测定陶瓷材料密度及其气孔率的方法

提出了利用电子天平测量陶瓷材料密度及其气孔率的方法。这种方法是利用电子天平的清零技术，可减少传统方法的实验步骤。结果表明，利用电子天平测定陶瓷材料密度及其气孔率可提高工作效率，并保证了实验的精确度。     

熔融沉积法3D打印制备氧化锆陶瓷及其力学性能研究

在传统熔融沉积方法的基础上, 采用颗粒混合料和螺杆挤出机构3D打印制备了致密和多孔氧化锆陶瓷, 系统研究了颗粒原料的打印性能、坯体显微结构特征和陶瓷材料的力学性能。研究结果表明, 该方法可以实现倾角达165°和跨度为5.5 mm的无支撑结构的打印成型。研究了两种打印路径对致密氧化锆陶瓷抗弯强度及抗弯强度Weibull模数的影响, 结果表明与传统单线填充模式相比, “单线+矩形”复合填充模式可以得到更高致密度和更优力学性能的陶瓷(抗弯强度达到637.8 MPa, Weibull模数达到9.10)。研究了不同气孔率多孔氧化锆陶瓷的压缩力学行为, 结果表明陶瓷的抗压强度和气孔率之间存在复合指数规律, 低气孔率时异面压缩的应力-应变曲线只呈现弹性阶段, 高气孔率时出现弹性阶段和坍塌阶段, 均未出现密实阶段。     

钾长石为助烧剂对β-SiC超精油石性能的影响

以β-SiC为主料,钾长石、硼玻璃、刚玉混合粉为烧结助剂,精萘作为造孔剂,采用低温无压烧结制备β-SiC超精油石。通过SEM、煮沸法、万能试验机及洛氏硬度测定等测试手段对油石试样的微观形貌、气孔率、密度、抗弯强度及硬度进行了表征,探索了钾长石质量分数的变化对β-SiC超精油石气孔率、密度、抗弯强度和硬度的影响,并且从微观结构方面探究了其变化的机理。结果表明:当钾长石含量为11%(wt,质量分数)时,超精油石气孔率为40.39%,密度为1.48g/cm~3、抗弯强度为27.17MPa,洛氏硬度为41.94HRB,达到最佳水平。     

粉煤灰-城市污泥基多孔陶瓷材料的制备及性能

为了提高工业废弃物的综合利用效率,以粉煤灰和城市污泥为主要原料,利用添加造孔剂法制备了多孔陶瓷。利用XRD、SEM表征了陶瓷的晶相和显微结构,并研究了粉煤灰和城市污泥的配比对多孔陶瓷显气孔率、抗折强度等性能的影响。结果表明,当粉煤灰和城市污泥的配比在1∶1~3∶1之间可制备出性能优良的多孔陶瓷;当配比为3∶2时,可制得显气孔率为41.91%、抗折强度为10.06MPa、体积密度为1.32g/cm~3的多孔陶瓷材料。     

超重力熔铸快速致密化技术制备YAG陶瓷材料的研究

超重力熔铸技术是将自蔓延高温合成技术和超重力离心力场耦合的一种新的材料制备技术,但单纯的超重力离心力场不足以使陶瓷产物完全致密,有较大的缩松区域,整体致密度约85%。在超重力熔铸过程中加上一个压力场,可以同步实现陶瓷材料整体致密化,这一技术称为超重力熔铸快速致密化技术,利用该技术制备了整体致密度达98%的YAG陶瓷材料。宏观照片和显微形貌结果显示,所制备的YAG陶瓷材料整体致密,无疏松区,并且晶粒得以细化。     

