Carbon Alloys part 16 pdf

Conversion of nitric oxide versus reaction time for reaction-regeneration cycles using carbon monoxide during regeneration of Ni-500-47.0.. These results show that amounts of carbon mon

Preparation of Metal-loaded Porous Carbons 509

$ 2 0 1 , , ,

0

0 5 10 15 20 25

Time [ h ]

Fig 13 Conversion of nitric oxide versus reaction time for reaction-regeneration cycles using carbon

monoxide during regeneration of Ni-500-47.0 (S, = 24000 h-') [ll]

when employing this regeneration method The lifetime of the catalyst after the first regeneration was less than the lifetime of the fresh catalyst This is because the catalyst was not completely regenerated during the first regeneration It is necessary and important to find optimum regeneration conditions Results so far indicate that a reducing regeneration method is effective to utilize the Ni2+ catalyst in practical applications

Next, carbon monoxide was intentionally added in the feed stream during the

reaction, because this gas may act as an in situ reducing agent Figure 14 shows the

changes in conversions of nitric oxide, the yields of nitrogen and the concentrations of oxides of carbon in the exit stream for Ni-500-47.0 In the presence of carbon monoxide, nitric oxide was completely removed for more than 20 h without regenera- tion even at 300°C The concentration of carbon monoxide was smaller than its feed

concentration by ca 500 ppm, and carbon dioxide, which was not detected in the absence of carbon monoxide, was formed in ca 500 ppm These results show that amounts of carbon monoxide consumed were almost the same as amounts of carbon dioxide formed or amounts of nitric oxide removed This means that almost no carbon

Reaction time [h]

Fig 14 Conversion of nitric oxide, yield of nitrogen, and concentrations of carbon monoxide and carbon dioxide in the effluent stream for the nitric oxide removal experiment with Ni-500-47.0 in the presence of

carbon monoxide at 300°C (S, = 24000 h-') [ll]

t-i I

855 850

865 860 Binding energy [ eV 1 Fig 15 Comparison of the XPS spectra of fresh catalyst (Ni-500-32.6), deactivated catalyst, and

regenerated catalyst and the spectrum of NiO powders [ll]

in the sample was lost during the reaction in the presence of carbon monoxide, maintaining the high catalytic activity for a long time The yield of nitrogen was kept at more than 90%, indicating that the decomposition of nitric oxide to nitrogen was enhanced in the presence of carbon monoxide Then, the overall reaction can approximately be written as

Thus, it is clear that the Ni2+ catalyst can be utilized for an extended time without loss

of carbon when a reducing agent is contained within the feed stream

5.4 Changes in the Chemical State oflvickel During Reaction

XPS studied changes in nickel forms in the Ni-500-32.6 during reactions Figure 15 compares the XPS spectra of the fresh, deactivated (used for 10 h at 3OO0C), and thermally regenerated samples with the spectrum of NiO powders The spectra of nickel in the fresh and the regenerated samples were similar to those of nickel, and were of metallic nickel On the other hand, the nickel in the deactivated sample was NiO These results indicate that metallic nickel is the active form of the catalyst, and that it is oxidized to NiO through the removal of nitric oxide and accordingly loses its activity NiO is reduced to nickel by carbon through the thermal regeneration reaction at 500°C as indicated by the formation of oxides of carbon during the regeneration

5.5 Reaction Mechanisms

Non-isothermal experiments, so-called temperature-programmed-reaction (TPR) experiments, were made to examine the mechanisms of the decomposition reaction of nitric oxide The sample was heated at 5 K m i d , from room temperature to 300"C, in

Preparation of Metal-loaded Porous Carbons 511

Fig 16 Change of conversion of nitric oxide and yield of nitrogen against the temperature during the TPR

experiment for Ni-500-47.0 (S, = 24000 h-') [ll]

a stream of 500 ppm of nitric oxide Figure 16 shows the concentrations of nitric oxide

and nitrogen versus increasing reaction temperature The concentration of nitric oxide decreased gradually with increasing temperature and fell to -50 pprn even at 200°C On the other hand, the concentrations of nitrogen was less than 25 pprn at temperatures < 200"C, and then gradually increased to reach about 210 pprn at 300°C These results indicate that nitric oxide is chemisorbed on the sample and then decomposes to form nitrogen

