Dielectric response of an epoxy resin when exposed to high temperatures

Epoxy resins are popular insulators that are used for the encapsulation of integrated circuits and for the fabrication of printed circuits boards. As such, it is important to evaluate their reliability when exposed to an environmental stress. This work reports on the influence of a high-temperature thermal stress (400 ^∘C) on the dielectric properties of an acid-anhydride cured DGEBA resin. Gold/epoxy/gold capacitors are used as a test structure. The studied electrical properties are the dielectric constant and the loss factor in the 10⁻¹ Hz100 kHz range, and the DC resistivity. It is found that cycling the sample for several minutes to temperatures as high as 400 ^∘C has almost no effect on its dielectric properties. It is believed that the gold electrodes prevent the thermo-oxidative degradation of the underlying epoxy. Electrical properties are also studied at high temperatures in the 200 ^∘C-400 ^∘C range. Above 200 ^∘C the DC resistivity is considerably increased, as well as the loss in the low-frequency part of the spectrum (< 1kHz). At high frequencies (> 1kHz) the epoxy maintains good dielectric performances up to 400 ^∘C.     

Investigation of microstructures and tensile properties of a Sn-Cu lead-free solder alloy

In recent years, the pollution of environment from lead (Pb) and Pb-containing compounds in microelectronic devices attracts more and more attentions in academia and industry, the lead-free solder alloys begin to replace the lead-based solders in packaging process of some devices and components. In this work, microstructures and mechanical properties of the lead-free solder alloy Sn99.3Cu0.7(Ni) are investigated. This paper will compare the mechanical properties of the lead-based with lead-free solder alloys (Sn99.3Cu0.7(Ni) and 63Sn37Pb). The tensile tests of lead-based and lead-free solder alloys (Sn99.3Cu0.7(Ni) and Sn63Pb37) were conducted at room and elevated temperature at constant strain rate; the relevant tensile properties of Sn99.3Cu0.7(Ni) and Sn63Pb37 were obtained. Specifically, the tensile strength of this lead-free solder- Sn99.3Cu0.7(Ni) in 25^∘C, 50^∘C, 75^∘C, 100^∘C, 125^∘C was investigated; and it was found that tensile strength of the lead-free solder decreased with the increasing test temperature at constant strain rate, showing strong temperature dependence. The lead-free solder alloy Sn99.3Cu0.7(Ni) was found to have favorable mechanical properties and it may be able to replace the lead-based solder alloy such as Sn63Pb37 in the packaging processes in microelectronic industry.     

Improved mechanical properties of acrylic bone cement with short titanium fiber reinforcement

Acrylic bone cements are widely used in total joint arthroplasties to grout the prosthesis to bone. The changes in the tensile properties and fracture toughness of polymethylmethacrylate (PMMA) bone cements obtained by the addition of control and heat treated short titanium fibers are studied. Heat treatment of titanium fibers is conducted to precipitate titania particles on the fiber surface to improve the biocompatibility of the metal. Control and heat treated short titanium fibers (250 μ long and 20 μ diameter) were used as reinforcements at 3 volume %. X-ray diffraction indicated the presence of a rutile form of titania due to the heat treatments. The tensile and fracture properties were improved by the addition of fibers. Bone cements reinforced with titanium fibers heated at 550^∘C for 1 h followed by 800^∘C for 30 minutes show the largest increase in fracture toughness along with the smallest changes in elastic modulus and needs to be further investigated.     

Influence of Microstructure on The Resistance to Salt Crystallisation Damage in Brick

In the article we study the variation of brick durability and, more specifically, its resistance to salt crystallisation produced by changes in its microstructure during firing. For this purpose, the evolution of both mechanical and pore structure properties are studied within a wide range of temperatures (700–1100^∘C). An increase in the firing temperature produces a more homogeneous and resistant brick, measured using ultrasound velocity and uniaxial compressive strength. This result is obtained thanks to the vitrification process and changes in the brick's pore structure: larger, rounder pores, which are quantified by their roundness and fractal dimension. As a result of these changes, an excellent durability is achieved in the bricks studied when fired at temperatures above 1000^∘C. Considering that few differences are noted in pore structure and brick strength between 1000 and 1100^∘C, the recommended firing temperature is, for raw materials with a similar composition and production process, 1000^∘C, as this involves a lower production cost than firing at 1100^∘C.     

