Aluminum Trihydroxide Research Articles

The assembly of rotaxane-like dye/cyclodextrin/surface complexes on aluminium trihydroxide or goethite

Simple azo-dyes carrying phosphonic acid and arsonic acid substituents such as 4-(4-hydroxyphenyl azo)phenylphosphonic acid (5) and 4-(4-hydroxyphenylazo)phenylarsonic acid (6) bind more strongly to high surface area oxides such as aluminium trihydroxide and goethite than their carboxylic and sulfonic acid analogues and the phosphonate-functionalized dyes have been shown to have greater humidity fastness when printed onto commercial alumina-coated papers. Adsorption isotherm measurements provide evidence for the formation of ternary dye/cyclodextrin/surface complexes. Dyes which form such ternary complexes show higher light fastness when printed onto alumina coated papers in an ink formulation containing alpha-cyclodextrin.

Effects of Manufacturing Processes on Hydration Ability of High Purity .ALPHA.-Al2O3 Powders

Commercial sub-micron high purity α-Al2O3 powders ground and not ground in the manufacturing process, produced by three different processes; in-situ chemical vapor deposition (A1, A2 and A3), hydrolysis of aluminum alkoxide (B1, B2 and B2) and thermal decomposition of ammonium alum (C1 and C2) methods, were thermally hydrated and the effects evaluated by DRIFT spectroscopy in dry air atmosphere. The hydration process was conducted by placing all powders, without contact with water, in a modified pressure cooker heated inside an oven at 100°C under water saturated pressure. The surface of powders ground in the manufacturing process was easily hydrated by the hydrothermal treatment and aluminum trihydroxide peaks were observed on the DRIFT spectra. The results demonstrate that grinding in the manufacturing process affects the hydration ability of high purity α-Al2O3 powder surfaces.

A one-pot synthesis of hybrid organo-layered double hydroxide catalyst precursors

Organo-layered double hydroxides (LDHs) have attracted much attention recently for their utility as solid base catalysts, providing an environmentally friendly heterogeneous phase alternative to conventional stoichiometric liquid bases. Here we describe a synthetic approach for the production of layered double hydroxides containing organic (acetate) anions by a method that requires no excess of base, filtering or washing of the product. A mixture of a slurry of aluminium trihydroxide (or its thermally treated form), magnesium oxide, and magnesium acetate are reacted under atmospheric or autogenous conditions to prepare MgAl-acetate LDHs of general formula Mg1−xAlx(OH)2(CH3CO2)x·yH2O. Using this synthetic procedure it has been found that MgAl-acetate LDHs with either a full or partial acetate loading may be prepared for a range of Mg/Al stoichiometries. The LDHs formed have been characterised by X-ray diffraction, infra-red spectroscopy, solid state nmr and thermal methods. Depending on the synthesis method, the acetate LDHs had an interlayer spacing of between ca. 8.4 and 14.8 A indicating the formation of monolayers and bilayers of acetate anions, respectively, in the LDH host.

Mechanism and Kinetics of Aluminum Nitride Powder Degradation in Moist Air

Aluminum nitride (AlN) powders manufactured via three major commercial processes, namely, chemical vapor deposition from triethyl aluminum, carbothermal reduction and nitridation of alumina, and direct nitridation of aluminum, were exposed to moist air at room temperature to investigate the degradation mechanism and kinetics. In the degradation, the powders were initially hydrolyzed to amorphous aluminum oxyhydroxide, which subsequently transformed into mixtures of crystallized aluminum trihydroxide (Al(OH)3) polymorphs, i.e., bayerite, nordstrandite, and gibbsite, forming agglomerates around the unreacted AlN. The data were fitted by using the unreacted‐core model. Three stages were found in the degradation: the stage of an induction period at the beginning, followed by a stage of fast hydrolysis with the chemical reaction being rate controlling, and finally, with gradual closing of pores in the structure of Al(OH)3 around AlN, changing to a stage of slow hydrolysis that was controlled by mass diffusion through Al(OH)3. The existence of an induction period was attributed to slow hydrolysis of the surface oxide/oxyhydroxide layer. The powder produced by the carbothermal process showed the longest induction period, which was attributed to its surface structure being different from other powders.

