Small Particle Size Range Research Articles

Optimization and Physicochemical Characterization of Chitosan and Chitosan Nanoparticles Extracted from the Crayfish Procambarus clarkii Wastes

The main objective of this study was to allocate and evaluate the most optimum condition to prepare the chitosan and chitosan nanoparticles that will, subsequently, give the best physicochemical characterization regarding the nanoparticles' size and surface morphology. Chitosan from the exoskeleton wastes of Procambarus clarkii with degree of deacetylation 87% was extracted. Viscometry indicated that the obtained chitosan had a low molecular weight that can be useful in many applications. Chitosan nanoparticles were prepared by using different concentrations of chitosan and the polyanion sodium tripolyphosphate (TPP). For the determination of the optimum condition for the prepared chitosan nanoparticles, three different ratios of chitosan to the polyanion TPP were used, 1:1, 3:1, and 1:3. A novel nanoparticle system composed of low molecular weight chitosan was successfully prepared by the ionotropic gelation technique under an aqueous-based condition. The physicochemical characteristics of chitosan and chitosan nanoparticles were elucidated by Fourier-transform IR spectroscopy, nuclear magnetic resonance spectroscopy, elemental analysis, scanning electron microscopy, transmission electron microscopy, and zeta potential. The best physicochemical characteristics were obtained by adding chitosan to TPP in a ratio of 1:1. The small particle size and narrow range distribution of the obtained chitosan nanoparticles may increase their chance for easy and efficient manipulation for several applications in various fields. In addition, the obtained positively charged chitosan nanoparticles can be used for the delivery of negatively charged compounds.

Purification of Industrial Wastewater from Methylene Blue (MB) Dye Using Organic and Inorganic Sol–gel Glasses

Organic and inorganic-doped sol-gel glasses have been synthesized via thermal followed by microwave treatment. Tetramethoxysilane (TMEOS) was used as a precursor, whereas dopants used were Neodymium oxide, Urea (carbamide) or Thiourea (thiocarbamide) and the obtained formulations werereferred as Nd, U, and THU, respectively along with the undoped or plain glass (P). Colors of the as-prepared sol-gel glasses ranged from transparent colorless (P) to opaque dark purple (Nd). The latter colorcould be owed to the presence of the inorganic transition element oxide (Nd2O3).In addition, THU had the smallest particle size range (< 250 microns), whereas the other three sol-gel glasses had larger particle sizes ranging from 250- 630 microns.Thesynthesized sol-gel glasses were tested for their capacity to adsorb and remove Methylene Blue (MB) dye from aqueous solutions. Uexhibited the highestsorptioncapacitiesof 12.6 and 2.6 mg/g with removal efficiencies of 50.3 % and 83.2 %at 12 and 2 mg/L MB, respectively.These values were almost twice and 1.7 times those obtained by P at the higher and lower MB concentrations, respectively which indicates that doping with urea enhanced sorption through introducing new functional groups.Fourier transform Infrared (FTIR)spectroscopy revealed that carbonyl group on urea could be responsible for adsorption via electrostatic interaction between the negatively charged carbonyl oxygen of urea and the positively charged nitrogen or sulfur on MB, or through redox reactions between them.

Temporal and spatial variability of atmospheric particle number size distributions across Spain

This study synthesizes for the first time results from simultaneous aerosol measurements performed at seven diverse locations distributed all over the Spanish geography. The observations were carried out during two field campaigns in 2012–2013, one-month each and during different seasons. These field campaigns were performed in the framework of the Spanish Network of DMAs (REDMAAS) activities. Measurement sites were grouped as polluted sites (urban background) and clean sites (rural background and high-altitude sites). Seasonal differences were more important at polluted sites, mainly related to meteorology and aerosol sources. Higher total particle concentrations were found during the cold period, driven mainly by Aitken-mode particles (traffic-related aerosol particles). In clean sites, particle concentrations were higher during the warm period. Mild meteorological conditions in combination with the absence of local sources during the cold period make atmospheric nucleation an important contributor to ultrafine particles. These results are reflected in aerosol dynamical processes. Ultrafine particle bursts were frequent in both periods at the clean sites and in the warm period at most polluted sites. Shrinkages processes were identified at three sites (two polluted and one clean site) during the warm period. Meteorology (wind speed and solar radiation) and a highly-volatile aerosol (formed from atmospheric nucleation or traffic emissions) explain this behaviour. Ultrafine particles exhibited a different behaviour at inland and coastal sites. The highest total particle concentrations were observed at coastal sites during the warm period. At these sites, the smallest particle modal diameters and the highest variations of particle number size distributions in the smaller particle size range were also found, particularly in the warm period. This may be the result of the high diffusion conditions and mixing of different air masses (clean and polluted) caused by sea-land breezes. Our findings can be explained by the local and regional characteristics of each site, such as meteorology and aerosol sources (types, proximity …) and the influence of meteorology on atmospheric transformation processes.

