Power Line Communications: An Overview - Part I

We give an overview of the power line communications (PLC) technology, its importance, its standards and an overview of the HomePlug standards associated with it. This is done is two parts due to publication constraints. In this part, we will concentrate on the PLC applications and the technical issues regarding it. We will also see the layers and methods that are needed to make it work

Power Line Communications: An Overview - Part I

We give an overview of the power line communications (PLC) technology, its importance, its standards and an overview of the HomePlug standards associated with it. This is done is two parts due to publication constraints. In this part, we will concentrate on the PLC applications and the technical issues regarding it. We will also see the layers and methods that are needed to make it work

Change of Structural and Adsorption Properties Due to Isomorphous Substitution in Hydrotalcite-like Materials

Samples of hydrotalcite-like compounds with the general formula [M 2+ 1-x M 3+ x (OH) 2 ] x+ •A x– •nH 2 O were prepared via coprecipitation through the addition of NaOH to mixed chloride salt solutions. On maintaining the M 2+ /M 3+ ratio equal to three, it was possible to effect isomorphous substitution. This led to the preparation of different compounds which could be compared to the parent material in which M 2+ = Ni and M 3+ = Al. Other divalent cations used were Mg 2+ and Zn 2+ with Cr 3+ and Fe 3+ being employed as trivalent cations. The ratio between cations of the same charge was unity in all the isomorphously substituted samples and substitution was conducted for one oxidation state only at a time. Hence, all samples contained a maximum of three different cations. The charge compensating anion in the interlayers, A, was identified as mainly CO 3 2– with the co-existence of Cl − anions to different extents. The structural and textural properties developed as a result of the substitutions effected were studied by XRD, IR, DTA, acid–base titration and mercury porosimetry measurements. Various samples were used for the adsorption of 4-chlorophenol to examine the effects on the adsorption properties arising from isomorphous substitution. The major effect having a marked influence on the adsorption properties arose from the nature of the compensating anion in the interlayers. Different tendencies of different cations to be accommodated in the layer structure resulted in different interlayer spaces and variable conformations of the charge compensating anion. In all cases, at low equilibrium concentrations, the adsorption of 4-chlorophenol (pH = 11) occurred at the edges of the layer structure accompanied by Cl − /OH − exchange. The increasing order in the amount of 4-chlorophenol adsorbed was matched by an increasing order in the interlayer space due to substitution. At higher values of the equilibrium concentration, the adsorption of both phenolate and OH − anions decreased. This was because such adsorption into the interlayer space to replace the CO 2– anion was diffusion-controlled, making the process improbable at high pH values

Solid Acids from Persulphated and Perchlorated Physical Mixtures of Zirconium and Titanium Hydroxides

Calcination at 650°C of a physical mixture of zirconium and titanium hydroxides led to the formation of the corresponding oxides, monoclinic zirconia and anatase. The adsorption of perchlorate or persulphate anions (as 0.05, 0.1, 0.2 or 0.4 M aqueous solutions) before calcination did not inhibit crystallization; however, perchlorate anions activated the formation of rutile in addition to the predominant anatase phase. Indeed, the adsorption of perchlorated anions prior to calcination allowed the thermodynamically less stable tetragonal phase of zirconia to be detected in addition to monoclinic zirconia at ambient temperature. In contrast, the adsorption of persulphate anions before calcination stabilized the tetragonal phase with no rutile phase being detected in this case. Infrared spectroscopy showed that adsorbed S 2 O 8 2– anions were held more strongly by the solid than ClO 4 − anions which tended to decompose when the solid was calcined. The acidities of the solid acids produced because of S 2 O 8 2– or ClO 4 − anion adsorption were studied via the adsorption of pyridine (pK a = 5.3) from cyclohexane solution. The amounts and strengths of the acid sites formed during persulphate treatment were higher than those resulting from perchlorate adsorption. The strength of the acid sites formed on samples calcined before loading with S 2 O 8 2– or ClO 4 − anions showed no significant differences. Variations detected in the structural aspects arising from S 2 O 8 2– or ClO 4 − anion adsorption were reflected in the texture as assessed by nitrogen adsorption at −196°C

Structural and Textural Properties of Perchlorated and Persulphated Mixed (Hydr)Oxides of Zirconium and Titanium

Perchlorated and persulphated mixed hydroxides of zirconium and titanium were prepared by coprecipitation and impregnation in aqueous HClO 4 or (NH 4 ) 2 S 2 O 8 solutions of 0.05, 0.10, 0.20 and 0.40 M concentrations. An alternate sequence of impregnation followed by calcination or vice versa was conducted and the samples obtained studied using XRD, FT-IR, pyridine titration and low-temperature (–196°C) nitrogen adsorption methods. XRD indicated that the presence of titanium stabilized the tetragonal modification of zirconia and almost completely prevented the usual tetragonal → monoclinic transformation upon calcination at 650°C. Both S 2 O 8 2– and ClO 4 − anions at their lowest concentration level (0.05 M) partially retarded the crystallization which occurred upon calcination at 650°C in their absence. However, the two anions showed different effects. Whereas the perchlorate anion prevented the formation of a crystalline titania phase (anatase) to a greater extent than that of crystalline zirconia, the persulphate anion showed the opposite effect. Complete inhibition was observed with both anions at a concentration of 0.4 M. This effect was attributed to adsorption of the anions on the hydroxy species of zirconium and titanium formed initially, as demonstrated by IR spectroscopy which showed that the anions were of lower symmetry, viz. C 2v , due to their bonding to the hydroxy species. Calcination at 650°C caused the material formed initially to lose virtually all its initial high surface area because of crystallization. The prevention of crystallization by added anions was reflected in the retention of a relatively high surface area even after calcination at 650°C. The recorded difference in the interactions of the anions with the hydroxy species formed initially was also reflected in the texture of the anion-modified solids. The protecting influence of the ClO 4 − anion increased with its increasing concentration in the system, whereas the corresponding effect with the S 2 O 8 2– anion increased up to 0.10 M concentration and then decreased at higher concentrations