水泥颗粒群粒度分布宽度的表征及其应用研究

用分形理论阐述了将水泥颗粒群粒度分布的分形维数作为定量表征其粒度分布宽度的正确性和可行性,测量了16种水泥颗粒群的粒度重量累积分布,在双对数条件下,水泥颗粒群的粒度重量累积含量与粒径之间呈直线关系,表明水泥颗粒群粒度分布结构具有分形特征,其分形维数可以定量表征水泥颗粒群粒度分布宽度;研究了水泥颗粒群粒度分布宽度与其空隙率的关系,结果表明,随着水泥颗粒群粒度分布宽度的增加,其空隙率减小,二者呈负相关。     

水泥颗粒形貌对其性能影响的研究(下)

（接上期）这表明水泥颗粒的球形化，减小了浆体中水泥颗粒与骨料颗粒相对滑动间的摩擦阻力。球形化水泥净浆标准稠度低，表明球形水泥较一般水泥需水量小，颗粒表面所需包裹水层小。我们对比分析了１号至４号样品的水泥颗粒圆形系数提高百分数与相应胶砂流动度增大幅度的关系（见图１１）。由图１１我们可以清晰地看出，水泥颗粒圆形系数提高幅度越大，即颗粒形貌越好，相应的胶砂流动性就越好。从中也可以看出，随水泥颗粒圆形系数的提高，水泥胶砂流动度有不断增大的趋势。水泥需水量低且胶砂和易性好，对混凝土施工很重要。因为在确保混…     

颗粒粒度分析测试对水泥质量的影响

颗粒粒度分析测试作为对水泥质量检测的一项重要指标,其检测的指标是否可以达到一定的标准直接影响着水泥的质量。但是,由于水泥颗粒粒度大小不同,而我们又不能用肉眼观察得出水泥颗粒直径。所以,水泥颗粒粒度分析测试工作是一项难度特别大的工作。而传统的分析检测方法也早已经不能满足水泥颗粒的各项参数了,由此颗粒粒度分析测试应用而生。目前,该技术尚未在我国的工业行业领域中得到广泛的应用,本文以颗粒粒度的概念为出发点,就颗粒粒度分析测试对水泥质量的影响进行深入的研究。     

不同物料对水泥颗粒分布及水泥性能的影响

模拟水泥生产实际,对不同组分单掺、双掺和复掺情况下混合粉磨对水泥颗粒分布及水泥性能的影响进行了试验研究。结果表明:(1)粉煤灰、石灰石部分替代矿渣后能够显著降低水泥的特征粒径和均匀性系数,促进水泥的整体粒度下降;(2)粉煤灰不能显著增加水泥中微粉含量,而石灰石可以显著增加水泥中微粉含量;(3)混合材料的复掺对于改善水泥颗粒分布的效果优于单掺或双掺。另外,不同物料混合粉磨对水泥性能的影响主要是由于水泥颗粒分布的拓宽、水泥中微粉含量的增加,提高了水泥颗粒的堆积密度造成。     

水泥颗粒分布对水泥颗粒堆积状态的影响

用不同组分、不同颗粒组成的水泥标准稠度用水量近似计算水泥颗粒的堆积孔隙率,分析研究了水泥颗粒组成对水泥颗粒堆积状态的影响规律和贡献。分析结果表明,水泥颗粒堆积孔隙率与水泥的颗粒组成具有良好的相关性,呈线性关系;在通常水泥的颗粒分布参数中,水泥颗粒的堆积状态与80 μm筛余、45 μm筛余最为相关,均匀性系数次之,而与3 μm筛余的相关性最差;在水泥颗粒分布参数中,均匀性系数对水泥颗粒堆积程度的影响最大,80 μm筛余次之。即水泥颗粒的堆积程度主要受颗粒分布宽窄、水泥中的粗颗粒粒径及含量的控制。在水泥整体粗细程度相近或相同的情况下,水泥颗粒分布越宽、水泥中的粗颗粒越大以及含量越高,水泥颗粒堆积的越紧密。     

陶瓷研磨体对水泥熟料粉磨性能影响的研究

在辊压机+球磨机水泥联合粉磨系统中,辊压机系统的主要任务是进行物料的预粉碎,以大大减小入磨物料的粒度,球磨机系统的主要任务是进行物料的研磨和整形。因此,使用低密度、高硬度的陶瓷研磨体可以提高球磨机的粉磨效率。本文分别以相近的陶瓷研磨体和金属研磨体的级配和填充率进行了水泥熟料的粉磨实验。实验结果表明,陶瓷研磨体粉磨的水泥颗粒级配更加合理,3~32μm颗粒含量可以提高3%左右,28d抗压强度可以提高4MPa左右,水泥标准稠度用水量可以降低2%左右,水泥颗粒的圆形度可以提高8.5%左右。     

