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2021 Vol. 26, No. 2
Published: 2021-04-15
91
Thermodynamic and thermal analysis on carbothermal reduction-carbonization of titanium and tungsten oxides
LIANG Yan, ZHANG Li, LI Xia, YU Peng, LIU Tao, LING Qun
HSC Chemistry thermodynamic analysis software, thermo-gravimetric and differential scanning calorimetric methods were used to analyze the evolution process of the reduction and carbonization of TiO
2
and WO
2.72
by carbon under the condition of an inert atmosphere. The results show that due to the increased reaction activity of the raw materials by ball-milling and the existence of gas-solid synergetic reaction, the actual reaction temperature is lower than the one of the thermodynamic calculation result. As the temperature increases, TiO
2
and WO
2.72
are gradually reduced and carbonized in the order of TiO
2
→Ti
4
O
7
→Ti
3
O
5
→Ti
2
O
3
→TiO→TiC and WO
2.72
→WO
2
→W→W
2
C→WC, respectively. The final reaction temperature is suggested to be above 1400 °C to speed up the kinetic process of the reaction.
2021 Vol. 26 (2): 91-98 [
Abstract
] (
466
)
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1617
)
99
Simplified reaction simulation of CH
3
SiCl
3
-H
2
-Ar chemical vapor deposition SiC
HAN Qianwu, LI Guodong
In order to produce large area of uniform SiC coating, the study of the variation law of deposition rate at different positions in the reaction chamber was required. The process of chemical vapor deposition of CH
3
SiCl
3
-H
2
-Ar system was simplified to a two-step reaction of gas phase cracking and surface deposition, and a two-dimensional reaction-transport model was established. The Computational Fluid Dynamics (CFD) software was used to analyze the effects of gas flow on the temperature field, velocity field, reactant concentration field and deposition rate in the direction of substrate height. The results show that, the deposition distribution shows different trends due to different retention time at different gas flow rates. The deposition thickness uniformity is better and the deposition rate is higher at moderate flow rates. Increasing the temperature can improve the inhomogeneity of deposition at high velocity. If the flow rate is constant and the pressure is too high, the natural convective vortex will be caused. The two-step simplified model can reflect the consumption of reactants and the uniformity of the coating under different conditions by comparing the calculated results with the relevant experimental data.
2021 Vol. 26 (2): 99-107 [
Abstract
] (
360
)
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)
108
Effects of SiO
2
/ZrO
2
composite ceramic components on friction and wear properties of copper-based friction materials
LI Zhengzhou, LIU Rutie, LIN Xueyang, CHEN Jie, WANG Lin, XIONG Xiang, LIAO Ning
6%(mass fraction) SiO
2
/ZrO
2
composite ceramic components was added into powder metallurgy copper-based friction materials to study the effect of the mass fraction changes of SiO
2
and ZrO
2
on the friction and wear properties of friction materials, and analyze the friction and wear mechanism of materials. The results show that with increasing
w
(SiO
2
)/
w
(ZrO
2
), the density and hardness of the copper-based friction material increase. When braking at high speed, the friction coefficient and friction stability factor of friction material are small. SiO
2
can effectively improve the friction coefficient, and ZrO
2
can reduce the wear rate of the friction pair. When
w
(SiO
2
)/
w
(ZrO
2
) is 2/4, the average friction coefficient during high-speed braking is 0.326, the friction stability factor is 0.71, which is at a high level, and the damage of the dual material is within the acceptable range, so the material has a relatively good friction and wear performance. SiO
2
is easy to fall off to form abrasive particles, and the interface between ZrO
2
and the matrix is in a better bonding state, so as the content of SiO
2
decreases. The main wear mechanism changes from abrasive wear to adhesive wear and abrasive wear and finally to delamination wear.
