Application of grinding kinetics analysis of inorganic powders by a stirred ball mill

The need for ultra fine particles has been increasing in the preparation field of raw powders such as fine ceramics and high functional products. A series of wet grinding experiments were carried out on inorganic powders such as calcite, pyrophyllite and talc by a stirred ball mill. The grinding rate constant K’ in the equation of grinding kinetics was examined based on the grinding kinetics analysis as the same type of function of a previous paper on a vertical type planetary ball mill. The experimental particle size distribution of the ground products was obtained in various grinding conditions. The grinding rate constants K and K’ were expressed by empirical equation involving experimental conditions by a stirred ball mill. The empirical equation on the grinding rate constant was expressed in terms of a function involving the ball diameter of grinding balls, the median diameter of feed material, and Bond’s work index of material, in the experimental conditions. The values of empirical constants C1 and C₂ were 21.13 and 0.0109 on K, while C₁ and C₂ were 120.99 and 0.0192 on K′, respectively. And the particle size distribution of ground products of each test material for a given grinding time was found to be expressing the selection function (the specific rate of breakage) which was obtained from the grinding kinetics analysis. In this study, the grinding rate change on calcite and pyrophyllite was similar at the same experimental operation condition. However, in the case of talc, it was observed that the grinding rate was not increased compared with other samples.     

Ultra-fine grinding mechanism of inorganic powders in a stirred ball mill

An experimental investigation on grinding mechanism for calcite used in a stirred ball mill was carried out. The slurry concentration and the amount of grinding aids were chosen as main experimental factors of the grinding process. The effect of grinding aids on particle size distribution and grinding efficiency, defined as the increases of specific surface area per the specific grinding energy, was investigated. It was demonstrated that the grinding rate for calcite could be improved by addition of grinding aids. The grinding energy efficiency by adding a specific grinding aids was improved approximately 45.2% in comparison with and without grinding aids (n=700rpm, J=0.7, d_B= 1.0 mm, C_s=60wt%). This paper was presented at the ‘First Asian Particle Technology Symposium’ held at Bangkok between December 13 and 15, 2000.     

新型无氯水泥助磨剂的试验研究

通过试验对A和B两类无氯助磨剂的助磨效果进行了系统的研究。利用红外光谱对助磨剂的结构及性质进行了分析，并利用SEM对掺加B类助磨剂的水泥颗粒进行了形貌观察。研究结果表明：含有聚合醇功能基团的助磨剂一般都具有良好的助磨效果，当掺入量为0．03％～0．10％，普通硅酸盐水泥的筛余值由4．5％降低到3．7％，比表面积由325m^2／kg增加到347m^2／kg；加入该类助磨剂还可以改善水泥的颗粒组成，特别是提高了3-30μm的细颗粒含量。     

助磨剂的助磨作用及对粉体流变性能的影响

选用五种助磨剂，对四种有代表性的物料进行了助磨实验，同时测试了磨后物料粉体的流变特性。分析了助磨效能、粉体流变性能和助磨机理三者的关系。研究结果显示：当助磨剂使粉体的流动性增强、堆积密度增大时，助磨效果趋于增强     

水泥助磨剂性能测定方法的试验研究

研究了三种高效助磨剂对普通硅酸盐水泥性能的影响。结果表明：不同助磨剂对水泥颗粒的粒径分布、筛余、流动性，尤其是对粒径3～32μm颗粒的含量以及水泥各龄期强度都有不同的影响。而对由透气法测得的勃氏比表面积无明显影响。水泥助磨剂的性能可用磨制的水泥的颗粒组成、45μm筛余、流动性、强度来表征或评价。而勃氏比表面积不适宜用来表征助磨效果。同时对助磨剂作用微观机理也进行了探讨。     

工业醇类煤沥青水浆制备磨矿动力学研究

对两种工业醇类煤沥青水浆的制备进行磨矿试验研究,结果表明甲醇煤沥青水浆的磨矿效果略好于乙醇煤沥青水浆;建立了乙醇煤沥青水浆和甲醇煤沥青水浆磨矿动力学方程式,分别为R(t)=100exp[-(-1.3564+0.43454.lnd).t(-0.42203+0.195241.lnd)]和R(t)=100exp[-(-0.02975+0.02908.d0.67972).t(-0.12083+0.13259.lnd)],据此可以求出任意磨矿时刻待磨粒级的分布率R(t)。     

The effect of interstitial gas on milling

In a research program on the influence of interstitial gas on the handling of fine powders, particle diameter less than 100 μm, the effect on milling is also investigated.The influence of the interstitial gas is exhibited through the drag force, due to velocity differences, which the gas exerts on the solid particles of the powder. These forces strongly influences the behavior of the powder.Our investigations of milling showed that the milling parameters, i.e. the specific rates of breakage and the breakage parameter, were dependent on the powder flow behavior. Two extremes were the regime of free-flowing powder, where the rate of breakage was high and the grinding of the individual particles was rather ineffective, and the regime in which the powder did not flow at all, where the rate of breakage was low, but where the grinding of the single particles was rather fine.     