胶凝材料颗粒组成对混凝土抗裂性能的影响

混凝土抗裂性能与其胶凝材料的堆积紧密程度有关。运用不同颗粒组成的水泥或粉煤灰调整胶凝材料的颗粒级配,可以拓宽颗粒分布范围,适当增加粗颗粒含量,提高混凝土抗裂性。用粉煤灰充当胶凝材料中的粗颗粒,不仅能改善混凝土抗裂性能,而且后期强度增进率较高,有利于提高耐久性;水泥企业应重视水泥颗粒级配的合理性,水泥中保持一定量的粗颗粒非常必要。试验表明,增加40μm以上颗粒含量就能起到改善混凝土抗裂性能的作用。     

超硫酸盐水泥实际与最密集堆积的灰色关联度与抗压强度的关系

本文采用激光粒度分析仪测试超硫酸盐水泥粉体粒径,用以反映超硫酸盐水泥的粒径分布;采用机械压力法制备的超硫酸盐水泥干粉压实体,其空隙率可以宏观上反映颗粒间的物理堆积密实度;根据Dinger-Funk数学模型得出粉体最佳颗粒群分布即最紧密堆积颗粒群分布;运用灰色关联分析原理考察粉体实际颗粒群分布与最紧密堆积颗粒群分布的相关性;基于以上分析建立水泥净浆抗压强度与超硫酸盐水泥堆积效应的关系.试验结果表明:超硫酸盐水泥粉体实际颗粒群分布与最紧密堆积颗粒群分布的相关性越高,压实体空隙率越低,抗压强度越高.     

不同颗粒群对水泥性能的作用及贡献

以水泥颗粒的粗粉微集料效应为理论依据,研究了不同水泥颗粒群对水泥性能的作用。结果表明,对水泥性能影响幅度最大的为水泥中的粗颗粒群和微粉颗粒群,中间颗粒的影响幅度远小于粗粉和微粉;粗颗粒群含量的提高有利于水泥使用性能的改善,而微细颗粒群含量的增加有利于力学性能的发挥。     

降低立磨水泥需水量的试验研究

同传统球磨机相比，立磨可以大大降低水泥工业的生产能耗，但将其作为水泥终粉磨系统制备的水泥需水量高，导致立磨水泥和易性差，限制了立磨作为水泥终粉磨系统的应用，本文分析了影响立磨水泥需水量的因素，认为立磨水泥颗粒级配窄是立磨水泥需水量高的主要原因之一，并从拓宽立磨水泥颗粒分布的角度研究了降低立磨水泥需水量的方法。     

Influence of Grain Size on the Indentation-Fatigue Behavior of Alumina

The surface fracture behavior of a high-purity, high-density alumina, as a function of grain size (3, 5, and 9 μm), was investigated using an indentation-fatigue technique. Increasing the grain size reduced the threshold for crack nucleation, reduced the resistance to surface spalling, and increased the volume of materials lost per spalling event. These results are explained in terms of residual stresses and fatigue damage.     

Residual Stresses in Alumina/Zirconia Composites: Effect of Cooling Rate and Grain Size

Alumina/zirconia composites with various compositions at the zirconia-rich part of the phase diagram have been prepared with various grain sizes of the starting alumina powders. After firing under identical conditions, the pellets have been cooled systematically, changing the cooling rates from 0.5 to 8000 K/min. Subsequently, the residual stresses in alumina have been determined by monitoring the frequency shifts of the R ₂ luminescence line of alumina (14 430 cm⁻¹). The data indicate that the stress in alumina is compressive in all cases, with increasing absolute values of the stress with decreasing alumina content. Within the same composition, the residual stress as a function of the cooling rate presents a minimum for values between 10 and 100 K/min, with no clear dependence on the alumina or zirconia grain size. An interpretation of the experimental data in terms of a Coble-type diffusional relaxation applies for intermediate cooling rates (from 10 to 800 K/min), but it fails to account for the large stresses at low cooling rates. The width of the stress distribution is narrow (∼150 MPa) and constant for all compositions and grain sizes at low cooling rates, but it increases for cooling rates >10 K/min, depending on the grain size but not on the composition. For fast cooling rates, a correlation is found when reporting the average width of the stress distribution as function of the average sintered grain-size distribution of alumina. Overall, zirconia grain size seems to influence the average stress, whereas alumina grain size determines the stress distribution.     

