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The PK-4 experiment is a continuation of the successful dusty plasma experiments PK-1, PK-2 and PK-3 conducted on board of the orbital space stations Mir and International Space Station. For all these experiments it is important to avoid the strong influence of gravity, exerting an external stress on the system. Whereas PK-3 and PK-3 Plus experiments are using a planar rf capacitive discharge, PK-4 studies complex plasmas in a long cylindrical chamber with a combined dc/rf discharge. Such a configuration of the chamber will provide a particular advantage for investigation of different dynamical phenomena in complex plasmas such as sheared laminar flow of a highly nonideal dusty liquid and its transition to the turbulent regime, nozzle flow, boundary layers and instabilities, shock waves (solitons) formation and propagation, dust particle lane formation, and space dust grain separation according to their size.

Alkylation of 5-aminotetrazole (1) with 2-chloroethanol leads to a mixture of the N-1 and N-2 isomers of (2-hydroxyethyl)-5-aminotetrazole. Treatment of 1-(2-hydroxyethyl)-5-aminotetrazole (2) with SOCl(2) yielded 1-(2-chlorethyl)-5-aminotetrazole (3). 1-(2-Azidoethyl)-5-aminotetrazole (4) was generated by the reaction of 3 with sodium azide. Nitration of 2, 3, and 4 with HNO(3) (100%) yielded in the case of 2 and 3 1-(2-hydroxyethyl)-5-nitriminotetrazole (5) and 1-(2-chloroethyl)-5-nitriminotetrazole (6). In the case of 4, 1-(2-nitratoethyl)-5-nitriminotetrazole monohydrate (7) was obtained. 1-(2-Azidoethyl)-5-nitriminotetrazole (8) could be obtained by nitration of 4 with NO(2)BF(4) via the formation of potassium 1-(2-azidoethyl)-5-nitriminotetrazolate (9). The reaction of 6 with NaN(3) resulted in the formation of the salt sodium 1-(2-chloroethyl)-5-nitriminotetrazolate (10 a). The deprotonation reaction of 6 was further investigated by the formation of the ammonium salt (10 b). The protonation of 2 and 4 with dilute nitric acid led to 1-(2-hydroxyethyl)-5-aminotetrazolium nitrate (11) and 1-(2-azidoethyl)-5-aminotetrazolium nitrate (12), respectively. Similarly, protonation of 4 with perchloric acid led to 1-(2-azidoethyl)-5-aminotetrazolium perchlorate monohydrate (13). Since 5-nitrimino-tetrazoles can be used as bidentate ligands, the coordination abilities of 5, 6, and 8 were tested by the reaction with copper nitrate trihydrate, yielding the copper complexes trans-[diaquabis{1-(2-hydroxyethyl)-5-nitriminotetrazolato-kappa(2)N(4),O(5)}copper(II)] (14), trans-[diaquabis{1-(2-chloroethyl)-5-nitriminotetrazolato-kappa(2)N(4),O(5)}copper(II)] dihydrate (15), and [diaquabis{1-(2-azidoethyl)-5-nitriminotetrazolato-kappa(2)N(4),O(5)}copper(II)] (16). All compounds were characterized by low-temperature single-crystal X-ray diffraction. In addition, comprehensive characterization (IR, Raman, and multinuclear NMR spectroscopy ((1)H, (13)C), elemental analysis, mass spectrometry, DSC) was performed. The heats of formation of selected compounds were computed by using heats of combustion obtained by bomb calorimetry or calculated by the atomization method. With these values and the densities determined from X-ray crystallography, several detonation parameter were calculated by the EXPLO5 program. Finally, the sensitivities towards impact and friction were determined using a BAM drop hammer and friction tester.

Dust-free regions around a Langmuir probe are studied in a complex plasma under microgravity. The dust particles settle in the presheath of the probe, where an equilibrium of the electric field force and the ion-drag force is established. The size and shape of the dust cloud are discussed with simple models. A more sophisticated presheath model is solved numerically to analyze the acting forces and the equilibrium position of the dust. The formation of distinct particle layers in the dust shell can be explained by the force gradients of the effective potential well.

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