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Mechanical Activation (mechanical + activation)
Selected AbstractsSynthesis of Dense, High-Defect-Concentration B4C through Mechanical Activation and Field-Assisted CombustionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2004E. M. Heian Dense fine-grained B4C was synthesized by the spark plasma sintering (SPS) method using mechanically activated elemental powders. Relative densities of up to 95% were achieved. When characterized by X-ray line broadening methods, the grains of the resulting product were determined to be nanometric in scale. However, transmission electron microscopy (TEM) observations showed the product to be composed of a mixture of fine (nanometric) crystallites and grains in the micrometer range. The TEM images showed a highly defective structure containing a high density of twins. Their presence is the reason for the discrepancy between the X-ray and TEM results. [source] Mechanical Activation of Tetracalcium PhosphateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2004Uwe Gbureck It was found that prolonged high-energy ball-milling of Hilgenstokite (tetracalcium phosphate, TTCP) resulted in a decrease in both particle and crystallite size, leading to a mechanical activation of the compound. This mechanically activated material demonstrated a high reactivity such that, in contrast to highly crystalline TTCP, a setting reaction with water to nanocrystalline hydroxyapatite (HA) and Ca(OH)2 could be achieved at 37°C. However, crystalline TTCP is practically unreactive at physiologic temperatures because of the formation of a thin HA layer on the particle surface preventing further reaction. [source] B-Site Order,Disorder Transition in Pb(Mg1/3Nb2/3)O3,Pb(Mg1/2W1/2)O3 Triggered by Mechanical ActivationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Xingsen Gao B-site cation order,disorder transition induced by mechanical activation was observed in Pb(Mg1/3Nb2/3)O3,Pb(Mg1/2W1/2)O3 (PMN,PMW) solid solution, which was examined using both XRD diffraction and Raman spectroscopic study. The order,disorder transition is composition dependent. Mechanical activation triggers the B-site disordering, which can be steadily recovered by thermal annealing at elevated temperature, i.e., at temperatures around 600°C. Raman spectroscopy demonstrated that there existed tiny ordered microdomains in 0.4PMN·0.6PMW subjected to up to 20 h of mechanical activation, although they cannot be shown by X-ray diffraction. This is a result of the equilibrium between the mechanical destruction and temperature-facilitated recovering at the collision points during mechanical activation. It is therefore unlikely that a complete disordering can be realized in PMN,PMW by mechanical activation. The disordering in PMN,PMW triggered by mechanical activation occurs simultaneously with the refinement in crystallite size at the initial stage of mechanical activation, suggesting that the fragmentation of crystallites is responsible for the order,disorder transition at least during the initial stage of mechanical activation. [source] Crystallization of Lead Niobate Glass by Mechanical ActivationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2001Junmin Xue Mechanical activation-triggered crystallization in PbNb2O6 -based glass was dependent on the initial presence of nuclei. The crystallization cannot be initiated by mechanical activation in a highly amorphous glass composition quenched from 1350°C where PbNb2O6 nuclei did not exist. The steady growth of nanocrystallites of PbNb2O6 was observed with an increasing degree of mechanical activation in the glass quenched from 1300°C, where a density of PbNb2O6 nuclei existed before mechanical activation. The inability to nucleate in the highly amorphous oxide glass by mechanical activation is consistent with the much higher structural stability as compared with that of metallic glasses, such as Fe-Si-B. The mechanical activation-grown PbNb2O6 nanocrystals were 10,15 nm in size as observed using HRTEM and their crystallinities were further improved by thermal aging at an elevated temperature in the range of 550° to 650°C. [source] Nanosized Barium Titanate Powder by Mechanical ActivationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2000Junmin Xue Mechanical activation, without any additional heat treatment, is used to trigger the formation of a perovskite BaTiO3 phase in an oxide matrix that consists of BaO and TiO2 in a nitrogen atmosphere. The resulting BaTiO3 powder exhibits a well-established nanocrystalline structure, as indicated by phase analysis using X-ray diffractometry. A crystallite size of ,14 nm is calculated, based on the half-width of the BaTiO3 (110) peak, using the Scherrer equation, and an average particle size of 20,30 nm is observed using transmission