助磨剂对普通硅酸盐水泥性能的影响及作用机理

研究了助磨剂对普通硅酸盐水泥的流动性、颗粒分散度及其砂浆性能的影响并对作用机理进行了探讨。结果表明 ,助磨剂加强了水泥的流动性、提高了水泥细度、增加了细粉量、对勃氏比表面积无明显改变、增加了水泥3d、2 8d强度 ;助磨剂的作用机理是减小了粉碎阻力、防止团聚和糊磨、提高流动性而加强了料和球的作用频率和效率 ,从而提高了粉磨效率。     

有机助磨剂对水泥性能的影响及其有机水泥化学分析(英文)

现代水泥、混凝土中大量使用化学外加剂,特别是有机化合物和高分子聚合物化学外加剂,例如：水泥助磨剂、混凝土超塑化剂、引气剂、增稠剂等,大量有机物的加入改变了水泥水化过程、水化动力学、微观结构的发展,传统的水泥混凝土化学不再能很好地解释其微观结构与宏观性能的关系。为此,提出一个新兴的水泥混凝土化学的补充分支—有机水泥化学,在未来的水泥混凝土研究中该给予更多的重视。以有机化学外加剂—助磨剂为例,说明其对水泥水化动力学、水化产物形态以及水泥浆体的超塑化剂需求量、流变特性、强度发展等宏观性能的影响。水泥中加入微量的助磨剂,不仅改变了水泥颗粒分布,还改变了水化动力学,促进起始离子的溶解和铝酸钙（C3A）和铁铝酸钙（C4AF）的早期水化,明显地提高早期强度和28 d强度。助磨剂吸附在水泥表面改变了水泥的表面性质,其中助磨剂和Ca2＋、Fe2＋螯合起关键作用。     

空气涡轮制冷机在粉碎EVA技术中的应用

低温粉碎是塑料,特别是低软化温度塑料超细粉碎的发展趋势。本文在深入研究了乙烯-醋酸乙烯共聚物（EVA）材料特性和粉碎机理的基础上,将空气涡轮制冷低温粉碎技术应用于EVA低温细碎中,有效地提高了EVA颗粒的超细粉碎效率;同时指出了该粉碎流程的关键技术及影响粉碎效果的主要因素,开辟了一条规模化、高质量、低能耗回收可再生塑料的新途径。此外,从能量守恒的角度出发,以工程应用为目标,对粉碎过程中的核心环节——冷冻和粉碎,初步进行了理论方面的计算分析。这些分析的结果有益于设备的完善及改进。     

Ball-mill grinding kinetics of master alloys for steel powder metallurgy applications

The grinding kinetics of three newly developed master alloys for steel powder metallurgy applications were investigated using a laboratory ball-mill. Non-first order grinding kinetic is observed for the three master alloys as the breakage rate increases with grinding time due to the work hardening of the ductile phase in the microstructure. Agglomeration of fine particles is observed after a critical time at which d₉₀ reaches its lowest value (~ 30 μm). Critical times are related to the hardness and the microstructure of the different master alloys. Agglomeration of fine particles can be overcome with the use of a process control agent. In this study, the addition of stearic acid to master alloy powders prior to grinding successfully eliminates agglomeration for long grinding times (d₉₀ ~ 16 μm after grinding for 270 min).     

Synthesis of fine zirconium carbide powder by carbothermal reaction of carbon‐coated zirconia particles

In this study, a novel method for the synthesis of fine ZrC powder was presented. It consists of chemical vapor deposition (CVD) of C from CH₄ on ZrO₂ particles followed by carbothermal reaction. Firstly, optimal CVD conditions (1300 K and 30 minutes) yielding the stoichiometric amount of C deposit (23 wt%) were determined. Carbothermal reaction behavior of the carbon‐coated oxide particles was then investigated in Ar flow at 1700‐1800 K for 0‐120 minutes. Mass measurements, XRD and SEM techniques were used to characterize the products at various stages of the process. Lattice constants and mass losses of the samples increased to the levels of ZrC with increasing temperature and time. Almost pure ZrC powder (oxygen content: 0.59 wt%) with a mean particle size of ~170 nm was synthesized at 1800 K within 120 minutes. The present study demonstrates that ZrC powder can be synthesized at lower temperatures and shorter reaction times using C‐coated ZrO₂ powders compared with the conventional method which uses a mixture of ZrO₂ and solid C particles.     

