Showing papers in "Materials Research Innovations in 1997"

Relaxor based ferroelectric single crystals for electro-mechanical actuators

Abstract: The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn1/3Nb2/3)O3−PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O3−PbTiO3 (PMN-PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O3 (PZTs), morphotropic phase boundary (MPB) compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d33’s ) >2200 pC/N and subsequent strain levels up to >0.5% with minimal hysteresis were observed. Crystallographically, high strains are achieved for oriented rhombohedral crystals, though is the polar direction. Ultrahigh strain levels up to 1.7%, an order of magnitude larger than those available from conventional piezoelectric and electrostrictive ceramics could be achieved, possibly being related to an E-field induced phase transformation. High electromechanical coupling (k33) >90% and low dielectric loss <1%, along with large strain make these crystals promising candidates for high performance solid state actuators.

Microwave processing of WC-Co composities and ferroic titanates

Abstract: The innovations in microwave processing of ceramics have been dominated to date by serendipitous discovery, because the interaction between such radiation as delivered via available tools and the materials of widely varying properties, sizes, and shapes is so complex that it has defied quantitative analysis. For over 10 years a wide variety of inorganic ceramic and semiconducting materials have been synthesized, sintered, and reacted in our own labs, including microwave hydrothermal synthesis of metals, ferrites, and electroceramic phases. These local results are summarized and used as the reference point for reporting on two different new advances: sintering of WC-Co composite tool bits and other similar objects in under 15 min, while retaining extremely fine microstructures, without any grain growth inhibitors; using reduced TiO2 or Ta2O5 for the synthesis of phases such as BaTiO3, Ba3MgTa2O9, and Pb(Zr.Ti)O3 in a few minutes in a 2.45 GHz field at the astonishing temperatures of 300–700 oC.

Cellulose derived composites—A new method for materials processing

Abstract: This research demonstrated for the first time a method for producing net shape polymer, ceramic and carbon composites using wood as a precursor. The conversion of wood to carbon has been practiced for centuries but the controlled thermal decomposition to form a monolithic carbon to be used as a template for composites as demonstrated by this research is a unique discovery. This was accomplished by thermal decomposition of wood under controlled conditions to produce a crack-free porous carbon monolith which was readily shaped by conventional methods. The shaped carbons have converted to carbon/polymer composites, carbon/carbon composites, ceramics, and ceramic composites without significant changes in dimensions. This research has demonstrated that composites derived from wood can eliminate several expensive processing steps. Specifically, no fiber lay-up or powder consolidation is required, and final grinding and polishing steps are minimized.

Phase transformations in materials studied by micro-Raman spectroscopy of indentations

Abstract: Phase transformations occurring in materials under high pressures are important for a wide range of problems in materials science and solid-state physics. Most of the results in this area have been...

Microwave enhanced reaction kinetics in ceramics

Abstract: &p.1: Numerous observations have been reported in the literature of enhanced mass transport and solid-state reaction rates during microwave heating or processing of a variety of ceramic, glass, and polymer materials. These empirical observations of microwave enhancements have been broadly called the “microwave effect”. In the past, these claims have been the source of significant controversy, due in part to the lack of a credible and verifiable theoretical explanation. Moreover, certain notable microwave heating experiments have failed to observe any resolvable reaction or transport rate enhancements. This paper describes a series of recent experimental and numerical investigations that have established the fact that strong microwave electric fields induce a (previously unknown) nonlinear driving force for (ionic) mass transport near surfaces and structural interfaces (e.g., grain boundaries) in ceramic materials. This driving force can influence reaction kinetics by enhancing mass transport rates in heterogeneous solid-state reactions. Most of the previously reported observations regarding “microwave effects” (both for and against) are consistent with the characteristics of this newly identified microwave-induced driving force. &kwd: Microwave processing · Microwave effect · Ponderomotive force · Ionic transport · Nonthermal · Sintering&bdy:

Chemical and physical ”hardness”

Abstract: A common theme links chemical, mechanical, and optical hardnesses. It is the gap in the bonding energy spectra of materials. This gap determines molecular stability, and therefore ”chemical hardness”. Chemists call it the LUMO-HOMO gap between anti-bonding and bonding molecular orbitals. Physicists call it the band-gap between the conduction and valence energy bands. It forms a basis of various properties; including: chemical reactivity, elastic stiffnesses, plastic flow resistance (dislocation mobility), crystal structure stability, and optical polarizability (refractive indices). These unifying relationships are the subject here. Manipulation of these gaps and their cross-connections plays a critical role in current technology and has led to recent new devices.