Low-pressure silica injection for porosity reduction in cementitious materials

The durability of building materials is related to the presence of cracks as they provide a fast pathway for the transport of liquid and gases through the structure. Restoration and preservation of historic buildings are the potential applications of this novel technique which uses nano-silica and silica fume particles for consolidation. The small particle size range and the high reactivity of nanoparticles allow them to interact with calcium sources naturally present in cement and concrete, forming binding and strengthening compounds such as calcium silicate hydrate. Nanoparticles act as a crack-filling agent, reducing the porosity and increasing the durability of existing materials. In this study we describe the injection of nano-silica, under low water pressure, into hydrated cement paste. This novel technique can tailor the mechanical and hydraulic properties of existing building materials using a simple and non-destructive procedure.

Retrieval method of cirrus microphysical parameters at terahertz wave based on multiple lookup tables

Cirrus is an important regulator for the flow of radiant energy in the earth-atmosphere system through the processes of scattering and absorption of radiation. In order to satisfy the urgent requirement for accurate retrieval of cirrus microphysical properties, terahertz wave is expected to be the best waveband for inverting cirrus particle size and ice water path, with terahertz wavelengths on the order of the size of typical cirrus particles. There is an urgent need for establishing stable and accurate inversion method. A new retrieval method for particle size and ice water path is developed based on multiple lookup tables for spaceborne measurements of brightness temperature spectrum of 183 GHz, 325 GHz, 462 GHz, 664 GHz, and 874 GHz channels. Five parameters are derived to quantify the effects of particle size and ice water path on terahertz radiation spectrum due to the scattering of ice clouds, manifested by brightness temperature difference, brightness temperature difference slope, etc. To retrieve cirrus microphysical parameters, a weighted least square fit that matches the modeled parameters is used. The analysis of retrieval errors are conducted by a simulated data series and the results are compared with those retrieved by the other two methods, i. e., difference method and slope method. The results retrieved by the multiple lookup table method are much closer to the simulated data series than those from the other two methods. It is indicated that the method introduced here is a stable and valid method of inverting particles between 50 and 500 m and ice water path between 10 and 500 g/m2. Compared with the errors from the difference-featured method and slope-featured method, the retrieval errors are reduced by 68.78% and 60.28% for particle size, 78.17% and 49.01% for ice water path. The analyses of retrieval uncertainties show that, in general, uncertainties of particle size and ice water path vary with particle size and ice water path. The ice water path uncertainties mainly spread in a range of 0-15 g/m2. The particle size uncertainties fluctuate within a range of 0-20 m. In other words, for small particle size range, the uncertainties are 0-5 m for thick clouds and 5-20 m for thin clouds. However, for large particle size range, the uncertainties are 0-5 m for particles larger than 300 m and 5-15 m for those smaller than 300 m. The results will be helpful for further developing the terahertz wave remote sensing of cirrus microphysical parameter technology. Moreover, it is also an important reference to the improvement of cirrus retrieval accuracy.

