Swelling Behaviour of Cured Urea–Formaldehyde Resin Adhesives with Different Formaldehyde to Urea Mole Ratios

As a part of understanding of the network structure of urea–formaldehyde (UF) resin adhesives, this study examined the swelling behaviour of cured UF resin adhesives with four different formaldehyde–urea (F/U) mole ratios, using Flory–Rehner thermodynamic theory and field emission-scanning electron microscopy (FE-SEM) to relate the swelling behaviour to consequently induce micromorphological changes. Cured UF resin films before and after acetone extraction were exposed to swelling in dimethyl sulphoxide at three different temperatures. For the first time, this study reported the experimentally determined swelling parameters, such as sol fraction (ω_sol), polymer volume fraction (φ_p), polymer–solvent interaction parameter (χ), and the number average molecular weight between cross-links (M_c), for cured UF resin adhesives. Both ω_sol and M_c decreased as the F/U mole ratio increased. But these values increased with an increase in the swelling temperature. The extraction resulted in negative ω_sol values, suggesting the removal of a scattered distribution of ω_sol in the cured UF resins. The micromorphology helped to explain the differences in the molecular integrity of the resins, indicating a close relationship between the swelling behaviour and the morphological changes after the swelling.     

Urea–formaldehyde resin prepared with concentrated formaldehyde

The characteristics of UF resin prepared with concentrated formaldehyde were studied in this paper. With the molar ratio F/U = 1.1, the UF resin prepared with concentrated formaldehyde showed better mechanical properties than that with formalin. The ¹³C-NMR and FTIR results indicated that there were more methylene groups, ether groups and urons in a UF resin system prepared with concentrated formaldehyde than those in a normal UF resin. The differential scanning calorimetry and DMA results showed that the curing temperature of UF resin with concentrated formaldehyde was lower than that of a normal UF resin. UF resin with concentrated formaldehyde showed worse thermal stability and higher thermal decomposition temperature.     

Poly(Urethane–Urea) Varnishes Containing Tributyltin Groups

New poly(urethane–urea) varnishes containing tributyltin groups were prepared by the reaction of dibenzyldiisocyanate in excess with a macrodiol (PEGA-2000), trimethylolpropane, diethylene glycol and a bisalcohol maleimide monomer containing tributyltin carboxylate group. Tributyltin maleimide monomers were obtained from 4-{3,4-bis[(2-hydroxyethyl)sulfanyl]-2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl}benzoic acid and bis(tributyltin) oxide. Structure of monomers and polymers was confirmed by the IR, NMR spectroscopy and elemental analysis. The polymer films were characterized by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), X-ray diffractions, thermogravimetric (TGA) and stress–strain measurements.     

Phase Equilibria in the Sections of the Ca(NO3)2–CO(NH2)2–H2O System and Deicing Properties of Nitrate–Urea Mixtures

Theoretical Foundations of Chemical Engineering - Phase equilibria in the sections of the Ca(NO3)2–CO(NH2)2–H2O system and the deicing properties of calcium nitrate and carbamide...     

Urea Manufacturers Enjoyed Good Result

PetroChina is the largest ureamanufacturing company inChina, with a capacity of 3.6million t/a, accounting for8.5% in the total. SinopecCorp. followed with 2.6 mil-lion t/a. But here CCR is dis-cussing the 2004 operatingresults of those urea manu-facturers who are listed in     

Urea Price Faced with Temporary Containment

Reporter:The relevant departments ofChinese government have recentlymade a decision that to ensure the needof fertilizers for spring plough,an ex-port tariff of RMB260 per ton will beimposed on the urea export for 3months starting from Jan.1,2005 as a     

Bond Strength–Disbonding Behavior and Dimensional Stability of Walnut and Poplar Impregnated with Some Chemicals and Bonded with PVAc,VTKA and Urea Formaldehyde

The aim of this study, is to describe the effects of adhesives (PVAc-Desmodur VTKA and Urea formaldehyde) on wooden materials (walnut and poplar) cut tangentially and radially impregnated with Protim Solignum, CCA and Celcure AC 500 and exposed to: humid–water–heat resistance; heating; and cooling tests. All these tests show a decreased in bonding strength. The conclusion is that poplar wood cut tangentially and impregnated with CCA, bonded with D-VTKA adhesive can be used as a material in damp conditions where good bond strength is required.     

Chitianhua Corporation:Benefited from Urea Price Rise

In 2004 Guizhou Chitianhua Corporation(600227)accomplished a main-businessrevenue of RMB732 million,an increaseof 24% over the previous year,a net profitof RMB106 million and a per-share earn-ing of RMB0.62,an increase of 48%.     

Effect of pH on the Catalytic Properties of Mo–V–Te–P–O Catalysts for Selective Oxidation of Isobutane

Mo–V–Te–P mixed oxide catalysts, prepared by a dry-up method at various pHs (in the range of about 1.0–9.0), have been tested in the partial oxidation of isobutane. The best catalytic performance was achieved over a catalyst prepared at a pH about 7.0. In this case, high selectivity to methacrolein (37.0%) at an isobutane conversion of 12.7% has been obtained at 380 °C. The surface V⁴⁺/V⁵⁺ ratios of the calcined samples were strongly influenced by the pH in the synthesized solution, which is one of the key factors in the catalytic performance for selective oxidation of isobutane.     

