Hartmuth Schröttner

Spray Drying of Mannitol as a Drug Carrier—The Impact of Process Parameters on Product Properties

Powders intended for the use in dry powder inhalers have to fulfill specific product properties, which must be closely controlled in order to ensure reproducible and efficient dosing. Spray drying is an ideal technique for the preparation of such powders for several reasons. The aim of this work was to investigate the influence of spray-drying process parameters on relevant product properties, namely, surface topography, size, breaking strength, and polymorphism of mannitol carrier particles intended for the use in dry powder inhalers. In order to address this question, a full-factorial design with four factors at two levels was used. The four factors were feed concentration (10 and 20% [w/w]), gas heater temperature (170 and 190°C), feed rate (10 and 20 L/h), and atomizer rotation speed (6,300 and 8,100 rpm). The liquid spray was carefully analyzed to better understand the dependence of the particle size of the final product on the former droplet size. High gas heater temperatures and low feed rates, corresponding to high outlet temperatures of the dryer (96–98°C), led to smoother particles with surfaces consisting of smaller crystals compared to those achieved at low outlet temperatures (74–75°C), due to lower gas heater temperatures and higher feed rates. A high solution concentration of the feed also resulted in the formation of comparably rougher surfaces than a low feed concentration. Spray-dried particles showed a volume-weighted mean particle size of 71.4–90.0 µm and narrow particle size distributions. The mean particle size was influenced by the atomizer rotation speed and feed concentration. Higher rotation speeds and lower feed concentrations resulted in smaller particles. Breaking strength of the dried particles was significantly influenced by gas heater temperature and feed rate. High gas heater temperatures increased the breaking strength, whereas high feed rates decreased it. No influence of the process parameters on the polymorphism was observed. All products were crystalline, consisting of at least 96.9% of mannitol crystal modification I.

Friction Stir Spot Welds between Aluminium and Steel Automotive Sheets: Influence of Welding Parameters on Mechanical Properties and Microstructure

Hybrid configurations between aluminium and steel are needed to meet today’s requirements for lightweight construction in the automotive industry. Different studies showed that Friction Stir Welding (FSW) as well as Friction Stir Spot Welding (FSSW) processes are suitable for joining aluminium to steel. In this work, dissimilar FSSW of aluminium AA5754 and galvanised steel HX 340LAD were examined. In particular the influence of different spindle speeds and dwell times on microstructure and the mechanical properties of the weld were analysed. In doing so, the cross-section microstructure of the weld interface was observed by light optical microscope (LOM) and scanning electron microscope (SEM). The strength of the welds was evaluated both by tensile shear and vibration fatigue tests. The influences of the individual parameters on the weld are presented in detail. The appearance of intermetallic phases (IMPs), a severe problem for conventional fusion welding processes between aluminium and steel, were investigated for the welded samples and a link to the mechanical properties is given.

A method to measure the total scattering cross section and effective beam gas path length in a low-vacuum SEM.

A method is presented to determine the total scattering cross section of imaging gases used in low-vacuum scanning electron microscopy or environmental scanning electron microscopy. Experimental results are presented for water vapor, nitrogen gas and ambient air for primary beam electron energies between 5 and 30 keV. The measured results are compared and discussed with calculated values. This method allows the effective beam gas path length (BGPL) to be determined. The variations of the effective BGPL with varying chamber pressure are presented.

Loss of Ductility Caused by AlN Precipitation in Hadfield Steel

Two modified X120Mn12 Hadfield steels, differing in the amount of the alloying elements Al and N, are analyzed with respect to AlN precipitation and its effects on ductility. Charpy impact tests are performed, demonstrating the loss of ductility in the one grade containing a high density of AlN precipitates. The characterization of the precipitates is carried out by high-resolution scanning electron microscopy (HRSEM). Depending on chemical composition, primary and secondary AlN precipitates are detected on prior austenite grain boundaries and within the bulk volume. The experimental observations are confirmed by thermokinetic simulations, using the software package MatCalc (Vienna University of Technology, Vienna, Austria).

Investigation of Friction Stir Welding of Stainless Steel Using a Stop-Action-Technique

Especially for aluminium and its alloys friction stir welding (FSW) has become an established welding process. In contrast FSW for steel is still challenging and in basic research. Some reasons are the high price of the tungsten based tools, the durability of the tools and the low welding speeds. For further development of the process, it is necessary to understand the metallurgical changes in the stirred material during welding. In this work, a 4mm thick stainless steel plate (1.4301) was welded with different types of tungsten-alloyed tools. A so called stop-action-technique was used at the end of the weld and the sheet was quenched immediately to prevent metallurgical changes caused by slow cooling. During the process, the temperatures on the top of the welded plate, close to the tool shoulder (10 mm beside the weld centre line) and at the bottom of the plate, directly below the weld centre were measured. On the bottom side, the temperature was also measured 35mm in front of the end of the weld to compare the differences in the cooling rate. The measured peak temperatures ranged from 330°C on top to about 1200°C on the bottom of the specimen. Moreover rotational speed was varied up to 1200 RPM to test the possibility to reduce the process forces and spindle torque. In addition the influences of the welding process parameters on the microstructural changes were investigated. E.g. the average grain size was measured which ranged from 6 to 12 µm in the stirzone.

Experimental determination of the total scattering cross section of water vapour and of the effective beam gas path length in a low vacuum scanning electron microscope.

Low Vacuum Electron Microscopy enables the investigation of non-conductive samples without special preparation procedures. The imaging gas inside the specimen chamber is responsible for the contrast formation by gas amplification and the generated positive gas ions suppress charging of the sample. But the gaseous environment inside the chamber is limiting the capability of the microscope by elastic and inelastic collisions of the primary beam electrons (PEs) with the gas molecules. This so called skirt effect degrades the signal to noise ratio by generating gaseous secondary electrons (SEs) as well as SEs from regions far away from the focused probe. Therefore the primary beam loses exponentially electrons to a broadly dispersed skirt along the beam gas path length (BGPL) (1).