Sliding Friction in Seawater Environment of Porous Carbon Materials made from Rice Hull

Transcription

1 191 Original Received January 31, 2014 Accepted for Publication June 3, Soc. Mater. Eng. Resour. Japan Sliding Friction in Seawater Environment of Porous Carbon Materials made from Rice Hull Takahiro SATO, Kai ENDO, Tsukasa SATO, Takeshi TAKAHASHI, Hiroshi IIZUKA and Michiaki SHISHIDO Department of Control and Information Systems Engineering, Tsuruoka National College of Technology, 104 Inookasawada, Tsuruoka, Yamagata, , Japan Department of Chemical and Biological Engineering, Tsuruoka National College of Technology Sanwa Yushi Co.Ltd., Tendo , Japan Department of Mechanical System Engineering, Faculty of Engineering, Yamagata University Jonan, Yonezawa, Yamagata , Japan i7622@edu.tsuruoka-nct.ac.jp Rice hull, which is one of the agricultural wastes in Japan, is required to be reused from a viewpoint of recycling. The rice hull silica carbon (RHSC), made from rice hull is manufactured by mixing rice hull particles with a phenol resin, pressure forming, drying, and then carbonizing the mixture in the nitrogen gas environment at high temperatures. RHSC contains about 30 mass% of inorganic constituent and 70 mass% of organic constituent. The main inorganic constituent is silica (SiO 2 ), which content is more than 95 mass%. Silica has excellent corrosion resistance and oxidation resistance. Thus, it can be expected improvement of water resistance. In this study, focusing on the sliding friction and the water resistance, which are a core competence, the sliding friction was evaluated through wear amount and dynamic friction coefficient in air and pure water and seawater. The results showed that the dynamic friction coefficient of RHSC in each environment was low excellent value from 0.11 to The wear amount in the air was about 50 μm in the 130 km running. By contrast, the wear amount in both pure water and seawater was reduced to 37 μm and 2 μm respectively. Thus, the use of RHSC can be expected in pure water and seawater. Key Words : Rice hull, Renewable resources, Sliding friction, Seawater resistance 1 INTRODUCTION Carbon materials have been used for a long time, they are used industrially. For example, Graphite, electrodes, mechanicals bearings, heat-resistant materials and heating elements are made of the carbon materials [1]. Recently, research of carbon nanotube composite material is also thriving [2], increasingly use of carbon material is spreading. While the carbon material has been developed, rice bran carbon (RBC) which is a porous carbon material using the natural porous structure of rice bran, has been developed by Sanwa-Yushi. With regard to the nature of the RBC, mechanical properties and sliding friction and electrical properties have been studied so far. Especially, the study of sliding material utilizing porosity and good sliding friction of the carbon material has been progressing. At present, practical use as a linear bearing has begun. Rice bran occurs in rice cleaning to obtain white rice. In addition, non-edible portion such as straw and rice hull occurs. Rice is staple food and its annual amount of production is about 10 million tons per year in Japan [3]. Rice hull occurs about 2.6 million tons by threshing. About 1.7 million tons of the rice hull is reused as fertilizer and soil conditioner, etc. However, about 900 thousand tons of the rice hull has been disposed as agricultural waste. Rice hull also has a porous structure. Therefore, it is considered possible to produce a porous carbon material made from rice hull by leveraging the knowledge of RBC. RHSC contains about 30 mass% of inorganic constituent and 70 mass% of organic constituent. The main inorganic constituent is silica [4]. Silica has excellent corrosion resistance and oxidation resistance. Thus, RHSC can be expected improvement of water resistance which has become a problem in the RBC. By the porous structure and component constituent, RHSC are showed excellent friction and abrasion resistance under unlubricating conditions, and good water resistance. However, application of RHSC is limited to a part of the linear slide rail. Expanded use and social background of energy situation are considered. Therefore RHSC is expected as a sliding materials and bearing of wind power, hydroelectric power and wave power generation in the coastal. In this study, experiments were conducted on the assumption of the actual use environment, in order to expand the applications of RHSC. Especially, dynamic friction coefficient and wear amount of RHSC were measured and evaluated.

