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1.
The present study aims at investigating the effect of granite particle size on the properties of Al-7%Si-0.3%Mg/granite particulate composites. The composites were fabricated with two different size fractions of granite (− 38 + 0.5 μm and − 0.5 μm). Al-Si-Mg/granite particulate composites were produced using stir casting method with varying amount of granite particles from 0 to 12 wt% at 3 wt% intervals. X-ray fluorescence (XRF) analysis on the granite particulates as well as determination of density and mechanical properties were conducted. The results showed that density of Al-Si-Mg/granite particulate reinforced composites decreased considerably with particles loading. The results further revealed that with increase in granite particulates, a considerable rise in hardness accompanied with a significant decrease in tensile and impact strengths except at 3 wt% addition is achieved. The microstructural analyzes of the produced composites were studied using optical microscope (OM) and Scanning Electron Microscope (SEM). Noticeably, in the micrographs and images obtained, Mg2Si and eutectic Si in α-Al matrix with granite particulates were observed. 相似文献
2.
In this study, QUV accelerated weathering of polyvinyl chloride (PVC) composites with different amounts of titanium dioxide (TiO 2) particle was conducted to investigate the effect of TiO 2 particle on the surface morphology and the mechanical properties. The results indicate that the surface morphology of PVC without TiO 2 particle did not exhibit changes up to 960 h, but exhibited a rough and brittle surface after 1920 h of QUV accelerated weathering. In addition, the tan δ intensity, the elongation at break, and the mean failure energy (MFE) decreased significantly with increasing exposure time due to embrittlement. In contrast, for TiO 2 particle‐loaded PVCs, no significant influence on the tan δ intensity and the mechanical properties after accelerated weathering were observed, despite the appreciable degradation that occurred in the surface layer. The weatherability, as determined by the mechanical performance, was improved with increasing loading of TiO 2 particle in the PVC composites. Although the TiO 2 particle in the PVC matrix acts as a photocatalyst to enhance the surface degradation, it is also an effective radiation screener that inhibits embrittlement and retards the decrease in mechanical properties caused by the accelerated weathering process. POLYM. COMPOS., 37:3391–3397, 2016. © 2015 Society of Plastics Engineers 相似文献
3.
Titanium dioxide nanoparticles (TiO 2NPs) are widely used in industrial and medicinal fields and in various consumer products, and their increasing use has led to an increase in the number of toxicity studies; however, studies investigating the underlying toxicity mechanism have been rare. In this study, we evaluated potential toxic effects of TiO 2NPs exposure on lungs as well as the development of asthma through the ovalbumin (OVA)-induced mouse model of asthma. Furthermore, we also investigated the associated toxic mechanism. TiO 2NPs caused pulmonary toxicity by exacerbating the inflammatory response, indicated by an increase in the number and level of inflammatory cells and mediators, respectively. OVA-induced asthma exposed mice to TiO 2NPs led to significant increases in inflammatory mediators, cytokines, and airway hyperresponsiveness compared with those in non-exposed asthmatic mice. This was also accompanied by increased inflammatory cell infiltration and mucus production in the lung tissues. Additionally, TiO 2NPs decreased the expression of B-cell lymphoma 2 (Bcl2) and the expressions of thioredoxin-interacting protein (TXNIP), phospho-apoptosis signal-regulating kinase 1, Bcl2-associated X, and cleaved-caspase 3 were escalated in the lungs of asthmatic mice compared with those in non-exposed asthmatic mice. These responses were consistent with in vitro results obtained using human airway epithelial cells. TiO 2NPs treated cells exhibited an increase in the mRNA and protein expression of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α with an elevation of TXNIP signaling compared to non-treated cells. Moreover, pathophysiological changes induced by TiO 2NP treatment were significantly decreased by TXNIP knockdown in airway epithelial cells. Overall, TiO 2NP exposure induced toxicological changes in the respiratory tract and exacerbated the development of asthma via activation of the TXNIP-apoptosis pathway. These results provide insights into the underlying mechanism of TiO 2NP-mediated respiratory toxicity. 相似文献
4.
