Experimental study of the direct reduction of sinterized zinc oxide by hydrogen

The gas-solid reaction between hydrogen and sinterized zinc oxide has been studied experimentally and theoretically. The attention has been focused on the influence that the elementary chemical and physical phenomena, taking place inside the pellet, have on the overall reaction rate. The experimental results, worked out according to the mathematical model proposed, allowed both to check the validity of this model and to determine the true kinetic constant and the activation energy of the reaction. The discrepancies between experimental results and theory are well within the limits of uncertainty affecting both the independently evaluated physical parameters (such as diffusivities, internal area, etc.) and the measured parameters for low values of the reaction times. On the contrary, the larger discrepancies found for larger values of time, may be attributed to the major difficulties connected with the modelling of the internal structure of a porous solid which is consumed during a reaction, for advanced states of consumption.The method adopted for analyzing continuously with time the reaction products, made use of a thermobalance working at room temperature.     

The fate and transport of RDX, HMX, TNT and DNT in the volcanic soils of Hawaii: a laboratory and modeling study

The adsorption and degradation behavior of RDX, HMX, TNT and DNT and the impact of pH, ionic strength and dissolved organic matter on sorption were examined for two volcanic soils of a former military training area on Hawaii Island, Hawaii, USA. The transport of these chemicals in the soil was also studied in small packed columns and simulated using a water-flow and solute-transport model, HYDRUS_1D. The results show that HMX and RDX are both significantly more mobile than TNT and DNT. The adsorbability of the four chemicals was ranked as: RDXRDX>DNT>TNT. No significant trend was observed for the effect of ionic strength, pH and dissolved organic carbon (DOC) on the adsorption of explosive compounds within the concentrations and pH ranges evaluated. The simulation results show that TNT and DNT would not leach beyond a depth of 30cm soil profile whereas a significant amount of HMX and RDX would pass the 30cm depth. It seems that the risk for contamination of groundwater is much higher for both HMX and RDX than for DNT and TNT as the substratum in this area consists of highly permeable lavas.     

Experimental features affecting the transparency of YAG ceramics

This article focuses on the importance of the ceramic production process for the final transparency and overall optical quality of materials to be used as laser hosts. YAG-based ceramics are prepared starting from commercial powders. The materials are prepared by reactive sintering in a clean atmosphere and under high vacuum. Nd or Yb are selected as active elements as the more appropriate for high energy and high peak power lasers. The powder type and treatment and the solvent removal technique are described in detail as well as the experimental conditions adopted during shaping. The influence of the pre-sintering and sintering cycles on the reaction among the involved oxides and on the microstructure after sintering is shown. The optical characterization is also reported.     

H mesh prosthesis in the treatment of ventral hernia

The Authors report their experience in the treatment of ventral hernias using a Marlex mesh moulded in an original way with a technique partially derived from plastic surgery. The complete mobilization of the umbilicus through a circular incision allows to fit this prosthesis symmetrically below the rectus abdominis muscles for the entire extension of the hernia.