Powder Processing Technique Research Articles

Development of low loss Mn–Zn ferrite working at frequency higher than 3 MHz

With the advance of modern electronic technology, there has been a critical need for Mn–Zn ferrites with even higher permeability and even lower power loss at higher frequencies. In this study, ferrite with extremely low losses than conventional ferrite materials at high frequency was developed employing a conventional ceramic powder processing technique. As a result, the core loss at 3 MHz, 10 mT and 100 °C is around 300 kW/m 3, and its cutoff frequency is 4 MHz. Furthermore, the electromagnetic characteristics and the microstructure of this new DMR50 material are also discussed.

Low Dielectric Loss PTFE/CeO2 Ceramic Composites for Microwave Substrate Applications

Cerium oxide (CeO2) filled polytetrafluoroethylene (PTFE) composites prepared by powder processing technique for microwave substrate application is presented in this paper. The PTFE is used as the matrix and the dispersion of CeO2 in the composite is varied up to 0.6 by volume fraction, and the dielectric properties were studied at 1 MHz and microwave frequencies. The relative permittivity and dielectric loss increased with increase in CeO2 content. For 0.6 volume fraction loading of the ceramic, the composite has ɛr of 5 and tan δ of 0.0064 at 7 GHz. Different theoretical approaches have been employed to predict the effective permittivity of composite systems and the results were compared with that of experimental data. The serial mixing model shows good correlation with the experimental results.

Thermal properties of polytetrafluoroethylene/Sr2Ce2Ti5O16 polymer/ceramic composites

AbstractPolytetrafluoroethylene (PTFE) composites filled with Sr2Ce2Ti5O16 ceramic were prepared by a powder processing technique. The structures and microstructures of the composites were investigated by X‐ray diffraction and scanning electron microscopy techniques. Differential scanning calorimetry showed that the ceramic filler had no effect on the melting point of the PTFE. The effect of the Sr2Ce2Ti5O16 ceramic content [0–0.6 volume fraction (vf)] on the thermal conductivity, coefficient of thermal expansion (CTE), specific heat capacity, and thermal diffusivity were investigated. As the vf of the Sr2Ce2Ti5O16 ceramic increased, the thermal conductivity of the specimen increased, and the CTE decreased. The thermal conductivity and thermal expansion of the PTFE/Sr2Ce2Ti5O16 composites were improved to 1.7 W m−1 °C−1 and 34 ppm/°C, respectively for 0.6 vf of the ceramics. The experimental thermal conductivity and CTE were compared with different theoretical models. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Approaches to the Design and Processing of Novel Titanium Alloys

The range of commercial titanium alloys available is currently extremely restricted, with one alloy (Ti-6Al-4V), and derivatives of it, accounting for a very large proportion of all applications. High performance alloys are costly to fabricate and limited to low-volume applications that can sustain the cost. With the emergence of new processing technologies that promise to reduce significantly the cost of production of titanium metal, especially in powder form, there is an emerging imperative for cost-effective near net shape powder processing techniques to permit the benefit of reduced metal cost to be passed on to higher-volume applications. Equally, there is a need for the design and development of new alloys that are intrinsically low-cost and lend themselves to fabrication by novel cost-effective net shape processing. The approaches that might be used to select, design and process both conventional alloys and novel alloy systems will be reviewed, with a focus on innovation in design of low-cost alloys amenable to new processing paths and increasingly tolerant of variability in composition.

Characterization of dry milled powders of LAST (lead–antimony–silver–tellurium) thermoelectric material

Although thermoelectric (TE) materials are often fabricated as cast ingots, there has been recent interest in the powder processing of these materials. Cast TE materials typically have grain sizes as large as several hundred microns, but powder processing (grinding, milling and then sintering) can produce dense specimens with a reduced grain size, an improved mechanical integrity and enhanced TE properties. In the TE literature when powder processing is employed, little or no description is provided of the powder processing techniques and the powder processing parameters are either not characterized or only a mean particle size is given. In this study, powders milled from solid cast ingots of the TE compound LAST (lead–antimony–silver–tellurium) were characterized via Coulter Counter, to measure the mean powder particle size and the size distribution, scanning electron microscopy (SEM), to examine the powder particle morphology, and X-ray diffraction (XRD), to detect possible phase changes or amorphization. The impurity levels in the milled powders were examined by wear rate measurements on the milling media, as well as by energy dispersive X-ray analysis and inductively coupled plasma measurements.