Packed-bed column biosorption of chromium(VI) and nickel(II) onto Fenton modified Hydrilla verticillata dried biomass

The present study represents the first attempt to investigate the biosorption potential of Fenton modified Hydrilla verticillata dried biomass (FMB) in removing chromium(VI) and nickel(II) ions from wastewater using up-flow packed-bed column reactor. Effects of different packed-bed column parameters such as bed height, flow rate, influent metal ion concentration and particle size were examined. The outcome of the column experiments illustrated that highest bed height (25cm); lowest flow rate (10mLmin−1), lowest influent metal concentration (5mgL−1) and smallest particle size range (0.25–0.50mm) are favourable for biosorption. The maximum biosorption capacity of FMB for chromium(VI) and nickel(II) removal were estimated to be 89.32 and 87.18mgg−1 respectively. The breakthrough curves were analyzed using Bed Depth Service Time (BDST) and Thomas models. The experimental results obtained agree to both the models. Column regeneration experiments were also carried out using 0.1M HNO3. Results revealed good reusability of FMB during ten cycles of sorption and desorption. Performance of FMB-packed column in treating secondary effluent was also tested under identical experimental conditions. Results demonstrated significant reduction in chromium(VI) and nickel(II) ions concentration after the biosorption process.

The Effect of Polyethylene Terephthalate Particle Size and Concentration on the Properties of Asphalt and Bitumen as An Additive

Research is extremely limited on the combination of polymeric materials, such as discarded polyethylene terephthalate (PET), with asphaltic materials indigenous to Trinidad and Tobago. This paper examines the effect of both concentration and particle size of added PET on the rheological properties of Trinidad Lake Asphalt (TLA) and Trinidad Petroleum Bitumen (TPB). The PET particle size ranges under study were &gt;0.30 mm to 0.60 mm, &gt;0.60 mm to 0.85 mm, and &gt;0.85 mm to 1.18 mm. These particle sizes were added in concentrations by weight ranging from 2% to 8% PET for TPB and 2% to 4% PET for TLA. Incorporating the waste polymeric material PET in TLA and TPB influenced the physical properties of the resulting blends. For TLA-PET blends, the largest particle size range produced values of complex shear moduli that were higher than pure TLA. The smallest particle size range had the opposite effect. The optimal concentration for fatigue cracking and rutting resistance occurred at 2% PET with the largest particle size range. For TPB-PET blends, the peak value of complex shear modulus generally occurred at concentrations above pure TPB for all particle size ranges and temperatures tested. As the particle size range increased, these peak values occurred at lower concentrations of PET. The 2% concentration for the largest particle size range provided the best fatigue cracking resistance, whereas the particle size range &gt;0.60 mm to 0.85 mm produced the best rutting resistance. This study demonstrated that incorporating waste PET as an additive in road paving mixtures could improve the overall quality of roads and also be a sustainable waste disposal option. Further research is recommended on the effect of PET particle size range and concentrations on TLA/TPB combinations commonly used in road paving applications along with accelerated weathering studies.

Formation of conductive networks with both segregated and double-percolated characteristic in conductive polymer composites with balanced properties.

Morphological control of conductive networks involves the construction of segregated or double-percolated conductive networks is often reported to reduce the electrical percolation threshold of conductive polymer composites (CPCs) for better balance among electrical conductivity, mechanical properties, and filler content. Herein, the construction of conductive networks with both segregated and double-percolated characteristics is achieved based on polypropylene (PP)/polyethylene (PE) and multi-wall carbon nanotubes (CNTs). CNTs were firstly dispersed in PE; then PE/CNTs were compounded with PP particles well below the melting temperature of PP. It is observed that the percolation threshold (pc) decreases with increasing PP particle size (size 3.6 mm, pc=0.08 wt %), which agrees with previous theoretical prediction and experiment in much smaller particle size range. To further study this, the amount of CNTs in PE is varied. It is shown that the degree of PE/CNTs coating on PP particles varies with CNTs as well as PE content in these composites, and have significant influence on the final electrical property. Furthermore, a model combines classical percolation theory and model for segregated network has been proposed to analyze the effect of particle size, degree of coating and thickness of coating on the percolation behavior of these CPCs. In such a model the percolation of CNTs in PE phase as well as PENT phase in the segregated structure can be described. Overall, through such method, a much better balance among mechanical property, conductivity, and filler content is achieved in these CPCs comparing with the results in literature.

Particulate size of microalgal biomass affects hydrolysate properties and bioethanol concentration.

