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1.
George Stiubianu Carmen Racles Maria Cazacu Bogdan C. Simionescu 《Journal of Materials Science》2010,45(15):4141-4150
Cellulose acetate was reacted in different ratios with poly[dimethyl(methyl-H)siloxane] containing 25 mol% Si–H side groups
along the chain. A dehydrocoupling reaction between Si–H and C–OH groups occurred in presence of Karstedt’s catalyst, leading
to the formation of Si–O–C bond, as proved by FTIR spectra, thus crosslinking the cellulose derivative. The networks were
processed as films by casting before the end of the reaction and were investigated by different techniques to emphasize the
morphology, thermal, dielectric and surface properties developed in correlation with the ratio between the two involved components
(cellulose and siloxane derivatives). A decrease of the dielectric constant values of cellulose acetate was noticed throughout
the studied frequency and temperature range as a result of crosslinking. 相似文献
2.
An investigation of the wettability of the intermetallic compound NiAl by a liquid Ni–4.5 wt% Si–3.2 wt% B filler metal is
presented in this paper. Dynamic observations of spreading of Ni–Si–B droplets, conducted using hot-stage light microscopy,
are correlated with post-cooling microscopy and analysis. The paper examines the influence of the oxide layer on the NiAl
substrates, on the progression of spreading of the Ni–Si–B liquid. Termination of spreading of the Ni–Si–B droplets by the
onset of isothermal solidification at the spreading front is considered.
Spreading of the Ni–Si–B droplets was found to be rapid until the onset of isothermal solidification at the spreading front.
However, once isothermal solidification commenced, negligible further spreading was observed. The Ni–Si–B filler metal was
observed to spread by undermining of the substrate oxide. However, a marked reaction occurred between the substrate oxide
and the Ni–Si–B filler metal. This reaction served to remove the substrate oxide layer. The paper contrasts the mechanisms
of substrate oxide undermining and isothermal solidification of liquid Ni–Si–B droplets on NiAl with those occurring during
the spreading of the same liquid on pure nickel and Ni–Cr alloys.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
3.
Takahiro Namazu Tomohiro Ishikawa Yoshio Hasegawa 《Journal of Materials Science》2011,46(9):3046-3051
In this article, strength evaluation of silicon carbide (Si–C) ceramics fabricated from polycarbosilane (PCS) precursor is
described. Si–C ceramics was prepared by firing a green body made of the mixture of Si–C nano-powders and a PCS solution at
1,273 K in N2 gas for an hour. To obtain dense Si–C, the solution was infiltrated into the produced body, and then it was fired again.
The polymer infiltration and pyrolysis (PIP) process was conducted up to 12 cycles. Si–C ceramics was diced to be rectangle
shape measuring 1.0 mm × 3.0 mm × 0.5 mm, and was subjected to the three-point bending test for measurement of the Young’s
modulus and bending strength. Si–C specimens fabricated through PIP processes less than 2 cycles showed non-linear force–displacement
curves like a polymer, whereas those through the processes more than 3 cycles showed linear relations and fractured in a brittle
manner. The Young’s modulus of 12-cycles-PIPs specimen was found to be 56 GPa on average, which was approximately 22-fold
of non-PIP specimen. The bending strength was also increased with an increase in the number of PIP process. The maximum value
was found to be 157 MPa. The cause of the influence of PIP process on the mechanical characteristics is discussed using a
PCS-derived Si–C model. 相似文献
4.
Nourmohammadi J Sadrnezhaad SK Ghader AB 《Journal of materials science. Materials in medicine》2008,19(12):3507-3514
In this study, the apatite-forming ability of the new resin-modified glass-ionomer cement was evaluated by soaking the cement
in the simulated body fluid. The Fourier Transform Infrared (FTIR) spectrometer and X-Ray Diffraction (XRD) patterns of the
soaked cement pointed to the creation of poorly crystalline carbonated apatite. It was found that the releasing of calcium
ions from the soaked cement will dominate the undesirable effect of polyacrylic acid on apatite formation. Consequently, the
ionic activity products (IAPs) of the apatite in the surrounding medium increased which accelerated apatite nucleation induced
by the presence of the Si–OH and COOH groups. Accordingly, the apatite nuclei started to form via primary heterogeneous nucleation
and continued by secondary nucleation. Therefore, nucleation and growth occurs as in the layer-by-layer mode so that finite
numbers of monolayers are produced. Subsequent formation of film occurs by formation of discrete nuclei (layer-plus-island
or SK growth). 相似文献
5.
