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originally predicted but the development growing more rapidly than the former characteristics. Single yarn bundles, costs continue to be high. Thus, only in the last few years. The other 20% of 0.1 mm in diameter and 1 mm long, are the big companies will remain. This the effort is concerned with the rheo- being carved out of unidirectional same sequence has occurred in the past, logical characteristics of mesophase samples. This operation is done with a for example, in the area of carbon fibers, pitch. Thus, the carbon effort consumes razor blade with lots of patience and a where 20 companies are now 5 to 7. about 60% of the total effort in this steady hand. Then, the bundle is gripped Similar declines have been seen in the group at this time.
and pulled out of the unidirectional areas of mesophase pitch, intercala- In general, Sakai is interested in the C/C sample. tion of carbonaceous materials, and “scientific” aspect of this field and will The other major area of research at the diamond surfaces.
only take financial support from indus- Toyohashi is the viscoelastic studies of It is recommended that communi- try if they are also interested in these different pitch systems. The transition cations be continued with this organic aspects. Sakai's general impression is of molten pitch from an amorphous to zation because of the diversity of the that industry does not readily use the a liquid crystalline or mesophase state R&D programs being conducted here talent at the Japanese universities in is of primary interest in order to underthat have resulted in a broad spectrum order to maintain their confidentiality stand the kinetics of how pitch enters of applications using carbonaceous status with respect to their competi- and diffuses throughout porous matematerials. Nippon Steel's strongly tors knowing what they are developing. rials that are being densified or how expressed desire to consider coopera. But industry is very eager to obtain his
But industry is very eager to obtain his pitches possess the ability to be drawn tive programs with the United States best students.
into fibers. Therefore, the phenomenolmay be useful in the support of research His experience has shown that 95% ogy of this transition is being investiprograms at universities in this country of the undergraduates and graduates gated by heat treating different types of
are employed by industry and the pitches at 400 °C to advance them into TOYOHASHI UNIVERSITY remainder go to the universities or the mesophase state. The viscosities of OF TECHNOLOGY government laboratories.
these various pitches are determined
as a means of studying their flow charDept. of Materials Science Program Status
acteristics. It has been found that if the Tempaku-cho, Toyohashi 440, Japan
mesophase concentration is less than Tel: (0532) 47-0111 x435
The general philosophy of the 60%, the flow characteristics are Fax: (0532) 45-0480
research here is to study the fracture Newtonian, whereas if it is greater than Date: 7 Jan 1991
physics from which the fracture mechan- 60%, the flow has viscoelastic charac
ics is subsequently derived. Specifically, teristics. The flow measurements are Background
the breadth of possible causes is very taken between 250 and 300 °C in order
impressive and ranges from the influ- not to advance the pitch while it is The host of this site visit was Prof. ence of atomic and molecular bonding being measured. Mototsugu Sakai, who is the head of to the overall strength and work to There is interest concerning the the ceramics and carbon materials effort fracture of these materials and how influence of matrix microstructure, but at this university. In addition, he is these forces are being modified by stress as yet the group's experience is with internationally known for his research shielding and crack wake effects. Frac- carbon matrices as they are just beginin the field of fracture phenomenology turing phenomena are being evaluated ning to work with samples that have and theoretical analysis. His staff con- on the basis of energy considerations. been heat treated to graphitization sists of 2 assistant professors and 15 Sakai believes that 80% to 90% of the temperatures. In general, their micrograduate students. The major research energy that is consumed in fracturing is structural examinations are performed emphasis of this group is in the areas of caused by fiber pullout, 15% to 10% is using optical methods. The SEM is the rheology of mesophase pitch and due to fiber bridging, and the remain- used only to evaluate fractured surunderstanding the science of micro- ing energy is consumed by cracking of
ing energy is consumed by cracking of faces. Crack growth is measured by fracturing of ceramics and carbonaceous the matrix. But it should be remem- optical means. As a result, there are materials.
