Application of electromagnetic processing for development of high-performance sintered powder metal parts

Electromagnetic processing was used to study the effects of electro-magneto forming on the dimensional control and thermal stability of sintered powder metal (PM) parts. The investigation was carried out on sinter-hardened, low chromium-molybdenum bainitic steel. The results show an increase in the microhardness of about 14% for the electromagnetic processed parts compared to the as-sintered parts. This was attributed to the 2% increase in the density, 17% and 29% reduction in the volume fraction of porosity and width of the bainitic lath, respectively, due to the electromagnetic processing. Dimensional characterization was carried out using a vertically aligned push-rod dilatometer. After four thermal cycles of heating and cooling, at a controlled rate of 5 °C/min to 1000 °C, the electromagnetic processed parts exhibited reduced dimensional change of about 44% lower than for the as-sintered parts. This is significantly important for applications that demand high dimensional tolerance and performance, especially at elevated temperatures.     

The effect of substitution on the thermo-physical properties of LaMnxV1−xO4−δ

LaMn_xV_1−xO_4−δ(0≤x≤1) samples were characterized using thermogravimetry, thermo-dilatometry, high-temperature X-ray diffraction (HTXRD) and temperature-programmed reduction techniques, with an objective to explore the role of substitution on their thermo-physical properties, which may have a direct bearing on their catalytic behavior. Even though the substituted compositions (x<0.8) were of a single phase, their reduction occurred in two steps, a lower temperature step corresponding to Mn⁴⁺→Mn³⁺/Mn²⁺ and another higher temperature one related to V⁵⁺→V³⁺. The dilatometric measurements gave similar values of linear thermal expansion coefficient (α₁) at temperatures up to 600 °C, both for LaVO₄ and substituted samples. A different behavior was, however, observed at higher temperatures, whereas thermal contraction was observed in case of LaVO₄ for measurements at temperatures above 700 °C, the value of α₁ remained almost constant in case of the substituted samples. Furthermore, the HTXRD data revealed expansion in cell volume for all temperatures up to 950 °C, irrespective of the substitution. These results therefore point to a higher degree of sintering in LaVO₄ as compared to Mn-doped samples on heating at temperatures above 700 °C. It is inferred that the resistance to sintering and the lowering of the reduction temperature are both responsible to the higher catalytic activity of the substituted samples and their compositional stability during the repeated cycles of reduction-reoxidation, as reported earlier [Appl. Catal. A 205 (2001) 295].     

Mechanochemical activation of minerals on the cordierite synthesis

The cordierite is commonly prepared by reaction of talc, clay and gibbsite within the range of 1200-1350 °C. This study deals with the effect of the amorphization by grinding of that mixture and its influence on the cordierite formation.The mixture previously mentioned underwent six different treatments: mixing without grinding (A) (only mixing); non-amorphizing grinding (A_M) and amorphizing grinding in oscillating mill at four different times (H samples). The phases formed by thermal treatment were studied using differential thermal analysis (DTA)-thermogravimetric analysis (TG)-DTG, dilatometries and X-ray diffraction (XRD) techniques in certain combinations.The thermal analysis of the A and A_M series were compared and they do not show significant differences, whereas the H samples present remarkable alterations in the DTA peaks as well as in the weight losses (TG). Thus, a great number of DTA peaks tend to decrease the temperature of the maximum and to lower the intensity as the amorphization time increases.Calcination tests performed within the range 900-1200 °C show important differences in the diffractograms obtained from the intermediate products. While at 1350 °C the A and H samples reach the same final phases, within the range 1200-1360 °C they present important differences in the DTA indicating that the sequence and direction of reaction are different. The same behavior can be observed by dilatometric analysis.     

Magnetostrictive behaviour of Fe73.5Si13.5B9Nb3−xMoxCu1 alloys

Magnetostriction, dilatation and calorimetric measurements were performed on FINEMET type as-quenched and heat treated ribbons. Nb was gradually replaced by Mo in order to study the influence of the refractory elements exchange on several magnetostriction parameters. The results could be correlated with magnetic and structural transformations throughout thermal treatments and assured that the whole series is suitable for technical applications.     

Synthesis, Characterization and Inhibition Effects of Vanadium Substituted Dawson-type Heteropoly Acids(Mo, P)

Four new vanadium substituted Dawson-type heteropoly acids H7[P2Mo17VO62]·39H2O(1), H8[P2Mo16V2O62]·41H2O(2), H9[P2Mo15V3O62]·51H2O(3) and H8[P2Mo14V4O62H2]·45H2O(4) were prepared respec-tively. Their structures were determined by IR and ICP. The inhibition effects of vanadium substituted Dawson-type heteropoly acids(Mo, P) on free radical polymerization of methyl methacrylate(MMA) were investigated by dilatometry. The results show that the rate of the polymerization of MMA decreases and the inhibition effe...     

