Ribbon Material Properties

EFG and RGS material both share very high carbon concentrations due to their contact to graphite containing materials near the liquid-solid interface (die or substrate). Oxygen concentration is very low for EFG and SR, and slightly higher for RGS. Grain size is smaller for RGS (0.1-0.5mm) as there are 

Material Grain size Dislocation density (cm 2) Thickness Resistivity (pm) (Qcm) [C] (cm 3) [O] (cm 3) As-grown Tdiff (pm) 

Additionally, transition metals are present in all materials, although mostly in concentrations not limiting material quality Nevertheless, some are effective recombination centres as point defects or in the form of precipitates and affect the as-grown material quality. 

The effects of an isolated defect on material quality (e.g. recombination activity of a clean, undecorated dislocation, capture cross sections of point defects) are well known for many defects present in crystalline silicon material, but the interactions of the impurities or structural defects form a major challenge in getting an improved understanding of the complex situation in the solidified silicon ribbon. Currently it is impossible to list a complete overview of the known interactions, but more information can be found in [49], 

It is known that clean dislocations without decoration reveal almost no recombination activity [55], but increasing decoration with impurities leads to recombination centres deep in the band gap, which significantly reduce carrier lifetime [56]. It can, therefore, be concluded that one of the most detrimental defects in EFG and SR apart from recombination active large angle grain boundaries are decorated dislocations. 

---

Critical variables may be characteristic of the materials and/or the process. Materials properties have already been discussed briefly and of course the equipment variables for the unit operations will depend upon differences in the raw materials. However, there are general relationships between the roller compaction process variables and the properties of the resulting ribbons and granules that can aid in process design. 

Soh JLP, Wang F, Boersen N, etal. Modeling the effects of raw material properties and operating parameters on ribbon and granule properties prepared in roller compaction using multivariate data analysis. Drug Dev Ind Pharm. Submitted. 

Table 7.2. Material properties of the three ribbon techniques under closer consideration...

Figure 1.13 The structure of glassy carbon. The entangled graphitic ribbons give rise to extraordinary rigidity and isotropic materials properties ( Cambridge University Press 1976).

Milling not only provides intimate mixing, but also eliminates variation in ribbon thickness and cmshes lumpy materials, eg, overdried soap, which might impact finished bar texture. Milling is also used for the formation of the proper bar soap crystalline phase, which plays a critical role in both the performance properties of the soap bar and the handling characteristics of the in-process soap. For example, too hot a milling temperature can create sticky soap that is difficult to process further. 

---