Properties of MgO–Fe–C refractories as linings of vanadium-extraction converter

For the purpose to extend the service life of MgO–C bricks used as linings of vanadium-extraction converters, MgO–Fe–C bricks with different carbon content were designed and the properties of this novel refractory were investigated by comparing to the traditional MgO–C bricks. The results showed that the poor service life of MgO–C bricks was due to the poor sinterability of the oxidized layer at 1400 °C, whereas the oxidized layer of MgO–Fe–C brick was well sintered due to the oxidation of Fe particles in the oxidized layer and formation of MgO–FeO_ss in air atmosphere. Excellent oxidation resistance and corrosion resistance against vanadium containing slag were also obtained due to the increase of compactness of oxidized layer and concentration of FeO in the oxidized layer compared to MgO–C bricks, and it is considered that MgO–Fe–C brick is a favorable substitute of MgO–C refractory to be used as linings of vanadium-extraction converters.     

Electrical transport properties of Co–Zn–Y–Fe–O system

Co–Zn substituted nanoferrites having stoichiometric composition Co_1?xZn_xY_0.15Fe_1.85O₄ (x = 0.0–1.0, step: 0.2) were synthesized by chemical co-precipitation method. Analysis of the XRD patterns confirms the formation of cubic spinel phase as main phase along with few traces of secondary phase. The lattice constant was found to increase from 8.378 Å to 8.438 Å with zinc contents which can be explained on the basis of difference in ionic radii. SEM micrographs indicate nearly uniform distribution of grains. The average crystal size was found to decrease from 38.41 nm to 14.25 nm with the increase of Zn contents. The physical density increases with the increase of Zn contents from 3.95 g/cm³ to 4.42 g/cm³. It was found that the resistivity decreases with the increase of Zn contents from 9.20 × 10⁷ Ω cm to 5.26 × 10⁶ Ω cm which may be attributed to the increase in the number of Fe²⁺/Fe³⁺ ions pairs at B-sites. The transition temperature of the samples with substitution level x = 0.6, 0.8, 1.0 changes at 373, 333 and 313 K, respectively. The transition temperature of the sample with x = 1.0 is close to the room temperature. This may be the Curie temperature. Low Curie temperature material can be used for the preparation of temperature sensitive ferrofluid. Dielectric loss tangent (tan δ) has been observed to increase with the increase of zinc contents. This can be attributed to the decrease in resistivity which in turn increases the dielectric loss tangent.     

Effect of sintering temperature electrical properties of ZNR doped with Pr–Co–Cr–La

The microstructure, electrical properties, and dielectric characteristics of the ZNR (zinc oxide-based nonlinear resistors), which are composed of zinc oxide-based ceramics doped with Pr–Co–Cr–La, were investigated at different sintering temperatures (1240, 1245, 1250, 1255, 1260, and 1300 °C). The increase of sintering temperature led to more densified ceramics, whereas it decreased the nonlinear properties and breakdown voltage. The highest nonlinearity was obtained from 1240 °C, with 79.3 in nonlinear coefficient and 0.3 μA in leakage current. As the sintering temperature increased, the donor density increased from 0.90 × 10¹⁸ to 2.59 × 10¹⁸/cm³, and the barrier height decreased from 1.90 to 0.67 eV, and the dielectric dissipation factor increased from 0.0874 to 0.2839.     

Investigation of the curing kinetics of alkyd–melamine–epoxy resin system

Properties of coatings based on alkyd resin can be improved via blending with other suitable resins. Recent studies assessed that many properties could be improved by blending with epoxy resins as well as with melamine resins. The aim of this work was to investigate the effect of epoxy resin content on the curing process in alkyd–melamine–epoxy three component blends. The coatings with two mixing ratios of alkyd/melamine (70:30 and 80:20) were formulated. They were made into baking enamels by blending with 3 and 5 wt% of epoxy resin on total resin solid. Curring kinetics was investigated by differential scanning calorimetry (DSC) and application of Ozawa isoconversional method. Fourier transform infrared spectroscopy (FTIR) was used to follow major curing reactions. The absorbance of –OH and –N–CH₂R, showed significant reduction and confirmed that the epoxy resin reacts and inserts in enamel structure. It was found that resin system with alkyd/melamine ratio of 70:30 and 3 wt% of epoxy resin has the lowest apparent activation energy of 141.5 kJ mol⁻¹ and needs the shortest time of 34.2 min to reach final apparent degree of cure. Isothermal DSC experiments have confirmed these findings. The samples with 30 wt% of melamine resin had higher hardness of baked enamels then samples with 20 wt%. They also showed an increase of hardness with the increase of epoxy resin content.     

