水泥浆体中连续粒径粉体的堆积密度研究

为了研究粒径分布对水泥石结构与性能的影响,通过测定多组粒径分布不同的矿粉在流动度相同情况下的需水量,得到矿粉不同粒径分布所对应的不同的堆积密度,推导了浆体中连续粒径粉体的堆积密度公式。用该公式计算上述不同粒径分布的矿粉浆体的堆积密度及需水量,计算结果与试验值基本吻合。说明该公式可以用来模拟诸如水泥、磨细矿渣、粉煤灰等胶凝材料细颗粒的堆积密度。     

水泥粒径分布对水泥石强度的影响

以水泥石水化物填充度最高为原则,综合考虑水泥水化度、水泥固相体积增量和水泥浆体初始堆积密度两个方面的匹配关系,通过理论推导和试验验证建立了多粒径(连续粒径分布)单组分水泥石强度与水泥粒径分布之间关系的计算方法,在此基础上就水泥粒径分布对水泥石强度的影响进行探讨。结果表明:计算值与试验值比较吻合,用本文中提供的方法可以根据水泥的粒径分布和各水灰比计算其不同龄期的填充度和抗压强度。     

尖棱状两组分颗粒堆积密度的研究

为了探讨耐火材料制品的密堆积结构特性,从而获得较好的颗粒堆积密度,研究了圆锥破碎机制得的粗、细两种离散颗粒体系的自由堆积密度变化．研究结果表明：当粗、细两种颗粒组分的拉径比大于5、且粗颗粒的质量分数在60%～70%之间时,体系的自由堆积密度较大；当粗、细两种颗粒的粒径比小于5、且无细粉存在时,离散颗粒体系的自由堆积密度变化不大。     

水泥粒径分布与水化速度间的关系研究

为了研究水泥颗粒粒径分布与水泥水化速度之间的关系,根据文献提供的水泥粒径分布与水化度的试验数据,拟合建立了连续粒径分布水泥颗粒的水化速度公式。用该公式计算已知不同粒径分布的水泥浆体的水化速度,通过水泥水化过裤中的热重分析,得出不同龄期的水泥石的水化度试验值。结果表明:计算值与试验值对比基本吻合。     

磷渣粉颗粒分布对水泥胶凝体系力学性能的影响

采用激光粒度仪对比表面积分别为340m~2/kg、420m~2/kg、500m~2/kg的磷渣粉颗粒粒度分布特征进行了分析,在此基础上运用灰色关联理论研究了磷渣粉颗粒分布与水泥胶凝体系3d、28d、180d力学性能的内在关联。结果表明:不同比表面积的磷渣粉具有不同的颗粒群粒度分布特征,磷渣粉颗粒分布中粒径大于20μm颗粒与水泥胶凝体系3d、28d抗折强度负关联、与180d抗折强度正关联;粒径小于20μm的磷渣粉颗粒对水泥胶凝体体系各龄期抗压强度均有促进作用,其中1~3μm的颗粒对3d抗压强度促进作用最显著、10~20μm的颗粒对28d、180d抗压强度发展促进显著。     

变温下SO_2~(-4)对水泥硬化浆体中Al~(3+)配位分布的影响

基于大体积混凝土内部的温度变化,利用27 Al魔角旋转核磁共振(27 Al MAS NMR)结合去卷积技术,研究变温下SO2-4对水泥硬化浆体中Al 3+配位分布的影响。结果表明,变温的高温阶段促进AFt、TAH(third aluminum hydrate)和掺杂在C-S-H结构中(C-S-A-H)的四配位铝(Al[4])向AFm转化;降温阶段促进TAH生成,利于AFm和C-S-A-H中Al[4]向AFt转化;而变温后20℃常温不仅利于AFt向AFm转化,TAH向Al[4]转变,而且利于Al[4]进入高钙硅比(Ca/Si)C-S-H结构。在5%Na2SO4溶液中,SO2-4在侵蚀3d时首先对AFm侵蚀,对TAH和C-S-A-H中Al[4]侵蚀作用较小;变温过程的高温加快SO2-4对AFm和TAH的侵蚀,并且对C-S-A-H凝胶有脱铝作用;变温后20℃常温有利于C-S-H凝胶与硫酸根竞争Al[4],低Ca/Si的C-S-A-H凝胶具有较强的抗SO2-4脱铝能力。     