Effective optimization of microalgae-to-bioethanol process systems hinges on an in-depth characterization of key process parameters relevant to the overall bioprocess engineering. One of the such important variables is the biomass particle size distribution and the effects on saccharification levels and bioethanol titres. This study examined the effects of three different microalgal biomass particle size ranges, 35 μm ≤ x ≤ 90 μm, 125 μm ≤ x ≤ 180 μm, and 295 μm ≤ x ≤ 425 μm, on the degree of enzymatic hydrolysis and bioethanol production. Two scenarios were investigated: single enzyme hydrolysis (cellulase) and double enzyme hydrolysis (cellulase and cellobiase). The glucose yield from biomass in the smallest particle size range (35 μm ≤ x ≤ 90 μm) was the highest, 134.73 mg glucose/g algae, while the yield from biomass in the larger particle size range (295 μm ≤ x ≤ 425 μm) was 75.45 mg glucose/g algae. A similar trend was observed for bioethanol yield, with the highest yield of 0.47 g EtOH/g glucose obtained from biomass in the smallest particle size range. The results have shown that the microalgal biomass particle size has a significant effect on enzymatic hydrolysis and bioethanol yield.

Ethylene glycol stabilized NaBH4 reduction for preparation carbon-supported Pt–Co alloy nanoparticles used as oxygen reduction electrocatalysts for microbial fuel cells

Three carbon-supported Pt–Co alloys with varying Pt to Co atom ratio (Pt2–Co/C, Pt–Co/C, Pt–Co2/C) were prepared by NaBH4 reduction in ethylene glycol at room temperature. As supported by X-ray diffraction, all the prepared Pt–Co nanoparticles have a single-phase face-centered cubic structure. Transmission electron microscopy indicates that all nanoparticles have small particle-size range and are highly dispersed on carbon support. Catalytic properties of the synthesized Pt–Co alloy catalysts were analyzed using cyclic voltammetry and linear sweep voltammetry methods, and the results suggested that Pt–Co/C catalysts exhibit the best Pt mass activity and the highest stability for the oxygen reduction reaction (ORR) when compared with Pt/C catalyst and other Pt–Co alloy catalyst in both acidic and neutral media. Kinetic analysis reveals that the ORR on Pt–Co alloy follows the four-electron pathway leading to water. As the cathode catalyst, the single-chamber microbial fuel cell tests indicated the much better performance of Pt–Co alloy than that of commercial Pt/C.

Influence of particle size on the hydrogenation in La(Fe, Si)13 compounds

The influence of particle size on the hydrogenation of La(Fe, Si)13 compounds is studied in detail. The average TC increases largely from 240 K to 308.5 K due to the enhancement of surface area by reducing the particle size. Besides, it is found that small particle size and narrow size range would improve the homogeneity of hydrogen distribution. The magnetic entropy change (ΔSM) decreases slightly after hydrogenation, but the maximum value of −ΔSM of small LaFe11.7Si1.3C0.2Hx still remains a relatively large value of 14.4 J/kg K for a low magnetic field change of 2 T. It is also noted that the hydrogen-saturated LaFe11.7Si1.3C0.2H1.7 exhibits a great stability under a high pressure of 1.36 GPa, and this result is favorable to the further processing and applications of La(Fe, Si)13 compounds.

Hydride formation in single palladium and magnesium nanoparticles studied by nanoplasmonic dark-field scattering spectroscopy.

Scrutinizing functional nanosystems and relating details in their size, chemistry, and geometry to functionality remains a significant experimental challenge. Following the concept of indirect nanoplasmonic sensing (INPS), the exploitation of truncated Au nanocones with functionalized tips, nanofabricated in a one step, are used as single nanoplasmonic sensors for dark-field scattering spectroscopy measurements of the hydride formation Au in single Pd and Mg nanoparticles.

Particle manipulation by ultrasonic progressive waves

This paper presents a numerical model to determine the trajectory of sphere particles when submitted to ultrasonic progressive waves. This model assumes that the following forces act on the particle: gravity, buoyancy, viscous forces and acoustic radiation force due to progressive wave. In order not to restrict the model to a small particle size range, the viscous forces that act on the sphere are modeled by an empirical relationship of drag coefficient that is valid for a wide range of Reynolds numbers. The numerical model requires the pressure field radiated by the ultrasonic transducer. The pressure field is obtained experimentally by using a calibrated needle hydrophone. The numerical model validation is done by dropping small glass spheres (on the order of 500 μm diameter) in front of a 1-MHz 30-mm diameter ultrasonic transducer. When the particles cross the transducer face, the radiation force produced by the transducer pushes the particles away. The glass particles trajectory is obtained by a CCD camera. The experimental trajectory shows good agreement with that predicted by the numerical model.