bered that this assessment is based problems in identifying the initiation About 80% of Sakai's group is primarily on current data that have point and specific growth rates of cracks working in fracture behavior and been obtained with C/Cs that are com- in C/Cs. mechanics. These efforts are about posed of carbon rather than graphitic The C/C samples from Nippon Steel equally divided between carbons and matrices. Fiber pullout tests are being are unidirectional with a phenolic ceramics, in which the latter has been conducted to determine their bonding prepreg and three to four pitch impregnations, where each cycle is heat The laboratory capabilities are Japan for C/Cs and there were too many treated to 1,000 °C. This type of mate- adequate to do the type of research that other organizations competing. At this rial is specially made for Sakai and is being conducted here. Much of it is time a major effort is being directed at consists of laying up fibers and then designed explicitly for the experiments the development of pitch-based carbon/ forming them by hot pressing into plates and it appears a lot of imagination and graphite fibers. High quality fibers, that are about 1 cm thick. Test samples creativity were used in developing the having > 100 Mpsi modulus of elasticcan then be cut from these plates. As techniques.
ity values, are being produced on a yet no samples have been made in this There was an excellent response to prototype production basis. The major group's laboratories as there is not the the idea of having cooperative pro- technological problem is to determine equipment nor the person power to grams with organizations in the United
grams with organizations in the United procedures for manufacturing these perform this type of work. Just recently States and especially with the Univer- fibers at a lower cost. It is necessary to sample material was received from sity of California at Santa Barbara reduce this cost by a factor of 2 to 2.5 in Schunk that is 2D layups of cloth den- (UCSB). Collaboration could take many order to be competitive with PAN-based sified with pitch and heat treated to forms, from discussions about data to fibers. This development effort is expen2,100 or 2,400 °C. These 2D layups are having an exchange of students and sive as the production plant requires the first samples that will be tested in even several week visits between faculty five persons per shift, three shifts per this laboratory that contain a graphitic members from Japan or the United day, and 7 days per week of continuous matrix. The carbon matrix samples have States.
operation. It is expected that a decision been tested in tension with a notch cut Based on the above observations, it will be made in about 3 years on whether in them and at different orientations is recommended that further commu- to continue this aspect of Koa Oil's according to the ply layups. As expected, nications be continued and that con- developmental program. there is a difference in the energy to sideration be given toward determin- The are 38 people in the carbon fracture with the least amount occur- ing the possible areas of common inter- R&D group, of which 10 are staff ring when the root of the notch is in the est for establishing one or more collab- members and the rest are support, plane of the layup and a maximum orative programs that would be of mutual including those who are on the shifts energy occurring when the root is per- interest to both Prof. Sakai and organi- for the fiber prototype production line. pendicular to these planes. A special zations in the United States.
In addition, there are three managers three-point bend test has been devel
who are responsible for the new mateoped here so the fibers in the C/Cs are KOA OIL COMPANY, LTD. rials efforts, which are fibers from only subjected to tensile loads. This in
mesophase pitch, elastic graphite, and done by using a steel pin on the com- Osaka Research Laboratory
sensors from carbonaceous materials. pression side of the bend sample. No. 1, 2-chome, Takasago Through this type of test it has been Takaishi, Osaka 592, Japan
Program Status found that the size of the yarn diameter Tel: (0722) 68-3640 is critical in determining the type of Fax: (0722) 68-3159
Research has been ongoing for about failure that occurs with the fibers. If the Date: 8 Jan 1991
7 years in thearea of pitch-based fibers. yarn diameter is less than the critical
The spinning process occurs between crack size, there will be a lot of fiber Background
400 and 480 °C with a light molecular pullout, whereas if the diameter is more
weight oil that is on the alkaline side than the critical crack size, the fibers Dr. Mitsunao Kakuta, the general with toluene insolubles in the range of will break with very little pullout. manager of this laboratory, was my host. 70 to 80 ppm and quinoline insolubles
The main purpose at this laboratory is from 30 to 35 ppm. It has been deterAssessment
to develop products from heavy oils mined that better spinnability, which
and pitches that are derived from the means more spinning time without The quality of the research is excel- company's refineries. These products
company's refineries. These products fracturing a fiber, and a higher degree lent under the leadership of Prof. Sakai include cokes, special carbonaceous of anisotropic orientation of the moleand it is expected that this will continue materials, and pitch-based fibers. C/C cules within the fiber are attained with for a number of years in the future. This composites were being developed for precursors that have molecular weights is one of two organizations in Japan about 7 years when this effort was ter- in the range of 500 to 1,400. Appardoing fundamental research in the area minated 3 years ago. This decision was ently, the larger values of the modulus of fracture phenomenology of C/Cs. made because it was estimated that of elasticity and the strengths of fibers
there would be a limited market in vary inversely with the molecular weight. The heat treatment temperatures can chemical absorptive surfaces, dry derived from fundamental studies to be as high as 2,800 °C in order to obtain chemical cells, and other uses where a develop new and different types of a modulus as high as 113 Mpsi, which is low density, compressible, and high carbonaceous materials. Furthermore, comparable to the values attained by surface area material can be used. it is one of the few remaining organizaAmoco. At this time a new and small Other R&D efforts have resulted in tions that is developing advanced types 2-micron-diameter fiber is being unique types of carbonaceous mate- of mesophase pitch-based carbon fibers developed. Although it is possible to rials that are being evaluated or mar- with both improved properties and lower process 2-micron fibers, their diameter keted, e.g., 200-micron-thick carbon production cost. Whether these costs has a variable cross section that must paper and electrodes or moisture sen- can be reduced sufficiently to be combe controlled.