Cr~(3+)、Pb~(2+)在不同水泥水化体系中的固化

研究了重金属离子Cr~(3+)和Pb~(2+)对硅酸盐水泥、硫铝酸盐水泥及混掺水泥(普通硅酸盐水泥与硫铝酸盐水泥进行混掺)三种水泥的浆体凝结时间和力学性能的影响,并借助X射线衍射技术(XRD)和电感耦合等离子体发射光谱(ICP)等研究了水泥水化产物特征、重金属元素在水泥浆体中的固化方式与溶出特性。结果表明:Cr~(3+)对三种水泥均产生促凝作用,而Pb~(2+)对普通硅酸盐水泥和混掺水泥产生缓凝作用,对硫铝酸盐水泥产生促凝作用。Cr~(3+)和Pb~(2+)的掺加引起AFt和Ca(OH)_2形成量的变化,影响程度与水泥品种有关,掺加Cr~(3+)的28d浆体中有新相Ca_2Cr(OH)_7·3H_2O生成。所研究的三种水泥中,硅酸盐水泥对Cr~(3+)的固化效果最好,当Cr~(3+)掺量为1%时,其Cr~(3+)浸出浓度仅为0.177mg/L;而硫铝酸盐水泥对Pb~(2+)的固化效果最好,当Pb~(2+)掺量为1%时,其Pb~(2+)浸出浓度仅为0.0064mg/L。     

Austenite grain size in the continuous casting process: Metallographic methods and evaluation

Austenite grain size is an important parameter for the ductility of steel at elevated temperatures. Therefore, indirect measurements of austenite grain size on slab samples and a specimen from laboratory experiments were carried out. To reveal the prior austenite grain boundaries three etchants (picric acid, ammonium persulfate and nital 3%) were used. One of the main objectives of the present work was to investigate how far the grain size distribution in the specimen from the laboratory experiment corresponds with the grain size distribution on – and beneath – the surface of a continuously cast slab. The measured grain size distribution of a slab and a laboratory experiment – both with an equivalent carbon content of 0.21 wt.% – show a good agreement. A clear maximum grain size can be found for a carbon equivalent of between 0.15 and 0.17 wt.%. The results of the presented metallographic examinations serve as an important basis for the development of an austenite grain growth model.     

粒度搭配对水雾化铁粉工艺性能的影响

为了研究粒度组成对水雾化铁粉松装密度、流动性、压缩性及压制过程的影响,将-80+100目和-325目两种粒径的水雾化纯铁粉以不同比例搭配进行研究.结果表明:通过控制不同的粒度组成,铁粉松装密度在2.84～3.42 g/cm3内变化、铁粉流动性在20～31 s/50 g内变化;与纯粗粉样品A相比,在粗粉中添加质量分数25%细粉的样品B在低压(300 MPa)下压坯密度增加,高压(≥300 MPa)时压坯密度减少;细粉质量分数为75%时的样品D与样品C相比,压坯密度均增加;全部采用-325目细粉的样品E与样品D相比,压坯密度均降低.当压制压力低于300 MPa时,压坯致密化主要由颗粒的滑移、重排决定;当压制压力高于300 MPa时,压坯致密化主要以粉末的塑性变形为主.     

A particle packing algorithm for packed beds with size distribution

A particle packing algorithm for simulating realistic packed beds of spheres with size distribution is described. The algorithm used the Monte Carlo method combined with the simulated annealing minimisation algorithm to solve the packed bed simulations. The objective function which was minimised was a combination of two functions, one describing the deviation from the target mean coordination number of the spheres in each size interval and the other the average fraction of overlapping volume of the spheres per contact. In this way a realistic bed structure was maintained while at the same time controlling the coordination number of the spheres. The algorithm used an experimentally validated model to predict the mean coordination number of the spheres in each size interval.     

