• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.863-863
• /
• 2006

• Korean Journal of Materials Research
• /
• v.9 no.12
• /
• pp.1170-1175
• /
• 1999

The microstructures and mechanical properties of $Si_3N_4$ ceramics produced by nitridation and post-sintering using semiconductor-waste-Si sludge were investigated. Lots of microcracks were observed in the waste-Si powders which contained some amounts of amorphous $SiO_2$. The nitridation rate of waste-Si compacts showed lower value than that of commercial Si powder compacts. The nitridation rate was increased with increasing nitridation temperature and then the percent of nitridation at 1470$^{\circ}C$ showed 98%. The phases of $Si_3N_4$ in the reaction-bonded bodies were mixed with ${\alpha}$ and ${\beta}$-type, and small amounts of $Si_2N_2O$ phase while those after post-sintering were ${\beta}$-$Si_3N_4$ and ${\alpha}$-Sialon. The sample post-sintered at 1950$^{\circ}C$ showed the fracture toughness of 5.6 $^MPa{\cdot}m^{1/2}$ and the fracture strength of 497 MPa which were lower than those of sintered body using commercial Si powder possibly due to the formation of ${\alpha}$-Sialon phase.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.13 no.5
• /
• pp.76-81
• /
• 2014

The Engineering ceramics have some excellent properties as materials for modern mechanical and electrical components. It is, however, not easy to polish them efficiently because they are strong and hard. This study is carried out to obtain a mirror surface on engineering ceramics by surperfinishing with high efficiency. To achieve this, we conducted a series of polishing experiments using representative engineering ceramics, such as $Al_2O_3$, SiC, $Si_3N_4$ and $ZrO_2$, using diamond abrasive film from the perspective of oscillations peed, the rotational speed of the workpiece, contact roller hardness, contact pressure and feed rate. Furthermore, the polishing efficiency and characteristics for engineering ceramics are discussed on the basis of optimal polishing time and surface roughness. Our results confirmed that efficient superfinishing conditions and polishing characteristics of engineering ceramics can be determined.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1121-1121
• /
• 2006

• Journal of Industrial Technology
• /
• v.20 no.A
• /
• pp.247-256
• /
• 2000

Precursor gels with the composition of $xZrO_2{\cdot}(100-x)SiO_2$ systems (x=10, 20 and 30 mol%) were prepared by the sol-gel method. Kinetic parameters, such as activation energy, Avrami's exponent, n, and dimensionality crystal growth value, m, have been simultaneously calculated from the DTA data using Kissinger and Matusita equations. The crystallite size dependence on tetragonal to monoclinic transformation of $ZrO_2$ was investigated using XRD, in relation to the fracture toughness. The crystallization of tetragonal $ZrO_2$ occurred through 3-dimensional diffusion controlled growth(n=m=2) and the activation energy for crystallization was calculated using Kissinger and Matusita equations, as about $310{\sim}325{\pm}10kJ/mol$. The growth of $t-ZrO_2$, in proportion to the cube of radius, increased with increasing heating temperature and heat-treatment time. It was suggested that the diffusion of Zr4+ions by Ostwald ripening was rate-limiting process for the growth of $t-ZrO_2$ crystallite size. The fracture toughness of $xZrO_2{\cdot}(100-x)SiO_2$ systems glass ceramics increased with increasing crystallite size of $t-ZrO_2$. The fracture toughness of $30ZrO_2{\cdot}70SiO_2$ system glass ceramics heated at $1,100^{\circ}C$ for 5 h was $4.84Mpam^{1/2}$ at a critical crystaliite size of 40 nm.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.321-322
• /
• 2006

Nano-structured ceramics, which consist of structural elements with nanometer-size crystallites, are expected to show various unusual properties. We developed the novel nano-structured ceramics which consists of $Si_3N_4$ and TiN and a self-lubricant material. The ceramics was fabricated by powder metallurgy process using mechano-chemical grinding process and short-time sintering process. Each grain size of matrix and the self-lubricant particle was under about 50 nm and a few namometer. It showed high wear resistance and low friction coefficient by controlling of microstructure.

