Different Groups Of Materials Research Articles

Distribution of electrons and holes in cuprate superconductors as determined from17OandCu63nuclear magnetic resonance

The distribution of electrons and holes in the CuO$_2$ plane of the high-temperature superconducting cuprates is determined with nuclear magnetic resonance through the quadrupole splittings of $^{17}$O and $^{63}$Cu. Based on new data for single crystals of electron-doped Pr$_{2-x}$Ce$_x$CuO$_4$(x=0, 0.05, 0.10, 0.15) as well as Nd$_{2-x}$Ce$_x$CuO$_4$ (x=0, 0.13) the changes in hole contents $n_d$ of Cu 3d$(x^2-y^2)$ and $n_p$ of O 2$p_\sigma$ orbitals are determined and they account for the stoichiometrically doped charges, similar to hole-doped \lsco. It emerges that while $n_d+2n_p=1$ in all parent materials as expected, $n_d$ and $n_p$ vary substantially between different groups of materials. Doping holes increases predominantly $n_p$, but also $n_d$. To the contrary, doping electrons predominantly decreases $n_d$ and only slightly $n_p$. However, $n_p$ for the electron doped systems is higher than that in hole doped La$_{1.85}$Sr$_{0.15}$CuO$_4$. Cuprates with the highest maximum $T_{\rm c}$s appear to have a comparably low $n_d$ while, at the same time, $n_p$ is very high. The rather high oxygen hole content of the Pr$_2$CuO$_4$ and Nd$_2$CuO$_4$ with the low $n_d$ seems to make them ideal candidates for hole doping to obtain the highest $T_{\rm c}$.

Application of DTA-TG-MS for determination of chemical stability of BaCeO3−δ-based protonic conductors

Thermogravimetry (TG) and Differential Thermal Analysis (DTA) techniques coupled with mass spectrometry were applied to evaluate the chemical stability of BaCeO3−δ-based materials in the CO2- and H2O-rich atmosphere. The different groups of materials were investigated: solid solutions of BaCeO3–BaTiO3 and BaCeO3–BaSnO3 acceptor doped by Y or In and composite materials with nominal composition (1−x)BaCe0.9Y0.1O3−δ-xYPO4. To evaluate the chemical stability towards carbon dioxide and water vapour samples were exposed to atmosphere containing CO2/H2O (7 % of CO2 in air, 100 % RH) at temperature of 25 °C for 350 h. Thermal analysis (TG/DTA) was applied to analyse the materials before and after the test. To support the interpretation of TG/DTA results, the analysis of gaseous products evoluted during thermal treatment of the samples was provided using mass spectrometer. This combined analysis clearly shows that during the exposition test, the conversion of barium cerate to barium carbonate and barium hydroxide occurs. The amount of BaCO3 and the degree of BaCeO3−δ conversion depend on the type of barium cerate modification. The mass loss observed after the exposition test can be treated as a measure of chemical instability of BaCeO3−δ-based materials. The correlation of chemical stability, described by the mass loss, on Goldschmidt tolerance factor, describing the deviation from ideal perovskite structure, was found in most of the materials investigated. However, the influence of the microstructure and the modification the grain boundaries on the chemical stability of BaCeO3−δ-based materials cannot be neglected.

An Elastoplastic Model for Coarse Grained Soils Obeying Lade's Dilatancy Rule

This paper discussed the mechanism of dilatancy in coarse grained soils. Large-scale triaxial tests were also conducted to study the dilatancy law of coarse grained soils. Based on the results of the previous studies, it is found that plastic potential function proposed by Lade can fit the test results well. Lades dilatancy rule was then applied to a practical two-yield-surface model. Elastoplastic formula of the two-yield-surface model was also deduced in detail. The new model was verified with several groups of different materials. Results showed that this model could predict the behaviors of coarse grained soils well.

50+ years of intrinsic breakdown

The basic quantum mechanical theory for intrinsic breakdown was developed by von Hippel and Frohlich over 70 years ago, but only now can we exploit their ideas accurately through the use of computational quantum mechanics. As shown above, von Hippel's low energy criterion for intrinsic breakdown provides remarkably good agreement with measured data for a range of both ionic and covalently bonded materials. We can correlate intrinsic breakdown with both bandgap and phonon cutoff frequency, although the relationships differ for different groups of materials. The challenge going forward is to move from intrinsic breakdown to engineering breakdown through inclusion of effects caused by morphology, chemical impurities (impurity states in the bandgap), and defects such as nanocavities. We believe that inclusion of these phenomena is possible using Monte Carlo computations with parameters computed using first principles methods, and we are pursuing this approach.

