RESUMEN
An efficient approach to improve the catalytic activity of titanosilicates is introduced. The Doehlert matrix (DM) statistical model was utilized to probe the synthetic parameters of mesoporous titanosilicate microspheres (MTSM), in order to increase their catalytic activity with a minimal number of experiments. Synthesis optimization was carried out by varying two parameters simultaneously: homogenizing temperature and surfactant weight. Thirteen different MTSM samples were synthesized in two sequential 'matrices' according to Doehlert conditions and were used to catalyse the epoxidation of cyclohexene with tert-butyl hydroperoxide. The samples (and the corresponding synthesis conditions) with superior catalytic activity in terms of product yield and selectivity were identified. In addition, this approach revealed the limiting values of each synthesis parameter, beyond which the material becomes catalytically ineffective. This study demonstrates that the DM approach can be broadly used as a powerful and time-efficient tool for investigating the optimal synthesis conditions of heterogeneous catalysts.
RESUMEN
Developing an understanding of the time-related performance of cement-treated materials is essential in understanding their durability and long-term effectiveness. A number of models have been developed to predict this time-related performance. One such model is the maturity concept which involves use of the 'global' activation energy which derives from the Arrhenius equation. The accurate assessment of the activation energy is essential in the realistic modelling of the accelerated ageing of cement-treated soils. Experimentally, this model is applied to a series of tests performed at different elevated temperatures. Experimental work, related to the results of a time-related performance on a contaminated site in the UK treated with in situ stabilisation/solidification was carried out. Three different cement-based grouts were used on two model site soils which were both contaminated with a number of heavy metals and a hydrocarbon. Uncontaminated soils were also tested. Elevated temperatures up to 60 degrees C and curing periods up to 90 days were used. The resulting global activation energies for the uncontaminated and contaminated soils were compared. Lower values were obtained for the contaminated soils reflecting the effect of the contaminants. The resulting equivalent ages for the uncontaminated and contaminated mixes tested were 5.1-7.4 and 0.8-4.1 years, respectively. This work shows how a specific set of contaminants affect the E(a) values for particular cementitious systems and how the maturity concept can be applied to cement-treated contaminated soils.
Asunto(s)
Dióxido de Carbono/química , Restauración y Remediación Ambiental/métodos , Suelo , Temperatura , Fuerza Compresiva , Modelos Químicos , Factores de TiempoRESUMEN
OBJECTIVE: To study the integrity of EPI vaccine storage during interruptions to the power supply. SETTING: Health centres in Colombo District. METHOD: An interviewer-administered questionnaire was used to collect information on staff compliance with regulations of the expanded program of immunisation (EPI) and alternative facilities available for refrigeration during power failure. The refrigerator and storage conditions were inspected. The stored vaccines were tagged with thermosensitive cold chain monitors, which were read on revisiting the clinic 14 days later. During the study period, power cuts of 2 hours' duration were in force daily. A control study was carried out when there was no interruption to power supply. RESULTS: Diphtheria-pertussis-tetanus (DPT) and measles vaccines had been exposed to temperatures outside the prescribed range during power cuts. Oral polio vaccine had adequate storage with power cuts of 2 hours' duration. CONCLUSION: Alternative facilities for vaccine storage during power cuts were not available and the potency of DPT and measles vaccines were compromised with interruptions to power of 2 hours' duration or more.