The effect of processing conditions on the microstructure of embossed polyethylene films

Film embossing is a mechanical process in which a flat film is transformed into an embossed product. During the process, thermal and stress fields are applied Lo the polymer, causing changes in the microstructure and physical dimensions of the material. The engineering analysis of the process requires the study of various aspects relating to the characterization of the microstructure before and after embossing, A variety of techniques were employed to characterize the properties and microstructure of the embossed film in relation to: crystallinity, orientation, mechanical properties, and dimensions of the embossed films. The thermal treatment of the polymer film was shown to be the most significant factor in the process. By controlling the thermal treatment of the film, it is possible to manipulate the properties and dimensions of the embossed film. The important aspects: influencing thermal treatment include the radiation heater temperature, preheat roll temperature, line velocity, and film thickness. The initial film orientation and embossing pressure have a minor effect on the final properties of the embossed film. The main effect of the embossing pressure is on the bulk thickness of the embossed film.     

Correlation of Rheological and Microstructural Properties in a Model Lipid System

Model systems having different microstructures and rheological properties were obtained by controlled crystallization from a mixture of high-melting and low-melting lipids. Based on analysis of confocal scanning light microscopic images, the microstructural characteristics of the systems were quantified by use of different approaches including microstructure density, Euler characteristic, nearest-neighbor analysis, fractal dimension of microstructure interface, and fractal dimension by the particle-counting method (PCM). The solid-fat content (SFC) of semisolid lipid samples was measured by nuclear magnetic resonance (NMR) spectroscopy and rheological properties were analyzed by compressive penetration tests with a texture analyzer. As expected, SFC had a major impact on rheological properties, but lipid crystalline microstructure also had significant effects. Correlation analysis showed that rheological properties were highly correlated with the various quantitative microstructural parameters, with the exception of the fractal dimension by the PCM. Empirical models adequately correlated rheological properties with SFC and microstructure density. Compression modulus increased by a factor of about ten as SFC increased from 0.28 to 0.51. However, for systems with the same SFC, compression modulus was dependent on microstructure. At low SFC compression modulus increased by about a factor of seven over the range of microstructures formed, whereas at higher SFC compression modulus only increased by a factor of about two.     

Use of the Retarded Solution-Reprecipitation Process to Attain a Higher Initial Permeability in MnZn Ferrites

We investigated the effect of various amounts of liquid phase on microstructure development during sintering and the resulting magnetic permeability of MnZn ferrite (MZF) samples. Our results revealed that the microstructure and the final magnetic permeability depend on the thickness of the liquid-phase film during sintering. The solution-reprecipitation (S-R) process, which is associated with an intensive microstructure development in MZF, starts when a continuous liquid-phase film of critical thickness δ_o, which wets the MZF grains, is formed. The solid-state sintering that takes place before the formation of the continuous liquid-phase film is essential for the final microstructure of MZF.     

Effects of nano‐fillers and process conditions on the microstructure and mechanical properties of microcellular injection molded polyamide nanocomposites

This paper presents the effects of process conditions and nano‐clay fillers on the microstructure (namely, size, density, and distribution of microcells within samples) and the resulting mechanical properties of microcellular injection molded polyamide‐6 (PA‐6) nanocomposite and its neat‐resin counterpart. Based on the design of experiments (DOE) matrices, samples were molded at various supercritical fluid (SCF) levels, melt temperatures, shot sizes, melt plastication pressures (MPP), and injection speeds. These samples were then subjected to scanning electron microscope (SEM) analysis, tensile testing, and impact testing. For both materials, the microstructure and the mechanical properties of the molded samples were found to be dependent on the process conditions and presence of nano‐clay, which could serve as microcell nucleating agent. At higher weight reductions, the nanocomposite samples exhibit much smaller microcells and higher cell densities than those obtained in the neat‐resin samples. The SEM micrographs reveal noticeable differences in microcell surface roughness between the nanocomposite and the neat resin. A statistical design analysis was used to identify the optimal process conditions that would result in desirable cell size and density and, thus, better mechanical properties. For example, the highest tensile strengths have been observed at the highest levels of shot size, MPP, injection speed, and SCF level, and at the lowest level of melt temperature.     

