Kinetics of Dissolution and Recrystallization of Sodium Chloride at Controlled Relative Humidity†

Marina Langlet1*, Frederic Nadaud2, Mohamed Benali1, Isabelle Pezron1, Khashayar Saleh1, Pierre Guigon1, Léa Metlas-Komunjer1 UTC/ESCOM, Équipe d’Accueil “Transformations Intégrées de la Matière Renouvelable” (EA 4297)1 UTC/ESCOM, Service d’Analyses Physico-Chimique2,

Abstract Both producers and users of divided solids regularly face the problem of caking after periods of storage and/or transport. Particle agglomeration depends not only on powder water content, temperature and applied pressure, but also on the interactions between the solid substance and water molecules present in the atmosphere, i.e. on relative humidity (RH) at which the product is stored. Ambient humidity plays an important role in most events leading to caking: capillary condensation of water at contact points between particles, subsequent dissolution of a solid and formation of a saturated solution eventually followed by precipitation of the solid during the evaporation of water. Here, we focus on the kinetics of dissolution followed by evapo-recrystallization of a hygroscopic sodium chloride powder under controlled temperature and RH, with the aim of anticipating caking by predicting rates of water uptake and loss under industrial conditions. Precise measurements of water uptake show that the rate of dissolution is proportional to the difference between the imposed RH and deliquescence RH, and follows a model based on the kinetic theory of gases. Evaporation seems to be governed by more complex phenomena related to the mechanism of crystal growth from a supersaturated salt solution. Keywords: Sodium chloride, hygroscopy, Knudsen law, vapor sorption, caking

humidity, DRH, of 75% at 25℃. Examples of systems 1. INTRODUCTION at risk include also cosmetics, agricultural chemicals, Water being ubiquitous in the atmosphere, the explosives and pharmaceuticals. Caking of such pow- influence of moisture on the chemical and physical ders is generally strongly influenced by dissolution stability of many dispersed systems and its impact on followed by recrystallization of the hygroscopic solid product manufacturability, quality and shelf-life is of substance present. A crystalline substance is said to great concern. In particular, the presence of water in deliquesce if it forms an aqueous solution when the an atmosphere where formulated products contain- ambient relative humidity reaches a certain threshold ing deliquescent hygroscopic substances are manipu- value. Below this critical RH, crystal surrounded by lated can have a pronounced effect on their end-use water vapor is thermodynamically favorable1,2) while properties such as particle aggregation and ability above the critical RH, the aqueous solution is the of powder to flow. Many industrial formulations, es- thermodynamically favored phase. It is of fundamen- pecially food products, contain sodium chloride, a tal interest to understand events taking place when deliquescent substance with a deliquescence relative particles containing a hygroscopic substance are exposed to the atmosphere containing water vapor. For

th example, it is well known that adsorbed water cannot † Accepted : September 10 , 2011 1 Rond-Point Guy Deniélou, 60200 Compiègne, France cause the dissolution of the solid substrate while 2 Rond-Point Guy Deniélou, 60200 Compiègne, France condensed liquid water can. Capillary condensation 3 1 allée du réseau Jean-Marie Buckmaster, 60200 Com- of water vapors leads to the formation of pendular piègne, France liquid bridges at the contact points between particles. * Corresponding author: Ｅ-mail: [email protected] This liquid water is likely to dissolve deliquescent TEL:（+ 33）344 234 744 crystalline substances present in the particles. Disso-