Two‐body wear of occlusal splint materials

This study investigates the wear resistance of four different types of occlusal splint materials based on two-body wear simulations under wet and dry conditions. Twenty specimens of each splint material (Dentalon Plus, Orthoplast, Biocryl C, and Eclipse), each with a diameter of 16 mm and a thickness of 3 mm, were tested, half under wet and half under dry conditions. Each wear test was performed using a device called chewing simulator CS-4 (n=10; test load: 50 N; number of cycles: 10000, 20000, and 30000; continuous rinsing with 30°C water for wet conditions); the antagonists were simulated using steel balls. Wear was determined using a 3D laser scanner and a surface analysis program. To detect significant statistical differences, wear data after 10000; 20000; and 30000 cycles were compared using the Kruskal-Wallis test and the Mann-Whitney U-test. The level of significance was set at 5%. Significant differences were found between the groups of different materials tested under wet conditions (P<0.05), whereas no differences between them were found under dry conditions (P>0.05). No significant difference was found between the wet and dry conditions for all materials and cycles (P>0.05). For groups of different materials tested under wet conditions, the degree of volume loss generated in the Chewing Simulator CS-4 was found to differ significantly for different numbers of cycles. The presence of water had no effect on the volume loss in the different material groups that were tested.

Recharge pattern of contemporary glass ionomer restoratives

As glass ionomers have the ability to reload fluoride from outside sources, the aim was to compare the recharge pattern of six glass ionomer cements after exposure to fluoride. Fuji VII, Fuji IX, Riva Pink, Riva Bleach, Ketac Fil and Fuji IX Extra were investigated. The fluoride-containing materials used were tooth paste and mouth wash (Colgate). Specimens of each material (n=15) were immersed separately in deionized water for 59 days. Then the samples of each material were divided into three groups of five each. Two groups were recharged for 2, 20 and 60 min daily during three consecutive weekly intervals and then no treatment for one week. The third group was used as control. Fluoride release measurements (μg/cm(2)/day) were made in every 24 h. One-way and repeated measures analysis of variance tests were used. Tooth paste recharged materials showed higher level of recharge. On day 1, the difference of fluoride release from different treatment groups of different materials except for Fuji IX Extra were not significant (P>0.05). On days 7 and 14, the differences observed were significant (P<0.05) for all materials except for Fuji VII (tooth paste versus mouth wash) and Trial Fuji IX (mouth wash versus control) and on day 14 for Rvia Pink (mouth wash versus control). On days 21 and 28, the differences observed were significant for all the materials (P<0.05) except for Riva Pink (toothpaste versus mouth wash), Riva Bleach, Ketac Fil and Trial FujiI X (mouth wash versus control) on day 28. A time tabled schedule of application of fluoride-containing materials could help to achieve high fluoride release.

Energetic Characterization of Lignocellulosic Biomass from Southwest Spain

Different lignocellulosic biomass sources were characterized energetically along a study period of two years in Huelva (southwestern region in Spain) for energy production. Then, the different kinds of lignocellulosic biomass obtained from these sources were evaluated and classified according to use, such as fuel for electric power generation in the area. The groupings of the average moisture content values and average gross heating values (over dry basis) of the samples analyzed were made based on the type of material, and for larger groups (with a significant dispersion of the gross heating values), the average values were estimated in subgroups or “characteristic groups.” A six-cluster scheme allowed us to classify the different groups of materials. The average gross heating values of the six different clusters (raw materials) showed significant similarities. It was observed that softwood and related materials typically have values in the region of 20.0 MJ/kg, and hardwood, such as that from Eucalyptus globulus, yields about 18.0 MJ/kg, whereas other deciduous plants (and their residues) give lower values.

