The amorphous boron nitride ceramic powders were prepared at 750-950 ℃ by the low-cost urea route, and the effects of preparation temperatures, molar ratios of the raw materials and oxidation treatment on the composi...The amorphous boron nitride ceramic powders were prepared at 750-950 ℃ by the low-cost urea route, and the effects of preparation temperatures, molar ratios of the raw materials and oxidation treatment on the composition, structure and surface morphology of the products were investigated through FT-IR, XRD and SEM. The results show that the products ceramize and crystallize gradually with the increase of the temperature. When the molar ratio and reaction temperature are 3:2 and 850 ℃, respectively, the products have high purity, compact structure and nice shape. The oxidation treatment at 450 ℃ will not impair the composition and structure of boron nitride but effectively remove the impurities.展开更多
We investigated synthesis and characterization of melamine-urea-formaldehyde(MUF) microcapsules containing n-alkane mixture as phase change core material for thermal energy storage and low-temperature protection. Th...We investigated synthesis and characterization of melamine-urea-formaldehyde(MUF) microcapsules containing n-alkane mixture as phase change core material for thermal energy storage and low-temperature protection. The phase change microcapsules(microPCMs) were prepared by an in situ polymerization using sodium dodecyl sulfate(SDS) and polyvinyl alcohol(PVA) as emulsifiers. Surface morphology, particle size, chemical structure, and thermal properties of microPCMs were, respectively, characterized by using scanning electron microscopy(SEM), field emission scanning electron microscopy(FESEM), Fourier transform infrared spectroscopy(FT-IR), differential scanning calorimetry(DSC), and thermal gravimetric analysis(TGA). Low-temperature resistance performances were measured at-15,-30,-45, and-60 ℃ after microPCMs were coated on a cotton fabric by foaming technology. The results showed that spherical microPCMs had 4.4 μm diameter and 100 nm wall thickness. The melting and freezing temperatures and the latent heats of the microPCMs were determined as 28.9 and 29.6 ℃ as well as 110.0 and 115.7 J/g, respectively. Encapsulation of n-alkane mixture achieved 84.9 %. TGA analysis indicated that the microPCMs had good chemical stability below 250 ℃. The results showed that the microencapsulated n-alkane mixture had good energy storage potential. After the addition of 10 % microPCMs, low-temperature resistance duration was prolonged by 126.9%, 145.5%, 128.6%, and 87.5% in environment of-15,-30,-45 and-60 ℃, respectively as compared to pure fabric. Based on the results, phase change microcapsule plays an effective role in lowtemperature protection field for the human body.展开更多
目的:探究糖尿病肾脏病(diabetic kidney disease,DKD)患者蛋白质摄入量(dietary protein intake,DPI)与肾脏不良预后之间的关系。方法:回顾性分析2014年01月—2021年01月于北京中医药大学东直门医院肾内科住院两次以上的DKD患者资料,根...目的:探究糖尿病肾脏病(diabetic kidney disease,DKD)患者蛋白质摄入量(dietary protein intake,DPI)与肾脏不良预后之间的关系。方法:回顾性分析2014年01月—2021年01月于北京中医药大学东直门医院肾内科住院两次以上的DKD患者资料,根据24 h尿尿素氮评估DPI,将DKD患者分为极低蛋白摄入(very low protein intake,VLPI)、低蛋白摄入(low protein intake,LPI)、中等蛋白摄入(moderate protein intake,MPI)三组(<0.6 g·kg^(-1)·d^(-1),0.6~0.8 g·kg^(-1)·d^(-1),>0.8 g·kg^(-1)·d^(-1)),比较三组间基线资料的差异。应用Kaplan Meier生存分析及Cox回归分析不同DPI对肾脏不良预后的影响。结果:纳入DKD患者81例,VLPI组22例,LPI组30例,MPI组29例,中位随访22.5(15.8,36.0)个月,其中21例(17.24%)出现肾脏终点事件,VLPI组6例、LPI组6例、MPI组9例。Kaplan Meier生存分析结果显示,患者DPI越高,累积生存率越低(Log rank检验χ^(2)=1.078,P=0.025)。多因素Cox回归模型显示,VLPI及MPI均为DKD患者肾脏不良预后的独立影响因素(HR=1.90,95%CI 0.78~2.18,P=0.037;HR=0.98,95%CI 0.64~6.26,P=0.042)。结论:VLPI及MPI均是DKD患者肾脏不良预后的影响因素。展开更多
基金Funded by the National Natural Science Foundation of China (Nos.50902150 & 90916019)the Graduate Innovation Foundation of the National University of Defense Technology(No.S100103)
文摘The amorphous boron nitride ceramic powders were prepared at 750-950 ℃ by the low-cost urea route, and the effects of preparation temperatures, molar ratios of the raw materials and oxidation treatment on the composition, structure and surface morphology of the products were investigated through FT-IR, XRD and SEM. The results show that the products ceramize and crystallize gradually with the increase of the temperature. When the molar ratio and reaction temperature are 3:2 and 850 ℃, respectively, the products have high purity, compact structure and nice shape. The oxidation treatment at 450 ℃ will not impair the composition and structure of boron nitride but effectively remove the impurities.
基金Funded by Tianjin Research Program of Application Foundation and Advanced Technology(No.15JCZDJC38400)the National Natural Science Foundation of China(Nos.51303131 and 51303128)
文摘We investigated synthesis and characterization of melamine-urea-formaldehyde(MUF) microcapsules containing n-alkane mixture as phase change core material for thermal energy storage and low-temperature protection. The phase change microcapsules(microPCMs) were prepared by an in situ polymerization using sodium dodecyl sulfate(SDS) and polyvinyl alcohol(PVA) as emulsifiers. Surface morphology, particle size, chemical structure, and thermal properties of microPCMs were, respectively, characterized by using scanning electron microscopy(SEM), field emission scanning electron microscopy(FESEM), Fourier transform infrared spectroscopy(FT-IR), differential scanning calorimetry(DSC), and thermal gravimetric analysis(TGA). Low-temperature resistance performances were measured at-15,-30,-45, and-60 ℃ after microPCMs were coated on a cotton fabric by foaming technology. The results showed that spherical microPCMs had 4.4 μm diameter and 100 nm wall thickness. The melting and freezing temperatures and the latent heats of the microPCMs were determined as 28.9 and 29.6 ℃ as well as 110.0 and 115.7 J/g, respectively. Encapsulation of n-alkane mixture achieved 84.9 %. TGA analysis indicated that the microPCMs had good chemical stability below 250 ℃. The results showed that the microencapsulated n-alkane mixture had good energy storage potential. After the addition of 10 % microPCMs, low-temperature resistance duration was prolonged by 126.9%, 145.5%, 128.6%, and 87.5% in environment of-15,-30,-45 and-60 ℃, respectively as compared to pure fabric. Based on the results, phase change microcapsule plays an effective role in lowtemperature protection field for the human body.