2021 Vol. 26 (2): 108-116 [
Abstract
] (
296
)
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400
)
117
Effect of nano-Y
2
O
3
on microstructure and properties of 97W-2Ni-Fe tungsten alloy
KANG Jun, LIN Zehua, ZHOU Yonggui, LIU Fangzhou, ZHOU Chengshang, YAN Wenmin
The 97W-2Ni-Fe and 96.5W-2Ni-Fe-0.5Y
2
O
3
alloys were prepared with W, Ni, Fe and nano-Y
2
O
3
powders as raw materials, and characterized by scanning electron microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), combined with the analysis of liquid content and contiguity, to explore the influence of sintering temperature and addition of nano-Y
2
O
3
powder on the microstructure and mechanical properties of high density tungsten alloy. The results show that with the increase of sintering temperature, the grain size and mechanical properties of tungsten alloy increase obviously. At the sintering temperature of 1 510 ℃ (liquid phase), the grain size of tungsten decreases from 21.6 μm to 7.8 μm, the area fraction of bonding phase increases from 4.45% to 5.35%, and the contact degree is 0.67. The mechanical properties of the alloy are improved significantly. The tensile strength reaches 611 MPa and the hardness (HRC) is 40.1. The tensile fracture morphology of 96.5W-2Ni-Fe-0.5Y
2
O
3
alloy is tearing of bonding phase and cleavage fracture of a small amount of W grains. The addition of nano-Y
2
O
3
increases the tearing ratio of bonding phase.
2021 Vol. 26 (2): 117-124 [
Abstract
] (
340
)
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715
)
125
Effect of Nb on mechanical properties and corrosion resistance of Zr-Ti based biomaterials
WANG Dong, LIU Libin, XUE Renhao, XU Xiaoning, ZHANG Ligang
In this paper, Zr-Ti-
x
Nb(
x
=6, 8, 10, mole fraction, %) alloy is prepared via vacuum non-consumable arc melting furnace. Then the ingot is further processed by forging technology and heat treatment in β single-phase zone. The effect of Nb element on the mechanical properties and corrosion resistance of Zr-Ti based alloys was studied through the measurement of microstructure, mechanical properties and corrosion resistance. Zr-Ti-
x
Nb(
x
=6, 8, 10) alloys are composed of β phase and α" phase. When the content of Nb element increases, the content of β phase increases, but α" phase content decreases, which indicates Nb improves the stability of β phase. With the increase of Nb content, the yield strength raised from 360 MPa to 780 MPa. The solid solution strengthening effect is obvious. At the same time, stress induced martensitic transformation during the deformation process can greatly improve the tensile strength and plasticity. The increase of Nb content also enhances the corrosion resistance, and the experiments show that those alloys all exhibit strong corrosion resistance in physiological saline.
2021 Vol. 26 (2): 125-131 [
Abstract
] (
363
)
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1119
)
132
Effect of the density of C/C composites and pre-oxidation process on SiC coatings
YANG Fan, XIE Aolin, ZHANG Bei, YI Maozhong
SiC coatings were prepared on the surface of carbon/carbon (C/C) composites with densities of 0.8, 1.4 and 1.8 g/cm
3
by the pack cementation. The samples with a density of 1.8 g/cm
3
were selected to research the effect of pre-oxidation treatment on structure and oxidation resistance of the coating. Scanning electron microscope and X-ray diffractometer were used to study the microstructure and phase composition of the coating. The anti-oxidation resistance of the coating was tested by static air oxidation at 1 500 ℃. The results show that as the density of the C/C composites increases, the thickness of the coating decreases, and the boundary between the coating and the substrate becomes more obvious. After the pre-oxidation treatment of 1.8 g/cm
3
C/C composites, the surface roughness increases, and the ring pores around the carbon fibers on the surface are generated. After pack cementation process, the thickness of coating increases and becomes more uniform and compact. After the sample is oxidized in static air at 1 500 ℃ for 334 h, the oxidation mass loss rate is 0.684×10
-4
g/(cm
2
·h). The mullite phase is formed on the surface of the sample, and the oxidation resistance was significantly improved.
2021 Vol. 26 (2): 132-138 [
Abstract
] (
372
)
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964
)
139
Preparation and properties of PVC-SN solid-state electrolyte via in-situ thermal polymerization
CHEN Minjian, ZHANG Siyu, MA Cheng, WEI Weifeng
The low ion conductivity of solid-state electrolyte and instable electrode-electrolyte interface are key factors to hindering the development of solid-state lithium battery. In this work, we synthesized a novel solid-state electrolyte combined poly (vinylene carbonate) and succinonitrile (SN) via in-situ thermal polymerization, and studied the effect of SN on solid-state electrolyte electrochemical properties and electrode-electrolyte interface. The results show that the high antioxidative SN are uniformly distributed in the solid-state electrolyte, which promotes the dissociation of lithium salts as well as the movement ability of polymer segments and hence enhances the network of ionic conductivity. After the introduction of SN, the ionic conductivity at room temperature increases from 2.4×10
-6
S/cm to 1.213×10
-3
S/cm, and the decomposition potential increases from 4.58 V to 5.52 V. The solid-state electrolyte with
w
(SN)=10% delivers excellent cyclability with a high discharge capacity of 163.1 mAh/g. During the charging process, the nitrile group with lone pair electrons on the SN can coordinate with the highly reactive transition metal ions, which suppresses the parasitic reactions on the electrode-electrolyte interface and thus enhances the structural stability of cathode materials.