Structures,morphological control,and antibacterial performance of tungsten oxide thin films

The present work describes structural, morphological, and antibacterial properties of thin film coatings based on tungsten oxide material on stainless-steel substrates. Thin films were prepared by RF magnetron sputtering of W targets in the oxygen/argon plasma environment in 60 W sputtering power. The characterization of the specimens was made on the basis of microstructure and antibacterial properties of the thin films surface. The effect of O₂/Ar ratio on the structure, morphology, and antibacterial properties of the tungsten oxide thin films was studied. Methods such as X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier Transform Infrared Spectroscopy (FTIR) were used to assess the properties of deposited thin films. XRD peak analysis indicates (100) and (200) of WO₃ phase with hexagonal structure. Moreover, the micro-strain, grain size, and dislocation density were obtained. It is noteworthy that by increasing the oxygen percentage from 10% to 20%, the grain size decreases from 81 to 23 nm while the film micro-strain and dislocation density increases. The SEM results illustrates that tungsten oxide thin films are made of interconnected nano-points in a chain shape with sphere-shaped grains with diameter variation from 10 to 100 nm. The FTIR spectra displays four distinct bands corresponds to O–W–O bending modes of vibrations and W–O–W stretching modes of the WO₃ films. The antibacterial effects of tungsten oxide thin films on steel stainless substrate against Escherichia coli bacteria are also examined for the first time and our observation shows that the number of bacteria on all tungsten oxide samples decreases after 24 h. The samples exhibit an excellent antibacterial performance. This paper renders a strategy through which the tungsten oxide thin films for antibacterial purpose and proposes that WO₃ thin films are ideal for various medical applications including stainless steel medical tools, optical coatings, and antibacterial coatings.     

Dielectric Properties of Electrophoretically Deposited and Isothermally Pressed BaTiO3 Thick Films

Thick BaTiO₃ films were prepared on platinum metallic foils by the electrophoretic deposition (EPD) technique using BaTiO₃ nanoparticles. In order to increase the density of the thick film, the green film was pressed under an isostatic pressure of 200 MPa before high-temperature sintering. The microstructures of deposited films were examined using X-ray diffraction and scanning electron microscopy techniques. Dielectric properties of the thick films were investigated. As the films grow thicker, the dielectric constant increases gradually and the dielectric loss decreases slightly. The experimental results indicate that isostatic pressing is an effective method to process thick films with dense microstructure and better dielectric properties.     

Relations between the deposition conditions,the microstructure and the defects in PECVD hydrogenated amorphous carbon films; influence on the electronic density of states

The relationships between the deposition conditions, the growth mechanisms, the microstructure and the electronic density of states of hydrogenated amorphous carbon (a-C:H) films prepared by PECVD from hydrocarbons are not yet fully understood. We therefore performed a systematic study using several complementary techniques to determine the changes in the microstructure and in the optical properties of a-C:H samples deposited from a dual micro-wave/radio-frequency discharge in methane as a function of the negative r.f. bias voltage applied to the substrate −V_b. The results reveal the existence of two successive film growth regimes when varying −V_b from −30 to −600 V, i.e. when increasing the ion bombardment during deposition, which lead to different types of sp² C atoms clustering and H incorporation, but to the same density of paramagnetic defects. Models of the a-C:H microstructure are proposed in each case, and their influence on the electronic states density is analysed in detail. It is shown that the H content and the proportion of sp² C atoms play a minor role on the electronic properties, as compared to the nature, the size, the number and probably the distortions of the π-bonded clusters.     

Biaxial orientation of poly(vinyl chloride) compounds: Interaction between drawing,structure, and properties

Rigid poly(vinyl chloride) (PVC) sheets were stretched uniaxially (at constant width), equally biaxially, and unequally biaxially to various draw ratios. Tensile properties, density, and birefringence of the stretched sheets were measured, and their wide angle X-ray diffraction traces recorded. Comparison of results showed the highest crystallite and overall orientation and density in the uniaxial samples, and lowest values for the equal biaxial samples. Drawing resulted in the alignment of some existing crystallites in the plane of the film, together with the formation of new mesomorphous structures. Changes in tensile strength were attributed to overall orientation.     