Based on the above results the following reaction mechanism was proposed for nitric oxide decomposition reaction at 300°C on the Ni-loaded porous carbons in the absence of reducing agents

NO + Ni -+ Ni-NO

2Ni-NO + 2Ni0 + N,

( 3 )

(4) Nitric oxide is first chemisorbed on nickel (Reaction (3)) The chemisorbed nitric oxide decomposes to form nitrogen and oxidizing nickel to NiO (Reaction (4)) At 300"C, about 20% of the nitric oxide removed remains in the sample As NiO is not active for the nitric oxide decomposition reaction, the activity gradually decreases with the progress of reaction However, the initial activity of the catalyst was high because a large amount of metallic nickel (-50 wt%) was highly dispersed within the porous carbon

The regeneration reaction is the reduction of NiO to Ni Carbon in the sample reduces NiO to Ni forming carbon monoxide at 500°C (Reaction (5)) Carbon

monoxide formed through the reduction by carbon also reduces NiO (Reaction (6))

At 400°C the activity of Ni-500-47.0 remained for more than 40 h without regenera- tion, because the regeneration Reactions ( 5 ) and (6) occur simultaneously

A novel method for preparing porous carbons with highly dispersed metals is pre- sented The method carbonizes ion-exchange resins exchanged by different cations

Of the various carbons prepared, the proposed method uses a nickel-loaded porous carbon which shows high catalytic activity for the decomposition of nitric oxide to nitrogen The following results were obtained

A nickel-loaded porous carbon, Ni-500-47.0, removed nitric oxide completely

for 5 h (S, = 24000 h-') at 300°C without any gaseous reducing reagent The

high activity of Ni-500-47.0 resulted from the large amounts of highly dispersed nickel loaded into the porous carbon

The activity of deactivated sample could be completely recovered by heat treatment at 500°C in a helium atmosphere, but the regeneration method consumed carbon by reducing nickel oxide (NiO) to nickel

To overcome this limitation to thermal regeneration, regeneration using carbon monoxide as a reducing agent was examined This regeneration method minimized carbon loss suggesting the possibility to use the NiZf catalyst in practical applications

In the presence of the reducing agent carbon monoxide, Ni-500-47.0 com- pletely removed nitric oxide for more than 20 h at 300°C without regeneration This was because carbon monoxide regenerated nickel oxide (NiO) to nickel during the reaction This regeneration consumes little carbon and so the supported catalyst can be used for an extended

Nitric oxide is first chemisorbed onto active sites of the metallic nickel, and subsequently decomposes to produce nitrogen and nickel oxide (NiO) The activity is gradually lost with the formation of nickel oxide (NiO) which can be removed by reducing agents such as carbon monoxide or carbon to recover the catalytic activity

Preparation of Metal-loaded Porous Carbons 513

Lett.: 521-524, 1977

3 S Kasaoka, E Sasaoka and H Iwasaki, Vanadium oxides (V,O,) catalysts for dry-type and simultaneously removal of sulfur oxides and nitrogen oxides with ammonia at low tempera- ture Bull Chem SOC Jpn., 6 2 1226-1232, 1989

4 A Nishijima, Y Kiyozumi, A Ueno, M Kurita, H Hagiwara, S Toshio and N Todo, Metal halide catalyst for reduction of nitric oxide with ammonia Bull Chem SOC Jpn., 52: 37243727,1979

5 L Singoredjo, M Slagt, J van Weers, F Kapteijn and J.A Moulijn, Selective catalytic re- duction of nitric oxide with ammonia over carbon supported copper catalysts Catal Today,