2021 Vol. 26 (2): 139-146 [
Abstract
] (
501
)
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1144
)
147
Effect of K
2
SO
4
space-holder on pore structure of NiCu alloy porous membrane
FENG Luli, YU Linping, GAN Qingzhan, GAO Haiyan, HE Yuehui
The Ni-K
2
SO
4
mixed powder, in which Ni element powder is the raw material, and K
2
SO
4
powder is the space-holder, is added into the polyvinyl butyral (PVB) ethanol solution to make a slurry, which is coated on the Cu foil. NiCu alloy porous membrane was prepared basing on Kirkendall effect by vacuum sintering. The influence of K
2
SO
4
contenton on area shrinkage, permeability, pore size, macro and micro morphologies of porous membrane and the influence of K
2
SO
4
on the pore structure of porous membranes at different temperatures were investigated. The effect mechanism of K
2
SO
4
on pore structure of the porous alloy membrane during sintering process was also studied. The results show that with the increase of
w
(K
2
SO
4
) in Ni-K
2
SO
4
mixed powder, the permeability of porous membrane first increases and then decreases. When the mass fraction of K
2
SO
4
is lower than 40%, with the increase of K
2
SO
4
content, the shrinkage rate of the film decreases and the permeability increases. The maximum permeability is 2 361 m
3
/(m
2
·h·kPa). The maximum pore diameter of the sample with little change is about 45 µm. When the
w
(K
2
SO
4
) is more than 40%, the permeability and pore diameter of the porous film both decrease obviously. When the
w
(K
2
SO
4
) is more than 60%, the permeability of the film layer is lower than that of the lower limit of the test instrument. Proper amount of K
2
SO
4
can improve the permeability of porous alloy membrane through hindering sintering densification based on the space occupying effect in the Ni coating, but excessive amount of K
2
SO
4
will block the diffusion of Cu atoms to Ni powder layer, which makes it difficult to form through-pores on the Cu foil, resulting in a significant decrease in permeability.
2021 Vol. 26 (2): 147-154 [
Abstract
] (
341
)
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426
)
155
Microstructure and properties of Al-Si coating on NiCrW-based superalloy prepared by slurry method
GAO Shan, ZOU Jianpeng
Aero-engine turbine blades should be coated for protection to improve the high temperature oxidation resistance of the alloy substrate. In this study, an Al-Si coating was prepared on the surface of NiCrW-based superalloy with CaCl
2
as the activator by slurry method. X-ray diffractometer (XRD), scanning electron microscope (SEM) and energy spectrometer (EDS) were used to analyze the surface and cross-section of the coating. The results show that the aqueous solution of polyvinyl alcohol can be used as an effective binder for preparing aluminized/aluminized-silicon coatings by slurry method, and the temperature and the heating time of high-temperature diffusion significantly affect the thickness of the aluminized coating. When the composition of binder is 5%Si+30%Al (mass fraction), the coating is composed of aluminum-rich layer, NiAl layer and silicon-containing transition layer from the outside to the inside. The NiAl coating is dense and has no obvious defects, and the thickness is about 57 μm. While the compositions of binder are 10%Si+25%Al, 15%Si+20%Al and 20%Si+15%Al, the coatings are divided into three layers: Aluminum-rich layer, nickel-rich layer and silicon-containing transition layer from the outside to the inside. Silicon is mainly exist in the silicon-containing transition layer in the form of silicon-containing deposition phases, and a small amount of silicon is deposited on the outer layer. The addition of a small amount of Si can significantly affect the diffusion process of aluminum and nickel elements, and reduce the thickness of the coating, and transform the phase of the coating from a single NiAl phase to an aluminum-rich phase, nickel-rich phase.
