Pierre Guigon

High velocity impact of particles on a target — an experimental study

Abstract In order to study communition in a jet mill, an experimental rig was built to investigate the breakage phenomena. Particles were accelerated with air in a nozzle to velocities ranging from 120 to 250 m/s and collided with a target. Energy loss during impact was evaluated by measuring particle velocities before and after impact. Two different systems for measuring particle velocities were implemented. The first one was designed to work at very low loading (particles are considered to hit the target individually). The velocities are measured by a high shutter speed video camera (up to 1 μs). The particle traces on a frame were analysed by an image analyser. The second method, used for medium to high solid loading, consists of two sets of emitter-receptor optic fibres. Signals, collected by a 500kHz acquisition card, are cross-correlated in order to obtain the velocity. Influence of solid loading and initial air flowrate on characteristics of broken particles were evaluated. The influence of target nature and orientation were established.

A grindability test to study the influence of material processing on impact behaviour

Abstract The behaviour of a powder impacted on a target depends on its size, its particle size distribution (PSD), the material mechanical properties and the industrial rig. A methodology for the study of impact in an air jet mill allows one to evaluate the relation between the impact energy and the grindability of the impacted solids. Moreover, the behaviour of an impacted powder is determined by its process conditions. An example is given with the study of different hydrargillites and aluminas produced in different ways and having different morphologies. The impact test allows one to classify these solids with grindability and attrition criteria. Morphological analysis relates them to external structural descriptors.

Fragmentation by high velocity impact on a target: a material grindability test

Abstract An experimental test rig for the study of impact in an air-jet mill (up to 500 m s −1 ) allows the evaluation of the relationship between the impact energy and the fineness of the impacted solids. In single impact tests, so far, three types of behaviour are found: brittle (for glass, sand, polyamide and NaCl), “complex” (for Al(OH) 3 ) and ductile (for PMMA). A classification is obtained from the definition of grindability parameters. A multi-impact study reveals the non-equivalence between multiple impact and single impact: a solid is not broken similarly if a given total energy is provided in one or several impacts.

Chapter 7 Coating and encapsulation processes in powder technology

Publisher Summary Coating of particulate materials is a fundamental operation widely practiced in a variety of chemical industries including pharmaceuticals, food, fertilizer, cosmetics, biomedical, and nuclear. The coating process involves the covering of particulate materials including seeds, agglomerates, pellets, and powders with a surrounding layer of a coating agent (or coating material). The coating process can be applied to a variety of substrates ranging from submicron particles to very large objects. The coating thickness might vary from a few nanometers (chemical deposition) to several micrometers (film coating) or even several millimeters (e.g. sugar coating). There are several methods to introduce the coating agent into the system: dispersed or dissolved in an easily evaporable solvent, molten, or applied in the form of a very fine dry powder. In majority of cases, the final deposited layer (or coating layer) is a solid-phase material called a “shell.” In a few singular applications the coating layer can also be a liquid film. Furthermore, the introduction of a liquid into a particulate system leads most often to formation of liquid bridges among wetted particles. This behavior results in agglomeration phenomenon, which consists of adhesion of several elementary particles to form bigger entities called “agglomerates.” Another term subject to controversy in the technical and scientific literature is “encapsulation,” which is generally admitted to be a special kind of coating. In this chapter, the term encapsulation is used to distinguish one of the two following special cases: (1) the coating process is performed by immersion in a liquid phase, and (2) the product core constitutes of a liquid-phase formulation.

Chapter 5 Roll pressing

Publisher Summary Roll compaction is a continuous dry granulation process which is widely employed in the pharmaceutical, chemical, minerals, and food industries in order to manufacture free-flowing agglomerates. Roll compaction is conceptually very simple: the feed powder is passed through two counter-rotating rolls with the flow being induced by the friction acting upon the surfaces of the rolls. The powder is subjected to high pressure in the narrow gap among the rolls, leading to the formation of a compact in the form of a continuous strip or discrete briquettes. Roll compaction is designed to improve the flow properties, increase the bulk density, and ensure the uniformity of particulate formulations, in order to prevent the segregation of pharmaceutical drugs, for example. It offers advantages compared with wet granulation for processing physically or chemically moisture-sensitive materials because a liquid binder is not required. A further advantage is that it does not require a drying stage and is therefore suitable for use with compounds that either have a low melting point or degrade rapidly upon heating. The key factor in roll compaction is that the binding of particles results from the compression forces alone. The choice of powder to be compacted is therefore critical. Some active ingredients can be compressed directly. Others may be processed in combination with another material, which is selected for its favorable compaction properties. Consequently, the bulk of the material to be compacted often consists of an excipient or mixture of excipients, which are the materials that are mixed in with a drug in order to control drug delivery, to enhance patient acceptability and to aid in the tabletting process.