ⓒ 2011 Hosokawa Powder Technology Foundation 168 KONA Powder and Particle Journal No.29 (2011) lution gives rise to the formation of a saturated solu- ture of small individual particles and agglomerates tion from which recrystallization of solute follows if of a hygroscopic substance is subjected to high RH, water is evaporated, for example due to the changes small particles might completely dissolve long be- of ambient conditions of relative humidity and/or of fore large agglomerates are dissolved (as presented temperature. Usually the re-crystallized solid bridges in step 5). This means that not all parts of the solid mechanically bind the particles in contact more ef- sample are in equilibrium with their environment. In ficiently than the pendular liquid bridges between order to better understand the kinetics of the deli- them. The mechanical strength of solid bridges quescence of hygroscopic substances under well-con- depends not only on temperature, humidity and pres- trolled ambient conditions, we propose the use of Dy- sure, but it depends also on the mass transfer, the namic Vapor Sorption (DVS) apparatus. We examine solubility of the powder in water and the number of dissolution of a solid followed by its recrystallization contact points, i.e. on the coordination number of via the precise measurements of water uptake and particles in the powder bed3). water loss at variable conditions of ambient relative A schematic representation of the adsorption of wa- humidity. In such a way we provide an original meth- ter molecules followed by capillary condensation and od for the precise determination of deliquescence dissolution of the solid phase is proposed in Fig. 1. relative humidity. Modeling the dissolution of a solid The time sequence of phenomena taking place when and the evaporation of water from a solution so ob- hygroscopic crystals are brought in contact with an tained is tempting on the basis of the kinetic theory atmosphere containing water vapor is the following: of gases with the aim of predicting the corresponding adsorption of water molecules on the solid surface at kinetics at different ambient conditions of RH similar low vapor pressure (steps 1 and 2), followed by the to those met in industrial applications. multilayer formation and capillary condensation at This work will focus on the partial dissolution and contact points/lines/surfaces at intermediate vapor recrystallization of sodium chloride, a classic model pressures (step 3). In the case of good wetting of the hygroscopic solid. Sodium chloride is present in at- solid by liquid water, capillary condensation can oc- mospheric aerosols where it represents the majority cur at quite low vapor pressures, i.e. at low RH, but of solid particles1). For that reason, a significant quan- the quantity of liquid water, determined by the so- tity of highly reliable data concerning NaCl-water called Kelvin radius, will remain small. At higher RH, binary systems, as well as various other mixtures both Kelvin radius and the corresponding quantity of relevant to atmosphere science, has been published liquid water will increase rapidly. Deliquescence of in the last few decades1,4,5). Moreover, salt dissolu- the solid takes place if RH becomes equal or higher tion in water is of particular interest also because of than DRH, i.e. when the ambient vapor pressure be- its occurrence in food and other industrial products. comes equal or higher than the vapor pressure of the Yet these formulations are often complex mixtures of saturated solution of NaCl (steps 4 to 6). When a mix- ingredients influencing each other’s behavior. Issues

Fig. 1 Hygroscopic crystals in water vapors: adsorption of water vapor and condensation of liquid water followed by dissolution of a solid (adapted from Peters4), Zasetsky5) and Mauer2)).

KONA Powder and Particle Journal No.29 (2011) 169 concerning caking phenomena in multi-component of the ambient gas, P, linearly. The proportionality systems are currently under study in our laboratory. coefficient is dependent on temperature, molar mass In Fig. 2, one can find the well-known P-T diagram of the condensed phase and exchange surface. It is for pure water in the temperature range between 0℃ represented by a “Knudsen coefficient”, KKnudsen. If we and 30℃ (in dark continued line). It is completed by define the sticking-coefficient as the probability for a an analogous curve for a saturated solution of NaCl water molecule to remain at the surface after impact, in water (in light continued line). One can verify that and considering that the condensed phase has a non- the NaCl curve closely follows the shape of the pure negligible pressure, ps, the net flux of molecules, dm/ water curve, and that the vapor pressure of the satu- dt, entering the condensed phase is: rated solution of NaCl is approximately 75% to 76% of dm = K (P p ) Eq. (1) vapor pressure for pure water for this temperature dt Knudsen − s range in accordance with DRH values for sodium Moreover, as P corresponds to the relative humidity chloride cited in literature. The curves of vapor pres- and ps corresponds to the deliquescence relative hu- sure for pure water and the aqueous solution of NaCl midity, one can write: are completed by the vapor pressures corresponding dm K P = Knudsen 0 (RH DRH) Eq. (2) to 60, 70, 80 and 90% RH (dotted lines). These condi- dt 100 − tions of RH are chosen for their relevance in powder or, caking. One can also note that in this temperature dm = K P (a a∗ ) Eq. (3) range, moderate variations of vapor pressure per- dt Knudsen 0 w − w mit setting up conditions for the dissolution of NaCl where aw is the water activity of the substance in so- (when RH>DRH) and its recrystallization (when RH lution and aw the water activity of the saturated solu-

