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The new synthetic form of microporous crystalline silica, denoted as ITQ-12, shows a high potential for the separation of propane and propene from its mixtures.

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Single-phase perovskites in the solid solution series La1 - x Na x MnO3+ δ have been obtained using a soft treatment, which makes possible strict stoichiometric control. Under these conditions, it becomes possible to systematically study the influence of the sodium content on the electronic properties of materials in this series. As long as all the samples have practically the same Mn4+ content (33%), the number of vacancies at A and B sites of the perovskite structure depends on the sodium content, and it decreases as x increases. Susceptibility to alternating current, magnetization, resistivity, and magnetoresistivity measurements have allowed us to establish relevant points of the electronic phase diagram of this alkali-metal-doped lanthanide manganate system. These results, together with those previously obtained for La1 - x K x MnO3+ δ, reveal the existence of a correlation between the critical temperature for ferromagnetic ordering and the concentration of vacancies at the B sites, v B, in samples with a fixed concentration of Mn4+. Such a correlation can be understood in terms of a magnetic phase segregation model in which the materials are thought of as composed by clusters, formed by the vacancies (trapping centers for mobile holes) and neighboring Mn cations (on which holes are trapped), and a matrix, formed by the remaining Mn cations. Within this model, the decrease in the number of mobile holes in the matrix is the cause of the decrease in the critical temperature with v B.

In this paper we present the precipitation of hydroxyapatite (HA), Ca5(OH)(PO4)3, from highly concentrated CaCl2 and K2HPO4 solutions, carried out by a continuous method in a MSMPR reactor. The procedure consists of adding the reagents in a ratio Ca to P equal to 1.67, maintaining a temperature of 85 °C, inert N2 atmosphere inside the reactor, and monitoring and adjusting automatically the pH by means of a pH‐stat system (pH = 9.0 ∓ 0.1). Under these conditions HA with a Ca to P ratio equal or close to the stoichiometric composition (Ca/P=1.667), with a high yield (up to 99%) and a high production rate (up to 1.17 g/l.min) is obtained at steady state. The CSD, morphology, crystallinity of the precipitates and impurities present fit the requirement for its biomedical applications.

Precipitation of Stoichiometric Hydroxyapatite by a ContinuousMethod.-Ca 5 (OH)(PO 4 ) 3 powders are prepared by mixing two highly concentrated solutions of CaCl 2 and K 2 HPO 4 (Ca:P = 1.67) in a continuous flow MSMPR reactor (85 • C, N 2 , continuous adjustment of the pH to 9.0±0.1, yield up to 99%). The samples are characterized by XRD, IR spectroscopy, and TEM. The precipitates are composed by aggregates of submicrometric needlelike crystals with ratios (Ca:P) equal or close to the stoichiometric composition. The prepared material fits the requirements for biomedical applications. -(GOMEZ-MORALES, J.; TORRENT-BURGUES, J.; BOIX, T.; FRAILE, J.; RODRIGUEZ-CLEMENTE, R.; Cryst. Res. Technol. 36 (2001) 1, 15-26; Inst.