A. E. Karantzalis A. Lekatou E. Georgatis H. Mavros 《Journal of Materials Science》2010,45(8):2165-2173
Novel metal matrix composites have been produced by cast production route. TiC and WC ceramic reinforcing particles have been
successfully introduced into Al 6060, Al 319, Al 356, Al–7Si–5Mg, Al–20Cu and Al 2007 alloys. Refined grain structure and
various intermetallic phase formation have been observed. Particle–melt and particle–solidification front interactions, solidification
sequence and particle–matrix interfacial characteristics have been examined by means of metallography, SEM examination and
EDX analysis. Particle distribution, intermetallic phase formation and location and grain structure are discussed in terms
of ceramic-melt wetting characteristics, alloying element interfacial segregation and particle–solidification front thermal
behaviour. 相似文献
6.
7.
Jihoon Oh Sunyoung Chang Jiyoung Jang Seungkwang Roh Jaehong Park Jungwoo Lee Daewon Sohn Whikun Yi Yeongri Jung Sung-Jin Kim 《Journal of Materials Science: Materials in Electronics》2007,18(8):893-897
We investigated field emission (FE) properties of imogolite including the turn-on field and lifetime stability. Imogolite
is an excellent electron emitter with a turn-on field of approximately 2.5–3.5 V/μm. A lifetime test revealed that imogolite
protects itself during FE under exposure to O2 gas. We also measured the current–voltage characteristics of the imogolite as a function of the amount of water adsorbed
on the surface. The results suggested that the electrode-containing imogolite device could be a useful water sensor in a nanoscale
environment. 相似文献
8.
The subcritical crack growth resistance in water of a Y–Si–Al–O and Y–Si–Al–O–N glasses has been investigated with three point bending experiments. It has been shown that the SCG behaviour of the Y–Si–Al–O–N glass is superior to that of the Y–Si–Al–O glass. This is reflected by the power law exponent n which is 21 for the Y–Si–Al–O glass and 63 for the Y–Si–Al–O–N glass. Mechanistic implications of these observations are discussed. 相似文献
9.
M. López-Álvarez E. L. Solla P. González J. Serra B. León A. P. Marques R. L. Reis 《Journal of materials science. Materials in medicine》2009,20(5):1131-1136
The aim of this study consisted on investigating the influence of silicon substituted hydroxyapatite (Si–HA) coatings over
the human osteoblast-like cell line (SaOS-2) behaviour. Diatomaceous earth and silica, together with commercial hydroxyapatite
were respectively the silicon and HA sources used to produce the Si–HA coatings. HA coatings with 0 wt% of silicon were used
as control of the experiment. Pulsed laser deposition (PLD) was the selected technique to deposit the coatings. The Si–HA
thin films were characterized by Fourier Transformed Infrared Spectroscopy (FTIR) demonstrating the efficient transfer of
Si to the HA structure. The in vitro cell culture was established to assess the cell attachment, proliferation and osteoblastic
activity respectively by, Scanning Electron Microscopy (SEM), DNA and alkaline phosphatase (ALP) quantification. The SEM analysis
demonstrated a similar adhesion behaviour of the cells on the tested materials and the maintenance of the typical osteoblastic
morphology along the time of culture. The Si–HA coatings did not evidence any type of cytotoxic behaviour when compared with
HA coatings. Moreover, both the proliferation rate and osteoblastic activity results showed a slightly better performance
on the Si–HA coatings from diatoms than on the Si–HA from silica. 相似文献
10.
