Intermetallic Ti-Al-based coatings were synthesized by mechanical alloying in a vibratory ball mill and subsequent annealing. A titanium layer was deposited on aluminum specimens and an aluminum layer and aluminum-titanium mixture were deposited on titanium specimens. Under the effect of milling balls, powder particles deposit at the substrates, forming layers that have a very good cohesion with the substrate. During subsequent heating, diffusion layers on the basis of titanium-aluminum phases are synthesized as a result of the chemical interaction between titanium and aluminum. In the case of titanium layer deposited on aluminum, the temperature interval of transformations is 600–650°C; first, a Ti3Al5-based phase is formed; then, as diffusion saturation with Al increases, an Al2Ti-based layer appears; and finally, the Al3Ti compound is formed. The reaction rates depend on the temperature and the duration of annealing. On titanium with a (Ti + Al) layer deposited on its surface, the Al3Ti, Al2Ti, TiAl, and Ti3Al compounds are formed in a temperature interval of 600–900°C. In the case of deposition a homogeneous aluminum layer on titanium, only Al3Ti and Ti3Al phases were observed after annealing. 相似文献
Two acoustic emission (AE) parameters, event count rate (ER) and the skewness of the peak amplitude distribution (PAD), were found to correlate with mechanical and damage mechanisms in unidirectional Kevlar-epoxy composites loaded in tension. The ER of the AE reached a local maximum at about 0.3σcu (σcu= composite tensile strength), a minimum at about 0.6–0.7σcu, and increasing ER rates were noted as failure stress approached, with a peak at final failure.Along with our proposed approach to evaluate the PAD as a tool for characterizing processes, damage mechanisms and failure modes, the third statistical moment of the PAD, the skewness, was found to be able to distinguish between various mechanisms. From the beginning of loading until completion of the fibre straightening process, 0.6–0.7σcu, the value of the skewness steadily decreased, and then gradually increased to final failure. This behaviour is explained by a model based on the non-elastic mechanisms which contribute to the monitored AE. At final failure, the PAD's skewness value was affected by macroscopic failure modes. When this mode comprises fibre fracture with little matrix and interface splitting, the skewness decreased; when fibre failure was accompanied by matrix and interface splitting, its value changed slightly or even increased. 相似文献
Summary By reacting esterification of phenolphtalein with methacrylate chloride, phenolphtalein dimethacrylate was obtained. Based on the results of elemental analysis, FTIR, 1H-NMR and 13C-NMR spectra, the structure of the product was proposed. The dimethacrylate was used as new crosslinker to crosslink poly(methyl methacrylate) (PMMA). The influence of the amount dimethacrylate on the crosslink density and some properties of the crosslinked polymers networks such as swelling, mechanical properties (tensile strength and elongation at break) and thermal stability were examined. 相似文献
The selective catalytic oxidation of ammonia to nitrogen (NH3-SCO) has been studied over hydrotalcite derived mixed metal oxides containing Cu, Co, Fe or Ni. XRD, BET, NH3-TPD and TPR techniques were used for catalysts characterization. Results of NH3-SCO were compared with those of selective catalytic reduction of NO with NH3 (NO-SCR). Reaction mechanism was studied by temperature-programmed surface reaction (TPSR) and activity tests with a various contact time. Catalytic performance of the studied samples depends on both kind and loading of transition metals in the mixed metal oxide system. The Cu-containing samples have been found to be the most active catalysts of the NH3-SCO process. Transition metal loading strongly influences distribution of ammonia oxidation products. The highest selectivity to N2 was measured for the catalysts with the lowest transition metal content. 相似文献
A simple and sensitive method has been devised to determine the amounts of volatile carbonyl compounds in vegetable oils and
fried potato chips, using a chemical reaction trap and absorption spectrophotometry. A sample of oil or fried potato chips
is heated and simultaneously purged with a flow of nitrogen gas which further bubbles through a tube (trap) containing a hydroxylamine
hydrochloride solution. The volatile carbonyl compounds are removed from the sample with the purge gas and retained in the
trapping solution as they react to form the less volatile oxime derivatives. These are subsequently estimated by ultraviolet
absorption, at wavelength 212 nm for the total oximes and at 272 nm specifically for conjugated diene carbonyl oximes, including
furfural if present. Volatile carbonyls can be determined by this method at levels as low as 0.1–0.5 ppm of the sample. The
method has been applied to the analysis of samples of canola (low erucic acid rapeseed) oil, cottonseed oil, and potato chips,
all before and after storage. The method should be suitable also for other types of fried food. 相似文献
Recently used models relating basic properties of the feed material, roller press design and its operating parameters are reviewed. In particular, we discuss the rolling theory for granular solids proposed by J.R. Johanson in the 1960s, later trials utilizing slab method and newly developed final element models. These methods are compared in terms of efficiency and accuracy of predicting the course of basic process variables like nip angle, pressure distribution in roll nip region, neutral angle, roll torque and roll force.
