26,219 research outputs found
Emulsion polymerization of tetrafluoroethylene: effects of reaction conditions on particle formation
No full textThe emulsion polymerization of TFE was carried out with a surfactant (FC-143) and an initiator (ammonium persulfate) under various reaction conditions. Two different shapes of PTFE dispersion particles were produced by the emulsion polymerization, rods and spherical particles. Variables, except for surfactant concentration, do not affect the initial and final particle morphology when no coagulation occurs. Rod-like particles are formed when the surfactant concentration is near or above the critical micelle concentration (CMC) of the surfactant. At below CMC, however, spherical particles are dominant. No hexagon-shaped particles or abrupt changes in the particle morphology are observed during polymerization. When no coagulation occurred, the size and number of polymer particles suddenly increased in the early stages of emulsion polymerization and then steadily increased as time progressed. Most particles are formed in the early stages (within 5 min), and the size of particles formed was in the range 60-80 nm in diameter. The particle sizes ranged from 100 to 230 nm at 250 g/l of a specific TFE uptake concentration (the PTFE dispersion had a solid content of about 20%). It was found that the size and number of polymer particles formed are almost independent of the temperature, pressure, concentration of initiator and stabilizer (anti-coagulant), whereas the surfactant concentration, kinds of stabilizer, and agitation speed are important. The particle size decreased gradually as the dispersion concentration increased, whereas the particle number increased exponentially. When the PTFE dispersion coagulated during polymerization under certain conditions (high temperature and agitation speed, and low concentration of surfactant), the particle size suddenly increased, the particle number suddenly decreased, and the rate of the polymerization decreased, indicating that the polymerization occurred on the surface of the polymer particles. (C) 1999 Elsevier Science S.A. All rights reserved
Emulsion polymerization of tetrafluoroethylene: Effects of reaction conditions on the polymerization rate and polymer molecular weight
No full textThe emulsion polymerization of tetrafluoroethylene (TFE) was carried out in a semibatch reactor using a chemical initiator (ammonium persulfate) and a fluorinated surfactant (FC-143). The effects of the reaction condition were investigated though the polymerization rate, molecular weight of polytetrafluoroethylene (PTFE), and stability of the dispersion. The emulsion polymerization of TFE was different from conventional emulsion polymerization. The polymerization rate was suppressed when the polymer particles were significantly coagulated. The polymerization rate increased with operating temperature, surfactant concentration, and agitation speed, due to the enhanced stability of the polymer particles. However, once the parameter value was reached, the rate decreased due to the coagulation of the particles, Stable PTFE dispersion particles were obtained when the surfactant concentration was in the range between 3.48 X 10(-3) and 32.48 X 10(-3) mol/liter, which is below critical micelle concentration (CMC). The molecular weight of the PTFE obtained was a function of the surfactant and initiator concentrations, and the polymerization temperature. The molecular weight increased as each parameter decreased. This is against the phenomena observed in a conventional emulsion polymerization. A stable PTFE dispersion polymer having a high molecular weight was obtained by optimizing the reaction conditions. (C) 1999 John Wiley & Sons, Inc
Study of Cu(In,Al)Se2 thin films prepared by selenisation of sputtered metallic precursors for application in solar cells