Experimental investigation of related properties of asphalt binders containing various flame retardants

The improved flame retardancy of asphalt binders containing various kinds of flame retardants including antimony trioxide, decabromodiphenyl ether (EBPED), aluminium trihydroxide (ATH) and zinc borate (ZB) under different additive concentrations was investigated by limited oxygen index (LOI) and differential scanning calorimetry (DSC) test. To assess the effects of the type and concentration of the flame retardants on rheological properties of asphalt binders, the softening point, penetration, ductility, storage stability and viscosity were tested. The thin film oven test (TFOT) was used to investigate the effect of short-term oxidation on flame-resistant asphalt binders. Experimental results indicated that all of selected flame retardants had a relatively small effect of rheological properties of the asphalt binders, but a great effect on flame retardancy. Asphalt binder with LOI of 25.9 was obtained by adding 6 wt% mixed flame retardants of EBPED: antimony trioxide: ZB=3:1:1 by mass. Asphalt binder was transformed from inflammable materials into flame retardant materials. Therefore, the asphalt binder with both good flame retardancy and rheological properties is a novel road functional material to meet two respects' demands as flame retardant materials and road materials at the same time.

Monomer recovery from aluminium hydroxide high filled poly(methyl methacrylate) in a fluidized bed reactor

The yield of methyl methacrylate (MMA) was optimized by pyrolysis of aluminium tri-hydroxide (ATH) filled poly(methyl methacrylate) (PMMA), because an introducing experiment at a laboratory plant led to a yield of just 53% of methyl methacrylate at a temperature of 450 °C instead of more than 90% feeding pure PMMA. Additional experiments with pyrolysis–GC–MS (Py–GC–MS) have shown that the reduction of the temperature to 400 °C increases the yield significantly up to 75%. Further reduction of temperature led to an incomplete decomposition of the polymer. Reduced feed rate of PMMA to the half of the introducing experiment led also to a higher yield of MMA of 69%, while reduced gas residence time in the reactor had just a small effect. A final experiment at a temperature of 400 °C and the half feed rate of PMMA increased the MMA-yield to 80%. The most of ATH was converted into aluminium oxide and water. Water leads to a partial saponification of MMA producing methacrylic acid (2–11 wt% of organic products) and methanol (2–9 wt%). The part of gas (2–8 wt%) was higher than from the pyrolysis of other PMMA materials. The main components of the gas were carbon oxides.

Structural Refinement of the High‐Pressure Phase of Aluminum Trihydroxide: In situ High‐Pressure Angle Dispersive Synchrotron X‐Ray Diffraction and Theoretical Studies.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ammonium polyphosphate–aluminum trihydroxide antagonism in fire retarded butadiene–styrene block copolymer

In this paper the effect of aluminum trihydroxide (Al(OH) 3—ATH) on the surface protection from fire for a styrene butadiene rubber (SBR) provided by ammonium polyphosphate ([NH 4PO 3] n —APP) is studied. The combustion behaviour is studied by means of Cone Calorimetric tests: a maximum fire retardant effect is observed with 10–12 wt.% of APP. ATH, less effective as fire retardant, has been added at 60 wt.% to reach comparable results as measured by cone calorimetry for 12 wt.% APP. Replacement of ATH in the best performing SBR + 12 wt.% of APP shows an antagonistic effect with as little as 1 wt.% of ATH. The combustion behaviour is explained with the mechanism of interaction between SBR, APP and ATH, in which formation of aluminum phosphates negatively affects the surface protection provided by the ultraphosphate surface coating formed on heating APP in SBR.

Structural Refinement of the High-Pressure Phase of Aluminum Trihydroxide: In-Situ High-Pressure Angle Dispersive Synchrotron X-ray Diffraction and Theoretical Studies

In-situ high-pressure synchrotron angle-dispersive X-ray diffraction for gibbsite (aluminum trihydroxide) was performed at room temperature up to 20 GPa. A pressure-induced phase transition was observed at 2.6 GPa. The new high-pressure phase can be recovered at ambient pressure. Rietveld refinement shows that the new phase of Al(OH)(3) has an orthorhombic structure, spacegroup Pbca, and the lattice parameters at ambient condition are a = 868.57(5) pm, b = 505.21(4) pm, c = 949.54(6) pm, V = 416.67(6) x 10(6) pm(3) with Z = 8. The compressibility of gibbsite and the high-pressure polymorph was analyzed, and their bulk moduli were estimated as 49.8 +/- 1.8 and 81.0 +/- 5.2 GPa, respectively. First-principles calculations of the high-pressure phase were performed to determine the hydrogen positions and to confirm the structural stability of the new phase.

