Preparation of alumina foams by the thermo-foaming of powder dispersions in molten sucrose

The alumina powder disperses in molten sucrose due to the hydrophilic interaction between the particle surface and sucrose hydroxyls. The thermo-foaming of the dispersions is due to the bubbles created by the water vapour produced by the OH condensation at 150 °C which are stabilized by the alumina particles adsorbed on the gas–liquid interface as well as the increase in viscosity. The foaming time, the foam setting time and the foam volume depend on the alumina powder to sucrose weight ratio. The alumina foams have interconnected cellular microstructure and the cells are having a near spherical morphology. The porosity (97.84–93.29 vol.%.) decreased and the average cell size (0.54–1.2 mm) increased with the increase in alumina powder to sucrose weight ratio (0.4–1.4). The alumina foams with density in the range of 0.239–0.267 g/cc showed compressive strength in the range of 1.02–1.47 MPa.     

Foam Physics

The physics of foams faces interesting new challenges in metal foam fabrication. The range of possibilities may be greatly extended by proposed experiments in space.     

Preparation of finely macroporous SiOC foams with high mechanical properties and with hierarchical porosity via pyrolysis of a siloxane/epoxide composite

Mechanically strong SiOC foams were prepared via pyrolysis of polysiloxane composites, into which 20–70 wt% of epoxy powder were incorporated as sacrificial filler. The chosen epoxy filler degrades practically quantitatively during the pyrolysis in nitrogen, due to a high content of polyoxypropylene chains. The pyrolysis of the composite precursors yielded SiOC foams with apparent densities between 1.31 and 0.62 g/cm³, which corresponded to macro-porosities of 35–69%. A hierarchical porosity was obtained due to a relatively wide distribution of the sacrificial filler grains׳ size. Compressive strength between 15 and 38 MPa was achieved, depending on the apparent density of the SiOC foams: the best result was obtained for the foam with 56% porosity. In the case of denser foams, their strength was reduced by the presence of pyrolysis cracks, while at 70% porosity, the thinner pore walls led to a reduced strength. The elastic modulus of the most promising foam (56% porosity) was found to be 10 GPa.     

Environmental,health and safety concerns of decorative mouldings made of expanded polystyrene in buildings

Decorative tiles and mouldings made of polymeric foams are getting more popular in buildings. There are health, safety and environmental concerns on these products and their use in the buildings. In this paper, we report the results of the study and discuss about concerns of decorative mouldings made of expanded polystyrene (EPS). Physical damage to the structure of the building, potential harms to residents and health hazards were found as main concerns in this regard. The use of decorative mouldings made of EPS in the buildings is the subject to some considerations. The climate conditions play significant role in the feasibility of usage of decorative mouldings in the buildings. Although these products may add some aesthetic effects to the building's exterior view, the observations and results of this study do not support the use of the products in the buildings. Decorative mouldings bring significant safety and health risks, and it is recommended that for usage in buildings, particularly residential ones, the decorative moulding to be made of non-flammable light-weight materials or to be completely excluded from the buildings.     

Natural additives in protein coagulation casting process for improved microstructural controllability of cellular ceramics

Aiming to improve the microstructural controllability of porous ceramic, starch was introduced as a natural additive into an environmental friendly process-protein coagulation casting. Results indicated that the viscosity of alumina/starch slurries was affected by the combined effect of the total solid loading and the water uptake of starch. Furthermore, as pore former and wet foam stabilizer, starch helped to increase the open porosity and obtain a more uniform distribution of microstructures in the fabricated alumina foams. A better microstructural controllability of the alumina foam prepared by the modified protein coagulation casting process was realised which is believed to be beneficial to the multifunctional application of these ceramic foams.     

Design and Evaluation of a New Transdermal Formulation Containing Chlorpheniramine Maleate

The antihistamine chlorpheniramine maleate (CPM) is used for symptomatic relief of hypersensitive reactions and in pruritic skin disorders. The objective of the present study was to develop a topical formulation that contained CPM to increase patient compliance. Compliance was increased by exploiting foams that, given their application methods, avoid direct contact with the afflicted area. The study also aimed to optimize the permeability of the CPM by discerning an adequate carrier, as well as choosing the correct enhancer. The foams were formulated using aqueous solutions. In vitro studies were carried out using Franz cells with the formulations, as well as with the available pharmaceutical product Polarmin Crema®, which contains CPM. These studies showed that the permeability of the CPM in the solutions is increased more then 100 times with respect to the water-in-oil emulsion Polarmin Crema. In particular, the highest permeability was obtained using limonene as an enhancer.     

On interactions between imperfections in cellular solids

A number of studies have indicated that imperfections in cellular solids can have a very large influence on their mechanical behavior. Waviness in cell walls can drastically reduce elastic stiffnesses, and various irregularities can reduce the effective strengths by large factors. These imperfections have in many instances been studied in isolation, i.e., only a singe type of imperfection was studied at a time. The goal of the present paper is to shed light on how different kinds of imperfections interact. There is a potential risk that when multiple kinds of imperfections are present, the mechanical properties of the cellular solid are worse than what would be predicted from each one in isolation. The present study is focused on linear elastic properties, although many of the conclusions apply also for other properties. The method employed is based on statistical averages and Taylor expansion arguments. Such techniques have in previous papers been applied to a single imperfection type. The conclusion from the present analysis is that, up to the third order in “small” parameters describing the severity of the imperfections, there is no interaction between a number of different types of imperfections.     

Compressive characteristics of metal matrix syntactic foams

The compressive behaviour of eight different metal matrix syntactic foams (MMSFs) are investigated and presented. The results showed that the engineering factors as chemical compositions of the matrix material, the size of the microballoons, the previously applied heat treatment and the temperature of the compression tests have significant effects on the compressive properties. The smaller microballoons with thinner wall ensured higher compressive strength due to their more flawless microstructure and better mechanical stability. According to the heat treatments, the T6 treatments were less effective than expected; the parameters of the treatment should be further optimised. The elevated temperature tests revealed ∼30% drop in the compressive strength. However, the strength remained high enough for structural applications; therefore MMSFs are good choices for light structural parts working at elevated or room temperature. The chemical composition - microballoon type - heat treatment combinations give good potential for tailoring the compressive characteristics of MMSFs.