The photoelectrochemical properties of titanium dioxide layers, prepared by thermal oxidation of titanium at 500–750 °C, were
compared with those of layers of particulate (Degussa) P25, especially for oxidation of oxalic acid. The thermally formed
oxide layers had rutile structures with a particle size of about 100 nm. Values of incident photon-to-current conversion efficiencies
increased with rutile layer thickness and reached a maximum at about 1 μm. Photocurrents for particulate TiO 2 layers were about one order lower than those for thermal layers, due to the poor contact among individual particles, resulting
in high electric resistance of the whole layer. The presence of oxalic acid had no effect on the photocurrent of thermal TiO 2 layers, while in the case of porous particulate layers, the photocurrent increased strongly, due to oxalate adsorption and
subsequent enhanced oxidation rate with photogenerated holes. For oxalic acid concentrations ≤10 −3 M, the photocurrent decayed due to mass transfer limitations, resulting in oxalate depletion in the porous particulate layer. 相似文献
5.
Titanium dioxide is one of the best described photosensitive materials used in photocatalysis, solar cells, self-cleaning coatings, and sunscreens. The scientific and industrial attention has been focused on the highly photoactive crystalline phase of titanium dioxide (TiO 2). It is commonly accepted that the smaller TiO 2 particles, the higher photoactivity they present. Therefore, titanium dioxide nanoparticles are massively produced and widely used in everyday products. The amorphous phase of titanium dioxide has been treated with neglect, as the lack of its photocatalytic properties is assumed in advance. In this work, the complex experimental proof of the UV-protective properties of the nano-sized amorphous TiO 2 phase is reported. Amorphous n-TiO 2 is characterized by photocatalytic inactivity and, as a consequence, low cytotoxicity to fibroblast cells. When exposed to UV radiation, cells with amorphous TiO 2 better survive under stress conditions. Thus, we postulate that amorphous n-TiO 2 will be more beneficial and completely safe for cosmetic applications. Moreover, the results from in situ FTIR studies let us correlate the low toxicity of amorphous samples with low ability to form hydroperoxo surface species. 相似文献
6.
Miniemulsification technology was used to encapsulate TiO 2 particles inside a styrene/ n‐butyl acrylate copolymer with high loading levels (11 to 70% PVC (pigment volume concentration)). In this approach, a St/BA copolymer dissolved in toluene in the presence of a costabilizer (hexadecane) was mixed with a dispersion of TiO 2 particles in toluene and sonified, and then emulsified in an aqueous surfactant solution by sonification. The effect of sonification time on both the dispersibility of the TiO 2 particles in the presence of the copolymer and hexadecane and on the encapsulated particle size was investigated. Particle size analysis by dynamic light scattering showed that these composite latexes are quite stable. It was also found that as the TiO 2 loading increased from 11 to 43% PVC, the particle size of the TiO 2 dispersion decreased while the polymer‐encapsulated TiO 2 particle size increased. The effect of surfactant concentration (sodium lauryl sulfate, SLS) on the encapsulated particle size was investigated using four different SLS concentrations in the 11% PVC system. The results showed that as the SLS concentration increased the particle size decreased, as expected. Also it was found that the minimum surfactant concentration that gives stable encapsulated TiO 2 particles is above 10 m M SLS. The role of HD in the recipe was studied for an artificial latex containing no TiO 2 and one prepared at 11% PVC, in terms of particle size before and after solvent stripping, and its effect on the Tg. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4504–4516, 2006 相似文献
7.