Effect of Processing Parameters on the Mechanical Properties of Injection Molded Thermoplastic Polyolefin (TPO) Cellular Foams

In this study, the effects of processing parameters on the mechanical properties of injection molded thermoplastic polyolefin (TPO) foams are investigated. Closed cell TPO foams were prepared by injection molding process. The microstructure of these foamed samples was controlled by carefully altering the processing parameters on the injection molding machine. The foam morphologies were characterized in terms of skin thickness, surface roughness, and relative foam density. Tensile properties and impact resistance of various injection molded TPO samples were correlated with various foam morphologies. The findings show that the mechanical properties are significantly affected by foam morphologies. The experimental results obtained from this study can be used to predict the microstructure and mechanical properties of cellular injection molded TPO foams prepared with different processing parameters.

     

The effects of nanoparticle addition on the densification and properties of SiC

The effects of nanoparticle addition on the pressureless sintering of injection molded and thermally debound silicon carbide (SiC) samples were studied. The influence of increased powder content and reduced particle size on the densification, microstructure and properties are discussed. The sintered parts of bimodal μ–n SiC mixtures exhibited comparable sintered density but lower shrinkage than the corresponding monomodal μ-SiC powder mixtures. Additionally, the mechanical and thermal properties of sintered monomodal and bimodal SiC samples were measured and compared with literature data for conventional monomodal μ-SiC systems.     

Microstructure and magnetic properties of nickel-zinc ferrite ceramics fabricated by spark plasma sintering

Dense nickel-zinc (NiZn) ferrite ceramics were successfully fabricated within tens of seconds via spark plasma sintering. The phase composition and microstructure of the sintered samples were characterized by X-ray diffraction and scanning electron microscopy, respectively. The static magnetic properties at room temperature and Curie temperature of the samples were investigated by vibrating sample magnetometry. The results indicated that the main phase of the sintered samples was Ni_0.75Zn_0.25Fe₂O₄ with spinal structure, and the sintering temperature and heating rate observably affected the microstructure and density, then the magnetic properties of the sample. The Joule heat generated by NiZn ferrite during spark plasma sintering was very important for the rapid preparation of the sample with high density and small grain size. The low sintering temperature and heating rate would be helpful to obtain samples with small grain size, high density, and then good magnetic properties. The samples sintered at 900 °C with the heating rate of 5–10 °C/s were characterized of the relative density above 95%, 4πM_s value beyond 4000 Gs and coercivity below 27.7 Oe.     

Effect of temperature and film thickness on structural and mechanical properties of c-axis oriented Zn0.95Mg0.05O thin films

Zn_0.95Mg_0.05O solutions were synthesized by the sol-gel technique using Zn and Mg-based alkoxide. The structure, microstructure, and mechanical properties of the c-axis oriented Zn_0.95Mg_0.05O thin films were investigated as a function of film thickness and temperature. Zn_0.95Mg_0.05O thin films were grown on a glass substrate using the sol-gel dip-coating method. Then, the thin films were annealed at various temperature values (500–600 °C for 30 min) under air. X-ray diffraction of the Zn_0.95Mg_0.05O thin films results indicated that all samples had a ZnO wurtzite structure and (002) orientation. The photoluminescence (PL) measurements revealed the near-band emission (NBE), the Zn_i related emission, and the excess oxygen interstitials and their complexes with zinc vacancies. The surface morphologies and microstructure of all samples were characterized by using Scanning Electron Microscope (SEM). It was observed that surface morphologies of Zn_0.95Mg_0.05O thin film were dense, uniform, crack free and without pinhole. Effects of film thickness and temperature on stress in Zn_0.95Mg_0.05O thin films were analyzed theoretically to see whether there was any crack inside of the thin films and substrate or not. It was found that the stress component values of thin films were compressive; however, for glass substrate they were tension.     