Sculptured thin films—I. Concepts

Abstract: A report on the conceptualization of sculptured thin films (STFs), as well as on recent theoretical advances thereon, is presented. The morphology of a STF is described in terms of a spatially varying unit vector called the director, whose piecewise specification assists in setting up frequency-dependent constitutive relations of the STF. These relations lead in turn to a 4×4 matrix differential equation for the propagation of electromagnetic waves in the STF. Optical, suboptical, infrared and even millimeter-wave applications are possible, as well as acoustic and piezoelectric ones.

New applications of photostrictive ferroics

Abstract: Photostriction in ferroelectrics arises from a superposition of photovoltaic and inverse piezoelectric effects. (Pb,La)(Zr,Ti)O3 ceramics doped with WO3 exhibit large photostriction under irradiation of near-ultraviolet light, and are applicable to remote control actuators and photoacoustic devices. Using a bimorph configuration, a photo-driven relay and a micro walking device have been developed, which are designed to start moving as a result from the irradiation, having neither electric lead wires nor electric circuits. The mechanical resonance of the bimorph was also induced by an intermittent illumination of purple-color light; this verified the feasibility of applying photostriction for ”photophone” applications.

Inventory on innovative research: the case of C3N4

Abstract: Two prominent examples of the interaction between predicting and failing to synthesize new inorganic materials include metallic hydrogen and the so-called ”harder than diamond” form of C3N4. In both cases there has been much speculation and calculation but years of experimentation have failed to produce the desired phases, and the intriguing interplay continues. This note is a brief appraisal of the status of the claims regarding C3N4 made by counting and analyzing published papers on the topic, in an attempt to inventory and evaluate ”innovative research” on materials.

Standard free energy change of formation per unit volume: a new parameter for evaluating nucleation and growth of oxides, sulphides, carbides and nitrides

Abstract: The present paper introduces a thermodynamic parameter, the standard free energy changes of formation of oxide, sulphide, carbide and nitride per unit volume, as a criterion for comparing the formation tendency of these compounds. The diagrams for the standard free energy change of formation of common oxides, sulphides, carbides and nitrides per unit volume vs temperature have been calculated and established based on the available thermodynamic data. It is believed that these diagrams can provide better explanations to some oxidation phenomena including the effects of reactive elements on the selective oxidation of Cr2O3 and Al2O3.

Evidence for fullerene in a coal of Yunnan, Southwestern China

Abstract: In two types of coal from a coal mine in Yunnan Province, Southwestern China, the presence of fullerene is confirmed. The fullerene had been suggested earlier by its characteristic infrared absorption spectrum. The present work reports verification by a high performance liquid chromatograph. A critical step leading to the confirmation is in the process of preparation of the liquid solution from the coal for chromatography and this is described. Possible conditions for the search of natural fullerenes are suggested.

Fabrication and characterisation of neodymium-doped silica glass by sol-gel process

Abstract: &p.1: Neodymium-doped silica glass possesses many properties ideal for high-power laser applications. These include low thermal expansion coefficient, high temperature stability, and low nonlinear index of refraction. For the first time, the sol-gel process has been successfully employed to prepare highly doped neodymia silica glass, up to 5wt% Nd for homogeneous dopant distribution. The optical characteristics of the silica glass and its in-process gel, including the UV/VIS absorption spectra, infrared absorption spectra, fluorescence emission spectrum and the fluorescence lifetime, are measured and analyzed. The structure of the sample is also characterized by means of XRD and SEM. A porous gel is observed to have formed when the heat treatment temperature reaches 300oC. Wavelength shifts in the absorption peak corresponding to the 4 I9/2 to 4 F5/2 transition have been observed during the densification process and for different Nd weight contents. The FTIR spectra have shown that high temperature heat treatment can greatly reduce the amount of OH groups and organic residue in the silica. We have also shown that a high OH content contributes to weak fluorescence intensity and short fluorescence lifetimes. &kwd: Sol-gel process · Rare-earth glass · Silica glass&bdy:

New rapid diamond synthesis technique; using multiplexed pulsed lasers in laboratory ambients

Abstract: QQC, Inc. has developed a revolutionary diamond deposition technique which does not require a vacuum, or H2, or ”chemical” or physical pre-treatment of surfaces. The process utilizes a combination of various pulsed lasers and is performed at the laboratory p−t conditions: with CO2 and N2 as shrouding gases. Crystalline diamond films and DLC or, more accurately, tetrahedral non-crystalline carbon (TNC) have been formed on various substrates. On WC cutting tools the rate of deposition of crystalline diamond is approximately 1 µm/sec. In the context of fabricating a diamond coating on a substrate, the entire pre-surface treatment and material synthesis process including a coating regime, is performed in one step.