Phase field simulation of abnormal grain growth mediated by initial particle size distribution

The uniform initial particle size distribution was considered to be an important condition for the preparation of dense ceramics. With the rapid development of templated grain growth method, it is necessary to add large template particles into small matrix to promote the epitaxial growth of grains. However, abnormal grain growth will inevitably occur in this process. In this work, a phase field method was employed to study the growth behavior of the large grains into the small matrix. The effect of initial particle size distribution on the grain growth kinetics was investigated. Our simulations revealed that the growth rate of large grains slowed down as the initial grain size distribution widened. Regulating the initial grain size distribution will be an effective way to control abnormal growth of grain. It was found that the growth rate of a large grain was proportional to the number of surrounding grains. These results have implications for the design of the functional ceramics with a target grain microstructure.     

Effect of particle-size distribution and specific surface area of different binder systems on packing density and flow characteristics of cement paste

The particle-size distribution (PSD) and specific surface area (SSA) of binders significantly affect the fresh and hardened characteristics of cement-based materials. An experimental investigation was undertaken to evaluate the influence of PSD and calculated SSA of various binary and ternary binder systems on flow characteristics, packing density, and compressive strength development of cement paste. The influence of dispersion state of the binder on packing density was evaluated using the wet packing density approach to determine the optimum water demand (OWD) needed to achieve maximum wet density. The modified Andreasen and Andersen (A&A), Rosin–Rammler (RR), and power law grading models were employed to optimize the PSD of binder system to achieve maximum packing density, while maintaining relatively low water demand. The incorporation of high-range water reducing admixture (HRWRA) is shown to decrease the OWD and increase the packing density resulting from greater degree of dispersion of the binder. The combined effect of lower OWD, greater packing density, and higher SCM reactivity results in higher compressive strength. The increase in SSA from 425 to 1600 m²/kg results in an enhancement in packing density from 0.58 to 0.72, while further increase in SSA from 1600 to 2200 m²/kg reduces the packing density from 0.72 to 0.62. Binder systems using a distribution modulus between 0.21 and 0.235 determined from the A&A model exhibited 18%–40% lower minimum water demand (MWD) to initiate flow, 8%–35% higher OWD to reach maximum wet density, and 15%–25% higher packing density compared to the binder with 100% cement. Binder systems with lower A&A distribution modulus resulted in higher relative water demand (RWD) required to increase fluidity, thus reflecting greater level of robustness. Good correlations were established between the A&A distribution modulus, SSA, RR spread factor, and power law distribution exponent.     

牙科复合树脂中无机填料的堆积孔隙率与其粒度分布的关系

通过测定松装密度和振实密度 ,研究了牙科复合树脂中无机填料的粒度分布与其堆积孔隙率之间的关系。使用Mathematica软件和SAS/STAT软件 ,用非线性回归的方法得到了无机填料的粒度分布与其堆积密度之间关系的经验公式 ,结论为无机填料 (BG)的平均粒径为 1μm ,可以作为影响堆积优化的判据     

ODS ferritic steel engineered with bimodal grain size for high strength and ductility

An attractive way to enhance the ductility of ODS ferritic steels is to develop an alloy with a bimodal grain size distribution, in which the micron-sized coarse grains provide high ductility. The nanometer-sized fine grains enhance the tensile strength. The microstructures were obtained by blending the gas-atomized powders and mechanical alloyed powders, followed by hot forging and annealing. The homogeneously distributed nanometer-sized oxide nanoparticles can also be detected. Mechanical properties tests revealed a great improvement in ductility in comparison with other ODS ferritic steels, and high strength over the whole range of test temperatures, owing to the fine grains and oxide nanoparticles. The combination of high ductility and high strength makes this ODS ferritic steel much promising in high-temperature application.     

颗粒尺寸及温度对羰基铁粉磁化性能的影响

为了揭示颗粒尺寸及温度对羰基铁粉磁化性能的影响规律,利用振动样品磁场计分别测试了两种不同粒径羰基铁粉在室温条件下的磁化特性曲线,并以粒径为7μm的颗粒为对象,研究了温度对其磁化性能的影响。结果表明,粒径较大的颗粒具有更为优良的磁化性能,相同磁场作用下,其磁化强度较大而矫顽力却较小;温度升高将导致颗粒达到相同磁化强度所需磁场强度减小且对应磁化强度值降低,并且这种影响随温度的升高而逐渐加剧;当长期处于高温下工作后,由于表面氧化层的形成,颗粒磁性将会出现较大程度的减弱。