Pulse plating of cobalt–iron–copper alloys

Pulse plating of cobalt–iron–copper (CoFeCu) alloys was studied. A simple theoretical model with an analytical solution developed for binary alloys is applied to predict the copper content of the pulse plated ternary alloys. Studied compositions are in the range of Co_90-x Fe₁₀Cu _x with x varying between 5 to 20 wt%. These compositions are of interest as soft magnetic materials with high saturation magnetization. The deposits were produced from a boric acid and sodium acetate electrolyte with low concentrations of copper and iron. All experiments were carried out under well-controlled mass transport conditions and current distribution using a recessed rotating cylinder electrode (rRCE) or an inverted rotating disc electrode (IrRDE). With the latter design alloys can be plated on flat substrates with or without application of a magnetic field to induce uniaxial magnetic anisotropy. Results show that by changing pulse parameters one can increase and decrease in opposite ways the copper and the iron content in the deposits. To test the influence of pulse parameters on the coercive field strength, a microstructure dependent property, theoretical predictions were used to produce films of identical composition with different pulse parameters. Within the range of pulse parameters studied the coercive field strength of this alloy does not vary. Transmission electron microscopy confirms that the deposits have the same nano-size grain structure.     

Processing–microstructure–properties relationships of MoSi2–SiC composites

Silicon carbide green bodies with and without carbon-fibre reinforcement have been infiltrated with MoSi₂–Si–X in order to produce high-temperature resistant materials. X is Cr, Ti, Al or B respectively. By adding silicon and one of these components to MoSi₂ the melting point is lowered dramatically. The composites therefore could be gained by melt infiltration at max. 1600 °C. During infiltration the additives react within the infiltrated body with carbon or silicon to form high-temperature resistant carbides or silicides. Thermodynamic calculations have been performed to analyse the reactions during infiltration. The infiltration parameters have been studied with respect to the resulting microstructure and properties. By fitting the amount of additives to the quantity of carbon in the SiC-body (or vice versa) no decrease in strength could be observed up to 1500 °C. The fracture toughness can be increased by the use of high-modulus carbon fibres. The most promising X-element for a high-temperature resistant material is titanium.     

Microstructure and mechanical properties of TiC–TiN–Zr–WC–Ni–Co cermets

Cermet cutting tools are widely used for semi-finishing and finishing work on steel and cast iron. However, their brittleness is still an unavoidable limitation for their utilizations. Zirconium was added to improve the fracture toughness of Ti(C, N) based cermets. The microstructure and the fracture surfaces of cermets were studied by using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The experimental results reveal that Zr dissolved and formed solid solutions during the sintering process. The amount of grains with typical core/rim structure decreases and that of coreless grains increases with increasing Zr addition. Moreover, the fracture toughness is improved clearly due to the increased amount of the coreless grains, the spinodal decomposition in cermets, as well as the crack deflection and crack branching mechanisms. Additionally, hardness and relative density were also measured, respectively.     

Preparation and properties of Ge–Ga–La–S–AgI chalcogenide glass

Chalcogenide glasses of 65GeS₂–(25–x)Ga₂S₃–10AgI–xLa₂S₃ (x=0, 1, 3, and 5 mol%) were fabricated through the traditional melt-quenching method. The effects of addition of La₂S₃ on physical, thermal and optical properties of the glass system were investigated. The results showed that the fabricated glasses possess considerably high glass transition temperature, exhibit improved mechanical property and excellent infrared transmission. A redshift at the visible absorbing cut-off edge is observed with increasing of La₂S₃ content. The direct and indirect optical band gap values are also calculated. Raman spectra analysis indicated that the band at 265 cm⁻¹ decreased in amplitude and a new peak at 230 cm⁻¹ was detected manifesting the formation of La-S bond in the network. In addition, the mid-infrared emission at 3.74 µm of the glasses doped with Tm³⁺ ions was achieved. The results indicated that the glasses are promising materials for mid-infrared applications such as imaging, remote sensing and lasers.     

An experimental study of immiscible liquid–liquid dispersions in a pump–mixer of mixer–settler

Drop size distribution(DSD) or mean droplet size(d32) and liquid holdup are two key parameters in a liquid–liquid extraction process. Understanding and accurately predicting those parameters are of great importance in the optimal design of extraction columns as well as mixer–settlers. In this paper, the method of built-in endoscopic probe combined with pulse laser was adopted to measure the droplet size in liquid–liquid dispersions with a pump-impeller in a rectangular mixer. The dispersion law of droplets with holdup range 1% to 24% in batch process and larger flow ratio range 1/5 to 5/1 in continuous process was studied. Under the batch operation condition, the DSD abided by log-normal distribution. With the increase of impeller speed or decrease of dispersed phase holdup, the d32 decreased. In addition, a prediction model of d32 of kerosene/deionized system was established as d_(32)/D = 0.13(1 + 5.9φ)We~(-0.6). Under the continuous operation condition, the general model for droplet size prediction of kerosene/water system was presented as d_(32)/D = C_3(1 + C_4φ)We~(-0.6). For the surfactant system and extraction system, the prediction models met a general model as d_(32)/D = bφ~nWe~(-0.6).