Low-density graphene/carbon composite aerogels prepared at ambient pressure with high mechanical strength and low thermal conductivity

RSC Advances ◽  
2015 ◽  
Vol 5 (7) ◽  
pp. 5197-5204 ◽  
Author(s):  
Kang Guo ◽  
Zijun Hu ◽  
Huaihe Song ◽  
Xian Du ◽  
Liang Zhong ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Mechanical Strength ◽  
Compression Strength ◽  
Ambient Pressure ◽  
Carbon Matrix ◽  
Carbon Composite ◽  
Low Density ◽  
High Mechanical Strength ◽  
Low Thermal Conductivity ◽  
Composite Aerogels

SEM and TEM pictures show that GNSs can be well-dispersed in a carbon matrix. The resultant composite CAs exhibited high compression strength and extremely low thermal conductivity of 0.028 W m−1 K−1.

scholarly journals Mechanically Strong, Low Thermal Conductivity and Improved Thermal Stability Polyvinyl Alcohol–Graphene–Nanocellulose Aerogel

Gels ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 170
Author(s):  
Xiuya Wang ◽  
Pengbo Xie ◽  
Ke Wan ◽  
Yuanyuan Miao ◽  
Zhenbo Liu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Thermal Stability ◽  
Polyvinyl Alcohol ◽  
Low Density ◽  
Composite Aerogel ◽  
Ternary Composite ◽  
Low Thermal Conductivity ◽  
Good Thermal Stability ◽  
Composite Aerogels

Porous aerogel materials have advantages of a low density, low thermal conductivity and high porosity, and they have broad application prospects in heat insulation and building energy conservation. However, aerogel materials usually exhibit poor mechanical properties. Single-component aerogels are less likely to possess a good thermal stability and mechanical properties. It is necessary to prepare multiple-composite aerogels by reinforcement to meet practical application needs. In this experiment, a simple preparation method for polyvinyl alcohol (PVA)–graphene (GA)–nanocellulose (CNF) ternary composite aerogels was proposed. This is also the first time to prepare ternary composite aerogels by mixing graphene, nanocellulose and polyvinyl alcohol. A GA–CNF hydrogel was prepared by a one-step hydrothermal method, and soaked in PVA solution for 48 h to obtain a PVA–GA–CNF hydrogel. PVA–GA–CNF aerogels were prepared by freeze drying. The ternary composite aerogel has advantages of excellent mechanical properties, a low thermal conductivity and an improved thermal stability, because strong hydrogen bonds form between the PVA, GA and CNF. The composite aerogels were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffractometry, Brunauer–Emmett–Teller analysis, dynamic thermal analysis, thermogravimetry and thermal constant analysis to characterize the properties of the ternary composite aerogels. The lightweight, low-density and porous PVA–GA–CNF composite aerogels withstood 628 times their mass. The thermal conductivity of the composite aerogels was 0.044 ± 0.005 W/mK at room temperature and 0.045 ± 0.005 W/mK at 70 °C. This solid, low thermal conductivity and good thermal stability PVA–GA–CNF ternary composite aerogel has potential application in thermal insulation.

scholarly journals Robust Silica–Polyimide Aerogel Blanket for Water-Proof and Flame-Retardant Self-Floating Artificial Island

2021 ◽  
Vol 8 ◽  
Author(s):  
Riyong Liu ◽  
Jin Wang ◽  
Jianhe Liao ◽  
Xuetong Zhang
Keyword(s):  
Thermal Conductivity ◽  
Flame Retardant ◽  
Silica Aerogel ◽  
Ambient Pressure ◽  
Sol Gel ◽  
Three Dimensional ◽  
Ambient Pressure Drying ◽  
Low Density ◽  
Low Thermal Conductivity ◽  
Sol Gel Transition

A robust silica–polyimide (PI) aerogel blanket is designed and synthesized using the PI foam as the matrix and silica aerogel as the filler through an in situ method, where sol–gel transition of silica precursor occurs in pores of the PI foam, followed by the hydrophobization and ambient pressure drying. The density of the aerogel blanket ranges from 0.036 to 0.196 g/cm3, and the low density is directly controlled by tailoring the silica concentration. The specific surface area of the aerogel blanket reaches 728 m2/g. These features of the blanket result in a low thermal conductivity of 0.018 W/mK, which shows a remarkable reduction of 59% compared to that of the PI foam (0.044 W/mK). As a result, a remarkable decrease of 138°C is achieved using the silica blanket as the thermal insulator on a hot plate of approximately 250°C. In addition, the temperature degradation of the blanket is around 500°C, and up to 86% of mass remaining at 900°C is obtained. The blanket is resistant at extremely harsh conditions, e.g., 600°C for 30 min and 1,300°C for 1 min, and no open flame is observed, suggesting a significant flame-retardant of the blanket. Owing to the three-dimensional (3D) porous framework of the PI foam, the silica aerogel is encapsulated in the PI foam and the blanket exhibits strong mechanical property. The silica–PI aerogel can be reversibly compressed for 50 cycles without reduction of strain. The contact angle of the blanket is 153°, which shows a superior waterproof property. Combining with the low density, low thermal conductivity, flame-retardant, and strong mechanical strength, the aerogel blanket has the potential as an artificial island, which is safe (waterproof and flame-retardant), lightweight, comfortable, and easy to be moved.

