覆膜陶瓷粉末激光线扫描烧结温度测试

目的 研究覆膜陶瓷粉末激光线扫描烧结成型过程中温度的测试技术。方法 应用红外测温仪及热电偶实际测量了已烧结粉末层的温度。并用理论计算值进行了比较。结果 实际测量值同理论计算值符合得很好。结论 应用作者所开发的测温系统。可迅速并准确地完成８温度场的测试。从而为后续位移及应力场的分析与缺陷预测打下坚实的基础。     

选择性激光烧结用尼龙12覆膜Cu粉的制备

提出了溶剂沉淀法制备选择性激光烧结(SLS)用尼龙12覆膜Cu粉复合粉末材料,利用扫描电镜(SEM)观察了复合粉末材料的微观形貌,通过差示扫描量热分析(DSC)、热重分析(TGA)对复合粉末材料的熔融、结晶行为,烧结温度窗口及热稳定性进行了研究,并测试了其烧结件的力学性能。结果表明,复合粉末材料的熔点、结晶速度及热稳定性较纯尼龙粉末有所提高,烧结温度窗口变宽,因而烧结性能优于纯尼龙粉。复合粉末材料烧结件的弯曲强度、弯曲模量、硬度均高于纯尼龙粉的烧结件。     

覆膜不锈钢粉末选择性激光烧结成型机理研究

制备了一种适合于选择性激光烧结快速成型技术的覆膜不锈钢(1Cr18Ni9Ti)粉末材料,应用激光烧结快速成型机对自行开发的覆膜不锈钢粉末进行了烧结成型实验.应用微观分析方法研究了覆膜不锈钢粉末激光烧结成型动态过程,在此基础上建立了覆膜不锈钢粉末的激光烧结成型过程机理模型,当加热温度100℃＜T＜130℃时,粘性流动为主要的成型机理;当加热温度T＞130℃时,可以用熔化/固化机理来描述.     

放电等离子体烧结(SPS)制备多晶La_(0.4)Pr_(0.6)B_6块体及其发射性能研究

采用氢直流电弧法制备了LaH2和PrH2粉末,然后利用放电等离子体烧结(SPS)技术制备了多晶的La0.4Pr0.6B6致密块体.系统分析了烧结温度对样品微观结构及性能的影响,研究结果表明:烧结温度高于1350℃时可形成La0.4Pr0.6B6纯相,且样品致密度随着烧结温度的升高而增加.所制备材料的密度、维氏硬度和抗弯强度的最大值分别达到4.82g/cm3、19.14GPa和225.13MPa;测试了40MPa、1400℃烧结样品的热电子发射性能,当阴极温度为1873K时最大发射电流密度为30.65A/cm2;利用Richardson直线法求出了所测试样品绝对零度时的逸出功φ0为2.165eV,并计算出了样品在不同加热温度时的有效逸出功φeff,其平均值为2.84eV。     

水热法制备ZST微波陶瓷粉体

采用水热法制备了(Zr0.8Sn0.2)TiO4粉体,并借助于XRD、SEM、热分析等手段对反应后的结晶粉末进行了表征.实验结果表明,粉末性能受反应溶液pH值的影响显著.随着pH值的增大,晶粒的生长更加充分,完整.反应后的晶粒粒度为纳米尺度,表面活性大,有利于烧结.烧结温度在1260-1320℃之间,比传统固相法制备的ZST陶瓷烧结温度降低了300多度.     

草酸共沉淀法制备Sm掺杂CeO2粉末研究

采用草酸盐共沉淀法制备Sm2O3掺杂CeO2粉末(SDC),XRD分析结果表明为纯相的Sm2O3掺杂CeO2(SDC)固溶体.采用XRD、SEM、TG/DSC、激光粒度分析仪等对粉末的性质和制备工艺条件进行了研究.通过优化沉淀反应pH值,草酸溶液浓度和沉淀物的煅烧温度等制备工艺条件,得到高烧结活性的SDC粉末,沉淀反应pH值为6～7,草酸浓度为0.3mol·L-1形成的草酸沉淀物在700℃煅烧的氧化物粉末,1350℃烧结可以达到95%的理论密度.     