传统压痕法识别陶瓷材料断裂韧性的有效性研究

基于虚拟裂纹闭合法对传统压痕法测试陶瓷材料断裂韧性的数值模型进行计算,以此为基础,分析比较传统压痕法的几种典型公式识别陶瓷材料断裂韧性的测试误差和所测材料的适用范围。结果表明:传统压痕法的Anstis公式较Evans公式,Lawn公式,JISR公式和Niihara公式,在材料比功0.3≤We/Wt≤0.45时所测断裂韧性值与理论计算值较为接近,其最大误差为12.9%,测试结果相对准确;当0.45We/Wt≤0.7时,传统压痕法对陶瓷材料断裂韧性的测试误差随比功增加迅速增大,特别是当We/Wt=0.7时,Anstis公式,Evans公式,Lawn公式,JISR公式和Niihara公式所测断裂韧性值与理论计算值的最大误差分别为70%,148.5%,48.8%,98.7%和166.6%,在此材料比功范围内传统压痕法所测断裂韧性值误差较大。     

支柱绝缘子陶瓷材料的结构与性能

从成分、物相、组织结构和力学性能测试分析以及抗热震性能试验等方面,比较两种典型支柱绝缘子陶瓷材料的组织结构与性能的不同特点。结果表明:硅质绝缘子陶瓷材料中莫来石相含量高,气孔数量高,圆整度低,致密度低,SiO2颗粒与基体基本脱粘;而铝质绝缘子陶瓷材料中刚玉含量高,气孔含量少,圆整度高,组织较更致密,且Al2O3颗粒与基体结合紧密。铝质瓷的抗弯强度和弹性模量较大,而硅质瓷的抗热震性更高。     

浸液法测定硅砖真密度的不确定度评定

根据GB/T 5071-1997规定的浸液法对一批硅砖进行真密度测试,对真密度测试的不确定度分量进行分析、评定、合成,并给出了不确定度报告。结果表明:该测试的不确定度主要来自重复性试验。     

SiC晶须增强NiFe2O4基惰性阳极材料烧结工艺研究

为改善铝电解惰性阳极用NiFe2O4 尖晶石材料存在的不足,首次采用固态合成法制备了NiFe2O4/SiCw 复合材料。利用扫描电子显微镜观察显微组织,由X射线衍射分析物相,研究了烧结温度和保温时间对体积密度、气孔率和微观结构的影响,通过DTA分析证明了低于1200℃时NiFe2O4 与SiC的热力学相容性,试验结果表明,当烧结温度为1180℃时试样微观结构最为均匀致密,当烧结时间>6h时密度和气孔率的变化趋于稳定, NiFe2O4/SiCw 复合材料最佳的烧结工艺为1180℃×6h。     

制备工艺对BaO-TiO2-B2O3-SiO2体系LTCC性能和微观结构的影响

研究了溶胶-凝胶法、高温熔融法、预煅烧法分别制备的BaO-TiO2-B2O3-SiO2体系LTCC的介电性能、烧结性能以及微观结构.研究发现,溶胶-凝胶法制备的LTCC材料烧结温度较低,坯体在880℃烧结即可达到最大收缩,其烧结收缩率大于高温固相法制备的LTCC;高温熔融法制备的LTCC介电性能稳定,但烧结温度偏高,大约950℃才能达到最大收缩;预煅烧法制备粉体简单、有效,烧结温度在900℃左右,但LTCC中活性成分较多,容易造成气孔率偏高,致密化难度增大且介电常数稳定性不好等缺点;在总结这3种制备工艺对LTCC玻璃陶瓷材料性能和微观结构的基础上,利用适量掺杂Al2O3等添加剂的方法,在保证介电性能满足应用的前提下,大大提高了预煅烧法制备LTCC的烧结体致密度.     