electron microscopy for the activation-derived BaTiO3 powder. [source] ChemInform Abstract: Thermal Explosion in Al,Ni System: Influence of Mechanical Activation.CHEMINFORM, Issue 8 2010Jeremiah D. E. White Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Enhancement of Lithium Amide to Lithium Imide Transition via Mechanical Activation.CHEMINFORM, Issue 5 2007Tippawan Markmaitree Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Mechanical activation of precursors for nanocrystalline materialsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2003H. Heegn Abstract Nanostructured materials win big scientific interest and increasingly economic meaning through their specific exceptional properties. Precursors that were compacted by pressing and sintering are normally used preparation of materials. In present work, the influence of mechanical activation by grinding on the structure as well as on compacting and sintering behavior of oxides from magnesium, aluminium and silicon has been investigated. Starting materials for each metal oxide differ in microstructure, dispersity, and porosity. The influence of mechanical activation on the destruction of crystalline structure to nanocrystalline, as well as to the amorphous stage and the compaction of powders with nano-particles, as well as structures with nanoscale pores have been compared. The possibilities of the consolidation of nanostructured materials were investigated. The mechanical activation took place in a disc vibration mill. The mechanical activated materials as well as their pressing and their sintering products were characterized by density, particle-sizedistribution, specific surface, pore-structure, microstructure, and crystallite size by X-ray powder diffraction (XRD). The mechanical activation of the model-substances led, in most cases, to an improvement of the compaction properties; thus, this improvement can be achieved with subsequent sintering densities up to 98% of the theoretical density. From these experiments, generalizations transferable to other materials can be made. [source] B-Site Order,Disorder Transition in Pb(Mg1/3Nb2/3)O3,Pb(Mg1/2W1/2)O3 Triggered by Mechanical ActivationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Xingsen Gao B-site cation order,disorder transition induced by mechanical activation was observed in Pb(Mg1/3Nb2/3)O3,Pb(Mg1/2W1/2)O3 (PMN,PMW) solid solution, which was examined using both XRD diffraction and Raman spectroscopic study. The order,disorder transition is composition dependent. Mechanical activation triggers the B-site disordering, which can be steadily recovered by thermal annealing at elevated temperature, i.e., at temperatures around 600°C. Raman spectroscopy demonstrated that there existed tiny ordered microdomains in 0.4PMN·0.6PMW subjected to up to 20 h of mechanical activation, although they cannot be shown by X-ray diffraction. This is a result of the equilibrium between the mechanical destruction and temperature-facilitated recovering at the collision points during mechanical activation. It is therefore unlikely that a complete disordering can be realized in PMN,PMW by mechanical activation. The disordering in PMN,PMW triggered by mechanical activation occurs simultaneously with the refinement in crystallite size at the initial stage of mechanical activation, suggesting that the fragmentation of crystallites is responsible for the order,disorder transition at least during the initial stage of mechanical activation. [source] Nanosized Barium Titanate Powder by Mechanical ActivationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2000Junmin Xue Mechanical activation, without any additional heat treatment, is used to trigger the formation of a perovskite BaTiO3 phase in an oxide matrix that consists of BaO and TiO2 in a nitrogen atmosphere. The resulting BaTiO3 powder exhibits a well-established nanocrystalline structure, as indicated by phase analysis using X-ray diffractometry. A crystallite size of ,14 nm is calculated, based on the half-width of the BaTiO3 (110) peak, using the Scherrer equation, and an average particle size of 20,30 nm is observed using transmission electron microscopy for the activation-derived BaTiO3 powder. [source] Optimal Left Ventricular Lead Position Predicts Reverse Remodeling and Survival After Cardiac Resynchronization TherapyCONGESTIVE HEART FAILURE, Issue 2 2009David Tepper MD Background., A nonoptimal LV pacing lead position may be a potential cause for nonresponse to CRT. Methods., The site of latest mechanical activation was determined by speckle tracking radial strain analysis and related to the LV lead position on chest x-ray in 244 CRT candidates. Echocardiographic evaluation was performed after 6 months. Long-term follow-up included all-cause mortality and hospitalizations for heart