Effect of processing on the melt degradation of starch‐filled polypropylene

Compounded polypropylene powders with various concentrations of corn starch were processed in a Haake torque rheometer at constant temperature, 180 °C, for different times in a closed system. A scanning electron micrograph of 5‐min processed sample shows a fine dispersion of starch particles in the polypropylene (PP) matrix. A good distribution and interaction of the starch particles are seen with increasing processing time (up to 15 min). Infrared spectroscopy evidence on the extracted films shows that most interactions between PP and starch are obtained after about 10 min processing. The presence of 2–6 wt% starch in the PP has a melt‐stabilising effect by reducing melt flow index and increasing apparent viscosity with a good correlation. However, 6 wt% starch gives complete inhibition of the PP melt degradation up to 20 min processing. Carbonyl groups are not formed during processing of PP containing 6 wt% starch. This is also an indication of a starch stabilising effect on the PP chemical structure. An increase in elongation at break of PP films having 6 wt% starch, when compared with the controls, is observed, while their ultimate tensile strength remains almost the same. © 1999 Society of Chemical Industry     

The effect of swirling flow on elutriation in a vortexing fluidized bed

The elutriation of fine particles in a vortexing fluidized bed (VFB) was studied by a batch and binary system. The diameter of the coarse particles was 545 Μm, and the diameter of the fine particles for the elutriation test was 81, 97, 115, 137, 163, and 193 Μm, respectively. It was found that the swirling flow caused by the secondary air injection is the dominating factor to influence the elutriation rates. The effect of primary air velocity, swirling flow, injection angle of secondary air nozzle, and diameter of fine particles on the elutriation rate constant was also studied. The Taguchi experimental method and Regular analysis are used to identify the effects of various operating variables. A correlation was developed to estimate the specific elutriation rate constant (K _∞ ^* ) in the vortexing fluidized bed. The specific elutriation rate constant (K _∞ ^* ) was found to be a function of the primary air velocity, the diameter of fine particles, the secondary air velocity, and the height of secondary air injection.     

Effects of Coarse Particles on the Gelcasting of Ceramic Foams

In order to study the effects of coarse particles on the gelcasting of ceramic foams, a coarse powder with a similar sintering ability as that of fine powder was designed. It was prepared by grinding the presintered foams manufactured using fine powder and by sieving with 200-mesh sieves. The resultant coarse powder was mixed with the fine powder to manufacture ceramic foams by direct foaming and the gelcasting method. The viscosities of suspensions with different fractions of coarse powder were close to each other at high shear rates. The flexural strength of the foams obtained by the mixed powders was about 10 MPa, which was about 25% lower than that obtained by the fine powder, while the permeability of the foams by mixed powders was about 30% higher than that without coarse powder. On the other hand, both the flexural strength and the permeability of the foams by the mixed powders had no clear relation with the fraction of coarse powder when it varied in the range of 5%–40%.     

粉体制备中助磨剂的应用研究现状

在分析总结大量文献资料的基础上,对助磨剂在粉体制备中的作用机理及其在超细粉体制备过程中的应用研究现状进行了综述。     

Behaviour of Cohesive Powders in a Powder‐Particle Spouted Bed

Behaviour of cohesive powders in a powder‐particle spouted Bed (PPSB) has been investigated under several operating variables and solids properties. The elutriation rate constant based on the hold‐up of fine powders in the bed decreased with a decrease in the size of fine powders, and with an increase in the size of coarse particles under a constant superficial gas velocity. This finding is quite different from the elutriation phenomena of particles more than 100 µm in size. Moreover, the mean residence time of fine powders increased with a decrease in the superficial gas velocity and the size of fine powders, and decreased with a decrease in the size of coarse particles.     

助磨剂在矿渣微细粉制备中的应用与研究

该文研究了几种助磨剂在矿渣微细粉制备中的应用,分析探讨了助磨剂的作用、机理、在使用中应注意的问题及其选择原则。研究结果表明,在矿渣微细粉的制备中引入适当的助磨剂能显著提高微细粉的比表面积、节约单位电耗、降低机械磨耗,而且还能改善微细粉的颗粒形态并使微细粉的粒度分布均匀。     

An analysis of fine dry grinding in ball mills

The kinetics of dry grinding of several cement clinkers and two coals were investigated in a laboratory tumbling ball mill. The kinetic process is first-order at first, but the rates of breakage decrease as fines accumulate in the bed. It was demonstrated that the slowing of the breakage rates applies to all sizes in the mill, indicating that the cushioning action of fines affects the whole breakage process, even though mill power remains constant. Tests on cleaning or non-cleaning the balls showed that the major factor was not the build-up of a coating on the balls. Radio-tracing tests showed that the effect was not due to pelletizing of fines into larger particles. The quantitative magnitude of the cushioning action was different for different materials. It is, therefore, postulated that cushioning is affected not only by air trapped in the bed of fine particles but also by the cohesive attraction of fine particles, which is a function of the material.     

Fine grinding of aggregated powders

In many cases, including natural ores as well as synthetic powders, fine grinding involves the breakage of bound aggregates rather than solid particles. The characteristics of breakage in such systems have been investigated by experimental studies of grinding kinetics, in a model system of partially sintered alumina particles, ground in a laboratory centrifugal ball mill. The effects of aggregate strength (extent of sintering) and energy input (mill speed) on the breakage rates and breakage distributions have been evaluated. Breakage appears to occur primarily through splitting of the aggregated mass into two or three smaller aggregates accompanied by release of the primary particles, leading to strongly bimodal breakage distributions.