Characterization of low-temperature solution-processed indium–zinc oxide semiconductor thin films by KrF excimer laser annealing

We have employed KrF excimer laser annealing (ELA) treatment on sol–gel derived indium–zinc oxide (IZO) precursor films to develop a method of low thermal-budget processing. As-coated IZO sol–gel film was dried at 150 °C and then annealed using KrF excimer laser irradiation under ambient air. The laser irradiation energy density was adjusted to 150, 250, 350, and 450 mJ/cm² to investigate the effects of laser irradiation energy density on the microstructure, surface morphology, optical transmittance, and electrical properties of laser annealed IZO thin films. Results of GIXRD and TEM-SAED indicated that the ELA IZO thin films had an amorphous phase structure. The surface characteristics and electrical properties of laser annealed IZO thin films were significantly affected by the laser irradiation energy density. It was found that the dried IZO sol–gel films irradiated with a laser energy density of 350 mJ/cm² exhibited the flattest surface, the highest average optical transmittance in the visible region, and the best electrical properties among all ELA samples.     

Development of a new magnetic aluminum matrix nanocomposite

This article presents the results of a comparative investigation on microstructure, mechanical properties and magnetic characteristics of aluminum matrix nanocomposites reinforced with nickel ferrite nanoparticles. Magnetic nickel ferrite (NiFe₂O₄) nanoparticles with average size of 35?nm were synthesized via citrate-nitrate route and were used as the reinforcement phase in commercially pure aluminum matrix. Aluminum matrix samples with 0, 1, 2.5, 5 and 10?wt% ceramic reinforcement were fabricated using the powder metallurgy process. The sintered samples were then extruded at 400?°C to improve the density and homogeneity of the composite. Optical microscopy, SEM, FESEM, densitometry, XRD, DSC and VSM analyses were all used to evaluate the microstructure, porosity distribution, density, existing phases, possible reactions between the matrix and the reinforcements and magnetic properties of the samples. The results showed that the relative density of the composites decreased as the reinforcement weight percent was increased. The samples yield stress and ultimate tensile strength increased by increasing the weight percent of the reinforcement up to 5?wt%, however, they dropped at 10?wt% reinforcement content. The compressive yield stress, magnetization and coercivity of the composites were all observed to increase as the reinforcement content increased. However, the elongation of composite samples decreased considerably as the reinforcement content increased.     

Elaboration of lead-free Na0.5Bi0.5TiO3–BaTiO3 (NBT-BT) thick films by aerosol deposition method (ADM)

Thick and dense ceramic films of lead-free 0.94Na_0.5Bi_0.5TiO₃-0.06 BaTiO₃ (NBT-BT) composition were elaborated by aerosol deposition method (ADM) at room temperature. A powder of suitable grain size was elaborated by solid state reaction. Using this powder, two samples were elaborated by ADM respectively on glass and metallic substrates, in order to check for microstructure and electrical properties. This process allowed obtaining a thick film (3.2 µm) with dense microstructure. Measurement of electrical properties revealed a lossy dielectric behavior indicating interfacial phenomena at the electrode–film interface. The measurement of the ferroelectric hysteresis cycle does not show any characteristics of a ferroelectric behavior, but corresponds well to the one of a lossy non-linear dielectric. The absence of ferroelectricity is probably due to the low grain size of the obtained thick film (130 nm). Further experiments are in progress in order to try to obtain ferroelectric properties.     

Tribomechanical and microstructural properties of cathodic arc-deposited ternary nitride coatings