Low Dielectric Loss Polytetrafluoroethylene/TeO2 Polymer Ceramic Composites

TeO2 particle‐filled PTFE composites were prepared by the powder processing technique. The structure and microstructure of the composites were investigated by X‐ray diffraction and scanning electron microscopic methods. The effect of the ceramic content (0–0.6 volume fraction) of TeO2 on the dielectric properties of the composites was studied at 1 MHz and 7 GHz. The dielectric constant and dielectric loss increased with an increase in the TeO2 content. For 60 vol% of TeO2, the composite has a dielectric constant of 5.4 and a loss tangent of 0.006 at 7 GHz. The measured dielectric constant (ɛr) is compared with the effective dielectric constant calculated using different theoretical models. The observed dielectric constants are in agreement with that calculated using effective medium theory. The coefficient of thermal expansion of the composites decreases with the TeO2 content, reaching a minimum of 32 ppm/°C for 60 vol% loading.

Novel polyaniline/PVDF/BaTiO 3 hybrid composites with high piezo-sensitivity

Polyvinylidene fluoride (PVDF)–barium titanate (BaTiO 3)–polyaniline (PANI) hybrid composites were prepared by conventional powder processing technique which exhibited remarkably high piezo-sensitivity. The effect of poling of these semi-insulating composites on their piezo-response was quite dramatic. Sensitivity factors of 3000 could be achieved for even small poling voltages as low as 180 V/mm. The synergistic effect was obtained only when all three components, viz. PANI, PVDF and BaTiO 3 were present at certain proportion below percolation threshold in the composite. The results have been explained on the basis of charge storage in the piezo components due to the high fields generated, even for low external applied field, at the inter-granular sites between the semi-conducting polyaniline phase dispersed in the insulating matrix.

Calcium Phosphate Biomaterials Composite Device: In-Vitro and In-Vivo Investigation

Low crystalline apatite (LCA) and calcium phosphate cements (CPC) based on amorphous calcium phosphate and dicalcium phosphate dihydrate (1 to 1 ratio) were combined with bioresorbable PLGA copolymer (0 to 20 wt.%) for preparation of solid-formed devices. A pilot manufacturing based on powder processing techniques using isostatic pressure (44,000 psig) was conducted. Processing parameters such as isostatic pressure, temperature, times and device dimension were varied to achieve appropriate mechanical properties comparable to that of allograft bone dowel used as a gold standard in clinical application. The solid-form devices were characterized for physico-chemical and mechanical performance, as well as subjected to an in-vitro wet environment incubation at body temperature (37°C). Fluid diffusion was investigated to evaluate the fluid absorption (through microporosity) and the compressive strength of wet devices vs. incubation time (up to 30 days) was also studied. The shear strength and compressive strength of pure LCA dowels was respectively 26 and 122 MPa, which corresponds to a process densification of about 30%. The compressive strength was dramatically improved with addition of various amounts of copolymer. The maximum compressive strength of 180 MPa was obtained for dowels containing 10 wt.% copolymer. Calcium phosphate composite also increased the shear strength to about 42 MPa. These mechanical performances were significantly higher than that of allograft bone dowel (MD-II™), reported about 10 MPa. A pilot sheep interbody fusion of lumbar spine (L3/L4 and L4/L5) demonstrates mechanical integrity and intervertebral fusion at 6 months. LCA was found to be the most suitable CaP material because of its biocompatibility, chemical composition, nano-structure and high specific surface area that exhibits in-vivo biointegrity and cell mediated process.