failure. Results., Significant LV reverse remodeling (reduction in LV end-systolic volume from 189±83 mL to 134±71 mL, P<.001) was noted in the group of patients with a concordant LV lead position (n=153, 63%), whereas patients with a discordant lead position showed no significant improvements. In addition, during long-term follow-up (32±16 months), less events (combined for heart failure hospitalizations and death) were reported in patients with a concordant LV lead position. Moreover, a concordant LV lead position appeared to be an independent predictor of hospitalization-free survival after long-term CRT (hazard ratio: 0.22, P=.004). Conclusions., Pacing at the site of latest mechanical activation, as determined by speckle tracking radial strain analysis, resulted in superior echocardiographic response after 6 months of CRT and better prognosis during long-term follow-up. [source] Mechanical activation of precursors for nanocrystalline materialsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2003H. Heegn Abstract Nanostructured materials win big scientific interest and increasingly economic meaning through their specific exceptional properties. Precursors that were compacted by pressing and sintering are normally used preparation of materials. In present work, the influence of mechanical activation by grinding on the structure as well as on compacting and sintering behavior of oxides from magnesium, aluminium and silicon has been investigated. Starting materials for each metal oxide differ in microstructure, dispersity, and porosity. The influence of mechanical activation on the destruction of crystalline structure to nanocrystalline, as well as to the amorphous stage and the compaction of powders with nano-particles, as well as structures with nanoscale pores have been compared. The possibilities of the consolidation of nanostructured materials were investigated. The mechanical activation took place in a disc vibration mill. The mechanical activated materials as well as their pressing and their sintering products were characterized by density, particle-sizedistribution, specific surface, pore-structure, microstructure, and crystallite size by X-ray powder diffraction (XRD). The mechanical activation of the model-substances led, in most cases, to an improvement of the compaction properties; thus, this improvement can be achieved with subsequent sintering densities up to 98% of the theoretical density. From these experiments, generalizations transferable to other materials can be made. [source] Polymorph transitions of bicalutamide: A remarkable example of mechanical activationJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2008Zoltán Német Abstract Bicalutamide, an active pharmaceutical ingredient possessing antiandrogenic activity, is known to exhibit polymorphism. The higher melting Form I relates monotropically to the lower melting Form II. The amorphous form can be easily produced by quench cooling the melt, but it is known to crystallize spontaneously to Form II at room temperature within days. Our results show that crystallization of amorphous bicalutamide is greatly influenced by experimental conditions and sample treatment. The effect of mechanical activation on the polymorph transitions is investigated in detail. Seeds of Form I can be formed in the amorphous phase even due to gentle mechanical treatment, which results in crystallization to the more stable structure at elevated temperature. The crystalline Form II may as well be transformed to the stable modification through mechanical activation at elevated temperature. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97: 3222,3232, 2008 [source] Fe3+ Ions Acting as Probes and Agents in Aggregation Processes and Solid-State Reactions in AlO(OH)/Al2O3 MatricesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2010Reinhard Stößer The fate of doped iron species during various mechanically and thermally initiated redox reactions and aggregation processes in crystalline and amorphous AlO(OH) or Al2O3 matrices was investigated. The amorphization of the matrix was performed by chemical (i.e., via sol,gel processes) or mechanochemical treatment (high-energy ball milling). Thermal analysis, coupled with mass spectrometry (TA-MS), Mössbauer spectroscopy, and electron spin resonance (ESR), was used. The TA under various gas atmospheres allowed preparing samples under a controlled temperature regime, together with a controlled gas influence. Both the effect of mechanical activation and the influence of the iron doping could be followed macroscopically via the down-shift of the peak temperature of the corundum formation. The ESR data characterize the Fe3+ ions and their interaction with the magnetic surrounding based on the fine structure parameters. The Mössbauer data allowed the characterization of the