• Korean Journal of Materials Research
• /
• v.5 no.3
• /
• pp.268-274
• /
• 1995

세라믹재료의 동탄성계수 측정을 위한 공진주파수 측정장치를 구성하였다. 구조용 세라믹 재료로 이용되는 $Al_{2}$O_{3}$, SiC, $Si_{3}$N_{4}$의 온도를 120$0^{\circ}C$까지 5$0^{\circ}C$의 온도간격으로 올리면서 torsional resonant frequency와 flexural resonant frequency를 측정하고, 측정된 공진주파수로부터 각 재료의 탄성계수를 구하였다. SiC의 경우는 120$0^{\circ}C$의 온도까지 탄성계수가 선형적으로 감소하였으나, $Al_{2}$O_{3}$와 $Si_{3}$N_{4}$의 경우에는 각각 100$0^{\circ}C$와 80$0^{\circ}C$까지는 선형적으로 감소하나, 그 이상의 온도에서는 탄성게수의 감소폭이 증가하는 현상을 보였다. 이러한 현상은 다결정재료에서의 grain boundary sliding에 의한 것으로 알려져 있다. 상온에서 공진법으로 측정된 동탄성계수의 측정결과는 초음파법으로 측정한 결과와 비교하였는데, 4% 내에서 서로 일치하는 결과를 보였다.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.11 no.3
• /
• pp.86-92
• /
• 2002

In this study, experiments were carried out to investigate the characteristics of grinding and wear process of diamond wheel far ceramic materials. Normal component of grinding resistance of $Al_2$O$_3$ was less then that of $Si_3 N_4$ and $ZrO_2$. This seems to be the characteristics of ceramic tools on work pieces both of high hardness. For the case of $Si_3 N_4$ and $ZrO_2$, as the mesh number of wheel increases, the surface roughness decreases. For the case of $Al_2 O_3$, the surface roughness does not decreases. Specific binding energy decreases as the material removal rate per unit time increases. For the case of $Si_3 N_4$ and $ZrO_2$, grinding is carried out by abrasive wear processes. For the case of $Al_2 O_3$, grinding is carried out by grain shedding process due to brittle fracture.

• Journal of the Korean Ceramic Society
• /
• v.47 no.6
• /
• pp.503-508
• /
• 2010

$Eu^{2+}$-doped $\beta$-SiAlONs ($Si_{6-z}Al_zO_zN_{8-z}:Eu_y$) are recognized as promising phosphor materials to build an white LED for lighting application due to its excellent absorption/emission efficiency in the long wave length region. In this research, the fabrication of $\beta$-SiAlON:Eu plate phosphor by sintering was investigated with fixed Eu content(y) and varied composition of the host lattice(z). The addition of the activator $Eu_2O_3$ lead to enhanced densification by forming the transient liquid phase. The refinement of a composition by the calculated lattice parameter indicated that the measured composition of the fabricated specimens is nearly same to that of designed one. The single phase $\beta$-SiAlON:Eu plate with relative density of 96.4% was achieved by addition of 2 wt% CaO, which implies the possibility of full densification by adjusting the processing variables.

• Tribology and Lubricants
• /
• v.11 no.3
• /
• pp.11-23
• /
• 1995

The friction and wear behavior of $Al_{2}O_{3}$, SiC, and $Si_{3}N_{4}$ under the different sliding conditions were investigated. The cylinder-on-disc wear tester was used for a wear test method. Using the servo-motor, the sliding speed did not alternate due to the frictional forces. Three kinds of loads were selected to watch the variation of the wear rates and the frictional forces under a constant speed. Three kinds of sliding conditions were used to see the effects of the oxidation and the abrasion. The dominant wear mechanisms of $Al_{2}O_{3}$ were the abrasion and the formation of transfer layers. The abrasion has a great effect on the wear of SiC. The wear of $Si_{3}N_{4}$ was due to the asperity-failure and the oxidation. Also, the wear rate of each ceramic is shown to be related to the frictional power provided to the tribological system.