Efficient Use of Graphene Oxide in Layered Cement Mortar

Graphene oxide (GO) has been found to be an attractive nanomaterial to improve the properties of cementitious composites. However, the use of GO in the industry is limited by its high cost. To achieve a higher cost/performance ratio, GO can be strategically applied in certain parts of cementitious composites structure according to the principle of functionally graded materials. In this study, graded distribution of GO in cement mortar was achieved by sequentially casting a fresh GO-incorporated cement layer on another cement mortar layer. The mechanical properties, especially flexural strength, of layered cement mortar were found to be dependent on the GO content, the delay time, and the interface formed due to layering fabrication. With the GO incorporated in the tensile region only (30% of the total depth), the flexural strength of the layered beam attained 90.91% of that of the beam, with GO uniformly distributed throughout the sample. Based on the results of rapid chloride migration tests, when 12 mm GO-incorporated cement mortar layer was used, the chloride migration coefficient was reduced by 21.45%. It was also found that the measured chloride migration coefficient of layered cement mortar agreed with the series model. The present investigation provides an efficient approach to use GO in cement-based materials from the perspective of mechanical and durability properties.     

可摘局部义齿钴铬铸造支架和数字化打印支架的临床失败率对比

目的 对比可摘局部义齿钴铬铸造支架和数字化打印支架的临床失败率差异。方法 通过回顾性研究,追踪2020—2021年通过铸造技术和数字化打印技术(SLM)制作的可摘局部义齿钴铬合金金属支架1 020例,统计临床失败率差异,分析失败原因。结果 钴铬合金传统铸造支架的临床失败率略高于SLM支架。铸造支架失败的主要原因是支架精密性不良(如不稳定和就位不良等),占3.42%;折断率较低,占0.22%。SLM支架失败的主要原因是支架折断,占1.75%;精密性不良占0.88%。两种支架的大连接体折断率有统计学差异,其余失败原因均无统计学差异。结论 钴铬合金传统铸造支架的临床失败率略高于SLM支架,铸造支架失败的主要原因是支架精密性不良,SLM支架失败的主要原因是支架折断。     

Bending and Straightening of a Medium Carbon Steel Continuous Casting Slab with Low Temperature End Plastic Groove

The high temperature brittleness range of medium carbon microalloyed steel under an actual continuous casting process was determined by the high temperature tensile test. The test results revealed that only a third of the brittle temperature range from 650–825 °C was due to intergranular ferrite in the experimental steel. In addition, it was found that the plastic recovery was fast and stable when the temperature was lower than 725 °C (the lowest plastic temperature). Bending/straightening operation in this temperature range was conducive to controlling the generation of corner cracks. In order to keep the corner temperature at the low temperature end of the plastic curve when the slab was bent/straightened, the cooling water scheme of the secondary cooling zone of the continuous caster was formulated by numerical calculation. By appropriately increasing the cooling water flow in the foot roll and the secondary cooling zones 1–5, the corner temperature of slab during bending operation was 600–700 °C, avoiding the brittle temperature range. The industrial test was then carried out. The results showed that after using the optimized water volume, the corner grains of the slab were uniform and the microstructure was mainly pearlite + ferrite. In addition, the abnormally large grain size was reduced, and a large amount of ferrite was generated inside the grain, which avoided stress concentration at the corner of the slab during bending/straightening operation, and basically eliminated the corner crack of the slab.     

NiO–Ba0.95Ca0.05Ce0.9Y0.1O3−δ as a Modified Anode Material Fabricated by the Tape Casting Method

The development of new chemically resistant anodes for protonic ceramic fuel cells (PCFCs) is urgently required to avoid the costly deep hydrogen purification method. Ba_0.95Ca_0.05Ce_0.9Y_0.1O_3−δ (5CBCY), which is more chemically resistant than BaCaCe_0.9Y_0.1O_3−δ, was here tested as a component of a composite NiO–5CBCY anode material. A preparation slurry comprising 5CBCY_, NiO, graphite, and an organic medium was tape cast, sintered and subjected to thermal treatment in 10 vol.% H₂ in Ar at 700 °C. Differential thermal analysis, thermogravimetry, quadrupole mass spectrometry, X-ray diffraction analysis, scanning electron microscopy, the AC four-probe method and electrochemical impedance spectroscopy were used for the investigation. The electrical conductivity of the Ni–5CBCY in H₂–Ar at 700 °C was 1.1 S/cm. In the same gas atmosphere but with an additional 5 vol.% CO₂, it was slightly lower, at 0.8 S/cm. The Ni–5CBCY cermet exhibited repeatable electrical conductivity values during Ni-to-NiO oxidation cycles and NiO-to-Ni reduction in the 5CBCY matrix, making it sufficient for preliminary testing in PCFCs.     