Fe(0), Fe2+, and Fe3+ species, together with providing information about their coordinative surrounding. Both methods provided general complementary spectroscopical information. Unexpectedly, (FeOx)n and (FexAl1,x)2O3 aggregates could also be detected in the range of low Fe concentrations. It was demonstrated that even in the low-level doped systems [(FexAl1,x)2O3 with x,0.01], all the essential spectroscopic phenomena occur. At higher Fe concentrations, they were discovered to be caused by magnetic and spin exchange interactions as well as by solid-state reactions during and after the mechanical activation. [source] Mechanical Activation of Tetracalcium PhosphateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2004Uwe Gbureck It was found that prolonged high-energy ball-milling of Hilgenstokite (tetracalcium phosphate, TTCP) resulted in a decrease in both particle and crystallite size, leading to a mechanical activation of the compound. This mechanically activated material demonstrated a high reactivity such that, in contrast to highly crystalline TTCP, a setting reaction with water to nanocrystalline hydroxyapatite (HA) and Ca(OH)2 could be achieved at 37°C. However, crystalline TTCP is practically unreactive at physiologic temperatures because of the formation of a thin HA layer on the particle surface preventing further reaction. [source] B-Site Order,Disorder Transition in Pb(Mg1/3Nb2/3)O3,Pb(Mg1/2W1/2)O3 Triggered by Mechanical ActivationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Xingsen Gao B-site cation order,disorder transition induced by mechanical activation was observed in Pb(Mg1/3Nb2/3)O3,Pb(Mg1/2W1/2)O3 (PMN,PMW) solid solution, which was examined using both XRD diffraction and Raman spectroscopic study. The order,disorder transition is composition dependent. Mechanical activation triggers the B-site disordering, which can be steadily recovered by thermal annealing at elevated temperature, i.e., at temperatures around 600°C. Raman spectroscopy demonstrated that there existed tiny ordered microdomains in 0.4PMN·0.6PMW subjected to up to 20 h of mechanical activation, although they cannot be shown by X-ray diffraction. This is a result of the equilibrium between the mechanical destruction and temperature-facilitated recovering at the collision points during mechanical activation. It is therefore unlikely that a complete disordering can be realized in PMN,PMW by mechanical activation. The disordering in PMN,PMW triggered by mechanical activation occurs simultaneously with the refinement in crystallite size at the initial stage of mechanical activation, suggesting that the fragmentation of crystallites is responsible for the order,disorder transition at least during the initial stage of mechanical activation. [source] Crystallization of Lead Niobate Glass by Mechanical ActivationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2001Junmin Xue Mechanical activation-triggered crystallization in PbNb2O6 -based glass was dependent on the initial presence of nuclei. The crystallization cannot be initiated by mechanical activation in a highly amorphous glass composition quenched from 1350°C where PbNb2O6 nuclei did not exist. The steady growth of nanocrystallites of PbNb2O6 was observed with an increasing degree of mechanical activation in the glass quenched from 1300°C, where a density of PbNb2O6 nuclei existed before mechanical activation. The inability to nucleate in the highly amorphous oxide glass by mechanical activation is consistent with the much higher structural stability as compared with that of metallic glasses, such as Fe-Si-B. The mechanical activation-grown PbNb2O6 nanocrystals were 10,15 nm in size as observed using HRTEM and their crystallinities were further improved by thermal aging at an elevated temperature in the range of 550° to 650°C. [source] Mechanical Activation-Assisted Synthesis of Pb(Fe2/3W1/3)O3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2000Seok Khim Ang Perovskite Pb(Fe2/3W1/3)O3 (PFW) was prepared via a mechanical activation-assisted synthesis route from mixed oxides of PbO, Fe2O3, and WO3. The mechanically activated oxide mixture, which exhibited a specific area of >10 m2/g, underwent phase conversion from nanocrystalline lead tungstate (PbWO4) and pyrochlore (Pb2FeWO6.5) phases on sintering to yield perovskite PFW, although the formation of perovskite phase was not triggered by mechanical activation. When heated to 700°C, >98% perovskite phase was formed in the mechanically activated oxide mixture. The perovskite phase was sintered to a density of ,99% of theoretical density at 870°C for 2 h. The sintered PFW exhibited a dielectric constant of 9800 at 10 kHz, which was ,30% higher than that of the PFW derived from the oxide mixture that was not subjected to mechanical activation. [source] | ||||||||||