Ultrafine Materials Research Articles

In vivo micronucleus studies with 6 titanium dioxide materials (3 pigment-grade & 3 nanoscale) in orally-exposed rats

Six pigment-grade (pg) or ultrafine (uf)/nanoscale (anatase and/or rutile) titanium dioxide (TiO2) particulates were evaluated for in vivo genotoxicity (OECD 474 Guidelines) in male and female rats by two different laboratories. All test materials were robustly characterized. The BET surface areas of the pg and uf samples ranged from 7 to 17 m2/g and 50 to 82 m2/g respectively. The materials were assessed for induction of micronuclei and toxicity in bone marrow by analyzing peripheral blood reticulocytes (RETs) by flow cytometry. Single oral gavage doses of 500, 1000 or 2000 mg/kg body weight (bw) of each material were implemented with concurrent negative (water) and positive controls (cyclophosphamide). Approximately 48 and 72 h after exposure, blood samples were collected and 20,000 RETs per animal were analyzed. For each of the six tests, there were no biologically or toxicologically relevant increases in the micronucleated RET frequency in any TiO2 exposed group at either time point at any dose level. In addition, there were a lack of biologically relevant decreases in %RETs among total erythrocytes. All six TiO2 test substances were negative for in vivo genotoxicity effects; however, it is noted that the exposure to target tissues was likely negligible. One pigment grade and one ultrafine material each were evaluated for potential systemic exposure/uptake from the gastrointestinal tract by analysis of TiO2 into blood and liver. No significant increases in TiO2 over controls were measured in blood (48 or 72 h) or liver (72 h) following exposures to 2000 mg/kg bw TiO2. These data indicate that there was no absorption of the test material from the gastrointestinal tract into the blood circulation and the lack of genotoxic effects is therefore attributed to a lack of exposure due to the inability of the test material to migrate from the gastrointestinal tract into the blood and then into target tissues.

Orientation mapping by transmission-SEM with an on-axis detector

Conventional orientation mapping in a scanning electron microscope (SEM) is a valuable technique for characterizing crystalline materials, but its application to ultrafine or nano-grain materials is limited by its spatial resolution. The resolution can be increased by collecting transmission diffraction patterns in SEM. In previous works, such patterns were collected using off-axis detectors in nearly vertical position. To avoid some drawbacks of such arrangement, a new configuration was devised in which the scintillator is located underneath the thin foil on the optical axis of the microscope, and the light is reflected towards the camera by a mirror. This simple configuration gives intense patterns even at very low probe currents, and can be potentially used for collecting maps of relatively high spatial resolution. Example maps reveal details with dimensions of about 5nm. Because of its resolution and geometric simplicity, the proposed configuration will open new opportunities in SEM-based characterization of nanocrystalline materials.

Effects of Grain Size on the Groove Depths in Microlaser Cutting of Austenitic Stainless Steel SUS304

Over the last decade, developments of fine grained materials and investigations of the effects of grain size on mechanical processing at the micro scale have been reported. There are several papers and reports on the function improvements achieved due to enhanced edge quality. However, it is difficult to identify the studies about the effects of grain size on the processed surface in laser processing because ultrafine grain materials were not supplied in the market. In this study, the effect of grain size on the depth of groove by laser processing is investigated. Microgrooves are produced using a picosecond laser machine. The grooves are observed with a non-contact 3D measuring machine, and the depth and surface conditions are determined. There are obvious differences on the depth between the different grain sizes. Specimens were cut to allow the observation of the phase transformation of grains in the cross section using scanning electron microscope (SEM) and electron back scatter diffraction (EBSD). There are several obstacles when producing deeper grooves. As a result, smaller grained stainless steels are suitable for producing microparts by microlaser cutting.

