Kaolin in paper filling and coating

Kaolin is the most extensively used particulate mineral in the filling and coating of paper. It improves paper appearance, which is characterized by gloss, smoothness, brightness and opacity, and of greatest significance, it improves printability. Paper is also filled with kaolin to extend fiber.The characteristics of kaolin that have the greatest influence on the quality of paper are the purity, rheology and particle geometry of the processed mineral. Generally, the most deleterious impurities for brightness of kaolin are iron oxide and titanium oxide minerals. The rheology of kaolin-binder-water suspensions at high solid: liquid ratios (as much as 65%) must be approximately Newtonian for efficient blade coating at speeds as great as 1300 meter/min. Particle geometry, defined as particle size, particle size distribution, particle shape and aggregate structure, has a dominant influence over the rheological character of kaolin slurries, as well as on the properties imparted by the kaolin to filled and coated paper.Increase in the aspect ratio of kaolin, as opposed to increase in surface area, exerts the dominant influence on the increase in low-shear viscosity. Although low-shear viscosities of undelaminated coating grades of kaolin show good correlation with surface area, the relationship breaks down for delaminated grades. Particle packing is believed to be the controlling parameter for viscosity at high rates of shear.Opacity, gloss, printability and, to a lesser extent, brightness of paper imparted by coating and filling with kaolin, are largely functions of particle size and particle size distribution. The strength of coated and filled paper generally decrease with decrease in particle size. An increase in coating void volume generally has a deleterious effect on strength.The principal commercial printing systems today are rotogravure and offset. Although other parameters are important, coating structures containing numerous voids generally give superior rotogravure printing, whereas smooth, relatively ink-impermeable surfaces are generally most favorable for offset printing.     

Micrometer-scale 3-D shape characterization of eight cements: Particle shape and cement chemistry, and the effect of particle shape on laser diffraction particle size measurement

Eight different portland cements were imaged on a synchrotron beam line at Brookhaven National Laboratory using X-ray microcomputed tomography at a voxel size of about 1 µm per cubic voxel edge. The particles ranged in size roughly between 10 µm and 100 µm. The shape and size of individual particles were computationally analyzed using spherical harmonic analysis. The particle shape difference between cements was small but significant, as judged by several different quantitative shape measures, including the particle length, width, and thickness distributions. It was found that the average shape of cement particles was closely correlated with the volume fraction of C₃S (alite) and C₂S (belite) making up the cement powder. It is shown that the non-spherical particle shape of the cements strongly influence laser diffraction results, at least in the sieve size range of 20 µm to 38 µm. Since laser diffraction particle size measurement is being increasingly used by the cement industry, while cement chemistry is always a main factor in cement production, these results could have important implications for how this kind of particle size measurement should be understood and used in the cement industry.     

Hydrothermal synthesis of nano-kaolinite from K-feldspar

Development of sustainable routes for the synthesis of kaolinite in nano-scale (nano-kaolinite) is very significant for producing high quality kaolinite of paper-coating grade in kaolin industry. Duplicating chemical weathering processes in nature, two routes were developed and compared for the synthesis of nano-kaolinite from K-feldspar. Kaolinite of uniform plate-like morphology with thickness of around 14?nm was obtained in this study. Both synthesis routes may lead to the comprehensive utilization of K-feldspar for the synthesis of pure kaolinite for not only high quality paper-coatings but also medical and other uses.     

Structure of coke powder heat-treated with boron

Coal tar pitch-based coke powder with a fine mosaic texture was heat-treated with various concentrations of boron powder at 2900°C. Increasing the boron amount led to smaller d₀₀₂ and larger d₁₁₀, and made the original fine texture coarser. Some small particles showed specific structures of polyhedrons, of which surfaces are 002 planes of graphite lattice, after heat treatment with boron. The size of the polyhedron increased with boron content. Boron concentration was lower at the surface than at the inner portions of particles for a powder heat-treated with a higher amount of boron, while it depended less on the depth for that heat-treated with a lower amount of boron. The formation mechanism of the polyhedron particle is discussed.     

Structure and magnetic properties of Co3O4/SiO2 nanocomposite synthesized using combustion assisted sol-gel method

This paper reports on novel cobalt oxide nanoparticles (NPs) embedded in an amorphous silica (SiO₂) matrix, synthesized using a modified sol-gel method. SEM and TEM images show as-synthesized particles to aggregate in the shape of spheres and less than 5 nm in size, while XRD and SAED analysis both point to well crystallized cubic spinel cobalt oxide phase with an average crystallite size of about 4.6 nm. Raman analysis confirms the formation of cobalt (III) oxide (Co₃O₄) NPs. As-synthesized Co₃O₄ single-nanocrystallite has magnetic properties that correlate with finite size effects and uncompensated surface spins. Temperature dependence of ZFC-FC magnetization curves reveals a sharp peak around 10 K which corresponds to the blocking temperature. A Curie-Weiss behavior of magnetization above 25 K shows lower Néel temperature of the sample compared with its bulk counterpart T_N=40 K (possibly due to crystal defects and nano-dimensionality of the particles). The magnetic measurements exhibit high magnetization at low temperatures (M_S=54.3 emu/g) which can be associated with random canting of the particles’ surface spins and uncompensated spins in the core which tends to interact ferromagnetically at low temperatures. The initial magnetization curve falls out from the hysteresis loop at 5 K, which could be also the effect of surface spins.     