Stability, oxygen permeability and chemical expansion of Sr(Fe,Al)O3 − δ- and Sr(Co,Fe)O3 − δ-based membranes

Perovskite-type SrFe_0.7Al_0.3O_3 − δ and SrCo_0.8Fe_0.2O_3 − δ, and two related dual-phase composites with nominal compositions (SrFeO_3 − δ)_0.7(SrAl₂O₄)_0.3 and (SrCo_0.8Fe_0.2O_3 − δ)_0.7(SrAl₂O₄)_0.3, were comparatively studied employing controlled-atmosphere dilatometry, thermogravimetry, Mössbauer spectroscopy, and measurements of steady-state oxygen permeation fluxes through dense ceramic membranes. The composite materials display lower thermal and chemical expansion compared to the parent single-phase perovskites. The thermal expansion coefficients at 1023-1223 K are however still high, (20-23) × 10^− 6 K^− 1 at atmospheric oxygen pressure and (17-18) × 10^− 6 K^− 1 at p(O₂) = 10 Pa, thus limiting the range of possible membrane reactor configurations. Sr(Co,Fe)O_3 − δ-based materials exhibit extensive vacancy-ordering processes in inert atmospheres, resulting in a slow relaxation of the oxygen nonstoichiometry, chemical expansion and oxygen permeation fluxes. In comparison to Sr(Fe,Al)O_3 − δ, the stability of cobalt-containing ceramics in CO₂ is also poor, which leads to a partial blocking of the membrane surface by decomposition products and degradation of the oxygen transport. Thermogravimetric analysis showed that the interaction with carbon dioxide occurs even at elevated temperatures, up to 1223 K. Under high oxygen chemical potential gradients such as air/(H₂-H₂O), the composite membranes showed kinetically stable operation without bulk decomposition at 1073 K. The kinetic stabilization associated with surface-limited oxygen permeation was confirmed by the conversion-electron Mössbauer spectroscopy analysis of one (SrFeO_3 − δ)_0.7(SrAl₂O₄)_0.3 membrane exposed to dry CH₄ at 1173 K, where no traces of Fe²⁺ and metallic iron were detected in the reduced surface layer.     

A STUDY ON THE CRYSTALLIZATION KINETICS OF NYLON 1010

The kinetic behavior of isohermal and nonisothermal crystallization of nylon-1010has been studied by means of dilatometry and differential scanning calorimetry, respec-tively. The isothermal and nonisothermal process can be descibed by Avrami equationand Ozawa equation, respectively. From the experimental results the kinetic paramters ofcrystallization and crystalline mechanism for isothermal and nonisothermal measurementsare discussed.     

Interplay of structure and magnetism in ruthenocuprates: a Raman scattering and dilatometry study

We present a Raman scattering and dilatometry study of polycrystalline samples of the magnetic superconducting ruthenocuprates RuSr₂Gd_2−xCe_xCu₂O_10+δ (RuGd₁₂₂₂) and RuSr₂GdCu₂O₈ (RuGd₁₂₁₂). In the Raman spectra a high-temperature diffusive-like laser-tail develops below the magnetic ordering temperature (T_M) into an underdamped peak which shifts up to 130 cm⁻¹. A line assigned to O(Ru) phonons hardens, narrows and strengthens strongly below T_M. Finally, a phonon peak appears below T_M at 590 cm⁻¹. These three magnetic-order-dependent features are observed for RuGd₁₂₁₂ and for RuGd₁₂₂₂ with x=1.0, but do not appear for x=0.5. Dilatometry measurements, on the other hand, evidence a change of the expansion coefficient at T_M. These results point to a structural effect accompanying the magnetic order, and suggest a complex interplay of spin and lattice degrees of freedom in these ruthenocuprates.     

Simultaneous measurement of thermal expansion and heat capacity using temperature modulation technique

An instrument for simultaneous measurement of thermal expansion and heat capacity was developed using temperature modulation technique. The instrument was designed for thin films in order to avoid temperature distribution in the sample. Electric capacitance was measured to obtain temperature dependence of the sample thickness. The instrument was applied to the glass transition of polystyrene and it was confirmed that reliable comparison between the dilatometric and calorimetric results could be made.