2 192 Takahiro SATO et al. 2 EXPERIMENTAL PROCEDURE 2.1 Test Material Figure 1 shows the manufacturing process of RHSC. At first, the rice hull is impregnated with a thermosetting resol-type phenol resin (25 mass%), and then carbonizing in nitrogen gas environment at 900 for three hours. After carbonizing, the rice hull is crushed and aligning the granularity. Afterwards, the rice hull is impregnated with a thermosetting resol-type phenol resin again, pressure forming, drying, and then carbonizing in the nitrogen gas environment at 900 for three hours again. When the second carbonizing, the phenol resin function as a binder for the rice hull. The dimension of the molding material is 150(w) 75(d) 5(t)mm. Figure 2 shows the shape of the testpiece for sliding. The dimension of the testpiece which was cut from molding material is 3.5(w) 3.5(d) 2(t)mm. 2.2 Experimental Methods Figure 3 shows the photograph of measuring equipment. Sliding tests were conducted in the block-on-ring method. A drum of stainless steel as an opposite material of the sliding test, and the testpiece which was contacted with the opposite material were immersed in the tank filled with seawater. Seawater environment during the test was constructed by their environment. Figure 4 shows the testpiece and the friction slide drum. Dynamic friction coefficient measurement was done by giving load to the ground plane of the testpiece and rotating the opposite material by motor. Then, the resistance value was detected by sliding of the testpiece. Finally, dynamic friction coefficient was converted from it and evaluated. The torque converter was Figure 3 Measuring equipment of sliding tests Figure 4 Testpiece and friction slide drum used for detector of resistance values. Sliding speed was 1.5 m/s, mileage was 130 km (24 h), load was 10 N, SUS304 (Ra 0.3~0.5) was used as the opposite material of the testpiece. In the dynamic friction coefficient measurement, the wear amount was measured by a laser displacement meter attached to the upper portion of the testpiece. Experiments in air and pure water were also conducted for comparison with the experiments in seawater. 3 EXPERIMENTAL RESULT Figure 1 Manufacturing process of RHSC Figure 2 Shape of testpiece for sliding 3.1 Dynamic Friction Coefficient Figure 5 shows the relationship between dynamic friction coefficient and sliding distance of RHSC in each environment. After making the testpiece running about 50 km in air, dynamic friction coefficient is stabilized and asymptotic. This stable condition is related to fit in RHSC surface with opposite material surface. Comparing the average values of dynamic friction coefficient in the mostly stable region, the dynamic friction coefficient in pure water is low. The dynamic friction coefficient of the RHSC in each environment was value from 0.11 to Therefore, the dynamic friction coefficient of RHSC is not affected by seawater. 3.2 Wear Amount Figure 6 shows the measurements of the wear amount of RHSC in each environment. The wear amount in the air was about 50 μm in the 130 km running. By contrast, the wear amount in the water was about 37 μm, it was reduced. Wear amount in the seawater was

3 Sliding Friction in Seawater Environment of Porous Carbon Materials made from Rice Hull 193 Figure 5 Relationship between dynamic friction coefficient and sliding distance of RHSC in each environment Figure 6 Measurements of wear amount of RHSC in each environment about 2 μm, it was considerably reduced. The result is considered to be associated with the occurrence of hydroplaning. 3.3 Wear Surface Observation Figure 7 shows the SEM observation of the wear surface in each environment. Gray area is the contact surface with the opposite material and white area is the porosity and the falling trace by shedding of debris occurred by friction. In all testpieces, surface crack and falling trace on the entire contact surface were observed. The surface crack is caused by the shear force between the opposite material and testpiece. The surface crack propagating and the debris falling off are considered to be the cause of the wear mechanism. 4 DISCUSSION Dynamic friction coefficient of RHSC showed low excellent values from 0.11 to 0.15 in each environment. The common ceramics such as silicon carbide and alumina are from 0.2 to 0.8. Comparing these values, RHSC is sufficient as the sliding material [5]. The factor of a low excellent dynamic friction coefficient is considered to be two things. First, RHSC has the porosity due to porous structures. Figure 8 showed internal structure of the rice hull. Contact area of the friction surface is reduced by the porous structures of rice hull. It is Figure 7 SEM micrographs of wear surface considered water enters into the pores and lubricity was increased. Second, the interfacial shear strength decreases due to soft amorphous carbon made by carbonizing. RHSC in the microstructure has crystal structure of the graphite. Graphite is a layered crystal structure [6], it is known as a typical of solid lubricant. C atoms in the plane are bound by strong covalent bonds. By contrast, adjacent layers are bound by weak van der Waals forces and they are easily sheared [7]. Therefore, the low excellent dynamic friction coefficient is realized. According to the previous research results, RHSC has stable mechanical properties such as compressive strength and swelling in pure water. Figure 9 shows the relationship between immersion time and compressive strength of RBC and RHSC. After 1000-hour immersion, the compressive strength of RBC was reduced about 40%. By contrast, compressive strength of the RHSC was not decreased even after immersion of 1000-hour. Figure 10 shows the relationship between immersing time and hygroscopic expansion of RBC and RHSC. The strain of RBC was converged to 0.2% and the strain of RHSC was converged to 0.08%.

