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2023
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How to distinguish CVD synthetic diamonds from HTHP synthetic diamonds
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HPTP diamonds and CVD diamonds are two methods for producing synthetic diamonds; the resulting man-made diamonds do not have identical physical and chemical properties, and they exhibit subtle differences in certain respects.
How to distinguish CVD synthetic diamonds from HTHP synthetic diamonds
HPT‑grown diamonds and CVD diamonds are two methods for producing synthetic diamonds; the resulting gemstones do not exhibit identical physical and chemical properties, and subtle differences persist in certain respects.
1. In terms of color, HPHT‑grown diamonds are predominantly yellow and brownish‑yellow, with fewer colorless or blue stones, whereas CVD‑grown diamonds are mostly brownish‑tinted, though some are also colorless or blue.
2. In terms of crystal structure, HPHT‑grown diamonds typically occur as octahedral–cubic polyhedral aggregates; their crystals are well‑formed and often exhibit irregular dendritic growth patterns, whereas CVD‑grown diamonds are predominantly tabular or thick‑tabular in habit.
3. On the color zoning, HPHT synthetic diamonds generally exhibit uneven coloration; yellow synthetic diamonds often display hourglass‑shaped or Maltese cross‑shaped color zoning.
4. In terms of internal characteristics, HPHT‑grown diamonds typically contain needle‑like, dust‑like, crumb‑like, and various irregularly shaped metallic inclusions. By contrast, CVD‑grown diamonds generally exhibit fewer inclusions; only occasional needle‑like features, black amorphous carbon particles, or graphite are observed.
5. Under a polarizing microscope, HPHT‑grown diamonds exhibit very weak dichroism and display faint black cross‑shaped bright bands, with barely perceptible changes in interference colors, whereas MPCVD‑grown diamonds show more pronounced extinction and resemble natural diamonds more closely.
6. In fluorescence and phosphorescence detection, HPHT‑grown diamonds typically exhibit yellow‑green fluorescence under shortwave (SW) UV, with SW > LW; in contrast, CVD diamonds generally show more variable responses under both longwave (LW) and shortwave (SW) UV, ranging from inert to orange fluorescence.
Accordingly, given these distinct characteristics, different methods can be employed to identify synthetic diamonds. HTHP and CVD diamonds exhibit distinct fluorescence signatures, allowing for their differentiation by analyzing the intensity and color of their fluorescence signals.
The crystal structures of HTHP diamonds and CVD diamonds are not identical, so they can also be distinguished using X-ray diffraction patterns. Additionally, Raman spectroscopy can be employed to differentiate between these two types of diamonds; their Raman spectra exhibit distinct features, allowing for their identification through spectral analysis.
Synthetic diamond
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