Innovation in non-contact ultrasonic analysis: applications for hidden objects detection

Abstract: This paper describes unusual applications of ultrasound that are based upon recent advances in transduction efficiency in air and gaseous media. Piezoelectric transducer devices – capable of generating extremely high intensity ultrasound in ambient air up to 5 MHz – have been successfully developed and tested. This is in addition to the obvious uses for gas analysis, remote sensing, liquid level, gap, and thickness measurement, and proximity analysis. These new generation transducers make it possible to analyze solids and liquids not only non-destructively, but also without physically contacting the test sample. Among various applications to the non-destructive characterization (NDC) of industrial materials, we also describe the feasibility of a forensic application. This concerns the detection of objects such as knives, guns, contraband drugs, dead bodies, etc., hidden inside false compartments or walls.

Biomaterials innovation: it’s a long road to the operating room

Abstract: An innovative process for forming a wide variety of porous biomaterials was conceived of and developed over several years at a University and later by a company that licensed the early patents. The family of patents formed the basis for several promising innovative biomaterials devices. However, only one commercial product has been realized. That product is the very successfull coralline hydroxyapatite (HA) now widely used in orthopaedic surgery, oral and maxillofacial bone repair and plastic surgery. This paper challenges the equation of discovery with a genuine innovation which reaches the marketplace. The paper reviews several aspects of the innovation and development history with an emphasis on the challenges of bringing any new biomaterial through all the conceptual, developmental, business and regulatory hurdles. New class three medical devices require huge investments of time and money typically requiring a minimum of eight years and 15–20 million dollars per new device to take it from concept to an approved product. These hurdles are so high that most research innovations in biomaterials never get put into the developmental pipeline. This paper is presented from an anecdotal perspective of an innovator who has had a continuous research and development involvement in the technology but has no significant management involvement beyond the early startup activities. It differs from predecessors is that it deals not only with the initial step of discovery but in the very difficult steps that follow on the road to a real innovation. Several strategies that may help other R&D groups outside the biomedical industry shorten the development cycle and increase the probability that a given biomaterials innovation can be seen through to approved product are discussed. Guidelines are suggested for culling out ideas that are technically sound but that likely won’t lead to successful products.

The steady-state temperature as a function of casket geometry for microwave-heated refractory caskets

Abstract: This study demonstrates experimentally that for a fixed microwave input power, the steady-state temperature for microwave ”caskets” (specimen enclosures) can vary significantly as the casket geometry changes. Also, the steady-state casket temperatures are very similar for caskets with and without an included specimen, as long as the specimen’s volume and mass are small compared to the casket’s volume and mass. In addition to the experimental work, a simple model is presented that describes the variation in steady-state temperature as a function of casket geometry. The model also describes how the steady-state casket temperature scales with microwave input power level. For the single-mode microwave cavity operated at 2.45 GHz that is used in this study, the steady-state casket temperature at 600 Watts of input power ranged from 1112°C to 1519°C as the casket geometry changed for caskets composed of porous zirconia cylinders with aluminosilicate end pla tes.

Precipitation of diamond from MexCyHz solutions at 1 ATM

Abstract: We describe herein a new process for the synthesis of diamond in the presence of various metals and atomic H in a microwave plasma. Along with the traditional high pressure high temperature (HPHT) process and the chemical vapor deposition (CVD) process, for diamonds synthesis this makes it a third route for this purpose. Starting materials used are intimate mixtures of various forms of carbon with one of many metals. These are exposed to a pure H2 microwave-assisted plasma at temperatures in the range 600–1100o C. Novel amorphous alloys are formed containing 40 to 70 atomic percent of carbon. From these liquid alloys diamonds are precipitated with temperature change and/or with possible evaporation of complex, hydrogen-rich Me−C−H species. The carbon content of the metallic liquid drops sequentially down to 5–6%C as more and more diamonds are precipitated therefrom. Au, Ag, Fe, Cu, Ni, and many other metals are used in most runs. Others e.g. La, Mn, Sn, each give distinctive habits or morphology to the diamonds grown. Single crystals have been grown from these MexCyHz metallic liquids on natural diamond substrates, using the same low pressure solid state source (LPSSS) technique. They show high perfection. A mechanism is proposed quite analogous to the HPHT process, to explain this precipitation from metallic solutions, with atomic hydrogen ”substituting” for high pressure.

