On the electrodeposition and characterization of niobium from fused fluoride electrolytes
The electrodeposition of niobium from a binary electrolyte consisting of KF and NaF was characterized and compared with that from the ternary electrolyte of LiF, NaF and KF. The deposition experiments were conducted at current densities between 5 and 35 mA cm−2 and electrolyte temperatures between 725 and 800°C. DTA measurements indicated the melting points to be 450 and 710°C for the ternary and binary electrolytes with added K2NbF7; however, it was necessary to operate both electrolytes above 725°C to obtain dense coherent deposits. Coating morphology was described by optical and scanning electron microscopy studies, while coating structure and properties were characterized by X-ray diffraction analysis. In particular, a series of diffraction measurements were reported to describe the changes in the microstructure of the deposited material as a function of the preparation conditions.
Electrodeposition of Coherent Deposits of Refractory Metals I . Niobium
A general method has been found for the electrodeposition of coherent, dense deposits of refractory metals by electrolysis of molten salts. By dissolving the refractory metal fluoride in mixtures of alkali metal fluorides, one may deposit coherent thick coatings of chromium, hafnium, molybdenum, niobium, tantalum, tungsten, vanadium, and zirconium. Not only do the deposits in all cases have the theoretical density, but in most cases are extremely pure and equal to or better in mechanical properties than electron beam melted material available commercially. While differences exist from metal to metal in the details of the compositions of the electrolyte and the valence state of the refractory metal, the general process can be described in terms of one of the first metals studied, niobium. Niobium metal is eleetrodeposited from a solution about I0 w/o NbFs in a mixture of alkali fluorides at a temperature of about 775~ and a current density of about 50 ma/cm 2 with commercially pure niobium as anode material. Anode and cathode efHciencies are close to 100% and deposits with hardness of 85-100 DPH are obtained regularly. Deposits with densities of 99.8% of theoretical and higher are obtained and the throwing power of the bath is better than that usually associated with commercial nickel plating. There is no major restriction on substrates, since steel, stainless steel, graphite, copper, Hastelloy alloys, and others have been used. Thicknesses up to I/4 in. have been electrodeposited with a surprisingly smooth surface. The microstructures of the deposits are the typical columnar grain structure usually observed in electrodeposits without addition agents and their soundness has been confirmed by mechanical testing. Also, successful electrorefining has been accomplished.
Development of polyamide curable modified epoxy novolac resins with improved adhesion and chemical resistance
Purpose – To prepare modified epoxy resins from resorcinol, cresol and phenol for improved adhesion and chemical resistance. To evaluate the properties of such modified epoxy resins.Design/methodology/approach – Epoxy novolac resins (ENRs) were synthesised by condensing epichlorohydrin with novolacs based on different types of substituted phenols for improving adhesion and chemical resistance. Various compositions were made by incorporating different proportions of polyamide resin. The chemical and adhesive strengths of the conventional epoxy and the modified epoxy resins were characterised.Findings – The modified ENR using substituted phenols showed significant enhancement of chemical and adhesive strengths over the conventional DGEBA resin. The modified ENR had an increased number of glycidyl groups (thus increased functionality) of resin, which was responsible for improved chemical and adhesive strengths over the conventional DGEBA resin.Research limitations/implications – The EPN resins used in the pr...