仿血管聚氨酯基复合材料的激光烧结工艺研究

激光选区烧结(SLS)技术在生物医学领域的应用日渐广泛,但是由于材料的限制,大部分SLS打印的产品都是合成塑料、陶瓷、合金等刚性零件,研究能用于激光选区烧结技术的柔性材料成为当前的迫切需求。本工作采用聚氨酯(TPU)粉末为主料,研究并制备了一种可用于激光选区烧结技术的复合材料,其烧结制件具有较高的强度及成形精度,可用于制作仿血管等柔性医疗模型。首先通过正交试验法对TPU/PS复合粉末进行激光选区烧结实验,并对制件进行测试,获得加工工艺参数对制件强度、成形精度及烧结密度的影响规律。其次对不同配比的TPU/PS复合粉末进行激光选区烧结实验,得到拉伸试件和弯曲试件,通过对制件的尺寸测量、力学强度测试及通过扫描电镜对复合粉末和拉伸试样断口进行显微组织观察,得到了不同组分配比对烧结制件显微组织及拉伸强度、弯曲强度的影响,确定了仿血管柔性材料的理想配比。     

陶瓷微结构件的注射成形工艺及其微观组织

采用粉末微注射成形技术制作了ZrO2陶瓷微结构件,分析了其注射成形工艺,包括喂料配制、注射工艺及烧结工艺对微观组织的影响.实验结果表明,粉末体积分数为55%的生坯注射成形后在1 500℃下烧结2 h,采用排水法测得其微结构相对密度高达98.5%,采用纳米硬度分析法得到其微结构的显微硬度值为13.75 GPa.扫描电子显微镜(SEM)结果表明,提高模具温度和注射压力,有利于微结构的填充,进而改善微结构件的微观组织;高的烧结温度可以增加零件的致密度,但容易导致晶粒的过度长大和尺寸不均匀.激光共聚焦光学显微镜观察结果表明,使用亚微米级陶瓷超细粉得到的微结构具有良好的表面质量,其烧结前、后的表面粗糙度值分别为0.33μm和0.28μm.此外,提高粉末含量可以减小零件收缩率,从而有利于微结构的尺寸精度控制.     

均相共沉淀法制备钇铝石榴石(YAG)纳米粉末

以Y2O3、Al(NO3)3·9H2O、(NH4)2SO4为原料,尿素为沉淀剂,正硅酸乙酯作为添加剂,采用均相共沉淀法制备出YAG前驱体粉末,在沉淀过程中采用静电稳定、聚合物位阻以及共沸方法相结合有效地防止了纳米颗粒硬团聚的形成,前驱体颗粒尺寸小于100nm.采用DTA/TG、IR、XRD和TEM测试手段对粉末材料进行了表征,根据Scherrer公式计算出晶粒大小,研究了晶粒尺寸分布及其变化情况.研究结果表明前驱体粉末经过1200℃温度烧结后,全部转化YAG相,其晶粒尺寸小于50nm,随着烧结温度提高,晶粒平均尺寸增大.     

电流直加热动态热压烧结炉的研制与温度场模拟

研制了一种电流直加热动态热压烧结炉,钢模具内衬电绝缘陶瓷片,实现了电流直加热;3个时间继电器控制主电路继电器的开合,实现了动态热压烧结;热电偶测量与温度场模拟相结合确定烧结温度.此烧结炉可实现利用低电压、大电流在短时间内对产品瞬时高温烧结的效果,大大缩短粉末烧结时间,提高生产效率,节约能源.     