sors for the water content of different petitive with PAN-based fibers is still a Another research effort has been types of atmospheres that are used in question. It is expected these R&D directed toward the development of an chemical processing steps. In both directions will continue for the next 3 "elastic graphite.” This is a material applications, the electrical resistivity
applications, the electrical resistivity to 5 years. It is interesting to note that with a very low density between 0.2 and of the material is altered, adjusting the 5 to 8 years ago there were more than 0.5 g/cc and a surface area of 10 to degree of the feed stock's acidity in 15 companies in Japan involved in the 30 m2/g that is composed of spherical order to adjust its process procedures development of methods for the manparticles that are 10 to 300 micrometers to provide the desired characteristics. ufacture of pitch-based carbon fiber. in diameter. Each one of the spheres is For example, the resistivity of this Now this number has been reduced to hollow with a wall thickness that is material can be made high, which means three or four. approximately one-tenth of the particle's small currents will pass through it. But The question of possible collaboradiameter. The microstructure of the if moisture is absorbed into the mate- tion between Koa Oil and other U.S. walls is very unique and gives this rial from the atmosphere, the electrical organizations was discussed. In genmaterial its unusual properties. TEM resistivity will decrease, the current will eral, there is very little collaboration observations show that they are com- increase, and a change of humidity will with any organization or individuals in posed of a graphitic structure where be indicated.
Japan. However, there might be the the a-b planes are oriented in a circum- A laboratory tour was conducted of possibility of a limited amount in the ferential manner, like onion skins. In the R&D prototype production facility United States on the basis of programs general, this material is formed by dis- for pitch-based carbon fibers. This facil- that are of mutual interest to both parties. persing the mesophase in an alkaline ity has a capacity of 20 kg/day and it was In addition, there would have to be aqueous solution that is heat treated at installed about 5 years ago. In addition strict controls on how the derived inforabout 300°C to form the material with to the spinning facility, whose temper- mation is communicated outside of Koa a final heat treatment at 2,400 °C to ature is controlled within 1°, there is a obtain the graphitic microstructure. It stabilization furnace through which the It is recommended that further is this special type of structure that fibers are oxidized in air at between 200 communications be continued because allows the material to be compressed and 300 °C and a graphitization fur- this organization has shown the capato <50% of its original thickness with nace that can operate up to 2,800 °C. bility of developing new concepts in a pressure of 5,000 kg/cm2 and to return Other laboratory facilities were visited the development of materials, includto its original dimension when the and it was evident that equipment is ing pitch-based fibers. pressure is released. This recovery can available to test for the physical and occur because microcracking takes place chemical properties of the precursors SHIKIBO LTD. in the walls of the spheres as pressure is that are used in the various processes applied, which allows the walls to be and to characterize the finished prod- 1500-5 Shibahara flattened and still retain their integrity. ucts. These facilities included an SEM, Minami, Yakaichi, Shiga 527, Japan When the pressure is released, these an NMR for the characterization of Tel: 0748-25-1732 microcracks close and allow the spheres organic substances, and a laser diffrac- Fax: 0748-25-1763 to return to their original shapes. Thus, tometer to measure the diameter of Date: 10 Jan 1991 and 16 Mar 1992 this material can be recompressed
fibers. innumerable times without losing it
Background original shape. There are many possibil- Assessment ities for applying this material, such as
My host for this visit was Tokuzo for gaskets, absorbers of vibrational This organization shows that it is Kadotani, the director/general manager mechanical energy, catalytic and capable of using information that is of the research department of the
Industrial Textile Division. My contact turbine rotors, where the blades are an Although I didn't tour the laborawas Takeshi Tanamura, who is in charge integral part of the hub. To do this a tory, I was informed that equipment is of the processing R&D. The third per- fourth and a fifth yarn are introduced available for making all the thermalson in this discussion was T. Hirokawa, so that the thickness of the blades can mechanical property determinations who is in charge of R&D of composite be increased as the radius gets closer to that are necessary as well as the chemmaterial, including C/Cs.
