Correlation between metal-ceramic bond strength and coefficient of linear thermal expansion difference

The purpose of this study was to evaluate the metal-ceramic bond strength (MCBS) of 6 metal-ceramic pairs (2 Ni-Cr alloys and 1 Pd-Ag alloy with 2 dental ceramics) and correlate the MCBS values with the differences between the coefficients of linear thermal expansion (CTEs) of the metals and ceramics. Verabond (VB) Ni-Cr-Be alloy, Verabond II (VB2), Ni-Cr alloy, Pors-on 4 (P), Pd-Ag alloy, and IPS (I) and Duceram (D) ceramics were used for the MCBS test and dilatometric test. Forty-eight ceramic rings were built around metallic rods (3.0 mm in diameter and 70.0 mm in length) made from the evaluated alloys. The rods were subsequently embedded in gypsum cast in order to perform a tensile load test, which enabled calculating the CMBS. Five specimens (2.0 mm in diameter and 12.0 mm in length) of each material were made for the dilatometric test. The chromel-alumel thermocouple required for the test was welded into the metal test specimens and inserted into the ceramics. ANOVA and Tukey's test revealed significant differences (p=0.01) for the MCBS test results (MPa), with PI showing higher MCBS (67.72) than the other pairs, which did not present any significant differences. The CTE (10-6 oC-1) differences were: VBI (0.54), VBD (1.33), VB2I (-0.14), VB2D (0.63), PI (1.84) and PD (2.62). Pearson's correlation test (r=0.17) was performed to evaluate of correlation between MCBS and CTE differences. Within the limitations of this study and based on the obtained results, there was no correlation between MCBS and CTE differences for the evaluated metal-ceramic pairs.

Thermal expansion of the V(5)Si(3) and T(2) phases of the V-Si-B system investigated by high-temperature X-ray diffraction

The thermal expansion anisotropy of the V(5)Si(3) and T(2)-phase of the V-Si-B system were determined by high-temperature X-ray diffraction from 298 to 1273 K. Alloys with nominal compositions V(62.5)Si(37.5) (V5Si3 phase) and V(63)Si(12)B(25) (T(2)-phase) were prepared from high-purity materials through arc-melting followed by heat-treatment at 1873 K by 24 h, under argon atmosphere. The V(5)Si(3) phase exhibits thermal expansion anisotropy equals to 1.3, with thermal expansion coefficients along the a and c-axis equal to 9.3 x 10(-6) K(-1) and 11.7 x 10(-6) K(-1), respectively. Similarly, the thermal expansion anisotropy value of the T(2)-phase is 0.9 with thermal expansion coefficients equal to 8.8 x 10(-6) K(-1) and 8.3 x 10(-6) K(-1) along the, a and c-axis respectively. Compared to other isostructural silicides of the 5:3 type and the Ti(5)Si(3) phase, the V(5)Si(3) phase presents lower thermal expansion anisotropy. The T(2)-phase present in the V-Si-B system exhibits low thermal expansion anisotropy, as the T(2)-phase of the Mo-Si-B, Nb-Si-B and W-Si-B systems. (C) 2009 Elsevier Ltd. All rights reserved.

Influence of temperature and excitation procedure on the athermal behavior of Nd(3+)-doped phosphate glass: Thermal lens, interferometric, and calorimetric measurements

In this work, thermal and optical properties of the commercial Q-98 neodymium-doped phosphate glass have been measured at low temperature, from 50 to 300 K. The time-resolved thermal lens spectrometry together with the optical interferometry and the thermal relaxation calorimetry methods were used to investigate the glass athermal characteristics described by the temperature coefficient of the optical path length change, ds/dT. The thermal diffusivity was also determined, and the temperature coefficients of electronic polarizability, linear thermal expansion, and refractive index were calculated and used to explain ds/dT behavior. ds/dT measured via thermal lens method was found to be zero at 225 K. The results provided a complete characterization of the thermo-optical properties of the Q-98 glass, which may be useful for those using this material for diode-pumped solid-state lasers. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3234396]

