Invited review paper
Progress in developing spray-drying methods for the production of controlled morphology particles: From the nanometer to submicrometer size ranges

https://doi.org/10.1016/j.apt.2010.09.011Get rights and content

Abstract

Control of particle size and morphology has increasingly captured the attention of researchers for decades. The exploration of unique sizes and shapes as they relate to various properties has become a great quest for large field applications. To meet these demands, this review covers recent developments in particle processing. An aerosol-assisted self-assembly technique, with a spray-drying method as a representative of it, to create particles is thoroughly reviewed. Its popularity and its broad use in industry for producing particles are the main reason of this review; thus, elucidation of this method is important for the improvement of particle technology. A practical spray-drying method is described from the step-by-step process to the selection of apparatus types (merits and demerits). Elaboration of particle processing of several morphologies (sphere, doughnut, encapsulated, porous, hollow, and hairy) is discussed in terms of the selection of material types, the addition of supporting materials, and the change of process conditions. Controllable size is also discussed in terms of the adjustment of the droplet size, initial precursor concentration, and the addition of specific techniques. A comparison between a theoretical mechanism and current experimental results (over a 15-year period) are shown to clarify how particles with various sizes and morphologies are designed. This method must be considered an art rather than a science because of its advantages in creating wonderful and unique particle shapes. The performance of various particle morphologies is also demonstrated, which is essential for an understanding of the importance that shape can exert on practical use. Because the method outlined here can be broadly applied to the production of various types of functional materials, we believe that this report contributes new information to the field of chemical, material, environmental, and medical engineering.

Introduction

Recently, control of particle morphology has received a tremendous amount of attention [1]. The change of shapes has caused unprecedented chemical and physical properties that differ markedly from those of bulk or dense material [2]. Great potential for use in various applications could be achieved with morphological control: electronics, catalysts, drug carriers, sensors, pigments, and magnetic and optical materials, etc., [3].

Effective strategies to tailor nanomaterials reliably and predictably are important [4]. Interest in them has increased in the past decade, especially when there is a need to control for different characteristics, such as size distribution, crystallinity, composition, and purity. Efforts toward the functionalization, formulation, and production of morphology have focused on making them applicable in industry. Many alternative methods have been proposed to realize production of particles with a controllable morphology: mechanical milling, precipitation, lyophilization, freeze-drying, spray-drying, pyrolysis, supercritical fluid, emulsion-based methods, and a simple combination of chemical-process synthesis. Achievement from the current suggested processes for the use in practical applications has been reported. Controllable particle size within the desired range is also possible under specific conditions. However, exceptions and significant difficulties associated with the above methods remain: (i) particle size distribution; (ii) inadequate powder dispersibility; (iii) insufficient process control; (iv) contamination; (v) high-cost processing; (vi) excessive heat production problems; (vii) complexity of the processes; (viii) loss of chemical activity; (ix) yield of the products; and, (x) scaling-up the process [5].

Among the above processes, an aerosol-assisted self-assembly technique has been the most promising [6]. When the principles of this technique are combined with a drying process, an effective method can be created – namely, the aerosol-assisted spray method [6]. This method efficiently produces dry powder from either a liquid or a slurry [2]. The advantages of this method are prospective for many applications. A very versatile process that is compatible with various materials is the main promising merits. Particles with a high-purity product can be produced simply using an economical, a continuous way [7], and a rapid process [8]. Furthermore, this method produces particles with a spherical shape that are agglomeration-free and have a relatively monodispersed size, which is very useful for material processing.

The spray method is well-trusted in practical uses, which has been confirmed by its use in the manufacturing of dried food, fertilizers, oxide ceramics, and pharmaceuticals. A magnificent number of the uses of spray method have been reported, in which more than 15,000 industrial-size spray dryers are currently in operation. This number would approximately double if the use in pilot plants and laboratories was added to the calculation [9].

Several developments of the spray method have been reported with no limitations to a particular type of process: spray-pyrolysis, spray-drying, flame-spray, low-pressure, and electro-spray [3]. The principle for all these processes is almost the same. A starting solution is prepared usually by dissolving the metal component of an intended product in a solvent. The droplets, which are atomized from the starting solution, are introduced to the solvent evaporator. Evaporation of the solvent, diffusion of solute, drying, and precipitation may occur inside the furnace to form the final product. The reaction among reactants, and sometimes with surrounding gas, is dependent on the type of the initial solution [10].

Here, at this juncture, we presented a review of all recent developments in particle processing using aerosol-assisted self-assembly technique. We focus only on the spray-drying method as representative of this technique to fabricate particles with a controllable size and morphology (Fig. 1). In addition, while our research group has had a considerable amount of success in research on this topic [10], we will not limit our review to work from own group; rather, our review will be highly comprehensive.

