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The uniaxial compaction of dry ceramic nanopowder under powerful ultrasound action is described. The description of nanopowder compaction using a dimensionless equation allows the determination all of the basic pressing parameters to optimize the coefficients of die-wall, interparticle friction, and springback. As a result, a homogeneously dense, unstrained green compact is formed.

Our objective was to elucidate the physical reasons of the velocity limitation in the plasma armature (PA) railgun at the 6 k d s level. To do this, we have designeda simple system having no vacuum and no preaccelerator. The 1-2 g mass projectile is launched at the maximum possible constant acceleration4he limit of the projectile strength or the electrothermal explosion of rail surfaces, while making use of the effects of the material strengthening under the great confining pressure and rail current redistribution due to the presence of conducting shields. Such an approach provides the maximum possible energy efficiency of the launcher at its minimum conceivable length (as short as 50-80 cm). This greatly simplifies the design and fabrication but leads inevitably to the idea of the "fixed round"-"one assemblyone shot". Our experiments have confirmed the known hypothesis that the cause of the velocity saturation at the 6 k d s level is drag and decay of PA o'Wing to the increase of the inductive counter-emf with velocity and overload of PA with the ablated matter. The use of a compacted PA allowed us to overcome the "6 km/s limit" and to launch a 1 g projectile to 7.1 k d s in a bore length of 56 cm at a total efficiency of 10%. We believe that the simplest way to furtber velocity increase, while taking advantage of the compacted PA, is to increase the barrel length along with a corresponding increase of the energy stored. discussed below in a comp'uison with our experimental results which shed some light on the reasons for the "6-km/s limit". This will be followed by experiments carried out with acomp'xt PA which demonstrate the possibility of overcoming this limit.Our dztzz suggest that the velocity saturation is un'mbiguously due to the PA sprmding along the b'mel, so that to force the plasma to function properly, one should maintain the PA in the compact sme.In the ideal case of neglecting the losses for heating, wall ablation, friction etc. EM speed-up of a body in a railgun at a constant current I ('and, accordingly, constant acceleration a) is described by simple relations [4] Here V is the final projectile velocity, L' = const is the electrode unit length inductance, At is the acceleration time, 'and Q = IAt is the total electric charge consumed in At. This velocity is rtxzched at the lengthI . THE "G-KM/S LIMIT" IN PLASMA ARMATURE S = V A t / 2 = L'Q2/4m (2) RAILCUN LAUNCHING which paradoxically does not depend on acceleration time 'and ( h l y limited progress in EM 'acceleration of solid bodies has been reported in the fifteen years after the pioneering work of Rashleigh and Marshall [l] who accelerated a lexan projectile of 3 g in mass to 5.9 km/s in a 4 m-long railgun by means of a plasma armature (PA). Despite a comprehensive thwretical development of the EM launch problems 'and somewhat contradictory 'announcements of a velocity 8.5 km/s rexhed with m = 2 g [2], the published results obtained by other researchers remain at the 1978 level. An increase of the energy input and variation of the launc...

The conditions of in ultrasound (US) transmission through a nanodispersed powder (NP) and possible effects of US-action at compacting of NP ZrO2 − Y2O3 are analyzed. These effLcts include agglomerate crushing, NP particle activation under the conditions of acoustic flows; dense NP compacting with the preservation of a compact nanostructure in the absence of acoustic flows. It was shown that the result of 13S action was dcfined by the compacting pressure P and ItS intensity level I, the values of which were divided into the ranges by the critical parameters PC and IC NP transfers from the state of gas-dispersed medium to the state of a solid porous body at P = PC, and IC characterizes the threshold of acoustic flows appearance in the powder body.

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