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Research Papers

# Microindentation Test for Assessing the Mechanical Properties of Silicone Rubber Exposed to a Simulated Polymer Electrolyte Membrane Fuel Cell Environment

[+] Author and Article Information
Jinzhu Tan1

College of Mechanical and Power Engineering, Nanjing University of Technology, Nanjing, Jiangsu 210009, China

Y. J. Chao2

Department of Mechanical Engineering, University of South Carolina, 300 Main Street, Columbia, SC 29208chao@sc.edu

Xiaodong Li

Department of Mechanical Engineering, University of South Carolina, 300 Main Street, Columbia, SC 29208

J. W. Van Zee

Department of Chemical Engineering, University of South Carolina, Columbia, SC 29208

1

Present address: University of South Carolina, Columbia, SC 29208.

2

Corresponding author.

J. Fuel Cell Sci. Technol 6(4), 041017 (Aug 18, 2009) (9 pages) doi:10.1115/1.3008030 History: Received July 11, 2007; Revised April 02, 2008; Published August 18, 2009

## Abstract

The elastomeric materials used as seals and gaskets in polymer electrolyte membrane (PEM) fuel cells are exposed to acidic environment, humid air, and hydrogen, and subjected to mechanical compressive load. The long-term mechanical and chemical stability of these materials is critical to both sealing and the electrochemical performance of the fuel cell. In this paper, mechanical degradation of two elastomeric materials, Silicone S and Silicone G, which are potential gasket materials for PEM fuel cells, was investigated. Test samples were subjected to various compressive loads to simulate the actual loading in addition to soaking in a simulated PEM fuel cell environment. Two temperatures, $80°C$ and $60°C$, were selected and used in this study. Mechanical properties of the samples before and after exposure to the environment were studied by microindentation. Indentation load, elastic modulus, and hardness were obtained from the loading and unloading curves. Indentation deformation was studied using Hertz contact model. Dynamic mechanical analysis was conducted to verify the elastic modulus obtained by Hertz contact model. It was found that the mechanical properties of the samples changed considerably after exposure to the simulated environment over time. The temperature and the applied compressive load play a significant role in the mechanical degradation. The microindentation method is proved to provide a simple and efficient way to evaluate the mechanical properties of gasket materials.

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## Figures

Figure 1

Schematic of the specimen preparation under compressive load and soaked in the ADT solution

Figure 2

Schematic of the indentation test showing the contact between the indenter tip (rigid ball) and the sample surface

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Hysteresis loss energy for the Silicone G samples: a before exposure, b after 45week exposure at 60°C, c after 45week exposure at 80°C, d after 47week exposure at 80°C with an applied pressure of 0.18MPa, e after 47week exposure at 80°C with an applied pressure of 0.36MPa, and f after 47week exposure at 80°C with an applied pressure of 0.77MPa

Figure 8

Hysteresis loss energy for the Silicone S samples: a before exposure, b after 45week exposure at 60°C, c after 45week exposure at 80°C, d after 47week exposure at 60°C with an applied pressure of 0.18MPa, and e after 47week exposure at 60°C with an applied pressure of 0.36MPa

Figure 9

Indentation load versus displacement curves at the indentation depth of 0.30mm for Silicone G samples: a before exposure, b after 45week exposure at 80°C, c after 47week exposure at 80°C with the applied pressure of 0.18MPa, d after 47week exposure at 80°C with the applied pressure of 0.36MPa, and e after 47week exposure at 80°C with the applied pressure of 0.77MPa

Figure 10

Indentation load versus displacement curves at a peak indentation depth of 0.30mm for Silicone G samples: a before exposure, b after 47week exposure at 60°C with the applied pressure of 0.18MPa, c after 47week exposure at 60°C with the applied pressure of 0.36MPa, d after 47week exposure at 60°C with the applied pressure of 0.77MPa, and e after 45week exposure at 60°C without any load

Figure 11

Bar charts of indentation load at a peak depth of 0.30mm for Silicone G samples: A before exposure, B after exposure at 60°C without any load, C after exposure at 80°C without any load, D after exposure at 60°C with a compressive pressure of 0.18MPa, E after exposure at 80°C with a compressive pressure of 0.18MPa, F after exposure at 60°C with a compressive pressure of 0.36MPa, G after exposure at 80°C with a compressive pressure of 0.36MPa, H after exposure at 60°C with a compressive pressure of 0.77MPa, and I after exposure at 80°C with a compressive pressure of 0.77MPa

Figure 12

Indentation load versus displacement curves at a peak depth of 0.15mm for the Silicone S samples: a before exposure, b after 47week exposure at 60°C with the applied pressure of 0.18MPa, c after 45week exposure at 60°C without any load, d after 47week exposure at 60°C with the applied pressure of 0.36MPa, and e after 45week exposure at 80°C without any load

Figure 13

Bar charts of indentation load at a peak depth of 0.15mm for the Silicone S samples: A before exposure, B after 47week exposure at 60°C with the applied pressure of 0.18MPa, C after 47week exposure at 60°C with the applied pressure of 0.36MPa, D after 45week exposure at 60°C, and E after 45week exposure at 80°C

Figure 14

Indentation loading curves obtained by microindentation and Hertz contact model for the Silicone G samples before exposure (unexposed) and after 47week exposure at 80°C with an applied pressure of 0.18MPa (C10SG80)

Figure 15

Elastic moduli for the Silicone G samples A before exposure, B after exposure at 60°C without any load, C after exposure at 80°C without any load, D after exposure at 60°C with an applied pressure of 0.18MPa, E after exposure at 80°C with an applied pressure of 0.18MPa, F after exposure at 60°C with an applied pressure of 0.36MPa, G after exposure at 80°C with an applied pressure of 0.36MPa, H after exposure at 60°C with an applied pressure of 0.77MPa, and I after exposure at 80°C with an applied pressure of 0.77MPa

Figure 16

Elastic moduli for the Silicone S samples: A before exposure, B after exposure at 60°C with the compressive pressure of 0.18MPa, C after exposure at 60°C with the compressive pressure of 0.36MPa, D after exposure at 60°C without any load, and E after exposure at 80°C without any load

Figure 17

The mean contact pressure at the peak depth of 0.30mm for Silicone G samples: A before exposure, B after 45week exposure at 60°C, C after 45week exposure at 80°C, D after 47week exposure at 80°C with an applied pressures of 0.18MPa, E after 47week exposure at 80°C with an applied pressures of 0.36MPa, and F after 47week exposure at 80°C with an applied pressures of 0.77MPa

Figure 18

The mean contact pressure at the peak depth of 0.20mm for Silicone S samples: A before exposure, B after 47week exposure at 60°C with the applied pressure of 0.18MPa, C after 47week exposure at 60°C with the applied pressure of 0.36MPa, D after 45week exposure at 60°C, and E after 45week exposure at 80°C

Figure 19

Modulus and tanδ versus temperature for Silicone S sample obtained by DMA

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