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Green Silicon Carbide for Optical Glass Polishing

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Green Silicon Carbide for Optical Glass Polishing

1. Properties of Green Silicon Carbide

Green silicon carbide has a purity of over 98.5% with a Mohs hardness of 9.3, harder than optical glass, which endows it with powerful cutting capacity. It boasts self-sharpening performance: once the particle edges wear flat, new sharp cutting edges form spontaneously, greatly lifting processing efficiency.

Green silicon carbide features high thermal conductivity, which rapidly dissipates heat generated during grinding. This prevents optical glass from thermal deformation, surface pitting and haze induced by grinding heat.

It has stable chemical properties with resistance to both acids and alkalis, classified as an inert substance. It will not corrode optical coatings or glass substrates during grinding.

Production Process of Green Silicon Carbide

Crush green silicon carbide ingots → Add oxalic acid for pickling to remove iron impurities → Hydraulic classification under controlled water pressure → Sedimentation after classification → Drying → Loose screening.

Pickled and hydraulically classified green silicon carbide delivers narrow particle size distribution free of oversized coarse grains. It effectively reduces scratch defects on optical glass and improves finished product yield.

2. Common Grades of Green Silicon Carbide for Optical Glass Grinding

Optical glass processing is divided into three stages: rough grinding, medium grinding and fine grinding.

Rough grinding grades: GC #240, #320, #400
These coarse grits eliminate cutting marks, burrs and edge chippings on optical glass.
D50 particle size: 20~35μm. Cut glass blanks often have uneven surfaces, deep cutting traces and cracked edges. Coarse green silicon carbide powder removes such defects efficiently via wet grinding with cast iron lapping plates, ideal for rough machining of lens and prism blanks.
Medium grinding grades: GC #600, #800, #1000
Medium grinding removes deep scratches left in rough grinding.
D50 particle size: 11~20μm. This is the mainstream process for mass production of optical lenses, balancing material removal rate and surface roughness.
Fine Grinding / Pre-Polishing (refine surface textures to prepare workpieces for final cerium oxide polishing)
Applicable grits: #1500 / #2000 / #2500
D50 particle size: 3~7μm. It lays the foundation for mirror finish of optical lenses, suitable for glass parts requiring ultra-smooth mirror surfaces.

European Standard	F230 F240 F280 F320 F360 F400 F500 F600 F800 F1000 F1200 F1500 F2000
Japanese Standard	#240 #280 #320 #360 #400 #500 #600 #700 #800 #1000 #1200 #1500 #2000 #2500 #3000 #4000 #6000 #8000 #10000

JIS STANDARD macrogrit particle size distribution
Size		D0(um)	D3(um)	D50(um)		D94(um)
#240		≤127	≤103	57.0±3.0		≥40
#280		≤112	≤87	48.0±3.0		≥33
#320		≤98	≤74	40.0±2.5		≥27
#360		≤86	≤66	35.0±2.0		≥23
#400		≤75	≤58	30.0±2.0		≥20
#500		≤63	≤50	25.0±2.0		≥16
#600		≤53	≤41	20.0±1.5		≥13
#700		≤45	≤37	17.0±1.5		≥11
#800		≤38	≤31	14.0±1.0		≥9.0
#1000		≤32	≤27	11.5±1.0		≥7.0
#1200		≤27	≤23	9.5±0.8		≥5.5
#1500		≤23	≤20	8.0±0.6		≥4.5
#2000		≤19	≤17	6.7±0.6		≥4.0
#2500		≤16	≤14	5.5±0.5		≥3.0
#3000		≤13	≤11	4.0±0.5		≥2.0
#4000		≤11	≤8.0	3.0±0.4		≥1.8
#6000		≤8.0	≤5.0	2.0±0.4		≥0.8
#8000		≤6.0	≤3.5	1.2±0.3		≥0.6
FEPA STANDARD
Size	D3(um)		D50(um)		D94(um)
F230	≤103		57.0±3.0		≥40
F240	≤87		48.0±3.0		≥33
F280	≤74		40.0±2.5		≥27
F320	≤66		35.0±2.0		≥23
F360	≤58		30.0±2.0		≥20
F400	≤50		25.0±2.0		≥16
F500	≤41		20.0±1.5		≥13
F600	≤37		17.0±1.5		≥11
F800	≤31		14.0±1.0		≥9.0
F1000	≤27		11.5±1.0		≥7.0
F1200	≤23		9.5±0.8		≥5.5
F1500	≤20		8.0±0.6		≥4.5
F2000	≤17		6.7±0.6		≥4.0

3. Performance Comparison: Green Silicon Carbide vs White Fused Alumina vs Cerium Oxide for Optical Glass Polishing

Abrasive

Mohs Hardness

Application Scenarios

Advantages & Disadvantages

Green Silicon Carbide (GC)

9.3

Rough grinding, medium & fine pre-polishing of hard optical glass and fused silica

Advantages: Highest material removal rate, excellent heat dissipation

Disadvantages: Not suitable for final mirror polishing, leaves relatively coarse texture

White Fused Alumina (WA)

9.0

Medium grinding of soft and ordinary glass

Advantages: High toughness

Disadvantages: Slow cutting speed, prone to heat accumulation, low efficiency on hard glass

Cerium Oxide (CeO₂)

7~8

Ultra-precision final mirror polishing

Advantages: Produces nano-level ultra-smooth surface

Disadvantages: Weak cutting force, only used for finishing processes

4. Types of Optical Glass Suitable for Green Silicon Carbide Grinding

Hard optical glass: Borosilicate glass, fused silica, UV optical lenses, optical flats, optical windows
Conventional optical components: Camera lenses, microscope prisms, telescope lenses, optical filters, rough grinding of optical fiber preforms
Special brittle crystals: Pre-grinding treatment for sapphire substrates and piezoelectric ceramics

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