In this study, the effect of gas pressure on the shape and size of the AZ91 alloy powder produced by using the gas atomization method was investigated experimentally. Experiments were carried out at 820°C constant temperature in 2-mm nozzle diameter and by applying 4 different gas pressures (0.5, 1.5, 2.5 and 3.5 MPa). Argon gas was used to atomize the melt. Scanning electron microscope (SEM) to determine the shape of produced AZ91 powders, XRD, XRF and SEM-EDX analysis to determine the phases forming in the internal structures of the produced powders and the percentages of these phases and a laser measuring device for powder size analysis were used. Hardness tests were carried out to determine the mechanical properties of the produced powders. The general appearances of AZ91 alloy powders produced had general appearances of ligament, acicular, droplet, flake and spherical shape, but depending on the increase in gas pressure, the shape of the powders is seen to change mostly towards flake and spherical. It is determined that the finest powder was obtained at 820°C with 2 mm nozzle diameter at 3.5 MPa gas pressure and the powders had complex shapes in general.
Manual measurements of distribution of gas velocity in conduits of flue gas installations using systems with differential pressure sensors of velocity are often performed for the requirements of determining emissions of dust pollutants from industrial process plants to the atmosphere. The aim is to determine an axial velocity profile. Flows in measuring sections are not always coaxial along the run of the duct; they are characterized by different directions of the velocity vector at various measuring points. The determination of actual directions of vectors of local velocities giving a guarantee of an accurate calculation of the axial velocity is often not possible from the technical point of view and the measurement of the velocity is carried out with the parallel setting of the sensor head in relation to the axis and the walls of the conduit. Then the knowledge of the directional sensitivity of the applied velocity sensor allows either to eliminate the axial velocity measurement error or to take it into account by the uncertainty of this measurement. For specific situations of two-dimensional variation of direction of the velocity vector, the directional sensitivity characteristics and in consequence the characteristics of error have been determined for three sensors adopted to tests: a zero pressure dust sampling probe with the anemometric function as an element of the gravimetric dust sampler and comparatively - two commonly used Pitot tubes: types S and L.
Oxygen is used for medical treatment and general anesthesia. However, high concentrations of oxygen can have toxic effects on cells. In veterinary medicine, 100% oxygen is usually used during general anesthesia and it can be toxic to animals. However, there is little concern about its harmful effects in humans. The objective of this study was to demonstrate that using a high con- centration of oxygen increases the partial pressure of oxygen in arterial blood (PaO2) more so than a lower concentration, by comparing PaO2 at three different oxygen concentrations (100%, 60%, and 40%) in six dogs under general anesthesia for 3 hours. The mean PaO2 and standard error values at the 100%, 60%, and 40% oxygen concentrations were 535.8 ± 24.01, 374 ± 17.19, and 239 ± 8.78 mmHg, respectively (p<0.05). These results show that 100% and 60% oxygen concentrations could increase oxidative stress. Further studies are needed to examine the oxygen concentration that causes toxicity.
The paper concerns the problem of discontinuity in high pressure die castings (HPDC). The compactness of their structure is not perfect, as it is sometimes believed. The discontinuities present in these castings are the porosity as follow: shrinkage and gas (hydrogen and gas-air occlusions) origin. The mixed gas and shrinkage nature of porosity makes it difficult to identify and indicate the dominant source. The selected parameters of metallurgical quality of AlSi9Cu3 alloy before and after refining and the gravity castings samples (as DI - density index method), were tested and evaluated. This alloy was served to cast the test casting by HPDC method. The penetrating testing (PT) and metallographic study of both kinds of castings were realized. The application of the NF&S simulation system allowed virtually to indicate the porosity zones at risk of a particular type in gravity and high-pressure-die-castings. The comparing of these results with the experiment allowed to conclude about NF&S models validation. The validity of hypotheses concerning the mechanisms of formation and development of porosity in HPDC casting were also analyzed.