Abstract: The ultrafine CaCO₃ crystal growth controlled by Na₅P₃O₁₀ in the carbonation of Ca(OH)₂ suspension, was investigated by using SEM.
The results show that CaCO₃ nucleates along with the nucleus growth. The presence of Na₅P₃O₁₀ accelerates the CaCO₃ nucleation. At the
initial stage, a large number of CaCO₃ nucleus engender, and metastable tiny crystallites (R=23～26nm) can be observed in SEM imagine. The CaCO₃ crystal
growth controlled by short distance diffusion when mass pass through the crystal interface, does not correspond to Zener-Ham theory. At the next stage, the metastable
tiny crystallites disappear in SEM imagine. The CaCO₃ crystal growth abides by the long distance control model R(t)=λ_i(Dt)ⁿ, in which the time coefficient
n is 0.4874～0.4992 (theory value n=0.5) and the constant λ_i Dⁿ decreases from 16.69 to 11.36. Consequently, Na₅P₃O₁₀ can effectively inhabit the CaCO₃ crystal growth.

Key words: ultrafine CaCO₃, Na₅P₃O₁₀, crystal growth control, diffusion growth mode