The spray-drying method is similar to other types of spray (e.g. spray pyrolysis, spray freeze drying, etc.), except for the type of precursor (usually colloidal particles or sols) and the fact that there is almost no available reaction during the drying process. The ability to produce uniformly spherical particles from nano to micron sizes is one of the main advantages of this method. Other merit gained from this method is that when the suspension consists of colloidal nanoparticles (primary particles), the resulting particles are comprised of nanoparticles that form a nano-structured powder. Therefore, the spray-drying method may be suitable for consolidating nanoparticles into macroscopic compacts, and submicron spherical powders that have nanometer-scaled properties can be obtained. A suitable process can be adjusted using this method, in which a striking feature of the initial raw material (e.g. initial particle size, type of material, physical and chemical properties, and surface charge) and process conditions play an important role in producing various product shapes [11]. Although the current spray-drying method is known to create particles by managing several parameters, no comprehensive report has described and reviewed all processes used to prepare particles with specific morphologies. In fact, due to this excellent prospect, in order to construct and design particles with a controllable morphology, it is important to understand the mechanisms and the regulations of the initial raw material and process-condition parameters when using the spray-drying method.

An overview of the current research on particle processing with its ability to control size and morphology to suit certain applications is described in this paper, which is believed to be the first detailed review of particle design (control of size and morphology). The main text comprises five sections, with the last being a summary. Section 2 provides a definition of the spray-drying method for the production of particles. Section 3 discusses the techniques for controlling particle morphologies. The manipulation of factors (i.e. process conditions and addition of supporting components) to realize particles of varying morphologies is thoroughly explained. The support of current results (described in the nanoparticle analysis (i.e. an X-ray diffraction (XRD), a scanning electron microscope (SEM), and a transmission electron microscope (TEM))) are also added to confirm the effectiveness of the above factors in producing particles with specific shapes. Theoretical explanation, as well as mechanism illustration, is also described in this section to support and clarify the design of particles with various sizes and morphologies. Section 4 shows the effectiveness of various particle morphologies in several applications, which is important for understanding the significance of the effects of particle size and shape.

Section snippets

A spray-drying method: technical considerations for particle production

A representative of the spray-drying method is illustrated in Fig. 2. The main principle of this method is to deliver and rapidly heat an initial solution/slurry via the direct injection of very small droplets (Fig. 2a). The primary steps include atomization, droplet-to-particle conversion (solvent evaporation), and particle collection [3]. Details of the illustration apparatus of the spray-drying method, including atomizer, solvent evaporator, and particle collector types, are shown in Fig. 2

Various particles morphologies

The spray-drying method has great potential for the synthesis of particles that are rich in desirable properties. A simple process can be achieved, which involves only solvent evaporation and self-assembly of materials inside the droplet system, as described above. The control of particle shape is also possible by adding some technical modifications. The features of the initial raw material (e.g., initial particle size, type of material, physical and chemical properties, and surface charge) and

Particle morphologies – opportunities and potential roles

Particles with engineered features and morphologies are believed to enhance material performance [2]. Coordination of size and shape is important in order to gain the optimum particle properties. Exposition of surface performance is one of the advantages of a change in particle morphology. The ratio of active-to-inactive areas becomes a serious concern when expensive precious materials are used for a specific application (e.g., platinum as a catalyst) [59]. Control of particle sizes down to

Summary

Critical issues, associated with the development of the aerosol-assisted self-assembly technique to obtain effective strategies in designing particle morphology, have been discussed. The spray method, as the representative of this technique, has been verified for the production of particles with various features and morphologies. The types and the concentrations of precursors, the selection of process conditions, and the addition of supporting materials all play significant roles in the

Acknowledgements

A scholarship provided by the Japanese Ministry of Education, Science, Sports, and Culture (MEXT) for A.B.D.N. is gratefully acknowledged. We also thank the Hosokawa Micron Foundation for providing a research allowance to ABDN. We thank Tuswadi of the Faculty of IDEC of Hiroshima University for preparing materials and assistance in this report. We are also grateful to Dr. Ferry Iskandar of the Department of Physics of Institut Teknologi Bandung (ITB) and Dr. Chris Hogan of the Department of

References (113)

  • W. Widiyastuti et al.

    Sintering behavior of spherical aggregated nanoparticles prepared by spraying colloidal precursor in a heated flow

    Advanced Powder Technology

    (2009)
  • Z. Yu et al.

    Preparation and characterization of microparticles containing peptide produced by a novel process: spray freezing into liquid

    European Journal of Pharmaceutical Biopharmaceutics

    (2002)
  • R. Vehring et al.

    Particle formation in spray drying

    Journal of Aerosol Science

    (2007)
  • H. Krier et al.

    Combustion of single drops of fuel

    Combustion and Flame

    (1972)
  • K. Okuyama et al.

    Preparation of functional nanostructured particles by spray drying

    Advanced Powder Technology

    (2006)
  • H.W. Chang et al.

    Optical properties of dense and porous spheroids consisting of primary silica nanoparticles

    Journal of Aerosol Science

    (2002)
  • F. Iskandar et al.

    Control of the morphology of nanostructured particles prepared by the spray drying of a nanoparticle sol

    Journal of Colloid and Interface Science

    (2003)
  • A. Gharsallaoui et al.

