ON THE DYNAMICS OF THE COMBUSTION OF SINGLE CHAR PARTICLES

Diffusion and reaction models of varying complexity are used to study the stability of the combustion of single char particles. In contrast to past studies which have considered only the reaction of carbon with oxygen, both the heterogeneous reactions of carbon with oxygen and carbon dioxide and the homogeneous oxidation of carbon monoxide are taken into account in the formulation of the mathematical models. Emphasis is placed on the investigation of the feasibility of occurrence of oscillatory combustion. Our results show that high rates of the C-O₂ reaction and high concentration of O₂ in the ambient favor the occurrence of multiple steady states and oscillatory solutions, but the appearance of oscillatory instability is suppressed by the homogeneous reaction in the gas phase and the presence of CO and CO₂ in the ambient. The parametric investigation of the problem reveals, in agreement with the results of past studies, that the heat capacity of the porous solid, the Lewis number, and the thickness of the stagnant film are three key parameters for the occurrence of the oscillatory response of the system. Reasonably large values of solid heat capacity practically eliminate the possibility of oscillatory combustion, but an appropriate combination of large values of stagnant film thickness and small Lewis numbers may offset the effect of solid heat capacity     

Preadhesion Laser Treatment of Aluminum Surfaces

An excimer laser may be used for preadhesion treatment of aluminum alloys. This method presents an alternative to the use of ecologically unfriendly chemicals involved in conventional anodizing pretreatments.

Experimental results indicate that preadhesion laser surface treatment significantly improved the shear strength of modified-epoxy bonded aluminum specimens compared with untreated and anodized substrates. The best results were obtained with laser energy of about 0.2 J/Pulse/cm² where single lap shear strength was improved by 600-700% compared with that of untreated Al alloy, and by 40% compared with chromic acid anodizing pretreatment.

The mode of failure changed from adhesive to cohesive as the number of laser pulses increased during treatment. The latter phenomenon has been correlated with morphology changes as revealed by electron microscopy, and chemical modification as indicated by Auger and infrared spectroscopy.

It can be concluded that the excimer laser has potential as a precise, clean and simple preadhesion treatment of Al alloys.     

The hydration of jet cement at 20°C

Two types of jet cement having different retarders were investigated. Both physical properties such as mechanical strength, pore size distribution and porosity and chemical processes of hydration such as rate of hydration and the kind of hydrate produced upon hardening of jet cement are strongly affected by the method of the regulation of setting. The difference between the mechanical strength developed is discussed.     

Comparison of selective cytotoxicity of alkyl lysophospholipids

Alkyl lysophospholipids have been shown to be cytooxic to a number of neoplastic tissues. One, ET-18-OCH₃, has been used to selectively purge leukemic cells from mixtures with normal marrow progenitor cells,in vitro andin vivo. We have measured the 50% inhibitory (IC₅₀) effect of a series of ether, lipids (EL) on leukemic cells (HL60, K562, Daudi, KG-1, KG-1a) and normal marrow progenitor cells. Cells were incubated with varying concentrations of EL for 4 hr and assayed for viability, [³H]thymidine incorporation and clonogenicity in semi-solid media. The effect on protein kinase C (PKC) activity was assayed for each compound. Compounds tested included three glycerophosphocholine analogs-ET-18-OCH₃, ET-16-NHCOCH₃, and BM 41.440. In addition, a lipoidal amine, CP 46665, an ethyleneglycolphospholipid, AEPL, and four single chain alkylphosphocholine analogs, HePC₂, HePC₃, HePC₄ and HePC₆ were also tested. During the period of incubation, the cells remained viable (>70%) as judged by trypan blue dye exclusion. The glycerophosphocholines were the most active and showed the highest therapeutic index. The lipoidal amine was active, but toxic to normal marrow progenitor cells. The ethyleneglycolphospholipid was active against HL60, but not against the other cell lines. The single chain alkylphosphocholine analogs were less active. All of the compounds inhibited PKC activity; however, the glycerophosphocholines were the most inhibitory. Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl Ether Lipids, Tokyo, Japan, May 1989.     

Effect of additives on formation of natural gas hydrate

The formation of natural gas hydrate (NGH) is studied in this work. Kinetics data of hydrate formation with no agitation were collected at various concentrations of the aqueous solutions with different additives such as alkylpolyglucside, sodium dodecyl benzene sulfonate and potassium oxalate monohydrate. Various kinds of additive increased the formation rates of NGH and its storage capacity and reduced the induction time of NGH formation. Moreover, the storage capacity, the induction time and the hydrate formation rate were influenced by the concentration of the aqueous solution.     

Simulation of Fe-Al compounds developed during single superphosphate manufacture

In order to analyse iron phosphate complexes and gel-like phases encountered in the single superphosphate process, experiments were performed with a free-Al, Fe apatite crystal of Durango from Mexico phosphate rock and sulfuric acid. Reaction products were studied by X-ray diffraction and surface analysis methods namely X-ray photoelectron spectroscopy and scanning electron microscopy. Results show that in a free Al, Fe-system, part of the Ca(H₂PO₄ )₂.H₂O (MCPM) forms before precipitation of any CaSO₄(CS) and gel-like phase such H₂SO₄.yH₃PO₄.xH₂O is formed. When iron is added, the precipitation rate of (CS) and (MCPM) increases and Fe₃(H₃O)H₈(PO₄)₆.6H₂O is formed. When Fe and Al are added, a gel-like phase is quickly formed with a molar ratio that changes with time and develops into crystalline compounds. The composition of this gel may be represented as a mixture of two phases: H₂SO₄.yH₃PO₄.xH₂O and a gel containing Al-Fe-Si.     

Small-angle neutron scattering studies of polyethylene crystallized at high pressure

The technique of small-angle neutron scattering (SANS) has been used to study the chain configuration in pressure crystallized polyethylene. Two narrow molecular weight fractions of deuterated molecules (PED) of M_w 23 000 and 54 000 were solution blended with a protonated matrix polymer of M_w 81 500. Although pressure crystallization was shown to have produced a clustering of the PED molecules, the radii of gyration $\text{〈}\text{S}{}^2\text{〉}{}_{\mathrm{z}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ were, nevertheless, shown to be consistent with a model in which the PED molecules possessed rod-like configurations. The predicted rod lengths were in close agreement with the molecular stem lengths of the PEH matrix polymer, which were independently determined by nitric acid etching. Furthermore, a doubling of the PED molecular weight produced no change in the value of $\text{〈S}{}^2\text{〉}{}_{\mathrm{z}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. This was interpreted in terms of a chain folding mechanism in which a molecule is bounded by the surfaces of a lamellar block and is therefore unable to increase its' rod length.     

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