Koji Matsumaru

Surface hydration states of commercial high purity α-Al2O3 powders evaluated by temperature programmed desorption mass spectrometry and diffuse reflectance infrared Fourier transform spectroscopy

Abstract The surface of three different grades of commercial high-purity α-Al2O3 powders produced by hydrolysis of aluminum alkoxide, which differ each other in SSA are evaluated by temperature programmed desorption mass spectrometry (TPDMS) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. For the DRIFT evaluation the powders were heated in situ under vacuum from 25 to 700 8C. The TPDMS spectra of desorbed H2O were obtained by heating the samples under ultra high vacuum at a rate of 20 K minK1 up to 1200 8C. The presence of hydrogen bonded water molecules, amorphous Al(OH)3 and AlOOH structures, as well as associated and isolated hydroxyl groups on the surface of all the a-Al2O3 powders investigated is demonstrated. On the surface of one of the powders the presence of crystalline Al(OH)3 structures, as evidenced by an additional sharp peak in the H2O TPDMS spectrum, is confirmed.

Advanced thin dicing blade for sapphire substrate

Abstract Advanced thin dicing blades for cutting sapphire were fabricated and evaluated for cutting performance with respect to dicing blade wear and meandering of cutting lines. Three kinds of different commercial blades were used to compare the cutting performance. These blades had the same thickness and the same diamond grain size. The matrix material of one dicing blade was nickel–phosphorus alloy and two other were a vitric material. Newly developed dicing blades consisted of a vitric material with pore. A dicing machine was used for cutting sapphire. Turning velocity, cutting depth and feeding rate were 20,000 min–1, 200 mm and 1 mm s–1, respectivity. Cutting directions were and . All blades could cut 1000 mm and more in the direction. On the other hand, commercial dicing blades generated meandering lines and were broken only by 50 mm of cutting length in direction. Fabricated blade can cut 1000 mm and more in direction. The wear of fabricated dicing blade was the largest in the dicing blades. Although cutting performance of commercial dicing blades depended on the sapphire orientation, that of fabricated blade was independent of the sapphire orientation. It has been confirmed that the fabricated dicing blade was kept a cutting ability by flash diamonds on the dicing blade surface, which were created by wear of blade during cutting sapphire. Low cutting ability of commercial blades increased cutting force between with increase of cutting length. The increased cutting force produced to bend a blade and cutting lines, and finally a fracture of blade.

Isothermal Oxidation of Sintered β-FeSi2 in Air

High-temperature oxidation of sintered β-FeSi2 doped with Mn and Co was evaluated at 800°C in air. Amorphous SiO2 was developed as an oxide scale. Granular ε-FeSi also appeared below the SiO2 scale as a result of consumption of Si in β-FeSi2. Growth of the oxide scale on doped FeSi2 followed a parabolic law and its rate was similar to oxidation of undoped samples. Thermoelectric properties of sintered β-FeSi2 were also evaluated before and after oxidation at 800°C for 7 days. There was no significant change in thermoelectric properties after high-temperature oxidation on β-FeSi2 sintered bodies.

Development of Porous Material with High Young’s Modulus and Low Thermal Expansion Coefficient in SiC-Vitrified Bonding Material-LiAlSiO4 System

Machines for manufacturing large scale flat displays are enlarging as the size of glasses increases. This work develops porous materials with a low thermal expansion coefficient and a high Young’s modulus. SiC and LiAlSiO4 were used for a positive and a negative thermal expansion materials, respectively. Compositions of powders for porous materials were determined to obtain a desirable Young’s modulus and thermal expansion coefficient by using SiC-VBM-LiAlSiO4 phase diagram at 20 % of porosity. The empirical values of Young’s modulus and a thermal expansion coefficient are close to the theoretical values by using the diagram. Fabricated porous material had high enough Young’s modulus of 87 GPa, and low enough thermal expansion coefficient of 2 x 10-6 K-1 at temperatures ranging from -17 °C to 190 °C with 22 % of porosity.