4.5 4 30 3.5 25 3 20 2.5 2 15 1.5 10 Vapor pressure [kPa] 1 Vapor pressure [Torr] 5 0.5 0 0 0 5 10 15 20 25 30 Temperature [°C]

Fig. 2 Pressure-Temperature diagram of water (in dark continued line) (data from Mullin’s book6) and of saturated aqueous NaCl solution (in light dotted line) (data are adapted from Apelblat and Korin7). Curves of water vapour pressure at 90%, 80%, 70% and 60% RH are represented in dotted lines from top to bottom, respectively.

170 KONA Powder and Particle Journal No.29 (2011) perature at 2℃ and by varying the pressure of the 2. EXPERIMENTAL water vapor between about 3 and 5 Torr (400 and Dynamic Vapor Sorption (DVS) 666 Pa), significant variations of RH can be imposed Sodium chloride crystals of about millimeter in in the observation chamber. Under such conditions, size and a purity of 99.5% were used as provided by dissolution of NaCl crystals can be observed if the Merck. Samples, typically of 8 to 25 mg, were sub- imposed RH is greater than 75% RH, while recrystal- mitted to the continuous gas flow of 200 cm3/min lization can be observed when the pressure of water containing pure nitrogen and water-vapor-saturated vapor is lowered to the values corresponding to RH< nitrogen in proportion corresponding to the desired 75% RH. relative humidity. Mass variations due to the uptake of water from the gas phase were measured by an ac- 3. RESULTS AND DISCUSSION curate microbalance system (DVS, Surface Measure- ment Systems) with a precision of 0.1 µg; its varia- Dissolution mechanism tion with respect to time, dm/dt, was calculated The images in Fig. 4 illustrate the phenomenon of on a lapse of time of 10 min with an acquisition every capillary condensation at the contact area between minute. Temperature and humidity were controlled two crystals at RH close to DRH. Fig. 4a shows two to 0.1℃ and 0.5% RH, respectively. NaCl crystals in contact at 72% RH, i.e. RH

Temperature Controlled Microbalance Incubator

Sample holder Reference

Temp/Humidity Probes

Dry Nitrogen Flow Vapor Humidifier Mass flow Controllers Fig. 3 Schematic representation of the Dynamic Vapor Sorption apparatus.

KONA Powder and Particle Journal No.29 (2011) 171 a b

Fig. 4 Capillary condensation of water on NaCl crystal.

The dissolution of an ensemble of NaCl crystals in ing under industrially relevant conditions very well, condensed water can be observed in Fig. 5. Images one should keep in mind that they are qualitative are acquired by ESEM at RH>DRH by progressively observations and not representative of the kinetics increasing the vapor pressure in the observation of dissolution mechanism. Consequently, a quantita- chamber to the values corresponding to RHs between tive study is necessary to complete the description 75% RH and 80% RH. In Fig. 5a one can observe of phenomena taking place. The quantity of water one individual crystal of approximately 30 by 50 µ taken by the powder during the chosen time can be m in size in the upper part of the figure and two ag- determined experimentally by weighing the sample. gregates of unequal size of a few hundred µm in the As shown earlier for highly hygroscopic ammonium lower left-hand corner. The dissolution starts by a nitrate8), the same quantity can be obtained from the smoothing of the surfaces until the individual crystal Knudsen formula: by integrating Eq. (2) under the disappears and a perfectly circular drop of aqueous assumption that the exchange area and sticking coef- solution is formed (Fig. 5c). Simultaneously, on the ficient remain constant, one can calculate the number surface of the aggregates, one can see that water of water molecules taken by the sample as a function spreads over the surface and a rounding of crystals of time for each imposed RH [see ref. 8) for details]. composing the aggregate can be observed, the quan- Experimental verification of the model was provided tity of the liquid phase progressively increases from by the DVS technique. Fig. 5d to Fig. 5f, but traces of the solid phase are Quantitative DVS experiments of the present work still visible in the lower left corner of Fig. 5f. consist of exposing a NaCl powder sample during Although ESEM images illustrate what is happen- a fixed period (4 hours) to a chosen constant RH>

a b c

d e f

Fig. 5 Time sequence of ESEM images of the dissolution of NaCl at RH>DRH (a to f); size bar is 100µm in all images.