Effect of Calcination Temperature of Kaolin Microspheres on the In situ Synthesis of ZSM-5

ZSM-5 zeolite has been successfully synthesized in-situ on calcined kaolin microspheres by the hydrothermal method using n-butylamine as a template. The supported ZSM-5 was characterized by X-ray diffraction and scanning electron microscopy. The effect of calcination temperature of kaolin microspheres on the in-situ synthesis of ZSM-5 was investigated. The influence of the pretreatment temperature on the properties of kaolin microspheres including phase transformation, amounts of active SiO₂ and Al₂O₃, and pore structures, was studied using fourier transform infrared (FT-IR), nitrogen adsorption and chemical analysis. The results showed that when the calcination temperature increased from 300 to 900 °C, the amount of active SiO₂ in the kaolin microspheres increased slightly and the amount of active Al₂O₃ initially increased rapidly and then decreased steadily. The surface area and pore volume of the kaolin calcined at both low and high temperatures was less than those of kaolin calcined at a medium temperature. The property changes of kaolin caused the relative crystallinity of in situ synthesized ZSM-5 to vary.     

Conversion of wooden structures into porous SiC with shape memory synthesis

Synthesis of structured silicon carbide materials can be accomplished using wooden materials as the carbon source, with various silicon impregnation techniques. We have explored the low cost synthesis of SiC by impregnation of carbon from wood with SiO gas at high temperatures, which largely retains the structure of the starting wood (shape memory synthesis). Suitably structured, porous SiC could prove to be an important type of catalyst support material. Shape memory synthesis (SMS) has earlier been tried on high surface area carbon materials. Here we have made an extensive study of SMS on carbon structures obtained from different types of wood.     

Shape modification of graphite particles by rotational impact blending

To modify particle shape of graphite materials, a rotational impact-blending machine was utilized and the effect of operational conditions was investigated in relation to the size and shape of particles. It was also examined on the specific surface area and the crystal structure of particle surface.As a result, a particle shape index, defined as a ratio of short to long axis of an approximated ellipse by Fourier analysis, got large, whereas the particle size became small a bit, as the peripheral velocity of a rotor and the treatment time increased. The specific surface area more or less increased after treatments, and R value of Raman spectroscopy also increased with the treatment time as the lattice defects grow on the particle surface by surface milling or impact. Then, it temporarily decreased due to the generation of new surfaces with a few defects by volumetric grinding. Finally, two regression analyses were carried out on the relationship between the operational conditions and the particle properties like the diameter and the shape index so as to get proper particles.     

Kaolinite Dehydroxylation Kinetics

The rates of dehydroxylation of three kaolinites which varied in particle thickness were studied from 417° to 480°C under very low water vapor partial pressures. The dehydroxylation rate was directly proportional to the surface area and had an activation enthalpy of 41.0 kcal/mol. The data did not fit either a diffusion-controlled or a phase-boundary-controlled reaction in the radial direction, even when the particle diameter distribution was taken into account. The reaction appears to proceed through the kaolin particles by a pseudo-phase-boundary-controlled mechanism, principally in the [001] direction.     

Comparison of surface properties of carbons gasified in nitrous oxide and in oxygen

Surface structures and reactivities of carbons gasified in N₂O and in O₂ are compared in this study. The carbon employed was derived from pyrolysis of phenol-formaldehyde resins. It was found that greater surface area and pore volume are created for the carbon gasified in O₂ than that in N₂O. At high extents of burn-off the carbon gasified in N₂O shows a larger mesopore volume than that in O₂. The reactivity per unit surface area of the carbon in N₂O decreases with the extent of burn-off, while that in O₂ remains relatively constant at various extents of burn-off. Surfaces in carbon micropores do not appear to be fully utilized in the N₂O-carbon reaction. It is confirmed that standard N₂ or CO₂ surface area is not a proper characterization of the reactive surface area of carbon gasified in N₂O.     

