Small angle X-ray scattering (SAXS) is a useful tool for the study of the structure of porous materials with nano-sized pores. The scattering by an ideal two-phase porous system with sharp boundary obeys Porod's law. If there are disorder or thermal density fluctuation within solid phase, it will give rise to an additional relatively low scattering mixed with the SAXS intensities of pores and then lead to a positive deviation from Porod's law. It is therefore necessary to correct the deviation for studying the pore structure. In this paper, a new method of positive deviation correction for the slit-smeared SAXS intensities of porous materials is developed: (1) plotting the In[q^3I(q)]～q^2 curve, which shows a positive deviation from Porod's law; (2) fitting this curve in the high angle region with a positive slope using the equation ln[q^3I(q)] =InK'＋σ^2q^2, where K' is Porod constant and σ is a parameter in relation to the size of the electron density micro-inhomogeneity; then (3) deducing the σ^2; and finally (4) plotting the In[q^3I(q)] - σ^2q^2～q^2 curve, which will show no deviation from Porod's law, and the scattering intensities of the pores can then be obtained by , I'(q)=exp{In[q^3I(q) ]- σ^2q^2}/q^3.

Key words: X-RAY SMALL ANGLE SCATTERING ANALYSIS