Christian Mensing
February 13, 1998
The praparation methods used in solid state chemistry are based primary
on heterogenic reactions of all combinations of solid - gas, solid - liquid,
solid - solid, and liquid - liquid.
These reactions take place usually at higher
temperatures. The preparator has to have control over all agents
involved in the reaction. So he has to consider, besides the purity,
the prehistory of the
introduced educts, including reaction vessels, to prevent contamination
through oxigen, moisture or nitrogen. Reactions up to 1100°C are usually
carried out inside sealed quartz tubes while avoiding direct contact to the
capsule. At even higher temperatures, welded metal tubes, which have to
be protected against oxidation, are practicable. The danger of introducing
material from the tube
to the reaction increases with temperature, so above that
limit other techniques like arc melting are required.
When solid - solid reactions are expected, the diffusion of the elements
will control the reaction. A close
contact between the reaction participants is achieved by previous
pelleting of the reaction mixture.
What follows is a listing of the available infrastructure in our group to achieve these tasks.
For most applications ordinary resistivity tube furnaces up to 1100°C are sufficient Heraeus Ro 4/50 Nearly 20, most of them in a special furnace room, are available for preparation. Some allow the adjustment of temperature gradients nescessary to realize transport reactions. For high temperature preparation (up to 1700°C) we use a GERO HTRV 40-250 furnace with a vertical inlet allowing molten reactions inside metal ampules (niobium or tantalum) and which are hold inside an evacuated high density alumina tube.
Although usually used under atmosphere conditions, additional devices allow the use of our chamber furnaces under inert gas conditions.
For the preparation of hard materials we installed an electric arc furnace inside a dry box filled with argon preventing the products to be inadvertently decomposed by atmosphere attack. The preparation for reaction as well as the collection of the producs is easyly accomplished. The unit was acquired from Johanna Otto and the drybox was supplied by MBraun who build in the furnace.
Responsable person: Franziska Rohrer
Like most chemical laboratories, usual preparation material is disposable.
Since nearly every reaction product handled in our lab is air sensitive, we installed everywhere argon or nitrogen facilities with pumping units to operate properly. As inert gas we use mainly argon to be able working with lithium. On some places, where liq. nitrogen traps are nescessary, nitrogen is used instead. The commercial high grade gas (5.9) is passed through an additional absorber to revove even last rests of impurities.
Mostly two stage rotary pumps (Balzers/Pfeiffer DUO 008 B) are placed at the working places.
The central operating places of our labs are the dryboxes (MBraun MB150) with 4 simultaneous working places each. They are equipped with automatic gas conditioners extracting permanently residues of moisture and oxigen which can be monitored through control devices. Some areas inside are reserved for permanent experiments, mainly for electrochemistry (in melts) or conductivity measurements at high or low temperature.
For reactions or measurements where solvents are involved, a separate drybox with an additional zeolite absorber is installed. (MBraun Labmaster 130)
Like the electrochemical experiments, we installed our electric arc furnace inside a separate dry box MBraun Labmaster 130.
One lab is equipped for making solvent chemistry, additionally it includes as usual inert gas facilities.
In order to identify and characterize the products obtained, we use different methods
For the phase analysis of powders we use position sensitive detectors (PSD), which allows us to obtain X-ray patterns of powders in 15 minutes. With a high temperature attachement measurements up to 1000C in quarz capillaries can be performed. High resolution patterns, which are suitable for structure solution and Rietveld refinements or determination of accurate lattice constants can be obtained over night.
After testing on precession cameras (one of them equipped with a CCD detector),
single crystals can be examined with a classical four-circle diffractometer, an image plate system or an
diffractometer equipped with a CCD detector. For measurements at low temperatures (down to about 80 K) two cooling systems
are availabe. In addition we build a helium cooling device for temperatures around 4 K.
For measurements at high temperatures or growing crystals from a melt in capillaries, a self designed laser heating can be used.
High pressure experiments can be done in a diamond cell.
Responsable person: Dr. Michael Wörle
Besides the self designed Very low temperature Measuring Unit we dispose of a commercial liq. nitrogen cooler for 77 K.
To develop the obtained photographic material a darkroom for b/w work is installed near by.
The need of screening the magnetic preperties of the found new materials a Squid magnetometer was installed.
The wide range of electrochemical methods is partially represented in our group by some of them. Besides universal instruments, some highly speciallized are available.
Non electronic conductivity obeys time laws and which can be analyzed using different frequencies when measuring the resistivity. We use a HP 4192 A Impedance Analyzer for frequences ranging from 5 Hz - 13 MHz. Temperature dependent measurements lead to diffusion coefficients of ions.
Self designed devices combined with universal instruments and control
programs (VIEWDAC of Keithley) allows the individual setup for the experiments.
We can measure inside a drybox the temperature dependence of the
resistivity of pellets or
in some cases even of single cristals from room temparature down to 11 K
using a
A heating bank allows measurements above room temperature allowing the determination of band gaps but the risk of oxigen gathering increases since the samples are not capsuled during the heating. A separate external evacuable device permits a rising up to 600°C.
Responsable person: Christian Mensing
For qualitative screening of the thermal behaviour of reactands or products a high temperature DTA (up to 1500 °C) is disposal. Samples sealed in stainless steel or niobium crucibles permit the study of reaction temperatures, transformations or melts. We use a
Responsable person: Christian Mensing
A separate info is actually available.
Most of the mentioned equipment is not only for scientific investigation
but for educational proposals. The hard to introduce
matter of crystallography
is highly simplified using visualization tools such as touchable models.
A specially designed
An other very important tool is the possibility of creating adecuate videos.
We installed a video studio for this task.
Last modified: February 13, 1998