13 research outputs found
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CRADA final report for CRADA number C/Y-1203-0211, gelcasting of soft ferrite parts
Soft ferrite parts utilized in areas such as high-energy physics have been successfully gelcast from powders supplied by the industrial partner. To achieve this, several modifications were necessary. First, the as-received ferrite powder was heated to 300, 500 or 800{degrees}C. X-ray analysis showed no changes in the crystal structure of the heat-treated powder even at 800{degrees}C, and particle size distribution and surface area analyses indicated that powders heat treated at 300 and 500{degrees} had mean size and surface area similar to those of the as-received powder. Second, to prevent the parts from shattering during the combined binder burn-off and sintering cycle, the solids loading of the gelcasting slurry was adjusted from 42 vol % to at least 50 vol % and the sintering schedule was modified slightly. These modifications resulted in the production of fired gelcast soft ferrite parts (50 mm {times} 13 mm pucks, {approximately} 125 mm OD {times} 100 mm ID {times} 25 mm rings) which sintered to {approximately}98% of the theoretical density. The partner was satisfied with the parts it received and has discussed pursuing follow-up activities in order to gelcast more complex shapes and large toroids
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Assessment of Recuperator Materials for Microturbines
Microturbines in production (or nearly in production) use metal recuperators with gas inlet temperatures of less than 700 C to raise their efficiency to about 30%. To increase their efficiencies to greater than 40% (which is the DOE Advanced Microturbine Program goal) will require operating at higher gas inlet temperatures, if the compression ratio remains less than 6. Even at higher compression ratios, the inlet temperature will increase as the efficiency increases, necessitating the use of new materials of construction. The materials requirement for recuperators used in microturbines may be categorized by their maximum operating temperatures: 700, 800, and {approximately}900 C. These limits are based on the materials properties that determine recuperator failure, such as corrosion, oxidation, creep, and strength. Metallic alloys are applicable in the 700 and 800 C limits; ceramics are applicable in the 900 C range. Most of the heat exchangers in the current microturbines are primary surface recuperators (PSR), compact recuperators fabricated in 347 stainless steel by rolling foil that is a few (>5) mil thick into air cells; the metal recuperators are operated at temperatures below 650 C. Preliminary research indicates that the use of 347 stainless steel can be extended to 700 C. However, additional directed research is required to improve the current properties of 347 stainless steel and to evaluate extended demonstrations on recuperators fabricated from it. Beyond 700 C and up to about 800 C, advanced austenitic stainless steels or other alloys or superalloys become applicable. Their properties must be measured in the expected operational environment, and recuperators fabricated from them must be evaluated for an extended period. Temperatures beyond 900 C exceed the limits of metals, and ceramic materials will be needed. The relevant properties of Si{sub 3} N{sub 4} and SiC, (creep, corrosion, and oxidation) have been studied extensively. Prototype ceramic recuperators have been fabricated from both cordierite and RBSN; consequently, their properties and those of other low-cost applicable ceramic materials need to be investigated further. Because no ceramic microturbine recuperators are in production, it will be necessary to fabricate prototype units and evaluate their properties over an extended demonstration period. A comprehensive workshop for those involved in recuperators for microturbines is recommended to determine how the technology can be accelerated to support the development of ultra-efficient microturbines. The immediate emphasis should be on the cost-effective manufacture of higher-temperature metallic recuperators; the development of ceramic recuperators should be considered a long-term objective
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Optimization of the gelcasting of a silicon nitride formulation
An optimum gelcasting condition for a silicon nitride formulation was determined using the Taguchi statistical method. An L{sub 8}(4{sup 1} {times} 2{sup 4}) design, in which the effects of one factor at four levels and four factors at two levels were evaluated in only eight experiments, was used. The factors at two levels were: the total monomer concentration, the monomer/crosslinker ratio, the initiator concentration, and the initiator/catalyst ratio; the factor at four levels was the initiator concentration per mass of the slip. The primary criterion used to determine optimum design was the green strength of the dried part, although three other parameters were measured: initial slip viscosity, time for the slip viscosity to reach 300 mPa.s. at 25 C, and time for the slip to gel at 50 C. The optimum gelcasting conditions from the designed experiments predicted 80% increase in green strength (4.3 MPa versus 2.4 MPa, the initial value). The confirmation runs showed only a 60% increase (3.8 MPa)