纯钛义齿支架铸造缺陷回顾性研究

目的:通过分析铸造纯钛义齿制作过程仔的铸造缺陷,总结纯钛铸造缺陷规律及可能原因,以提高铸造成功率。方法:对156件铸造纯钛可摘局部义齿支架和总义齿基托进行回顾性研究,对发生的铸造缺陷的情况进行分析。结果:全部156件铸件中12件有内部气孔,占7.69%;铸造不全6件,占3.85%;5件存在表面缺损或粗糙,占3.21%。铸造缺陷中内部气孔最常发生部位是卡环起始、大连接体处,其次是铸件边缘较厚处。铸造不全最常见于铸造基托中央,其次是卡环末端。远离铸道处,铸道与铸件衔接处,铸件形状变化急剧处易出现铸造缺陷。结论:铸造纯钛义齿支架存在较高比例的铸造缺陷。铸件的形状、铸道的设计是影响铸造缺陷的重要因素。     

A Study on High Strength,High Plasticity,Non-Heat Treated Die-Cast Aluminum Alloy

The non-heat-treated, die-cast aluminum alloy samples were prepared meticulously via die-casting technology. The crystal structure, microstructure, and phase composition of the samples were comprehensively studied through electron backscatter diffraction (EBSD), metallographic microscopy, spectrometer, and transmission electron microscopy (TEM). The microhardness and tensile properties of the samples were tested. The die-cast samples were found to have desirable properties by studying the structure and performance of the samples. There were no defects, such as pores, cold partitions, or surface cracks, found. The metallographic structure of the samples was mainly α-Al, and various phases were distributed at the grain boundaries. Before heat treating, α-Al grains were mainly equiaxed with a great number of second phase particles at the grain boundaries. After heat treating, the α-Al grains were massive and coarsened, and the second phase grains were refined and uniformly distributed, compared with those before the heat treating. The EBSD results showed that the grain boundary Si particles were solid solution decomposed after heat treatment. The particles became smaller, and their distribution was more uniform. Transmission electron microscopy found that there were nano-scale Al-Mn, Al-Cu, and Cu phases dispersed in the samples. The average microhardness of the samples before heat treating was 114 HV_0.1, while, after the heat treating, the microhardness reached 121 HV_0.1. The mechanical features of the samples were tremendous, and the obtained die-cast aluminum alloy had non-heat-treatment performance, which was greater than the ordinary die-cast aluminum alloys with a similar composition. The tensile strength of the aluminum alloys reached up to 310 MPa before heat treatment.     

纳米氧化锆的含量对纳米氧化锆增韧氧化铝陶瓷力学性能和显微结构的影响

目的 探讨纳米氧化锆的含量对纳米氧化锆增韧氧化铝陶瓷力学性能和显微结构的影响。方法 将纳米氧化锆、氧化铝、复合添加剂等粉料与一定比例的醇-水混合后,球磨制备浆液,采用离心渗透注浆法成坯,在1 450 ℃下烧结8 h。烧结体打磨抛光后,测试其物理性能和力学性能。通过扫描电镜观察烧结体表面和断面的微观结构。结果 不同实验组的三点抗弯曲强度、维氏硬度的差异均有统计学意义（P＜0.01）;20%氧化锆组的断裂韧性与另外两组差异有统计学意义（P＜0.05）,10%氧化锆组和30%氧化锆组间的断裂韧性差异没有统计学意义（P＜0.05）。 当纳米氧化锆含量为20%时,其力学性能显著高于10%及30%组,三点抗弯曲强度为（433±19） MPa,断裂韧性达（7.50±0.56） MPa·m1/2 。显微结构观察到内晶-晶界复合型结构、晶间及穿晶断裂。结论 内晶-晶界复合型结构具有强烈的增韧效果,可提高陶瓷的强度和韧性。纳米氧化锆含量为20%时,具有较好的增韧效果,适合口腔修复材料。     