172 KONA Powder and Particle Journal No.29 (2011) DRH and measuring the increase of sample mass due imposed RHs were chosen so that the differences be- to the absorption of water. Subsequently, the same tween RH and DRH are identical (in absolute value) sample is exposed during the same period of time during dissolution of a solid and solution evaporation. to a chosen constant RHDRH, while the right-hand side corre- absorption (2 points situated on the right-hand side sponds to the evaporation and recrystallization of the of point M at 75% RH) and evaporation (7 points situ- solid at three different RH

12 kg]

-6 10 [10

m 8

2 Masswater uptake, 0 0 5000 10000 15000 20000 25000 30000 Time, t [s]

Fig. 6 Water uptake for samples containing between 12.5 and 13.5 mg of NaCl exposed to 95% RH ( ■ ), 90% RH ( ● ) and 85% RH ( ▲ ) and water loss at 55% RH ( ■ ), 60% RH ( ● ) and 65% RH ( ▲ ) at 25℃

KONA Powder and Particle Journal No.29 (2011) 173 1 0,5 M

dm/dt 0 -0,5 -1 kg/s]

-9 -1,5

[10 -2 -2,5 -3 Rate of water uptake/loss, uptake/loss, ofwater Rate -3,5 DRH 0 10 20 30 40 50 60 70 80 90 100 Relative humidity, RH [%] Fig. 7 Water uptake/loss rate at different constant relative humidities at 25℃ during partial dissolution followed by recrystallization of NaCl; point M corresponds to DRH.

Experimental data suggest that, in the case of partial four days of rainy weather followed by a period of dry dissolution followed by evaporation; both processes weather. In this case (and by taking the simplifying can be described by a simple model: water uptake/ assumption that there is no interaction with other loss is dependent on the difference between the constituents present in the product), the amount of imposed relative humidity and the deliquescence dissolved NaCl and the required time for recrystalli- relative humidity, RH-DRH. Moreover, according to zation as a function of relative humidity can be calcu- ESEM observations at high relative humidity, dis- lated. Some values are reported in Table 1: solution seems to be a homogeneous process where all particles, individual crystals as well as aggregates, Recrystallization at RH

Table 1 Percentage of NaCl dissolved (1a) and time needed for complete recrystallization (1b) as a function of imposed RH at 25℃ (mass of NaCl: 0.1g) 1a Amount of dissolved NaCl after 4 days 1b Required time for recrystallization at at indicated RH at 25℃ indicated RH at 25℃ if 57.3% of NaCl was dissolved RH [%] Percentage dissolved RH [%] Time for recrystallization 80 25.5% 60 3 days 85 57.3% 45 1.5 days 90 80.3% 30 1 day

174 KONA Powder and Particle Journal No.29 (2011) a b c

d e f

Fig. 8 Time sequence of ESEM images of the recrystallization of NaCl at RH＜DRH (a to f); size bar is 100 µm in all images. rapidly evaporating from the agglomerate while the separate clusters (Fig. 9a), one bigger but more size of spherical solution droplet seems unchanged. compact cluster is obtained after recrystallization The cluster looks completely dry on Fig. 8d, while (Fig. 9b). The ensemble of ESEM observations the drop did not yet show the appearance of a solid. proves that due to the dissolution/recrystallization of Only in Fig. 8e can one see the beginning of faceting crystals, caking is accompanied by significant chang- on the periphery of the droplet. Fig. 8f shows the es with respect to initial size and shape of particles. emergence of the solid phase while the agglomer- By means of ESEM observations of sample dry- ate seems unchanged. The image in Fig. 8f reveals ing at microscopic scale, two distinct phenomena the final stage of drying: from the spherical solution responsible for caking can be identified: the first one droplet, one unique compact crystal has re-crystal- corresponds to the crystal growth from partially dis- lized with a shape different from the initial crystal solved bigger aggregates, while the second one rep- before dissolution (initial crystal can be seen in the resents the formation of a crystal from homogeneous insert on the top left-hand side of Fig. 8f). aqueous solution formed previously by complete The importance of modifications induced by partial dissolution of the small crystal. In order to verify this dissolution followed by recrystallization is further qualitative observation, one can perform quantitative illustrated in Fig. 9 where the shape of NaCl aggre- analysis of dissolution and recrystallization kinetics. gates before dissolution and after recrystallization The drying experiments shown in Fig. 10 were per- is compared. It shows clearly that starting from two formed on the same sample but at different RH. Each

