Enhancement of energy efficiency for mechanical production of fine and ultra-fine particles in comminution

This paper presents the energy requirements for mechanical production of fine and ultra-fine particles in comminution. Recent approaches for effective size reduction and energy saving in comminution are described, viz., （a） development and application of new mills/classifiers, （b） adjustment of the bead characterization in stirred bead mills, （c） hybrid comminution systems with roller-press and media mill, （d） assisted methods, and （e） simulation.2007 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V.     

Surface Modification of Clays and Related Materials

Abstract

This review analyzes various ways by which the surfaces of clay particles and related minerals can be non‐covalently modified, as well as some of the analytical approaches with which these surface modifications can be measured and quantified. Among the principal methods of modification of the surface properties of clays and other metal oxide surfaces is treatment with cationic surfactants comprising long‐chain alkyl groups. Using the Cassie equation, the percentage coverage by alkyl groups can be ascertained, from advancing contact angle data. Also, by measuring both advancing and retreating contact angles (e.g., with drops of water) on various surfaces, the percentage liquid coverage of such surface (or, if one wishes, the percentage contamination by the contact angle liquid) can be ascertained, using the Cassie equation. It was found that talc, treated with octadecyl amine (OA) became 100% covered with octadecyl groups when mildly heated with 1 wt.% OA. Treatment with higher concentrations did not increase the coverage, but gave the appearance as if the particles were covered with pentyl, not octadecyl groups, judging by the lowering of the apolar surface tension component of the treated talc surface. Coating of glass or mica surfaces with hexadecyl groups, via hexadecyl‐quaternary ammonium groups, yielded about 42% coverage. As an improvement, coating with hexadecyl cationic surfactants yielded 82% coverage. However, when coating was done by application of pre‐compressed monolayers formed on a Langmuir trough, 100% coverage (of eicosyl groups) could be achieved. Finally, if solidity of attachment, in addition to 100% coverage, is needed (as is very desirable in coatings applied to mica‐covered half cylinders in Israelachvili's force balance), the compressed Langmuir trough layer approach, coupled to a further 2 hours worth of annealing at 100°C yields the most robust attachment, as shown by Wood and Sharma (Wood, J.; Sharma, R. How long is the long‐range hydrophobic attraction. Langmuir 1995a, 11, 4797–4802). There are two other, totally different ways of making hydrophilic mineral particles more hydrophobic. The first one is by addition of plurivalent cations (e.g., Ca²⁺, La³⁺) to negatively charged inorganic particles, such as ground glass, ground calcite, or montmorillonite. When such initially hydrophilic, negatively charged particles, in stable aqueous suspension, have their negative surface potential diminished by the addition of small amounts of plurivalent cations, the particles become hydrophobic, and flocculate (Wu, W.; Giese, R.F.; van Oss, C.J. Linkage between ζ‐potential and electron donicity of charged polar surfaces 1. Implications for the mechanism of flocculation of particle suspensions with plurivalent counterions. Colloids. Surfaces. A 1994, 89, 241–252) even though the electrostatic repulsion energy still exceeds the mutual van der Waals attraction, thus furnishing a new and drastically modified explanation of the Schultze‐Hardy effect. Finally, grinding hydrophilic solids or particles makes them hydrophobic by causing a strong decrease in their surface electron‐donicity, most likely as a consequence of an increased liberation of electron‐accepting sites through diminution, causing the neutralization of a substantial part of the electron‐donating sites which, prior to grinding, were responsible for the material's hydrophilicity.     

Solvent-free and direct C(sp)–H amination of adamantanes by grinding

A facile, direct and environmentally benign conversion of C(sp³)–H bonds to C(sp³)–N bonds using substoichiometric amount of aprotic superelectrophiles polyhalomethane–AlX₃ has been achieved by grinding under solvent-free conditions at room temperature in air. It is a general and simple method for the direct amination of adamantanes, and a series of aminoadamantanes of azoles, arylamines or heteroarylamines were obtained in good to excellent yields. The advantages of this amination are atom economy, solvent-free, chemoselectivity, short reaction time and high yields.     

研磨破乳的规律及其机理

报道了研磨破乳的实验规律，讨论了研磨破乳的基本步骤：（１）过滤过程中乳状液内相液滴在研磨剂表面铺展成膜并进一步聚结──过滤破乳；（２）研磨剂的相互碰撞使乳状液的分散液滴受到摩擦力和剪切力，导致液滴聚结──研磨破乳。     

A generic mathematical model of single point cutting tools in terms of grinding parameters

The paper presents the analytical geometric details of the mathematical modeling of a single point cutting tool with a generic profile. The grinding angles and the ground depths on the tool are allowed to vary along the tool flanks and face, altering the cutting angles from point to point. The surface modeling begins with the creation of a tool blank model. Then unbounded surfaces are considered and transformed to get the cutting tool surfaces. The intersection of these surfaces gives the complete model of the tool. Starting from the basic model where the tool face and flank are planar, the generalization of the geometric design has been done in two steps to give free-form shapes to the tool surfaces, termed as the two generations of the generic profile. Then a forward and inverse mapping has been presented for the basic model and the two generations of the generic tool to relate the grinding angles with the prevalent nomenclatures (ASA, ORS and NRS). The model has been validated and the variation of tool angles with the grinding parameters has been illustrated with an example.     