Debye equation versus Whole Powder Pattern Modelling: Real versus reciprocal space modelling of nanomaterials

Real space methods like the Debye equation are increasingly being employed as an alternative to traditional Line Profile Analysis (LPA) techniques for the study of size and strain effects in nanomaterials. Until recently, the use of this technique in modelling was hindered by the time necessary to complete a calculation. This limitation encouraged development of the alternative, reciprocal-space Whole Powder Pattern Modelling, which on the other hand lacks physical validation when applied to the study of very small atomic clusters ( V) of 2.7 nm and 4.0 nm, respectively; while the standard deviations of the natural logarithm (σ) used were 0.15 and 0.40, resulting in a narrow and wide distribution for each set. (See ref. 6, and references therein, for a precise definition of V and σ.) In order to perform the Debye function simulation [3,7], a series of increasingly large spherical Au clusters with fcc structure were created. The diameter that related to less than .1 percent of the assumed volume weighted size distribution defined the maximum sphere size used in the simulations. Since in these constructions the diameter was not a continuous variable, two rules to govern the step size have been assumed: i) that the radius difference Δr between consecutive clusters is constant, ii) that the volume increment between consecutive clusters is an integer multiple of the Wigner-Seitz unit cell volume. Using these two assumptions it is simple to see that Δr = a(3/2π)/2=0.39a. This discrete spacing is arbitrary but also sensible, as confirmed by our results. Clusters have been processed in order to obtain sets of interatomic pair distances and multiplicities. If we imagine that each unique distance is a Dirac delta weighted by its multiplicity, we can see that the pair distance density distribution is a Dirac comb. Immediately, though, the generated set of unique distances is fed into the sampling routine, which convolutes the distance Dirac comb with a suitable Gaussian profile [7], sampling the resulting continuous distance density. As the sampling step is inversely related to the maximum diffraction vector length Qmax, the sampling is performed simultaneously with different steps ranging from 0.03 to 0.96 A, covering quite all possible experimental conditions. The sampled pseudodistance sets were then used to calculate diffraction patterns via a suitably adapted Debye formula, which is amenable to a fast transZ. Kristallogr. Suppl. 30 (2009) 87 form. More details on the fast Debye simulation algorithms can be found elsewhere [3,7]. Three levels of Poisson noise were then added to the simulated intensity to obtain patterns with signal-to-noise ratios (SNR=√Imax) of 316.2, 100, and 31.6 (max noise added). Then simulated patterns were modelled with the WPPM approach [4,5,8], refining the parameters of the fcc lattice, size distribution, small angle scattering contribution and a Chebyshev polynomial background. A range of trial size distribution forms was assumed including: continuous and discrete lognormal distributions, and a continuous gamma distribution. The results of these analyses for each distribution are given in the following sections. Continuous lognormal distribution The patterns calculated by the Debye approach were first modelled assuming a continuous lognormal distribution of spheres in the WPPM framework. The obtained size distributions matched exactly the expected Debye distribution for all studied patterns. Even at the small particle size range of 1-10 nm, the WPPM method was able to accurately distinguish the different lognormal parameters of two size distributions with the same Scherrer size (integral breadth). The exact match between the discrete distribution used in the Debye simulations and the continuous curve employed in WPPM was beyond expectations (cf. figure 2). The lower residual and weighted sum of squares (wss ≡∑[(IDebye-IWPPM)/IDebye]) for the distributions with a larger Scherrer size of 4.0nm was an expected result (cf. figure 1). As the size increases the differences between the discrete Debye crystal, and the spatially averaged reciprocal space method, become less influential. Furthermore, at larger sizes the shape of the particle created in the Debye approach is increasingly well represented by a sphere. 20 40 60 80 100 120 140 0.0 5.0x10 1.0x10 20 40 60 80 100 120 140 0.0 5.0x10 1.0x10 20 40 60 80 100 120 140 0.0 5.0x10 1.0x10 -1500