Some of the properties of flame retardant medium density fiberboard made from rubberwood and recycled containers containing aluminum trihydroxide

The flame retardancy of medium density fiberboard (MDF) made from mixture of rubberwood fibers and recycled old corrugated containers was studied. Aluminum trihydroxide (ATH) was used as a fire retardant additive and mixed with the fibers to manufacture experimental MDF panels using wet process. Phenol formaldehyde (PF) resin in liquid, 2% based on oven dry weight of fibers, was used along with 0%, 10%, 15% and 20% of ATH. The flame retardant test was done using the limiting oxygen index (LOI) test. The other properties investigated include internal bond strength, thickness swelling and water absorption. The results showed that ATH loading increased as the LOI of MDF increased. This demonstrated that ATH could improved the fire retardant property of MDF at sufficient loading. An increase in concentration of ATH showed an increase in the IB values of MDF made without resin. MDF panels made without resin showed a progressive increase in internal bond as the composition of recycled old corrugated containers fiber increased. Addition of resin improved internal bond strength and reduced thickness swelling, and water absorption. Thickness swelling of panel increased as the composition of recycled old corrugated containers fiber increased. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) showed that there is indication of ATH and resin filling the void space in between fibers.

Properties of polypropylene/aluminum trihydroxide composites containing nanosized organoclay

Montmorillonite is a promising substitute for aluminum trihydroxide in flame-retardant polypropylene/aluminum trihydroxide (PP/ATH) composites. Study was made of the partial substitution of organoclay for ATH in PP/ATH composites. The total concentration of filler was kept at 30 wt%. The composites were compatibilized with two types of compatibilizer: commercial maleic anhydride functionalized polypropylene (PP-g-MA) and hydroxyl-functionalized polypropylene (PP-co-OH) prepared with metallocene catalyst. The effect of compatibilization on the morphology was studied by the transmission electron microscopy and the scanning electron microscopy. Mechanical properties were characterized by tensile and impact measurements, and flammability properties with a cone calorimeter. Addition of compatibilizer and stearic acid (SA) treatment of the ATH particles contributed to the dispersion of the fillers. Both compatibilizers produced organoclay with exfoliated structure and improved adhesion between the fillers and the matrix. Toughness improved and decomposition and flammability were reduced. POLYM. ENG. SCI. 45:1568–1575, 2005. © 2005 Society of Plastics Engineers

클로로프렌 고무의 난연성 및 내방사선 특성 향상

This study has investigated radiation degradation of chloroprene rubber in the presence of some fire retardant. Ammonium polyphosphate, aluminium trihydroxide, magnesium hydroxide, calcium carbonate and antimony trioxide were selected as flame retardant. Samples were irradiated using a Co<TEX>$^{60}$</TEX> <TEX>${\gamma}$</TEX> -ray and ray up to 2000 kGy at a dose rate of 5 kGy/hr in the presence of air atmosphere at room temperature. After irradiation, samples were assessed fire retardancy with electrical properties and mechanical properties. Some considerations concerning the effects of the fire retardants added to chloroprene rubber on the radiation and thermal stability of chloroprene rubber are presented. From fire retardancy with electrical and mechanical property measurements, it was found that addition of magnesium hydroxide resulted in maximum fire retardant effect.

Thermal Properties and Flammability of Ethylene-Vinyl Acetate Copolymer/Montmorillonite/Polyethylene Nanocomposites with Flame Retardants

Ethylene-vinyl acetate copolymer (EVA)/montmorillonite (MMT) composite was blended with a linear low density polyethylene (LLDPE). X-ray diffraction and transmission electron microscopy (TEM) image of the EVA/MMT composite are in support of an intercalated with partially delaminated nanocomposite. The tensile strength of the nanocomposite is about 20% higher than that without layered silicates, MMT. Furthermore, the incorporation of MMT into polymer blend delays the main thermo-oxidative degradation. Cone calorimeter test points out that the addition of layered silicates into the pristine EVA/LLDPE blend or the blend with a low smoke non-halogen (LSNH) fire retardants, aluminum trihydroxide, and antimony trioxide, can reduce the maximum heat release rate by 30–40%. The smoke suppressing effect of layered silicates is only observed in the nanocomposite containing flame retardants. According to the limiting oxygen index (LOI) data and cone calorimeter test, the addition of the nanodispersed layered silicate and LSNH flame retardants to the EVA/LLDPE exhibits a synergistic effect on the flame retardancy and smoke suppression.