Microhardness Distribution and Microstructural Evolution in Pure Aluminum Subjected to Severe Plastic Deformation: Elliptical Cross-Sectioned Spiral Equal-Channel Extrusion (ECSEE)

Elliptical cross-sectioned spiral equal-channel extrusion (ECSEE), one of the severe plastic deformation techniques, is of great efficiency in producing bulk ultrafine or nanostructured materials. In this paper, the simulation and experimental researches on ECSEE of high-purity aluminum were conducted to investigate the equivalent strain distribution and microhardness distribution on three orthogonal planes, as well as microstructural evolution. Simulation result shows a significant strain gradient on three planes. Microhardness tests comprise the similar results to strain distribution. According to transmission electron microscopy (TEM) results, microstructural evolution ranged from coarse structures to ultrafine structures by undergoing the shear bands, subgrains, high-angle misorientation grain boundaries and equiaxed structures. There are also some distinctions with reference to grain refinement level, grain boundary styles and dislocation distribution on different positions. The TEM investigations are in good agreement with microhardness tests.

Production of geopolymer composites enhanced by nano-kaolin material

Nowadays kaolin raw material is usually used to produce nano-kaolin for geopolymer enhancement by using firing method. In the present study, kaolin used was taken from the Naqus Formation (Cambro-Ordovician age), west of Gabal El Gunna, Sinai, Egypt. Nano-kaolin material is an ultrafine material and was prepared from the taken kaolin by the firing process at 800 for 2 ℃ h with a heating rate of 5 /min. Six mixes were prepared and their laboratory specimens were made ℃ and cured up to 90 days. Water cooled slag was used as starting material, and sodium hydroxide and sodium silicate were used in the study as activators for the used kaolin. The formed geopolymer mixes with different ratios (1%, 1.5%, 3%, 5%, and 7%) of nano-kaolin as a partial replacement for the raw kaolin were investigated. Gelenium Ace super plasticizer was added in the ratio of 4% from the dry weight to ensure good dispersing of the used nano clay. Results showed that increasing the percentage of nano-kaolin up to 3% results in an enhancement in the mechanical properties as compared with the control mix up to 90 days of curing, while higher ratios are not preferable where they lead to agglomeration of the added nano materials and matrix dilution.

Studies on carbon flotation from fly ash

The separation of carbon from fly ash significantly improves the potential end-us of combustion byproducts. Froth flotation is the most effective separation technique for ultrafine material. Diesel dosages, conditioning time, and impeller rotating speeds' influences on carbon flotation performance were studied. From flotation products, +25 and −25μm fractions were screened out to study their different flotation behaviors. At a given impeller speed, carbon recovery of +25μm fraction increased significantly from 38.46% to 74.22% over a range of diesel dosage from 0.5 to 4.5kg/t, while that of -25μm fraction was relatively constant at 85% over the same diesel dosage range. Morphologies and microstructures of coarse and fine carbon were studied by using scanning electron microscope. Porous structures of coarse carbon were observed. It's difficult for diesel droplets of several microns to penetrate the pores of coarse carbon particles, which increases diesel consumption. Increasing impeller speeds from 1200 to 1600rpm during conditioning improved the carbon recovery and separation efficiency of +25μm fraction by 79% and 110%, respectively, which significantly reduced diesel consumption. Flotation kinetic studies indicate that increasing impeller speeds during conditioning stage can improve the flotation rate constant and maximum carbon recovery for both +25 and −25μm fractions.

Durability performance of self-compacting concrete (SCC) with binary and ternary mixes of fly ash and limestone filler

The basic objective of this work is to evaluate the durability of self-compacting concrete (SCC) produced in binary and ternary mixes using fly ash (FA) and limestone filler (LF) as partial replacement of cement. The main characteristics that set SCC apart from conventional concrete (fundamentally its fresh state behaviour) essentially depend on the greater or lesser content of various constituents, namely: greater mortar volume (more ultrafine material in the form of cement and mineral additions); proper control of the maximum size of the coarse aggregate; use of admixtures such as superplasticizers. Significant amounts of mineral additions are thus incorporated to partially replace cement, in order to improve the workability of the concrete. These mineral additions necessarily affect the concrete’s microstructure and its durability. Therefore, notwithstanding the many well-documented and acknowledged advantages of SCC, a better understanding its behaviour is still required, in particular when its composition includes significant amounts of mineral additions. An ambitious working plan was devised: first, the SCC’s microstructure was studied and characterized and afterwards the main transport and degradation mechanisms of the SCC produced were studied and characterized by means of SEM image analysis, chloride migration, electrical resistivity, and carbonation tests. It was then possible to draw conclusions about the SCC’s durability. The properties studied are strongly affected by the type and content of the additions. Also, the use of ternary mixes proved to be extremely favourable, confirming the expected beneficial effect of the synergy between LF and FA.

