The crystal habit of barium sulfate formed by the rapid mixing of Ba2+ and SO:-containing brines at 95°C has been investigated and the effects of coprecipitated K + , Mg2+, Ca2+ and Sr2+ ions, supersaturation ratio and barium-to-sulfate mixing ratio on the crystal morphology studied. The most marked crystal morphological changes were induced by varying the supersaturation and mixing ratios. The foreign ions produced relatively subtle effects. At high supersaturations (within the homogeneous nucleation regime), eightpointed star-like crystals were formed, whilst at low supersaturations, the equilibrium rhombohedra1 crystal form was recovered. All precipitates were single crystals.In the presence of crystal growth modifiers, marked morphological changes could be induced. For example, certain polymers induced the formation of millimetre long bundles of needles at pH x 6 and fractal-like hollow cones at pH x 5. In contrast, a range of phosphonate-based molecules, designed to act as barium sulfate scale inhibitors, produced oblate spheroids and very distorted star-like crystals 1 5-20 times smaller than the unmodified crystals. These particles were found to be porous on the nanometer scale. All the precipitates described were single crystals.We have found that the control and prevention of barium sulfate precipitation by phosphonate-based materials at high Ba2 + concentration and low pH (ca. 4.5) are complicated. In the absence of Ca2+ ions in solution, little or no inhibition occurs and evidence suggests that calcium phosphonate complexes are the active inhibitors. In addition, although the inhibitors may act by the classical mechanism of blocking crystal growth sites, they also act as nucleation promoters. This provides an additional mechanism for scale inhibition involving depletion of scaling ions from solution. As part of this work, using dynamic light scattering, we have for the first time demonstrated the presence of 1-10 nm microcrystallites in fully and partially inhibited barium sulfate scaling systems.Many of the brines found in the oil-bearing strata of offshore reservoirs contain high concentrations of alkaline-earth-metal ions (Ba2+, Ca2+, Sr2+ and Mg2+). During secondary oil recovery, seawater (containing SO:-) is injected into the reservoir to maintain the pressure. When the waters come into contact in the region of the well-bore, a solid precipitate can form which blocks production tubing and which can also cause damage to

The formation of liquid crystals of P,y-distearoylphosphotidylcholine (DSPC) in N-ethylammonium nitrate, a low-melting fused salt, has been documented with polarizing microscopy and small-angle X-ray scattering.The Lr -P, -L, transitions with increasing temperature are present in analogy with the behavior of DSPC in water. For a 1:l (by weight) mixture the d spacing for the L, phase is 63 8, and the surfactant head group area is 76 A2.

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