What is X-ray small angle scattering method?

When X-rays pass through a medium with microscopic inhomogeneities (such as ultrafine particles, microporous impurities, dislocations, holes and other scatterers), scattering will occur. Since the size of the scatterers is much larger than the wavelength of the X-ray, scattering The angular domain is very small (about ±2o),

Therefore, it is called X-ray small angle scattering.

For a single spherical particle, Scattering intensity I=I₀m²ф² (KR)

In the formula, m——the difference between the number of electrons in the particle and the number of electrons in the surrounding medium of the same volume, which can be written as m=ρ_e V(R),ρ_eis the electron density difference between the particle and the surrounding medium;

ф(KR)——Scattering coefficient of spherical particles ф(KR)=3/(KR)³

(sinθKR-KRcos),K=4πsinθ/λ，λ is the wavelength of incident X-ray, sinθ≌ε/2, and ε is the scattering angle.

Therefore, the scattering intensity can be written as I=I₀V(R)R³ф² (KR).

For a polydisperse particle system, assuming the particle distribution function is W(R), then we have

In the formula, the coefficient

C is a constant, so the particle size distribution can be calculated from the scattering intensity at different scattering angles measured experimentally.

There are imported X-ray small-angle scattering instruments, and their particle size testing range is 0.003~0.5um. Two points should be noted in the method:

① Just like the laser particle size analyzer, there is a complex scattering problem; ② Since X-ray scattering is related to the number of electrons in the particles, when the surface of the particles is oxidized (such as metal particles) or the surface absorbs water (such as oxides, etc.), the number of electrons will change. Calculations need correction.