碳酸钙形态结构对增塑糊黏度的影响

研究形态结构不同的碳酸钙对PVC增塑糊黏度及稳定性能的影响.结果表明:增塑糊的黏度与碳酸钙吸油量不呈现简单的线性关系,还与颗粒粒径分布、比表面积以及颗粒形态相关.当碳酸钙粒径大小及分布存在显著差异时,其颗粒大小及分布成为决定增塑糊黏度的主要因素.     

Flooding and floating in latex paint

Flooding and floating are problems in many paint applications. If pigment concentration is uniform on the surface but not through the thickness of the film, one refers to ‘flooding’ (horizontal separation). If, however, concentration differences are visible across the surface of the paint film, one refers to ‘floating’ (vertical separation). In this article, the influence of pigment, filler, additives, and processing conditions on the flooding and floating of colored latex paint were investigated. It was discovered that too broad a distribution of pigment and filler particle size can lead to flooding and floating. Different levels of pigment (TiO₂) or filler (kaolin) loading cause diverse degrees of flooding and floating. Waterborne coatings that do not exhibit flooding or floating may show these conditions when diluted. Using dispersants or thickeners with hydrophobic constituents, increasing viscosity, reducing surface tension, etc., all help to prevent or reduce flooding and floating. Comparison tests revealed little influence of processing conditions on flooding or floating.     

Physical structure and combustion properties of super fine pulverized coal particle

Physical structures and combustion properties of super fine pulverized coal particles of eight Chinese coals, Heshan subbituminous coals and Jincheng lean coals from two areas of China, have been investigated using accelerated surface area and porosimetry, thermobalance (TGA), and Fourier transform infrared spectrometer. Results showed that the particle specific surface area and pore volume increased greatly when the coal particle size was reduced. The higher the carbon content on a dry ash-free basis is, the larger the particle specific surface area and pore volume are. When the coal particle size decreases, the combustion process can be largely improved, ignition temperature is reduced, and SO₂ emission from coal combustion is also lower.     

The electrocatalytic behavior of Ru0.8Co0.2O2−x—the effect of particle shape and surface composition

The electrocatalytic activity of Ru_0.8Co_0.2O_2−x nanocrystals was studied using diffraction, microscopic and spectroscopic techniques to elucidate the role of particle shape and surface chemical composition in the electrocatalytic evolution of oxygen and chlorine. The prepared Ru_0.8Co_0.2O_2−x samples are of the rutile structure, their chemical composition, however, differs. The samples with the smallest particle size compensate for the Co doping by oxygen deficiency. The materials featuring bigger particle size show tendency to compensate for the presence of cobalt by higher valency of Ru. Regardless of the particle size or actual surface composition of the Ru_0.8Co_0.2O_2−x electrodes, the chlorine evolution precedes that of oxygen by ca. 100 mV. The Ru_0.8Co_0.2O_2−x electrodes retain high affinity to oxygen evolution once the reaction becomes possible. This behavior can be ascribed to a stabilization of the six-valent ruthenium, which represents the major intermediate for the oxygen evolution process, at the electrode surface due to the presence of di-valent and tri-valent cobalt. This effect precludes the possible effects of the particle shape and crystal edge distribution.     

Enhanced machinability of SiCp/Al composites with laser-induced oxidation assisted milling

In this study, an innovative machining process called laser-induced oxidation assisted milling (LOM) is proposed. A polycrystalline diamond (PCD) cutting tool is applied to machine 55% SiC_p/Al composites. The laser-induced oxidation mechanism is investigated. Under the condition of average laser power of 10 W, laser scanning pitch of 15 μm, laser scanning speed of 6 mm/s and oxygen-rich atmosphere, the effect of laser-induced oxidation is optimal. A loose oxide layer and a sub-layer with the hardness of 160 ± 40 HV are generated where the composition of the oxide layer is mullite (2Al₂O₃·SiO₂). Comparative investigation on the cutting force, surface quality and tool wear are performed. Compared with the conventional milling (CM), the normal force and thrust force of LOM decrease by 39% and 55%, respectively. The reduction of cutting forces is attributed to thermal failure of the interface layer. The dominant surface defects of the machined surface are particle fracture, particle pull-out, matrix tearing and matrix coating. Among the investigated parameters, the minimum surface roughness S_a is 0.37 μm when the feed per tooth and the cutting depth are 0.005 mm/z and 0.2 mm, respectively. The dominant tool wear modes of LOM include diamond spalling and edge chipping. The tool wear modes of CM are diamond spalling, edge chipping, abrasive wear, and adhesive wear. LOM can prolong the tool life and achieve better surface quality under the same cutting length.     