改进的穿线法的卡尺图像识别

为了提高卡尺显示的数字识别效率及识别精度,提出了一种基于改进的穿线法的数显卡尺图像识别算法。传统的穿线法在数字图像识别时对图中数字垂直方向有倾斜的数字图像的识别会频繁出现错误,实用性差,有缺陷,无法在智能制造现场大范围推广。针对这个问题,先采用Radon变换对数字图像的垂直方向倾斜角进行估计,再利用该估计角度的倾斜直线代替传统穿线法竖直直线,进而通过数字图像分割和处理,实现高效率识别。实验结果表明,该算法识别率约为98%,很好地满足了工业测量中大范围高密集度的数字图像识别的使用要求。     

内部孔隙率对硝化棉基烟花药燃烧性能的影响

为研究内部孔隙率对硝化棉基烟花药燃烧性能的影响规律,采用捏合塑化 剪切造粒工艺以及添加致孔剂、高温水煮的处理方法,制备了疏松结构的硝化棉基烟花药样品,并对样品的内部孔隙率、表观密度、堆积密度、表观燃速和定容燃烧性能进行了研究。结果表明:添加致孔剂和高温水煮可以明显降低硝化棉基烟花药的表观密度和堆积密度,提高内部孔隙率,显著提高表观燃速,减少定容燃烧时间;当采用30 mL致孔剂和100 ℃水煮条件时,与原样相比,内部孔隙率与表观燃速分别提高了113.8%和354.9%。     

对JJG30-2002通用卡尺检定规程的学习与探讨

新近发布的JJG30—2002《通用卡尺检定规程》。取代了原先相关测量器具：游标卡尺、带表卡尺、数显卡尺、深度卡尺等的5个检定规程。新老规程相比较，有5条条款发生较大的变化。现就5条变化条款，从新老规程所改变的表征、改变的原由以及将会产生的后果等方面进行探讨。     

Assessment of a three-dimensional measurement technique for the porosity evaluation of PMMA bone cement

In vitro testing of bone cement has historically resulted in the belief that porosity should be minimised to help reduce the risk of prosthesis failure through aseptic loosening. Traditional porosity measurement techniques rely on the analysis of a two dimensional representation of a three dimensional structure. However, with an increasing interest in the number, size and distribution of pores in bone cement, the reliability of a two dimensional approach is questionable. The purpose of this study was to investigate the use of micro computed tomography (micro-CT) for the three dimensional measurement of bone cement porosity by comparison with two traditional techniques. Eighteen bone cement specimens were analysed for porosity using each technique. Levels of agreement between techniques were evaluated, and technique precision was assessed in terms of repeatability and sensitivity to changes in threshold. Micro-CT data was used to illustrate the effectiveness of predicting the porosity of a whole structure from a sample region; an approach often used with traditional techniques. In summary, poor agreement was found between all techniques. However, micro-CT was found to be significantly more repeatable and less sensitive to changes in threshold. The results demonstrated that porosity cannot be reliably determined using traditional techniques and that a large proportion of a specimen is required to provide an accurate porosity measurement.     

Accelerated strength and testing of concrete using blended cement

Accelerated strength testing using the boiling water procedure of ASTM C 684 was performed to evaluate this test method for use in the routine quality control of concrete made of local materials with particular emphasis on the use of blended cements, and in the prediction of potential quality and strength of concrete at later ages. Large number of groups of standard concrete specimens are sampled; in each group one cube represented the accelerated strength and is tested at 28.5 h while the other one is normally cured and tested at 28 days. Test results were recorded and statistically evaluated. A computer program was developed to carry out the numerical statistical computations and regression analysis. Correlation between the 28-day compressive strength and the corresponding accelerated strength was established considering the utilization of local materials and practices. The outcome of this study in the form of prediction models confirm that accelerated strength testing could be accepted in lieu of the standard 28-day testing. The conclusions derived may provide experimental evidence in favor of implementing the standard boiling water method for use in relation to quality control and prediction of concrete strength at later ages. Advanced Cement Based Materials 1997, 5, 49–56.     