Densification Mechanism of Fine Ni-20Cr Powder during Pulsed Electric Current Sintering

Microstructure observation and kinetic analysis were conducted on fine Ni-20Cr powder (spherical shape and 5 m in average particle diameter) to understand the sintering mechanism of fine metallic powder during pulsed electric current sintering (PECS). Insulation of the sample during PECS was carried out to investigate the influences of pulsed electric current passing through the sample. Temperature at the sample/die interface was measured as sample temperature. Pulsed electric current did not influence densification. The microstructure observation revealed that the necks between particles had very small curvature radius, which means the neck formation by compressive deformation of particles owing to creep. As results of the kinetic analysis of the densification, the creep rate of fine Ni-20Cr powder was two digits larger than the extrapolated values of the steady-state creep on PECS of coarse Ni-20Cr powder and creep tests reported previously. The larger creep rate of fine Ni-20Cr powder during PECS may be influenced by not only smaller grain size of powder particles but also contribution of the initial creep, which was faster than the steady-state creep.

Laser Processing as Surface Conditioning of Grinding Stones for Precision Machining Ceramics

The surface topography of a laser-dressed grinding stone used for ceramics machining is carefully studied to obtain abrasive-grain distributions using a confocal laser-scanning microscope. Effective cutting edge distributions calculated from grain distributions obtained through observations reasonably agree with distributions of ground grooves formed on a ceramic surface after grinding. In comparison with a mechanically dressed grinding stone, a laser-dressed grinding stone can achieve higher surface precision on a ground material surface with more number of ground grooves and more aligned grooves with respect to depth since the laser dressing method has an excellent advantage of selective removal of a matrix material without grain dislodgment. Introduction Engineering ceramics have been widely spread being used in electronic, optical, and magnetic devices, and as a result, they become essential materials in manufacturing. For the machining of engineering ceramics, a grinding stone (GS) consisting of diamond particles as abrasive-grains is a key tool. Diamond abrasive-grains distributed on the surface of a GS interact with a ground material to cut during grinding process, and therefore, the surface topography of a GS greatly affects its grinding performance and the surface precision of a ground material. Under the use of a GS, grinding-surface conditioning plays a great role on its surface topography. The surface conditioning, called a dressing or truing process, is a necessary process to control the surface topography, including abrasive grain distribution, of a GS for highly precise and efficient grinding. The authors have developed a dressing method by laser, achieving the selective removal of a matrix material with a minimal damage on grains and can control the removal amount [1,2]. In this report, we consider abrasive-grain distribution on a laser dressed surface as a topographical parameter to quantitatively confirm how the laser dressed surface influences the surface precision of a ground ceramic. In order to evaluate the surface precision on ceramics ground by abrasive-grains, an effective cutting edge distribution, which forms ground groove distribution on the ground surface, is obtained through surface observations and mathematical calculations, and described in detail in the present study. As a comparison, a mechanical dressing process was also studied in the same manner. Experimental Grinding Stone Fabrication and Dressing Process A porous cast-iron matrix diamond GS used in this study was prepared by sintering [3]. A mixture of a cast-iron powder (3.1mass% C, 5 μm) and diamond abrasive-grains (150-200 μm), prepared by dry-mixing with alumina balls for 6 h, was sintered in a graphite mold by a pulsed electric current sintering method under a uniaxial pressure of 10 MPa. The sintering temperature was 780 o C + 2 K measured at 5 mm away from the surface of a sintered body in the mold, and kept for 5 min. A sintered body contained 56 vol% of cast-iron, 19 vol% of diamond, and 25 vol% of pores. A sintered body was machined to form one face in a size of 4 mm x 13 mm. A prepared GS specimen was ground by a cup-shaped GC80V (vitrified bonded #80-green carbide grinding stone) with a water supply of 10 mm 3 s -1 as a surface-truing process. A GS specimen was fed by 50 μm at each pass onto the surface of the GC truer rotating in a speed, Vs, of 12 m s -1 as shown in Fig. 1. Three arrows, z Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 751-756 doi:10.4028/www.scientific.net/KEM.264-268.751