Influence of Li<Superscript>+</Superscript> dopants on the properties of the ZnO piezoelectric films

ZnO piezoelectric films with the preferred 002-orientation were prepared by sol-gel method. The annealing temperature was 600^∘C and the resistivity of the ZnO film was 1 × 10⁶ Ω ⋅ cm. Li₂CO₃ and LiCl were added respectively into ZnO precursor as source of Li⁺-ion. The molar ratio of [Li⁺]/[Zn^{2 +}] was 0.05. It is observed that the annealing temperature for forming preferred 002-orientation of ZnO films decreases from 660 to 550^∘ C after Li₂CO₃ being doped. When Li₂CO₃ and LiCl are doped, the resistivity of ZnO films increases to 10⁸Ω ⋅ cm and 10⁹Ω ⋅ cm, respectively, with an annealing temperature of 550^∘ C. When annealing temperature is 600^∘ C, the resistivity of the ZnO film with LiCl dopant increases to 10⁷Ω cm. The influence mechanism of the two dopants on the properties of the ZnO films is analyzed.     

Identification and characterization of diffusion barriers for Cu/SiC systems

The promise of CuSiC metal matrix composites (MMCs) as a thermal management material is to provide increased power density and high reliability for advanced electronic systems. CuSiC will offer high thermal conductivity between 250 and 325 W/mK with corresponding adjustable thermal expansion coefficient between 8.0 and 12.5 ppm/^∘C. The major challenge in development of these materials is control of the interface interactions. Cu and SiC react at high temperatures between 850 and 1150^∘C, needed for fabrication of the CuSiC material, with an expected decrease in thermal conductivity of the CuSiC MMCs as the Si product of reaction dissolves into the Cu. The application of barrier coatings onto SiC was observed to control chemical reaction of Cu and SiC. In the current study, the effectiveness of four barriers to prevent Cu diffusion and reaction with SiC were evaluated between 850 to 1150^∘C. Immersion experiments were conducted at 1150^∘C to understand the reaction between copper and silicon carbide. Reaction products were identified with transmission electron microscopy (TEM) and electron diffraction. Laser flash thermal diffusivity measurements confirmed thermal conductivity to decrease with increasing silicon content of the copper as determined by induction coupled plasma mass spectrometry (ICPMS) and glow discharge mass spectrometry (GDMS). An erratum to this article is available at .     

Structural and electrical properties of perovskite ruthenate-based lead-free thick film resistors on alumina and LTCC

CaRuO₃ perovskite-based lead-free thick-film resistors (TFRs) were prepared on 96%-alumina and Low Temperature Co-fired Ceramic (LTCC) substrates. The microstructure evolution, possible interactions, and electrical properties of resistors were investigated. The hot and cold TCR values of all the resistors were measured in the temperature range (+20 to +120 ^∘C) and (+20 to −120 ^∘C), respectively. TFRs with 25% by vol. of CaRuO₃ on alumina exhibit a sheet resistance R_s = 5kΩ/sq. with hot and cold TCR of 225 and 470 ppm/^∘C respectively, whereas the same composition gives 1.2 kΩ/sq., 16.5 kΩ/sq. and 0.7 kΩ/sq. for co-fired, post-fired resistors on LTCC and buried resistors, respectively. The hot (HTCR) and cold (CTCR) values were evaluated; HTCR = 190 ppm/^∘C and CTCR = 314 ppm/^∘C were found for co-fired structures; HTCR = 216 ppm/^∘C and CTCR = 205 ppm/^∘C for post-fired samples and HTCR = 520 ppm/^∘C and CTCR = 350 ppm/^∘C for buried in LTCC structures.     