Centre of Panel Thermal Conductivity Performance Analysis of Aerocor-Centrifugal Hybrid Ultrafine Glass Fiber VIP Core Materials

This paper includes analysis on the recent advancement of glass fiber core based vacuum insulation panels (VIPs) in China, including the experimental development of mixed ultrafine fiberglass prototype core material consisting of Centrifugal and Aerocor glass wool mixture at different ratios. Pore sizes exhibited by these prototypes generally range between 15-25μm. Extensive centre of panel thermal conductivity (Kcop) were performed from which thermal performance graphs were extracted and analyzed prudently. Kcop analysis verified superior performance of the prototypes over traditional glass fiber core samples, hinting greater service life. The study concludes that in order to optimize the long term performance of current industrial glass fiber core material reduction of pore size at less than 10μm range as well as reduction of x-z axis fiber orientation angle to less than 450 would potentially decrease core structural sensitivity towards both gaseous and solid conductivity at increase of internal pressure.

Finite element analysis of the plastic deformation in tandem process of simple shear extrusion and twist extrusion

Abstract Recently, simple shear extrusion (SSE) and twist extrusion (TE) are introduced to fabricate ultrafine grained bulk rod metallic materials. The SSE and TE processes generate significant deformation inhomogeneity, with higher and lower strains in the center, respectively, which easily causes mechanical instability of the materials. In this study, to overcome this deformation inhomogeneity problem in SSE and TE, a tandem process of SSE and TE (TST) is suggested. The finite element method is applied for plastic deformation behavior during the TST process. The results demonstrate that the TST process can produce relatively homogeneously deformed materials. In particular, the effects of back pressure and processing order on the plastic deformation behaviors in the TST process are systematically analyzed.

Microcompression tests of single-crystalline and ultrafine grain Bi2Te3 thermoelectric material

Abstract

Comparative analysis of the effect of solvent on the structural and dynamic characteristics of film and nonwoven fiber materials prepared from polyurethane and styrene acrylonitrile

Structural and dynamic analysis, combining thermophysical measurements by differential scanning calorimetry and measurements of segmental mobility by the EPR microprobe technique, is performed for films and nonwoven fiber materials prepared from polyurethane (PU) and a styrene-acrylonitrile copolymer (SAN), as well as mixed compositions thereof. The effect of the tetrahydrofuran, ethyl acetate, and acetone solvents on the structure and molecular dynamics of films and matrices based on ultrathin PU and SAN fibers is examined. A weak effect of solvent on the molecular dynamics of chains in the PU film and nonwoven materials and a strong influence on the molecular mobility in SAN films and films of mixed compositions with a high SAN content are observed. For fibers, such influence is negligible. In PU and PU/SAN mixed formulations, mesomorphic structures are formed in both the film and nonwoven materials. The temperature dependence of the rotational correlation time τ of the probe exhibits a kink at temperatures close to the melting point of the mesomorphic structures in the PU/SAN mixtures. All the studied dependences for both the films and fibers feature a kink at PU/SAN = 50/50, which is associated with phase inversion in the compositions. The probe measurements show the impact of an oxidant (ozone) on the amorphous phase in these polymers. Measuring the rotational dynamics of the probe before and after exposure to ozone of the film and ultrafine fiber materials showed that, for both the PU films and fibers, ozonation produces practically no effect on the molecular dynamics, while for PU/SAN compositions and pure SAN, τ changes significantly.