Production of a functionally graded artificial tooth root by unique sequence of processes

Abstract: A unique sequence of processes is used to produce a prototype of a functionally graded artificial tooth root: (1) Dry-jet spraying of the mixture of Ti and Al2O3 ultrafine particles (UFPs) produced by radio-frequency plasma onto the surface of a cylindrical Ti rod, where the composition of the UFPs is changed gradually in the outward radial direction from Ti to Al2O3; (2) Temperature-gradient sintering of the deposited composite, where the Ti – and the Al2O3– rich sides are heated simultaneously at about 1400 K and 1800 K, respectively; (3) Plasma spray coating of hydroxyapatite (HAP) onto the outermost Al2O3 surface of the sintered composite. The final product has compressive strength of more than 200 MPa and is durable against fatigue test of 107 stress cycles at 1000 N. The adhesion strength between the Ti substrate and the Ti-Al2O3 functionally graded layer exceeds 65 MPa. No contamination with heavy metals is detected throughout the processes and biological cell growth is confirmed to occur on the HAP surface. With these mechanical and biochemical properties the composite produced here is considered to be highly suitable for an artificial tooth root. A series of processes developed here are expected to be applied to the production of various kinds of fine-grained functionally graded materials with complicated forms.

Microstructure and mechanical properties of Y2O3/SiC nanocomposites

Abstract: Y2O3-based nanocomposites were fabriacted by hot-press and the microstructures and mechanical properties were investigated. Transmission-electron-microscope observations revealed that the SiC particles were distributed both within Y2O3 matrix grains and at the grain boundaries. Significant mechanical properties improvements were identified particularly at high temperatures above 1000 oC both in air and inert atmospheres.

Innovation in diamond

Abstract: This historical review of the progress of innovation in diamond research is discussed comparing it with the history of other materials. The innovation steps in current diamond technology are shaped by the fact that diamond is a functional material. This series of innovations was mainly brought about by the discovery of CVD methods of synthesizing diamond from the gas phase. Many kinds of expected applications have been proposed. Success in demonstrating diamond electronic devices has been achieved, and atomic scale observations on diamond growth are reported. Thus, even atomic scale control in synthesizing diamond looks quite realistic in the near future. Although such new data enhance the applications of diamond, most industrial applications of diamond still rely on its hardness. Innovation with diamond will be accelerated when a product using diamond as a functional material is used widely.

TEM observations of void-lobed defects and the origin of stringers in copper rod and drawn magnet wire

Abstract: Utilizing transmission electron microscopy (TEM), we have discovered a defect, which we call a void-lobed defect, in copper precursor rod and in sections of failed copper magnet wire. This defect is the origin of, or basis for, stringers or stringer defects in copper rod and wire, and consists of a contaminated, solidified copper microdroplet which is entrained in the solidifying rod, and is disconnected at its ends in the rod drawing direction, forming voids and elongated void lobes at the ends of the copper inclusion. Utilizing a novel technique to build up fine wires by copper electroplating, we have followed their progress in the magnet-wire drawing process using TEM. Detailed examination of wire failures showed that these defects are forced to the wire axis by successive drawing stages forming coalesced void/debris channels which provide a mechanism for failure. There was no evidence for copper oxides either as stringer components or in connection with debris channels in failed wires. These defects and therefore stringers in precursor rod are created as contaminated or reacted ”copper rain” prior to the solidification stage, and entrained in the rod. The process is usually intermittent and may be reduced or eliminated by properly adjusting the equilibrium chemistry through hydrogen control for oxygen reduction and steam formation; thereby producing high-quality rod for magnet wire produciton. This is an extraordinary example of TEM application in the solution of a contemporary industrial problem which has been otherwise intractable.