2021 Vol. 26 (2): 155-165 [
Abstract
] (
514
)
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(1 KB)
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(1025 KB) (
994
)
166
Effect of active fillers on direct ink writing 3D SiC on polycarbosilane suspension
ZHAO Lianzhong, LI Zhouyao, XIONG Huiwen, ZHOU Kechao, ZHANG Dou
SiC ceramic matrix composites were prepared by 3D direct ink and phrolysis writing using nano Ti and NiO particles as active fillers, polycarbosilane (PCS) as SiC ceramic precursor, n-hexane as solvent to prepare slurries. The rheological properties of the slurries were investigated. The phase and morphology of the ceramic matrix composites were characterized. The effects of active fillers (nano Ti particles and nano NiO particles) on the phase and morphology of 3D-SiC ceramic matrix composites were studied. The results show that the viscosity of the slurry is proportional to the mass fraction of PCS, and it has shear thinning phenomenon. The slurry with 75% PCS has stable printing performance. The nano Ti powder can effectively reduce the mass loss rate and linear shrinkage rate during pyrolysis at 1 450 ℃, and the mass loss and linear shrinkage decrease from 18.29% and 24.38% to 14.05% and 12.13% respectively, the ceramics contains TiC and SiC phases. Compared with Ti powder, NiO can be used as a surface modification catalyst for SiC, and SiC whisker clusters can be grown in situ on the surface of SiC ceramics through the gas liquid solid (V-L-S) growth mechanism.
2021 Vol. 26 (2): 166-173 [
Abstract
] (
373
)
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(1 KB)
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(893 KB) (
556
)
174
Improving the hydrophilia of diamond film by high temperature oxidation and in situ boron doping
YU Yanglei, LI Songbo, AN Junjie, BAO Shengyou, KANG Huiyuan, KANG Aolong, WEI Qiuping
Hot filament chemical vapor deposition (HFCVD) was used to prepare high-quality diamond films and boron doped diamond films on single-crystal silicon substrates by using H
2
, CH
4
and B
2
H
6
as gas source. After 600-800 ℃ high temperature oxidation treatment, the morphology, composition and hydrophilic of the diamond film were characterized by scanning electron microscope, Raman spectroscopy, X-ray diffraction and normal temperature contact angle instrument. The effects of high temperature oxidation and in-situ boron doping on the hydrophilic of diamond films were also studied. The results show that with the increase of high temperature oxidation temperature, the film was gradually etched to micropore morphology. The contact angle of pure diamond film decreases from 68.1° to 21.5° after oxidation at 700 ℃, and the hydrophilicity of the film is improved. With the increase of boron concentration, the micropores gradually disappear. The minimum contact angle is 14.1° when the boron-doped diamond film was prepared under the conditions of
V
(H
2
):
V
(CH
4
):
V
(B
2
H
6
)=97.0:3.0:0.4, and after oxidation at 800 ℃. Under the synergistic effect of in-situ boron doping and high-temperature oxidation, the composition of the film changes, and the perfect diamond configuration defects appear, as well as the surface energy of diamond film increases due to micropores. This method can effectively improve the hydrophilic of diamond film.
2021 Vol. 26 (2): 174-181 [
Abstract
] (
373
)
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(1 KB)
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(544 KB) (
1108
)
182
Thermal and mechanical properties of paper-based friction materials with nano-Al
2
O
3
modified phenolic resin
XIE Maoqing, WANG Leigang, LUO Yiqin, ZHAO Zaojun
The paper-based friction materials using nano-Al
2
O
3
modified phenolic resin as binder were prepared by paper-making process. The effects of resin contents (mass fraction) and curing temperatures on the heat resistance, shear strength, compressure resilience were studied. The results show that with the increase of resin contents, the heat resistance of the paper-based friction materials decreases slightly, the shear strength increases. In the first to fourth compression-rebound tests, the rebound rate increases greatly at the first compression-rebound cycle, while the rebound rate is close to each other from the second to fourth compression-rebound cycle and is less affected by the resin content. The compression rate decreases with the increase of resin content, and the compression rate at the first compression-rebound cycle is obviously higher than that of the following three times. At higher curing temperature, the materials have the higher heat resistance and shearing strength, meanwhile, the compression rate decreases obviously and rebound rate increases obviously with the increase of curing temperature at the first compression-rebound cycle. However, from the second to fourth compression-rebound cycle, the compression rate and rebound rate are close to each other, and are less affected by the curing temperature. The paper-based friction material possess the better heat resistance, higher shear strength, higher compression rate and high rebound rate when the modified phenolic resin is 40% and the curing temperature is 160 ℃.
2021 Vol. 26 (2): 182-188 [
Abstract
] (
389
)
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(1 KB)
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(1209 KB) (
754
)
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