical Strength for Thermal Insulation Applications

2011 ◽  
Vol 1306 ◽  
Author(s):  
Wenting Dong ◽  
Wendell Rhine ◽  
Shannon White
Keyword(s):  
Thermal Conductivity ◽  
High Performance ◽  
Ambient Conditions ◽  
Separation Membranes ◽  
Low Dielectric ◽  
Aging Conditions ◽  
Hybrid Aerogels ◽  
Mechanical Strengths ◽  
The Relationship ◽  
Silica Hybrid

ABSTRACTHigh performance polyimides have been widely investigated as materials with excellent thermal, mechanical, and electronic properties due to their highly rigid structures. Aspen has developed an approach to prepare polyimide aerogels which have applications as low dielectric constant materials, separation membranes, catalyst supports and insulation materials. In this paper, we will discuss the preparation of polyimide-silica hybrid aerogel materials with good mechanical strengths and low thermal conductivities. The polyimide-silica hybrid aerogels were made by a two-step process and the materials were characterized to determine thermal conductivity and compressive strength. Results show that compressive moduli of the polyimide-silica hybrid aerogels increase dramatically with density (power law relationship). Thermal conductivity of the aerogels is dependent on the aging conditions and density, with the lowest value achieved so far being ~12 mW/m-K at ambient conditions. The relationship between aerogel density and surface area, thermal stability, porosity and morphology of the nanostructure of the polyimide-silica hybrid aerogels are also described in this paper.

scholarly journals Experimental Evaluation of the Mechanical Strengths and the Thermal Conductivity of GGBFS and Silica Fume Based Alkali-Activated Concrete

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7717
Author(s):  
Eliana Parcesepe ◽  
Rosa Francesca De Masi ◽  
Carmine Lima ◽  
Gerardo Maria Mauro ◽  
Giuseppe Maddaloni ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Silica Fume ◽  
Raw Materials ◽  
Carbon Dioxide Emission ◽  
Experimental Tests ◽  
Ambient Conditions ◽  
Environmental Aspect ◽  
Mechanical Strengths ◽  
Alkali Activated Concrete ◽  
Alkali Activated

Alkali-activated concrete (AAC) could be a solution to use a cement-less binder and recycled materials for producing concrete reducing the carbon dioxide emission and the demand for raw materials, respectively. In addition to the environmental aspect, AACs can achieve mechanical characteristics higher than those of ordinary Portland concrete (OPC) but also an improvement of the thermal insulation capacity. Despite the positive results available in the scientific literature, the use of AACs in construction practice is still limited mainly due to the absence of codification for the mix design and consequently of specific design rules. In this paper, AAC produced by ground-granulated blast-furnace slag (GGBFS) and silica fume is investigated for the production of structural elements and to discuss the reliability of formulations for evaluating mechanical properties, necessary for structural design. The mechanical strengths (compression strength, tensile strength, flexural strength) are evaluated by experimental tests according to different curing times (7, 14, 28, 90 days) in ambient conditions and the thermal conductivity is measured to understand the effect that the material could have on thermal losses for a sustainable building perspective. The results showed that AAC strengths depend on the curing time and the exposure conditions, and the insulation properties can be improved compared to the traditional Portland cement with the proposed composition.

Porous reaction-sintered AlN tapes for high-performance microelectronics application

2002 ◽  
Vol 17 (2) ◽  
pp. 306-314 ◽  
Author(s):  
F. Y. C. Boey ◽  
A. I. Y. Tok ◽  
W. J. Clegg
Keyword(s):  
Thermal Conductivity ◽  
Dielectric Constant ◽  
High Performance ◽  
Coefficient Of Thermal Expansion ◽  
Linear Trend ◽  
Dielectric Constants ◽  
Sintering Behavior ◽  
Low Dielectric ◽  
Novel Approach ◽  
Controlled Porosity