Thermal lens and interferometric method for glass transition and thermo physical properties measurements in Nd(2)O(3) doped sodium zincborate glass

In this work the time resolved thermal lens method is combined with interferometric technique, the thermal relaxation calorimetry, photoluminescence and lifetime measurements to determine the thermo physical properties of Nd(2)O(3) doped sodium zincborate glass as a function of temperature up to the glass transition region. Thermal diffusivity, thermal conductivity, fluorescence quantum efficiency, linear thermal expansion coefficient and thermal coefficient of electronic polarizability were determined. In conclusion, the results showed the ability of thermal lens and interferometric methods to perform measurements very close to the phase transition region. These techniques provide absolute values for the measured physical quantities and are advantageous when low scan rates are required. (c) 2008 Optical Society of America

Effect of Alloying Elements on Thermal Diffusivity of Gray Cast Iron Used in Automotive Brake Disks

The purpose of this work was to experimentally investigate the thermal diffusivity of four different gray cast iron alloys, regularly used to produce brake disks for automotive vehicles. Thermal diffusivity measurements were performed at temperatures ranging from room temperature to 600 A degrees C. The influence of the thermal conductivity on the thermomechanical fatigue life is also briefly presented. The measurements were sensitive to the influence of the carbon equivalent and alloying elements, such as molybdenum, copper and chromium. Molybdenum, unlike copper, lowered the thermal diffusivity of the gray cast iron, and alloy E (without molybdenum), besides presenting a relatively low carbon equivalent content and an increase in the values of the thermal diffusivity, presented the best performance during the thermomechanical fatigue. The molybdenum present in alloys B and C did not fulfill the expectations of providing the best thermomechanical fatigue behavior. Consequently, its elimination in the gray cast iron alloy for this application will result in a significant economy.

Thermal Transport and Strong Mass Renormalization in NiCl(2)-4SC(NH(2))(2)

Several quantum paramagnets exhibit magnetic-field-induced quantum phase transitions to an anti-ferromagnetic state that exists for H(c1) <= H <= H(c2). For some of these compounds, there is a significant asymmetry between the low-and high-field transitions. We present specific heat and thermal conductivity measurements in NiCl(2)-4SC(NH(2))(2), together with calculations which show that the asymmetry is caused by a strong mass renormalization due to quantum fluctuations for H <= H(c1) that are absent for H >= H(c2). We argue that the enigmatic lack of asymmetry in thermal conductivity is due to a concomitant renormalization of the impurity scattering.

Angular dependence of the thermal-lens effect on LiSrAlF(6) and LiSrGaF(6) single crystals

We apply thermal-lens (TL) spectrometry to measure the angular dependence of the TL effect on colquiriite single crystals. The experiments were performed with LiSrAlF(6) and LiSrGaF(6) using a two-beam mode-mismatched configuration. The results show that it is possible to minimize the TL effect by selecting the appropriate crystal orientation. Our data also show that the anisotropy of the linear thermal expansion coefficient drives the amplitude of the TL effect, including the inversion from focusing to defocusing as the crystal orientation angle tends to the c-axis direction. The results may be useful for those working to develop a high-power laser using LiSrAlF(6)(:Cr) and LiSrGaF(6)(:Cr) single crystals, allowing for optimization of the designed laser cavity. (C) 2008 Optical Society of America.

