Studies of the polymerization of methacrylic acid via free-radical retrograde precipitation polymerization process

In this paper, we present some new results of our work in a novel polymerization process (called the free-radical retrograde precipitation polymerization, or FRRPP, process) that occurs at temperatures above the lower critical solution temperature. Our polymerization experiments basically involve the methacrylic acid–poly(methacrylic acid)–water system. Experimental results indicate a gradual increase in conversion with time after what seemingly is the onset of phase separation. In an equivalent solution polymerization system, conversion of methacrylic acid reaches almost 100% at a much shorter time than in the FRRPP system. Molecular weights of poly(methacrylic acid) at different times for the FRRPP system are not dramatically different from those obtained in the solution system. However, the FRRPP system yields a relatively narrow molecular weight distribution at a wide range of conversion compared to that obtained in the equivalent solution system. The unique characteristics of the FRRPP process is shown in the asymptotic time behavior of the free-radical concentration compared to the decay behavior in other polymerization systems. © 1996 John Wiley & Sons, Inc.     

Solubility and solution stability studies of different amino acid prodrugs of bromhexine

Objective: The aim of the present study was to prepare the amino acid prodrugs of bromhexine hydrochloride to improve its solubility. Methods: All the prodrugs were synthesized by first reacting bromhexine with tert-butoxycarbonyl (Boc) protected amino acid and then deprotection was carried out by using trifluoroacetic acid. These prodrugs were characterized by their melting points, NMR, mass and FTIR spectroscopy. Solubility and partition coefficient of bromhexine and various prodrugs were determined. The solution stability of various prodrugs was also determined in various buffers of pH ranging from 2 to 10. Degradation rate constants and half-life were also determined at various pH. Results and discussion: The structures of all the synthesized prodrugs were confirmed by NMR, mass and FTIR spectra. The prodrug 2-N-l-alanyl-bromhexine hydrochloride showed maximum solubility and minimum partition coefficient value. These prodrugs may hydrolyze by one or more mechanisms. The order of decreasing rates of hydrolysis was 2-N-l-prolyl-bromhexine hydrochloride > 2-N-glycyl-bromhexine hydrochloride > 2-N-l-alanyl-bromhexine hydrochloride. All the prodrugs exhibited maximum stability in the acidic pH range and undergo base catalyzed hydrolysis. Conclusion: Solubility studies and partition coefficient values indicated that the synthesized prodrug, 2-N-l-alanyl-bromhexine hydrochloride, was least lipophilic as compared to other synthesized prodrugs. Solution stability studies showed that this prodrug undergo minimum hydrolysis at 37°C. So, it is concluded that 2-N-l-alanyl-bromhexine hydrochloride exhibits better solubility and stability as compared to other synthesized prodrugs.     

Empirical modeling of shot peening parameters for welded austenitic stainless steel using grey relational analysis

The attempt of this paper is to present an effective approach for the optimization of the shot peening process of welded AISI 304 austenitic stainless steel with multi performance characteristics using Grey relational analysis (GRA) based on Taguchi orthogonal array. Twenty-seven experimental runs are performed to determine best process parameters level. An analysis of variance (ANOVA) is carried out to identify significant peening parameters. The response tables are obtained for analyzing the optimal levels of shot peening parameters and major factors that affect the quality function. The multiple performance characteristics including tensile strength, surface hardness and surface roughness are the quality functions considered for the optimization. Further mathematical models are developed using regression analysis for the tensile strength, surface hardness and surface roughness. It will be very helpful to the engineers in deciding the levels of the shot peening parameters for desired performance characteristics.     

Effect of nozzle orifice geometry on spray, combustion, and emission characteristics under diesel engine conditions

Diesel engine performance and emissions are strongly coupled with fuel atomization and spray processes, which in turn are strongly influenced by injector flow dynamics. Modern engines employ micro-orifices with different orifice designs. It is critical to characterize the effects of various designs on engine performance and emissions. In this study, a recently developed primary breakup model (KH-ACT), which accounts for the effects of cavitation and turbulence generated inside the injector nozzle is incorporated into a CFD software CONVERGE for comprehensive engine simulations. The effects of orifice geometry on inner nozzle flow, spray, and combustion processes are examined by coupling the injector flow and spray simulations. Results indicate that conicity and hydrogrinding reduce cavitation and turbulence inside the nozzle orifice, which slows down primary breakup, increasing spray penetration, and reducing dispersion. Consequently, with conical and hydroground nozzles, the vaporization rate and fuel air mixing are reduced, and ignition occurs further downstream. The flame lift-off lengths are the highest and lowest for the hydroground and conical nozzles, respectively. This can be related to the rate of fuel injection, which is higher for the hydroground nozzle, leading to richer mixtures and lower flame base speeds. A modified flame index is employed to resolve the flame structure, which indicates a dual combustion mode. For the conical nozzle, the relative role of rich premixed combustion is enhanced and that of diffusion combustion reduced compared to the other two nozzles. In contrast, for the hydroground nozzle, the role of rich premixed combustion is reduced and that of non-premixed combustion is enhanced. Consequently, the amount of soot produced is the highest for the conical nozzle, while the amount of NO_x produced is the highest for the hydroground nozzle, indicating the classical tradeoff between them.     