Indentation testing and its acoustic emission response: applications and emerging trends

This review summarises the state of knowledge on acoustic emission (AE) techniques applied to material property evaluation during indentation (e.g. hardness) testing. There are two aspects of application of AE technique to indentation which makes it unique, i.e. (1) enhancing the understanding of the evolution of material accommodation mechanisms under loading and (2) qualitative and quantitative evaluation of mechanical properties such as fracture toughness and bond strength from the AE signal. Both of these aspects have the potential to improve our understanding of the structure property relationships of current and future generation materials. In addition, the knowledge developed here can be incorporated to improve the AE based condition monitoring systems for stress critical applications. This review concentrates on the phenomena which occur during indentation and how its examination can be used to study more fundamental behaviour of materials such as deformation and fracture. The uncertainty in quantifying and measuring the total crack surface in indentation makes a simple fracture mechanics based assessment of toughness difficult. It is therefore expected that correlation between AE and fracture patterns will lead to an improved method for material’s quality evaluation. The main part of this review is presented on AE of material classifications. These classifications include ceramics, glasses, composites, metals and metallic foams, thin solid films and thermally sprayed coatings. Apart from quasi‐static indentation testing, attention has also been paid to studies on various AE instrumented indentation systems so that information can be derived about the progress of deformation and cracking processes. This review discusses the studies summarising those aspects that have so far been established and the areas of controversy and/or lack of knowledge. The prospect of using AE techniques to monitor indentation tests is also assessed, taking into account those few studies that have been reported so far in different groups of materials. Although with some limitations, it is concluded that AE monitored indentation testing has considerable scope to assess in much more detail the deformation and cracking properties of materials under localised stress condition. It is possible to construct empirical relationships and develop theoretical understanding linking mechanical parameters with AE signal characteristics and its derived features. However, the occurrence of multiple events at different locations superimposing the AE signal requires more advanced signal processing techniques. With the advancement of very thin films and nanomaterials, it is anticipated that AE response measured during nanoindentation will be critical for enhancing our understanding of future generation applications, as it allows individual events to be investigated without resorting to more complex signal processing techniques. In terms of material accommodation, the understanding of physical mechanisms generating AE require a multiscale approach, e.g. correlations exist between fracture and sudden release of AE energy, dislocations and Bremsstrahlung and Frank–Reid sources, and maternsitic phase transformation with rapid variation in the shape of deformation volume generating AE exist; however, integration of continuum elastic–plastic and molecular dynamics models is necessary to enhance our understanding of the physical mechanisms generating AE response. This multiscale approach can be further helped by the experimental data using AE instrumented nanoindentation as it allows very localised and fine scale measurement in load or displacement control.

δ18O and chemical composition of Libyan Desert Glass, country rocks, and sands: New considerations on target material

– Oxygen isotope and chemical measurements were carried out on 25 samples of Libyan Desert Glass (LDG), 21 samples of sandstone, and 3 of sand from the same area. The δ18O of LDG samples range from 9.0‰ to 11.9‰ (Vienna Standard Mean Ocean Water [VSMOW]); some correlations between isotope data and typological features of the LDG samples are pointed out. The initial δ18O of a bulk parent material may be slightly increased by fusion due to the loss of isotopically light pore water with no isotope exchange with oxygen containing minerals. Accordingly, the δ18O of the bulk parent material of LDG may have been about 9.0 ± 1‰ (VSMOW). The measured bulk sandstone and sand samples have δ18O values ranging from 12.6‰ to 19.5‰ and are consequently ruled out as parent materials, matching the results of previous studies. However, separated quartz fractions have δ18O values compatible with the LDG values suggesting that the modern surface sand inherited quartz from the target material. This hypothesis fits previous findings of lechatelierite and baddeleyite in these materials. As the age of the parent material reported in previous studies is Pan-African, we measured the δ18O values of bulk rock and quartz from intrusives of Pan-African age and the results obtained were compatible with the LDG values. The main element abundances (Fe, Mg, Ca, K, Na) in our LDG samples conform to previous estimates; Fe, Mg, and K tend to be higher in heterogeneous samples with dark layers. The hypothesis of a low-altitude airburst involving silica-rich surface materials deriving from weathered intrusives of Pan-African age, partially melted and blown over a huge surface by supersonic winds matches the results obtained.

Measurement and Compensation of Spring-back of a Hybrid Composite Beam

Fiber-reinforced composite materials have been advanced in various applications for their excellent mechanical and electromagnetic properties. On their manufacturing processes, however, thermo-curing inherently produces the undesired thermal deformation, so-called spring-back, mainly caused by temperature drop from the process temperature to room temperature. In order to fabricate designed part geometry, the spring-back must be understood especially in hybrid composites consisting of distinct groups of different materials. In this research, the spring-back of a hybrid composite beam is measured by a series of experiments, and is predicted by the classical lamination theory (CLT) and finite element analysis (ANSYS). To confirm the predicted spring-back, {glass fiber/epoxy} + {carbon fiber/epoxy} asymmetric hybrid composites are fabricated under various conditions such as cure cycle, laminate thickness, stacking sequence, and curing sequence. The results from CLT and FEA agree well with the experimental data, but the spring-back cannot be removed completely. To fabricate flat hybrid composite beams, a web-based spring-back compensation service is developed. The CLT-based code allows the user to predict spring-back and to fabricate a mold that compensates spring-back.

