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This study examined the effect of waste-derived calcium sulfate additions (2 to 8 weight percent) on the tribological properties of a sintered high-carbon steel material, commonly used for frictional applications. The calcium sulfate powder was obtained by crushing and subsequent calcination of waste plaster molds previously used for slip casting of ceramics. Samples were made using the powder metallurgy method. Powder mixtures were uniaxially die compacted and sintered at 1,100°C for 30 minutes in a reducing atmosphere. It was found that the density of the samples decreased with increased amounts of calcium sulfate. This was due to the lower theoretical density of the calcium sulfate as well as volumetric expansion of the samples. Ball-on-disc tribological testing was performed at room temperature. The addition of calcium sulfate resulted in an increase of the kinetic friction coefficient. The measured wear volume was slightly reduced with the addition of calcium sulfate less than 6 weight percent, beyond which the wear increased. The hardness of the samples was reduced with the addition of calcium sulfate. Increased calcium sulfate content decreased the sample deformation resistance while increasing the kinetic friction coefficient and the wear. This was likely due to the microstructural changes of the samples, which will be discussed.

Lignite bottom ash is an industrial byproduct from the combustion of lignite coal in electric power plants. The ash is composed of various hard metal oxides, and therefore may be suitable for use as a low cost friction modifier in friction materials. This research studied the effect of lignite bottom ash additions (up to 20 weight percent) on the tribological properties of a graphite-steel composite (5 weight percent graphite and 95 weight percent high carbon steel). The powder compositions were uniaxially pressed with 300 MPa applied pressure to produce disc shaped samples. The samples were sintered at 1,100 °C for 30 minutes in a reducing atmosphere of 90 percent nitrogen and 10 percent hydrogen. The friction coefficients were measured using a ball-on-disc tribometer. It was found that the addition of bottom ash increased the friction coefficients of the samples due to the increased abrasiveness provided by the bottom ash. The density of the samples was reduced due to the lower theoretical density of the bottom ash compared to the steel that it replaced. The hardness of the samples were found to be independent of the amount of lignite bottom ash, possibly as a result of a hard particle reinforcement effect.

Bottom ash is a waste byproduct generated from the combustion or incineration of materials such as coal and household waste. It is a mixed oxide powder of variable composition, though typically high in silica. As a low-cost, readily available material, it has found applications primarily in construction for use as backfill. As a silica-rich, mixed oxide powder though, it may also have glass forming ability. This research studied the possibility to use domestically produced bottom ash powder in glass making. Two bottom ash powders were used, one from a waste incinerator (Phuket) and the other from a coal-fired electric plant (Mae Moh Power Plant, Lampang). The bottom ash was milled into a fine powder and melted within the temperature range of 1300-1500 oC, for 2 hours. The melts were cast in a brass mold and then annealed at 500 oC for 2 hours. It was found that both bottom ashes could successfully produce glasses. The Vickers hardness, refractive index and specific gravity of the glasses will be discussed.

This research studied the effects of content and particle size of lignite bottom ash (LBA) on the density of a bronze-based friction material. LBA from the Mae Moh power plant, Lampang province, Thailand, was pulverized and screened into three particle size ranges (

In this study, the effect of natural anhydrite (CaSO4) powder additions on the microstructure and hardness of a Cu-8Sn bronze composite, prepared by a powder metallurgy process, were examined. Natural anhydrite powder, ranging in content from 2 to 8 percent by weight was added to a premixed powder composed of copper and tin. The samples were uniaxially compacted into a disc shape with a diameter of 20 mm and a thickness of 3 mm under an applied pressure 281 MPa. The samples were sintered at 650 °C for 30 minutes in a reducing atmosphere. It was found that the green density of the samples decreased with increased anhydrite content. The sintered densities were higher than the green densities owing to densification of the samples. From microstructural images, the specimens were composed of twinned grains of bronze, pores, and anhydrite particles. The average hardness of the samples ranged between 65 to 80Hv. The hardness deviation was due to the porous microstructure of the multiple phase material. There was a slight increase of hardness with an increase of anhydrite content within the range examined. Phase analysis by X-ray diffraction found that the samples contain calcium sulfite instead of calcium sulfate anhydrite after sintering.