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EARLY ENTRANCE COPRODUCTION PLANT
The overall objective of this project is the three phase development of an Early Entrance Coproduction Plant (EECP) which uses petroleum coke to produce at least one product from at least two of the following three categories: (1) electric power (or heat), (2) fuels, and (3) chemicals using ChevronTexaco's proprietary gasification technology. The objective of Phase I is to determine the feasibility and define the concept for the EECP located at a specific site; develop a Research, Development, and Testing (RD&T) Plan to mitigate technical risks and barriers; and prepare a Preliminary Project Financing Plan. The objective of Phase II is to implement the work as outlined in the Phase I RD&T Plan to enhance the development and commercial acceptance of coproduction technology. The objective of Phase III is to develop an engineering design package and a financing and testing plan for an EECP located at a specific site. The project's intended result is to provide the necessary technical, economic, and environmental information needed by industry to move the EECP forward to detailed design, construction, and operation. The partners in this project are Texaco Energy Systems LLC or TES (a subsidiary of ChevronTexaco), General Electric (GE), Praxair, and Kellogg Brown & Root (KBR) in addition to the U.S. Department of Energy (DOE). TES is providing gasification technology and Fischer-Tropsch (F-T) technology developed by Rentech, GE is providing combustion turbine technology, Praxair is providing air separation technology, and KBR is providing engineering. During Phase I the team identified several potential methods to reduce or minimize the environmental impact of the proposed EECP. The EECP Project Team identified F-T catalyst disposal, beneficial gasifier slag usage (other than landfill), and carbon dioxide recovery for the gas turbine exhaust for study under this task. Successfully completing the Task 2.10 RD&T provides additional opportunities for the EECP to meet the goals of DOE's Vision 21 Program. The gasification section offers several opportunities to maximize the environmental benefits of an EECP. The spent F-T catalyst can be sent to landfills or to the gasification section. Testing in Phase II shows that the spent F-T catalyst with a small wax coating can safely meet federal landfill requirements. As an alternative to landfilling, it has been proposed to mix the spent F-T catalyst with the petroleum coke and feed this mixture to the gasification unit. Based on ChevronTexaco's experience with gasification and the characteristics of the spent F-T catalyst this appears to be an excellent opportunity to reduce one potential waste stream. The slag from the gasification unit can be commercially marketed for construction or fuel (such as cement kiln fuel) uses. The technical and economic benefits of these options must be reviewed for the final EECP before incorporating a specific alternative into the design basis. Reducing greenhouse gas emissions, particularly carbon dioxide, is an important goal of the EECP. The Texaco gasification process provides opportunities to capture high purity streams of carbon dioxide. For Phase II, a carbon fiber composite molecular sieve (CFCMS) was tested to determine its potential to remove high purity carbon dioxide from the exhaust of a gas turbine. Testing on with a simulated gas turbine exhaust shows that the CFCMS is able to remove high purity carbon dioxide from the exhaust. However, more development is required to optimize the system
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Forming of silicon nitride by gelcasting
Gelcasting is a near-net-shape forming technique that is applicable to various types of powders. It is accomplished by casting a concentrated suspension of a commercial ceramic powder in a solution of a polymerizable monomer and then polymerizing. The monomer used in the process is acrylamide which undergoes a vinyl polymerization. A filled gel is formed, which is dried and processed further. Gelcasting of alumina, sialon and silicon nitride has been carried out as the principal part of the Oak Ridge National Laboratory (ORNL) program. Two rotors have been gelcast as part of a cooperative research agreement between Allied-Signal Aerospace Company and ORNL. Emphasis is placed on the unit-operations of the process. Because a requirement of the process is a castable suspension of more than 50 vol % solids loading, good dispersion is crucial. Drying, another key process, has been studied extensively. Data on the relationship of physical properties of products to some of the more significant processing variables is discussed. Environmental, safety and hygiene issues are summarized. 9 refs., 7 figs