直接法制备细小颗粒RDX工艺条件研究

在乌洛托品硝解制备ＲＤＸ的工艺基础上,采用先氧化后结晶工艺,研究如何控制结晶过程的各种因素来制备符合美军标〔ＭＩＬ－ｇ８Ｃ〕的细小粒度的ＲＤＸ产品。     

纳米二氧化钛粉体粒径表征研究

采用水解沉淀法制备了纳米二氧化钛粉体，对其XRD衍射谱用Voigt函数拟合精修，得到精确的(101)和(200)面晶粒度，将结果与SEM和TEM测定的粒径进行比较，结果表明：3种方法所测值差异较大，3种粒径相比，XRD测定的粒径值小但变化较大，其平均值与TEM测定值比较接近；SEM测定的粒径大但相对比较稳定，平均增加约53％；TEM测定的粒径比较稳定。产生上述结果的主要原因：一方面是分析测试手段如XRD的精修参数和计算模式选择不同所致，另一方面与粉体样品的制备过程，以及纳米颗粒的结构特征有关。     

Effects of particle size and dispersion methods of In2O3‐SnO2 mixed powders on the sintering properties of indium tin oxide ceramics

Three group samples were used to investigate the effects of particle size and dispersion methods of In₂O₃‐SnO₂ mixed powders on the sintering properties of ITO ceramics by BET, SEM, XRD, and EPMA, etc. High‐density (99.8% of TD) ITO ceramics, with dimensions of 350 × 250 × 8 mm³ for the industrial application, were obtained by the mixed powders of In₂O₃ calcined at 1000°C and SnO₂ with BET 6.0 ± 0.5 m²/g and collocation use of ball mill for 300 minutes, stirred mill for 60 minutes, and sand mill for 3 minutes. The results indicate that: (i) the larger the SnO₂/In₂O₃ particle size ratio, the higher the density of ITO ceramics, (ii) the dispersion of mechanical ball‐mill methods for nanosized In₂O₃ and SnO₂ powders is beneficial to the densification and structural homogeneity, and (iii) the smaller the relative grain size, the more uniform the distribution of grain size.     

微晶纤维素的微细结构研究

研究了各种纤维素材料及不同酸浓度水解制成的微晶纤维素的聚合度，并用X-射线衍射法研究结晶度、结晶形态、晶粒尺寸和颗粒大小；用透射电镜（TEM）观察颗粒形状和大小，发现不同纤维素材料达到平衡聚合度（LODP）的盐酸浓度略有不同；在酸水解过程中纤维素的结晶形态、晶粒尺寸和颗粒大小基本不变，而且用X-射线衍射及TEM测出的颗粒不是纤维素晶粒，而是微原纤。     

Predicting the Grain-Size Distributions in High-Density, High-Purity Alumina Ceramics

This paper discusses the image-analyzer-based grain-size distributions (GSDs) of fully densified ceramics obtained from pressure casting a high-purity alumina powder, develops an algorithm for predicting the GSDs as a function of sintering time and temperature, and compares of the GSDs thus predicted with those experimentally observed. The GSD data for all sintered specimens, when nondimensionalized in terms of the median grain size, reduced to a single self-preserving GSD curve. The median grain was predicted as a function of sintering time and temperature using the classical kinetics equation. The GSDs predicted using the algorithm developed tallied well with those that were experimentally obtained.     

Methods of determining suspension fractional composition

A set of properties determines the working lives of ceramic components under various conditions. The most important properties that various ceramics should have are microstructure, porosity, permeability, mechanical strength, and many others. Various properties can be influenced by the correct choice of grain size in the powder. Out of the methods of determining particle size in initial molded materials, the most reliable results are provided by the laser analyzer, which working automatically can determine the entire spectrum of particles from nanodimensions to millimeter sizes in a short time. Translated from Novye Ogneupory, No. 4, pp. 124 – 131, April, 2009.     

Influence of grain boundary and grain size on the mechanical properties of polycrystalline ceramics: Grain-scale simulations

The Orowan-Petch relation is a famous model to describe the strength of polycrystalline ceramics covering a wide range of grain sizes. However, it becomes difficult to explain the strength trend when the grain size decreases to the sub-microscale or nanoscale. This is because some microstructural parameters (such as grain size, grain boundary fracture energy, and grain boundary defects) vary with different processing technologies, and their coupling effects on mechanical properties are still unclear. In this study, a finite element method (FEM) was applied to investigate the dependence of mechanical properties, such as strength and damage resistance, on the abovementioned microstructural parameters on example of alumina. The numerical results show that the grain boundary energy is weakly coupled with the grain size and grain boundary defects. The grain size and grain boundary are intercoupling, which affects mechanical properties. The mechanical properties could be improved by increasing the grain boundary fracture energy and decreasing the grain size and the grain boundary defect density.     

Synthesis of Fine-Grained Polycrystalline Diamond Compact and Its Microstructure

Sintering of a fine-grained polycrystalline diamond compact with grains less than 1 μm in size was successfully carried out by making a laminate on a WC/Co powder compact under sintering conditions of 5.8 GPa and 1430° to 1480°C for 30 min, in which small amounts of poly(ethylene glycol) and fine powder of cubic boron nitride were added to the starting diamond powder. The former played the role of preventing agglomeration of the diamond powder and the latter of suppressing abnormal grain growth during sintering. Microstructural observation of the polycrystalline diamond showed that in the regions near the WC/Co layer a comparatively large amount of Co metal was present between diamond grains, but in other regions the amount of Co decreased, and the diamond grains were seen to be bonded strongly. The Vickers hardness of the polycrystalline diamond was 55 ± 5 GPa with 19.6 N load.