A novel approach was undertaken in producing porous AlN microelectronics tapes with high thermal conductivity and low dielectric constant. This method involved polymer microspherical powders used as a sacrificial mold to introduce controlled porosity into the green tapes during pyrolysis. The Al2O3-rich porous green tapes were then reaction sintered at 1680 °C for 12 h to create porous AlN tapes. This work builds upon a previously developed novel reaction sintering process that densified and converted Al2O3-rich tapes (Al2O3–20 wt% AlN–5 wt% Y2O3) to AlN tapes at a relatively low sintering temperature of 1680 °C. The sintering behavior of the porous tapes was investigated, and the effects of the microsphere particle size and volume addition were studied. The microspheres successfully contributed to the significant reduction of tape density by porosity, and this contributed to lowering its dielectric constant. Dielectric constants of the AlN tapes were reduced to about 6.8 to 7.7 while thermal conductivity values were reasonable at about 46 to 60 W/mK. Coefficient of thermal expansion (CTE) values showed a linear trend according to phase composition, with the porous AlN tapes exhibiting CTE values of 4.4 × 10−6 to 4.8 × 10−6/°C, showing good CTE compatibility with silicon at 4.0 × 10−6/°C. The added porosity did not significantly affect the CTE values.

scholarly journals Preparation and characterization of polysaccharide - silica hybrid aerogels

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Gabrijela Horvat ◽  
Milica Pantić ◽  
Željko Knez ◽  
Zoran Novak
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Surface Area ◽  
Nitrogen Adsorption ◽  
Silica Aerogels ◽  
Drastic Increase ◽  
Organic Precursors ◽  
Hybrid Aerogels ◽  
Silica Hybrid

Abstract Hybrid aerogels based on polysaccharides - silica were prepared and characterized. Tetramethylorthosilicate (TMOS) was used as inorganic precursor and various polysaccharides (alginate, pectin, xanthan and guar) were used as organic precursors. TMOS was added to polysaccharide aqueous solutions, resulting in stable wet gels. There were no additional chemicals or cross-linkers in the process. Produced wet gels were dried under supercritical conditions with CO2 in order to preserve their structure. The nitrogen adsorption results were compared to pure polysaccharide aerogels, prepared in our previous research. It is shown, that the addition of silica to pectin, xanthan, alginate and guar significantly improved their structural properties, primarily seen in the drastic increase of the surface area. Guar-silica aerogels reached the highest surface area of 679 m2 g−1. The thermal properties, including thermal degradation and thermal conductivity were highly improved. Among the prepared hybrid aerogels, pectin-silica samples had the lowest thermal conductivity of 19 mWm−1 K−1.

scholarly journals Recent progress on the poly(arylene ether)s-based electrospun nanofibers for high-performance applications

2021 ◽  
Author(s):  
Pan Wang ◽  
Xidi Liu ◽  
Dengyu Wang ◽  
Mengxue Wang ◽  
Dawei Zhang ◽  
...  
Keyword(s):  
High Performance ◽  
Volume Ratio ◽  
Electrospun Nanofibers ◽  
Anion Exchange Membranes ◽  
Water Separation ◽  
Separation Membranes ◽  
Low Dielectric ◽  
Arylene Ether ◽  
Engineering Plastics ◽  
Oil Water Separation

Abstract Poly(arylene ether)s (PAEs) engineering plastics are a type of high-performance material which are excellent in thermal resistance, mechanical properties, and have low dielectric constant and anti-corrosion. Over recent decades, PAEs further combined with the electrospinning technology to fabricate as large surface-to-volume ratio and porosity membrane materials for high-performance applications. In this review, progresses of PAEs-based electrospun nanofibers and fiber reinforced composites including proton/anion exchange membranes, oil-water separation membranes, bio-scaffolds and humidity sensors, etc. are presented together with their corresponding high-performance applications in the fields of fuel cell, wastewater treatment, bioengineering and flexible durable sensor. Finally, current challenges and future development directions of PAEs electrospun nanofibers are discussed.