Effect of pH, temperature and Cl− concentration on electrochemical behavior of NiTi shape memory alloy in artificial saliva

The cooperation of pH, temperature and Cl⁻ concentration on electrochemical behavior of NiTi shape memory alloy in artificial saliva was studied using orthogonal test method. The results showed that the pitting potential for NiTi in artificial saliva decreased at low and high pH; at 25^∘C, the pitting potential was the lowest compared to those at 10^∘C, 37^∘C and 50^∘C; when the Cl⁻ concentration was not less than 0.05 mol/L the pitting potential decreased with the increase of Cl⁻ concentration. The free corrosion potential of austenitic NiTi was lower than that of mixture of austenite and martensite.     

The effect of pressure during sintering on the strength and the fracture toughness of hydroxyapatite ceramics

Hydroxyapatite (HA) is known to be biocompatible and osteoconductive, and can be synthesized chemically. The objective of the present study is to clarify the effect of pressure during sintering on the mechanical properties of HA. HA was sintered using a hot press system at a uniaxial pressure ranging from 7.81 to 62.5 MPa at a maximum temperature of 1200^∘C with a heating rate of 10^∘C/min. The density of the HA increased with increasing pressure and peaked at the sintering pressure of 31.2 MPa. Four-points bending tests and fracture toughness measurements with indentation method were conducted to clarify the effect of sintering pressure. Bending strength decreased at the pressure > 31.2 MPa. This result indicates that residual stress generated during sintering process became larger with increasing pressure. Fracture toughness were also lower with high density HA.     

Physical and chemical assessment of lime–metakaolin mortars: Influence of binder:aggregate ratio

This work evaluates the influence of binder:aggregate ratio on the mineralogical and mechanical properties of air lime–metakaolin mortars.Mineralogical analysis showed that binder:aggregate ratio affects the extent of carbonation and pozzolanic reactions with curing. The pozzolanic reaction occurs mostly at lower curing times (28 days), while, at higher curing ages, carbonation reaction is mostly dominant. The exceptions are mortars with 1:1 (air:lime) volumetric ratio with 30% and 50% MK in which the pozzolanic reaction is still dominant.The reduction in the mechanical resistance of some compositions observed from 28 to 90 days is related to the calcium aluminate hydrate instability in the presence of free lime. This instability is expected to disappear after the total consumption of free lime, either by pozzolanic or carbonation reaction.     

The Effect of flux types on the formation of green light emitting phosphor particles with spherical shape and filled morphology

(CeTb)MgAl₁₁O₁₉ (CTMA) phosphor particles were prepared by high-temperature spray pyrolysis from spray solutions with various types of flux materials. The particles prepared from spray solutions with ammonium dihydrogen phosphate and lithium carbonate fluxes had spherical shape and filled morphology at temperatures of 900^∘C and 1650^∘C. On the other hand, the particles prepared from spray solutions without flux material had hollow and fractured morphology at temperatures of 900^∘C and 1650^∘C. The melting of flux material formed the spherical intermediate particles with filled morphology. These spherical intermediate particles were formed from spray solutions with flux material that transformed into spherical CTMA phosphor particles with filled morphology at a high-preparation temperature. The phosphor particles prepared by spray pyrolysis from the spray solution with appropriate flux materials at 1650^∘C had high photoluminescence intensities, spherical shape, and filled morphology.     

