Showing papers in "American Ceramic Society Bulletin in 1997"

Materials for ultrahigh temperature structural applications

Abstract: Advanced ultrahigh temperature materials are critical to the development of next-generation rocket engines and hypersonic spacecrafts.

Gelcasting foams for porous ceramics

Abstract: A gel-cast foam process has been used to produce porous alumina ceramics having a bending strength as high as 26 MPa.

Glass-ceramics from municipal incinerator fly ash

Abstract: In countries where the population density is high and the availability of space for landfilling is limited, such as the west-European countries and Japan, the significance of municipal solid waste incineration, as part of the waste management strategy, is continuously increasing. In Germany and Switzerland, for example, more than {approximately}40% of unrecycled waste is being or will be incinerated. Also, in other countries, including the US, the importance of waste incineration will increase in the next few years. Although incineration reduces the volume of the waste by {approximately} 90%, it leaves considerable amounts of solid residues, such as bottom and boiler ashes, and filter fly ashes. Consequently, new technological options for the decontamination and/or inertization of incinerator filter fly ash are being developed with the objective of rendering a product that can be reused or, at least, be deposited in standard landfill sites with no risk. The proposed alternatives include immobilization by cement-based techniques, wet chemical treatments and thermal treatments of vitrification. Of these, vitrification is the most promising solution, because, if residues are melted at temperatures > 1,300 C, a relatively inert glass is produced. In the present investigation, glass-ceramics were obtained by a controlled crystallization heat treatment ofmore » vitrified incinerator filter fly ashes. The mechanical and other technical properties of the products were measured with special emphasis on assessing their in vitro toxic potential.« less

A practical approach to sintering

Abstract: Sintering has been recognized as a complicated process for a long time. It involves the evolution of microstructure through the action of several different transport mechanisms. In this article, the new concept of a master sintering curve (MSC) is introduced. The parameters in the sintering-rate equation are separated, with those related to the microstructure and the temperature terms on opposite sides of the equation. The two sides of the equation then are related to each other experimentally. The MSC can be used to estimate sintering activation energies and to predict sintering results under different sintering paths. Deviations from the assumptions for the MSC--e.g., surface diffusion or exaggerated grain growth--can be detected if they are present to a significant extent.

Density gradient evolution during dry pressing

Abstract: Defects caused by size segregation, density gradients and humidity might not be observed visually but can be present in pressed parts.

Developing a pink pigment for glazes

Abstract: Ceramic, sol-gel and coprecipitation methods and three mineralizers were used to determine the best approach to form pink pigment for crystallized and opaque glazes.

An ideal reinforcement for structural composites

Abstract: Different criteria and accumulated data lead to the conclusion that discontinuously reinforced metal-matrix composites (DR MMCs) will become an engineering material of general use. At the end of 1970s, the automobile and transport industries had a strong interest in and high expectations for DR-MMCs because of their superior specific strength and rigidity when compared with conventional aluminum alloys. After two decades of development, the first DR-MMC application, an engine connecting-rod, is ready to market. Major applications in the automobile industry, such as brake rotors and drive shafts, are now in the later stages of development, and other engineering applications are well advanced. DR-MMC technology is now recognized worldwide, and research groups are able to introduce remarkable applications of these materials to the market. Three main problems must be solved to facilitate the expanding application of DR-MMCs with light-metal-alloy matrices. They are: (1) superior cost performances; (2) active implementation of environmental concerns; (3) improved ductility. The immediate solution of these problems is impossible. However, many researchers and managers firmly believe that solutions will be found if the same amount of energy is devoted to solving these problems as has been expended during the past two decades of DR-MMCs R and D.

