Boron-polymer composites engineered for compression molding,foaming, and additive manufacturing

Boron (specifically ¹⁰B) is the element of choice to shield thermal neutrons due to its large (n, α) cross-section; however, very few polymer composites containing high boron concentrations are available. This study aimed to determine the maximum possible amount of boron that could be introduced into a polymer matrix. Diverse manufacturing techniques, ranging from additive manufacturing to compression molding, were employed to fabricate inks and filaments for 3D printing, foams, and flexible pads. Composites using siloxanes, poly(lactic acid), and acrylonitrile butadiene styrene containing up to 80 wt% boron were sucessufully fabricated. The addition of known plasticizers (polyethylene glycol) and reinforcing agents (carbon nanofibers and fumed silica) helped to overcome fabrication problems such as clogging of the printing nozzle or crumbling of compression molded parts. In addition, the thermal-mechanical properties of these novel boron composites were determined and shown to vary according to boron concentration, presence of additives, and fabrication techniques utilized.     

TiO2 coated urchin-like SnO2 microspheres for efficient dye-sensitized solar cells

Urchin-like SnO2 microspheres have been grown for use as photoanodes in dye-sensitized solar cells （DSSCs）. We observed that a thin layer coating of TiO2 on urchin-like SnO2 microsphere photoanodes greatly enhanced dye loading capability and light scattering ability, and achieved comparable solar cell per- formance even at half the thickness of a typical nanocrystalline TiO2 photoanode. In addition, this photoanode only required attaching -55% of the amount of dye for efficient light harvesting compared to one based on nanocrystalline TiO2. Longer decay of transient photovoltage and higher charge recombination resistance evidenced from electrochemical impedance spectroscopy of the devices based on TiO2 coated urchin-like SnO2 revealed slower recombination rates of electrons as a result of the thin blocking layer of TiO2 coated on urchin- like SnO2. TiO2 coated urchin-like SnO2 showed the highest value （76.1 ms） of electron lifetime （＇r） compared to 2.4 ms for bare urchin-like SnO2 and 14.9 ms for nanocrystalline TiO2. TiO2 coated SnO2 showed greatly enhanced open circuit voltage （Voc）, short-circuit current density （Jsc） and fill factor （FF） leading to a four-fold increase in efficiency increase compared to bare SnO2. Although TiO2 coated urchin-like SnO2 showed slightly lower cell efficiency than nanocrystalline TiO2, it only used a half thickness of photoanode and saved -45% of the amount of dye for efficient light harvesting compared to normal nanocrystalline TiO2.     

Simplified models for the performance evaluation of desiccant wheel dehumidification

In the present communication, simple models have been presented to evaluate the performance of rotary desiccant wheels based on different kind of solid desiccants e.g. silica gel and LiCl. The first part of the paper presents ‘Model 54’ which is developed for silica gel desiccant rotor. The model has been derived from the interpolation of experimental data obtained from the industry and the correlations have been developed for predicting outlet temperature and absolute humidity. The ‘Model 54’ consists of 54 coefficients corresponding to each correlation for outlet absolute humidity and temperature and it is found that the model predicts very well the performance of silica gel desiccant rotor (Type-I). In the second part of the paper, a psychrometric model has been presented to obtain relatively simple correlations for outlet temperature and absolute humidity. The developed psychometric model is based on the correlations between the relative humidity and enthalpy of supply and regeneration air streams. The model is used to predict the performance of three type of desiccant rotors manufactured by using different kind of solid desiccants (Type I, II and III). The model is tested corresponding to a wide range of measurement data. The developed psychometric model is simple in nature and able to predict very well the performance of different kind of desiccant rotors. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis and performance of a novel polyurethaneurea as pervaporation membrane for the selective removal of phenol from industrial waste water

Hydroxyterminated polybutadiene (HTPB) was reacted with 2,4-toluene diisocyanate (TDI) followed by the addition of a diamine chain extender (prepared by the condensation reaction of 4,4'diaminodiphenylsulfone and terepthalaldehyde) to prepare an imine containing polyurethaneurea (PIUU). The prepared polyurethaneurea was caste in order to obtain polymer film. The new polyurethaneurea film showed high phenol selectivity as pervaporation membrane. About 88% phenol was obtained in condensed permeate when pervaporation was performed at 50°C with 7% aqueous phenol solution as feed and permeate side pressure was maintained at 5 mm of Hg.     

Crystal structure and resistivity studies on PrBa2 −x Pr x Cu3O7 −y oxide system

The compound PrBa₂Cu₃O_{7 −y} is not superconducting while most other RBa₂Cu₃O_{7 −y} (R=rare earth) compounds exhibit superconductivity in the 90K range. The system PrBa_{2 −x} Pr _x Cu₃O_{7 −x} has been prepared to study the effect of excess Pr at the Ba site on the structure, resistivity and magnetic behaviour of this system. It is observed that single-phase compounds in the above series form forx=0·8—that is up to the composition Pr_1·8Ba_1·2Cu₃O_{7 −y} . While stoichiometric PrBa₂Cu₃O_{7 −y} is orthorhombic, the compounds with excess Pr show tetragonal structure. Four-probe dc resistivity measurements show that all the single-phase compounds in the above series do not exhibit superconductivity and are semiconducting down to 12 K. Magnetic susceptibility measurements reveal deviation from Curie-Weiss behaviour starting at a characteristic temperature, which is taken to be the ordering temperature (T _N ) of the Pr moments. BothT _N and overall resistivity decrease with increasingx and may have a common origin.     

Renewable energy programme and vision in India

In the present world, renewable sources of energy have begun to make a significant contribution to meeting heat and power needs. In India, the Government is implementing a wide ranging programmes on renewable energy technologies. Several policy and fiscal measures have contributed to the rapid expansion of the progress during the last few years. This paper presents a review of renewable energy programme and vision in India. The present situation is seen to be much more promising and favourable for renewables.     

Hybrid solar water distillation system: A techno-economic study

The paper presents a techno-economic model to evaluate the performance of a hybrid solar still. For this, three different sources of auxiliary energy, namely electricity, kerosene, and liquefied petroleum gas (LPG) have been considered. To appreciate the model, numerical calculations have also been made using prevailing prices of different fuels in the Indian market for the climate of Delhi, India.