小波奇异熵在燃气轮机传感器周期故障检测中的应用

燃气轮机电厂实际运行中,利用传感器得到的数据来进行燃机的状态评估。而传感器的状态直接影响到各个热参数的观测值。常见传感器故障中的周期故障由于故障幅值较小,易被噪声掩盖而无法检测到。应用小波奇异熵(Wavelet Singular Entropy,WSE)构建传感器周期故障检测的方案。介绍小波奇异熵的定义和计算方法,并通过仿真的方法,比较小波奇异熵相对小波变换在周期故障检测方面的优势,并证明小波奇异熵与故障幅值无关。以实验室的小型燃机的燃烧室出口温度传感器为实例进行验证,证明该方法对燃机传感器的周期故障检测有较好的工程应用价值。     

用散斑干涉光谱分布检测瞬态温度

为了提高对瞬态温度检测的灵敏度,提出了基于散斑干涉条纹光谱分析的瞬态温度反演算法.系统利用散斑干涉形成干涉条纹,由于瞬态温度的变化会使材料应变,从而使散斑干涉条纹改变.被测表面形变前后获得的干涉条纹由面阵 CCD 采集,其对应的光谱密度分布函数也会发生相应的改变,即由散斑干涉条纹反演得到的中心波长振幅发生改变.通过对两次中心波长幅值的比值的检测和计算,即可获得被测的瞬态温度.在分析计算了瞬态温度变化与材料应变、材料应变与干涉条纹变化的函数关系的基础上,推导了瞬态温度变化与干涉条纹振幅及相位函数关系.实验采用660 nm 半导体激光器,SI6600型面阵 CCD 探测器,从获得的光谱分布函数中提取中心波长处幅值比值,通过计算和标定,最终温度检测精度可达到±2℃.相比传统的直接检测干涉条纹的变化量,由被测面形变量推导温度的方法精度提高了近一个数量级,其精度更高、检测均匀性更好、稳定性更好.     

Simultaneous coherent anti-Stokes Raman scattering and two-dimensional laser Rayleigh thermometry in a contained technical swirl combustor

The simultaneous application of vibrational coherent anti-Stokes Raman scattering (CARS) and the two-dimensional (2D) UV laser Rayleigh technique is reported for the investigation of a highly turbulent swirl frame inside a contained technical combustor. The CARS technique has been used to determine accurate temperature values at one point within the 2D Rayleigh-probed combustion field. These values were necessary to normalize the Rayleigh data to overcome influences of absorption effects along the detection path of the Rayleigh-scattered light through the exhaust gas volume and by the sealing window of the combustion chamber. At several different downstream positions, 500 simultaneous measurements with the point and with the 2D technique were performed to cover the whole combustion field. These data can be used for both the evaluation of 2D temperature structures in single frames and for the calculation of temperature probability density functions from the Rayleigh data at one single camera pixel over 500 frames. With this information, characterization of a highly turbulent flame is possible.     

An approximate numerical method of solving collision integrals for the Morse potential in a wide parameter interval

The calculation technique for the collision integrals with model potentials has been refined. The collision integrals were calculated for the Morse potential in wide ranges of the reduced temperature and the parameter β. The applicability limits of the calculation of the collision integrals for the Morse potential at small β values have been found. The calculated values of the collision integrals have been fitted with analytical functions. The obtained results were compared critically with the published data. The temperature derivatives of the collision integrals have been analyzed.     

Equation of state for gaseous propane determined from the speed of sound

An equation of state in the form of a truncated virial series has been developed for gaseous propane. Second, third, and fourth virial coefficients and their temperature derivatives were calculated from model two- and three-body intermolecular potentials, the parameters of which were fitted to experimental values of the speed of sound in the gas; no other data were used. The resulting model predicts accurately thermal and caloric properties of the gas over a wide range of temperatures at densities up to about one-quarter of the critical. The second and third (but not the fourth) virial coefficients are in very close agreement with directly measured values. To facilitate rapid calculation of thermodynamic properties, a look-up table for the virial coefficients and their temperature derivatives is provided together with a recommended means of interpolation.     