Technical properties of compounded kaolin sample from Griva (Macedonia, Greece)

The purpose of this paper is to establish the possible industrial applications of Griva kaolin. This kaolin comes from the alteration of gabbroic rocks from the Griva area, Macedonia, Greece. Mineralogically, the kaolin is composed mainly of kaolinite associated with vermiculite and plagioclases, and traces of quartz, amphiboles, halloysite and smectites. The kaolin grain-size analysis shows that the kaolin is mostly finer than <20 μm with 20% of <2 μm. The amounts of Fe, Mg and Ca for the < 20 μm fraction are higher than those of standard commercial kaolins. The kaolinite is disordered with low crystallinity. Kaolinite crystals do not present typical pseudohexagonal stackings, showing irregular morphology, and vermicular aggregates booklets. The Brookfield viscosity of about 450 cp (at 70% solids 12 rpm), the high brightness (83% on < 20 μm fraction) and the dispersability in water suspensions would favour its use as filler in the paper and paint industries. However, the low crystallinity kaolinite precludes its use as filler in rubber industry. The kaolin shows a liquid limit of about 48% and a plastic limit of 34%. The firing characteristics indicate its possible use as a ceramic raw material for stoneware and sanitary ware products.     

Engineered clay products for the paper industry

The need for kaolin pigments by the paper industry with controlled optical and physical properties have significantly changed the type of filler and coating clays available to the paper industry. Processing equipment now used in the production of kaolin products is much more sophisticated and controllable than in the past. Better understanding of the mineralogy and the physical and chemical properties of kaolins, in addition to improved processing techniques, has allowed the kaolin processors to produce engineered or tailored grades that meet particular needs of the user. Particle size and shape, brightness, gloss, opacity, and viscosity can be altered and controlled to meet specific requirements of the paper coater. Examples of several types of engineered products available for use by the paper industry are discussed.     

Electrophoretic deposition of TiO2 nanoparticles in viscous alcoholic media

In the present study, highly viscous alcoholic media, pentanol, hexanol and heptanol were used for electrophoretic deposition of ceramic (TiO₂) nanoparticles as a new approach in the EPD process. Optical and scanning electron microscopy of the obtained deposits at 50 V revealed that layers with a fairly uniform microstructure were obtained in pentanol and hexanol while the layer formed in heptanol suffered from lack of uniformity and did not cover the substrate even at higher voltages up to 200 V. It was also revealed by the atomic force microscope (AFM) studies that surface roughness of the deposited layers decreased with increasing suspension viscosity. This behavior was directly attributed to high viscosity of heptanol which strongly hinders particles movement through the media. The low dielectric constant of heptanol was also considered to decrease particle deposition.     

Formation enthalpy and magnetic properties of Bi-YIG powders

The formation enthalpy and magnetic properties of bismuth-doped yttrium iron garnet powders were investigated. The formation enthalpy and the crystallization temperature both decreased with increasing bismuth substitution for Bi_xY_3−xFe₅O₁₂ (0.25 ≦ x ≦ 1.25) powders prepared by the coprecipitation process. Bi substitution for Y can significantly reduce crystallization temperature for bismuth-doped yttrium iron garnet powders, and the magnetic properties (saturation magnetization, remanence, and coercive force) are independent of Bi substitution amounts. The average particle size has been determined by the specific surface area. As Bi substitution for Y increased, the average particle size also increased, while the specific surface area decreased.     

Properties of NiFe2O4 ceramics from powders obtained by auto-combustion synthesis with different fuels

Nickel ferrite (NiFe₂O₄) powders derived by auto-combustion synthesis using three different fuels (citric acid, glycine and dl-alanine) have been characterized. The sintering behavior of ceramics using these powders has been compared. Oxygen balance (OB) setting for the chemical reaction is found to regulate the combustion reaction rate. A rapid reaction rate and a high flame temperature are achieved with dl alanine fuel yielding single phase NiFe₂O₄ powder in the as-burnt stage, whereas powders derived with citric acid and glycine fuels show poor crystallinity and necessitate post-annealing. The powder particles are largely agglomerated with a non-uniform distribution in shape and size, and the average particle size is estimated in the range ~ 54–71 nm. Powders derived from dl-alanine fuel show better phase purity, smaller crystallite size, larger surface area and superior sintering behavior. Additional Raman modes discerned for dl-alanine derived powder support a 1:1 ordering of Ni²⁺ and Fe³⁺ at the octahedral sites relating to microscopic tetragonal P4₁22 symmetry expected theoretically for the formation of NiFe₂O₄ with inverse spinel structure. Microstructure of sintered ceramics depends on the precursor powders that are used and sintering at 1200 °C is found to be optimum. Citric acid and glycine derived powders yield high saturation magnetization (M_s~47–49 emu/g), but poor dielectric properties, whereas dl-alanine derived powders yield ceramics with high resistivity (~3.4×10⁸ Ω cm), low dielectric loss (tan δ~0.003 at 1 MHz) and high magnetization (46 emu/g). Dielectric dispersion and impedance analysis show good correlation with the changes in the ceramic microstructure.