Various lead-free ceramics have been investigated in search for new high-temperature dielectrics. In particular, Bi_4Ti_3O_（12） is a type of ferroelectric ceramics, which is supposed to replace leadcontaining cerami...Various lead-free ceramics have been investigated in search for new high-temperature dielectrics. In particular, Bi_4Ti_3O_（12） is a type of ferroelectric ceramics, which is supposed to replace leadcontaining ceramics for its outstanding dielectric properties in the near future. Ferroelectric ceramics of Bi_4Ti_3O_（12） made by conventional mixed oxide route have been studied by impedance spectroscopy in a wide range of temperature. X-ray diffraction patterns show that Bi_4Ti_3O_（12） ceramics are a single-phase of ferroelectric Bi-layered perovskite structure whether it is calcined at 800 ℃ or after sintering production. This study focused on the effect of the grain size on the electric properties of BIT ceramics. The BIT ceramics with different grain sizes were prepared at different sintering temperatures. Grain becomes coarser with the sintering temperature increasing by 50 ℃, relative permittivity and dielectric loss also change a lot. When sintered at 1 100 ℃, r values peak can reach 205.40 at a frequency of 100 k Hz, the minimum dielectric losses of four different frequencies make no difference, all close to 0.027. The values of Ea range from 0.52 to 0.68 e V. The dielectric properties of the sample sintered at 1 100 ℃ are relatively better than those of the other samples by analyzing the relationship of the grain, the internal stresses, the homogeneity and the dielectric properties. SEM can better explain the results of the dielectric spectrum at different sintering temperatures. The results show that Bi_4Ti_3O_（12） ceramics are a kind of dielectrics. Thus, Bi_4Ti_3O_（12） can be used in high-temperature capacitors and microwave ceramics.展开更多
为了研究扩散型时间-温度指示器(time-temperature indicator,TTI)对奇异果品质的预测情况,分别研究了不同贮藏温度(5、10、15、20℃)下指示器的颜色变化和奇异果品质(失重率、可溶性固形物含量、VC含量和总酸度)变化情况,通过Arrheniu...为了研究扩散型时间-温度指示器(time-temperature indicator,TTI)对奇异果品质的预测情况,分别研究了不同贮藏温度(5、10、15、20℃)下指示器的颜色变化和奇异果品质(失重率、可溶性固形物含量、VC含量和总酸度)变化情况,通过Arrhenius方程计算TTI反应和奇异果品质变化的活化能Ea值,并将指示器颜色变化与奇异果品质变化的Ea值进行比较,从而评估使用TTI预测奇异果品质的可能性。研究结果表明,贮藏温度及时间对TTI颜色和奇异果品质变化均有影响,贮藏温度越高,TTI颜色变化速度越快,奇异果失品质变化速度越快,同时TTI的RGB值减小速度越快。研究获得TTI的Ea值为37. 302 4 k J/mol,TTI颜色变化与奇异果品质变化的Ea差值在±25 k J/mol以内,因此可以将时间-温度指示器用于奇异果品质的预测,也表明了该指示器在食品品质预测方面具有应用潜力。展开更多
采用动态真空安定性（DVST）方法研究了叠氮化铅（LA）和羧甲基纤维素叠氮化铅（CMC-LA）的热分解过程。利用微分法分析了测试数据。获得了LA和CMC-LA的反应机理函数和表观活化能,剖析了羧甲基纤维素钠晶型控制剂对LA安定性和热分解反...采用动态真空安定性（DVST）方法研究了叠氮化铅（LA）和羧甲基纤维素叠氮化铅（CMC-LA）的热分解过程。利用微分法分析了测试数据。获得了LA和CMC-LA的反应机理函数和表观活化能,剖析了羧甲基纤维素钠晶型控制剂对LA安定性和热分解反应动力学参数的影响。结果表明,在非等温阶段,60~100℃,LA热分解反应的机理函数为Zhuralev-Lesokin-Tempelman方程,表观活化能（Ea）分别是86.53、42.26、39.43、38.09 k J·mol-1和10.84k J＂mol-1。在60~70℃,CMC-LA热分解反应的机理函数为Avrami-Erofeev方程,Ea分别是133.02 k J·mol-1和41.87 k J·mol-1,在80~100℃,CMC-LA热分解反应的机理为减速型α-t曲线,Ea分别是43.07、34.34 k J·mol-1和33.46 k J·mol-1。添加羧甲基纤维素钠改变了LA的反应机理函数,使得CMC-LA在60~70℃产气量更小,热安定性更好。展开更多