    Applications of spray-drying in microencapsulation of food ingredients: an overview

    Food Research International

    (2007)
  • A.B.D. Nandiyanto et al.

    Design of a highly ordered and uniform porous structure with multisized pores in film and particle forms using a template-driven self-assembly technique

    Acta Materialia

    (2010)
  • F. Iskandar et al.

    Preparation of microencapsulated powders by an aerosol spray method and their optical properties

    Advanced Powder Technology

    (2003)
  • F. Iskandar et al.

    Direct synthesis of hBN/MWCNT composite particles using spray pyrolysis

    Journal of Alloys and Compounds

    (2009)
  • M. Inagaki et al.

    Nanocarbons – recent research in Japan

    Carbon

    (2004)
  • S.R.C. Vivekchand et al.

    Carbon nanotubes by nebulized spray pyrolysis

    Chemical Physics Letters

    (2004)
  • L.F. Su et al.

    Continuous production of single-wall carbon nanotubes by spray pyrolysis of alcohol with dissolved ferrocene

    Chemical Physics Letters

    (2006)
  • A.B.D. Nandiyanto et al.

    Rapid synthesis of a BN/CNT composite particle via spray routes using ferrocene/ethanol as a catalyst/carbon source

    Materials Letters

    (2009)
  • A. Taguchi et al.

    Ordered mesoporous materials in catalysis

    Microporous and Mesoporous Materials

    (2005)
  • A.B.D. Nandiyanto et al.

    Synthesis of spherical mesoporous silica nanoparticles with nanometer-size controllable pores and outer diameters

    Microporous and Mesoporous Materials

    (2009)
  • S.V. Krupa

    Effects of atmospheric ammonia (NH3) on terrestrial vegetation: a review

    Environmental Pollution

    (2003)
  • Y. Endo et al.

    Analysis of fluid permeation through a particle-packed layer using an electric resistance network as an analogy

    Powder Technology

    (2009)
  • W.N. Wang et al.

    One-step synthesis of titanium oxide nanoparticles by spray pyrolysis of organic precursors

    Materials Science and Engineering B-Solid State Materials for Advanced Technology

    (2005)
  • Y.C. Kang et al.

    Preparation of high-surface-area nanophase particles by low-pressure spray-pyrolysis

    Nanostructured Materials

    (1995)
  • R. Strobel et al.

    Aerosol flame synthesis of catalysts

    Advanced Powder Technology

    (2006)
  • P.S. Kuts et al.

    Modeling of gas dynamics in a pulse combustion chamber to predict initial drying process parameters

    Chemical Engineering Journal

    (2002)
  • I.W. Lenggoro et al.

    Preparation of ZnS nanoparticles by electrospray pyrolysis

    Journal of Aerosol Science

    (2000)
  • A.R. Frost

    Rotary Atomization in the Ligament Formation Mode

    Journal of Agricultural Engineering Research

    (1981)
  • C.S. Parkin et al.

    Measurement of drop spectra from rotary cage aerial atomizers

    Crop Protection

    (1990)
  • R. Rajan et al.

    Correlations to predict droplet size in ultrasonic atomisation

    Ultrasonics

    (2001)
  • F. Gao et al.

    Preparation and characterization of nano-particle LiFePO4 and LiFePO4/C by spray-drying and post-annealing method

    Electrochimica Acta

    (2007)
  • R.X. Sun et al.

    Preparation and characterization of hollow hydroxyapatite microspheres by spray drying method

    Materials Science & Engineering C-Biomimetic and Supramolecular Systems

    (2009)
  • W.H. Suh et al.

    Porous, hollow, and ball-in-ball metal oxide microspheres: preparation, endocytosis, and cytotoxicity

    Advanced Materials

    (2006)
  • J.H. Bang et al.

    Applications of ultrasound to the synthesis of nanostructured materials

    Advanced Materials

    (2010)
  • F. Iskandar et al.

    Functional nanostructured silica powders derived from colloidal suspensions by sol spraying

    Journal of Nanoparticle Research

    (2001)
  • K. Masters

    Spray drying handbook

    (1994)
  • W.N. Wang et al.

    Investigation on the correlations between droplet and particle size distribution in ultrasonic spray pyrolysis

    Industrial & Engineering Chemistry Research

    (2008)
  • F. Iskandar et al.

    Enhanced photocatalytic performance of brookite TiO2 macroporous particles prepared by spray drying with colloidal templating

    Advanced materials

    (2007)
  • R. Vehring

    Pharmaceutical particle engineering via spray drying

    Pharmaceutical Research

    (2008)
  • G.A.E. Godsave, In studies of the combustion of drops in a fuel spray: the burning of single drops of fuel, Fourth...
  • W.H. Finlay

    The Mechanics of Inhaled Pharmaceutical Aerosols

    (2001)
  • M. Rhodes

    Introduction to Particle Technology

    (2008)
  • available from...
  • Cited by (0)

    View full text