No full textCu-In, Cu-Al and Cu-In-Al metallic precursor layers were deposited using radio-frequency magnetron sputtering and selenised to produce thin films of CuInSe2 (CIS), CuAlSe2 (CAS) and CuIn1-xAlxSe2 (CIAS), respectively. The selenisation stage of this 2-stage process was carried out in a tube furnace (TF) or a rapid thermal processor (RTP) in the presence of elemental Se, either deposited on top of the precursor film or provided from an external source in the chamber, in order to fabricate the chalcopyrite material. The aim was to produce single phase, device quality CIS, CAS and CIAS for use as an absorber layer material in thin film photovoltaic solar cells. Profilometry performed on the as-deposited Cu-In-Al metallic precursors showed an important increase in surface roughness compared to the Cu-In and Cu-Al precursors. This was found to be due to the preferential formation of Cu9(In,Al)4, which stoichiometry led the excess In to form island-shaped In phases at the surface of the bulk, while only Cu2In and CuIn2 formed in Cu-In precursors. Regarding the selenisation, temperatures ranging from 250°C to 550°C were used, and the resulting samples were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS) and glow-discharge optical emission spectroscopy (GD-OES). Thin films of single phase CIS and CAS were successfully produced with energy band gaps of 0.99 eV and 2.68 eV, respectively. However the incorporation of Al proved to be difficult. The results showed that no incorporation of the Al into the chalcopyrite lattice was achieved in the samples selenised in the RTP, which was believed to be due to the oxidation of the element Al into amorphous Al2O3. In the tube furnace, possibly due to lower levels of oxidation, incorporation occurred more readily but Al and In segregated towards the back and front of the layer, respectively. The causes of the segregation were studied and solutions to avoid it developed, resulting under certain conditions in successful production of CuIn1-xAlxSe2. Samples were tested in a photoelectrochemical cell and showed (apparent) external quantum efficiency values comparable to a CuInSe2 (CIS) sample used as a standard
UTILISING Zn AND Cu PRODU T IN THE CORN MEAL SUBSTRATE AT Saccharomyces cerev s ae BIOPRO ESS AND ITS IMPLEMENTATION ON INTERNAL QUALITY OF BROILER
No full textThis research was conducte to find out the effect and optimal percentage of adding Zn and Cu
proteinat supplement product of fermentation by Saccharomyces cerev s ae in the ration on internal
quality of the broiler.The experiment use 125 broiler day ol chicken with a Completely Randomize
Design.The ration treatments were R0 (control),R1 (99%R0 +1%supplement Zn and Cu proteinat),R2
(98%R0 +2%supplement Zn and Cu proteinat),R3 (97%R0 +3%supplement Zn and Cu proteinat)and
R4 (96%R0 +4%supplement Zn and Cu proteinat)where each treatment was repeate five times and
each replication consiste of five broiler chicks.Variable analysis were body cut weight,carcass
percentage,liver relative weight,and the content of cholesterol broiler meat.Conclusion of the research
showe that by using 3%of Zn and Cu proteinat supplement substrat in the ration gave the best internal
quality of broiler,increase body cut weight,carcass percentage,otherwise liver relative weight and the
content of cholesterol broiler meat were normal.
Keywords :Zn and Cu prote nat supplement,rat ons ,bro ler nternal qual t
Ordering of organic molecules on templated surfaces
No full textThis thesis describes the controlled growth of molecular nanostructures using modified metallic and semiconductor surfaces. The Ag/Si(lll)-(root3 x root3),the Sn/Cu(100) surface alloy system and the Bi/Si(100) nanolines and (2xn) surfaces were all investigated as suitable substrates for the controlled growth of pentacene, (C22H14) or trimesic acid, (C6H3(COOH)3) organic molecules. The following techniques were used in this study; Scanning Tunnelling Microscopy (STM), Low Energy Electron Diffraction (LEED), Normal Incident X-Ray Standing Waves (NIXSW) and Temperature Programmed Desorption (TPD).
The room temperature growth and ordering of trimesic acid on the AgfSi(ll1)-(root3 x root3) surface was investigated. An oblique unit cell was determined and a model proposed for the highly ordered close-packed domains.
The discovery of a new submonolayer phase on Sn/Cu(100) and the re-examined known phase are discussed. New models for these reconstructions are proposed. Adsorption of trimesic acid at room temperature on the clean substrate the lowest Sn coverage phase were studied. Two new Sn coverage dependent structures were discovered and bonding schemes in upright and flat orientations are discussed.