Early-age hydration of cement is enhanced by slightly soluble mineral additives (ie, fillers, such as quartz and limestone). However, few studies have attempted to systematically compare the effects of different fillers on cementitious hydration rates, and none have quantified such effects using fillers with comparable, size-classified particle size distributions (PSDs). This study examines the influence of size-classified fillers [ie, limestone (CaCO 3), quartz (SiO 2), corundum (Al 2O 3), and rutile (TiO 2)] on early-age hydration kinetics of tricalcium silicate (C 3S) using a combination of experimental methods, while also employing a modified phase boundary and nucleation and growth model. In prior studies, wherein fillers with broad PSDs were used, it has been reported that between quartz and limestone, the latter is a superior filler due to its ability to partake in anion-exchange reactions with C-S-H. Contrary to prior investigations, this study shows that when size-classified and area matched fillers are used—which, essentially, eliminate degrees of freedom associated with surface area and agglomeration of filler particulates—the filler effect of quartz is broadly similar to that of limestone as well as rutile. Results also show that unlike quartz, limestone, and rutile—which enhance C 3S hydration kinetics—corundum suppresses hydration of C 3S during the first several hours after mixing. Such deceleration in C 3S hydration kinetics is attributed to the adsorption of aluminate anions—released from corundum's dissolution—onto anhydrous particulates’ surfaces, which impedes both the dissolution of C 3S and heterogeneous nucleation of C-S-H. 相似文献
8.
The effect of particulates on both the rheological properties during cure and the curing kinetics of unsaturated resin has been investigated. For the investigation, a general-purpose unsaturated polyester resin was used, with calcium carbonate and clay as inorganic particulates and high-density polyethylene powder as organic particulates. It has been found that, as the particulate content increases, the resin/particulate mixture gives rise to shear-thinning behavior and the rate of cure increases. It has also been found that the CaCO 3 particles helped control shrinkage during cure when the material was subjected to steady shear deformation and that the gel time tη∞ is shorter for mixtures of resin and particulates than for the neat resin alone. Differential scanning calorimetry (DSC) is found useful for determining the curing kinetics of resin/particulate mixtures. We have combined rheological and DSC measurements to obtain a correlation between viscosity and the degree of cure during isothermal curing operations. 相似文献
9.
Investigated was the effect of particle size of starting powder material on the calciothermic reduction of TiO 2 in the TiO 2-Ca system. According to XRD results, TiO 2 did not react with Ca after 40 h of ball milling. DTA data indicated that a decrease in the particle size of starting material resulted in lower reaction temperatures between molten Ca and TiO 2 (decrease from 1073 to 1044°C). The XRD results showed that titanium metal can be produced from nanosized starting material, and the reduction reaction progressed at lower temperatures upon a decrease in the particle size of TiO 2. Also, the particle size of the products decreased with decreasing particle size of starting TiO 2. The concentration of residual oxygen depended on the particle size of TiO 2 due to increasing surface of contact with deoxidizer (Ca). 相似文献
10.
Characterizing nanoparticle dispersions and understanding the effect of parameters that alter dispersion properties are important
for both environmental applications and toxicity investigations. The role of particle surface area, primary particle size,
and crystal phase on TiO 2 nanoparticle dispersion properties is reported. Hydrodynamic size, zeta potential, and isoelectric point (IEP) of ten laboratory
synthesized TiO 2 samples, and one commercial Degussa TiO 2 sample (P25) dispersed in different solutions were characterized. Solution ionic strength and pH affect titania dispersion
properties. The effect of monovalent (NaCl) and divalent (MgCl 2) inert electrolytes on dispersion properties was quantified through their contribution to ionic strength. Increasing titania
particle surface area resulted in a decrease in solution pH. At fixed pH, increasing the particle surface area enhanced the
collision frequency between particles and led to a higher degree of agglomeration. In addition to the synthesis method, TiO 2 isoelectric point was found to be dependent on particle size. As anatase TiO 2 primary particle size increased from 6 nm to 104 nm, its IEP decreased from 6.0 to 3.8 that also results in changes in dispersion
zeta potential and hydrodynamic size. In contrast to particle size, TiO 2 nanoparticle IEP was found to be insensitive to particle crystal structure. 相似文献
11.