An Experimental Investigation on Thermal Conductivity and Viscosity of Graphene doped CNTs /TiO2 Nanofluid

2020 ◽  
Vol 17 (3) ◽  
Author(s):  
A.M. Zetty Akhtar ◽  
M.M. Rahman ◽  
K. Kadirgama ◽  
M.A. Maleque
Keyword(s):  
Thermal Conductivity ◽  
Zeta Potential ◽  
Base Fluid ◽  
Minimum Quantity Lubrication ◽  
Cutting Fluid ◽  
Cutting Zone ◽  
Observation Method ◽  
The Stability ◽  
The Relationship ◽  
Zeta Potential Analysis

This paper presents the findings of the stability, thermal conductivity and viscosity of CNTs (doped with 10 wt% graphene)- TiO2 hybrid nanofluids under various concentrations. While the usage of cutting fluid in machining operation is necessary for removing the heat generated at the cutting zone, the excessive use of it could lead to environmental and health issue to the operators. Therefore, the minimum quantity lubrication (MQL) to replace the conventional flooding was introduced. The MQL method minimises the usage of cutting fluid as a step to achieve a cleaner environment and sustainable machining. However, the low thermal conductivity of the base fluid in the MQL system caused the insufficient removal of heat generated in the cutting zone. Addition of nanoparticles to the base fluid was then introduced to enhance the performance of cutting fluids. The ethylene glycol used as the base fluid, titanium dioxide (TiO2) and carbon nanotubes (CNTs) nanoparticle mixed to produce nanofluids with concentrations of 0.02 to 0.1 wt.% with an interval of 0.02 wt%. The mixing ratio of TiO2: CNTs was 90:10 and ratio of SDBS (surfactant): CNTs was 10:1. The stability of nanofluid checked using observation method and zeta potential analysis. The thermal conductivity and viscosity of suspension were measured at a temperature range between 30˚C to 70˚C (with increment of 10˚C) to determine the relationship between concentration and temperature on nanofluid’s thermal physical properties. Based on the results obtained, zeta potential value for nanofluid range from -50 to -70 mV indicates a good stability of the suspension. Thermal conductivity of nanofluid increases as an increase of temperature and enhancement ratio is within the range of 1.51 to 4.53 compared to the base fluid. Meanwhile, the viscosity of nanofluid shows decrements with an increase of the temperature remarks significant advantage in pumping power. The developed nanofluid in this study found to be stable with enhanced thermal conductivity and decrease in viscosity, which at once make it possible to be use as nanolubricant in machining operation.

OLIN C197

Alloy Digest ◽  
1999 ◽  
Vol 48 (1) ◽  
Keyword(s):  
Thermal Conductivity ◽  
Wear Resistance ◽  
Physical Properties ◽  
Tensile Properties ◽  
High Performance ◽  
Corrosion And Wear ◽  
Contact Forces ◽  
High Current ◽  
Lower Strength ◽  
Current Carrying Capability

Abstract Olin C197 is a second-generation high performance alloy developed by Olin Brass. It has a strength and bend formability similar to C194 (see Alloy Digest Cu-360, September 1978), but with 25% higher electrical and thermal conductivity. High conductivity allows C197 to replace brasses and bronzes in applications where high current-carrying capability is required. Also, the strength of C197 provides higher contact forces when substituted for many lower strength coppers. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion and wear resistance as well as forming and joining. Filing Code: CU-627. Producer or source: Olin Brass.

Study of Transcrystallization in Polymer Composites

1989 ◽  
Vol 170 ◽  
Author(s):  
Benjamin S. Hsiao ◽  
J. H. Eric
Keyword(s):  
Thermal Conductivity ◽  
Free Energy ◽  
Carbon Fiber ◽  
Plasma Treatment ◽  
Polymer Composites ◽  
High Performance ◽  
Interfacial Strength ◽  
Fiber Surface ◽  
Semicrystalline Polymers ◽  
First Case

AbstractTranscrystallization of semicrystalline polymers, such as PEEK, PEKK and PPS, in high performance composites has been investigated. It is found that PPDT aramid fiber and pitch-based carbon fiber induce a transcrystalline interphase in all three polymers, whereas in PAN-based carbon fiber and glass fiber systems, transcrystallization occurs only under specific circumstances. Epitaxy is used to explain the surface-induced transcrystalline interphase in the first case. In the latter case, transcrystallization is probably not due to epitaxy, but may be attributed to the thermal conductivity mismatch. Plasma treatment on the fiber surface showed a negligible effect on inducing transcrystallization, implying that surface-free energy was not important. A microdebonding test was adopted to evaluate the interfacial strength between the fiber and matrix. Our preliminary results did not reveal any effect on the fiber/matrix interfacial strength of transcrystallinity.

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