Terry A. Ring

Fundamentals of crystallization: Kinetic effects on particle size distributions and morphology

Abstract This article, which discusses the key concepts involved in powder precipitation, is organized in the following manner: After an introduction, where the thermodynamics of phase transformation is discussed, sections on nucleation and growth follow. With the kinetics established, the subject of crystal shape is reviewed. Following this, sections on particle morphology and size distributions are presented, which consider the population balances of idealized industrial reactors.

Room Temperature Co-Precipitation Synthesis of Magnetite Nanoparticles in a Large pH Window with Different Bases

Magnetite nanoparticles (Fe3O4) represent the most promising materials in medical applications. To favor high-drug or enzyme loading on the nanoparticles, they are incorporated into mesoporous materials to form a hybrid support with the consequent reduction of magnetization saturation. The direct synthesis of mesoporous structures appears to be of interest. To this end, magnetite nanoparticles have been synthesized using a one pot co-precipitation reaction at room temperature in the presence of different bases, such as NaOH, KOH or (C2H5)4NOH. Magnetite shows characteristics of superparamagnetism at room temperature and a saturation magnetization (Ms) value depending on both the crystal size and the degree of agglomeration of individual nanoparticles. Such agglomeration appears to be responsible for the formation of mesoporous structures, which are affected by the pH, the nature of alkali, the slow or fast addition of alkaline solution and the drying modality of synthesized powders.

Effect of a sterically stabilizing surfactant on the nucleation, growth and agglomeration of monosized ceramic powders

Abstract Hydroxypropyl cellulose (HPC) has been shown to provide steric stabilization during the precipitation of TiO 2 from alcohol solution, allowing the precipitation of high solids loading of monosized particles by preventing agglomeration. The adsorption isotherm for HPC on TiO 2 in ethanol was determined to account for the effect of HPC on the nucleation, growth and agglomeration of particles during the hydrolysis of titanium tetraethoxide in ethanol. Agglomeration is essentially prevented by HPC.

Heterocoagulation II. Interaction energy of two unequal spheres

Abstract The problem of interactions of unequal spheres of any surface potential at close distance is analyzed in terms of the Poisson—Boltzmann equation in its two-dimensional form. The electrical double-layer interaction energy is obtained and compared to that of Hogg et al. [Hogg, R., Healy, T. W., and Fuerstenau, D. W., Trans. Faraday Soc. 62, 1638 (1966)]. These two energy functions are of similar shape when plotted against the separation distance. However, the values calculated by the methods derived in this work are consistently higher, differing by nearly an order of magnitude at close separations.

Particle size distribution effects on sintering rates

Recent interest in the use of near‐monosize powders for ceramic processing has provoked questions concerning the dependence of the processing on the particle size distribution. One such factor is the sintering rate of the compact produced from a powder with a narrow particle size distribution. This issue is addressed theoretically by considering a log‐normal particle size distribution which is characterized by a mean particle size and a width parameter. The sintering rates derived for model systems are examined for both the initial and intermediate stages, and these rates are found to be a strong function of the distribution width parameter. The sintering ability of a compact decreases with a broader particle size distribution and this effect becomes dramatic in the intermediate stage when grain growth is considered.

Steric stability of alkoxy-precipitated TiO2 in alcohol solutions

Abstract An experimental program is described which evaluated the suitability of various surfactants as steric stabilizers for ethanol suspensions of alkoxy-precipitated TiO 2 particles. This experimental program included surfactant solubility, the effect of the polymer on the critical coagulation concentration of LiCl, and determination of the critical polymer concentration required to prevent coagulation. The results of these experiments allowed the selection of four surfactants from the twenty-seven evaluated which would sterically stabilize the particles against coagulation. In addition, hydroxypropyl cellulose allowed the precipitation to proceed in its presence. Adsorption during growth allowed for nearly complete protection from particle coalescence.

Indium-tin oxide thin films by metal-organic decomposition

In 2 O 3 –SnO 2 films were produced by thermal decomposition of a deposit which was dip coated on borosilicate glass substrates from an acetylacetone solution of indium and tin acetoacetonate. Thermal analysis showed complete pyrolysis of the organics by 400 °C. The thermal decomposition reaction generated acetylacetone gas and was found to be first order with an activation energy of 13.6 Kcal/mole. Differences in thermal decomposition between the film and bulk materials were noted. As measured by differential scanning calorimetry using a 40 °C/min temperature ramp, the glass transition temperature of the deposited oxide film was found to be ∼462 °C, and the film crystallization temperature was found to be ∼518 °C. For film fabrication, thermal decomposition of the films was performed at 500 °C in air for 1 h followed by reduction for various times at 500 °C in a reducing atmosphere. Crystalline films resulted for these conditions. A resistivity of ∼1.01 × 10 −3 Ω · cm, at 8 wt. % tin oxide with a transparency of ∼95% at 400 nm, has been achieved for a 273 nm thick film.

The effects of agglomeration in a continuous stirred tank crystallizer

Abstract Spherical TiO 2 powders were formed by the controlled hydrolysis of ethanol solutions of titanium tetraethoxide in a continuous stirred tank crystallizer. Particle size distributions were evaluated and the results used to determine both nucleation and growth rate as a function of reactant concentration. At high concentration, nucleation and growth were less important than agglomeration. A theoretical model incorporating agglomeration is presented. It predicts the conditions when agglomeration is observed in the continuous stirred tank.

Brittle and Ductile Fracture Mechanics Analysis of Surface Damage Caused During CMP

This work reviews the mechanical properties and fracture mechanics of materials important in the manufacture of multilayer interconnects on silicon chips in order to understand surface damage caused during chemical mechanical polishing (CMP). It gives an explanation for chatter marks, surface flaking in interlayer dielectric material, and rolling indenter and plastic plow lines in copper on the wafer surface during CMP of silicon chips.

Nano-sized cluster nucleation

Abstract Classical nucleation theory good for slowly nucleating systems is reviewed. A new theory for fast nucleating systems, based on a population balance, is presented that uses the energetics of clusters of various geometries determined from ab initio quantum mechanical calculations. This theory predicts cluster population dynamics during nucleation, as well as the spectrum of light emitted during nucleation-crystalloluminescence.