scholarly journals Study of the Turning Nickel Base Alloy Pyromet® 31V (SAE HEV8)

2011 ◽  
Vol 278 ◽  
pp. 312-320 ◽  
Author(s):  
Marcos Valério Ribeiro ◽  
André Luís Habib Bahia
Keyword(s):  
Thermal Conductivity ◽  
Mechanical Strength ◽  
High Temperatures ◽  
Base Alloy ◽  
Production Costs ◽  
Machining Parameters ◽  
Nickel Base Alloy ◽  
Low Thermal Conductivity ◽  
Nickel Base ◽  
Coated Carbide

Considering the constant technological developments in the aeronautical, space, automotive, shipbuilding, nuclear and petrochemical fields, among others, the use of materials with high strength mechanical capabilities at high temperatures has been increasingly used. Among the materials that meet the mechanical strength and corrosion properties at temperatures around 815 °C one can find the nickel base alloy Pyromet® 31V (SAE HEV8). This alloy is commonly applied in the manufacturing of high power diesel engines exhaust valves where it is required high resistance to sulphide, corrosion and good resistance to creep. However, due to its high mechanical strength and low thermal conductivity its machinability is made difficult, creating major challenges in the analysis of the best combinations among machining parameters and cutting tools to be used. Its low thermal conductivity results in a concentration of heat at high temperatures in the interfaces of workpiece-tool and tool-chip, consequently accelerating the tools wearing and increasing production costs. This work aimed to study the machinability, using the carbide coated and uncoated tools, of the hot-rolled Pyromet® 31V alloy with hardness between 41.5 and 42.5 HRC. The nickel base alloy used consists essentially of the following components: 56.5% Ni, 22.5% Cr, 2,2% Ti, 0,04% C, 1,2% Al, 0.85% Nb and the rest of iron. Through the turning of this alloy we able to analyze the working mechanisms of wear on tools and evaluate the roughness provided on the cutting parameters used. The tests were performed on a CNC lathe machine using the coated carbide tool TNMG 160408-23 Class 1005 (ISO S15) and uncoated tools TNMG 160408-23 Class H13A (ISO S15). Cutting fluid was used so abundantly and cutting speeds were fixed in 75 and 90 m/min. to feed rates that ranged from 0.12, 0.15, 0.18 and 0.21 mm/rev. and cutting depth of 0.8mm. The results of the comparison between uncoated tools and coated ones presented a machined length of just 30% to the first in relation to the performance of the second. The coated tools has obtained its best result for both 75 and 90 m/min. with feed rate of 0.15 mm/rev. unlike the uncoated tool which obtained its better results to 0.12 mm/rev.

scholarly journals Silica Aerogel Monoliths Derived from Silica Hydrosol with Various Surfactants

Molecules ◽  
2018 ◽  
Vol 23 (12) ◽  
pp. 3192 ◽  
Author(s):  
Dong Chen ◽  
Xiaodong Wang ◽  
Wenhui Ding ◽  
Wenbing Zou ◽  
Qiong Zhu ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Stability ◽  
Silica Aerogel ◽  
Low Cost ◽  
Ambient Pressure ◽  
Silica Aerogels ◽  
Ambient Pressure Drying ◽  
Low Thermal Conductivity ◽  
Silica Hydrosol ◽  
High Production Cost

Owing to their ultra-low thermal conductivity, silica aerogels are promising thermal insulators; however, their extensive application is limited by their high production cost. Thus, scientists have started to explore low-cost and easy preparation processes of silica aerogels. In this work, a low-cost method was proposed to prepare silica aerogels with industrial silica hydrosol and a subsequent ambient pressure drying (APD) process. Various surfactants (cationic, amphoteric, or anionic) were added to avoid solvent exchange and surface modification during the APD process. The effects of various surfactants on the microstructure, thermal conductivity, and thermal stability of the silica aerogels were studied. The results showed that the silica aerogels prepared with a cationic or anionic surfactant have better thermal stability than that prepared with an amphoteric surfactant. After being heated at 600 °C, the silica aerogel prepared with a cationic surfactant showed the highest specific surface area of 131 m2∙g−1 and the lowest thermal conductivity of 0.038 W∙m−1∙K−1. The obtained low-cost silica aerogel with low thermal conductivity could be widely applied as a thermal insulator for building and industrial energy-saving applications.

From micro/nano structured isotactic polypropylene to a multifunctional low-density nanoporous medium

RSC Advances ◽  
2016 ◽  
Vol 6 (109) ◽  
pp. 108056-108066 ◽  
Author(s):  
Mehdi Saniei ◽  
Minh-Phuong Tran ◽  
Seong-Soo Bae ◽  
Piyapong Boahom ◽  
Pengjian Gong ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Thermal Conductivity ◽  
Porous Medium ◽  
Supercritical Carbon Dioxide ◽  
Isotactic Polypropylene ◽  
Low Density ◽  
Low Thermal Conductivity ◽  
Supercritical Carbon

A homogeneous low-density nano-porous medium of isotactic polypropylene (iPP) with a low thermal conductivity was fabricated using supercritical carbon dioxide (scCO2).

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