This study examined the effect of natural anhydrite (CaSO4) powder additions on the microstructure and frictional properties of a 95 Bronze - 5 Graphite composite prepared by a powder metallurgy process. Natural anhydrite powder, ranging in content from 2 to 8 weight percent, was added to a premixed bronze powder composed of copper and tin and mixed, before the graphite was added. The powder mixture was compacted into disc shaped samples under a pressure of 500 MPa. The compacted samples were sintered at 750 °C for 30 minute in a reducing atmosphere. The green and sintered densities of the samples were measured. A microstructural analysis of the sintered samples was also performed. It was found that the green density of the samples decreased with increased anhydrite content. The sintered densities were lower than the green densities due to sample expansion. A finer microstructure was observed in the samples containing anhydrite. The anhydrite additions resulted in the reduction of both the friction coefficient and wear of the bronze-graphite samples. The amount of anhydrite from 2 to 8 weight percent clearly altered the microstructure of the bronze-graphite samples, however, the level of reduction of the friction coefficient and wear were quite similar among the anhydrite containing samples.

The aim of this research was to study the effect of bottom ash additions to a bronze-graphite composite on the sintering behavior, as well as on the resultant physical, mechanical and tribological properties. The composites were produced by a powder metallurgy technique from prealloyed Cu-10Sn bronze powder, graphite powder and milled bottom ash powder. The compositions studied were Cu-10Sn bronze with constant 5 wt.% graphite, and 0-20 wt.% bottom ash. Samples were die compacted under 795 MPa and sintered at 850 oC for 30 minutes in an open atmosphere furnace. It was found that the sintered density of the composites decreased with increasing amounts of bottom ash. The hardness of the samples increased with bottom ash additions and reached a maximum at 5 wt.% and decreased with further additions. The frictional properties were studied using a ball-on-disc test at ambient temperature. It was found that both the friction coefficient and the wear rate were increased with increasing amounts of bottom ash.

Bronze-based composite materials are well known for use as friction materials. They are produced by powder metallurgy techniques from bronze powder, which acts as a matrix, and various friction modifying additives. The objective of this work was to study the effect of compaction pressure and sintering time on the properties of the unmodified bronze matrix. The bronze powder used was prealloyed with a composition of Cu-10Sn. The specimens were pressed by uniaxial die compaction with pressures of 282 to 339 MPa. The sintering experiments were conducted in an alumina tube furnace at 800 °C with sintering times of 30, 45, and 60 min under a vacuum pressure of 2.25x10-2 Torr. From the results, it was found that the density of the samples increased with increasing compaction pressure. A microstructural examination of the samples for the different sintering times showed them to look very similar. Finally, the highest sintered density of 7.30 g/cm3 was obtained at 800 °C for 60 min.

This study examined the effect of calcium sulfate additions on the microstructure and frictional properties of a 95bronze-5graphite material, commonly used for frictional applications. The samples were prepared using a powder metallurgy process. The calcium sulfate powder was obtained from recycled plaster molds previously used for ceramic slip casting. The plaster molds were cleaned, crushed and ball milled to obtain powder, which was calcined at 400 °C for 4 hours and screened. 2 to 8 weight percent calcium sulfate powder was added to a premixed powder composed of copper and tin and mixed before the graphite was added. The powder mixture was compacted into a disc shape under a pressure of 500 MPa. The compacted samples were sintered at 750 °C for 30 minutes in a reducing atmosphere. It was found that the green density of the samples decreased with increased amounts of calcium sulfate. After sintering, the densities were found to have decreased due to sample expansion. A finer microstructure was observed in the samples containing calcium sulfate powder, possibly due to a grain boundary pinning effect. The addition of calcium sulfate resulted in the reduction of both the measured friction coefficient and wear of the bronze-graphite samples. However, the addition of calcium sulfate powder above 6 weight percent appeared to show decreasing effects.

Zirconia toughened alumina (ZTA) ceramic has been fabricated by the powder injection moulding process. The ZTA ceramic, composed of 80 wt% alumina and 20 wt% zirconia, was mixed with a water-soluble, multi-component binder system. The binder ingredients were polyethylene glycol (PEG), polyvinyl butyral (PVB) and stearic acid (SA). Powder injection moulding was performed with powder loadings in the range of 48-52 vol%, using a laboratory-scale injection moulding machine. Water leaching was used for partial binder removal prior to thermal debinding and then sintering at 1650 °C for 2 hours. Microstructural examination of the ZTA ceramic revealed that zirconia inhibited alumina grain growth and, therefore, improved the mechanical and physical properties of the specimens. It was found that powder loading had an influence on density, hardness and strength of the specimens. A flexural strength of 334 MPa and hardness value of 2093 kg/mm2 was obtained from specimens injection moulded with 52 vol% powder loading feedstock. The highest sintered density achieved was 97% of the theoretical value.