4 194 Takahiro SATO et al. Figure 10 Relationship between immersion time and hygroscopic expansion of RBC and RHSC Figure 8 Internal structure of rice hull Figure 9 Relationship between immersion time and compressive Figure 11 Chemical components of porous carbon material Figure 11 shows the chemical components of the porous carbon material. RBC includes the inorganic constituents, which are K, Mg, P from the rice bran and Na from the resol-type phenol resin. The water resistances are affected by deliquescent compounds such as K 2 NO 3 and Na 2 CO 3 made from K and Na included in the rice bran, and hygroscopic inorganic compounds such as K 3 PO 4 and Na 3 PO 4. Since RBC includes these compounds, RBC shows unstable properties in pure water such as the decrease of the swelling or the decrease of compressive strength. By contrast, 95 mass% of the inorganic constituents of RHSC is SiO 2.Thus, deliquescent and hygroscopic compounds are not produced on RHSC [8]. Therefore, RHSC is not affected by pure water. Removing the inorganic constituents of RBC that make deliquescent constituents improves the swelling significantly [9]. Seawater is composed of salt and water. Table 1. showed components of the salt in the seawater. Hygroscopic compounds and deliquescent compounds of the RBC are affected by water. Further, it is considered hygroscopic compounds and deliquescent compounds are more produced by Na ions contained in the seawater. RHSC is not affected by water. Further, it is considered not to react with Cl and Na etc. in the Table 1. Components of salt in seawater seawater because it has a simple structure of SiO 2 and C. Compared to RBC that includes those inorganic constituents, RHSC has the stable water-resistance in seawater. The wear amount in the water was about 37 μm. Also the wear amount in the seawater was about 2 μm. The difference of wear amount is occured by the pure water and sea water. It is considered difference of the components in pure water and seawater are related.

5 Sliding Friction in Seawater Environment of Porous Carbon Materials made from Rice Hull 195 Thus, RHSC is expected to be used as the stable sliding material in a seawater environment. 5 CONCLUSION The sliding test was carried out for the porous carbon materials made from rice hull (RHSC). Wear amount and dynamic friction coefficient of RHSC were measured and sliding friction of RHSC was evaluated. The summary of the obtained results was shown as follows. (1) The dynamic friction coefficient of RHSC was shown low excellent value from 0.11 to (2) The dynamic friction coefficient in pure water and seawater were shown low excellent value. RHSC was not affected by pure water and seawater. (3) The wear amount in pure water and seawater were reduced in comparison to the air. References [1] Yamada, S.; "carbon zairyou ouyou gijutu (in Japanese)", nikkankogyou shinbunsya, 53, (1992). [2] Okuyama, M. and Tomimura, T.; "Flame Synthesis of Carbon Nanomaterials by Combustion Enhancement Using Radiative Energy Recirculation", Journal of the Combustion Society of Japan, 47, No.142, (2005). [3] Ishitani, T. and Ohtsubo, K.; "The Science of Rice (in Japanese)", Asakura Shoten (1995). [4] S, Chandrasekhar., K, G, Styanarayana., P, N, Pramada. and P, Raghavan.;"Processing Properties and Applications of Reactive Silica from Rice Husk", J. Mater. Sci., 38, (2003). [5] Japan Soc. of Lubrication Engineers; "Tribology of new material (in Japanese)", (1991). [6] Honda, H. and Kobayashi, K.; "Haiteku tanso-zairyou (in Japanese)", Kogyou-chosakai (1987). [7] Takagi, R.; "junkatu (in Japanese)", 28 (1983). [8] Shishido, M., Kubo, S.,Yoshida, K. and Iizuka, H.; "Water Resistance and Mechanical Properties of Modified Porous Carbon Materials made from Rice Hull", J. Soc. Mater. Sci., Jpn, 56, 3, (2007). [9] Kubo, S., Iizuka, H., Shibata, Y. and Shikano, S.; "Improvement of Water Resistance in Porous Carbon-material Made from Rice Bran", Proceeding of the International Conference of Materials Resources, p.25 (2005). [10] Okabe, T., Saito, K., Hokkirigawa, K., Otsuka, M., Hushitani, M. "Woodceramics (in Japanese)", Uchida roukakuho, 2 (1996). [11] Takeuti, H.; "Mechanical Properties of RB ceramics" (2001).