Silica Alumina Particles Research Articles

Synergistic flame retardancy of solid acid, hindered N‐alkoxy amine, and halogen compound for polypropylene

AbstractPolypropylene (PP) is a thermoplastic resin widely used in various industrial applications. However, the flammability of PP is a severe drawback that lowers operational safety. This study demonstrates the development of flame‐retardant PP. The co‐adding with various solid acids and a hindered N‐alkoxy amine (NOR116 – Flamestab® NOR 116 FF) affects the combustion behavior of PP in a vertical flame test. The co‐adding of silica alumina (SA) and NOR116 with PP promoted the melt drip, suppressed upward combustion heat, and shorter the combustion time. The decomposition products of NOR116 induced the cleavage of the main chain of PP, and it quenched the radicals on the surface of the SA particles because SA has abundant acidic sites and large pores, facilitating the adsorption of a substantial quantity of NOR116. The molecular weight of PP was controlled to 103 ~ 104 before the combustion to achieve an increase in the melt flow ability and suppress the upward combustion. Furthermore, a small amount of a halogen‐based flame retardant was incorporated into the PP/SA/NOR116 sample, and the specimens could instantly self‐extinguish on the gas phase by radical trap.

Investigating agglomeration of kaolinite particles in the presence of dodecylamine by force testing and molecular dynamics simulation

Kaolinite, one of the main components of clay minerals, is detrimental to slime water sedimentation. Sedimentation, adsorption, surface tension, contact angle, and interaction force measurements were conducted to study the hydrophobic agglomeration mechanism in kaolinite particles in the presence of dodecylamine (DDA). The results showed that DDA could be adsorbed on the kaolinite surface, improving the surface hydrophobicity and promoting hydrophobic particle agglomeration. Kaolinite hydrophobic sedimentation was enhanced with increased DDA concentration. The settling velocity and the adsorption of DDA on slurry particles were optimal when the DDA concentration was 14 × 10-4 mol/L. The shape and size distribution significantly affected the particle-surface interaction. Reliable force data could not be obtained from colloidal probes made of actual clay particles. Therefore, silica-silica and silica-alumina systems were used to replace clay mineral particles for force testing. AFM results showed that electrostatic repulsion existed in silica-silica and silica-alumina particles in ultrapure water. With DDA addition, the electrostatic repulsive force in silica-silica and silica-alumina particles decreased, the hydration film was destroyed, and an adhesion force was generated. In addition, the silicon-oxygen (001) surface of kaolinite adsorbed DDA more easily than the aluminum-oxygen (001̅) surface. The adsorption behavior of DDA+ on the kaolinite (001) and (001̅) surfaces was calculated by molecular dynamics simulation to explore the adsorption mechanism of DDA on kaolinite surfaces. The results suggested that the DDA+ polar head groups were adsorbed on the kaolinite surface, whereas the non-polar groups faced the solution. DDA+ adsorbed more easily on the (001) surface than on the (001̅) surface.

Instantaneous Formation of Metal and Metal Oxide Nanoparticles on Carbon Nanotubes and Graphene via Solvent-Free Microwave Heating

Microwave irradiation was shown to be an effective energy source for the rapid decomposition of organic metal salts (such as silver acetate) in a solid mixture with various carbon and noncarbon substrates under completely solvent-free conditions. The rapid and local Joule heating of microwave absorbing substrates (i.e., carbon-based) resulted in the instantaneous formation of metal and metal oxide nanoparticles on the substrate surfaces within seconds of microwave exposure. Other less absorbing substrates (such as hexagonal boron nitride) required longer exposure times for the salt decomposition to occur. Details of the effects of microwave reaction time, temperature, power, and other experimental parameters were investigated and discussed. The solvent-free microwave method was shown to be widely applicable to various organic metal salts with different substrates including single- and multiwalled carbon nanotubes, graphene, expanded graphite, hexagonal boron nitride and silica-alumina particles, forming substrate-supported metal (e.g., Ag, Au, Co, Ni, Pd, Pt) or metal oxide (e.g., Fe₃O₄, MnO, TiO₂) nanoparticles in high yields within short duration of microwave irradiation. The method was also successfully applied to large structural substrates such as nanotube yarns, further suggesting its application potential and versatility. To demonstrate one potential application, we successfully used both carbon nanotube powder and yarn samples decorated with Ag nanoparticles prepared via the above method to improve data acquisition in surface enhanced Raman spectroscopy.