在本文中,研究了热风温度(60、70、80、90℃)和热烫处理对油豆角丝热风干制动力学参数的影响。结果表明:油豆角丝薄层热风干燥是内部水分扩散控制的降速干燥过程,热风温度升高和热烫处理可显著加速干制速率,缩短干制的时间(p<0.05)...在本文中,研究了热风温度(60、70、80、90℃)和热烫处理对油豆角丝热风干制动力学参数的影响。结果表明:油豆角丝薄层热风干燥是内部水分扩散控制的降速干燥过程,热风温度升高和热烫处理可显著加速干制速率,缩短干制的时间(p<0.05)。采用Newton,Page,Two term exponential,Henderson and Pabis,Approximation of diffusion等5种常见食品薄层干燥模型对干燥实验数据进行非线性拟合回归分析,结果显示Page模型具有最大的决定系数(R^2)、最小的卡方(χ~2)和均方根误差(RMSE),该模型能较准确地表达和预测油豆角丝热风干燥过程的水分变化规律。热烫处理和热风温度增加促使D^(eff)的增加,在干制温度范围内,水分有效扩散系数(D^(eff))的值在0.7981~2.5724×10^(-9)m^2/s之间变化。通过阿伦尼乌斯公式计算出的热烫和非热烫的油豆角丝的活化能(E_a)分别为32.03、37.62 kJ/mol。研究结果可以为油豆角丝干制工业化生产和控制提供理论依据。展开更多
混凝土中氯离子侵蚀过程与外部环境条件、混凝土自身性能等因素密切相关。通过开展2~40℃5个不同环境温度和28、56及90 d 3个养护龄期的室内盐水浸泡试验,研究环境温度和养护龄期对普通混凝土和高性能混凝土氯离子侵蚀规律的影响。结果...混凝土中氯离子侵蚀过程与外部环境条件、混凝土自身性能等因素密切相关。通过开展2~40℃5个不同环境温度和28、56及90 d 3个养护龄期的室内盐水浸泡试验,研究环境温度和养护龄期对普通混凝土和高性能混凝土氯离子侵蚀规律的影响。结果表明：环境温度影响混凝土中氯离子的扩散速度,随着环境温度的升高,混凝土中氯离子扩散系数增大,并且环境温度对氯离子扩散速度的影响程度及混凝土活化能Ea与混凝土性能、养护龄期相关;在对南北不同地区混凝土耐久性设计和施工时,应充分考虑混凝土材料的差异性及养护时间对活化能Ea取值的影响。展开更多
基金Funded by Hubei Provincial Department of Education(No.D20161006)
文摘Various lead-free ceramics have been investigated in search for new high-temperature dielectrics. In particular, Bi_4Ti_3O_（12） is a type of ferroelectric ceramics, which is supposed to replace leadcontaining ceramics for its outstanding dielectric properties in the near future. Ferroelectric ceramics of Bi_4Ti_3O_（12） made by conventional mixed oxide route have been studied by impedance spectroscopy in a wide range of temperature. X-ray diffraction patterns show that Bi_4Ti_3O_（12） ceramics are a single-phase of ferroelectric Bi-layered perovskite structure whether it is calcined at 800 ℃ or after sintering production. This study focused on the effect of the grain size on the electric properties of BIT ceramics. The BIT ceramics with different grain sizes were prepared at different sintering temperatures. Grain becomes coarser with the sintering temperature increasing by 50 ℃, relative permittivity and dielectric loss also change a lot. When sintered at 1 100 ℃, r values peak can reach 205.40 at a frequency of 100 k Hz, the minimum dielectric losses of four different frequencies make no difference, all close to 0.027. The values of Ea range from 0.52 to 0.68 e V. The dielectric properties of the sample sintered at 1 100 ℃ are relatively better than those of the other samples by analyzing the relationship of the grain, the internal stresses, the homogeneity and the dielectric properties. SEM can better explain the results of the dielectric spectrum at different sintering temperatures. The results show that Bi_4Ti_3O_（12） ceramics are a kind of dielectrics. Thus, Bi_4Ti_3O_（12） can be used in high-temperature capacitors and microwave ceramics.
