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1

Frothers and gas dispersion: A review of the structure-property-function relationship

Tan Y. H., Finch J. A.

Physicochemical Problems of Mineral Processing

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2018

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Vol. 54, iss. 1

40--53

EN

Over the past 20 years quantitative measures of frother functions have been developed to try to replace such qualitative descriptors as “weak” and “strong”. One of these metrics is the critical coalescence concentration (CCC) that quantifies a frother’s ability to reduce bubble size; another is the concentration at minimum velocity (CMV) that quantifies a frother’s ability to reduce bubble rise velocity. The experimental procedure for the two measures is briefly outlined and the measures are shown to be related. Using CMV, based on more than 50 surfactants from the two main frother families, alcohols and polyglycols, the frother structure-property-function link is investigated. The structure variables were: in alcohols, alkyl chain length, and position of the methyl branch and hydroxyl group(s); and in polyglycols, alkyl chain length, and number of propylene oxide (PO) or ethylene oxide (EO) groups. On the argument that low CMV represents the desired outcome, the main findings are: the dominant effect of alkyl chain length in both alcohols and polyglycols; that for alcohols branched-chain isomers are superior to straight chain, with the best combination being OH at the terminus and the methyl branch as far away as possible; and for polyglycols, PO-based are superior to EO-based. Interpretation of these observations included the effect of structure on the following properties: surface activity, mass transfer rate, H-bonding, and molecule packing.

2

Effect of pH and time on hydrodynamic properties of dodecylamine

Zhou X., Tan Y. H., Finch J. A.

Physicochemical Problems of Mineral Processing

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2018

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Vol. 54, iss. 4

1237--1244

EN

Gas holdup and froth height in the presence of dodecylamine (DDA, pKa = 10.63) are reported at three pH values. The results revealed a strong time effect for DDA: stability was reached at pH 3; not at natural pH, for example, gas holdup declining to the water only value; and at pH 11, while stability was reached quickly gas holdup was now less than in water alone indicating coalescence. In the first two cases, the time effect is attributed to loss of amine from the system as molecular amine, observed at natural pH as precipitates on the column wall. An argument for precipitation at pH < pKa is presented. At pH 11, coalescence is attributed to the oily nature of the molecular amine present as colloidal aggregates. Noting a difference in literature steady state gas holdup data at natural pH, it is speculated that varying steady states can be reached that corresponds to different levels of amine loss.

3

Polishing of poly(methyl methacrylate), polycarbonate, and SU-8 polymers

Zhong Z. W., Wang Z. F., Zirajutheen B. M. P., Tan Y. S., Tan Y. H.

Materials Science Poland

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2007

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Vol. 25, No. 1

103--112

EN

Polymers such as poly(methyl methacrylate), polycarbonate, and SU-8 epoxy resin replace silicon as the major substrate in microfluidic system (or BioMEMS) fabrication. Chemical-mechanical polishing is an important technology for many advanced microelectromechanical systems (MEMS) and microoptoelectromechanical system applications. In this study, the chemical-mechanical polishing of polycarbonate, poly(methyl methacrylate), and SU-8 polymers was investigated. Four types of slurry were tested for chemical-mechanical polishing of polycarbonate and poly(methyl methacrylate). Experiments were then designed and performed to investigate the effects of two key process parameters. Experimental results show that an increase in head load or table speed causes an increase in material removal rates. Within the chosen experimental parameter ranges, the variation of table speed introduced a more significant change in material removal rates than that of head load. An analysis of variance was also carried out, and it was found that the interaction of head load and table speed had a significant effect (95% confidence) on the surface finish of polished poly(methyl methacrylate) samples, while table speed had a significant effect on the surface finish of polished polycarbonate samples. Chemical-mechanical polishing is also a process well suited for polishing SU-8 structures with high aspect ratios. Polished polycarbonate, poly(methyl methacrylate), and SU-8 surfaces had nanometer-order surface roughness, acceptable for most MEMS applications.