6 D Mehandjiev and E Bekyarova, Catalytic neutralization of NO on carbon-supported co- balt oxide catalyst J Colloid Interf Sci., 166: 476480,1994

7 J Imai, T Suzuki and K Kaneko, N2 formation from NO over metal oxide-dispersed microporous carbon fiber Catal Lett., 2 0 133-139, 1993

8 H Nakagawa, K Watanabe, Y Harada and K Miura, Control of micropore formation in the carbonized ion-exchange resin by utilizing pillar effect Carbon, 37: 1455-1461,1999

9 K Miura, H Nakagawa and K Hashimoto, Carbon, 33: 275-282,1995

10 D Dollimore and G.R Heal, An improved method for the calculation of pore size distribu- tion from adsorption data J Appl Chem., 56: 109-113, 1964

11 K Miura, H Nakagawa, Ryo Kitaura and T Satoh, Low-temperature conversion of NO to

N, by use of a novel Ni loaded porous carbon Chem Eng Sci., 5 6 1623-1629,2001

12 M Iwamoto, H Yahiro, Y Mine and S Kagawa, Excessively copper ion-exchanged ZSM-5 zeolites as highly active catalysts for direct decomposition of nitrogen monoxide Chem Lett.: 213-216, 1989

7 157-165,1990

515

Chapter 32

Minoru Shiraishi

Tokai University, School of High-technology for Human Welfare, Department of Material

Science and Technology, Numam, Shizuoka, 410-0395 Japan

Abstract: Micro-organisms rapidly f i i onto carbon fiber surfaces when the fibers are placed in

the sea The objective is to create an artificial bed of seaweed so establishing a food chain of bacteria, algae, zoo-plankton, small animals, and fish Initial studies in fresh water indicated that this approach had considerable potential and should therefore be extended to seawater

Keywords: Carbon fiber, Sea, Seaweed bed, Algae, Micro-organisms

1 Introduction

The fixation of micro-organisms onto carbon fibers has recently been undertaken in freshwater systems, one application being the purification of sewage [1,2] On the other hand, there is no basic information on the fixation of micro-organisms onto carbon fibers in seawater systems Therefore, carbon fibers were placed (anchored) in the sea to observe fixation phenomena of marine micro-organisms Basic data on the utilization of this artificial bed of seaweed, in terms of fish population, were collected [31

2 Rapid Fixation of Marine Organisms

To gain basic information on the fixation of marine organisms, field experiments were undertaken at the Marine Laboratory of Tokai University and also at the seawater intake of the Shinsihmim thermal power station of Chubu Electric Power Co Inc in the Shimizu harbor basin, Shizuoka The Marine Laboratory is in a stagnant location beyond the intake, located at the back in the bay and near to a timber yard

Polyacrylonitrile (PAN)-based carbon fibers with a tensile strength of 3.4 GPa, tensile modulus of 230 GPa, diameter of 7 pm, density of 1.77 g cm-3 and 12,000 filaments per strand were used A simple apparatus, as shown in Fig 1, was sunk about 1 m under the surface of the sea and, during the first experiments, was withdrawn from the seawater at intervals of a few days A plastic float of 30 cm

Fig 1 Carbon fiber bundles attached to the experimental apparatus

diameter was attached to the upper part of the rope which installs the apparatus, and

a 3 kg weight was tied to the lower end of the rope to keep the fibers on the sea floor Observations were made directly through the naked eye, an underwater camera and

an optical microscope

Small organisms (algae) were almost not observed on carbon fiber surfaces after the first day of the experiment However, a weak adhesive property appeared on the fiber surfaces to provide an adhesive membrane and so the fiber surfaces adopted a membrane-like feature, as shown in Fig 2 This phenomenon was observed in the sea

at the two locations throughout the year To facilitate access to the interior fibers of the strand for this membrane formation, it was found necessary to separate the strands into filaments A colony grew homogeneously from these fibers on the agar medium in one or two days There are differences between the colonies proliferated

by carbon fibers picked up and the seawater without carbon fibers from the same place The results indicate that the adhesive material was preferentially fixed to

carbon fibers in the sea and was made up of micro-organisms such as Bacillus carboniphilus, discovered by Matsuhashi [4]