the hub. Block-shaped preforms have ical evaluations of the precursors. There The primary C/Ceffort at Shikibo is been woven as large as 4 by 4 by 16 inches is also a close cooperative program to weave carbon fiber substrates of all or plates 6 by 6 by 2 inches thick. The with the GIRI Osaka laboratory where shapes and then to densify them. The possible geometries, including cylinders high temperature equipment can be initial patent for the weaving methods and cones, are not limited by the weaving used if it is not available at Shikibo. was bought from the Research Insti- procedures. At this time it is estimated tute of Polymers, which is located in that it $
costs about $200 per pound of Assessment Tsukuba, Japan. Using the principles preform and it is Shikibo's goal to reduce of the basic method, other weaving this by a factor of two.
Shikibo has demonstrated a unique variations and improvements have been Currently densification of the pre- capability in Japan for weaving 3D made. In addition, processing proce- forms is accomplished by both liquid
forms is accomplished by both liquid preforms and densifying them. Shikibo dures have been developed to densify and gaseous impregnation methods. The seems to be innovative in its approaches these preforms. Shikibo does not take combination of prepregging followed for developing advanced materials. It any money from the Government, so by multiple liquid impregnations is the appears that the research being conits techniques do not have to be divulged. preferred procedure because it is faster, ducted here is closely tied to the develThe C/C development group consists more reliable, and less costly to attain opment phase of its operation. The of about 10 persons, with half of these a given density of the preforms. An company is certainly interested in colhaving university degrees. This opera- autoclave with a maximum pressure of
autoclave with a maximum pressure of laborating, especially if it could supply tion has been going on for about 7 years. *1,400 psi at a temperature of 650 °C is material that would be analyzed for its
being used to obtain 3D C/Cs with fracturing behavior in the United States. Program Status
densities of about 1.8 g/cc. It is recog- It is recommended that communi.
nized that the CVD method of impreg- cations be continued with this organiThe general concept of the Shikibo nation is most useful in filling veryzation, especially as it may relate to weave is that the x and y yarns are small pores. Its main disadvantage is advanced weaving techniques. woven into a cloth, which is laid up and that the deposition times may be hunstacked to form the third dimension. dreds of hours to prevent density gradi. KOBE STEEL, LTD. These layers are held together by a ents through the thickness of the precontinuous yarn that is threaded in the form. This prolonged procedure obvi- 3-18, Wakinohamacho 1-chome z direction between the x and y yarns. ously increases the fabrication cost. Mr. Chuo-ku, Kobe, Hyogo 651, Japan Consequently, the z yarns form a loop Tanamura is now investigating whether Tel: (078) 261-4601 on the outside of the preform as it exits the CVD method can be effectively Fax: (078) 261-4671 and reenters the preform. No z yarns used as the last impregnation cycle to Date: 11 Jan 1991 are broken as they are in France or the fill the smallest pores and possibly United States. Furthermore, no x or y increase the mechanical properties of Background yarns are broken as they are by the the preform. A representative value of Societe Europeenne de Propulsion the bendingstrength of a 3D preform is My host was Dr. Mitsuo Suzuki, (SEP) method of piercing the fabrics in “24,000 psi (162 MPa), where the load- who is the general manager of this order to tie them together. Apparently ing direction is in the x direction and research center and an advisor to the the Shikibo method can produce pre- the fiber content is 41%, 50%, and 9% technical development group of the forms with a maximum fiber volume of in the x, y, and z directions, respec- corporation. The contact was Katsunori 60% and with yarn spacings of less than tively. This range of values is consid- Shimasaki, who is a senior researcher 1 mm if 1K yarns are used. Also, the ered to be comparable to what other in the Chemical Technology Research weaving procedure is capable of plac- investigators are attaining. Shikibo is Laboratory. ing the yarns at different orientations interpreting its data as suggesting that This center is primarily directed of0°, 45°, and 90°. Both PAN and pitch C/C mechanical properties are primarily toward the development of processes fibers are used to weave different shapes based on the fiber architecture. that will enhance the reliability of existing including L and T cross sections or
products and the invention of new products. The approach is to use data is performing R&D in the area of C/Cs softening point will usually result in that are obtained from carefully selected consists of 10 researchers and 12 the maximum carbon yield in the preform and controlled laboratory experiments. technicians.