Synthesis and gas sensing properties of perovskite CdSnO3 nanoparticles

The CdSnO3 semiconducting oxide that can be used as a gas-sensitive material for detecting ethanol gas is reported in this paper. CdSnO3 nanoparticles were prepared by a chemical co-precipitation synthesis method, in which the preparation conditions were carefully controlled. The n-type gas-sensing semiconductors were obtained from the as-synthesized powders calcined at 600°C for 1 h. The phase and microstructure of the obtained nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) method with a gas adsorption analyzer. CdSnO3 has a small particle size range of 30–50 nm and a high surface area of 9.12 m2/g, and a uniformity global shape. The gas sensitivity and operating temperature, and selectivity of CdSnO3-based sensors were measured in detail. The gas sensors fabricated by CdSnO3 nanoparticles had good sensitivity and selectivity to vapor of C2H5OH when working temperature at 267°C, the value of gas sensitivity at 100 ppm of C2H5OH gas can reach 11.2 times. Furthermore, gas-sensing mechanism was studied by using chromatographic analysis.

Delineating the First Few Seconds of Supramolecular Self-Assembly of Mesostructured Titanium Oxide Thin Films through Time-Resolved Small Angle X-ray Scattering

The early stages of evaporation induced self-assembly of titanium oxide mesophases from a precursor solution containing TiCl4 and the Pluronic triblock copolymer F-127 in HCl-water-ethanol solution have been studied using time-resolved SAXS techniques. Two experimental protocols were used to conduct these experiments. In one of these, the precursor solution was pumped around a closed loop as solvent was allowed to evaporate at a constant humidity-controlled rate. In the second protocol, a film of precursor solution was measured periodically as it dried completely to a residue under a stream of dry air. This permitted the detailed monitoring of changes in solution chemistry as a function of the elimination of volatile components followed by the actual drying process itself. The SAXS data were modeled in terms of two Guinier radii for soft nanoparticles while a broad Gaussian feature in the scatter profiles was accounted for by particle-article scattering interference due to close packing. For the initial precursor solution, one Guinier radius was found to be about 17 angstroms while the other ranged from 4 to 11 angstroms. Changing the rate of evaporation affected the two radii differently with a more pronounced effect on the smaller particle size range. Analysis gave an interparticle distance in the range 55-80 angstroms for the initial precursor solution which decreased steadily at both of the humidities investigated as evaporation proceeded and the particle packing increased. These results represent the first attempts to monitor in a precise fashion the growth of nano building blocks during the initial stages of the self-assembly process of a titanium oxide mesophase.

Laboratory bentonite colloid migration experiments to support the Äspö Colloid Project

One of the objectives of the Äspö Colloid Project is to evaluate the potential of bentonite colloids to facilitate radionuclide transport. Since bentonite colloids are not stable in Äspö groundwaters, the field-scale experiments performed at Äspö needed to be limited to using latex colloids. To support the Äspö Colloid Project, laboratory scale colloid migration experiments, using both bentonite and latex colloids, were performed in the Quarried Block (QB) sample, a 1 m × 1 m × 0.7 m block of granite containing a single, well characterized, through-going, sub-horizontal, variable aperture fracture. The main purpose of this laboratory program was to provide additional information that cannot be obtained on the field-scale regarding bentonite versus latex sphere colloid transport, particularly at low flow rates. Tracer tests were performed as dipole experiments within the fracture plane using a borehole pair with a separation distance of 380 mm. Flow rates and ionic strength were varied between tests. With low ionic strength water, results showed that at high flow velocities typical of forced-gradient field-scale tracer tests (10’s cm/h), bentonite colloids and 100 nm latex colloids were mobile and had similar transport behaviour. Differences in transport behaviour between the two colloid types became evident as flow velocity was reduced to centimeter per hour and then millimeter per hour, the latter being more typical of certain natural flow conditions. Bentonite colloid recoveries were reduced by up to a factor of three and eluted colloid sizes were predominately in the smallest particle size range (4–15 nm), particularly at low flow velocities. With high ionic strength, Äspö-type, water, bentonite colloids were not mobile in the QB fracture and could not readily be re-mobilized by subsequent injection of low ionic strength water.

