graphite lattice model (Q55779)

I've described models of three types of elemental carbon, "Buckyballs", "Nanotubes", and a "Diamond Lattice Model". Graphite, the most common form of carbon, remains to be done. The Naval Research Laboratory crystal site has a very nice section on carbon http://cst-www.nrl.navy.mil/lattice/struk/carbon.html that has information about 3 forms of graphite. Coordinates of the forms are available as well as rotatable models that can be viewed with a javascript applet. November 13, 2019 - The NRL site seems to have been discontinued - See "Carbon and Related Structures" at - https://homepage.univie.ac.at/michael.leitner/lattice/ The common A9 hexagonal form appears to be the easiest to print. It's simple enough so that coordinates can be calculated with pencil and paper allowing one to position the model for the benefit of the printer. The A9 graphite structure consists of planar sheets of carbon atoms with a bond distance of 1.42 Angstroms in a hexagonal array. Alternate layers are directly above one another at a distance of 6.7 Angstroms. The intermediate layer, which is 3.35 Angstroms from the layer above and below is an identical hexagonal array, It is positioned so that a line drawn between the centers of the hexagons on the upper and lower sheets goes through a carbon atom in the intermediate layer. The fortran program, expand_graphite.f, makes the model using simple geometry and outputs openSCAD module calls. Comment statements in the program help explain how this was done. The program is a bit of a hack; it grew longer and longer as more hexagons and atoms were added. The object was to orient the sheets to be at right angles to the build surface and make it larger than the version available from the Naval Research Laboratory, I checked the finished fortran, openSCAD version against the NRL version in netfab Studio. The two versions superimposed perfectly. Two models are provided. A sturdy model, with atoms, that prints and scales well, Graphite7_x4_2c.stl. It is the output of makegraphite7.scad scaled up by a factor of 4 and with two added rings (outer diameter 44 mm, hole 30 mm, thickness 2 mm). Graphite11_x4_2c.stl is a more open model without atoms, that shows only the hexagonal lattice. The shift between the hexagonal layers can clearly be seen.