Thermal decomposition of precipitated fine aluminium trihydroxide

Fine (1.5 μm) aluminium trihydroxide (ATH), prepared from Bayer liquor, was subjected to dehydration at various temperatures up to 1400°C. The fine ATH was found to be gibbsitic in nature. XRD data indicated the formation of various transitional phases before becoming a stable α‐Al2O3 phase. Boehmite phase formation, that is unlikely at such a fine particle level, started at around 250°C and completed its transformation at 400°C. Formation of boehmite phase was also observed with 0.25 and 1 μm sized particles. Beyond 400°C, various transitional phases were formed. At 500°C, chi‐alumina formation was found; kappa‐alumina phase transformation started at 900°C and completed at 1000°C. Coarser particles (∼100 μm) also followed the similar trend. In the case of coarse ATH, α‐Al2O3 transformation was found at around 1200°C, whereas for fine particles, α‐Al2O3 transformation temperature was found to be 1400°C. FTIR spectra showed the presence of molecular water and Al–O bonds in gibbsitic material. Characteristic vibrations at 3098, 2099 and 1070 cm−1 were found for boehmite particles at 400°C. Lattice parameters and hkl values were calculated and reported. Determination of crystallite size, cell volume, number of atoms/unit cell and number of unit cell/crystallite were also undertaken and reported.

Atomic force microscopy study of the growth mechanism of gibbsite crystals

A combination of atomic force microscopy (AFM) and scanning electron microscopy (SEM) has been used to investigate the crystal growth mechanism of gibbsite (aluminium trihydroxide) in pure solutions. Under the conditions studied, the growth on the basal face of synthetic gibbsite prepared from sodium aluminate solution proceeds by a continuous birth and spread mechanism. The nuclei formed on the surface of the basal face of gibbsite grow both laterally and vertically, with lateral growth being much faster than vertical growth. Moreover, a remarkable cyclical, smooth→rough→smooth→rough process has been directly observed. The effect of alkali ions on the crystal growth of gibbsite has been investigated. Curved features and a growth hillock were observed for the first time on the basal face of gibbsite prepared from potassium aluminate solution; whereas, steps terminating within the plane and hexagonal shaped features tilted at an angle and related to the symmetry of the face were imaged on the basal faces of gibbsite prepared from sodium aluminate solution. The results suggest faster growth on the basal face of gibbsite prepared from potassium aluminate compared to that prepared from sodium aluminate, leading to the observed elongated morphology.

Study on the effect of humate and its removal on the precipitation of aluminium trihydroxide from the Bayer process

A process to remove humate from Bayer spent liquor using polymers of diallyldimethyl ammonium chloride (polyDADMAC) has been developed. Using a UV–visible spectrometric technique, the concentration of humate in spent liquors obtained from an alumina refinery was found to be 5 ± 1 g/l. The humate removal process is based on its selective reaction with polyDADMAC, which can be added at 1:1 weight ratio (with respect to the humate content) to effectively remove humate from the spent liquors. The process involves, first the reaction between polyDADMAC and humate. Next, acidification to convert humate to humic acid in carried out, which follows by an esterification step using tertiary butanol. The ester formed is then causticized at pH 9 to be recovered to humate and butanol. Results from precipitation test showed that an increase in humate concentration does not adversely affect the yield of the precipitated aluminium trihydroxide (Al 2O 3 · 3H 2O) product. However the presence of humate during precipitation causes a decrease in the average particle size of the final precipitate product. The particle size range most affected was found to be 20–80 μm, after 48 h precipitation using seeds of average size of 73.6 μm. By removing humate from the spent liquors, the whiteness of the aluminium trihydroxide for specialty alumina could also be improved.

