Generally low angle XRD shows the mesoporosity of the materials. but i dont know how it does this. Can any body explain it?
BET adsorption isotherms will be a better method to determine the mesoporosity of a material that give you an idea about the pore diameter, surface area, type of mesoporous materials etc
SAXS usually give information regarding how these mesopores are ordered or symmetrically distributed. it will give an idea about a material whether mesopores are hexagonally ordered or cubically ordered.
You can estimate the wall thickness of your mesoporous material from the d100 values, which can be extracted from your SAXS measurements. Still you need to know the pore diameter of your material to get the wall thickness, which you get from BET measurements
Could you say whats the difference between a mixed oxide and composite? How can XRD differentiate them?
From XRD, normally the identification of species is done with the 2theta of peak positions. For each material, there are accepted fingerprints or set of peaks at various peak positions at various peak intensity(you can tell peak height for understanding). A CuO powder will give three - four peaks in an xrd (only example), at various 2theta values of 39, 24, 57 etc. having maximum intense peak at 39, next bigger peak at 24 and next one at 57 etc. If you get a similar matching profile for your material also, even without chemical analysis you can say, its CuO. Similarly for meso porous materials, peak at 2theta
Can any one suggest a good book for characterization of porous materials?
I think for mesoporosity, XRD can't help you a lot for determining your material is mesopore or micropores, just help you what kind of you crstal type. For mesopority, the best way is using BET measurement because you can determine the surface area.. btw, your material is mesopore fully or just combination between mesoporosity and microporosity
The low angle peak in XRD ensures an ordered arrangement in a mesoporous structure. The sharpness of a peak suggests the amount of ordered arrangement present in a structure while in most of the cases just a hump or a broadened peak indicates incorporation of randomness in a structure. But it is always a good idea to cross-check the XRD results with a BET isotherm (typically a type IV curve) or a TEM cross-sectional micrograph, both of which indicates the presence or absence of an ordered arrangement.
Dear Dr. Chakravati
Many thanks for your valuable remarks in this topic.
Mesoporosity (pore size distribution) is revealed from the gas adsorption isotherm (BJH analysis) as many pointed out, but that is not BET. The BET theory deals with only monolayer adsorption at p/po
I am also asking the question? What is the relationship between small angle X-ray peaks and mesoporosity?
Low angle XRD doesn't show the mesoporosity of the materials. But the peaks at low angle imply to the pore ordering.
Small angle scattering (SAXS or SANS) would do this for you. There are plenty of good reference books on the subject, plus many useful websites. Try this one: http://smallangle.org/content/Learning-About-SAS
and good resources here:
http://www.diamond.ac.uk/Beamlines/Soft-Condensed-Matter/small-angle/Beginners-Guide.html
Nice links Edward! Thanks!
"Beam projection: Because of the grazing-incidence angle, the focused x-ray beam (e.g. 50 μm tall) is projected into a long stripe over the sample surface (e.g. a 50 μm beam at 0.1° incidence is projected to 29 mm). For many samples, this will in fact spill over the up/down-stream edges of the sample (i.e. over-illuminate the sample in the beam direction). This wide area illumination has the advantage of dramatically increasing the effective scattering volume, and thus the measured signal. This also inherently averages over a wide area, yielding data that is statistically representative of the entire film. (On the other hand, this wide-area probing has the disadvantage of making more local probing difficult in GISAXS.)" http://gisaxs.com/index.php/GISAXS
I'm beginning to understand my thin film 2D XRR data a lot better :-)
Attached are examples of XRR (GISAXS) data from the NIST 2000 SRM and a Pt thin film on Si substrate. We were using a 20+mm x0.5mm 2D beam size approximately instead of the "point source". I'd target doing the same with a collimated "point source" as well next time I have the luxury of being in front of a beam. I need to understand how to quantify the "porosities" on these surfaces from the 2D data we have. Any references would be appreciated :-)
https://www.researchgate.net/post/Would_anyone_have_a_clue_as_to_the_origin_of_unexpected_spots_in_the_real_time_2D_XRR_signal_from_thin_film_samples_on_substrates_Yuneda_Spots?_tpcectx=profile_questions
Theoretically, SAXS is very useful techniques to reveal a size distribution and its shapes if the sample is in nano scale ranging 1 ~ 100 nm. Because small angle X-ray will act with particles and generate incoherent scattering, not coherent (diffraction by ordered interplanes). By measuring a profile by 1D or 2D, we can estimate properties of nano materials by using indirect fitting via fourier transformation, least square minimization comparing related functions.
And, it doesn't matter what is inside of the sample. I mean SAXS results only distinguish the X-ray contrast between nano and background. So, nano-sized particles, pores and composites will make a scattering in a small angle region. After that the analyst has to analyze what the result is meaning for. But, if there are co-existing with nano-particles and pore, that would be problem to distinguish properly.
Dear Daniel lee
I did XRD for Nanoporous gold sample. I do not get peak of silicon substrate in Nanoporous gold,but I got silicon substrate peak in non porous sample why?
- Badges
- Science method
- Similar topics
- Methodology
- Crystallography
- X-ray Diffraction