Gas permeability in the polystyrene films uniaxially drawn under CO2 plasticizing

Abstract: Gas permeability coefficients, Ps, of CO2, O2, and N2 have been measured in four kinds of polystyrene (PS) films: an unconditioned film with no orientation (1), a high pressure CO2-conditioned film with no orientation (2), an uniaxially hot-drawn film with some orientation (3), and a film uniaxially drawn under CO2 plasticizing with some orientation (4). Wide angle X-ray diffraction (WAXD) scans for each sample have also been made. High-pressure CO2-conditioning effect was confirmed from the result that P values for any permeation gas in sample 2 were larger than those in sample 1. Values of P for any gas in sample 3 were almost close to those in sample 1 and decreased slightly with Hermans orientation function, f. Gas permeability coefficients in sample 4 are larger than those in sample 3 over the whole range of f studied in this work and increased with f. These results were discussed from a viewpoint of inter-segmental distances for PS films.

Metals with structural vacancies: prediction of radiation stability

Abstract: A solution to the problem of radiation stability of metallic materials for nuclear power reactors is suggested. It is by selecting and creating alloys with structural (unhealable) vacancies, whose concentration is determined precisely by the stoichiometry of alloys, but being independent of temperature and any other external influences. The advantages as well as difficulties arising from the technical application of radiation stable alloys proposed are considered.

Reverse ulta-microtomy: a new method of TEM sample preparation

Abstract: Two variations of a new method of TEM metal sample preparation are proposed, hereby labeled RUM1 and RUM2, for ”reverse ultra-microtomy” 1 and 2, respectively. With these techniques, the TEM samples are formed from bulk specimens by successively slicing off layers, with an ultra-microtome, until the remnant is partially thinned to electron transparency. This requires the sample to be embedded with excellent adhesion in a mounting material whose mechanical properties resemble that of the sample. While these methods are by far slower than ordinary microtomy wherein the individual slices are used as samples, preparation times are comparable to those for creating TEM samples by standard techniques. Furthermore, the methods (i) can be used where electropolishing fails, (ii) can be favorably applied to finely layered materials and composites, (iii) permit studies of near-surface structure gradients, and (iv) permit the simultaneous observation of an original surface and the underlying material. The methods have been successfully demonstrated through comparisons between samples created through RUM1 and 2 and standard TEM samples. Artifacts caused by the new method of reverse microtoming are shown to be very much reduced compared to direct microtoming.

A novel application of atomic force microscope to identify the Ag and I planes of β-AgI single crystals

Abstract: Atomic Force Microscopy is used to determine the crystallographic polarity of the surfaces of β-AgI single crystals. The studies reveal that the hexagonal packed Ag+ plane is the (001) and the I– plane is the (001–). This observation is also consistent with the earlier x-ray diffraction measurements and chemical etching techniques as well as the polarizability and electronegativity of the ions.

A hot-pressed PLZT under DC bias for field-stabilized pyroelectric detector applications

Abstract: The temperature dependence of the pyroelectric response of a hot-pressed PLZT (lead lanthanide zirconate titanate) (9.5/65/35) under a modest dc electric bias field has been investigated in an assessment of the performance of this material for applications in small-area pyroelectric devices. A strong pyroelectric response has been induced in the material at and above its transition temperature by the application of an electric field. The electrical resistivity, relative dielectic constant, loss tangent, ferroelectic hysteresis, and pyroelectric coefficients are reported. The material shows a very high figure of merit for a dielectric bolometer application that is competitive with existing relaxor ferroelectric materials such as Pb(Mg1/3Nb2/3)O3 (PMN) and Pb(Sc1/2Ta1/2)O3 (PST).

Microstructural characteristics of alumina-based composite prepared by in situ reaction of alumina-silicon carbide-nickel system

Abstract: In situ reaction of nickel and silicon carbide has been attempted to prepare alumina-based composites containing some kinds of dispersed phases. The composites were fabricated by reducing and sintering of Al2O3/NiO/SiC mixtures. Reaction products (Ni3Si and C) and metallic Ni were found to disperse at the matrix grain boundaries, while Ni was partly trapped into Al2O3 grains. In addition, carbon nanoballs encapsulating Ni3Si were produced and dispersed in the composites. The carbon cages were approximately 80–100 nm in diameter with polyhedral shape, and had lattice spacing of 0.35 nm that was typical for the graphite. Encapsulated Ni3Si had facet planes which were parallel to the carbon layers surrounding. Production of metal encapsulated carbon nanoball within ceramic materials is the first successive result that might promote researches on such novel ceramic composites.