This study examined the feasibility of utilizing lignite bottom ash as a partial substitute for ball clay in an insulating brick composition. Lignite bottom ash is a waste byproduct that is high in alumina and silicates and is therefore a candidate material for replacing aluminosilicate minerals such as clay. The lignite bottom ash powder was obtained from the Mae Moh power plant, Thailand. Small brick specimens were produced by die pressing a mixture of lignite bottom ash, ball clay and aluminum hydroxide. The composition of the mixture contained a fixed amount of aluminum hydroxide, while the lignite bottom ash replaced from 30 to 70% of the ball clay. The pressed samples were sintered at 1300 oC for 1 hour in air. The density, porosity, strength and thermal properties of the samples were measured. A microstructural analysis of the sintered brick was also performed. It was found that the porosity of the samples increased from 35 to 45% with increased lignite bottom ash content. The modulus of rupture and the thermal conductivity of the bricks were reduced with increased lignite bottom ash content, likely due to the increased amount of porosity. Dilatometric analysis found that the thermal expansion increased with increased amounts of lignite bottom ash, possibly as a result of an increased amount of glassy phase. Despite the high thermal expansion coefficient at high temperature, the feasibility of using lignite bottom ash in the insulating brick composition was demonstrated.

In this paper, the thermal oxidation behavior, adhesion and tribological properties of TiAlON films coated on hastelloyX substrate, typically used for fuel nozzle in gas turbine engine application, have been studied. The uncoated and coated samples were heated to different temperatures, i.e. 950, 1050 and 1150 °C in the controlled atmosphere. The surface appearance, microstructure, chemical composition and adhesion of films were investigated. The thermal oxidations were observed in all testing conditions showing thicker oxide film at higher temperature. However, spalling of oxide scales was found in hastelloyX and TiAlON coated at 1150°C suggesting the maximum working temperature of < 1150 °C. The critical loads corresponding to the full delamination of the thermal oxidation coated specimens were found to be higher than the non-thermal oxidation specimens. The effect of thermal oxidation on damage patterns during scratch tests, i.e. less chipping and cracking for thermal oxidation specimen, were also observed. The tribological properties were also investigated under different load under room temperature and 600 and 1000°C. The results suggested significant improvement in wear resistance of coated sample especially at low load at all temperatures.

As an alternative route to hot-pressing fine powders for obtaining fine-grained microstructures, coarse spherical polycrystalline particles having a fine-grained microstructure were hot pressed. Three size fractions of particles, nominally 25, 45, and 75 μm, were prepared by presintering Tosoh yttria-stabilized zirconia (Y-TZP) spray-dried granules. Samples were hot pressed at 1350°C for 1 h using pressures of 6, 10, 20, and 40 MPa. It was found that dense (>98%) 3Y-TZP monolith could be produced at 40 MPa, which retained the fine grain size (0.3 μm) of the starting polycrystalline particles. The densification rate was particle size independent when the pressure was at least 10 MPa. It was determined that the densification rates agreed with Helle et al.'s predicted rates based on superplastic creep-controlled hot pressing.

To study hot-pressing densification rates of single-grain and multi-grain zirconia powders, spray-dried granules of ZrO 2 -3%Y 2 0 3 (D(10-90) = 35-90 μm) were densified at 1400 °C. Ball milling was utilized to break up the inter-agglomerate bridges. The resulting powder represented the multi-grain particle (MGP). Single-grain particle (SGP) of comparable grain size was obtained by intensive ball milling of the dense granules to the grain size (-0.35 μm diameter). To compare the densification behavior of these powders, specimens of each powder were hot-pressed in a SiC die at 1350 °C for 1 hour. The highest density was achieved by hot pressing MGP screened to +75 pm. The MGP densities by particle creep of the polycrystalline powder controlled by the diffusion distance on the order of the grain size while the SGP is thought to densify primarily by pressure-assisted sintering, i.e., diffusion along the neck between particles. The difference in final density reflects the initially higher packing density of the MGP powder.