Adsorption of lead ions in aqueous solution using silica–alumina nanoparticles

The adsorption of lead ions in aqueous solution on the surface of silica–alumina nanoparticles is reported. The removal of lead ions from simulated industrial wastewater was performed using silica–alumina particles synthesized by the sol–gel method with a molar ratio of 1:1. Small amounts of lead ions were added to the sol until the critical flocculation concentration was reached and the particles flocculated forming aggregates which sediment down, being removed from the sol. The flocculation kinetics was followed using Dynamic Light Scattering that measures the particle size as a function of time. The amount of lead ions adsorbed by the nanoparticles was determined using Atomic Absorption Spectroscopy. The lead concentration was reduced from 140 ppm to below 10 ppb; this final concentration fulfills the corresponding legislation requirements.

X-ray mapping as a tool to characterize mixtures of large zeolite ZSM-5 crystals with amorphous impurities

During the synthesis of large crystals of zeolite ZSM-5 in aluminum-rich gels, two phases formed. Instead of large crystals of aluminum-rich zeolite ZSM-5, ZSM-5 crystals with a relatively low aluminum content and amorphous silica–alumina particles crystallized simultaneously. This was demonstrated using X-ray mapping and NMR spectroscopy.

Evaporation of water from air-fluidized porous particles

The drying rate of wetted porous silica–alumina particles, FCC catalyst, was measured in a 15 cm diameter air-fluidized bed with a cloth distributor, containing about 1.5 kg catalyst. The particles tolerated the addition of remarkably large quantities of liquid water, up to 50% of the dry weight, without upsetting the fluidization characteristics: evidently the water was accommodated within the porous particle structure. The drying rate was measured in two ways: (1) by mounting the whole fluidized bed on a balance and (2) by measuring the inlet and outlet air humidities by wet and dry bulb thermometers and measuring also the air flow rate. The change in weight from method (1) agreed well with results from (2) using a material balance. Tests with two methods of injecting the water, locally and evenly distributed, gave the same drying rate after an initial transient, showing that water readily distributes itself amongst the catalyst particles. The wet catalyst exhibited a constant drying rate followed by a falling rate. At the transition between these rate laws, the water content is consistent with the N 2 BET area of the catalyst being covered by a monolayer of water; this could be of practical value to designers and operators of dryers. During the constant-rate period, the exit air had a relative humidity which was constant at 60–70%. Calculations show that there is excellent air–solids contact, so the exit air appears to be in equilibrium with the wet catalyst. During the falling-rate period, it appears that the area of the monolayer diminishes, as also does its equilibrium vapour pressure. These characteristics make FCC catalyst an admirable material for a hospital fluidized bed to support a patient with certain injuries, e.g., serious burns, for which dry conditions and an ability to absorb liquid are important.

Flocculation process of alumino-silicate particles using different metal ions in aqueous and alcoholic solutions

Silica–alumina particles prepared by the sol–gel method were used to adsorb metal ions in aqueous and alcoholic solutions. The flocculation kinetics of particles with a Si:Al molar composition 1:1 were studied in the presence of several metal ions by monitoring the particle growth with time using dynamic light scattering (DLS). Flocculation experiments were carried out following the two different routes: (a) adding small amounts of metal ions until the critical flocculation concentration was reached; (b) injecting the critical flocculation concentration all in one shot. The flocculated samples were characterized by atomic absorption spectroscopy (AA).