Miniemulsion copolymerization of styrene/ n‐butyl acrylate was investigated as a means of encapsulating hydrophilic titanium dioxide (TiO 2) in a film‐forming polymer. Dispersion studies of the TiO 2 were first carried out to determine the choice of stabilizer, its concentration, and the dispersion process conditions for obtaining stable TiO 2 particles with minimum particle size. Through screening studies of various functional stabilizers and shelf‐life stability studies at both room and polymerization temperatures, Solsperse 32,000 was selected to give relatively small and stable TiO 2 particles at 1 wt % stabilizer and with 20–25 min sonification. The subsequent encapsulation of the dispersed TiO 2 particles in styrene/ n‐butyl acrylate copolymer (St/BA) via miniemulsion polymerization was carried out and compared with a control study using styrene monomer alone. The lattices resulting from the miniemulsion encapsulation polymerizations were characterized in terms of the encapsulation efficiencies (via density gradient column separations; DGC) and particle size (via dynamic light scattering). Encapsulation efficiencies revealed that complete encapsulation of all of the TiO 2 by all of the polymer was not achieved. The maximum encapsulation efficiencies were 79.1% TiO 2 inside 61.7% polystyrene and 63.6% TiO 2 inside 38.5% St/BA copolymer. As the density of the particles collected from the DGC increased from one layer to another, both the average particle size and the number of the TiO 2 particles contained in each latex particle increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3479–3486, 2006 相似文献
12.
TiO 2 is a commonly used semiconductor photocatalyst but, as a paradox, it is also widely used as UV filter in sunscreens. Moreover, its capacity to form free radicals under UV irradiation generates reactive free radicals that provoke sunscreens degradation. In this work a hierarchical composite made of ZnO nanoparticles anchored onto TiO 2 microparticles is developed in a safe-by-design way by using the sol-gel method. The aim of this composite is to gain the advantages of inorganic nanoparticles avoiding their potential drawbacks. The hierarchical composite presents higher UV absorption than the pure TiO 2 or ZnO counterparts. The functional stability study on standard sunscreen reveals a 50% high Solar Protection Factor (SPF) values over time for the hierarchical composite lowering the photodegradation of the formulation. Under authors' knowledge, it is the first time that the combination of these oxides increases the UV attenuation as inhibits the negative effects of free radicals. The high UV absorption without degradation opens a new orientation for the effective use of UV-absorbers without the photocatalyst adverse effects. The results in sunscreens generate a proposed mechanism of functionality that explains the observed differences on the efficiency of photocatalytic activity of these materials for other application fields. 相似文献
13.
BackgroundIn order to examine whether myeloperoxidase (MPO) can be a useful marker for evaluating the pulmonary toxicity of nanomaterials, we analyzed MPO protein in bronchoalveolar lavage fluid (BALF) samples obtained from previous examinations of a rat model. In those examinations we performed intratracheal instillation exposures (dose: 0.2–1.0 mg) and inhalation exposures (exposure concentration: 0.32–10.4 mg/m3) using 9 and 4 nanomaterials with different toxicities, respectively. Based on those previous studies, we set Nickel oxide nanoparticles (NiO), cerium dioxide nanoparticles (CeO2), multi wall carbon nanotubes with short or long length (MWCNT (S) and MWCNT (L)), and single wall carbon nanotube (SWCNT) as chemicals with high toxicity; and titanium dioxide nanoparticles (TiO2 (P90) and TiO2 (Rutile)), zinc oxide nanoparticles (ZnO), and toner with external additives including nanoparticles as chemicals with low toxicity. We measured the concentration of MPO in BALF samples from rats from 3 days to 6 months following a single intratracheal instillation, and from 3 days to 3 months after the end of inhalation exposure.ResultsIntratracheal instillation of high toxicity NiO, CeO2, MWCNT (S), MWCNT (L), and SWCNT persistently increased the concentration of MPO, and inhalation of NiO and CeO2 increased the MPO in BALF. By contrast, intratracheal instillation of low toxicity TiO2 (P90), TiO2 (Rutile), ZnO, and toner increased the concentration of MPO in BALF only transiently, and inhalation of TiO2 (Rutile) and ZnO induced almost no increase of the MPO. The concentration of MPO correlated with the number of total cells and neutrophils, the concentration of chemokines for neutrophils (cytokine-induced neutrophil chemoattractant (CINC)-1 and heme oxygenase (HO)-1), and the activity of released lactate dehydrogenase (LDH) in BALF. The results from the receiver operating characteristics (ROC) for the toxicity of chemicals by the concentration of MPO proteins in the intratracheal instillation and inhalation exposures showed that the largest areas under the curves (AUC) s in both examinations occurred at 1 month after exposure.ConclusionThese data suggest that MPO can be a useful biomarker for the ranking of the pulmonary toxicity of nanomaterials, especially at 1 month after exposure, in both intratracheal instillation and inhalation exposure. 相似文献
14.
