Bulk Particle Density, Abrasive

In addition to surface area, pore size distribution, and surface chemistry, other important properties of commercial activated carbon products include pore volume, particle size distribution, apparent or bulk density, particle density, abrasion resistance, hardness, and ash content. The range of these and other properties is illustrated in Table 1 together with specific values for selected commercial grades of powdered, granular, and shaped activated carbon products used in Hquid- or gas-phase appHcations (19). 

A wide variety of materials have been implemented as abrasive particles in CMP processes. They include alumina, silica, ceria, zirconia, titania, and diamond. The effectiveness and suitability of these particles in CMP with particular applications are greatly influenced by their bulk properties (density, hardness, particle size, crystallinity etc.) and the surface properties (surface area, isoelectric electric point (lEP), OH content, etc.). This section will focus on the evaluation of alumina, silica, diamond, and ceria as the major abrasives used for the CMP of metals. 

Babu and coworkers [78] established that the abrasive particle density indeed offered a means for characterizing the hardness of submicron abrasive particles based on the material removal rates. The polishing rates of both Cu and Ta were measured for slurries of submicron-sized alumina particles with varying bulk densities ranging from 3.2 to 3.8 g/cm, dispersed in DI water. It was found that the polishing rate increased significantly when the dry powder bulk density exceeded a threshold value. 

The bulk density of abrasives also has a direct impact on the slurry dispersion stability. The weight of the abrasives might overcome the repulsive forces among particles required for the stability of the slurry system. For example, the particle settling issue is much more severe for alumina-based slurry than that for silica because of the difference in particle density [79]. 

A higher density sol—gel abrasive, produced by the introduction of seed crystaUites formed by wet-milling with high alumina media or by introduction of submicrometer a-alumina particles, was patented (28) and designated Norton SG. The microstmcture of this abrasive consists of submicrometer a-alumina crystals (Fig. 1) and its bulk density approaches that of fused alumina. Norton SG has proven to be an exceptional performer in coated and bonded abrasive products it was awarded the 1989 ASM Engineering Materials Achievement Award (29). 

In the United States, a number of physical tests are performed on siUcon carbide using standard AGA-approved methods, including particle size (sieve) analysis, bulk density, capillarity (wettabiUty), friabiUty, and sedimentation. Specifications for particle size depend on the use for example, coated abrasive requirements (134) are different from the requirements for general industrial abrasives. In Europe and Japan, requirements are again set by ISO and JSA, respectively. Standards for industrial grain are approximately the same as in the United States, but sizing standards are different for both coated abrasives and powders. 

Belt with nucleonic sensor <25 (or <0.3 m3/s) 0.5 to 1 Preferred when material is difficult to handle, e.g. corrosive, hot, dusty, or abrasive. Accuracy greatly improved when particle size, bulk density, and moisture content are constant, when belt load is 70-100 per cent of maximum. 

The following factors are important in specifying a feeder lor a particular application particle si/c. bulk density, adhesion, cohesion, abrasion, moisture, segregation, degradation, and various control factors, sneti that the required ea.se and sensitivity of control may he provided, fhher factors... 

Density of a substance may be defined as the weight of a substance per unit volume. In principle, the bulk density of agglomerated particles in the slurry can offer an indirect measurement of the abrasive particle hardness. The bulk density of the particle can be calculated by using Equation 7.16, excluding the open pores and voids from the volume calculation, where p stands for the specific gravity of the slurry measured using a pycnometer [77]. 

In addition to bulk density, particle crystallinity is another physical property that can be related to its hardness and potential effectiveness in providing the mechanical force in CMP. For example, alpha alumina abrasive has a higher hardness, thereby producing higher removal rate in comparison to its gamma crystalline counterpart [80]. As expected, the number of defects is also higher for alpha alumina due to the inherent hardness [81]. 

To eliminate intraparticle transport limitations, the particle size and average pore size must be carefully controlled during manufacture. Other physical properties that become important in industry have to do with the physical integrity of the catalyst particles. These properties include bulk density, crush strength, resistance to abrasion, and attrition. These properties are very important when working with reactors that contain a large amount of a particular catalyst. Fig. 2 lists a number of chemical and physical properties that affect catalyst performance. 

Abrasiveness of bulk solids, i.e. their ability to abrade or wear surfaces with which they come into contact, can be assessed in several different ways. It can be implied from the relative hardness of the particles and the surface with which they are in contact, using Mohs hardness scale. It can also be described by an Abrasion Index60 which, as a characteristic number, combines the effects of particle hardness, shape, size distribution and bulk density in one factor, independent of the nature of the contacting surface. 

Product Particle size and distribution/dust Strength/abrasion resistance Bulk density/porosity Dispersibility/solubility/reactivity Processing time ... 

Both the particle size distributions and the methods for their determination are standardized. The standard for bonded abrasive applications [243] differ from those for coated abrasives [244]. The bulk density depends both on the particle size distribution and on the particle shape. It is measured by weighing a known volume of SiC grains [245]. The packed density is often determined instead of the bulk density [246]. 

Material characteristics. Bulk density and particle size and abrasiveness. 

Various modifications to the commercial process have been suggested in the patent literature. These are primarily focused on the production of STTP with particular properties such as low bulk densities [7], increased abrasion resistance [8], and improved solubility properties [9,10]. Crystalline or coarse tripolyphosphate particles can also be obtained by spraying seed crystals with the desired characteristics during the production process [11]. The use of rotary kilns to obtain a granular product in both stages of the two-stage process has been discussed previously [12]. In this case, the intermediate product is ground and water is added before calcination. 

The overall value of a filler is a complex fimction of intrinsic material characteristics, such as average particle size, particle shape, intrinsic strength, and chemical composition of process-dependent factors, such as particle-size distribution, surface chemistry, particle agglomeration, and bulk density and of cost. Abrasion and hardness properties are also important for their impact on the wear and maintenance of processing and molding equipment. 

Besides the common types of conveyor, CEMA standards also address classifications and definitions of bulk materials. CEMA 550, for example, presents an alphanumeric method for classif5dng bulk density, particle size, flowability, abrasiveness, and handling characteristics of solids. The identifier contains, in order ... 

For example, sodium sulfite is described by 96B646X and pebble lime by 55Ci/225HU. These show that sodium sulfite heis a normal bulk density of about 96 Ib/ft lime is coarse, with a particle size of about Vi" sodium sulfite flows sluggishly (4) while pebble lime is relatively free-flowing (2) sodium sulfite is moderately abrasive (6) while lime is only mildly so (5) sodium sulfite packs under pressure (X) and may become more difficult to handle and lime is hygroscopic (U) and may decompose or deteriorate in storage (H). 

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