The growth mechanism of ordered nanoporous alumina

The paper scrutinizes the peculiarities of porous alumina growth during electrochemical anodic oxidation in the orthophosphoric acid solution at constant potential of 100 Volt. On the basis of atomic-force microscopy data the paper presents consecutive stages of ordering pores in the oxide with the formation of hexagonal dense package after two-stage anodic treatment.

The Morphology of the Alumina Films Formed tn The Anodization Process of Aluminium in the Orthophosphoric Acid Solution. The Co-Fe Alloys Electrodeposition Into Obtained Alumina Pores

The optimal parameters of the anodic oxidation of aluminium in orthophosphoric acid solution was determined. In the pores of the obtained Al2O3 membranes with the ordered nanometric structure Co-Fe alloys were electrodeposited. The Al2O3 membranes were obtained in the two-stage anodic oxidation of aluminium in the 0.17 M H3PO4 solution in the temperature 1°C and at the electrolysis voltage 180 V. The influence of the anodizing process parameters on the thickness of oxide films and the diameter of pores and the distance between them in the alumina membranes were determined. The electrodeposition of Co-Fe alloys was carried out from sulphate baths containing sulphates (VI) of copper (II) and cobalt (II) of different composition, in potentiostatic conditions. The optimal electrolysis conditions were determined, where the cathodic deposits of the best quality were obtained. The conditions are: the electrolyte composition: 0.3 M Fe; 0.5 M Co; pH = 3, the potential: -0.760 V (vs. SHE1)).

An Investigation of the Synthesis Parameters of the Reaction of Hydroxyapatite Precipitation in Aqueous Media

Hydroxyapatite (HAP), described by the formula Ca10(PO4)6(OH)2, is one of the inorganic components of the hard tissues of living bodies such as bones and teeth. HAP is a calcium phosphate-based bio-ceramic, which has been used for several years in medicine and dentistry because of its excellent biocompatibility with human tissues. The success of its application in these fields depends upon factors such as the composition, crystallinity, size and morphology of HAP particles. This paper describes the work performed regarding the synthesis of this compound by a wet method comprising the direct precipitation of orthophosphoric acid solution to a calcium hydroxide solution, the process being described by the following reaction: 10 Ca(OH)2 + 6 H3(PO4) <=> Ca10(PO4)6(OH)2 + 18 H2O. Synthesis was performed in a laboratory reactor, 700mL in capacity, which was instrumented and controlled using a computer interface, so that the influence on process variables, such as reaction temperature, pH, medium inertization by N2, velocity of stirring and the flow rate input of H3(PO4), could be assessed. The influence of these parameters was, therefore, evaluated in terms of the required composition and morphology of HAP formed particles. The particles were analysed by FTIR, XRD, SEM and EPMA for the determination of the Ca/P ratio. From the obtained results, it can be concluded that HAP particles, having suitable properties for use in medicine, could effectively be prepared by this technique, provided that a good control of the involved process variables is maintained.

The Mechanical Properties and Microstructures of Cement Formed from Pyrophosphoric and Orthophosphoric Acids

In this study the setting times, compressive strengths and microstructures of cements formed using pyrophosphoric acid solution and b-tricalcium phosphate (β-TCP; Ca3(PO4)2) were compared with those of cement formed using orthophosphoric acid solution and b-TCP. It was found that cement formed using pyrophosphoric acid solution set more slowly than that formed using orthophosphoric acid and could be mixed to a higher powder to liquid ratio, facilitating the production of cement exhibiting compressive strengths, without pre-compaction, as high as 25 MPa. The use of pyrophosphoric acid as opposed to orthophosphoric acid resulted in a marked change in the microstructure of the cement.