Fig 2 Adhesive material spread to the membrane on carbon fiber surface

Formation of a Seaweed Bed Using Carbon Fibers 517

Fig 3 Minute algae (Navicula) fixed on carbon fibers

- v - i u

Fig 4 Diatoms grown on the periphery of carbon fiber bundles

Within a week after dipping, the carbon fibers had adopted the appearance of

brown bio-mud, as observed macroscopically or through the camera Minute algae, as

shown in Fig 3, were fixed to the carbon fibers as observed by optical microscopy These algae were diatoms to be seen in seawater at depths of about 2 m These algae were initially attached to the outside of the carbon fiber bundle, and then penetrated gradually to the inside of bundle They grew as a slender string as shown in Fig 4 at the Table 1

Changes with dipping time of varieties marine organisms fixed or living on carbon fibers in the sea

After dipping Marine organism

~-

1 day adhesive material

5 day diatom, zooplankton

diatom, zooplankton, Caprella, small shrimp (Maera serratipalma etc.)

small shrimp (Maera serratipalma etc.), Protohydroides elegans, Caprella, ascidian

small shrimp (Maera serratipalma etc), ascidian, Protohydroides elegans, Hydrozoa

small shrimp (Maera serratipalma etc.), Hydrozoa, barnacle, fish

small shrimp (Maera serratipalma etc.), barnacle, sponges, fish

Fig 5 Small shrimp (Maera seratipalma) observed in carbon fiber bundles

periphery of the fiber bundle Also, organisms of a size larger then several centimeters soon became associated with the bundles as well as zooplankton, as seen by optical microscopy

Small animals, several millimeters in size, seen after 10 days and shown in Fig 5,

were confirmed as small shrimp (Maera serratipalma and Photis reinhardi) The

development and growth rates of these animals were more rapid in the summer than

in the winter Large colonies of Maera serratipalma and Prehotis reinhardi, etc lived in

the apparatus in the sea during an autumn and winter

3 Food Chain Through a Carbon Fiber Seaweed Bed

The carbon fibers were pulled out of the sea and sampled to measure the population

of algae using the microscope The results show the growth rate of these minute algae with increasing number of days in the seawater (Fig 6) A maximum number of algae

appeared after about 30 days It is suggested that the zooplankton and small animals grow in numbers during this 30-day period and feed off these algae Other fish, such as

filefish (Stephanolepis cirrhifer) and globefish (Ostracion immaculatus) which swim

Dipping Time (days)

Fig 6 Variation of quantities of algae with time of dipping (submergence)

Formation of a Seaweed Bed Using Carbon Fibers 519

Fig 7 The sea-jungle appearance of the fibers after four months of dipping

externally to the carbon fiber bed, live off these smaller animals and algae Lugworms

(Polychaeta) inhabited the fiber bundle and algae apparently grew on the outside of

the carbon fiber bundle A feature of this apparatus is that it forms a sea jungle in three or four months, as shown in Fig 7

Later, comparatively larger animals such as ascidian (Ascidiacea), bivalve

(Bivalvia), barnacle (Balanomolpha) and hydroid (Hydrozoa) etc., several centi-

meters in size, lived in the apparatus and became abundant after several months At this time, and after the fixation and growth of the larger animals, the carbon fibers, which had originally been dispersed in the water, were apt to fasciculate (form bundles) and these included the lugworms, etc

A conclusion is that this carbon fiber system, acting as an artificial seaweed, established a marine food chain

4 Formation of an Artificial Bed of Seaweed Using Carbon Fibers [SI

Seaweed bed formation was developed further by sinking two larger experimental apparatus to the sea floor at a depth of 5-10 m in Suruga Bay near Numazu City One method was to fix a carbon fiber rope in the sea floor Carbon fibers were woven as a rope, 6 mm diameter and made into a grating-like net of 6 cm intervals The nets of