Fabrication of low thermal expansion SiC/ZrW2O8 porous ceramics

Low or zero thermal expansion porous ceramics are required for several applications. In this work near zero thermal expansion porous ceramics were fabricated by using SiC and ZrW2O8 as positive and negative thermal expansion materials, respectively, bonded by soda lime glass. The mixture of SiC, ZrW2O8 and soda lime glass was sintered by Pulsed Electric Current Sintering (PECS, or sometimes called Spark Plasma Sintering, SPS) at 700 °C. Sintered samples with ZrW2O8 particle size smaller than 25 μm have high thermal expansion coefficient, because ZrW2O8 has the reaction with soda lime glass to form Na2ZrW3O12 during sintering process. The reaction between soda lime glass and ZrW2O8 is reduced by increasing particle size of ZrW2O8. Sintered sample with ZrW2O8 particle size 45-90 μm shows near zero thermal expansion.

Influence of gas pressure on the surface composition of capsule-free HIPed borosilicate glass

Borosilicate glasses have been fabricated by capsule-free hot isostatic pressing. The oxidation reaction of carbon which come from graphite crucible and interfacial processes between carbon and borosilicate glass were important for carbon-rich layer formation on the surface of borosilicate glass material. It led to the evolution of color of glass surface. Effects of total gas pressure on HIP phase diagrams were considered to evaluate the difference of surface layer composition and melting behavior of borosilicate glasses at 1100°C under capsule-free HIPing. It was shown that, below total gas pressure of 40 MPa, CO gas was the most stable substance during glass melting and then carbon-rich layers were formed on the borosilicate glasses surface by precipitation-diffusion process during cooling when keeping high pressure, which led to the surface color change from black to gray under different pressure. When gas pressure was higher 40 MPa, the carbon was stable substance and the surface color was white.

Use of Fly Ash as Bonding Material on Low Thermal Expansion Porous Materials

In this work it was determined the effect of fly ash (FA) as bonding material during the fabrication of low thermal expansion porous materials. SiC, fly ash, Vitrified Bonding Material (VBM), and LiAlSiO4 powders were used as raw materials. Porous materials were sintered at 850°C and 950°C after manual milling and mechanical milling in a planetary ball milling at 800 RPM. SEM micrographs showed the presence of porous materials, and it was observed that fly ash particles did not melt at 850°C. However if sintering temperature increases at 950°C, FA starts to melt and it is forming bridges between SiC particles. Thermal expansion values were around 3.0x10-6 K-1. According to these results, it seems that it is possible to have a favorable synergy between FA and VBM to fabricate SiC porous materials with low thermal expansion values.

Abrasive Grain Efficiency and Surface Roughness in Machining Magnesium Alloys by Newly Developed Cup-Type Diamond-Grinding-Wheels

New cup-type diamond-grinding-wheels with hexagonal pattern have been developed. Grinding stone ratio, R is defined as the ratio between the hexagonal edge area containing abrasive grains and the total area of the wheel surface. In the present work, four kinds of hexagonal grinding wheels with different R (13 %, 19 %, 25 % and 36 %) and a conventional wheel (R: 100 %) were used to grind a light metals, which was represented by magnesium alloy AZ31B. Efficiency of abrasive grains and ground surface for machining a light metals were evaluated by calculating the number of abrasive grains which pass through a unit length of a sample surface for each grinding pass, Ng. The results show that surface roughness becomes smaller, i. e., smoother surfaces as Ng increases. Surfaces ground by the conventional wheel are rougher than those by using newly developed hexagonal grinding-wheels in spite of the larger Ng for the conventional wheel. Surface roughness data forms one curve in roughness vs. Ng graph for all hexagonal wheels, and forms another curve for the conventional grinding-wheel. The difference of two curves indicates that the number of effective working abrasive grains in hexagonal wheels is about 5 times higher than that of the conventional wheel. The similar results were obtained for machining sapphire according to our previous work. Hexagonal wheels show higher abrasive grain efficiency for machining not only hard-to-machine ceramics but also light metals such as magnesium alloys than conventional wheels.