Mechanical alloying process, as a solid-state technique, is a very useful method for fabrication of high melting point compounds
like metal carbides and nitrides, which additionally have nanocrystalline structure with improved properties. In this work
the development of several carbides including iron, aluminium and silicon carbides by the mechanical alloying process and
the effect of subsequent heat treatment were investigated. Mixtures of elemental powders of Fe–C, Si–C and Al–C were mechanically
alloyed, nominally at room temperature using a laboratory planetary ball mill. Structural changes of samples were studied
by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the aluminium carbide (Al4C3) could not be synthesized by mechanical alloying process alone, even after long milling times. A suitable subsequent heat
treatment was required to allow Al–C reaction to take place kinetically. In contrast mechanical alloying of Fe–C as well as
Si–C systems directly led to the formation of Fe3C and SiC carbides after sufficient milling time. In all cases the end product had a nanosized structure. 相似文献
11.
In order to solve the problem of the poor wear resistance in conventional austenitic stainless steels, a new type austenitic
stainless steel was designed based on Fe–Mn–Si–Cr–Ni shape memory alloys in this article. Studies on its wear resistance and
wear mechanism have been carried out by comparison with that of AISI 321 stainless steel using friction wear tests, X-ray
diffraction, scanning electron microscope. Results showed that the wear resistance of Fe–14Mn–5.5Si–12Cr–5Ni–0.10C alloy was
better than that of AISI 321 stainless steel both in dry and oily friction conditions owing to the occurrence of the stress-induced
γ → ε martensitic phase transformation during friction process. This article also compared the corrosion performance of the
two stainless steels by testing the corrosion rate. Results showed that the corrosion rate of Fe–14Mn–5.5Si–12Cr–5Ni–0.10C
alloy was notably lower in NaOH solution and higher in NaCl solution than that of AISI 321 stainless steel. 相似文献
12.
N. L Tawfik 《Journal of Materials Science》1997,32(11):2997-3000
Continuous uniform ribbons of Al–16 Si, Al–12.5 Si–1 Ni and Al–12.5 Si–1 Mg were prepared by melt spinning. Microhardness
was measured. The as-melt spun values were 1280, 1370 and 1500 MN m-2 which relax on thermal ageing to 700, 700 and 800 MN
m-2 for Al–16 Si, Al–Si–Ni and Al–Si–Mg, respectively. The hardness values of the melt spun ribbons are higher than the as-cast
rods from which the ribbons were produced by a factor ranging from 1.8–2.2 times. Tensile testing at room temperature shows
that the load–elongation curves are linear with a change of slope occurring in some of the specimens. These curves also show
serrations in the case of as-melt spun and the intermediately annealed Al–Si specimens, while no serration was observed in
the fully annealed samples. No serration was observed in the Al–Si–Ni and Al–Si–Mg alloys. UTS values were 420, 270 and 100
MN m-2 for Al–16 Si, Al–Si–Ni and Al–Si–Mg, respectively. These values show that the rapid solidification process improved
the tensile properties significantly in Al–16 Si and Al–Si–Ni alloys while no significant improvement can be detected for
Al–Si–Mg alloy. A discussion is given on hardness relaxation and tensile testing results in terms of silicon precipitation.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
13.
The microstructures, machinability and surface characteristics of Al–7Si and Al–7Si–2.5Cu cast alloys were studied after various
melt treatments like grain refinement and modification. Results indicate that combined grain refined and modified Al–7Si–2.5Cu
cast alloys have microstructures consisting of uniformly distributed α-Al grains, eutectic Al–silicon and fine CuAl2 particles in the interdendritic region. These alloys exhibited better machinability and surface characteristics in the cast
condition compared with the same alloy subjected to only grain refinement or modification. Performances of the turning inserts
(Un-coated, PVD and Polished CVD diamond coated) were evaluated in machining Al–7Si and Al–7Si–2.5Cu cast alloys under dry
environment using a lathe. The Polished CVD diamond coated insert outperformed the Un-coated or PVD-coated cutting inserts
which suffered from sizeable edge buildup leading to higher cutting force and poor surface finish. The Polished CVD diamond
coated insert shows a very small steady wear without flaking of the diamond film during cutting. This paper attempts to investigate
the influence of grain refinement, modification and combined action of both on the microstrutural changes in the Al–7Si and
Al–7Si–2.5Cu cast alloys and their machinability and surface finish when different turning inserts used. 相似文献
14.
