Sodium hypophosphite

About: Sodium hypophosphite is a research topic. Over the lifetime, 1695 publications have been published within this topic receiving 15932 citations.

Temperature responsive fibers with anisotropic transitional behavior

Abstract: Temperature sensitive polymer hydrogels are being extensively studied because of their potential applications in the biomedical, robotics, and chemical industries. However, major hurdles in their development have been their slow response, low efficiency (swelling/deswelling ratios), and poor mechanical properties due to difficulty in processing them into mechanically strong and fine structures. Fibers made from such polymers would be highly desirable. A temperature sensitive random linear copolymer of N-tert-butylacrylamide (NTBA) and acrylamide (Am) was synthesized by the solution polymerization method, using regulated dosing of comonomers. Using a novel approach, a high molecular weight poly(N-tert-butylacrylamide-ran-acrylamide::27 : 73) has been converted to insoluble strong fibers with fineness of 30–50 microns by solution spinning, drawing, and subsequent crosslinking. Fibers were solution spun in acetone using a 14% copolymer solution in acetic acid with polycarboxylic acid as a crosslinker and sodium hypophosphite as a catalyst. The crosslinks were formed, subsequent to drawing, between reactive amide side groups of the acrylamide moiety of the polymer and the carboxylic acid group of the crosslinker by thermal treatment at 160°C. The transition temperatures of the crosslinked fibers were found to shift towards the lower temperature from 37°C (in linear copolymer) to 22–25°C. These engineered fibers display sharp temperature sensitivity, extremely high reversible change in dimensions (1000% in diameter and ∼ 70% in length), and extremely fast response time (< 20 s for expansion and < 2 s for contraction). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 681–688, 2005

Hydrogen evolution, incorporation and removal in electroless nickel composite coatings on aluminium

Abstract: The mechanism of electroless nickel deposition involves generation of hydrogen which can be entrapped in the NiP layer. In this study hydrogen evolution in several electroless composite coatings, that is, NiP–X (X=SiC, Al2O3 and boron particles), deposited on an aluminium (6063-T6) substrate, was investigated by the solid extraction method. It was found that particle codeposition can promote hydrogen occlusion in the layers, a fact correlated with the adsorption capacity and affinity of particles towards water or hydrogen itself. Hydrogen removal efficiency from coatings, after heat treatment, increased with the applied temperature (130, 160 and 190 °C for 1.5h each). For the same heat treatment (190 °C for 1.5h), most composite coatings showed lower removal efficiencies (35–54%) compared to NiP layer (80%) and, as the amount of hydrogen in the composite coating increased, its removal efficiency decreased.

On the kinetics of copper electroless plating with hypophosphite reductant

Abstract: The electroless copper plating using sodium hypophosphite as the reductant and sodium citrate as the chelating agent was studied by gravimetric and electrochemical measurements. The effects of temperature, pH, boric acid, citrate, hypophosphite, nickel catalyst and copper concentration were tested. A chemical model was defined to determine the composition of all ionic species in the bath solution. The kinetics of the electroless copper deposition was interpreted on the basis of the dehydrogenation of the reductant, mixed potential theory and in the ionic speciation of the bath. Scanning electron microscopy, X-ray microanalysis by energy spectroscopy dispersion and X-ray diffraction applied on surfaces show that the deposits are composed by binary (Ni–Cu) and ternary alloys (Cu–Ni–P) and that their crystallinity depends on phosphorus content.

Pulse plating of hard chromium from trivalent baths

Abstract: A trivalent chromium bath is relatively non-toxic compared with a hexavalent chromium bath. It is difficult, however, to obtain thick chromium electrodeposits from a trivalent chromium bath with direct-current plating. This paper describes a study using pulsed current to plate thick chromium electrodeposits for hard chromium applications from a trivalent chromium bath, using either ammonium formate or sodium hypophosphite as the complexing agent. It was found that the chromium plating rate using pulsed current was higher than that for direct current. Pulsed current improved the maximum coating thickness that could be obtained from the trivalent chromium baths. In addition, pulsed current decreased the internal stress of a trivalent chromium deposit by 25 to 75 percent. The internal stress decreased with decreasing current density, duty cycle and pulse frequency. When sodium hypophosphite was used as the complexing agent in the trivalent bath, a significant quantity (15 to 30% ) of phosphorus co-deposited on the chromium coating. The phosphorus content increased with decreasing duty cycle and with increasing pulse frequency. The microhardness of a trivalent chromium deposit obtained with pulsed current was in the range of 610 to 850 on Knoop's hardness scale. These values were comparable to that obtained with direct current. Increasing pulse frequency in the range of 10-1000 Hz increased the microhardness of the chromium deposit.