for each densification step. The HIP Other data come from closely moni
process is also useful for impregnating tored runs that are being used to man- Program Status
preforms with compounds or elements ufacture material for sale to the public.
that are not in a carbonaceous state. A small fraction of the total C/C effort One of the topics of discussion was Additional studies show that preforms is for fundamental research to define the procedures used to densify C/Cs by impregnated by the HIP process have and select alternative paths for future the high pressure method of infiltrat- mechanical properties that are more developments.
ing preforms with liquid pitch. The isotropic. The range of tensile and flexThe efforts at this center are divided purpose of doing so is primarily to ural strengths of some of Kobe's multiinto different categories, namely: reduce production costs by minimizing directional C/Cs is between 300
the number of impregnations that must (143,500 psi) and 200 MPa (+29,000 psi). • New carbon products that include be performed so that the preform can The usual heat treatment conditions
woven carbon fiber composites. A attain a desired density. Data show that for the processing of C/Cs are 1,000 °C primary target for this activity is the for five impregnations, a 30% higher for carbonization and between 2,400 development of C/Cs for the Japanese density can be obtained in carbon fiber and 3,000 °C for graphitization. space plane. The efforts in C/Cs preforms than if the same type of pre- Measurements of the modulus of some started about 1985, although it was form was impregnated at 1 atm of pres- C/Cs show an increase of the effective not known outside the company until sure. Kobe's research indicates getting modulus of the fibers after being heat 2 or 3 years later. the pitch into the preform is no prob- treated
treated at these maximum temperatures. lem. The challenge is to keep the pitch It is not clear whether this is due to • Nonwoven or randomly oriented in the preform while it is undergoing changes of the fiber's modulus because
products such as brake disks for pyrolysis. This is because the pitch is the C/C heat treatment temperature high speed trains. Some of this generating gases that want to escape exceeds that at which the fiber was material has a relatively high den- from the preform. This action, in turn, processed. Another possibility is that sity of 1.6 g/cc. Included in this divi- tends to push the remaining pitch out the matrix has been graphitized and is sion of effort is the production of of the perform, thereby reducing the sufficiently bonded to the fibers to raise paper thin sheets of carbon that are efficiency of each impregnation opera- the effective modulus of the fibers. More composed of 5. to 10-micron- tion. Therefore, much R&D time has research is being performed to try and diameter carbon particles. This been devoted to determining what understand what is happening. material is also used in brakes and parameters must be considered to It is expected that the developmenfor self-lubricating applications. improve the HIP cycle. One of these tal efforts concerning C/Cs will con
parameters is defining what tempera- tinue until at least 1997, which is the • The development, production, and ture the pitch should be when the auto- time the support by MITI for the devel
sales of high pressure impregnation clave pressure is first applied to force opment of the Japanese space plane is autoclaves to be used for HIP oper- the pitch into the preform. Apparently, scheduled to end. In an unofficial ations for the densification of C/Cs. there are two boundary conditions to manner, some of the targets of the C/C Most of their units are sold in Japan, consider. One is to keep the pitch out- properties that are to be achieved for although a few units have been sold side the preform as long as possible this project were presented. For examabroad, such as in the United States.
while it is being heated to prevent the ple, at a temperature of 2,000 °C, the The maximum operating conditions gascous products that are being gener- tensile modulus should be 200 GPa for such units are in excess of ated from accumulating in the preform.
ated from accumulating in the preform. ("29 Mpsi) and the strength equal to 2,000 atm pressure and 1,000 °C. But as pyrolysis is occurring, the vis- 700 MPa (>100 kpsi) with a strain of Each of these units costs about cosity of the pitch is increasing and it -0.4%. Furthermore, this C/C material $100,000 including the controls. becomes more difficult to force the is to operate without any loss of prop
pitch into the small pores of the pre- erties for 200 hours. Several interestThe carbon development group has form, especially as the preform's den- ing C/Cs are being made for this projabout 30 persons, with two-thirds of sity is increased with multiple numbers ect. One is a <2-mm-thick cylinder these having university degrees, of which of impregnations. The Kobe studies whose diameter is to be 300 mm (*12 10 have Ph.D. degrees. The others are have shown that applying the pressure inches) with a length of 600 mm (24 support persons. Of this, the team that at about 150 °C above the pitch's inches). The other material is thin (-2