Experimental study of the porosity and microstructure of self-compacting concrete (SCC) with binary and ternary mixes of fly ash and limestone filler

Self-compacting concrete (SCC) can soon be expected to replace conventional concrete due to its many advantages. Its main characteristics in the fresh state are achieved essentially by a higher volume of mortar (more ultrafine material) and a decrease of the coarse-aggregates. The use of over-large volumes of additions such as fly ash (FA) and/or limestone filler (LF) can substantially affect the concrete’s pore structure and consequently its durability.In this context, an experimental programme was conducted to evaluate the effect on the concrete’s porosity and microstructure of incorporating FA and LF in binary and ternary mixes of SCC. For this, a total of 11 SCC mixes were produced: 1 with cement only (C); 3 with C+FA in 30%, 60% and 70% substitution (fad); 3 with C+LF in 30%, 60% and 70% fad; 4 with C+FA+LF in combinations of 10–20%, 20–10%, 20–40% and 40–20% fad, respectively.The results enabled conclusions to be established regarding the SCC’s durability, based on its permeability and the microstructure of its pore structure. The properties studied are strongly affected by the type and quantity of additions. The use of ternary mixes also proves to be extremely favourable, confirming the beneficial effect of the synergy between these additions.

Selected Parameters of Mortars Containing Fine-Grain Modification of Glass and Clay Brick

Today’s world trend in construction and development of building materials is focused to research and development of material systems with properties resulting from dimensions of the components in the micro and nanoscale. Improved mechanical and physical properties, better durability as well as environmental and economic benefits are expected. Such of improved materials represent significant benefit for sustainable construction. In current world, construction and demolitions waste (C&DW) represents useful source of secondary raw materials for production of new building materials. This paper is engaged to assessment of impact the fine particles obtained by grinding of C&DW to technological and physico-mechanical parameters of mortar. Two types of different C&DW which vary in strength and microstructure were used for the experiment: glass and clay bricks. For the assessment of the properties of mortars with application of those ultrafine materials as filler, recipes with 20 and 60% replacement of natural fine aggregate were prepared and tested. Water demand for specified consistency was tested in the fresh state of mortars, while flexural, compressive and adhesive strength was tested after 2, 7, and 28 days of setting and hardening. Given results show positive or negligibly impaired impact of fine grain modification of glass and clay brick on tested parameters.

Application of Ultrafine Weighting Materials in High-Density Oil-Based Drilling Fluid Technology

High-density oil-based drilling fluid already was considered as one of the most effective technologies during the HTHP Ultra-deep well drilling process. The weighting materials sag such as barite sag, however, always occurred because of the density contrast between the base oil and the weighting material, and hence sag can result in excessive torque, lost circulation and many other problems. This study applied three kinds of ultra-fine powder (particle size≤4μm), which are new weighting materials, to replace the common API barite (particle size10~70μm). The different kinds of high-density oil-based drilling fluids, which weighted with micronized barite, micronized ilmenite, manganese tetraoxide and API barite, were prepared and evaluated separately in lab. The performance data showed that compared with conventional weighting materials, the application of ultrafine powder technology could greatly optimize the rheology of high-density oil-based drilling fluids (ρ ≥ 2.3 g/cm3), reduce the amount of emulsifiers about 50% and dramatically enhance the dynamic suspension-stability of the system, Furthermore, OBM drilling fluids weighted with ultrafine weighting materials almost presented lower viscosity, shear force and sedimentation rate, which will meet more severe requirements of ultra-deep complex well drilling.

Facile synthesis of size controllable dendritic mesoporous silica nanoparticles.

The synthesis of highly uniform mesoporous silica nanospheres (MSNs) with dendritic pore channels, particularly ones with particle sizes below 200 nm, is extremely difficult and remains a grand challenge. By a combined synthetic strategy using imidazolium ionic liquids (ILs) with different alkyl lengths as cosurfactants and Pluronic F127 nonionic surfactants as inhibitors of particle growth, the preparation of dendritic MSNs with controlled diameter between 40 and 300 nm was successfully realized. An investigation of dendritic MSNs using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen physisorption revealed that the synthesis of dendritic MSNs at larger size (100-300 nm) strongly depends on the alkyl lengths of cationic imidazolium ILs; while the average size of dendritic MSNs can be controlled within the range of 40-100 nm by varying the amount of Pluronic F127. The Au@MSNs can be used as a catalyst for the reduction of 4-nitrophenol by NaBH4 into 4-aminophenol and exhibit excellent catalytic performance. The present discovery of the extended synthesis conditions offers reproducible, facile, and large-scale synthesis of the monodisperse spherical MSNs with precise size control and, thus, has vast prospects for future applications of ultrafine mesostructured nanoparticle materials in catalysis and biomedicine.