Explicit equations for laminar flow of herschel–bulkley fluids

There are three typical problems encountered in pipe flows: unknown friction factor, unknown flow rate, and unknown diameter problems. A major problem in determining the solution to these flow problems occurs due to the implicit nature of the Darcy–Weisbach friction factor. Though explicit equations for flow of Newtonian fluids and Power Law fluids are available, no such usable equations exist for Herschel–Bulkley fluids. In this paper, explicit equations have been given for flow of Herschel–Bulkley fluids in the laminar regime.     

Development of Materials Integration Strategies for Electroceramic Film-Based Devices Via Complementary In Situ and Ex Situ Studies of Film Growth and Interface Processes

We review our studies of film growth and interface processes performed using complementary in situ and ex situ characterization techniques that provide valuable information critical to the development of materials integration strategies for the fabrication of electroceramic film-based devices. Specifically, we review our work performed using in situ time-of-flight ion scattering and recoil spectroscopy (TOF-ISARS) / X-ray photoemission spectroscopy (XPS) / spectroscopic ellipsometry (SE), in conjunction with ex situ TEM and other techniques to study film growth and interface processes critical to the fabrication of non-volatile ferroelectric memories (NVFRAMs), dynamic random access memories (DRAMs), and high frequency devices based on high-K thin films. TOF-ISARS involves three distinct but closely related experimental methods, namely: ion scattering spectroscopy, direct recoil spectroscopy and mass spectroscopy of recoiled ions, which provide monolayer-specific information on film growth and surface segregation processes. Spectroscopic Ellipsometry enables investigation of buried interfaces. XPS provides valuable information on the chemistry of surface and interfaces. Specifically, we discuss: a) studies of oxidation of Ti-Al layers and synthesis and properties of La 0.5 Sr 0.5 CoO 9 /Ti-Al heterostructured layers for integration of PZT capacitors with Si substrates, and b) studies of BaSr x Ti 1 m x O 3 layer integration with Si substrates relevant to DRAMs, high frequency devices and high-K gate oxides for integrated circuits. This review shows the power of combined in situ / ex situ analytical techniques to provide valuable information for material integration strategies for electroceramic thin film-based devices.     

Plasma Etch Processes for Embedded FRAM Integration

We describe the etch processes used for integration of embedded ferroelectric random access memory (FRAM) within a standard CMOS logic flow. The ferroelectric module is inserted following front-end contact formation and prior to backend integration using only two additional mask levels: capacitor pattern and bi-level via pattern. The single-mask stack etch process employs a TiAlN hardmask to define Ir/IrO_x/PZT/IrO_x/Ir capacitors. Protective sidewalls can be formed using an etchback process. The bi-level via etch and subsequent metal fill processes complete the FRAM module formation. Functional 4 MB arrays embedded with 5 levels of Cu/FSG integration have been demonstrated.     

Note on flash and distillation systems

Flash and distillation systems evolving on the equilibrium manifold possess stable steady states when the molar flows and the boundary conditions are fixed and a vapor and liquid phase is present at all times. The results extend the range of validity of a local stability theorem for linear, constant molar overflow systems due to Acrivos and Amundson. The approach to stability analysis is motivated by the tangent plane method developed by Gibbs to open systems as it takes advantage of the negative curvature of the entropy surface to construct a Lyapunov function. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3322–3332, 2013     

The use of Zinc Oxalate Dihydrate in Establishing The Working Reproducibility of A Simultaneous Tg–Dta Unit

Abstract

Zinc oxalate dihydrate is a well characterized inorganic compound and the thermal degradation it undergoes is well known. It was therefore used in this study to establish the reproducibility of the simultaneous thermogravimetry- differential thermal analysis (TG-DTA) unit, as well as to establish other methods of recording thermal analysis data from such a unit using only a single run on the equipment. A kinetic evaluation of the dehydration and decomposition was made and the activation energy was found to be 100 KJ/mol for the dehydration and 299 KJ/mol for decomposition.