a b

Fig. 9 Environmental scanning electron microscopy images of dry NaCl aggregates (a) before dissolution and (b) after recrystallization; size bar is 100µm in both images.

KONA Powder and Particle Journal No.29 (2011) 175 drying sequence was preceded by partial dissolution to what was observed earlier for ammonium nitrate9). at 90% RH, meaning that one single NaCl sample was In such a case, the nucleation of a solid phase takes subjected to partial dissolution seven times. place when the solution reaches a critical concentra- The rate of water uptake or loss is deduced from tion and is followed by the growth of crystals at a rate quantitative measurements of sample mass as a func- which depends on the degree of supersaturation of tion of time (such as data shown in Fig. 6). One the solution contained in a drop. Indeed, ESEM ob- should note again that negative signs for water loss servations (Fig. 8c) show that the spherical droplet rates come from the fact that water evaporation is remains liquid even though all water seems to be measured. The first part of the curves represents evacuated from the aggregate. seven experiments at imposed RH=90% (time scale One can also observe that during drying, the time between 0 and 14 400s) carried out on one single for total evaporation of the water is dependent on the sample submitted to multiple cycles of partial dissolu- imposed RH: it is short for RH=0% ( ◆ ) and much tion followed by drying. The fact that the dissolution longer for RH=60% ( ● ). Likewise, the evaporation rate remains constant is in accordance with Eq. (2), rate during the first phase of crystallization and ac- and its remarkable reproducibility suggests that the celeration during the second phase both increase Knudsen coefficient remains constant. with decreasing imposed RH (i.e. by increasing the By contrast, the kinetics of recrystallization at vari- difference between DRH and imposed RH). Finally, able RH between 60% and 0% RH are all divided into the shoulder which appears more intensely at high two distinct periods: during the first one following RH (50 and 60% RH) at the end of evaporation can be the adjustment of RH to the imposed RH below DRH interpreted as the loss of residual water in the crys- (t >14400s), the loss of water taking place at approxi- tal matrix, which is more difficult to evacuate at low mately constant rate is observed. Subsequently, the driving force for crystallization (DRH-RH). Careful rate of evaporation seems to slow down slightly, goes examination of the kinetics of evaporation will allow a through a minimum (in absolute values) followed better insight into the mechanism of recrystallization. by a sequence where the rate seems to accelerate. Coming back to the pictures obtained by ESEM (Fig. 4. Conclusion 8), one can suppose that the constant rate of evaporation corresponds to the evaporation of water from Aiming at a better understanding of the caking solution bathing partially dissolved aggregates. The of hygroscopic solids, the role of ambient RH was process is governed by the imposed driving force for examined in detail. Several processes participating evaporation, i.e. DRH-RH. A subsequent decrease in caking depend on the water vapor pressure in the of the evaporation rate suggests that the solution in ambient atmosphere: condensation of liquid water liquid drops becomes more concentrated, similarly and subsequent formation of aqueous solution fol-

0.01 0.005 0 dm/dt -0.005 -0.01

kg/s] -0.015 -6 -0.02 [10 -0.025 -0.03

Water uptake/loss rate, -0.035 0 5000 10000 15000 20000 25000 30000 Time, t [s]