Effect of compaction on the kinetics of thermal decomposition of dolomite under non-isothermal condition

Many workers [1–9] studied the kinetics of dolomite decomposition to study the effects of different parameters like, gas (CO₂, N₂ etc.) pressures, water vapor, presence of other impurities, particle size and grain size of the dolomite samples, crystallinity etc. on the decomposition kinetics of dolomite using different tools like, thermal analysis, thermo-gravimetric analyses, XRD technique etc. and different values of the activation energies for the decomposition reaction, order of reactions have been reported. It has been observed that pure dolomite decomposed in only two steps. The first stage of the thermal decomposition of dolomite resulted in the formation of Mg-calcite [(CaMg)CO₃] and periclase (MgO), with the liberation of CO₂. It was further observed that under CO₂, dolomite decomposed directly to CaCO₃, accompanied by the formation of MgO between 550 and 765^∘C. Calcite decomposed to CaO between 900 and 960^∘C and under air, simultaneous formation of CaCO₃, CaO and MgO accompanied dolomite decomposition between 700 and 740–750∘C. At the latter temperature, the calcite began to decompose even though a significant amount of dolomite was still present and simultaneous decomposition of the two carbonates was terminated at 780^∘C. Also, changes in decomposition rates of the various phases correlated with changes in the rate of weight loss determined by derivative thermo-gravimetric analysis.     

Reutilization of waste inert glass from the disposal of polluted dredging spoils by the obtainment of ceramic products for tiles applications

The vitrification treatment has been successfully exploited as a solution for the disposal of polluted dredging spoils from the industrial area close to the Venice Lagoon. The addition of 20% by wt. of glass cullet to the calcined sediments in the vitrification batch provides a suitable chemical composition for the production of an inert glass, despite the compositional variations of the sediments. The obtained waste glass, after being finely ground, has been employed (i) as a raw material for the manufacture of sintered glass-ceramics, by cold pressing and single-step sintering at about 940^∘C, and (ii) as sintering additive (the maximum addition being 10% by wt.) for the manufacture of traditional red single firing ceramic tiles, with a maximum firing temperature of 1186^∘C. Both applications have proved to be promising: in the first case, the sintered glass ceramic product exhibits notable mechanical properties (bending strength > 130 MPa, HV ≈ 6.5 GPa); in the second case, the addition of waste glass does not modify substantially the investigated physical and mechanical properties of the traditional product (water absorption, linear shrinkage, bending strength, planarity).     

Annealing study of palladium–silver dental alloys: Vickers hardness measurements and SEM microstructural observations

Three Pd–Ag dental alloys for metal-ceramic restorations, W-1 (Ivoclar Vivadent), Rx 91 (Pentron) and Super Star (Heraeus Kulzer), were subjected to isothermal annealing for 0.5 hr periods in a nitrogen atmosphere at temperatures from approximately 400 ^∘ to 950 ^∘ C. The annealing behavior was investigated by Vickers hardness measurements (1 kg load) and SEM microstructural observations. The highest Vickers hardness occurred at approximately 700 ^∘ C for W-1 and 650 ^∘ C for Rx 91. For Super Star, there were two peaks in hardness at approximately 500 ^∘ and 650 ^∘ C. Additional use of light indenting loads (25 g for W-1; 10 g for Rx 91 and Super Star) revealed that hardness variations during annealing for W-1 and Rx 91 were related to the palladium solid solution matrix phase. For Super Star, the lower-temperature peak was controlled by multi-phase regions and the higher-temperature peak by the matrix phase. While microstructural changes due to annealing were evident with the SEM for Rx 91 and Super Star, no correlation was possible for W-1 because of its finer-scale microstructure. Although commercial Pd–Ag alloys have a relatively narrow composition range, their microstructures and annealing behavior can vary because of differences in proportions of secondary elements utilized for porcelain adherence and grain refinement elements, as well as other proprietary strategies employed by the manufacturers.     