Sintered carbides are promising materials for surfaces that are exposed to extreme wear. Owing to their high service load, ceramic-based thin films are coated on carbides using different techniques. In this study, non-toxic and cobalt-free powder metallurgy-sintered carbide samples were coated with TiN, TiAlN, CrAlN, and TiSiN ceramic-based thin film coatings by cathodic arc physical vapor deposition. The microstructure (phase formation, coating thickness, surface roughness, and topography), mechanical properties (hardness, modulus of elasticity, and plasticity indices), and tribological properties (nanoscratch and wear behavior) of the thin film coatings were investigated. No cracks or defects were detected in these layers. The ceramic-based ternary nitride thin film coatings exhibited better mechanical performance than the TiN coating. The TiN thin film coating had the highest average surface roughness, which deteriorated its tribological performance. The ternary nitride thin film coatings exhibited high toughness, while the TiN thin film coating exhibited brittle behavior under applied loads when subjected to nanoscratch tests. The wear resistance of the ternary nitride coatings increased by nearly 9–17 times as compared to that of the TiN coating and substrate. Among all the samples investigated, the substrate showed the highest coefficient of friction (COF), while the TiSiN coating exhibited the lowest COF. The TiSiN thin film coating showed improved mechanical and tribological properties as compared to other binary and ternary nitride thin film coatings.     

铝粉对刚玉-氮化硅复合材料微观结构和性能的影响

借鉴"过渡塑性相工艺"思想,在刚玉-氮化砖复合材料中引入12.5%(质量分数)的铝粉,研究了铝粉对刚玉-氮化硅复合材料成型性能以及1 600℃空气中烧成后样品的体积密度、显气孔率和耐压强度的影响:利用X射线衍射仪和扫描电镜对材料的物相和微观结构进行了分析.结果表明:在刚玉-氮化硅复合材料中引入铝粉,有利于成型过程中孔隙...     

Crystallization—morphology—polymer processing correlations for IUPAC low density polyethylenes

The crystallization behavior of three IUPAC low density polyethylene samples has been characterized by thermal analysis. Their rates of crystallization only are directly correlatable with their film forming ability in film blowing technology. The IUPAC samples possessed essentially indistinguishable physical properties, including differential scanning calorimetry (DSC) melting curves and rheological characteristics, but their propensity for crystallization was found readily to parallel their film forming ability and other characteristics associated with end-use performance. The application of thermal analysis to assess crystallization is a unique diagnostic tool for measuring polymer film processability, which is well illustrated here using a few simple experiments made on the original polymer specimens and a polymer blend. Although all samples exhibit similar small-angle X-ray periodicities, the morphological differences assessed, particularly by microtomy-optical microscopy, correlate with, and complement, the results of phase transformation kinetics responsible for film properties. Fractography-scanning electron microscopy proves to be inferior to optical methods for revealing the morphology of these low density polyethylenes.     

二次烧结温度对牙科氧化锆陶瓷组织和力学性能的影响

研究二次烧结温度对氧化锆牙科陶瓷微观组织和力学性能的影响。方法：氧化锆亚微米粉经过干压、冷等静压成型后在1050ºC预烧结,然后将预烧结牙科氧化锆瓷块在1300ºC-1600ºC进行二次烧结。对不同二次烧结温度下材料的线收缩率、烧结密度、物相、三点抗弯强度进行测量分析,并通过扫描电镜观察试样的断面形貌。结果：结果表明随着二次烧结温度提高,氧化锆的密度、弯曲强度呈上升趋势。在1350ºC时体积密度达到6.10g/cm³,1500ºC时的机械性能最优,三点弯曲强度为852MPa,主晶相为四方相。结论：亚微米氧化锆粉体烧结活性高,力学性能优良,能够满足口腔全瓷修复材料的要求。     

Microstructure effect on field emission from tetrahedral amorphous carbon films annealed in nitrogen and acetylene ambient

Tetrahedral amorphous carbon (ta-C) films have been deposited by filtered cathodic vacuum arc technique. The samples were then annealed at various temperatures in nitrogen and acetylene ambient. The surface morphologies and microstructure of the films were characterized using atomic force microscopy, scanning electron microscopy, visible and ultraviolet Raman spectroscopy. A thin layer of amorphous carbon was deposited on the surface of the ta-C films after annealed at 700 and 800 °C while submicro crystalline pyrolytic graphite was formed on the surface of the ta-C film annealed at 900 °C. The surface layer was found to enhance the sp² clustering of the underlying ta-C layer. Field emission results reveal that the sp² cluster size plays an important role in electron field emission properties. The threshold field decreases as the sp² cluster size increases. For the film annealed at 800 °C, the lowest threshold field and the largest cluster size concurred.