Fig. 10 Water uptake/loss rate of the sample of 12.92 mg of NaCl as a function of time at 25℃: dissolution at 90% RH followed by recrystallization at 0% RH ( ◆ ), 10% RH ( ■ ), 20% RH ( ▲ ), 30% RH ( × ), 40% RH ( ), 50% RH ( + ) and 60% RH ( ● )

176 KONA Powder and Particle Journal No.29 (2011) lowed by recrystallization if RH decreases. The be- ps Water vapor pressure of solution at satura- havior of such solutions under industrially relevant tion [Pa] conditions was studied on laboratory scale. By means RH Relative humidity [%] of a model based on the Knudsen law, the amount of t Time [s] dissolved salt as a function of time can be calculated. T Temperature [K] The required time for dissolution or recrystalliza- xNaCl Mass fraction of NaCl [-] tion can also be estimated for RHs corresponding to xwater Mass fraction of water [-] the storage/transport conditions of industrial powders. Moreover, by coupling the micro-gravimetric References measurements with ESEM observations, some light could be shone on the way the recrystallization from 1) Martin, S.T.(2000): Phase Transitions of Aqueous At- aqueous solutions proceeds. Two distinct processes mospheric Particles, Chem. Rev., 100, pp.403-3453. are evidenced: the first one is likely to correspond to 2) Mauer, L.J. and Taylor, L.S. (2010): Water Solid Inter- the growth of partially dissolved crystals, while the actions: Deliquescence, Annu. Rev. Food Sci. Tech- nol., 1, pp.41-63. second one should correspond to the formation of 3) Tanaka, T. (1978): Evaluating the caking strength of crystals in a supersaturated aqueous solution issued powders, Ind. Eng. Chem. Prod. Res. Dev, 17, n°3. from the previous total dissolution of small NaCl 4) Peters, S.J. and Ewing, G.E. (1997): Water on salt: An crystals. Studies currently underway shall allow a infrared study of adsorbed H2O on NaCl under ambi- better understanding of the behavior of mixtures of ent conditions, J. Phys. Chem. B, 101, pp.10880-10886. several crystalline powders. 5) Zasetsky, A.Y. (2008): Dissolution of solid NaCl nanoparticles embedded in supersaturated water vapor probed by molecular dynamic simulations, J. Acknowledgements Phys. Chem., 112,pp.3114-3118. 6) Mullin, J.W. (1971): “Crystallisation”, The Butterworth Financial support for this project provided by Group, London. the Department “Solid Products”, Nestle Research 7) Apelbat, A. and Korin, E. (1998): The vapor pressure Centre, Lausanne, Switzerland, is gratefully acknowl- of saturated aqueous solutions of sodium chloride, edged. sodium bromide, sodium nitrate, sodium nitrite, potas- sium iodate and rubidium chloride at temperatures from 227K to 323K. J. Chem. Thermodynamics, 30, Nomenclature pp.59-71. 8) Komunjer, L. and Affolter, C. (2005): Absorption/evap- aw Water activity [-] oration kinetics of water vapor on highly hygroscopic aw* Critical water activity [-] powder: Case of ammonium nitrate, Powder Technol- DRH Deliquescence relative humidity [%] ogy, 157, pp.67-71. DVS Dynamic Vapor Sorption 9) Komunjer, L. and Pezron, I. (2009): A new experimen- ESEM Environmental Scanning Electron Micros- tal method for determination of solubility and hyper- copy solubility of hygroscopic solid, Powder Technology, -1 -1 190, pp.75-78. KKnudsen Knudsen coefficient [kg.Pa .s ] 10) Tang, I.N. (1986): Water Activity Measurements with m Water mass [g] Single Suspended Droplets: The NaCl-H20 and KCI- P Imposed vapor pressure [Pa] H20 Systems, Journal of Colloid and Interface Sci- P0 Saturated vapor pressure of pure water ence, 114 (2), pp.409-415. [Pa]

KONA Powder and Particle Journal No.29 (2011) 177 Author’s short biography

Marina Langlet Born in 1985 in Cambrai (North of France), Marina Langlet studied in the engineering school, Ecole Supérieure de Physique et Chimie Industrielles de Paris (ESPCI), where she specialized in physical chemistry and environment. She graduated in January 2011. After receiving a Master’s degree in Environment at Mines of Paristech, she joined the team of the chemical engineering department of the Com- piègne University of Technology (UTC) in October 2010 for a PhD thesis, where her current study is focused on powder caking. The objective is to characterize the conditions and the kinetics which lead to damage for product quality under industrial conditions. Her work is focused on hygroscopic substances from the more ordered materials (crystals of NaCl) to mixtures of deliquescent substances and more complex amorphous substances.

