Thermal Conductivity Design and Evaluation of Zirconium Phosphate Bonded Silicon Nitride Porous Ceramics

2012 ◽  
Vol 508 ◽  
pp. 21-26 ◽  
Author(s):  
Jun Yan Wu ◽  
Fei Chen ◽  
Ming Zhong Li ◽  
Qiang Shen ◽  
Lian Meng Zhang
Keyword(s):  
Thermal Conductivity ◽  
Silicon Nitride ◽  
Pore Structure ◽  
Zirconium Phosphate ◽  
Effective Medium Theory ◽  
Porous Ceramic ◽  
Porous Ceramics ◽  
Medium Theory ◽  
Interconnected Pore ◽  
Interconnected Pore Structure

In this Paper, Five Fundamental Effective Thermal Conductivity Structural Models (Series, Parallel, Two Forms of Maxwell-Eucken and Effective Medium Theory) Were Used to Analyze and Design Silicon Nitride Porous Ceramics. Then α-Si3N4Matrix Porous Ceramics Were Prepared with ZrP2O7as a Binder and Thermal Conductivity of ZrP2O7Bonded Si3N4Porous Ceramic Was Evaluated. ZrP2O7Bonded Si3N4Porous Ceramic Had Open and Interconnected Pore Structure which is either in EMT or in Maxwell-Euken 2. The Thermal Conductivity of ZrP2O7Bonded Si3N4Porous Ceramics Changes from 2.0 to 0.5 W/m•K with Increasing the Porosity from 20% to 51%. The Obtained Results Showed that the External Porosity Material with Maxwell-Euken 2 Structure Had the Lowest Thermal Conductivity in All Porous Materials. The Open and Interconnected Pore Structure of ZrP2O7Bonded Si3N4Porous Ceramics Provided much Lower Thermal Conductivity.

Pressureless Sintering of Silicon Nitride Porous Ceramics with High Porosity and Bimodal Pore Structure

2012 ◽  
Vol 512-515 ◽  
pp. 873-877
Author(s):  
Fei Chen ◽  
Qiang Shen ◽  
Lian Meng Zhang
Keyword(s):  
Silicon Nitride ◽  
Pore Structure ◽  
Pore Size ◽  
Zirconium Phosphate ◽  
Porous Ceramics ◽  
Pressureless Sintering ◽  
High Porosity ◽  
Continuous Reaction ◽  
Bimodal Pore Structure

In this paper, silicon nitride porous ceramics with high porosity and bimodal pore structure were prepared using pressureless sintering at 900~1100°C. In these porous ceramics, zirconium phosphate (ZrP2O7) was used as a binder and starch and naphthalene powders were used as pore forming agents. The obtained results showed that the porosity could be controlled in the range of 34 % to 70 % by changing the content of pore forming agents. The pores were formed by the continuous reaction of ZrP2O7 at ~250 °C and burnout of starch at ~550 °C (when starch was used as a pore forming agent), or sublimation of naphthalene at 80°C (when naphthalene was used as a pore forming agent). The bimodal pore structure was produced with pore size of less than 0.5m and ~10 m when using starch as a pore forming agent and the pore size of less than 0.5m and ~30μm when using naphthalene as a pore forming agent.

scholarly journals Effect of Alignment on Enhancement of Thermal Conductivity of Polyethylene–Graphene Nanocomposites and Comparison with Effective Medium Theory

Nanomaterials ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 1291
Author(s):  
Fatema Tarannum ◽  
Rajmohan Muthaiah ◽  
Roshan Sameer Annam ◽  
Tingting Gu ◽  
Jivtesh Garg
Keyword(s):  
Thermal Conductivity ◽  
Thermal Management ◽  
Laser Scanning ◽  
Effective Medium Theory ◽  
Laser Scanning Confocal Microscopy ◽  
Effective Medium ◽  
Medium Theory ◽  
K Value ◽  
Graphene Nanocomposites ◽  
Scanning Confocal Microscopy

