Glycol ether additives control the size of PbS nanocrystals at reaction completion

In the colloidal synthesis of PbS quantum dots, added glycol ethers variably suppress the formation of metastable cluster intermediates. This achieves control of nanocrystal size in reactions run to completion.

Combustion Synthesis of Niobium Aluminide Matrix Composites

Combustion synthesis of NbAl3-matrix composites with Al2O3 and B additions was studied using the thermal explosion mode. The addition of B to the reaction mixture resulted in the formation of NbB2, small amounts of NbB and unreacted Al. The Al2O3 addition did not affect the NbAl3-matrix reaction completion but the final product density increased with increasing Al2O3 loading. In both NbAl3-matrix composites, the reaction was initiated above the melting point of Al.

A SIMPLE MODEL TO ESTIMATE AND COMPARE EFFICIENCY OF FLUIDIZED BED REACTOR WITHOUT AND WITH CIRCULATION

A simple model to estimate and compare efficiency of fluidized bed reactor without and with circulation is proposed. The model is based on the deterministic differential equations of a single particle motion in an upstream gas flow where the particle mass varies with time due to this or that physical or chemical process in the reactor. The particle mass variation is described by the equation similar to the equation of the first order chemical reaction kinetics. The constant of the reaction rate is proportional to the particle surface and the local velocity of gas flow around the particle. Numerical experiments with the model were done for the case when the particle volume remains constant but the particle density is decreasing. It corresponds, for example, to the process of particle drying without its shrinking. The rate of the process of particle treatment was estimated as the time, which is necessary to covert 95% of particle mass, which is capable to enter the reaction. It is shown that the rate of particle conversion grows with the gas flow velocity. However, at the same time, the particle residence time is getting smaller, and the degree of the reaction completion becomes less for direct-current reactor. It follows from that that in a direct-current reactor the bed close to the dense one is preferable. In a circulating fluidized bed reactor, the particle after reaching the top of it is directed to the bottom of the reactor and can participate in the process several times until it reaches the required degree of reaction completion. In this case much higher gas flow velocity is preferable because it intensifies gas-particle exchange, and the efficiency of the process can be considerably improved.