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Abstract: Long-term stable (>2years) hydrocolloids of hydroxyapatite (HA) were synthesized via a low-temperature (18–50°C) reaction of aqueous ammonium phosphate with calcium nitrate in the presence of citrate ions, followed by an aging process at high temperature (80–99°C) for 4h. Changing the reaction and/or aging temperature seldom yielded stable HA hydrocolloids. The as-prepared hydrocolloids were desalinated through ultrafiltration where their average particle size gradually decreased, bottomed out at 100–400μS/cm, and sharply increased in parallel with a decrease in solution conductivity. The colloid formation is most likely through a temperature-sensitive aggregates–breakdown process. During low-temperature reaction, citrate–calcium chelation bridges the growing HA particles into loose aggregates. High-temperature aging disrupts these inter-particle links and thus breaks the aggregates, imparting negative charges to the HA, forming colloidal particles stabilized by surface charge. The decrease in mean particle size during early ultrafiltration suggested that the aggregate breakdown further proceeded through desalination. In conclusion, the temperature-dependent interactions between citrate ions and calcium sites on HA particles played key roles in the synthesis and stability of the HA colloids. [Copyright &y& Elsevier]

Spinel–type oxides MgCo 2 O 4 and Co 3 O 4 nanowires (NWs) were successfully prepared using nickel foam (NF) as a template. The catalytic performance of MgCo 2 O 4 NWs on the thermal decomposition of ammonium perchlorate (AP) was investigated by differential scanning calorimetry (DSC) and simultaneous thermogravimetry–mass spectrometry (TG/MS) techniques. In the presence of MgCo 2 O 4 NWs, the process of the high temperature decomposition (HTD) and the low temperature decomposition (LTD) of AP was combined to one with a peak temperature of 277.35 ​°C. Meanwhile, the apparent activation energy decreased from 139.05 to 123.61 ​kJ·mol−1 on the basis of thermal analysis kinetics. This was attributed to the synergistic effect between the metals of this ternary metal oxide and the larger specific surface area of MgCo 2 O 4 NWs. Therefore, MgCo 2 O 4 with nanowires morphology holds a promise to catalyze energetic components. MgCo 2 O 4 nanowires were prepared using nickel foam as a template. DSC test confirmed that MgCo 2 O 4 /AP had faster decomposition reaction velocity, the process of the high temperature decomposition and the low temperature decomposition of AP was combined to one with a peak temperature of 277.35 ​°C. The excellent catalytic activity of MgCo 2 O 4 /AP can be attributed to the fact that MgCo 2 O 4 can accelerate the transfer of electrons and then promote the decomposition of AP. Image 1 • MgCo 2 O 4 can be prepared by replacing Co2+ in Co 3 O 4 with environmentally benign metal Mg2+. • Nickel foam (NF) reflects outstanding characteristics acts as a carrier for material growth. • Compared to Co 3 O 4 , MgCo 2 O 4 shows higher efficient catalytic activity ​when added into ammonium perchlorate (AP). • The synergistic effect and the larger specific surface area of MgCo 2 O 4 ​promote the decomposition of AP. [ABSTRACT FROM AUTHOR]