This study investigated the toxicity of Cu (1, 10, 15, and 25 mol%) loaded TiO 2 and pure TiO 2 nanometersized photocatalysts during the development of zebrafish embryogenesis. The hatch rate decreased in the Cu
x
TiO
y
nanoparticles exposed groups (10, 20 ppt) compared to pure TiO 2 nano-particles (10, 20 ppt) exposed or control groups. These Cu
x
TiO
y
and TiO 2 nanoparticles led to developing mutated embryos with abnormal notochord formation, no tail, damaged eyes and abnormal heart
development. Exposure to Cu
x
TiO
y
and pure TiO 2 nanoparticles led to glutathione increase, catalase activity increase, GST increase and GSR increase than control. Penetration
of the Cu
x
TiO
y
and pure TiO 2 nanoparticles to the embryo was also tested. It was observed that Cu
x
TiO
y
and pure TiO 2 nanoparticles penetrated into cells. Moreover Cu
x
TiO
y
penetrated into the skin, nerve and yolk sac epithelium cells on the zebrafish larvae as aggregated particles, which may
induce the direct interaction between nanoparticles and cell to cause adverse biological responses. As a result, the Cu-loaded
TiO 2 nanoparticles had the toxicity of zebrafish embryo and larvae in the water environment. 相似文献
15.
The photoelectrocatalytic performance of thermal and particulate TiO 2 films on Ti electrode substrates has been studied by photovoltammetry and bulk photoelectrolysis. The thermal TiO 2 film electrodes were prepared by Ti annealing in air at 700 °C and 500 °C while the particulate electrodes were prepared
from dispersions of Degussa P-25 TiO 2 deposited onto Ti substrates and subsequently sintered at 700 °C and 500 °C. The photocurrent in the absence and presence
of the model organic species of oxalate as well as its photooxidation rate depends on coating surface area, type (thermal
or particulate) and crystallographic form (anatase or rutile). A method is proposed to account for surface area variations
by normalising the data with respect to the electroactive surface area of the TiO 2 electrodes, as estimated by their surface electrochemistry in the dark. The thermal electrodes show high photocurrents both
in the absence and the presence of oxalate whereas the performance of particulate electrodes is significantly improved upon
oxalate addition. Nevertheless, the efficiency of thermal 700 °C TiO 2 for oxalate photooxidation during bulk photoelectrolysis is comparable to that of Degussa P-25 TiO 2-coated electrodes. 相似文献
16.
There is a contradiction in making completely opaque and white plastic film with a required high TiO 2 filling fraction, which resulted in inefficient pigment utilization and high cost. Two methods were used here to overcome the contradiction. Firstly, TiO 2 was grafted with poly(methyl methacrylate) (PMMA) by atom transfer radical polymerization to improve the pigment dispersion in poly(vinylidene) fluoride (PVDF). Secondly, minute amounts of carbon black (CB) were added into the PMMA‐ g‐TiO 2/PVDF system to enhance opacity and decrease TiO 2 fraction. The structure, morphology, and properties of PMMA‐ g‐TiO 2 hybrid particles and composite films were investigated by FTIR, TEM, TGA, SEM, DMA, covering power meter, and UV/VIS spectrophotometer, etc. It was observed that PMMA‐ g‐TiO 2 was dispersed uniformly as individual particles in PVDF due to the good compatibility between PMMA and PVDF. Therefore, the opacity of PMMA‐ g‐TiO 2/PVDF films was markedly higher than unmodified‐TiO 2/PVDF ones. Adding minute amounts of CB can significantly increase the opacity of the thin film due to its absorption effect on decreasing light transmittance. The contrast ratio (CR) of the PMMA‐ g‐TiO 2/PVDF film with 20 μm thickness and 25 vol % TiO 2 was 97.67%, lower than the critical CR 98% for a complete opacity, however, the CR of sample with 10 vol % TiO 2 was 98.1% as the CB concentration was 2 × 10 ?4 g/cm 3, saved more than 15% TiO 2. We proposed that a critical thickness d0 existed for the CB/PMMA‐ g‐TiO 2/PVDF composite films, under which the light reflectance increased as a function of thickness, otherwise, the reflectance kept constant. Besides, d0 could be decreased by increasing CB concentration. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43064. 相似文献
17.
