Operational Variables on the Processing of Porous Titanium Bodies by Gelation of Slurries with an Expansive Porogen

Colloidal processing techniques, based on the suspension of powders in a liquid, are very versatile techniques to fabricate porous structures. They can provide customized pores, shapes and surfaces through the control of operational parameters, being the base of the alternative additive manufacture processes. In this work disperse and stable titanium aqueous slurries has been formulated in order to process porous materials by the incorporation of methylcellulose (MC) as a gelation agent and ammonium bicarbonate as an expansive porogen. After casting the slurries and heating at mild temperatures (60–80 °C) the methylcellulose gels and traps the gas bubbles generated by the ammonium bicarbonate decomposition to finally obtain stiff porous green structures. Using an experimental design method, the influence of the temperature as well as the concentration of gelation agent and porogen on the viscosity, apparent density and pore size distribution is analyzed by a second-order polynomial function in order to identifying the influence of the operating variables in the green titanium porous compact. After sintering at 1100 °C under high vacuum, titanium sponges with 39% of open porosity and almost no close porosity were obtained.

Development of a 3D polyetheretherketone structure that mimics the cranial bone morphology for use in cranioplasty

Cranioencephalic traumatism (TBI) is a common situation in trauma hospitals and has become responsible for high rates of mortality worldwide. When the victim of TBI is affected by injuries to the skullcap with a need for grafting, problems regarding the availability of suitable and affordable materials eventually happen. In this study, a 3D structure of Polyetheretherketone (PEEK) that mimics the cranial bone morphology for use in cranioplasty was developed. Samples of different formulations, in the form of round bars, were obtained through uniaxial compression, and porosity was controlled by the salt leaching technique. Then, the specimens were characterized in terms of pore morphology and distribution, surface roughness, compression resistance and cytotoxicity. Results exhibited high levels of similarity of the 3D strutures of PEEK to the natural human bone, which indicates the effectiveness of the proposed method in mimicking the morphology of the compact/porous/compact system of the skullcap (diploe).

Fabrication and Characterization of Porous Silica/Carbon Nanotube Composite Insulation

In recent years, the demand for high performance thermal insulations has increased. While foam and aerogels have been researched for high performance thermal insulation, novel material design is required for further improvement. A porous silica has been found to have the potential to form a new thermal insulation material. However, porous silica is a powder and is difficult to form the porous compact. Therefore, we propose a composite insulation of powdered porous silica (p-SiO2), carbon nanotubes (CNTs) and sodium carboxy methyl cellulose (CMC). The fine voids and bulky structure of p-SiO2 greatly suppress gas and solid heat transfer. The composite of CNT can improve the moldability and enhance the mechanical properties. The moldability of thermal insulating materials improved even with the addition of 1 wt% CNT. With the addition of 1 wt% CNT, the increase in thermal conductivity was less than 0.01 W⋅m-1⋅K-1.

Thermally stable high-strength porous alumina

A two-step heating schedule involving pulse electric current sintering, a kind of pressure-assisted vacuum sintering, and a subsequent postsintering in air was used to fabricate sintered porous alumina compacts. During pressure-assisted vacuum sintering, a dense microstructure of the Al2O3–C system was obtained and in the second stage (i.e., during postsintering in air at different temperatures ranging from 800 to 1300 °C for more than 10 h) carbon particles present in the Al2O3–C system burned out to form a highly porous Al2O3 compact. In this work, the porosity (30%) was successfully controlled and did not change with the postsintering temperature. The intriguing aspect of this study is that porous alumina compacts are fabricated with high strength and remain stable against the postsintering temperature and extended soaking time. This behavior merits the material fabricated here as a potential porous compact, mechanically withstanding for high-temperature applications.

Dynamic modeling of the interaction of gas and solid phases in multistep reactive micropyretic synthesis

A mathematical model of micropyretic synthesis, including the consideration of pressure rise (due to gas evolution) in a porous compact, is developed for a multistep reaction. D'Arcy's law of gas flow, continuity equation, and gas law are combined to obtain a relationship between the pressure and temperature of gas. This equation for the gas pressure is solved along with the energy equations of gas and solid phase. The numerical analysis shows that the magnitude of pressure increase depends on the initial gas pressure, temperature, and permeability. When gas evolution is considered, the pressure increase depends on the variables that determine the kinetics of the gas evolution reaction, such as the activation energy and the pre-exponential factor. The pressure increase is maximum when the gas evolution takes place in the combustion reaction zone. The gas evolution is noted not to influence the combustion wave propagation.