• Nuclear Engineering and Technology
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• v.48 no.2
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• pp.299-303
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• 2016

Prompt gamma activation analysis using a thermal neutron-guided beam at Japan Atomic Energy Agency JRR-3M was applied for the precise determination of Si in silicon nitride ceramic reference materials [Japan Ceramic Reference Material (JCRM) R 003]. In this study, the standard addition method coupled with internal standard was used for the nondestructive determination of Si in the sample. Cadmium was used as internal standard to obtain the linear calibration curves and to compensate for the neutron beam variability. The analytical result of determining Si in JCRM R 003 silicon nitride fine powder ceramic reference materials using prompt gamma activation analysis was in good agreement with that obtained by classical gravimetric analysis. The relative expanded measurement uncertainty (k = 2) associated with the determined value was 2.4%.

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.318-324
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• 2012

Reaction-bonded silicon nitrides containing rare-earth oxide sintering additives were densified by gas pressure sintering. The sintering behavior, microstructure and mechanical properties of the resultant specimens were analyzed. For that purpose, $Lu_2O_3-SiO_2$ (US), $La_2O_3$-MgO (AM) and $Y_2O_3-Al_2O_3$ (YA) additive systems were selected. Among the tested compositions, densification of silicon nitride occurred at the lowest temperature when using the $La_2O_3$-MgO system. Since the $Lu_2O_3-SiO_2$ system has the highest melting temperature, full densification could not be achieved after sintering at $1950^{\circ}C$. However, the system had a reasonably high bending strength of 527 MPa at $1200^{\circ}C$ in air and a high fracture toughness of 9.2 $MPa{\cdot}m^{1/2}$. The $Y_2O_3-Al_2O_3$ system had the highest room temperature bending strength of 1.2 GPa.

• Tribology and Lubricants
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• v.5 no.1
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• pp.28-35
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• 1989

The wear tests of ceramic materials in dry rolling contact were carried out at room temperature to investigate their macroscopic wear characteristics. Both point contact and line cootact were adapted in the wear tests of them. Ceramic materials used in these tests were silicon nitride, silicon carbide, cermet of TiN and TiC, titania, and alumina. The wear test of the bearing steel was carried out to compare to the wear test results of the ceramic materials. The results showed that the wear rate of silicon nitride was smaller than any other ceramic materials and bearing steel. In the steady wear, the wear volume of ceramic materials increases linearly with the rolling distance. It was also found from the experimental results that fracture toughness and surface roughness dominate the wear process of ceramic materials in dry rolling contact.

• Korean Journal of Materials Research
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• v.17 no.7
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• pp.366-370
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• 2007

Silicon nitride ($Si_3N_4$) ceramics have been considered for various components of nuclear power plants such as the mechanical seal of a reactor coolant pump (RCP), the guide roller for a control rod drive mechanism (CRDM), and a seal support, etc. Corrosion behavior of $Si_3N_4$ ceramics in a high-temperature and high-pressure water must be elucidated before they can be considered as components for nuclear power plants. In this study, the corrosion behaviors of $Si_3N_4$ ceramics containing MgO and $Al_2O_3$ as sintering aids were investigated at a hydrothermal condition ($300^{\circ}C$, 9.0 MPa) in pure water and 35 ppm LiOH solution. The corrosion reactions were controlled by a diffusion of the reactive species and/or products through the corroded layer. The grain-boundary phase was preferentially corroded in pure water whereas the $Si_3N_4$ grain seemed to be corroded at a similar rate to the grain-boundary phase in LiOH solution. Flexural strengths of the $Si_3N_4$ ceramics were significantly degraded due to the corrosion reaction. Results of this study imply that a variation of the sintering aids and/or a control (e.g., crystallization) of the grain-boundary phase are necessary to increase the corrosion resistance of $Si_3N_4$ ceramics in a high-temperature water.

• Korean Journal of Materials Research
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• v.10 no.1
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• pp.83-89
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• 2000

$Si_3N_4$ powder with 2wt% $Al_2O_3$ and 6wt% $Y_2O_3$ additives was sintered by gas pressure sintering (GPS) technique. The variations in the unlubricated wear behavior depending on sintering time were compared. Tribological properties depending on sintering time are associated with fracture toughness as well as flexural strength of materials. When increasing the sintering time, the larger elongated grains were formed as a result of exaggerated grain growth. As the fracture toughness and flexural strength decreased, the wear volume increased. On the basis of these experimental results, the unlubricated wear properties of silicon nitride were found to be governed mostly by both the fracture toughness and the flexural strength of the material.

• Laser Solutions
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• v.12 no.4
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• pp.12-16
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• 2009

The engineering ceramic is one of the materials advantageous in various conditions with high strength, endurance at high temperature, abrasion resistance and corrosion resistance, etc. However, due to high strength and high brittleness, ceramic incurs high costs and long time on finishing process required after sintering. So a process for obtaining wanted measurements of them has been studied using the high temperature which makes ceramics softened and heat affected recently. This study makes an estimate of laser-assisted machining (LAM) if an economically practical process for manufacturing precision silicon nitride ceramic parts using laser beam. In this study, mechanical properties of silicon nitride at high temperature were observed. And during the LAM, it was observed that cutting force and tool wear were reduced and oxidation of machined surface was increased according to a increase of laser power.

• Proceedings of the Korean Society of Laser Processing Conference
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• 2006.11a
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• pp.34-40
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• 2006

• Proceedings of the Korean Ceranic Society Conference
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• 2003.10a
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• pp.118.2-118
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• 2003

• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.61-65
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• 2001

The fracture toughness of ceramics can be measure by such various methods as DT (double torsion), CN (chevron notch) etc. But, the application of these methods to the engineering ceramics is very difficult because of its very high hardness. So, IF (indentation fracture) method is generally used for the evaluation of fracture toughness of ceramics. The Median crack induced by the sharp Vickers indenter was compared with the detected AE (acoustic emission) signal. On the silicon nitride ceramics, the AE test results agree fairly well with the median crack occurance and growth process. But, on the alumina, very many complicated crack signals were detected besides median crack. It can be considered that the IF methods must be used in limited engineering ceramics materials.

• Journal of Powder Materials
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• v.8 no.3
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• pp.179-185
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• 2001

Through the observation of wear scar of two ceramic materials, microstructural wear mechanisms was investigated. As for the $Al_2O_3$-5 vol% SiC nanocomposite, the grain boundary fracture was suppressed by the presence of SiC nano-particles. The intragranular SiC particles have inhibited the extension of plastic deformation through the whole grain. Part of plastic deformation was accommodated around SiC particles, which made a cavity at the interface between SiC and matrix alumina. On the other hand, gas-pressure sintered silicon nitride showed extensive grain boundary fracture due to the thermal fatigue. The lamination of wear scar was initiated by the dissolution of grain boundary phase. These two extreme cases showed the importance of microstructures in wear behavior.