Having opened an experimental datafile using the Sampling page, you may now decide to input the Channel porosity rather than the Open porosity. As previously stated on the Sampling page, this is the porosity visible from an electron micrograph of the surface, as a channel passing through the sample. It will normally be less than the Open porosity, because if pores within the matrix of the porous material are larger than the throats connecting them to the surface, some or most of their volume will be concealed in a micrograph of the surface.
In the example case of the IG110 graphite shown below, the Open porosity is nominally 12.59%, but say we have measured the channel porosity from image analysis of an electron micrograph as 2.67%. Click on the small down-arrow next to Advanced, and scroll down the Advanced sub-screen until you see the relevant details. Enter the value of the channel porosity as shown:
Figure CP 1
On entering the channel porosity, the image analysis cylindrical equivalent void diameter range is displayed in grey-background number boxes, as shown above. The cylindrical-equivalent diameter d is related to the surface-visible area of a pore measured by image analysis as d = √(4 x area / π ) . To use the default values, i.e. the whole range of sizes, just click the Accept button.
However, it is very often impossible to carry out image analysis over the whole size range. If you have carried out the image analysis over a smaller size range, for example because any voids below 1.12 μm cylindrical-equivalent diameter cannot be distinguished from surface imperfections, then input the channel porosity range as shown below. Your entry is confirmed by the tick in the check-box next to it. Note that you do not have to input both limits of the range - if one limit is the same diameter as one of the percolation range limits, then leave it as zero, with the check-box not ticked beside it. So in the case below, the upper limit for image analysis will be 89.14 μm. If you wish to revert to the default values of the minimum or maximum diameter at any time, you can just type zero into the box
Figure CP 2
Having clicked the Accept button, you will probably be taken to the Curve Fitting window below.
Figure CP 3
Alternatively, if there has been an initial problem with any of the input parameters, you will be taken to a window showing only the sampling operation, as shown below.
Figure CP 4
In this case, click Run new operation... | Initialisation | Fitting to access the Curve Fitting screen shown above in Figure CP 3.
Figure CP 5
At this point it is likely that you will want to save the additional details of your sample datafile (i.e. channel porosity and minimum and maximum diameter of the image analysis range) so that you do not have to type them in every time you start a modelling session. To save them, on the Curve Fitting screen click the Go home / prepare for batch mode button
Figure CP 6
That will take you back to the Operations List screen shown above. Then click File | Save as ... PoreXpert file :
Figure CP 7
You will then arrive at a Save as screen with options below analogous to those shown here :
Figure CP 8
You are given a default file name, as shown, but if you use that it is important to remove the file type extension, in this case .csv, to avoid confusion. If you wish to be able to read the datafile, which is written in eXtended Markup Language (XML), then on the Save as type dropdown menu choose Uncompressed PoreXpert File:
Figure CP 9
Then, for your next modelling session, you can just load the .pXt or .poreXpert file at the outset. If you want to check its details, just double-click the datafile on the Operations list screen, Figure CP 4.
As you are in channel porosity mode, you will also need to check two extra parameters on the fitting page.