Applications and products
Solids may be subdivided into 5 groups: crystalline, poly- crystalline,
micro-crystalline, liquid- crystalline, semi-crystalline and amorphous. The
atomic or molecular arrangement in crystals is extremely regular in 3
dimensions due to translational symmetry. With X-ray diffraction the fuil
symmetry and the crystal lattice can be determined. Moreover, the positions of
all atoms in a crystal can be deterrnined, leading to a detailed deseription
of the molecular architecture and the molecular packing.
In poly- and micro-crystalline solids the atomic or molecular
arrangement is of (nearly) similar quality as stated above. In this case X-ray
diffraction is frequentiy used to identify the crystalline component(s) - even
in complicated mixtures - and to quantify the lattice imperfections or
crystallite sizes. In mixtures of crystalline components, quantitative
analysis of components is possibie through several methods. The type of method
is problem dependent.
At DSM Research this type of analysis is availabie under various conditions:
temperature (from -100"C to 1000"C), reduced atmospheric pressure and several
types of gases. This allows one to study phase transitions, solid state
reactions, therrnal stability etc.
In liquid- and semi-crystalline solids, the atomie or molecular
arrangement is - on the average - less regular than in the cases stated above.
A liquid-crystalline solid is a one phase system in which strot translational
symmetry may hold in 1 or 2 directions, while in the remaining directions
disorder occurs. The disorder may be of directional or positional type. X-ray
diffraction (in combination with optical microscopy) defines the character
(and lattice) of the liquid crystalline phase.
A serni-crystalline solid (mostiy a polymer) is at least a two-phase system.
lt contains an amorphous phase and a crystalline phase. The crystalline phase
can be macro-crystalline (quality equal to poly- crystalline),
micro-crystalline or para-crystalline (identical to liquid-crystalline). X-ray
diffraction can determine the crystallinity, crystallite sizes, long range
order of crystallites etc.
In a stress field solids (but also glasses and highiyviscous liquids)
may orient. With X-ray diffraction the orientation of all components in a
solid can be detected and quantified. This is irrespective of the type of the
component (crystalline, amorphous) and the nature of orientation
(uniaxial or biaxiao. For a crystalline phase a complete description of the
orientation factors (P2, P4 and higher) may be obtained for several lattice
directions. For the amorphous or glassy phase generally only P2 can be
determined.
Due to external stress also lattice strain can ocurr. Lattice strain can be
measured by rneans of X-ray diffraction.
In solutions (emuisions, colloids) particie sizes in the range of 1 to
1000 nm can be determined by means of X-ray diffraction.