The finite element method offers the most versatile approach because it incorporates adequate information about powder behavior, geometry and frictional conditions. This enables to perform realistic computer experiments minimizing costs, time and resources needed for process and equipment optimization. 相似文献
Results of calculations based on a linearized multicomponent mass transfer theory developed by Burghardt and Krupiczka are compared with experimental data of Modine for condensation-evaporation process in ternary systems. These data have been obtained for acetone-benzene-nitrogen and acetone-benzene-helium in a welted wall column. Models I and II, which take into account diffusional interactions of components in a mullicomponent mixture show good agreement with the experiments as well as with other calculation methods (Krishna-Standart and Toor-Stewart-Prober). When multicomponent mass transfer occurs in the presence of inert species, a straightforward Model II is recommended. Model I, which is more universal, requires some iterative calculations with respect to the sum of mass fluxes. According to theoretical considerations the latter model is limited to the case of low total mass flux. The results of calculations for the systems studied were reasonably good though the total mass fluxes were not small. The calculation procedure based on the presented linearized models are convergent to the proper solutions in contrast to the Krishna-Standart Model IV which in some cases can be unstable. 相似文献
Refractory Y-α-SiAlON with elongated grain morphology was obtained by utilizing La2O3 as a densification aid, which resulted in excellent room-temperature and high-temperature strength. Room-temperature strength of 1000 MPa was achieved when La2O3 was augmented by adding Y2O3 or removing AlN. With only La2O3, a temperature-independent strength of 800–950 MPa was maintained up to 1100°C, then gradually decreasing by 25% when reaching 1300°C. The R-curve measurements of fracture toughness showed relatively little dependence on microstructure, consistent with a strong interface that suppresses grain boundary decohesion. Compared with other densification aids such as SiO2, Al2O3, Sc2O3, Y2O3, and Lu2O3, a finer microstructure was obtained by using La2O3. High nitrogen content in the residual La–Si–Al–O–N glass in equilibrium with the nitrogen-rich α-SiAlON is suggested to be the cause of these findings. 相似文献
A proton transfer triggered by a ligand interacting with thereceptor had been suggested as the initial step in the activationof a receptor for the neurotransmitter serotonin (5-hydroxy-tryptamine;5-HT). To evaluate the role of the receptor macromolecule inmodulating the primary molecular event in ligand-mediated activation,the process of proton transfer was analysed in the environmentof a protein model for the 5-HT receptor. In the absence ofa detailed receptor structure, the enzyme actinidin was chosenas the model for the receptor based on criteria obtained fromstructure-activity considerations on the ligands. The firstsimulation of a mechanism for receptor activation was performedon this model using methods of theoretical chemistry to studythe effect of specific structural elements. The premise is thatthe role of the elements of secondary structure of soluble proteins(e.g. actinidin) in determining structure-function relationsin these macromolecules is maintained when these elements arepart of membrane-bound receptor proteins. Results from the calculationsof the effects of the six alpha helices of actinidin on theproton transfer process from the imidazolium side chain of His162 to the thiol side chain of Cys 25 in the protein show thatthe helices contribute in different ways to modulate the energyof proton transfer. The largest helix, Al, opposes the protontransfer through the effect of the helix dipole. The chargedresidues (primary structure) in helix A3 favor the proton transfer,and mask the effect of its helix dipole (secondary structure)which opposes the transfer. The direction of the proton transfersimulated for the activation mechanism is opposite to that assumedin the catalytic process of the thiol protease, and the entireprotein environment opposes the transfer. This supports thespecific role of the ligand in triggering the proton transferas a response to its binding. 相似文献
Micro-mesoporous aluminosilicates based on ZSM-5 zeolite, obtained by a dual template method, as well as in the presence of a dual-functional template (i.e. a Gemini-type surfactant), were tested in the oxidation of furfural with hydrogen peroxide. Even substantial changes in acidity and porosity of the catalysts result in minor variations of selectivity towards the desired products. Application of the synthesized zeolite-based materials in the oxidation of furfural with hydrogen peroxide leads to formation of 2(5H)-furanone (yield up to 28.5%) and succinic acid (up to 19.5%) as the main C4 reaction products. The kinetic model developed previously to treat the results for oxidation of furfural over sulfated zirconia was able to describe the data also for micro-mesoporous aluminosilicates.