2 x 2 m2 in size were fixed to the sea floor The other method was deigned to lift the carbon fiber up from the sea floor Bases of 30x30 cm size made with ceramics, natural stone, colored coral gravel and concrete and placed on the sea floor with carbon fibers attached The other ends of the fibers were tied to floats Some 100 bases and carbon fibers of 1600 strands in the area of 5 x5 m2 were used, as shown in Fig 8 Before this equipment was installed, Pisces (fish) seldom stayed though they sometimes swam through this area Diatoms fixed themselves onto the carbon fibers immediately after installation The small animals that lived off the fixed diatoms appeared near to the carbon fibers in one month after installation Small fish such as

Apogon semilineatus and filefish gathered in the circumference of this apparatus, as

Fig 8 Apparatus as placed on the sea floor

Fig 9 Small fish (Apogon semilineatus) grouped together

shown in Fig 9, and the food chain described in the preceding section was established again The fish colony contained 21 varieties including Apogon semilineatus and file-

fish, the number increasing to over 1000 some two months after the installation Comparatively, many types of fish gathered and the communities of the Pisces (fish)

are complicated In addition, scorpion fish appeared, including ichthyovorous which

do not live usually in such a sand base, and ichthyovorous horse mackerel have been

observed

However, there are also some problems which have to be solved For example, one

is the durability of carbon fibers Accumulation of silicon was observed on the surface

of carbon fibers in some places when the carbon fibers had been in the sea for a while, and the carbon fibers may become brittle Also, the quantity of the carbon fibers

Formation of a Seaweed Bed Using Carbon Fibers 521

considerably decreased in about three months after the dipping Fish appear to tear the carbon fibers when they eat their food (bait) which is fixed to the carbon fibers

The carbon fibers are apt to gather in bundles after ascidian and shellfish become attached The appearance of the fiber bundles changes greatly after some time in the seawater Though these organisms will be metabolized some day, regeneration in a one-year cycle, as recognized in nature, will be difficult with this system

References

1 A Kojima and S Otani, Environmental Conservation of Hydrosphere with Carbon Fiber Proc Int Workshop on Advanced Materials for Functional Manifestation of Frontier and Environmental Consciousness, pp 145-152,1997

2 S Otani, Application of carbon fiber to aquatic environmental protection Tanso, 2000: 276-287 (in Japanese)

3 M Ooishi, M Shiraishi and S Otani, Fixation of marine micro-organisms on carbon fiber The Bulletin of School of High-Technology for Human Welfare, Tokai University, 8: 7948,1998 (in Japanese)

4 M Matsuhashi, A.N Pankrushina, K Endoh, H Watanabe, H Ohshima, M Tobi, S Endo, Y Mano, M Hyodo, T Kaneko, S Otani, S Yoshimura, Bacillus carboniphilus cells respond to growth-promoting physical signals from cells of homologous and heterologous bacteria J Gen Appl Microbiol., 4 2 315-323, 1996

5 S Ueno, T Kosaka, Y Sat0 and M Shiraishi, Biological Functions of Artificial Seaweed Bed using Carbon Fiber Abst 27'h Annual Meeting of the Carbon Society of Japan, pp 180-183,2000 (in Japanese)

523

Chapter 33

Tatsuo Oku

Zbaraki Study Center, The University of the Air, Bunkyo, Mito, Ibaraki 3IO-0056, Japan

Abstract: The results of research into carbonkarbon composites and related materials are

reviewed and form part of the Carbon Alloys project The results are in fiie categories: (1) the development of high quality carbon fibers and new carbon coils, property evaluation, and applications; (2) novel material development and control of micro-structures; (3) improve- ments in properties of materials and correlations between properties and micro-structures; (4)

fracture phenomena and mechanism; and (5) assessments of micro-structures Achievements

of research into carbodcarbon composites are described Novel carbon materials, carbon fibers, carbon matrices, high quality carbon alloys and new material evaluation methods were developed within this project New processing methods for carbon/carbon composites and carbon related composites were explored Improvements to the following properties of carbon/carbon composites were made: oxidation resistance, mechanical properties, thermal conduction, electronic properties, and electro-magnetic wave absorption

