Browsing by Autor "R. Padilla"

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    Antimony production by carbothermic reduction of stibnite in the presence of lime
    (University of Belgrade, 2014) R. Padilla; L.C. Chambi; M.C. Ruiz
    Experimental work on the carbothermic reduction of Sb2S3 in the presence of lime was carried out in the temperature range of 973 to 1123 K to produce antimony in an environmentally friendly manner. The results demonstrated the technical feasibility of producing antimony by this method without producing SO2 gas. Complete conversion of Sb2S3 was obtained at 1023 K in about 1000 seconds and at 1123 K in less than 250 seconds using stibnite-carbon-lime mixtures with molar ratios Sb2S3:CaO:C = 1:3:3. It was found that the reduction proceeds through the formation of an intermediate oxide SbO2, which is subsequently reduced by CO(g) to yield antimony metal and CaS. The kinetics of the Sb2S3 reduction was analyzed by using the equation ln(1-X) = -kt. The activation energy was 233 kJ mol-1 in the temperature range of 973 to 1123 K. This value would correspond to an antimony catalyzed carbon oxidation by CO2.
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    Frecuencia de existencia de anomalías dentales en pacientes de la Facultad de Odontología, Mérida, Venezuela
    (2016) Patricia Lastra; Jorge Rincón; Carlos García Sívoli; R. Padilla
    The dental anomalies are caused by congenital or hereditary disorders that affect the normal process of odontogenesis. The development of anomalies can affect the size, position, shape, number, and structure of the teeth. The main objective was to determine the frequency of radiographic presence of dental anomalies in patients who attended the Adult Integral Clinic III of the Faculty of Dentistry Merida- Venezuela. This investigation is a descriptive retrospective study. The totality of the medical history of the patients that came to the clinic in the period 2012-2013 was revised including the corresponding panoramic xray. The review of the clinical history consisted on recording the personal data such as age and gender. The different groups of dental anomalies were observed through an x-ray viewer. The results showed that the group of abnormalities of shape was the most affected, as well as females and the age group between  50-60 years. The subtype of anomaly that predominated was the anodontia with 50 cases. It was concluded that there exists a frequency of dental anomalies regarding development in the integral clinic. It is recommended to do a proper radiographic interpretation and an extensive anamnesis.