A hybrid polygonal element method for fracture mechanics analysis of resistance spot welds containing porosity

A hybrid polygonal element (HPE) method is presented in this study for evaluating the effects of micro-porosity on the fracture behavior of resistance spot welds. The HPE method uses an arbitrarily shaped n-sided polygonal grid to characterize porosity distribution in a weld nugget. Compared with traditional finite element methods, HPE method possesses a number of unique features and advantages, such as mesh simplicity, computational efficiency, and easiness in performing parametric studies. Randomly distributed porosity in a resistance spot weld can be directly modeled using this method. The interactions between porosity and the main crack around the periphery of a weld nugget can be easily quantified. This is of particular importance for aluminum resistance spot welds as the automotive industries strive to produce light-weight vehicles by using more and more aluminum alloys. To demonstrate its effectiveness, HPE method was applied to carry out a series of fracture mechanics analyses for aluminum spot welds with various distributions of micro-porosity. Both lap shear and lap tension specimens were analyzed. The analysis results shed light on the effects of porosity on the fatigue strength of aluminum spot welds.     

含油制冷剂在泡沫金属圆管内流动沸腾的换热特性

实验研究了填充泡沫金属的圆管内制冷剂与润滑油混合物流动沸腾换热特性。实验对象为两根分别填充5PPI、90%孔隙率与10PPI、90%孔隙率泡沫铜的圆管,以及相同管径的光管。实验工况为蒸发压力995kPa,质流密度为10~30 kg/(m2.s),热流密度为3.1~9.3kW/m2,入口干度0.175~0.775,油浓度为0~5%。实验结果表明:纯制冷剂工况下,泡沫金属的存在强化流动沸腾换热,换热系数最多提高185%;含油工况下,泡沫金属强化换热的效果弱化;相同工况下,更小的孔径可以提高流动沸腾换热系数,相比5PPI泡沫金属的实验数据,10PPI的泡沫金属可以使换热系数最多提高0.6倍。基于流型建立了填充泡沫金属的圆管内制冷剂与润滑油流动沸腾换热系数的预测模型,预测模型与98%的实验数据误差在±30%以内。     

浸没凝胶相分离法制备聚己内酯多孔支架

为了制备结构和性能满足骨组织工程支架要求的聚己内酯(PCL)多孔支架材料,采用浸没凝胶相分离法,以冰醋酸和丙酮为混合溶剂,水为凝固剂,壳聚糖(CS)颗粒为添加剂制得一系列PCL多孔支架。探讨了溶剂组成、PCL浓度、CS添加量对PCL多孔支架结构和性能的影响。结果表明:添加CS颗粒有利于形成多孔三维支架,随着CS含量的增加,孔隙率略微下降,抗压强度提高。随着PCL质量分数的增加,孔隙率明显下降,但抗压强度增大。当溶剂组成中丙酮含量为50 wt%~60 wt%,PCL质量分数不高于10 wt%时,通过改变CS用量,可制得孔隙率和力学性能满足骨组织工程要求的相互贯通的三维多孔支架材料。     

模拟点腐蚀油气管线钢的力学性能

通过计算机产生随机数确定点腐蚀孔的位置,利用小钻头打孔的方法模拟X60管线钢基体多孔特征进行拉伸试验,测得其弹性模量、屈服强度和抗拉强度,并将理论计算值与前二者比较,给出了三者与孔隙率的函数关系.结果表明,多孔材料的弹性模量试验值随其孔隙率的变化在低孔隙率时与理论预测基本吻合;实测材料的屈服强度也随着孔隙率的增加而递减,与理论预测也基本吻合,特别是较高孔隙率时相近或相同;实测材料的抗拉强度随孔隙率的变化拟合曲线与屈服强度相似,但受孔隙率影响较大.     

FFC法制备海绵钛的TiO2电极行为研究

本文采用分析纯TiO2粉体、粘结剂及造孔剂制备了TiO2电极。通过水煮法测定所制备电极的孔隙率,同时还分析了其物相组成。在此基础上,采用不同电极组装方式进行了电解实验,对电解后的产物进行了X射线衍射仪分析。研究结果表明,所研制的TiO2电极孔隙率达到50%以上;烧结后的电极成份几乎都是金红石型TiO2;在确定的电极组装方式下进行电解实验,能够获得较大的电解电流,而且电解产物含钛量达到98%（w）以上。