Microwave assisted solid state reaction synthesis of MgAl 2O 4 spinel powders

Stoichiometric MgAl 2O 4 spinel powders were synthesized by microwave assisted solid-state reaction (MWSSR powders) in a domestic microwave (MW) oven (2.45 GHz frequency, 700 W power) from aluminum tri-hydroxide and caustic MgO in the presence of carbon black (10–50 wt.% with respect to total raw mix). 20% C was found to be sufficient to produce spinel powder with 82% spinel content within 100 min while 50% C was able to produce 93% spinel containing powder within the same time. In conventional solid-state reaction (CSSR), in order to obtain the powder with the same amount of spinel phase (i.e., ∼93%), the above raw mix was calcined at 1350 °C for 1 h and the total heating and cooling cycle time was more than 24 h. For the purpose of better comparison, three other stoichiometric MgAl 2O 4 powders were also prepared following conventional combustion synthesis using urea (CUCS powder) or sucrose (CSCS powder) as a fuel, and microwave assisted combustion synthesis using urea as a fuel (MWUCS powder), respectively. Effects of synthesis route on the powder properties were assessed by means of XRD, SEM, BET surface area, and particle size analysis. Among the various powders studied, the MWSSR powder was found to be superior as far as saving in processing time and power is concerned in addition to good sintering characteristics in terms of bulk density (B.D), apparent porosity (A.P) and water absorption (W.A).

An investigation into the decomposition and burning behaviour of Ethylene-vinyl acetate copolymer nanocomposite materials

Ethylene-vinyl acetate copolymer (EVA) is a widely used material, particularly as a zero-halogen material in the cable industry. It is frequently formulated with large quantities of inorganic filler material, such as aluminium trihydroxide (ATH). Used alone, EVA is known to form a protective layer which can inhibit combustion under well ventilated conditions, though this effect is not observed when used in formulations with ATH. The incorporation of nanoscale clay fillers into EVA appears to reinforce the protective layer. The stages of the decomposition under different conditions is described both for the 10 mg (TGA) and 200 mg (small tube furnace) scales. The latter allows the residues formed to be subjected to further analysis, to elucidate the mechanism of the reduction of decomposition and flammability. Enhancements in the thermo-oxidative stability of the EVA clay material were evident from both tube furnace and TGA experiments. The polymer-organoclay materials, prepared on a two-roll mill, showed poor dispersion when studied by SEM, suggesting that a significant portion was present as a microcomposite. However, when the char was analysed by SEM, layers of protective material were clearly evident on the char surface. From XRD spectra, there was no evidence of order within the polymer-organoclay, but ordering of the outer layer of char was demonstrated. This suggests that for EVA, which melts before burning, organoclay layers become nanodisperse at the surface of the burning polymer. These materials have also been studied in the Purser furnace, designed to replicate the conditions found in fully developed fires. This allows effluent yields, such as O 2, CO 2 and CO to be determined as a function of fire condition, by controlling the rate of burning and the ventilation rate. The effect of both the nanofillers and the protective layers are reported and discussed, under different ventilation conditions. Specifically, the relationship between equivalence ratio and hydrocarbon and carbon monoxide yield is focussed upon.

Preparation and Characterization of Bayerite Samples: Use of Diffuse Reflectance Infrared Spectroscopy to Monitor Purification

We show here how bayerite, a polymorphic form of aluminum trihydroxides, can be synthesized and characterized by simple spectroscopic methods. Purification of the product by washing with water can be monitored by diffuse reflectance infrared spectra. A product with extremely high purity is obtained after repeated washings.

Characterization of the aluminum hydroxide microcrystals formed in some alcohol–water solutions

The crystallization in water of non-crystalline Al(OH) 3 to form somatoids of aluminum trihydroxide bayerite is altered into other aluminum hydroxides when certain water-soluble alcohols are added. The crystalline and non-crystalline phases formed under the different environments were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray elemental microanalysis by using EDS/TEM and scanning electron microscopy (SEM). Ethylene glycol leads to nordstrandite and fibrillar pseudoboehmite. Methanol produces gibbsite and fibrillar pseudoboehmite. Ethanol has different effects according to its concentration: 20% produces bayerite+nordstrandite+fibrillarpseudoboehmite, 50% yields gibbsite+bayerite+pseudoboehmite, but 94% yields only fibrillar pseudoboehmite. Glycerol leads only to fibrillar pseudoboehmite. Isopropyl alcohol produces bayerite and nordstrandite. The presence of pseudoboehmite in the several systems suggests that the monohydroxide acts as an intermediate in the crystallization of the aluminum trihydroxides during aging in those alcohol–water solutions.