Thermal conductivity (k) of polymers is usually limited to low values of ~0.5 Wm−1K−1 in comparison to metals (>20 Wm−1K−1). The goal of this work is to enhance thermal conductivity (k) of polyethylene–graphene nanocomposites through simultaneous alignment of polyethylene (PE) lamellae and graphene nanoplatelets (GnP). Alignment is achieved through the application of strain. Measured values are compared with predictions from effective medium theory. A twin conical screw micro compounder is used to prepare polyethylene–graphene nanoplatelet (PE-GnP) composites. Enhancement in k value is studied for two different compositions with GnP content of 9 wt% and 13 wt% and for applied strains ranging from 0% to 300%. Aligned PE-GnP composites with 13 wt% GnP displays ~1000% enhancement in k at an applied strain of 300%, relative to k of pristine unstrained polymer. Laser Scanning Confocal Microscopy (LSCM) is used to quantitatively characterize the alignment of GnP flakes in strained composites; this measured orientation is used as an input for effective medium predictions. These results have important implications for thermal management applications.

On the Effective Thermal Conductivity of Nanofluids With Fractal Aggregation

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
C. G. Subramaniam
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Effective Medium Theory ◽  
Functionally Graded ◽  
Fractal Aggregates ◽  
Medium Theory ◽  
Analytical Approximations ◽  
Proposed Model ◽  
Dispersing Medium ◽  
Dilute Limit

A generalized effective medium theory (EMT) is proposed to account for the fractal structure of the dispersed phase in a dispersing medium under the dilute limit. The thermal conductivity of nanofluids with fractal aggregates is studied using the proposed model. Fractal aggregates are considered as functionally graded spherical inclusions and its effective thermal conductivity is derived as a function of its fractal dimension. The results are studied for self-consistency and accuracy within the limitations of the analytical approximations used.

Effect of Particle Size and Aggregation on Thermal Conductivity of Metal-Polymer Nanocomposite

2016 ◽  
Author(s):  
Xiangyu Li ◽  
Wonjun Park ◽  
Yong P. Chen ◽  
Xiulin Ruan
Keyword(s):  
Thermal Conductivity ◽  
Effective Medium Theory ◽  
Low Cost ◽  
Polymer Nanocomposite ◽  
Theoretical Models ◽  
Effective Medium ◽  
Metal Nanoparticle ◽  
Local Concentration ◽  
Medium Theory ◽  
Aggregation Effect

Metal nanoparticle has been a promising option for fillers in thermal interface materials due to its low cost and ease of fabrication. However, nanoparticle aggregation effect is not well understood because of its complexity. Theoretical models, like effective medium approximation model, barely cover aggregation effect. In this work, we have fabricated nickel-epoxy nanocomposites and observed higher thermal conductivity than effective medium theory predicts. Smaller particles are also found to show higher thermal conductivity, contrary to classical models indicate. A two-level EMA model is developed to account for aggregation effect and to explain the size-dependent enhancement of thermal conductivity by introducing local concentration in aggregation structures.

Corrosion Behavior of Enamel Coated Steel Rebar by EIS

2012 ◽  
Vol 450-451 ◽  
pp. 445-453 ◽  
Author(s):  
Fu Jian Tang ◽  
Gen Da Chen ◽  
Jeffery S. Volz ◽  
Richard K. Brow ◽  
Michael Koenigstein
Keyword(s):  
Corrosion Resistance ◽  
Pore Structure ◽  
Enamel Coating ◽  
Surface Condition ◽  
Corrosion Process ◽  
Coated Steel ◽  
Nacl Solution ◽  
Steel Rebar ◽  
Interconnected Pore ◽  
Interconnected Pore Structure

In this study, the corrosion process of enamel-coated deformed rebar completely immersed in 3.5 wt.% NaCl solution was evaluated over a period of 84 days by EIS testing. Three types of enamel coating were investigated: pure enamel, 50/50 enamel coating, and double enamel. Surface condition of the enamel coatings that were intentionally damaged prior to corrosion tests was visually examined at different immersion times. After 84 days of testing, the damaged coating areas were characterized by SEM, and the corrosion products on and adjacent to the damaged areas were collected and analyzed by XRD. Corrosion initiated at the damaged locations with no undercutting of the coating observed. The 50/50 enamel coating had the least corrosion resistance, due to its interconnected pore structure, and prior damage drastically reduced the corrosion resistance of pure and double enamel coated rebar.

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