New R-SiC extends service life in kiln furniture

Abstract: Silicon carbide kiln furniture systems are an essential part of modern high-temperature technology. SiC ceramics have exceptional high-temperature stability and thermal shock resistance., They show no plastic deformation (creep) under mechanical load and maintain their geometry after each high-temperature cycle. Therefore, various new kiln systems with light and open setting patterns can be realized where more fired goods can be produced with less kiln furniture ballast and within shorter firing cycles. The fast-firing technology of porcelain is an opportunity for new SiC kiln furniture ceramics. The new SiC ceramic systems available include: (1) recrystallized SiC (R-SiC); (2) silicon-infiltrated reaction-bonded SiC (SiSiC); and (3) nitride-bonded SiC (NSiC). The new SiC ceramics have an important production criterion in common. They show practically no shrinkage during production. This is important for the manufacture of large shapes, such as beams, rollers and setter plates, as well as tailored geometries that allow light and open kiln furniture construction. Because of the extraordinarily high thermal shock resistance, high strength and high-temperature creep stability of these SiC ceramics, delicate and precise kiln furniture configurations have been introduced. One application is the fast firing of tableware with automatic setting robots.

Obtaining dispersible Bayer-process aluminas in water

Abstract: Controlled surface hydroxylation and Na + -ion impurity content control slurry rheology of Bayer-process aluminas.

Friction and wear of HPSN bearing materials

Abstract: Paper presents data on wear and friction of hot-pressed silicon nitride (HPSN) and its composites in contact with ball-bearing steel. The coefficient of friction under unlubricated sliding conditio ...

Microwave sintering of Ce-Y-ZTA composites

Abstract: Microwave processing of ceramic materials--especially the sintering of Al{sub 2}O{sub 3}, ZrO{sub 2} and their composites--has been investigated during the past decade by many researchers. Electromagnetic waves interact with ceramic materials, leading to volumetric heating by dielectric loss. This enhances the sintering process and decreases sintering active energy and densification temperature. Microwave heating also has the potential for energy and cost savings when compared with conventional heating. Zirconia-toughened alumina (ZTA) has received attention for its rapid densification in a microwave furnace. This article examines the batch microwave sintering of ZTA--30 wt% ceria-yttria-stabilized tetragonal zirconia polycrystals (Ce-Y-TZP) + 70 wt% Al{sub 2}O{sub 3}--including: (1) the microwave process in a multimode cavity with a hybrid heating structure; (2) the flexural strength, fracture toughness and wear resistance of the microwave-sintered materials; (3) the relationship between sintering temperature and microstructure/mechanical properties of the sintered samples; and (4) the comparison between microwave-sintered and conventionally sintered materials.

Using ceramic-fiber materials in corrosive environments

Abstract: Products made of yttria-stabilized zirconia fiber have exceptional resistance to most corrosive environments. They undergo little attack by molten alkali-metal chlorides and carbonates at temperatures as high as 700 C (1,300 F) and to aqueous solutions of alkali-metal hydroxides at temperatures as high as 230 C (450 F). Fibrous yttria-stabilized zirconia can withstand short-term exposure to mineral acids at their boiling point and has outstanding resistance to oxidizing, reducing and vacuum atmospheres at high temperatures. High-density vacuum-formed zirconia insulation (type FBD) can withstand oxidizing and reducing conditions to temperatures as high as 2,200 C (3,992 F). Products made of high-purity alumina fiber with high-purity alumina binder systems show high resistance to chemical attack and provide long service life in many corrosive and demanding applications.

The nanostructured materials industry

Abstract: An overview of the developing nanostructured materials industry, including a summary of nanostructured material types, properties and commercial applications, as well as the history and structure of the industry and US markets for 1996 and 2001.

Using cobinders to improve manufacturability

Abstract: The substitution of a minor amount of hydroxyethyl cellulose binder for polyethylene glycol binder improved the mechanical strength and ejection of compacts without sacrificing either slurry spray drying or granule compaction performance.

Powder processing for fabricating Si3N4 ceramics

Abstract: The strength of spray-dried Si 3 N 4 powders containing Al 2 O 3 and Y 2 O 3 is controlled by polymeric dispersant content, which also influences sintering properties of the ceramics.

