Mechanical and tribological properties of TiCxN1−x wear resistant coatings

The aim of this work is to investigate the mechanical and tribological properties of TiC_xN_1−x wear resistant coatings grown on a Ti–0.2 Pd alloy substrate. Films were deposited by dual ion beam sputtering (DIBS) system with different proportions of N₂ and Ar in the assisting beam. The friction tests have been carried out with a pin-on-disc tribometer with different applied loads. The films present high hardness and elastic properties whose values depend upon preparation conditions. The mechanical properties and the tribological behaviour of the coatings seem to depend on their stoichiometry and microstructure. The coating TiC_0.5N_0.5 shows less hardness and better wear resistance than the coating with stoichiometry TiC_0.15N_0.85. The influence of the stoichiometry and the local structure of the films on its mechanical properties have been ruled out.     

Removing contaminants from tannery wastewater by chemical precipitation using CaO and Ca(OH)2

The removal of Cr, sulfates and Chemical Oxygen Demand(COD) from industrial tannery wastewater by chemical precipitation was carried out using Calcium oxide(CaO) and Calcium hydroxide(Ca(OH)_2). Different doses of alkalis,ranging from deficiency to excess hydroxyl species over the stoichiometric necessary, were used to remove theoretically the 100% of Cr [0.3–3.2 g alkali·(g Cr~(3+))~(-1)]. The precipitation was carried out at room temperature, 10 min of vigorous stirring, 200 r·min~(-1) and a settling time of 24 h, followed by separation and characterization of liquid product. As result of addition of alkalis, pH underwent increase as did the alkali concentration. The removal of Cr, and sulfates also increased as alkali concentration did, although for first species the changes at higher alkali contents were less evident. COD removal on the other hand, did not follow a unique trend, instead exhibited a maximum. Based on our results, selection of a specific dose of alkali was carried out taking as reference the efficiency on total chromium removal, keeping the pH in the range 7 to 9 to ensure Cr precipitation as chromium hydroxide. With those conditions,jar test was used to produce enough liquid product in order to determine the removal percent of several other species.The removal percent of the species was as follows: Cr, SO_4~(2-), ZnSO_4, FeSO_4, CN~(-1),NiSO_4,Fe_2[Fe(CN)_6] at 99.8%, 66.9%,99.6%, 21.4%, 70.9%, 52.8% and 76.4% with CaO, and 99.8%, 61.6%, 99.9%, 7.1%, 84.0%, 54.4% and 90.5% with Ca(OH)_2,respectively.     

Degradation of β-carotene in amorphous polymer matrices. Effect of water sorption properties and physical state

BACKGROUND: The use of encapsulation in amorphous matrices of carbohydrate and/or polymer formed during dehydration processes to enhance the stability and retention of labile compounds is increasing in the food and pharmaceutical industries. Efforts to improve encapsulating properties have been made using mixtures of carbohydrates with proteins or gums in different proportions. The objective of the present work was to study the stability of encapsulated β‐carotene and its degradation kinetics in maltodextrin/gum arabic and maltodextrin/gelatin matrices in relation to the physical properties and state of the dehydrated matrix. RESULTS: The degradation of β‐carotene followed a first‐order kinetic model of fractional retention for all encapsulating matrices. The Guggenheim–Anderson–de Boer (GAB) model was adequate to describe the sorption isotherms of the studied systems. β‐Carotene losses were observed mainly at relative humidities (RHs) above the glass transition temperatures (T_g) of the corresponding systems, where the matrices were fully plasticised and collapsed (75 and 92% RH). At these high RHs the best β‐carotene retention was obtained in the system containing gum arabic. CONCLUSION: The results showed that pigment degradation was determined by the physical state of the matrix, related to the degree of collapse. They represent a contribution to the knowledge of physical factors that affect the retention kinetics of labile biomolecules encapsulated in dehydrated matrices. Copyright © 2011 Society of Chemical Industry