The effect of Cu alloying additions on the crystallization of Fe–Si–B alloy was studied. The selected alloys compositions
are Fe77.5Si13.5B9 and Fe76.5Si13.5B9Cu1. By comparing their crystallization temperatures, activation energy of crystallization, phase formation and microstructural
evolution after heat treatment, the effect of Cu alloying additions was determined. It was found that Cu alloying additions
reduced the crystallization temperature as well as the activation energy of the crystallization. Although the phases formed
in both alloys were Fe3Si and Fe3B phases the microstructures were dramatically different: a dendritic microstructure was observed in the case of the Fe–Si–B
alloy, while spheriodal crystals around 100 nm in size were observed in the case of the Fe–Si–B–Cu alloy. Cu alloying addition
increased the saturation magnetization during primary crystallization whereas it decreased the saturation magnetization after
secondary crystallization began. Interestingly, for both alloys the same trends of the magnetization and coercivity measurements
were observed except that the extent of the changes were higher in the case of the Fe–Si–B–Cu alloy than that of the Fe–Si–B
alloy. 相似文献
15.
Masaki Narisawa Ryu’ichi Sumimoto Ken’ichiro Kita 《Journal of Materials Science》2010,45(20):5642-5648
Si–O–C ceramic fiber was synthesized from a kind of silicone resin with low carbon content. The melt-spun resin fiber was
exposed to SiCl4 vapor under a nitrogen gas flow, and the fiber was heated at 373 K for 2 h to complete the curing process. The cured fiber
was pyrolyzed at 1273 K in an inert atmosphere to be converted to Si–O–C fiber. The entire chemical composition of the pyrolyzed
fiber was almost identical to that of a previously reported resin which was pyrolyzed without curing. Auger spectrum analysis
indicated an increase in silicon content near the fiber surface. The Si–O–C fiber thus obtained was heat-treated at 1511 or
1603 K in an air flow to evaluate oxidation resistance. Elemental analysis, XRD measurement, and SEM image observations were
carried out on the oxidized Si–O–C fibers. Even with such thin fiber diameters, the oxidation process under these conditions
was slow and the formation of a thin oxide layer on the fiber surface was confirmed. The existence of a residual Si–O–C core
surrounded by a crystallized silica layer was observed in fractured fiber cross-sections after severe treatment conditions
of 24 h oxidation at 1511 K or 3 h oxidation at 1603 K. 相似文献
16.
Leonor IB Kim HM Balas F Kawashita M Reis RL Kokubo T Nakamura T 《Journal of materials science. Materials in medicine》2007,18(10):1923-1930
Covalent coupling of sulfonic group (–SO3H) was attempted on different polymers to evaluate efficacy of this functional group in inducing nucleation of apatite in
body environment, and thereupon to design a simple biomimetic process for preparing bonelike apatite-polymer composites. Substrates
of polyethylene terephthalate (PET), polycaprolactam (Nylon 6), high molecular weight polyethylene (HMWPE) and ethylene-vinyl
alcohol co-polymer (EVOH) were subjected to sulfonation by being soaked in sulfuric acid (H2SO4) or chlorosulfonic acid (ClSO3H) with different concentrations. In order to incorporate calcium ions, the sulfonated substrates were soaked in saturated
solution of calcium hydroxide (Ca(OH)2). The treated substrates were soaked in a simulated body fluid (SBF). Fourier transformed infrared spectroscopy, thin-film
X-ray diffraction, and scanning electron microscopy showed that the sulfonation and subsequent Ca(OH)2 treatments allowed formation of –SO3H groups binding Ca2+ ions on the surface of HMWPE and EVOH, but not on PET and Nylon 6. The HMWPE and EVOH could thus form bonelike apatite layer
on their surfaces in SBF within 7 d. These results indicate that the –SO3H groups are effective for inducing apatite nucleation, and thereby that surface sulfonation of polymers are effective pre-treatment
method for preparing biomimetic apatite on their surfaces. 相似文献
17.