Electronic ceramics R&D in the U.S., Japan. Part I : Patent history

Abstract: U.S. and Japanese patent history for dielectric ceramics, piezoelectric ceramics and ferroelectric thin films is reviewed to help predict future R&D trends.

Elastic properties of a calcium aluminate-cement-based concrete

Abstract: Calcium aluminate-cement concrete is the standard in many high-temperature applications and is widely considered for a variety of other applications. However, little research has been conducted on its elastic properties at elevated temperatures. Information on this subject is of great interest to engineers, especially those involved in designing structural concrete applications that are exposed to high temperatures. This paper is intended to provide some insight on the changes in the elastic modulus, shear modulus and Poisson`s ratio at elevated temperatures. The high-temperature properties of calcium aluminate-cement-based concrete are greatly affected by the purity of the cement and the choice of the aggregate. The purity of the cement is determined by the purity of the alumina source. Impurities lower the melting point of the cement, thus lowering its service temperature. Aggregates are generally prefired to a temperature above the anticipated service temperature of the concrete.

Rheological characterization of slips

Abstract: Differences in the rheological properties of suspensions based on particle concentration and deflocculation state were observed using steady and oscillatory test methods. The stress-controlled rheometer provided a complete rheological characterization of the test suspensions. Information on floc strength, structure and time dependency for these systems was obtained. A correlation was observed between steady and dynamic testing in measuring apparent yield in the samples.

Fabrication of Al2O3-Al composites by reactive melt infiltration

Abstract: Near-net-shape Al 2 O 3 -Al composites were fabricated by the infiltration of reacting aluminum melt at 950°-1200°C with borosilicate glass and oxygen as aids.

Electronic ceramics R&D in the U.S., Japan. Part II: Japanese view

Abstract: The results ofa questionnaire completed by Japanese technologists were used to help predict future R&D trends for dielectric ceramics, piezoelectric ceramics and ferroelectric thin films.

Tape casting reactive aluminas

Abstract: The formulation and processing modifications that must be made to account for particle-size and surface-area differences during the tape casting of three different aluminas are reported in detail.

Dielectric properties of AlB-BN composite ceramics

Abstract: Temperature and frequency have a significant effect on the dielectric properties of AlN-BN composites.

SO x emissions in firing ceramics

Abstract: Use of published SO x emission factors can lead to inaccurate emissions estimates because the sulfur content of raw materials varies considerably from mine to mine and because fuel type must be considered.

Cutting performance of advanced ceramic tools

Abstract: Four advanced ceramic cutting tools were used to machine the nickel-based super alloy Inconel 718 under various conditions.

Fracture toughness and strength of 96% alumina

Abstract: There exists a need to understand the controlling factors that simultaneously impact strength and toughness in 96% alumina. The enhancement of both strength and toughness enables designers to extend the use limits and reliability for structural ceramics. This article presents mechanical property results from a group study examining the use of different alkaline-earth aluminosilicate intergranular compositions containing magnesium, calcium and strontium oxides (RO) in 96% alumina. Principal results address trends in indentation strength toughness and modulus of rupture. Trends in the data are presented relative to existing theories of thermal expansion mismatch toughening, grain-bridging crack-wake effect and crack deflection mechanisms. Strength is addressed in terms of strength after indentation, crack growth of indentation flaws and Weibull characterization for the strength distribution.

Quality revolution tempers high tech with human measures

Abstract: Quality Expo International focused on the human element aspects of total quality management, concept engineering and the new environmental management system.

Quantifying the effect of slip control parameters

Abstract: Experimental design is a nontraditional concept that permits testing of the simultaneous effects of various parameters on many slip and cast properties, yet requires only a manageable amount of laboratory work.

Measuring capillary absorption coefficient of porous materials

Abstract: A new method for measuring the capillary absorption coefficient of porous materials is described and evaluated.