Internal Residual Stresses in Sintered and Commercial Low Expansion Li(2)O-Al(2)O(3)-SiO(2) Glass-Ceramics

We performed Synchrotron X-ray diffraction (XRD) analyses of internal residual stresses in monolithic samples of a newly developed Li(2)O-Al(2)O(3)-SiO(2) (LAS) glass-ceramic produced by sintering and in a commercial LAS glass-ceramic, CERAN (R), produced by the traditional crystal nucleation and growth treatments. The elastic constants were measured by instrumented indentation and a pulse-echo technique. The thermal expansion coefficient of virgilite was determined by high temperature XRD and dilatometry. The c-axis contracts with the increasing temperature whereas the a-axis does not vary significantly. Microcracking of the microstructure affects the thermal expansion coefficients measured by dilatometry and thermal expansion hysteresis is observed for the sintered glass-ceramic as well as for CERAN (R). The measured internal stress is quite low for both glass-ceramics and can be explained by theoretical modeling if the high volume fraction of the crystalline phase (virgilite) is considered. Using a modified Green model, the calculated critical (glass) island diameter for spontaneous cracking agreed with experimental observations. The experimental data collected also allowed the calculation of the critical crystal grain diameters for grain-boundary microcracking due to the anisotropy of thermal expansion of virgilite and for microcracking in the residual glass phase surrounding the virgilite particles. All these parameters are important for the successful microstructural design of sintered glass-ceramics.

Permeability optimization and performance evaluation of hot aerosol filters made using foam incorporated alumina suspension

Porous ceramic samples were prepared from aqueous foam incorporated alumina suspension for application as hot aerosol filtering membrane. The procedure for establishment of membrane features required to maintain a desired flow condition was theoretically described and experimental work was designed to prepare ceramic membranes to meet the predicted criteria. Two best membranes, thus prepared, were selected for permeability tests up to 700 degrees C and their total and fractional collection efficiencies were experimentally evaluated. Reasonably good performance was achieved at room temperature, while at 700 degrees C, increased permeability was obtained with significant reduction in collection efficiency, which was explained by a combination of thermal expansion of the structure and changes in the gas properties. (C) 2008 Elsevier B.V. All rights reserved.

Thermomechanical properties of biodegradable films based on blends of gelatin and poly(vinyl alcohol)

The aim of this work was to study the effect of the poly(vinyl alcohol) (PVA) concentration on the thermal and viscoelastic properties of films based on blends of gelatin and PVA using differential scanning calorimetry (DSC) and dynamic-mechanical analysis (DMA). One glass transition was observed between 43 and 49 degrees C on the DSC curves obtained in the first scanning of the blended films, followed by fusion of the crystalline portion between 116 and 134 degrees C. However, the DMA results showed that only the films with 10% PVA had a single peak in the tan 5 spectrum. However, when the PVA concentration was increased the dynamic mechanical spectra showed two peaks on the tan 6 curves, indicating two T(g)s. Despite this phase separation behavior the Gordon and Taylor model was successfully applied to correlate T, as a function of film composition, thus determining k = 7.47. In the DMA frequency tests, the DMA spectra showed that the storage modulus values decreased with increasing temperature. The master curves for the PVA-gelatin films were obtained applying the TTS principle (T(r) = 100 degrees C). The WLF model was thus applied allowing for the determination of the constants C(1) and C(2). The values of these constants increased with increasing PVA concentrations in the blend: C(1) = 49-66 and C(2) = 463-480. These values were used to calculate the fractional free volume of the films at the T(g) and the thermal expansion coefficient of the films above the T(g). (c) 2007 Elsevier Ltd. All rights reserved.

Columnar joints in the Patino Formation sandstones, Eastern Paraguay: a dynamic interaction between dyke intrusion, quartz dissolution and cooling-induced fractures

The Patino Formation sandstones, which crop out in Aregua neighborhood in Eastern Paraguay and show columnar joints near the contact zone with a nephelinite dyke, have as their main characteristics the high proportion of syntaxial quartz overgrowth and a porosity originated from different processes, initially by dissolution and later by partial filling and fracturing. Features like the presence of floating grains in the syntaxial cement, the transitional interpenetrative contact between the silica-rich cement and grains as well as the intense fracture porosity are strong indications that the cement has been formed by dissolution and reprecipitation of quartz from the framework under the effect of thermal expansion followed by rapid contraction. The increase of the silica-rich cement towards the dyke in association with the orthogonal disposition of the columns relative to dyke walls are indicative that the igneous body may represent the main heat source for the interstitial aqueous solutions previously existing in the sediments. At macroscopic scale, the increasing of internal tensions in the sandstones is responsible for the nucleation of polygons, leading to the individualization of prisms, which are interconnected by a system of joints, formed firstly on isotherm surfaces of low temperature and later on successive adjacent planes towards the dyke heat source.