Accurate Evaluation of the Specific Heat Capacity of Solids and its Application to MgO and ZnO Crystals

Using binomial coefficients, new, simple, and efficient algorithms are presented for the accurate and fast calculation of the heat capacity of solids depending on the Debye temperature. As will be seen, the present formulation yields compact, closed-form expressions which enable the straightforward calculation of the heat capacity of solids for arbitrary temperature values. Finally, the algorithm is used to simulate the variation of the specific heat capacity with temperature of MgO and ZnO crystals. The results were compared with those reported in the literature and found to be in close agreement with those of other studies.     

冷却塔全运行周期内动态出水温度计算方法

冷却水的进水温度受到多方面因素的影响,其值在空调运行周期内是动态变化的。以重庆地区的冷却塔空调系统为研究对象,针对不同类型的公共建筑,提出了在不同运行模式下的全运行周期内冷却水温度的动态计算方法。该计算方法同时考虑了气象参数、负荷率及冷却塔运行模式对冷却水温度的影响。同时对不同类型建筑在不同影响因素下的冷却水温度进行了动态计算,以计算结果为基础,提出了冷却塔出水温度与负荷率的关系。最后通过实验对所提出的计算方法进行验证。计算值与实验值的平均相对误差小于5%。     

Determination of the Thermal Diffusivity of Electrically Non-Conductive Solids in the Temperature Range from 80 K to 300 K by Laser-Flash Measurement

The adoption of the popular laser-flash method at temperatures far below 300 K is restricted by the weak signal-to-noise ratio and the limited spectral bandwidth of the commonly used mercury cadmium tellurite (MCT) infrared (IR) detector used as a non-contacting temperature probe. In this work, a different approach to measure the temperature rise in pulse heating experiments is described and evaluated. This method utilizes the change of the temperature-dependent electrical resistance of a thin strip of sputtered gold for the detection of a temperature rise as it was proposed by Kogure et al. The main advantage of this method at lower temperatures is the significantly higher signal-to-noise ratio compared to the commonly used IR detectors. A newly developed laser-flash apparatus using this detection method for the determination of the thermal diffusivity in the temperature range from 80 K to 300 K is presented. To test the accuracy of the new detection method, the thermal diffusivity of a borosilicate crown glass (BK7) specimen at 300 K was determined and compared to results derived with a MCT detector. Good agreement of the derived thermal diffusivity values within 3 % was found. The thermal diffusivity of BK7 and polycrystalline aluminum nitride (AlN) was measured at temperatures between 80 K and 300 K by a laser-flash method to test the functionality of the apparatus. Finally, the thermal conductivity was calculated using values for the specific heat capacity determined by temperature modulated differential scanning calorimetry (MDSC). Comparisons with literature data confirm the reliability of the experimental setup.     

On the critical temperature of strong coupling superconductors with paramagnetic impurities

We calculate the effects of paramagnetic impurities on the critical temperature of several intermediate and strong coupling superconductors by numerically solving the Eliashberg equations, and compare the results with the results of Abrikosov-Gorkov theory. For all the superconductors considered, the values of critical impurity concentration obtained from this exact numerical calculation are found to be considerably larger than the values given by Abrikosov-Gorkov theory. By generalizing a previous work of Leavens and Carbotte, we derive simple analytical expressions for the critical temperature and the critical concentration that give results much closer to the exact values than the corresponding BCS values.     

Thermoelastic coefficients of alpha quartz

Experimental measurements of alpha quartz thermal expansion as reported in the literature have been critically analyzed. A recommended set of best measured values over the temperature range -50 degrees C to +150 degrees C have been determined, as have values for the coefficient of thermal linear expansion (CTE) and the thermoelastic coefficients. The impact of using the coefficients on determinations of quartz material temperature coefficients and on the calculation of temperature coefficients of frequency for the case of the AT-cut is discussed.