Oligoimide-Mediated Graphene Oxide-Epoxy Nanocomposites with Enhanced Thermal Conductivity and Mechanical Properties.

The current study reports the preparation of thermally conductive polymeric nanocomposites. For this purpose, two epoxy-based nanocomposites were prepared by dispersing a different type of functionalized graphene oxide (GO) nanofiller in each series. Both these GO nanofillers were functionalized by covalently bonding oligoimide chains on their surfaces. In one series, these oligoimide chains were prepared by reaction of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) with a diamine 4,4'-methylenedianiline (MDA). While in the other case, BTDA was reacted with N,N'-[((propane-2,2-diylbis(4,1-phenylene))bis(oxy))bis(4,1-phenylene)]bis(4-aminobenzamide) (BDM) to mount oligoimide chains on the surface of GO. Both types of oligoimide chains have amino groups as chain-end functional groups. These modified GO nanofillers were added to the epoxy matrices separately to prepare their respective nanocomposites (MDA-B-GO-epoxy nanocomposites and BDM-B-GO-epoxy nanocomposites). The chain-end amino groups of oligoimide chains reacted with the epoxy ring developing a covalent bonding between oligoimide chains of GO and the epoxy matrix. Moreover, these oligoimide chains prevented the agglomeration of GO by acting as spacer groups leading to the uniform dispersion of GO in the epoxy matrix. Various analytical techniques were used to examine the attachment of oligoimide chains to the GO surface, and to examine the morphology, curing potential, mechanical strength, thermal stability, and thermal conductivity of the prepared nanocomposites. We demonstrated that the thermal conductivity of MDA-B-GO-epoxy nanocomposites increased by 52% and an increase of 56% was observed in BDM-B-GO-epoxy nanocomposites. Similarly, a significant improvement was observed in the mechanical strength and thermal stability of both types of nanocomposites.

Non-volatile immobilization of iodine by the cold-sintering of iodosodalite.

A cold-sintering process at a very low temperature (300 °C) achieved stable immobilization of simulated radioiodine waste incorporated in sodalite (iodosodalite). The reported sintering temperature was much lower than conventional ceramic waste form processing temperatures (600-1100 °C) and had no effect on the stability of the loaded iodine waste. Excellent iodine retention (>93%) with relative sintered density 91% were achieved by the cold-sintering at 300 °C, respectively. The sintered body exhibited a micro-hardness value of 3.9 ±â€¯0.1 GPa and compressive strength of 198 ±â€¯11 MPa. The seven-day product consistency test found iodine leaching rates on order of the magnitude 10-4 g/m2⋅d. These results are the first example of the low temperature consolidation of iodine-bearing sodalite without using any additional material (e.g. glass, cement, etc.). High retention of the loaded simulated radioiodine without volatilization warrants the cold-sintering process for the environmental-friendly disposal of radioiodine.

Efficient immobilization of ionic corrosion products by a silica-hydroxyapatite composite via a cold sintering route.

We have successfully demonstrated a new method of radioactive waste immobilization by hosting a waste-bearing form in another waste matrix. A cold sintering route was used to consolidate a silica-incorporated hydroxyapatite (Si-HAp) composite at 200 °C by applying a uniaxial pressure of 500 MPa for a short holding time of 10 min. The higher relative sintered density of up to 98.0 ± 1.3% was achieved by 25 wt% Si loaded HAp. Results from high resolution X-ray diffraction, micro-hardness, and high resolution scanning electron microscopy confirmed the densification with good mechanical strength (micro-hardness = 2.9 ± 0.3 GPa). For practical applications, two kinds of wastes (25 wt% ionic corrosion product-sorbed EDTA functionalized mesoporous silica and 75 wt% ionic corrosion product-sorbed HAp) were mixed, consolidated and tested. The chemical stability of the solidified composite matrix was positively assessed for low leaching rates of 5.9 × 10-9 to 1.2 × 10-5 g per m2 per day using a standard product consistency test. The consolidated composite can bear compressive stress up to 358 MPa, which is orders of magnitude higher than the waste acceptance criteria of 3.5 MPa. The low process temperature can make this sintering process very powerful for the immobilization of radionuclides with volatility and low boiling point. Such a low temperature solidified matrix hosting various wastes may be a promising path for waste management because of its simplicity, reliability, scalability, cost effectiveness and environmental friendliness.