Effect of SiC Nanoparticles on AZ31 Magnesium Alloy

Magnesium alloys are attractive for the production of lightweight parts in modern automobile and aerospace industries due to their advanced properties. Their mechanical properties are usually enhanced by the incorporation with reinforcement particles. In the current study, reinforced AZ31 magnesium alloy was fabricated through the addition of bulk Al and the incorporation of SiC nanoparticles using a stir casting process to obtain AZ31-SiC nanocomposites. Scanning electron microscope (SEM) investigations revealed the formation of Mg₁₇Al₁₂ lamellar intermetallic structures and SiC clusters in the nanocomposites. Energy dispersive spectroscopy (EDS) detected the uniform distribution of SiC nanoparticles in the AZ31-SiC nanocomposites. Enhancements in hardness and yield strength (YS) were detected in the fabricated nanocomposites. This behavior was referred to a joint strengthening mechanisms which showed matrix-reinforcement coefficient of thermal expansion (CTE) and elastic modulus mismatches, Orowan strengthening, and load transfer mechanism. The mechanical properties and wear resistance were gradually increased with an increase in SiC content in the nanocomposite. The maximum values were obtained from nanocomposites containing 1 wt% of SiC (AZ31-1SiC). AZ31-1SiC nanocomposite YS and hardness were improved by 27% and 30%, respectively, compared to AZ31 alloy. This nanocomposite also exhibited the highest wear resistance; its wear mass loss and depth of the worn surface decreased by 26% and 15%, respectively, compared to AZ31 alloy.     

产前超声心动图与解剖铸型观察胎儿完全性肺静脉异位引流

目的 采用产前超声心动图与解剖铸型观察胎儿完全性肺静脉异位引流（TAPVC）。方法 纳入9胎经产前超声心动图诊断为TAPVC的胎儿,对引产后3胎标本进行解剖、6胎标本制作胎儿心脏铸型,观察胎儿静脉回流特点及合并心内外畸形。结果 9胎TAPVC中,66.67%（6/9）为心上型,33.33%（3/9）为心下型。胎儿超声四腔心切面见左心房缩小,未见静脉与左心房相连;三血管气管切面见左心房后方赘余血管;6胎心上型TAPVC中,4胎肺静脉汇入右上腔静脉、2胎肺静脉汇入左上腔静脉;3胎心下型TAPVC肺静脉均汇入门静脉。9胎均合并心房异构综合征,8胎（8/9,88.89%）合并单心室,7胎（7/9,77.78%）合并肺动脉狭窄,合并单心房及完全型心内膜垫缺损各4胎（4/9,44.44%）;5胎（5/9,55.56%）合并永存左上腔静脉,合并双下腔静脉及左头臂静脉主动脉弓下走行各1胎（1/9,11.11%）;1胎（1/9,11.11%）合并膈疝。结论 TAPVC胎儿多合并心内外畸形及体静脉异常。产前超声具有重要诊断价值,解剖铸型有助于认识TAPVC胎儿血管走行及静脉引流途径。     

血管铸型方法检测组织工程骨修复羊胫骨缺损的远期血管化

目的采用血管铸型方法对组织工程技术修复中国青山羊胫骨大段骨缺损的远期血管化情况进行检测。方法中国青山羊3只，制备单侧胫骨20mm的骨与骨膜缺损，缺损部位内植入组织工程骨-珊瑚羟基磷灰石／骨髓基质干细胞（coral hydroxyapatite／bone marrow stem cells，CHAP／BMSCs）。术后3年分别行双侧后肢股动脉甲基丙烯酸甲酯血管铸型灌注，灌注后采用大体解剖、未脱钙骨片、扫描电镜等方法检测组织工程骨的远期血管化，并与健侧相同部位正常骨对照，观察其血管化效果。结果血管灌注后大体解剖观察示组织工程骨血管来源于周围软组织、髓腔血管及两端正常骨皮质。灌注后未脱钙骨磨片显示组织工程骨内微血管沿哈弗管和伏克曼管分布交织形成网状。采用图像分析仪比较组织工程骨与正常骨横切面磨片上血管相对面积，分别为（763．89±47．38）U／10万U与（788．00±65．83）U／10万U，差异无统计学意义（t=0．390，P〉0．05）。结论采用CHAP／BMSCs修复山羊胫骨大段骨缺损远期观察结果表明，新生骨远期血管化效果与正常骨无异，为组织工程骨下一步的临床应用提供可靠的依据。