PTFE/Sr 2Ce 2Ti 5O 16 polymer ceramic composites for electronic packaging applications

Sr 2Ce 2Ti 5O 16 ceramics filled PTFE composites were prepared by powder processing technique. The structure and microstructure of the composites were investigated by X-ray diffraction and scanning electron microscopic methods. The effect of Sr 2Ce 2Ti 5O 16 ceramic content (0–0.6 volume fraction) on the dielectric properties of the composites was studied at 1 MHz and 7 GHz. The dielectric constant and dielectric loss increased with the increase of Sr 2Ce 2Ti 5O 16 content. The measured dielectric constant ( ɛ r ) is compared with the effective dielectric constant calculated by Lichtenecker, Maxwell-Garnet, Jayasundere, Poon-Shin formulae and Effective Medium Theory. The observed dielectric constants are reasonably in good agreement with that calculated using Effective Medium Theory.

X-ray Diffraction Investigation of the Formation of Nanostructured Metastable Phases During Short-Duration Mechanical Alloying of Cu–Al Powder Mixtures

Mechanical alloying is a powder processing technique used to process materials farther from equilibrium state. This technique is mainly used to process difficult to alloy materials in which the solid solubility is limited, and to process materials where non-equilibrium phases cannot be produced at room temperature through conventional processing techniques. In the present work, mechanical alloying/milling of selected compositions in the Al–Cu binary alloy system was carried out at a ball-to-powder weight ratio (BPR) of 2 : 1, to investigate alloying and subsequent heat treatment on microstructural changes as a result of short milling times. Copper-aluminum powder mixtures containing 5, 20, and 40 wt% Al (11, 37, and 61 at% Al, respectively) were subjected to mechanical alloying, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC), after mechanical alloying and subsequent heat treatment. Nanometer-sized grains were observed in the as-milled crystalline powders in all compositions. Crystallite sizes were calculated using the Scherrer formula and found to be in the order of 10–20 nm after 360 minutes of milling time for all compositions. The XRD data show considerable solid solubility extension in these powders, and formation of intermetallic phases due to mechanical alloying and subsequent annealing. These changes are discussed in the context of the Al–Cu phase diagram.

Effect of V2O5-CaCo3-Nb2O5 contents on properties of low power loss Mn-Zn ferrites

Effect of the content of dopants in the manganese-zinc ferrites on the low power loss is studied by measuring magnetic properties and observing the grain boundary structures. The Mn0.738Zn0.206Fe2.056O4 composition powders were prepared by using conventional ceramic powder processing technique. The microstructure of grain boundary was observed by scanning electron microscope (SEM). It has been found that power loss is greatly dependent upon the content of the additives.

Microstructure and Mechanical Properties of Spark Plasma Sintered ZrO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub>-TiC<sub>0.5</sub>N<sub>0.5</sub> Nanocomposites

Future materials for wear resistant components require a combination of excellent mechanical properties such as hardness and toughness, short processing times and good electrical conductivity to facilitate shaping by electro discharge machining (EDM). In this work, the hardness and fracture toughness of t-ZrO2 based electro conductive composites was optimised, while short processing times below 20 minutes using spark plasma sintering were sufficient to obtain near fully dense materials. The influence of powder processing technique using TiC0.5N0.5 as the starting powder and yttria as a stabiliser on the mechanical properties of ZrO2-TiC0.5N0.5-Al2O3 based composites was investigated. Fully dense Y-TZP based composites possessed an excellent toughness of 9.2 MPa.m1/2 and an increased Vickers hardness of 1397 kg/mm².

APP-10: A Novel Processing Technique to Minimize the Residual Stress-Induced Camber in Fabricating Multi-Layered Ceramics and FGMs(APP-II: ADVANCED POWDER PROCESSING TECHNIQUE)

APP-10: A Novel Processing Technique to Minimize the Residual Stress-Induced Camber in Fabricating Multi-Layered Ceramics and FGMs(APP-II: ADVANCED POWDER PROCESSING TECHNIQUE)

APP-07: Bonding of Mechanically Alloyed Powder and Magnesium Alloy by Compressive Deformation(APP-I: ADVANCED POWDER PROCESSING TECHNIQUE)

APP-07: Bonding of Mechanically Alloyed Powder and Magnesium Alloy by Compressive Deformation(APP-I: ADVANCED POWDER PROCESSING TECHNIQUE)

