Report on metallographic preparation of ceramic spheres for nuclear fuel

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Report on metallographic preparation of ceramic spheres for nuclear fuel

2021-12-25

New Generation Nuclear Reactor Fuel Element, Metallography of Nuclear Fuel Ball TRISO Particles. The center is UO2, and the outer coating layers are Buffer, IPyC, SiC, OPyC in sequence, with a thickness of about tens of microns, and the columnar SiC matrix.

Equipment.consumables

Equipment

Trojan Alpha-600 automatic grinder&polisher;

Leica DM2700M metallographic microscope;

Hairdryer;

Consumables

Ethyl alcohol;Degreasing cotton;
Trojan diamond grinding disc (P400;P1500;P3000);
Trojan NL-JP white fiber polishing cloth(8in);
Trojan CS-JP blue natural silk polishing cloth (8in);
Trojan ZN-JP black polyurethane polishing cloth (8in);
Trojan 3μm polycrystalline diamond suspension;
Trojan 1μm polycrystalline diamond suspension ;
Trojan 0.05μm non-crystallizing silica.

Grinding

Polish the specimen with Alpha-600 automatic grinder&polisher. In order to improve the efficiency, you can use a coarse diamond grinding disc to quickly grind the position you want to observe. Then finely grinding the position for a long time to remove chippings and deep cracks from plane grinding.

Alpha-600 automatic grinder&polisher

Diamond grinding disc

P3000 grinding-50×

Equipment	Alpha-600 automatic grinder&polisher
Consumables	Diamond grinding disc:P400, P1500,P3000
Parameter	P400:pressure 24N,same direction 200rpm,time:Grind until it is close to the position to be observed P1500:pressure:22N,same direction:150rpm,time:20min P3000:pressure:22N,same direction:130rpm,time:3min

Polishing-plane polishing

Polish the specimen with Alpha-600 automatic grinder&polisher,use NL polishing cloth with 3μm polycrystalline diamond suspension for plane polishing. At the same time, add non-crystallizing silica suspension for chemical mechanical polishing.

NL-CP white fiber polishing cloth

diamond suspension

NL-polishing-50×

Equipment	Alpha-600 automatic grinder&polisher
Consumables	NL-CP white fiber polishing cloth,3μm polycrystalline diamond suspension+non-crystallizing silica suspension
Parameter	Pressure:25N,same direction:150rpm,time:600s

Polishing –medium polishing

Polish the specimen with Alpha-600 automatic grinder&polisher, use CS polishing cloth with 1μm polycrystalline diamond suspension for plane grinding,add non- crystallizing silica suspension for chemical mechanical polishing at the same time.

CS-JP blue synthetic silk polishing cloth

Diamond suspension

CS-polishing-50×

Equipment	Alpha-600 automatic grinder&polisher
Consumables	CS-JP blue synthetic silk polishing cloth,1μm polycrystalline diamond suspension+non- crystallizing silica
Parameter	Pressure:20N,same direction:150rpm,time:300s

Polishing-final polishing

Polish the specimen with Alpha-600 automatic grinder&polisher, Use ZN polishing cloth with non-crystallizing silica suspension for polishing.

ZN-ZP black polyurethane polishing cloth

Non-crystallizing silica suspension

ZN-polishing-50×

ZN-polishing-100×

Equipment	Alpha-600 automatic grinder&polisher
Consumables	ZN-ZP black polyurethane polishing cloth,1μm polycrystalline diamond suspension+non-crystallizing silica suspension
Parameter	Pressure:15N,reverse direction:120rpm,time:180s

Observation

Equipment	Leica DM2700M metallographic microscope
Consumables
Parameter	50×→500×

Analysis

Ceramic ball 50×

Ceramic ball 50×

Ceramic ball 100×

Ceramics are hard and difficult to grind with ordinary SiC abrasive paper, so resin-based diamond grinding discs can be used for grinding. However, coarse grinding discs tend to chip and crack the ceramic, so it takes a longer time to remove the larger pits and cracks on the ceramic surface during fine grinding.
Polishing requires the use of mechanochemical polishing to prepare a good surface. If the sample is not mounted well enough, not all the pellets can be ground out at the same time. In order to prevent the ceramic balls in the core from falling off, it is necessary to keep the position of the small balls evenly distributed during mounting. When grinding, the balls can be ground uniformly. As long as the grinding does not exceed the radius of the ball, the ball can be prevented from coming out.

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