The development of a UK kerbside scheme using known practice

Local authorities in the UK have been set challenging new targets for recycling household waste for 2003/4. This means many of them are urgently trying to determine which parameters in kerbside schemes are most important for increasing recycling rates. In this work information from previous kerbside schemes was used to plan significant improvements in an existing scheme in Horsham District, UK, and a trial was conducted using 1000 homes including a control group. It used fortnightly collection of residual waste with sets of recyclables collected on alternate weeks. The new scheme resulted in improvements of participation rates from 72 to 84%, and set-out rates from 45 to 59% (falling to 76 and 50% respectively, some months later). Details on participation and set-out for different groups of materials are given, as well as levels of excess waste and participation in the collection of garden waste.

Ion-induced photon emission under nanoparticle fabrication

Metal-ion implantation is well established as a suitable technique for fabrication of nanoparticles embedded in insulators. Photon emission induced by 60 keV Cu − incident ion was in situ measured over a wavelength range from 200 to 900 nm. Special attention was paid to the behavior of the Cu I atomic line emission related to the mass transport of implants. Based on comparison of experimental results for the wide band gap materials (SiO 2 and MgAl 2O 4) with those for metals (W, Mo, Al), it is concluded that, at the beginning of ion bombardment, the radiation is mostly emitted by backscattered atoms. The causes of this are different for the different groups of materials: the high backscattering yield in the case of metals and the high survival probability of the excited backscattered atoms in the case of insulators, when the excitation levels lie below the conduction band edge and the radiative decay is only the available channel for deexcitation. Significant contribution in the Cu I line intensity was observed with increasing dose due to sputtered Cu atoms.

Reference Free Part Encapsulation (RFPE): An investigation of material properties and the role of RFPE in a taxonomy of fixturing systems

Abstract The Reference Free Part Encapsulation (RFPE) method is a workholding system designed to “free up” the design space and greatly expand the possible range of parts that can be designed and then machined. Despite the increased capability of the RFPE technique, part warpage and debonding during RFPE have not yet been sufficiently documented. To address these problems, a set of experiments was conducted. The first test was designed to find a RFPE fixturing material with preferred thermomechanical properties for a given workpiece. Three different groups of materials were tested: (1) fusible alloys such as BiSn and BiSnZn, (2) thermoplastic polymers called Rigidax®, and (3) fixturing waxes. In the second test, the effect of preheating the workpiece for better interfacial shear strength and the effect of adding aluminum powders to the WI-Green Rigidax were examined. These processing conditions and composite materials allow manufacturing engineers to design, process plan, and fixture parts of complex geometrical shapes. A taxonomy of various fixturing systems is presented in this paper to describe the characteristics of RFPE relative to other fixturing methods.

Fullerene-Based Organic−Inorganic Nanocomposites and Their Applications

The development of new materials based on the novel and unique properties exhibited by the family of fullerenes is attracting growing interest from materials scientists. As the progress of the studies discloses new properties and basic knowledge is better established, three main fields are emerging in the preparation of materials from fullerenes: fullerene thin films, organic polymeric materials that contain fullerene molecules, and the incorporation of fullerenes and their derivatives in inorganic host matrixes to fabricate organic−inorganic nanocomposites. This last family of materials, in particular, opens several interesting perspectives for different applications, especially in nonlinear optics and photoelectrochemistry. Fullerene organic−inorganic nanocomposites have been prepared using porous media as a host matrix and different groups of materials synthesized via sol−gel, such as aerogels, porous inorganic oxides, and hybrid and mesoporous materials. Nanocomposite materials developed from fullerenes in inorganic host media are the objects of the present review.

Effect of molecular structure on dynamic mechanical properties of polyethylene obtained with nickel–diimine catalysts

Polyethylene made with a nickel–diimine catalyst was studied in order to understand the relationship between molecular structure and dynamic mechanical properties. Different branch lengths, from methyl to longer, and their contents in these ethylene homopolymers, dramatically affects the crystallinity of these polyethylene samples, as shown by differential scanning calorimetry (DSC) and crystallization analysis fractionation (CRYSTAF). Tm and CRYSTAF profiles are related not only to the branch content but also to the distribution on the chain. The dynamic mechanical thermal analysis showed three different groups of materials, where the stiffness varies according to the short-chain branching (SCB) content. Polyethylenes with high SCB showed a strong β-transition (tanδ>1) despite the lack of any detectable crystallinity.

