No abstract

Micro cellular polymer foams find numerous applications such as in filtration, tissue scaffolds, insulation, and catalyst carriers. This study reports on a solvent free approach to fabricate microcellular poly lactic acid foams through a combination of additive manufacturing and microwave foaming. This approach provides the capability to foam polymers in a repeatable and controllable manner with minimal human intervention. Initially, samples are 3D printed, followed by gas saturation, and microwave foaming. The effect of microwave foaming parameters, namely power, temperature and time on the pore morphology was analyzed using a complete parametric study. The results show that microwave foaming can successfully generate porous structure with power and temperature being the main factors affecting the pore morphology. A combination of midrange power and high temperature results in foams with desired properties of small pore size and high porosity. The resulting foams have pore size as small as 120 μm with porosity of 78%. These foams fabricated using a solvent free approach find applications in biomedical field as three dimensional tissue scaffolds for drug testing and bio‐artificial organ development.

There is a fast‐growing market for printable electronics, which requires new techniques for micro‐ and nanofabrication suitable for mass production of functional electronic products. This makes the evaluation and comparison of different printing techniques highly important. In this work, a coating process, referred to as “profile rod technique,” is presented as an alternative to the spin‐coating process for the production of nanoparticulate zinc oxide (ZnO) layers with thicknesses of several hundred nanometers. Such layers could be used, e.g., as semiconducting layers for printed thin film transistors. The profile rod technique, in contrast to spin‐coating, is a continuous process, which allows for easier mass production and reduction in manufacturing costs. To compare the spin‐coating and the profile rod process, submicrometer‐thick layers of ZnO nanoparticle dispersions in ethanol were prepared. Different dispersion techniques were studied concerning their applicability for the manufacture of nanosized particle dispersions because well‐dispersed suspensions are the basic requirement for the manufacture of submicrometer‐thick layers with high morphological quality. The quality of the deposited layers was evaluated concerning their microstructure. Moreover, the profile rod technique could be successfully used for the manufacture of submicrometer ceramic green tapes.

The relationship between microstructure and high temperature strength of 347H SS welded joints was investigated. The materials studied correspond t o t w o preheated furnaces of the petrochemical industry, working at 700 OC and 45 atm (called furnaces A and 6). Furnace A presented failures, hot fissure in the Heated Affected Zone, after 60 h operation, whereas furnace B operated for 70000 h. The microstructure research was made by a non conventional replica technique [I], which allowed more accuracy in the nature, quantity, morphology and distribution of the different phases. The probable cause of the remarkable different behaviour of the t w o materials, although both fulfil the A2131TB1347 H, ASTM standard requirements, has been discussed taking into account the chemical composition of the steels, matrix characteristics, nature of the inclusions, carbides, intermetallic particles and NIMn, AIIN, CINb relationships.