Review on Classification and Application Prospect of Ultrafine Powder Material

This paper summarized the basic properties and preparation methods of ultrafine powder, introduced the present situation and progress of ultrafine powder classification technology at home and abroad, also pointed out the application of ultra-fine powder material in the mold manufacturing, biomedical, electronic information, fine ceramics, food industry and coatings.

Plastic Deformation Macrolocalization. Local Stresses and Fracture in Ultrafine Grain Titanium

The process of plastic deformation in ultrafine grain titanium is considered. Using the methods of speckle photography and X-ray diffractometry, the distributions of local strains and of local elastic distortions were examined for the test sample work. It is shown that the method of atomic-force microscopy can be used effectively for qualitative and quantitative assessment of ultrafine grain material structure.

Accumulative Roll Bonding of Pure Copper and IF Steel

Severe plastic deformation is a new method to produce ultrafine grain materials with enhanced mechanical properties. The main objective of this work is to investigate whether accumulative roll bonding (ARB) is an effective grain refinement technique for two engineering materials of pure copper and interstitial free (IF) steel strips. Additionally, the influence of severely plastic deformation imposed by ARB on the mechanical properties of these materials with different crystallographic structure is taken into account. For this purpose, a number of ARB processes were performed at elevated temperature on the materials with 50% of plastic deformation in each rolling pass. Hardness of the samples was measured using microhardness tests. It was found that both the ultimate grain size achieved, and the degree of bonding depend on the number of rolling passes and the total plastic deformation. The rolling process was stopped in the 4th cycle for copper and the 10th cycle for IF steel, until cracking of the edges became pronounced. The effects of process temperature and wire-brushing as significant parameters in ARB process on the mechanical behaviour of the samples were evaluated.

Characterization of the deformation field in large-strain extrusion machining

Large-strain extrusion machining (LSEM) has been emerged as a promising severe plastic deformation methodology for the creation of nano or ultra-fined grained materials. To realize deformation control, the key issue involved is the strain estimation in LSEM. In order to characterize the deformation field in LSEM, the experiments of LSEM oxygen-free high-conductivity copper were conducted by using a specially designed LSEM device. Based upon the deformation field measured by high speed imaging and digital image correlation (DIC), a new strain estimation model considering the extrusion process of constraint is proposed in this paper. The theoretical predicted strain agrees well with the measurements.

CO2 capture performances of fine solid sorbents in a sound-assisted fluidized bed

Post-combustion CO2 capture processes have the greatest near-term potential for reducing greenhouse gas emissions because these processes can be retrofitted to existing units, thus providing a quicker solution to mitigate CO2 environmental impacts. Among all the post-combustion technologies, adsorption processes on solid sorbents are attractive due to their low energy requirements. Great interest is focused on ultra-fine materials, whose chemico-physical properties can be tuned at the molecular level. In this framework sound-assisted fluidization has already been proved to maximize the CO2 adsorption capacity of fine sorbents with respect to common technologies, due to the higher exploitation of the exposed surface. The aim of the present work is, therefore, to compare the adsorption performances of different materials (two activated carbons, two zeolites and a metal organic framework) under sound-assisted fluidization conditions (140dB–80Hz) in order to maximize the gas–solid contact efficiency and, in turn, minimize the limitations to the intrinsic adsorption capacity of the sorbents. All the tests were performed at ambient temperature and pressure with values of CO2 concentration typical of flue gases (5–10vol.%). The different behaviors exhibited by the materials were explained on the basis of their textural properties. In particular, the microporosity falling in the range of 8.3–12Å strongly affects the CO2 adsorption performances under the investigated operating conditions.