C. C. Fu J. S. C. Jang L. J. Chang T. Y. Lin C. M. Kuo 《Journal of Materials Science》2007,42(14):5327-5334
The effect of strain rate and environment on the mechanical behavior at different temperatures of the Ni–19Si–3Nb–0.15B–0.1C
alloy is investigated by atmosphere-controlled tensile testing under various conditions at different strain rates and different
temperatures). The results reveal that the Ni–19Si–3Nb–0.15B–0.1C alloy exhibits ductile mechanical behavior (UTS ∼ 1250 MPa,
ε ~ 14%) at temperatures below 873 K under different atmosphere conditions. However, the alloy without boron and carbon addition
shows ductile mechanical behavior only when the sample is tested in vacuum. This indicates that the microalloying of boron
and carbon does overcome the environmental embrittlement from water vapor at test temperatures below 873 K for the Ni–19Si–3Nb
base alloy. However, the boron and carbon doped alloy still suffers from embrittlement associated with oxygen at a medium
high temperature (i.e. 973 K). In parallel, both of the ultimate tensile strength and elongation exhibit quite insensitive
response with respect to the loading strain rate when tests are held at temperatures below 873 K. However, the ultimate tensile
strength exhibits high dependence on the strain rate in air at temperatures above 873 K, decreasing the ultimate tensile strength
with decreasing strain rate. 相似文献
18.
E. A. Elsharkawi E. Samuel A. M. Samuel F. H. Samuel 《Journal of Materials Science》2010,45(6):1528-1539
The presence of magnesium in Be-free Al–7Si–Mg alloys results in the formation of an undesirable iron-intermetallic known
as the π-AlMgFeSi phase. The effect of Mg, Fe, and Be on the formation of this phase in both unmodified and Sr-modified Al–7Si–xMg–yFe alloys containing 0.4–0.8-wt% Mg and 0.1–0.8-wt% Fe has been investigated at a dendrite arm spacing of 65 μm. A qualitative
microstructural examination was carried out to study the effect of solution heat treatment (540 °C/8 h) on the decomposition
of the π-AlMgFeSi phase (“π-phase”) in Al–7Si–xMg–0.1Fe alloys containing 0.4–1.0-wt% Mg. The results indicate that increasing the Mg and Fe content increases the amount
of the π-AlMgFeSi phase formed. Quantitative measurements revealed a reduction in the surface fraction of the π-phase after
solution heat treatment. Different levels of decomposition of the π-phase into needles of β-Al5FeSi iron intermetallic phase (“β-phase”) were observed at 0.4-, 0.6-, and 0.8-wt% Mg, after solution heat treatment. 相似文献
19.
Ali Sharafat Bertil Forslund Jekabs Grins Saeid Esmaeilzadeh 《Journal of Materials Science》2009,44(2):664-670
Glass formation in the system Sr–Si–O–N was investigated and properties of obtained glasses evaluated. The glass-forming region
was determined for glasses prepared by melting mixtures of Sr metal, SiO2 and Si3N4 powders in Nb crucibles at 1600–1750 °C in nitrogen atmosphere using a radio frequency furnace. The glasses were found to
be homogenous, translucent gray to opaque black, and to contain high contents of N (up to 45 e/o) and Sr (up to 36 e/o). The
glass transition temperature (790–973 °C), density (2.99–4.07 g/cm3), microhardness (8.10–10.50 GPa), and refractive index (1.65–1.93) are strongly correlated with the amounts of Sr and N.
The properties are compared with findings in other oxynitride silicate glass systems. 相似文献
20.
The microstructures and dry sliding wear behavior of Al–7Si and Al–7Si–2.5Cu cast alloys were studied after various melt treatments
like grain refinement and modification. Results indicate that combined grain refined and modified Al–7Si–2.5Cu cast alloys
have microstructures consisting of uniformly distributed α-Al grains, eutectic Al– silicon and fine CuAl2 particles in the interdendritic region. These alloys exhibited better wear resistance in the cast condition compared with
the same alloy subjected to only grain refinement or modification. The improved wear resistances of Al–7Si–2.5Cu cast alloys
are related to the refinement of the aluminum grain size, uniform distribution of eutectic Al-silicon and fine CuAl2 particles in the interdendritic region resulting from combined refinement and modification. This paper attempts to investigate
the influence of the microstructural changes in the Al–7Si and Al–7Si–2.5Cu cast alloys by grain refinement, modification
and combined action of both on the sliding wear behavior. 相似文献