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LTA and FAU zeolites were successfully synthesized from a Venezuelan sodium silicate solution, by hydrothermal crystallization under autogenous pressure at 100 °C, with 2 - 24 h crystallization times. The synthesized materials were characterized by XRD, BET specific surface area and SEM. A series of synthesis tests were performed to study the influence of the molar composition of the starting mixture over zeolites crystallization. The effect of crystallization time for a particular synthesis mixture composition was studied for both zeolites types. The reuse as alkaline medium of the mother liquor separated during filtration, and the effect of the aging before crystallization were additionally studied. The experimental results are in agreement with the crystallization mechanism proposed for zeolites synthesis in liquid phase. The use of a 2SiO2: Al2O3: 6.Na2O: 240H2O synthesis mixture composition allows obtaining LTA zeolite within 2 h of crystallization. For FAU zeolite, no aging period was needed when starting with a 4SiO2: Al2O3: 6.6Na2O:264H2O composition. It was possible to synthesize both zeolites with high purity and crystallinity and with adequate water adsorption properties. Zeolitas LTA y FAU fueron sintetizadas con éxito a partir de una solución de silicato de sodio venezolano, por cristalización hidrotérmica bajo presión autógena a 100 ° C, a tiempos de cristalización de 2- 24 h. Los materiales sintetizados se caracterizaron por DRX, área específica BET y SEM. Se realizaron una serie de pruebas de síntesis para estudiar la influencia de la composición molar de la mezcla de partida sobre la cristalización. Se estudió el efecto del tiempo de cristalización para una composición de mezcla de síntesis particular para ambos tipos zeolitas, la reutilización como medio alcalino del licor madre separado durante la filtración, y el efecto del envejecimiento antes de la cristalización. Los resultados experimentales están de acuerdo con el mecanismo propuesto de cristalización para la síntesis de zeolitas en fase líquida. El uso de una composición de 2SiO2: Al2O3: 6.Na2O: 240H2O en la síntesis permite la obtención de zeolita LTA a partir de 2 h de cristalización. Para la zeolita FAU, no se requirió de período de envejecimiento cuando se parte de la composición 4SiO2: Al2O3: 6.6Na2O: 264H2O. Fue posible sintetizar ambas zeolitas con alta pureza y cristalinidad y propiedades adecuadas de adsorción de agua.

Summary Background Previous trials of antiplatelet therapy for the prevention of venous thromboembolism have individually been inconclusive, but a meta-analysis of their results indicated reductions in the risks of deep-vein thrombosis and of pulmonary embolism in various high-risk groups. The aim of this large randomised placebo-controlled trial was to confirm or refute these apparent benefits. Methods During 1992–1998, 148 hospitals in Australia, New Zealand, South Africa, Sweden and the UK randomised 13 356 patients undergoing surgery for hip fracture, and 22 hospitals in New Zealand randomised a further 4088 patients undergoing elective arthroplasty. Study treatment was 160 mg daily aspirin or placebo, started preoperatively and continued for 35 days. Patients received any other thromboprophylaxis thought necessary. Follow-up was of mortality and of in-hospital morbidity up to day 35. Findings Among the patients with hip fracture, allocation to aspirin produced proportional reductions in pulmonary embolism of 43% (95% CI 18–60; p=0·002) and in symptomatic deep-vein thrombosis of 29% (3–48; p=0·03). Pulmonary embolism or deep-vein thrombosis was confirmed in 105 (1·6%) of 6679 patients assigned aspirin compared with 165 (2·5%) of 6677 assigned placebo, which represents an absolute reduction of 9 (SE 2) per 1000 and a proportional reduction of 36% (19–50; p=0·0003). Similar proportional effects were seen in all major subgroups, including patients receiving subcutaneous heparin. Aspirin prevented 4 (1) fatal pulmonary emboli per 1000 patients (18 aspirin-group vs 43 placebo-group deaths), representing a proportional reduction of 58% (27–76; p=0·002), with no apparent effect on deaths from any other vascular cause (hazard ratio 1·04 [95% CI 0·86–1·26]) or non-vascular cause (1·01 [0·84–1·23]). Deaths due to bleeding were few (13 aspirin vs 15 placebo), but there was an excess of 6 (3) postoperative transfused bleeding episodes per 1000 patients assigned aspirin (p=0·04). Among electivearthroplasty patients, rates of venous thromboembolism were lower, but the proportional effects of aspirin were compatible with those among patients with hip fracture.

Abnormal synthesis of type I collagen by fibrocartilage has been suggested as a mechanism involved in degenerative arthritis. Samples of normal and osteoarthritic adult femoral head cartilage were thus studied for histology and collagen composition. The electrophoretic analysis of the cyanogen bromide-derived peptides showed the sole presence of type II collagen in all normal and in all osteoarthritic samples, except those in which fibrocartilage was present. The sensitivity of the technique would not permit, however, the detection of a minute amount (less than 3%) of type I collagen in the samples. The results show that massive deposition of type I collagen occurs only when fibrocartilage is formed. It is suggested that this fibrocartilage is formed when the subchondral bone is damaged.