APP-08: Shape Memory Characteristics of TiNi Alloy Fabricated by Mechanically-Alloyed Powder(APP-I: ADVANCED POWDER PROCESSING TECHNIQUE)

APP-08: Shape Memory Characteristics of TiNi Alloy Fabricated by Mechanically-Alloyed Powder(APP-I: ADVANCED POWDER PROCESSING TECHNIQUE)

APP-01: A Numerical Study on Stresses in Graded Multilayers during Sintering and Cooling(APP-I: ADVANCED POWDER PROCESSING TECHNIQUE)

APP-01: A Numerical Study on Stresses in Graded Multilayers during Sintering and Cooling(APP-I: ADVANCED POWDER PROCESSING TECHNIQUE)

APP-04: Consolidation at Low Heat in Mechanically Alloyed Ti-Al Powders(APP-I: ADVANCED POWDER PROCESSING TECHNIQUE)

APP-04: Consolidation at Low Heat in Mechanically Alloyed Ti-Al Powders(APP-I: ADVANCED POWDER PROCESSING TECHNIQUE)

Hydroxyapatite whiskers provide improved mechanical properties in reinforced polymer composites

Synthetic hydroxyapatite (HA) whiskers have been utilized as a new, biocompatible reinforcement for orthopedic biomaterials. High-density polyethylene (HDPE) was reinforced with either the synthesized HA whiskers or a commercially available spherical HA powder using a novel powder processing technique that facilitated uniform dispersion of the reinforcements in the matrix prior to compression molding. Composites were processed for up to 60 vol % HA whiskers and up to 50 vol % spherical HA. The mechanical properties of the new composite biomaterials were examined by uniaxial tensile tests. As expected, increased volume fraction of either reinforcement type over 0-50 vol % resulted in increased elastic modulus, a maximum in ultimate tensile stress, and decreased work to failure. Composites reinforced with HA whiskers had higher elastic modulus, ultimate tensile strength, and work to failure relative to composites reinforced with spherical HA. Thus, HA whisker-reinforced HDPE composites possessed improved mechanical properties over those reinforced with spherical HA. HA whisker-reinforced composites were anisotropic due to alignment of the whiskers in the matrix during processing.

Direct laser deposition of in situ Ti–6Al–4V–TiB composites

Ti–6Al–4V–TiB composites have been in situ deposited from powder feedstocks consisting of a blend of pre-alloyed Ti–6Al–4V and elemental boron using the Laser Engineered Net-Shaping (LENS™) process. The microstructure of the as-deposited composites has been characterized in detail using scanning (SEM) and transmission electron microscopy (TEM). A homogeneous refined dispersion of TiB precipitates is formed within the Ti–6Al–4V α/β matrix. The scale of the microstructure is substantially refined as compared with composites produced using other recently developed powder processing techniques. In addition to the refined dispersion of the reinforcing phase, the influence of the TiB precipitation on the solid-state β→β+α transformation that takes place in the matrix has been examined using SEM and TEM. Finally, heat-treatments carried out post-LENS™ deposition, suggest that LENS™ fabricated composites are thermodynamically stable, exhibiting limited TiB coarsening.

The effect of nano-SiO 2 on the magnetic properties of the low power loss manganese–zinc ferrites

The effect of the addition of nano-SiO 2 on the power losses in the manganese–zinc ferrites has been investigated by measuring the magnetic properties and observing the grain boundary structures. The powders of Mn 0.72Zn 0.21Fe 2.07O 4 composition were prepared by using a conventional ceramic powder processing technique. Toroidal cores were sintered at 1340°C for 4 h using a tube furnace with atmosphere controlled by using the equation for equilibrium oxygen partial pressure. The microstructure of grain boundary was observed by AES and SEM. It has been found that the grain boundaries resistivity and magnetic loss are greatly dependent upon the content of nano-SiO 2. There is an optimum content of nano-SiO 2 to produce uniform grain structure and low magnetic loss. The eddy current losses were reduced by the addition of nano-SiO 2. These losses are thought to originate from the additive effect of Si atoms, which are enriched in grain boundaries to form a high resistivity layer and prevent Ca and Nb atoms being incorporated with the spinel lattice.