A deformation apparatus has been developed to study the mechanical behaviour of high pressure and ultra-high pressure metamorphic rocks. It is based on the conventional Griggs design and the molten salt cell concept introduced by H. E. Green II. Both, the axial loading and the confining pressure are servohydraulically controlled. Alternatively, a self-made multilayer pressure vessel or a commercial stripwound construction are used. The pressure cell is improved with respect to systems described previously by the use of different salt mixtures with low eutectic temperatures, by a mechanically stable arrangement of the thermocouples, and by an optimization of the frictional characteristics of the axial loading system. The apparatus has been successfully used in deformation experiments on cylindrical aragonite and coesite samples 3 to 4 mm in diameter and 6 to 10 mm in length at confining pressures up to 3.7 GPa and temperatures up to 1170°C.

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[1] We deformed synthetic polycrystalline aragonite aggregates in a Griggs-type apparatus using a molten salt cell at temperatures between 600 and 900°C, confining pressures between 1.6 and 2.8 GPa, and strain rates between 3 Â 10 À6 and 5 Â 10 À3 s À1 . At temperatures above 600°C, triaxial compression tests to $15% axial strain are characterized by a constant flow stress. The strength of the aragonite marble is comparable to strength data previously published for calcite rocks of comparable grain size, i.e., 50 to 100 mm. The mechanical data and microstructures of the deformed aragonite specimens indicate dislocation creep as the dominant deformation mechanism. A power law flow law, _ e = Aexp(ÀQ/RT)s n , fits the mechanical data with a preexponential factor]) = À0.6 ± 2.5, an activation energy Q = 249 ± 29 kJ mol À1 , and a stress exponent n = 5.2 ± 0.6. Extrapolated to natural strain rates, the flow law provides an upper bound to the strength of carbonate rocks at (ultra-) high-pressure metamorphic conditions.

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Dense-phase pneumatic conveying of solids offers many advantages over dilute-phase conveying. The lower air velocities, and, consequently, lower particle velocities, result in lower pipe wear and lower particle attrition. This paper describes an experimental program that has been undertaken to study the flow pattern of cohesionless solids in vertical transport and to measure the parameters influencing the pressure drop required to move a single plug of solids. Highspeed photographic techniques have been used to observe the flow pattern of polyethylene particles (diameter 5 3 mm) in the vertical riser section of a circulating unit constructed from pipes with an internal diameter of 50.8 mm. The flow pattern resembles that of square-nosed slugging in a fluidized bed. The solids move up as "plugs" of bulk solids that occupy the entire cross-section of the pipe. Particles are seen to "rain" down from the back of one plug and then to be collected by the front of the next plug. Collecting these particles causes a stress on the plug front which is transmitted by powder mechanics forces axially through the plug and radially to the wall. The pressure drop required to move a single plug of cohesionless solids through the transport pipeline was measured as a function of the plug length, particle properties, pipe diameter, and the frontal stress. The results of these experiments are compared with a theoretical model.Le transport pneumatique en phase dense de solides prksente de nombreux avantages pour le transport en phase diluke.Les vitesses d'air les plus basses et, en conskquence, les vitesses de particules les plus basses, entrainent une faible usure des conduites et une faible attrition des particules. Nous dtkrivons dans le prksent article un programme expinmental mis sur pied pour etudier le diagramme d'kcoulement de solides sans cohtsion dans le transport vertical et pour mesurer les paramktres qui influencent la perte de charge ntcessaire pour dkplacer un seul bouchon de solides. Nous avons fait appel B des techniques photographiques B haute vitesse pour observer le diagramme d'tcoulement de particules de polyethylkne (diamktre 3 mm) dans la section montante verticale d'un systkme de circulation compost de conduites de 50,8 mm de diamttre intkrieur. Le diagramme d'tcoulement resemble au bouillonnage a profil c a d dans un lit fluidist. Les solides se deplacent vers le haut comme des bouchons solides en occupant toute la section transversale de la conduite. I1 semble que les particules tombent en "pluie" de I'arritre d'un bouchon et qu'elles sont collectkes a I'avant du bouchon suivant. La collecte de ces particules cause une tension B I'avant du bouchon qui se transmet par les forces de mkchanique des poudres dans le sens axial dans le bouchon et dans le sens radial vers le mur. La perte de charge nkcessaire pour dkplacer un simple bouchon de solides sans cohtsion dans une conduite de transport a ktt mesurCe en fonction de la lonueur de conduit, des proprittes des particules, du diamktre du conduit et de la contrain...