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Liu Xiao-fu Lou Yan-chun Yu Bo Su Gui-qiao Li Chang-chun Guo Xin-li Li Biao Shui Guo-yan 《中国铸造》2019,16(1):23-30
In this work, some important factors such as ceramic shell strength, heat preservation temperature, standing time and withdrawal rate, which influence the formability of directionally solidified large-size blades of heavy-duty gas turbine with the liquid metal cooling(LMC) process, were studied through the method of microstructure analysis combining. The results show that the ceramic shell with medium strength(the high temperature flexural strength is 8 MPa, the flexural strength after thermal shock resistance is 12 MPa and the residual flexural strength is 20 MPa) can prevent the rupture and runout of the blade. The appropriate temperature(1,520 ℃ for upper region and 1,500 ℃ for lower region) of the heating furnace can eliminate the wide-angle grain boundary, the deviation of grain and the run-out caused by the shell crack. The holding time after pouring(3-5 min) can promote the growth of competitive grains and avoid a great deviation of columnar grains along the crystal orientation 001, resulting in a straight and uniform grain structure. In addition, to avoid the formation of wrinkles and to ensure a smooth blade surface, the withdrawal rate should be no greater than the growth rate of grain. It is also found that the dendritic space of the blade decreases with the rise of solidification rate, and increases with the enlarging distance between the solidification position and the chill plate. 相似文献
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Chao He Bin Du Juan Ma Hao Xiong Junjie Qian Mei Cai Anze Shui 《Journal of the American Ceramic Society》2022,105(5):3177-3188
Under the condition of constant thickness, improving the low-frequency sound absorption performance of conventional sound-absorbing materials is a challenging research topic. To address this issue, a new reduced graphene oxide/polyvinyl alcohol (RGO/PVA) porous composite ceramic was fabricated using freeze-drying and optimized by redesigning the internal connecting pores of porous ceramic matrixes with a reticular microstructure using RGO and PVA. The as-prepared porous structure showed significant enhancement in the low-frequency sound absorption band compared with pristine porous ceramics. In addition, the hybrid porous ceramics exhibited low thermal conductivity. These favorable properties indicate that the hybrid sound-absorbing ceramics have potential application prospects for noise reduction in the fields of construction and electrical and mechanical devices. 相似文献
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Qingliang Shan Qian Ma Jiawei Lian Caiyu Yao Anze Shui 《International Journal of Applied Ceramic Technology》2022,19(5):2675-2685
In this research, for studying the influence of size and heat treatment temperature of initial Al(OH)3 on the physical properties of porous mullite ceramics, porous mullite ceramics were prepared by in situ reaction sintering of amorphous silica and treated Al(OH)3. The transition phases χ-Al2O3, к-Al2O3, and stable phase α-Al2O3 can be obtained in turn when the treatment temperature of raw Al(OH)3 is 500, 1000, and 1500°C, respectively. The coarser the raw Al(OH)3, the higher the strength of porous mullite ceramics. When the sintering temperature is 1500°C, the bending strengths of PS500-C, PS1000-C, and PS1500-C (PSx-C represents that the specimen was prepared by the coarse grade Al(OH)3, which was previously treated at x°C) are 40.3 ± 2.1, 54.9 ± 5.2, and 64.8 ± 4.8 MPa, respectively. In addition, although the activated Al2O3 can decrease the formation temperature (∼100°C) of porous mullite ceramics, the strength and density of porous mullite ceramics prepared by activated Al2O3 will decrease at the same sintering temperature. It is believed that the increase of defects and pores during the phase transformation should be responsible for this phenomenon. 相似文献
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【摘要】 目的 探讨全数字化钨铑靶乳腺机三维立体定位系统在乳腺病变穿刺活检术中的应用价值。方法 对102例乳腺摄影发现病变的患者均行乳腺X线下三维立体定位穿刺,抽取部分组织进行活检,结合病理结果进行分析。结果 102例三维立体定位穿刺中,一次性准确定位穿刺97例,成功率为95%,3例定位穿刺多次,另有1例因乳房厚度小于射程,穿刺点无法准确选取。病理结果乳腺癌63例,占61.8%,乳腺良性病变39例,占38.2%。结论 全数字化钨铑靶乳腺机三维立体定位穿刺术,具有操作简便,安全可靠,定位精确,成功率高等优点,能较早地明确乳腺病变的定性诊断,尤其对临床未触及肿块、超声阴性的早期乳腺癌具有重要的临床价值。
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目的评价急性心肌梗死(AMI )并发心房颤动(房颤)/心房扑动(房扑)对患者近、中期临床预后的影响。方法2001年1月至2005年12月确诊的AMI 患者297例,分为房颤/房扑动组(33例)和无房颤/房扑组(264例)。比较两组30d及6个月内病死率、Killip分级、心源性休克、心律失常发生情况。以多普勒心脏超声测定患者AMI 后6个月的左室射血分数(LVEF)。结果房颤/房扑组与无房颤/房扑组比较:年龄大、CPK峰值高、心源性休克率高、既往发生过心肌梗死者比例高、入院时心功能Killip分级Ⅰ级比例低,多支血管病变率高,LVEF<40%比例高(P<0.05);与无房颤/房扑组比较,房颤/房扑组30d内及6个月病死率、心源性休克、恶性室性心律失常、再发心肌缺血率、再梗死率明显增高(P<0.05);二组LVEF比较差异有统计学意义(P<0.05)。结论AMI 并发房颤/房扑的患者其近中期病死率明显增加。 相似文献
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Bao-cai Xu Fu Han Jin-huan Shui Ya-wen Zhou 《Journal of surfactants and detergents》2009,12(4):351-354
A new family of lauryl trimethyl ammonium surfactants of the general formula CH3(CH2)11 N+(CH3)3X? (X = CH3OCOO, HCOO, CH3COO, CH3CHOHCOO) were prepared and characterized both structurally and as aqueous surfactants. Lauryl trimethyl ammonium mono-methyl carbonate was synthesized by using dimethyl carbonate (DMC) as the alkylating agent and lauryl dimethyl amine as the starting material. The latter compound was reacted with formic acid, acetic acid, and lactic acid, respectively, to give the corresponding quaternary ammonium salts with other counteranions. They were structurally characterized by IR, 1H NMR, MS. Members of this family reduced the surface tension of water to 32–38 mN/m at concentration levels of 10?2 mol/L. 相似文献