Modeling study of the effects of the coagulation kernel with van der Waals forces and turbulence on the particle size distribution

In this study, variations in the size distributions due to different assumptions for the coagulation kernel are investigated. In order to evaluate how the coagulation kernel influences the form of the particle size distribution and to describe the process of the Brownian coagulation, the Brownian coagulation kernel, including the van der Waals forces, is compared with the most frequently used coagulation coefficients. Retardation should be considered for interparticle interactions for particles larger than 1μm radius. However, for particle sizes larger than 0.1 μm, the Brownian kernel is not dominant, so the retardation effect can be ignored. The inclusion of the van der Waals forces in the Brownian coagulation kernel caused a faster coagulation process in the small particle size range. Taking account of the turbulent coagulation kernel, the turbulent coagulation kernel becomes more important when the turbulent intensity is higher. The turbulent coagulation kernel affects the large particle size range and ignoring the turbulent coagulation kernel will lead to overestimation of particle number concentration in model simulation. The results of this study indicate that the inclusion of van der Waals forces or the turbulent coagulation kernel in the total coagulation kernel impacts on the modeled particle size distributions and total particle number concentration.

Abrasivity of a Dentifrice containing Nano Carbonate Apatite

Carbonate apatite has a similar structure to the inorganic component of teeth and bone. Although carbonate apatite is widely used as a bone substitute, there are no reports on its use as a desensitizing dentifrice. This in vitro study evaluated the relative abrasivity of the dentifrice containing nano-sized carbonated apatite (n-CAPs) using a Surface Profile Method (SPM). The dentin specimens were made from the root of extracted human molars. The cervical part of the teeth was sectioned with a diamond wheel disk. The teeth were embedded into an epoxy resin mold and the surface was gradually polished using silicone carbide paper. After grinding, the degree of surface roughness was examined within the range of 2 mm with tapping. The British Standard Institution reference dentifrice (BSI: CaCO3 40%) and the experimental dentifrices (group 1: n-CAPs 30%, group 2: n-CAPs 15% and silica 15%, group 3: n-CAPs 5% and silica 25%, group 4: silica 30%, group 5: CaCO3 10% and SrCl2 10%) were compared. The dentifrice slurries were prepared by mixing 24 grams of the dentifrice in 12 ml distilled water. Each tooth specimen was brushed 1,000 times with the dentifrice slurries using a back-and-forth stroke. The relative abrasivity of each dentifrice was evaluated by determining the ratio of the BSI standard dentifrice to each experiment. The results were analyzed using one-way ANOVA and Tukey’s multiple comparisons using Window SPSS (Statistical analysis system) 12.0. According to the results, Group 1 (3.2), which contained only n-CAPs appeared to have the lowest abrasivity than the BSI dentifrice (100). However, Groups 2 (124.2), 3 (137.9) and 4 (178.1), which contained n-CAPs and silica, appeared to have a higher abrasivity than the BSI dentifrice (p&gt;0.05). The relative abrasivity of group 5 (38), which was a commercial desensitizing dentifrice, was relatively lower. It appears that the higher abrasivity of the experimental is due to the shape and size of the silica component. Therefore, n-CAPs itself has no influence on the abrasivity of the dentifrice. The main reason for the low abrasivity of n-CAPs is believed to be its small particle size (range 50-90nm).

Nano-fabrication and characterization of new conceptual platinum catalysts for low temperature fuel cells

In order to prepare the carbon supported platinum catalysts with high activity, high loading and high distribution, novel sub-substrate methods (a novel incipient wetness and impregnation methods) were used. As a substrate, the acid-treated Vulcan X (VC-X) and Ketjen Black (KB), which have large surface areas, were used and as a sub-substrate, fumed silica was used for the increment of surface area. All prepared catalysts showed the platinum lattice structure clearly and had a small particle size range of 2–5 nm. They also had face-centered cubic structures and showed a fine distribution in spite of high loading. From the TGA and ICP-AES analyses, it can be confirmed that all prepared catalysts showed similar compositions to the expected values within the error range of 0.5%. In case of the prepared catalyst with novel incipient wetness method, a large amount of platinum was located on the carbon surface compared to its loading level. This phenomenon is related to the active surface area, which participates in practical fuel cell reactions. In the Cyclic voltammetry (CV) experimental, Pt 33/KB catalyst showed a large electrochemical surface area of 102 m 2/Pt g. In addition, the unit-cell performance of this catalyst at 0.75–0.6 V showed higher values compared to the commercial catalyst. The merits of this experiment were to construct the mass production process with very simple methods and to be able to increase the yields of platinum utilization.