Magnetoelastic and thermal effects in the BiMn(2)O(5) lattice: A high-resolution x-ray diffraction study

High-resolution synchrotron x-ray diffraction measurements were performed on single crystalline and powder samples of BiMn(2)O(5). A linear temperature dependence of the unit cell volume was found between T(N)=38 and 100 K, suggesting that a low-energy lattice excitation may be responsible for the lattice expansion in this temperature range. Between T(*)similar to 65 K and T(N), all lattice parameters showed incipient magnetoelastic effects, due to short-range spin correlations. An anisotropic strain along the a direction was also observed below T(*). Below T(N), a relatively large contraction of the a parameter following the square of the average sublattice magnetization of Mn was found, indicating that a second-order spin Hamiltonian accounts for the magnetic interactions along this direction. On the other hand, the more complex behaviors found for b and c suggest additional magnetic transitions below T(N) and perhaps higher-order terms in the spin Hamiltonian. Polycrystalline samples grown by distinct routes and with nearly homogeneous crystal structure above T(N) presented structural phase coexistence below T(N), indicating a close competition amongst distinct magnetostructural states in this compound.

Thermal wave scattering by two overlapping and parallel cylinders

In this paper an analytical solution of the temperature of an opaque material containing two overlapping and parallel subsurface cylinders, illuminated by a modulated light beam, is presented. The method is based on the expansion of plane and cylindrical thermal waves in series of Bessel and Hankel functions. This model is addressed to the study of heat propagation in composite materials with interconnection between inclusions, as is the case of inverse opals and fiber reinforced composites. Measurements on calibrated samples using lock-in infrared thermography confirm the validity of the model.

Thermo-optics parameters measurements in photorefractive sillenite Bi(12)SiO(20) crystals by thermal lens technique

The present work reports on the thermo-optical properties of photorefractive sillenite Bi(12)SiO(20) (BSO) crystals obtained by applying the Thermal Lens Spectrometry technique (TLS). This crystals presents one high photorefractive sensitivity in the region blue-green spectra, since the measurements were carried out at two pump beam wavelengths (514.5 nm and 750 nm) to study of the light-induced effects in this material (thermal and/or photorefractive). We determine thermo-optical parameters like thermal diffusivity (D), thermal conductivity (K) and temperature coefficient of the optical path length change (ds/dT) in sillenite crystals. These aspects, for what we know, not was studied in details up to now using the lens spectrometry technique and are very important against of the promising potentiality of applications these crystals in non linear optics, real time holography and optical processing data.

Quasiharmonic elastic constants corrected for deviatoric thermal stresses

The quasiharmonic approximation (QHA), in its simplest form also called the statically constrained (SC) QHA, has been shown to be a straightforward method to compute thermoelastic properties of crystals. Recently we showed that for noncubic solids SC-QHA calculations develop deviatoric thermal stresses at high temperatures. Relaxation of these stresses leads to a series of corrections to the free energy that may be taken to any desired order, up to self-consistency. Here we show how to correct the elastic constants obtained using the SC-QHA. We exemplify the procedure by correcting to first order the elastic constants of MgSiO(3) perovskite and MgSiO(3) postperovskite, the major phases of the Earth's lower mantle. We show that this first-order correction is quite satisfactory for obtaining the aggregated elastic averages of these minerals and their velocities in the lower mantle. This type of correction is also shown to be applicable to experimental measurements of elastic constants in situations where deviatoric stresses can develop, such as in diamond-anvil cells.