Long-lasting UV-induced physical and/or physico-chemical modifications of nano-structured TiO 2 (anatase) films are highlighted in this work by electrochemical methods. These changes occurring in TiO 2 film upon UV exposure are analysed through electrochemical impedance spectroscopy (EIS) measurements. Interfacial capacity measurements show significant and long-lasting modifications of the semiconducting and dielectric properties of TiO 2 due to UV exposure. Furthermore, UV exposure significantly modifies the energetic distribution of surface states in the gap of TiO 2. Based on Mott-Schottky analysis, the relative dielectric constant is found to increase (from 440 to 870) after UV exposure. An explanation for such an effect is that UV exposure enables hydrogen insertion into the nano-columnar TiO 2 film and thereby increases the dielectric constant of the film. 相似文献
18.
In this study, nanocomposites of rigid poly(vinyl chloride) (UPVC) using the synthesized carbon‐coated titanium dioxide (TiO 2) nanoparticles and commercial powder of titanium dioxide (with rutile structure) were prepared by melt blending. The presence of carbon‐coated TiO 2 nanoparticles with rutile structure in UPVC matrix led to an improvement in photo stability of UPVC nanocomposites in comparison with commercial UPVC. The photocatalytic degradation behavior of nanocomposites was investigated by measuring their structural changes, surface tension, and mechanical and morphological properties before and after UV exposure for 700 h. It was found that mechanical and physical properties of UPVC nanocomposites are not considerably reduced after UV exposure in the presence of carbon‐coated TiO 2 nanoparticles even in small percentage of nanoparticles in comparison with the presence of commercial TiO 2 particles. Therefore, it can be concluded that UPVC/TiO 2 nanocomposite with low content of carbon‐coated TiO 2 nanoparticles(0.25 wt %) illustrated high stability under light exposure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40228. 相似文献
19.
Titania (TiO 2)–silica (SiO 2) nanoparticles were synthesized from sprayed droplets of a mixture of TEOS and TTIP by flame spray pyrolysis (FSP). The effect of molar ratio between TEOS and TTIP in the mixture on the particle properties such as particle morphology, average particle diameter, specific surface area, crystal structure, etc., were determined using TEM, XRD, BET, and FT-IR. A UV-spectrometer was also used to measure the absorption spectrum and the band gap energy of the product particles. As the molar ratio of TEOS/TTIP increased by increasing TEOS concentration at the fixed TTIP concentration, the average particle diameter of the mixed oxide nanoparticles increased with maintaining uniform dispersion between TiO 2 and SiO 2, and crystal structure was transformed from anatase to amorphous. The band gap energy of the TiO 2–SiO 2 nanoparticles increased with respect to the increase of the molar ratio due to the decrease of width of UV-absorption spectrum. Photocatalytic activity of TiO 2–SiO 2 composite particles decreased with the concentration of TEOS. 相似文献
20.
A structural design featuring rattle‐type silver/titania (Ag/TiO 2) core/shell, that is, Ag@TiO 2, composite microcapsules is produced. The TiO 2 shell protects the encapsulated, movable Ag nanoparticles from breaking away under moderate loading, minimizing hence adverse environmental and biological exposure due to the metal loss, whereas the mesoporous shell serves as conduits for Ag ions released from the caged Ag nanoparticles to kill Escherichia coli in aqueous solutions under dark condition. The anatase TiO 2 shell imparts an additional, synergistic photocatalysis activity under ultraviolet irradiation. A pronouncedly enhanced photocatalysis activity results when the Ag@TiO 2 composite capsules were thermally annealed under vacuum. This “rattle‐in‐ball” hybrid architecture enables bifunctional bactericide and photocatalysis capability under both light and dark conditions, as well as mitigated environmental and biological impact in practical use. 相似文献
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