文摘为了研究扩散型时间-温度指示器(time-temperature indicator,TTI)对奇异果品质的预测情况,分别研究了不同贮藏温度(5、10、15、20℃)下指示器的颜色变化和奇异果品质(失重率、可溶性固形物含量、VC含量和总酸度)变化情况,通过Arrhenius方程计算TTI反应和奇异果品质变化的活化能Ea值,并将指示器颜色变化与奇异果品质变化的Ea值进行比较,从而评估使用TTI预测奇异果品质的可能性。研究结果表明,贮藏温度及时间对TTI颜色和奇异果品质变化均有影响,贮藏温度越高,TTI颜色变化速度越快,奇异果失品质变化速度越快,同时TTI的RGB值减小速度越快。研究获得TTI的Ea值为37. 302 4 k J/mol,TTI颜色变化与奇异果品质变化的Ea差值在±25 k J/mol以内,因此可以将时间-温度指示器用于奇异果品质的预测,也表明了该指示器在食品品质预测方面具有应用潜力。
文摘采用动态真空安定性（DVST）方法研究了叠氮化铅（LA）和羧甲基纤维素叠氮化铅（CMC-LA）的热分解过程。利用微分法分析了测试数据。获得了LA和CMC-LA的反应机理函数和表观活化能,剖析了羧甲基纤维素钠晶型控制剂对LA安定性和热分解反应动力学参数的影响。结果表明,在非等温阶段,60~100℃,LA热分解反应的机理函数为Zhuralev-Lesokin-Tempelman方程,表观活化能（Ea）分别是86.53、42.26、39.43、38.09 k J·mol-1和10.84k J＂mol-1。在60~70℃,CMC-LA热分解反应的机理函数为Avrami-Erofeev方程,Ea分别是133.02 k J·mol-1和41.87 k J·mol-1,在80~100℃,CMC-LA热分解反应的机理为减速型α-t曲线,Ea分别是43.07、34.34 k J·mol-1和33.46 k J·mol-1。添加羧甲基纤维素钠改变了LA的反应机理函数,使得CMC-LA在60~70℃产气量更小,热安定性更好。
文摘在本文中,研究了热风温度(60、70、80、90℃)和热烫处理对油豆角丝热风干制动力学参数的影响。结果表明:油豆角丝薄层热风干燥是内部水分扩散控制的降速干燥过程,热风温度升高和热烫处理可显著加速干制速率,缩短干制的时间(p<0.05)。采用Newton,Page,Two term exponential,Henderson and Pabis,Approximation of diffusion等5种常见食品薄层干燥模型对干燥实验数据进行非线性拟合回归分析,结果显示Page模型具有最大的决定系数(R^2)、最小的卡方(χ~2)和均方根误差(RMSE),该模型能较准确地表达和预测油豆角丝热风干燥过程的水分变化规律。热烫处理和热风温度增加促使D^(eff)的增加,在干制温度范围内,水分有效扩散系数(D^(eff))的值在0.7981~2.5724×10^(-9)m^2/s之间变化。通过阿伦尼乌斯公式计算出的热烫和非热烫的油豆角丝的活化能(E_a)分别为32.03、37.62 kJ/mol。研究结果可以为油豆角丝干制工业化生产和控制提供理论依据。
文摘混凝土中氯离子侵蚀过程与外部环境条件、混凝土自身性能等因素密切相关。通过开展2~40℃5个不同环境温度和28、56及90 d 3个养护龄期的室内盐水浸泡试验,研究环境温度和养护龄期对普通混凝土和高性能混凝土氯离子侵蚀规律的影响。结果表明：环境温度影响混凝土中氯离子的扩散速度,随着环境温度的升高,混凝土中氯离子扩散系数增大,并且环境温度对氯离子扩散速度的影响程度及混凝土活化能Ea与混凝土性能、养护龄期相关;在对南北不同地区混凝土耐久性设计和施工时,应充分考虑混凝土材料的差异性及养护时间对活化能Ea取值的影响。