Mechanical properties of polypropylene hybrid fiber-reinforced concrete

This paper investigates the mechanical properties of polypropylene hybrid fiber-reinforced concrete. There are two forms of polypropylene fibers including coarse monofilament, and staple fibers. The content of the former is at 3 kg/m³, 6 kg/m³, and 9 kg/m³, and the content of the latter is at 0.6 kg/m³. The experimental results show that the compressive strength, splitting tensile strength, and flexural properties of the polypropylene hybrid fiber-reinforced concrete are better than the properties of single fiber-reinforced concrete. These two forms of fibers work complementarily. The staple fibers have good fineness and dispersion so they can restrain the cracks in primary stage. The monofilament fibers have high elastic modulus and stiffness. When the monofilament fiber content is high enough, it is similar to the function of steel fiber. Therefore, they can take more stress during destruction. In addition, hybrid fibers disperse throughout concrete, and they are bond with mixture well, so the polypropylene hybrid fiber-reinforced concrete can effectively decrease drying shrinkage strain.     

Composites between hydroxyapatite and poly(ε-caprolactone) synthesized in open system at room temperature

The hydroxyls present on the surface of hydroxyapatite (HA) granules, annealed at 700 ∘, 900 ∘ and 1100 ∘C, are able to initiate the polymerization of ε-caprolactone (CL), not only at 185 ∘C under vacuum, but also at room temperature in open system. A polymer layer ionically linked to the substrate is formed on HA surface, enhancing the compatibility between the organic phase and the inorganic one in composite biomaterials. We studied the characteristics of the polymer, produced by the reaction carried out at room temperature in open system, as well as the percentages of the poly(ε-caprolactone) (PCL) ionically bonded to the HA structure and of the “free” one. Both percentages appear very dependent on the annealing temperature; in particular, HA annealed for 1 h at 1100 ∘C is the most efficient initiator of the reaction leading to ionically bonded PCL. The percentages of “free” polymer are much higher than at 185 ∘C under vacuum. Its formation is attributed to the role of water in opening the CL rings, and to the presence of CO₃²⁻ and HPO₄²⁻ ions in the HA annealed at lower temperatures. The presence of water appears to be the limiting factor for the production of PCL not bonded to the HA structure.     

Effect of passivation and surface modification on the dissolution behavior and nano-surface characteristics of Ti-6Al-4V in Hank/EDTA solution

The aim of the present study was to investigate the effects of passivation treatment (34% nitric acid passivation, 400 ^∘C heated in air, and aged in 100 ^∘C de-ionized water) and surface modification (2 hr and 8 hr vacuum-brazed treatments) on the ion dissolution and nano-surface characteristics of Ti-6Al-4V exposed in Hank's solution with 8.0 mM ethylene diamine tetra-acetic acid (EDTA) at 37 ^∘C. The results indicated that the original nano-surface characteristics and microstructure would influence the ion dissolution but not change the capability of the Ca and P adsorption upon immersion. Of the three passivated treatments, 400 ^∘C thermal treatment for both 2 hr brazed Ti-6Al-4V (B2) and 8 hr brazed Ti-6Al-4V (B8) exhibits a substantial reduction in the constituent release compared to the acid passivated and water aged treatment, because the thicker thickness and rutile structure of surface oxide could provide the better dissolution resistance for 400 ^∘C-treated specimens. Moreover, the reduced Ti₂Cu and increased α -titanium structure in B8 specimen could also improve ion dissolution resistance in comparison with B2 specimen. After soaking in Hank/EDTA solution, the adsorbed non-elemental Ca and P for all groups of specimens were observed by XPS analysis, and the AES depth-profile analysis indicate that the oxide films of all groups of specimens thicken with the longer immersion periods. The increasing oxide thickness may be the factor in the improved dissolution resistance at the longer immersion periods. The relation between lower dissolution rate and thicker oxide films were observed for all groups of specimens. The results suggest that the dissolution kinetics was governed by the metal ion transport through the oxide film in this study.     