Metlas-Komunjer Lea Metlas-Komunjer studied physical chemistry in former Yugoslavia. After ob- taining her degree from the University of Zagreb, she joined the Laboratory for Precipitation Processes of the Rudjer Boskovic Institute in Zagreb to study crystallization phenomena under physiologically relevant conditions. After two years as a visiting fellow at the Laboratoire de Minéralogie et Cristallographie in Paris, she joined the Chemical Engineering Department of the Compiègen Univevsity of Technology (UTC) as a visiting professor. She currently holds a permanent posi- tion at the same university and her research interests include the stability of dispersed systems such as emulsions, dispersions and powders.

Mohammed Benali Dr. Mohammed Benali is a lecturer-researcher at the Ecole Supérieure de Chimie Organique et Minérale (ESCOM). He received his Master’s degree in chemical engineering and environment and his PhD in powder agglomeration from the Institut National Polytechnique of Toulouse (France) in 2006. After a post-doctoral degree with DSM Nutritional products in Basel (Switzerland), Dr Mohammed Benali spent one year at the Ecole Nationale Supérieure des Ingénieurs en Arts Chimiques Et Technologiques (ENSIACET) as a teacher-researcher in chemical engineering, he joined the ESCOM in 2008. His current research activities concern the size enlargement and treatment of powders, and liquid-solid reactions in a fluid bed reac- tor.

Khashayar Saleh Khashayar Saleh received a B.S. degree in chemical engineering from the Sharif (Aryamehr) university of technology (Tehran, Iran) in 1992. He prepared a PhD thesis on the coating of fine powders in the Chemical Engineering Laboratory of Toulouse and obtained his doctor’s degree in 1998 from the Institut National Poly- technique de Toulouse (France). Dr Saleh is currently associate professor in the chemical engineering department of the Compiègne University of Technology. His work is focused on powder technology including size enlargement technology and powder characterisation methods.

178 KONA Powder and Particle Journal No.29 (2011) Author’s short biography

Pierre Guigon Pierre Guigon is a chemical engineer from ENSIGC Toulouse (France 1971). He is a Master of Engineering Science, UWO London Ontario, (Canada 1974), a Docteur Ingénieur UTC Compiègne (France 1976), a Docteur es Science UTC Compiègne (France 1978), and also a fellow of the Institution of Chemical Engineers. He is head of the chemical engineering department of Compiègne University of Tech- nology. His research is in the field of particle suspensions (fluidization, pneumatic transport) and particle technology (comminution and agglomeration).

Isabelle Pezron Isabelle Pezron received an engineering degree from the Ecole Supérieure de Phy- sique et Chimie Industrielles (ESPCI, Paris) in 1985 and a PhD in physical chemistry (Université Paris VI) in 1988. After a post-doctoral stay at the Institute of Sur- face Chemistry in Stockholm (Sweden), she joined the Université de Technologie de Compiègne (UTC) in 1990. She also spent 4 years in the Department of Pharma- ceutical Sciences of the University of Missouri (Kansas City, USA) between 1997 and 2001 as a visiting associate professor. She is now professor in the Department of Chemical Engineering of UTC, and her current research activities concern the physical chemistry of interfaces and dispersed systems, and their role in chemical engineering processes.

Frederic Nadaud Born in 1971, Frederic Nadaud graduated from the University of Créteil (France) in physical measures with specialty in instrumental techniques (IUT de Créteil) in 1992. Since 1994, he has been in charge of ESEM techniques in the Service d’ Analyses Physico-Chimiques at the University of Compiègne.

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