Saudi tests of imported cements

As the pace of development increases in Saudi Arabia so imported materials become more numerous and competitive. The Materials Testing Laboratory in Riyadh recently compared samples of cements from abroad with those produced locally. The results, though primarily directed towards the cement chemists, may also be of more than local interest.     

Dielectric properties of new fully conjugated 2H‐ and metal‐pyrazinoporphyrazine network polymers

2,7‐Di‐tert‐butylpyrene was oxidized to 2,7‐di‐tert‐butylpyrene‐4,5,9,10‐tetraone. The latter through condensation reaction with vicinal diamine such as diaminomaleodinitrile afforded heterocyclic monomer, 2,7‐di‐tert‐butyl pyrene[4,5][9,10]bis(2,3‐pyrazine‐5,6‐dinitrile), which was cyclotetramerized to the corresponding 2H‐ and metal‐pyrazinoporphyrazine‐based network polymers (2H‐PyzPz and M‐PyzPz, M = Co, Ni, Zn, or Cu). Elemental analytical results, Infrared, and NMR spectral data of the new prepared molecules are consistent with their assigned formulations. Molecular masses and metal contents of the synthesized polymers proved to be of high molecular masses, which confirm the efficiency of tetramerization polymerization and complexation reactions. Dielectric permittivity, ε′, loss tangent, tan δ, and ac conductivity, σac(ω), of 2H‐PyzPz and M‐PyzPz films were studied as a function of temperature and frequency. It was found that dielectric permittivity, ε′, decreases with the increase of frequency and increases with the increase in temperature. Ac conductivity, σac(ω), is found to vary as Bωs and the frequency exponent, s, is less than unity around room temperature indicating a dominant hopping process. On the other hand, σac(T) of all samples is thermally activated with low activation energies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Mathematical modelling of mass transfer in the concentration polarisation layer of flat‐sheet membranes during clarification of pomegranate juice

Evaluation of membrane clarification of pomegranate juice showed that a cake layer is created at the beginning of the process. This evaluation was used as the basis for modelling the solute concentration in the concentration polarisation layer to control the fouling of the membrane. The model of changes in concentration as a function of time and distance (in its dimensionless form) was solved numerically using the Forward‐Time/Central‐Space (FTCS) method. Programming was performed using MATLAB software, and the predicted concentration on the membrane surface was compared with experimental data; the prediction fit well with the experimental data. The model showed that the solute concentration increased as distance to the membrane surface decreased, time increased, transmembrane pressure increased and velocity decreased. Also, the model matched the experimental data in that it showed the cake layer to be created in the early stages of the membrane clarification process.     

Synthesis of novel dyestuffs containing sulphonamido moieties and their application on wool and polyamide fibres

A new series of azo disperse dyestuffs were prepared by the reaction of sulphanilamidodiazonium chloride derivatives with indan-1,3-dione. Application of these dyes on wool and nylon 6.6 gave excellent results. The synthesised compounds show good biological activity towards different microorganisms.     

Synthesis,characterization and thermal dissociation of 2‐butoxyethanol‐blocked diisocyanates and their use in the synthesis of isocyanate‐terminated prepolymers

A series of blocked diisocyanates has been synthesized from toluene diisocyante (TDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), 4,4′‐diphenylmethane diisocyanate (MDI) and 2‐butoxyethanol. The synthesis of blocked diisocyanate adducts was confirmed by Fourier transform infrared, ¹H NMR, electron impact mass spectrometry and nitrogen analysis. Differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and carbon dioxide evolution were used to determine the minimum de‐blocking temperatures. De‐blocking temperatures determined by these three techniques were found to be in the order DSC > TGA > CO₂ evolution. The effect of different metal catalysts on thermal de‐blocking reaction of the blocked diisocyanates was studied, using the carbon dioxide evolution method. It was found that iron(III) oxide has the maximum catalytic activity on de‐blocking. The solubility of the blocked diisocyanate adducts was determined in different solvents. The study revealed that at 30 °C blocked IPDI and HDI adducts show better solubility than adducts based on TDI and MDI. Isocyanate‐terminated prepolymers of blocked diisocyanates and hydroxyl‐terminated polybutadiene (HTPB) were prepared. The storage stability and gelation times of the prepolymers were studied. Results showed that all the diisocyanate‐HTPB compositions are stable at 50 °C for more than three months. However, aliphatic diisocyanate‐HTPB compositions require greater gelation time than aromatic diisocyanate‐HTPB compositions at their respective de‐blocking temperatures. Copyright © 2007 Society of Chemical Industry     

Ability of adaptive filters to track carrier offsets and channelnonstationarities

This paper studies the tracking performance of adaptive filters operating in the presence of two sources of nonstationarities: carrier frequency offsets and random channel variations. Both impairments are common in digital communications due to mismatches between transmitter and receiver carrier generators and channel fading. The paper derives expressions for the mean-square error and shows how filter performance is degraded under such nonstationary conditions. Selections of step sizes for optimal tracking performance are derived, different adaptive algorithms are compared, and supporting simulation results are provided     

Investigation of electrical and optical properties of polyvinyl acetate doped with some polymers

Polyglycerol (PG) and polytriethanolamine(PTEA) have been prepared. The electrical resistivity (ρ) and the optical absorption of polyvinylacetate (PVAc) doped with polyglycerol (PG), polyaniline (PA), and polytriethanolamine (PTEA) have been studied. It was found that the conduction was mainly ionic in the temperature range from 20 to 120°C. The resistivity decreased with the increase of the dopant cocentration. The optical absorption spectra were determined in the wavelength range 400–2500 nm. The analysis of the absorption spectra showed that the intensity of the bands is remarkably affected by the dopant concentration. The optical energy gap of pure PVAc and the samples containing different dopants were estimated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1558–1563, 2002