Calcium phosphate fibres synthesized from a simulated body fluid

The biomimetic coating method was used for fabricating calcium phosphate fibres for biomedical applications such as bone defect fillers. Natural cotton substrate was pre-treated with phosphorylation and a Ca(OH)₂ saturated solution. The pre-treated samples were then soaked in simulated body fluid (SBF) of two different concentrations, 1.5 times and 5.0 times the ion concentration of blood plasma. The cotton was then burnt out via sintering of the ceramic coating at 950^∘C, 1050^∘C, 1150^∘C, and 1250^∘C. The results demonstrated that osteoblastic cells were able to cover the entire surface cotton fibres, and the cell coverage appeared to be independent of surface roughness and Ca/P ratio of fibres.     

Boron-doped zinc oxide thin films prepared by sol-gel technique

Multilayer transparent conducting boron-doped zinc oxide films have been prepared on glass substrates by the sol gel dip coating process. Zinc acetate solutions of 0.4 M in isopropanol stabilized by diethanolamine and doped with boron tri-i-propoxide were used. Each layer was fired at 400–650^∘C in a conventional furnace for 30 min. Selected samples were vacuum annealed at 400–450^∘C for 1 h to improve their electrical properties. The electrical resistivity curve with doping shows a minimum around 0.8 at.%. Excess boron caused a drop of the carrier mobility without acting as donors. Post-deposition annealing sequence was crucial for dopant partial regeneration. Films with an average optical transmittance exceeding 90% can be achieved reproducibly.     

Silicon carbide and diamond for high temperature device applications

The physical and chemical properties of wide bandgap semiconductors silicon carbide and diamond make these materials an ideal choice for device fabrication for applications in many different areas, e.g. light emitters, high temperature and high power electronics, high power microwave devices, micro-electromechanical system (MEMS) technology, and substrates. These semiconductors have been recognized for several decades as being suitable for these applications, but until recently the low material quality has not allowed the fabrication of high quality devices. Silicon carbide and diamond based electronics are at different stages of their development. An overview of the status of silicon carbide's and diamond's application for high temperature electronics is presented. Silicon carbide electronics is advancing from the research stage to commercial production. The most suitable and established SiC polytype for high temperature power electronics is the hexagonal 4H polytype. The main advantages related to material properties are: its wide bandgap, high electric field strength and high thermal conductivity. Almost all different types of electronic devices have been successfully fabricated and characterized. The most promising devices for high temperature applications are pn-diodes, junction field effect transistors and thyristors. MOSFET is another important candidate, but is still under development due to some hidden problems causing low channel mobility. For microwave applications, 4H-SiC is competing with Si and GaAs for frequency below 10 GHz and for systems requiring cooling like power amplifiers. The unavailability of high quality defect and dislocation free SiC substrates has been slowing down the pace of transition from research and development to production of SiC devices, but recently new method for growth of ultrahigh quality SiC, which could promote the development of high power devices, was reported. Diamond is the superior material for high power and high temperature electronics. Fabrication of diamond electronic devices has reached important results, but high temperature data are still scarce. PN-junctions have been formed and investigated up to 400 ^∘C. Schottky diodes operating up to 1000 ^∘C have been fabricated. BJTs have been fabricated functioning in the dc mode up to 200 ^∘C. The largest advance, concerning development of devices for RF application, has been done in fabrication of different types of FETs. For FETs with gate length 0.2 μ m frequencies f_T = 24.6 GHz, f_{max (MAG)} = 63 GHz and f_{max (U)} = 80 GHz were reported. Further, capacitors and switches, working up to 450 ^∘C and 650 ^∘C, respectively, have also been fabricated. Low resistant thermostable resistors have been investigated up to 800 ^∘C. Temperature dependence of field emission from diamond films has been measured up to 950 ^∘C. However, the diamond based electronics is still regarded to be in its infancy. The prerequisite for a successful application of diamond for the fabrication of electronic devices is availability of wafer diamond, i.e. large area, high quality, inexpensive, diamond single crystal substrates. A step forward in this direction has been made recently. Diamond films grown on multilayer substrate Ir/YSZ/Si(001) having qualities close those of homoepitaxial diamond have been reported recently.