Axial mixing and segregation in a gas-liquid-solid three-phase fluidized bed of solid particles of different sizes and densities

Sieved silica-alumina particles (diameter = 481 μm; density = 1990 kg/m3), glass beads (diameter = 516 μm; density = 2500 kg/m3) or mixtures thereof were fluidized in a vertical bubble column of 7 cm in diameter and 4.50 m in height. The bed was operated batchwise or continuously with respect to the feed of solid particles. Axial changes in gas and solid holdups in the bed were measured by simultaneously sectioning the column with 20 horizontal plates. The measured solid holdup of each component in the column was compared with the analytical results calculated by a one-dimensional sedimentation-dispersion model. Both experimental and calculated results were in satisfactory agreement over the entire column, which consisted of dense and dilute regions, as well as circulating quantities of liquid and solid particles.

Preparation of Monodispersed Spherical Silica-Alumina Particles by Hydrolysis of Mixed Alkoxides

Spherical colloidal particles of mixed silica-alumina composition of narrow size distribution were prepared by cohydrolysis of mixed alkoxides in the presence of sulfate ions. The ratio of the constituents could be altered by the solution pH and the reactant concentrations. Analysis of the composition of growing particles showed that they were internally inhomogeneous, which was substantiated by microelectrophoresis. The solids as prepared were partially crystallized to mullite on calcination at 1100°C. During this process the powders retained the spherical shape, but underwent some sintering.

Some Mechanochemical Considerations on the Numbers of Spins Induced by Ultraviolet Light

Abstract The number of spins/g (NOS) generated in a binary powder of glycolic acid and silica–alumina (SA) increased during ultraviolet (UV) irradiation. After stopping illumination, the NOS value was found to decrease up to a constant number of sping/g (CNS), which was remarkably greater than the NOS value obtained before UV irradiation. The CNS values, thus obtained, were influenced not only by the calcination temperature of SA (Tea) and by the atmosphere of storage, but also by the duration of UV irradiation (DI). The values of CNS obtained at a low Tca (below 400°C) were also influenced by the time interval between stopping shaking and the start of UV irradiation (ti). Values of NOS having attained CNS remained unchanged for a long period, but finally began to decrease. The duration of CNS (DCNS) was also affected by Tca, the atmosphere of storage, DI, and ti DCNS decreased when CNS increased, and became unchanged when CNS reached a constant value. Values of CNS and DCNS induced by UV light were also influenced by the size of SA particles and by the mechanical energy given by shaking or compressing. Such mechanochemical effects are available, at least for studying the generation mechanism of UV-induced surface activity, for an improvement of the reproducibility of physicochemical data obtained during or after UV irradiation, and for the method of obtaining materials of constant efficiency.

MEASUREMENT OF FLOW OF SOLID PARTICLES IN GAS FLUIDIZED BED*

The flow of fine solid particles was measured in a gas fluidized bed of 12-cm i.d., where silica alumina particles, 60-65 μm in diameter, were fluidized by air. The minimum fluidizing velocity of the solid particles was 0.2-0.4 cm/s. The measuring system was composed of bifurcated optical fiber probes and a data processing unit. Silica fibers and plastic fibers were used for guiding ultraviolet light and collecting fluorescent visible light, respectively. Sensitivity and accuracy of the system were substantially improved over that of the previous system. The pulse response curves of fluorescent tracer particles were measured more than 100 times under the same conditions and were statistically analyzed. The time-averaged velocity and the root mean square of velocity fluctuation of solid particles were determined in upward, radial and oblique directions at the center of the fluidized bed. The results were in agreement with literature data.

Adsorption-desorption kinetics of acetic acid on silica-alumina particles in aqueous suspensions, using the pressure-jump relaxation method

Adsorption-desorption kinetics of acetic acid on silica-alumina particles in aqueous suspensions, using the pressure-jump relaxation method

The kinetics of deuterium-neopentane exchange: effects of desorption and diffusion

The product distribution of isomers from the deuterium exchange of neopentane over palladium supported on silica-alumina particles is influenced by the competition among three rate processes: desorption, diffusion, and surface exchange. The theory based on a single-step surface mechanism is presented and given quantitative treatment, suitable for large conversions. The experimental results show a very wide variety of product distributions over the same catalyst, and can be quantitatively correlated by the theory.