Structure and Stability of High CaO- and P2O5-Containing Silicate and Borosilicate Bioactive Glasses

Calcium-Doped Boron Nitride Aerogel Enables Infrared Stealth at High Temperature Up to 1300 °C

Boron nitride (BN) aerogels, composed of nanoscale BN building units together with plenty of air in between these nanoscale building units, are ultralight ceramic materials with excellent thermal/electrical insulation, great chemical stability and high-temperature oxidation resistance, which offer considerable advantages for various applications under extreme conditions. However, previous BN aerogels cannot resist high temperature above 900 °C in air atmosphere, and high-temperature oxidation resistance enhancement for BN aerogels is still a great challenge. Herein, a calcium-doped BN (Ca-BN) aerogel with enhanced high-temperature stability (up to ~  1300 °C in air) was synthesized by introducing Ca atoms into crystal structure of BN building blocks via high-temperature reaction between calcium phosphate and melamine diborate architecture. Such Ca-BN aerogels could resist the burning of butane flame (~  1300 °C) and keep their megashape and microstructure very well. Furthermore, Ca-BN aerogel serves as thermal insulation layer, together with Al foil serving as both low-infrared-emission layer and high-infrared-reflection layer, forming a combination structure that can effectively hide high-temperature target (heated by butane flame). Such successful chemical doping of metal element into crystal structure of BN may be helpful in the future design and fabrication of advanced BN aerogel materials, and further extending their possible applications to extremely high-temperature environments.

Bioactive Glass Nanoparticles for Tissue Regeneration

Sol-gel-derived bioactive glass nanoparticles have attracted special interest due to their potential as novel therapeutic and regenerative agents. Significant challenges are yet to be addressed. The fabrication of sol-gel-derived nanoparticles in binary and ternary systems with an actual composition that meets the nominal has to be achieved. This work addresses this challenge and delivers nanoparticles in a ternary system with tailored composition and particle size. It also studies how specific steps in the fabrication process can affect the incorporation of the metallic ions, nanoparticle size, and mesoporosity. Sol-gel-derived bioactive glass nanoparticles in the 62 SiO₂-34.5 CaO-3.2 P₂O₅ (mol %) system have been fabricated and characterized for their structural, morphological, and elemental characteristics using Fourier transform infrared spectroscopy, X-ray diffraction analysis, scanning electron microscopy associated with elemental analysis, transmission electron microscopy, and solid-state nuclear magnetic resonance. The fabricated nanoparticles were additionally observed to form the apatite phase when immersed in simulated body fluid. This work highlights the effect of the different processing variables, such as the nature of the solvent, the order in which reagents are added, stirring time, and the concentrations in the catalytic solution on the controlled incorporation of specific ions (e.g., P and Ca) in the nanoparticle network and particle size.