Free upper-disk rotational speed under loose abrasive grinding in conventional machines

Equations representing stable upper-disk rotational speed under loose abrasive grinding processes of flat optical elements, using conventional machines, are introduced. Solution was reached via two interpolations on a wide set of experimental data. Experimental upper-disk rotational speeds were interpolated by means of a power function on six enhanced variables. Enhanced variables are combinations of physical variables that interconnect independent machine and upper-disk three-dimensional experimental spaces. The exponents found were subsequently least-squares interpolated in upper-disk and machine experimental spaces. This process was performed twice to provide two perspectives on loose abrasive wear: one where machine variables lead both interpolations and upper-disk variables to play a secondary role through enhanced variables. On the second representation, disk and machine variables interchange roles.     

HDP-HSMM的磨削声发射砂轮钝化状态识别*

在高精度金属材料磨削加工中,刀具即砂轮的状态对加工效率和加工质量具有重要的影响。钝化程度较高的砂轮不适于加工精密工件,需提前预警并修整更换砂轮。该文提出一种通过磨削声发射信号来检测砂轮钝化状态的方法。首先,对于采集到的信号进行小波软阈值降噪。然后,将其分割成多个有重叠的帧,并提取每帧信号的8个特征组成声发射数据集。最后,通过分层Dirichlet过程-隐半马尔可夫模型来建立声发射数据集和不同的砂轮钝化状态之间的非线性关系,旨在识别砂轮钝化状态。结果表明,上述检测方法能有效识别砂轮的不同钝化状态并能对整个加工过程中的砂轮钝化程度进行自动划分,其在测试数据集上的准确率达到93.7%,可以为实际工业应用提供理论指导。     

Effects of high power ultrasonic vibration on temperature distribution of workpiece in dry creep feed up grinding

Temperature history and distribution of steel workpiece (X20Cr13) was measured by a high tech infrared camera under ultrasonic assisted dry creep feed up grinding. For this purpose, a special experimental setup was designed and fabricated to vibrate only workpiece along two directions by a high power ultrasonic transducer. In this study, ultrasonic effects with respect to grinding parameters including depth of cut (a_e), feed speed (v_w), and cutting speed (v_s) has been investigated. The results indicate that the ultrasonic vibration has considerable effect on reduction of temperature, depth of thermal damage of workpiece and width of temperature contours. Maximum temperature reduction of 25.91% was reported at condition of v_s = 15 m/s, v_w = 500 mm/min, a_e = 0.4 mm in the presence of ultrasonic vibration.     

Roughness measurement of metallic surfaces based on the laser speckle contrast method

A method of measuring surface roughness of flat lapped, ground and polished metallic surfaces, by the far-field speckle contrast method is presented in this paper. The laser speckle contrast technique depends on the existence of an approximately linear relationship between the speckle contrast and the roughness of the illuminated surface. Initially it was shown that the linear relationship existed up to 0.1 μm Ra (centre-line average) roughness using Helium–Neon light, after which a saturation effect was observed. The effect of varying the incident angle of illumination was investigated with a view to extending the measurement range. The use of high incident angles of illumination has been found to increase the surface roughness range up to 0.4 μm measurement Ra.     

Mechanochemical synthesis of rutile-type CrMO4 (M=V, Sb) and their solid solutions

Grinding a mixture of hydrous amorphous chromium oxide (Cr₂O₃·nH₂O), vanadium oxide (V₂O₅) and antimony oxide (Sb₂O₅) was conducted by using a planetary ball mill, to investigate their mechanochemical reactions to form chromium vanadium oxide (CrVO₄) and chromium antimony oxide (CrSbO₄). The synthesis reactions proceed with an increase in grinding periods of time. The ground samples consist of agglomerates with particle size of about ten nanometers. The synthesized CrVO₄ sample exhibits a rutile-type tetragonal crystal structure, which is a high pressure phase. Additionally, solid solutions, CrV_1−xSb_xO₄ (x=0∼1, Δx=0.25), have been synthesized mechanochemically from the mixtures of Cr₂O₃·nH₂O, V₂O₅ and Sb₂O₅.