Keywords: Carbon fiber, Carbon matrix, Interface, Composite, Microstructure, Properties

1 Introduction

Carbon/carbon composites, carbon fiber-reinforced carbon matrix composites, under the Carbon Alloys project have been investigated to develop new starting (parent) materials and new functionalities Carbon/carbon composites consist of carbon fibers and carbon matrices However, despite an abundance of research papers, there is a need for high performance carbon fibers to develop high performance carbonharbon composites The term ‘carbon fibers’ includes carbon fibers, carbon nanotubes and

micro-carbon coils Carbon matrices can contain fullerenes such as CH,, graphite, and composites of carbon with metals Selected combinations of carbon fibers with carbon matrices produce high performance carbordcarbon composites Reviews and books

on carbon/carbon composites, including applications to nuclear fission and fusion

fields, are available [1-4]

First we discuss fundamental research on carbon fibers with high compressive strengths Carbon coils with new functions have been developed with applications to carbonkarbon composites being investigated Novel composites containing carbon

microscopy

2 Carbon Fibers and Carbon Coils

2.1 Improvement in Compressive Strength of Carbon Fibers

Carbon fibers with high compressive strength were investigated Korai et al [5]

successfully prepared anisotropic pitches of high spinnability by heat treatment of isotropic pitches synthesized from naphthalene and methyl-naphthalene using BFBF, as a catalyst As-spun and graphitized fibers made from these pitches were studied by X-ray diffraction (Table 1) Crystallite sizes in the isotropic pitch spun fibers increased with increasing soak time Carbon fibers of high compressive strength could be made from this naphthalene pitch Figure 1 shows the relationship between Young’s modulus and compressive strength for such carbon fibers the compressive strength increasing with heat-treatment The compressive strength varies inversely with the Young’s modulus The relationship was improved by heat treatment

Table 1

The degree of preferred orientation of fibers 151

Heat-treated time (h) Degree of preferred orientation (%)

CarbonlCarbon Composites and Their Properties 525

lo00

800

600

400

Young's modulus I GPa

Fig 1 Compressive strength and Young's modulus of heat-treated pitch-based fibers [SI

These heat-treated pitch carbon fibers showed high compressive strengths How- ever, the whole fiber does not have uniform structure because the pitches contain both isotropic and anisotropic components The central isotropic domain was larger than peripheral regions of the fiber It is considered that as the components are non-Newtonian fluids their viscosity decreases when large shear stresses are applied and that they will tend to gather in the central part of the fiber because the flow speed increases

2.2 Devebpment of Carbon Coils

Motojima et al [6-8] and Chen et al [9] prepared carbon micro-coils and micro-pipes

by the Ni-catalyzed pyrolysis of acetylene containing a small amount of thiophene at 7504300°C The carbon coils were coated with pyrolytic carbon layers using a gas mixture of CH, + Ar at 900-120OoC They were usually double helicals and regularly

coiled with a coil diameter of 3-6 pm and coil length of 0.05-5 pm Typical carbon micro-coils are shown in Fig 2 Coil gaps were hardly seen and the micro-coils were densely packed The electromagnetic reflection loss was measured using a Field

Analyzer (ADVANTEST, U4342) and indicated that the coated coils have an excellent reflection loss of electro-magnetic waves Figure 3 shows the reflection loss

for the coated coils obtained at different reaction times for long carbon coils, 1-10

mm, when used as source coils As-grown carbon coils hardly absorb electromagnetic waves; however, carbon micro-coils coated with pyrolytic carbon films absorb 9 6 9 9 %

of electromagnetic waves of 400-900 MHz The reason for this is not clear at present