Identification of Solid Materials by Correlation Analysis Using a Microscopic Laser-Induced Plasma Spectrometer

The primary goal of this work was the instant identification of solid materials on the basis of spectral libraries stored in a computer using laser-induced plasma spectroscopy. The libraries were obtained prior to analysis and consisted of representative spectra from different groups of materials to be analyzed. Special attention was paid to identification of samples with very similar chemical composition, such as certain series of stainless steel and cast iron standards. Both linear and rank correlation methods were applied. Rank correlation proved to be more reliable, yielding probability of correct identification close to unity for almost all studied samples. This technique should have applications in the metallurgical, mineralogical, and semiconductor industries and in medical and forensic sciences.

Parameterstudie an metallographischen Schliffproben mit der lonenätzanlage RES 010 / A Study of the Parameters for Etching Metallographical Specimens in the RES 010 Ion Beam Unit

A systematic study of the parameters used for ion beam etching metallic materials was carried out in order to optimize the process. When etching the metallographically prepared specimens the extent of the etched area and the intensity by which the sample is attacked depend on voltage, current, and time set as well as on the material to be etched. The three parameters were varied for different groups of materials like steels, copper and a copper alloy, an aluminium alloy and titanium. The results reveal a correlation between the trial conditions and the etched microstructure of the materials documented by optical light microscope photographs.

Rationale for composition-specific ageing schedules for particle-reinforced metal-matrix composites

Optimised age-hardening treatments are vital if aluminium-based particle-reinforced metal-matrix composites (PRMMCs) are to achieve widespread use as an engineering material. This paper shows that for some PRMMCs ageing may not be optimised, and suggests why this is the case. Composites of a 7 xxx-series aluminium alloy containing a number of volume fractions of SiC were investigated. On ageing, the materials were found to fall into two groups: (i) the 10% SiC composite, which followed an ageing sequence similar to the unreinforced alloy, and (ii) those containing greater than 15% SiC, which followed a different sequence. The implication of this work is that substantially different ageing schedules need to be devised for the two different groups of materials if the full potential of age-hardenable composites is to be realised in the higher volume-fraction materials.

Fatigue Crack Growth Rate of Metal by Plastic Energy Damage Accumulation Theory

The fatigue crack growth phenomenon is analyzed by means of postulated damage accumulation theory herein. By considering the plastic component of J integral as a damage factor, the proposed damage accumulation theory successfully leads to a simple formula for the fatigue crack growth rate. This formula covers all three regions of the fatigue crack growth rate and shows a high potential in future application to different groups of materials. This research yields the following results: (1) The crack growth rate is not simply a function of ΔK, but a function of average local yielding strength, fracture toughness, and amplitude of the applied effective stress intensity factor in regions II and III; (2) the behavior of the fatigue crack growth rate (FCGR) near the threshold value is found to be dominated by maximum value of applied effective stress intensity factor instead of its amplitude; (3) the onset instability value of ΔKc is a specimen geometrical‐dependent parameter; and (4) the average yielding local ...

Solid lubricants for applications at elevated temperatures

Relative motion between mating surfaces at elevated temperatures often causes substantial material degradation due to friction and wear. Conventionally, solid lubricants have been used to reduce wear damage and friction drag under extreme conditions where liquid lubricants do not function properly. The recent trend towards higher operating temperatures in advanced power generating systems, i.e. turbomachinery, gas turbines, and hot adiabatic diesel engines, has imposed severe limitations on the currently available solid lubricants. The unusually aggressive conditions in these systems phased out most conventional solid lubricants and gave impetus to the search for more efficient materials. This paper discusses the lubricating characteristics of four different groups of materials known to provide lubricity under elevated temperature conditions. These groups are polymers, laminar solids, metal fluorides and metal oxides. Polymer lubricants are efficient lubricants within the range from room temperature to about 300 °C. Laminar solids extend that range to about 450 °C. Graphite, also a laminar solid, is an exception since it can offer excellent lubricity beyond 450 °C in the form of gaseous oxidation products. Stable fluorides and metal oxides are useful lubricants between 500 and 1000 °C, though their performance is rather poor at lower temperatures.