BifSi(100)-(2xn) surface was exploited as a template for the ordered growth of pentacene, which exhibited orientation specific adsorption. The Bi/Si(100)-(2xn) single domain surface created on vicinal silicon was used to test the suitable of Daresbury 4.2 beamline for NIXSW Imaging experiments and the quality of the results are discussed
Short Review: Cu Catalyst for Autothermal Reforming Methanol for Hydrogen Production
No full textHydrogen is a promising alternative energy sources, hydrogen can be used in fuel cell applications to pro-ducing electrical energy and water as byproduct. Therefore, fuel cell is a simple application and environ-mentally friendly oriented technology. Recent years various methods have been conducted to produce hy-drogen. Those methods are derived from various sources such as methanol, ethanol, gasoline, hydrocarbons. This article presents a brief review a parameter process of that affects in autothermal reforming methanol use Cu-based catalysts for production of hydrogen. Copyright © 2012 BCREC UNDIP. All rights reserved
Adsorption and chemical reaction of Cu(hfac)(vtms) on CU(111)
No full textWe have investigated the adsorption and reaction of Cu(hfac) (vtms) (hexafluoroacetylacetonate, hfac; vinyl trimethyl silane, vtms) on a Cu(1 1 1) surface. The recombinative desorption of Cu(hfac)(vtms) and disproportionation reaction between adsorbed Cu(hfac) molecules were observed to occur between 240 and 400 K. The adsorption geometries of Cu(hfac) on Cu(1 1 1) have been also calculated by means of the extended Huckel method. It is found that the standing Cu(hfac) is more stable and favored for a cleavage of Cu-O bonds than the lying-down Cu(hfac) on the Cu(1 1 1) surface. (C) 2001 Elsevier Science B.V. All rights reserved.This work was supported by the Korea Science and Engineering Foundation (no. 98-0501-01-01-3) and Brain Korea 21 program
Strong enhancement of room-temperature thermoelectric properties of Cu-doped Bi2Te2.7Se0.3
No full textWe investigate thermoelectric properties of Cu-doped Bi2Te2.7Se0.3 fabricated using a simple doping process and spark plasma sintering. Through precise control of Cu doping, it is found that Cu atoms preferentially occupied Bi sites and then intercalated into the van der Waals gap with an increasing Cu content. Electrical transport properties of Cu-doped samples were systemically controlled using this mechanism. At the same time, thermal conductivities of the Cu-doped samples were reduced by the enhancement of point defect phonon scattering due to the Cu atoms. Compared to that of pristine samples, the dimensionless thermoelectric figure of merit ("ZT") of 0.98 at 323 K for the Cu-doped sample was increased by more than 92% owing to these synergetic effects. Furthermore, the shift of maximum ZT to room temperature provides advantages for enlarging the applications of thermoelectric effects at room temperature. © 2022 Author(s).1
Heat-shock protein-70 genes and response to antidepressants in major depression. Prog Neuropsychopharmacol Biol Psychiatry. 2007 Jun 30;31(5):1006-11.
No full textThe impacts of social media on destination branding. Case study based on Hanoi city – the capital of Vietnam.
No full textThe purpose of the thesis was to discover the current situation of social media in destination branding with a use case of a developing city in Vietnam while weighing the impacts of social media marketing brings to advertise the destination.
In the theoretical chapters of the thesis, the author aimed to understand the general state of social media at the moment. Moreover, the author wanted to understand the impacts that social media has on the image of Hanoi. So that he could utilize the advantages and minimize the disadvantages affecting directly to the image of Hanoi. There were a few studies that only focus on the general picture of the relationship between social media marketing and destination branding. However, they did not concentrate on the specific purpose of the effectiveness of social media marketing in a destination. According to the data which was collected after six interviews, the author had an overview of the current impacts of social media marketing and the ways of improving them from the experts in this field.
Combined with previous studies, the influences of social media on the destination have been seen. Besides, there are more suitable proposals to improve and promote the image of Hanoi in the future. At the end chapter of the thesis, the author also gave a few pieces of advice as a guideline to build an effective social media marketing plan
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