Preparation of a ternary hybrid of P-g-C3N4@PGS-Ti and its enhancement of the flame retardancy of epoxy resins

A novel ternary hybrid flame retardant named P-g-C₃N₄@PGS-Ti was prepared through step-by-step method. First, titanium dioxide was loaded on PGS to make PGS-Ti (where PGS = palygorskite), and then, PGS-Ti was decorated by phosphor-doped g-C₃N₄ (abbreviated as P-g-C₃N₄) to prepare a ternary flame retardant of P-g-C₃N₄@PGS-Ti. It showed that P-g-C₃N₄@PGS-Ti could efficiently improve the flame retardancy of epoxy resins (EP). The structure and the morphology of P-C₃N₄@PGS-Ti were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scaanning electron microscopy and hermogravimetric analysis (TGA). The flame retardancy and the burning behavior of 5 wt% P-g-C₃N₄@PGS-Ti composited EP were well investigated through TGA, limiting oxygen index (LOI), cone calorimeter test (CCT) and vertical burning test (UL-94 standard). It was found that the peak heat releasing (pk-HRR) of the EP/P-g-C₃N₄@PGS-Ti composite reduced 36% (from 1459 to 852 kW/m²) with the addition of 5 wt% of P-g-C₃N₄@PGS-Ti flame retardant to the matrix of EP. The combustion residue analysis showed that the EP/P-g-C₃N₄@PGS-Ti composite gained the most continuous and firmest char yield due to the synergistic effect of PGS, TiO₂ and the introducing of P element. The mechanism proved that the combination of gas phase and condensed phase flame-retardant processes were well coordinated to improve the fire retardancy for EP. We tested and studied the mechanical properties of EP/P-g-C₃N₄@PGS-Ti composites. Only 2.4% decreasing of flexural strength and 23.5% decreasing of impact strength in EP/P-g-C₃N₄@PGS-Ti composites compared to pure EP, respectively. But according to the test results of EP/P-g-C₃N₄@PGS-Ti composite material and the control sample in the system, EP/P-g-C₃N₄@PGS-Ti composite material had the highest flexural modulus and impact strength.     

A study of complex effects of alumina addition on conductivity of stabilised zirconia

When zirconia is used as electrolyte material in intermediate temperature solid oxide fuel cells, the influence of impurities on conductivity becomes more significant than at high temperature. It is, therefore, important to understand the effect of impurities and if possible remove them. SiO₂ is an impurity known to be present in zirconia and to have a negative effect on conductivity. Since the early 1980s, several groups have reported Al₂O₃ to act as a scavenger of SiO₂ in zirconia. However, conflicting results have been obtained. Both increases and decreases in grain boundary conductivity have been found along with a decrease in grain interior conductivity. The effect of Al₂O₃ seems to be dependent on the ratio between Al₂O₃ and SiO₂ in the material, and on the concentration and the distribution of Al₂O₃ in zirconia. Here, the results described in literature are reviewed and compared with new results obtained on Sc_0.16Y_0.04Zr_0.80O_1.9 and Tosoh TZ8Y. The samples were investigated with respect to conductivity (impedance spectroscopy) and microstructure (scanning and transmission electron microscopy) in order not only to find a trend but also to understand the mechanism of Al₂O₃ addition.     

Role of water vapor in oxidative decomposition of calcium sulfide

CaS formed from the CaO sorbent during desulfurization in coal gasifiers has to be converted to CaSO₄ before disposal. CaS is mainly decomposed to CaO and SO₂ by O₂ and then CaO is converted to CaSO₄ by SO₂ and O₂. The role of H₂O in the oxidative decomposition of CaS with O₂ was studied using reagent grade CaS and H₂¹⁸O. The following results were obtained: (1) there is a synergistic effect of H₂O and O₂ on the oxidative decomposition of CaS to CaO and SO₂; (2) H₂O reacts with CaS to form CaO, SO₂ and H₂ in the absence of O₂; (3) the oxidative decomposition of CaS to CaO and SO₂ occurs stepwise; (4) H₂O directly reacts with CaS in the presence of O₂; (5) H₂O plays an important role in the oxidative decomposition of CaS even if the O₂ concentration is high.     

Rates of reaction of SO2 with metal oxides

Rates of sorption of SO₂ from synthetic flue gas by 14 metal oxides were determined. These oxides had been selected for their potential applicability to processes for removing SO₂ from flue gas using thermal regeneration of sorbent. Measurements were performed using thermogravimetric analysis, and rates were fitted to semi-empirical expressions; CeO₂, Co₃O₄, Cr₂O₃, CuO, Fe₂O₃, and NiO displayed measurable rates in the range 200° to 500°C, and were converted to sulphates. Rates were immeasurably small at 25° to 800°C for Al₂O₃, Sb₂O₅, SnO₂, TiO₂, V₂O₅, WO₃, ZnO, and ZrO₂, CuO and CeO₂ showed the highest rates     

Formation and properties of solid solutions of zirconium dioxide with oxides of rare earth elements

Conclusions Interaction of zirconium dioxide with oxides of cerium, yttrium and lanthanum in solid phases occurs at 1400°C with the formation of solid solutions with the cubic structure.Sintering of the specimens may result at 1700–1750°C with a 3-h soak. At 1400°C and a 6-h soak the porosity of the specimens was 30–40%.Complete stabilization of the zirconia is attained by heating to 1700–1750°C with additions of 20 mol.% CeO₂, 15% Y₂O₃ or 25% La₂O₃. An addition of ceria and yttria displaces the effects of polymorphic inversion of the zirconia to the lower temperature region.New highly refractory materials may be obtained from solid solutions of ZrO₂-20% CeO₂, ZrO₂-80% CeO₂, ZrO₂-15% Y₂O₃, ZrO₂-80% Y₂O₃ and ZrO₂-25% La₂O₃ and firing to 1750°C. Some of them have a low coefficient of thermal expansion compared with ZrO₂, stabilized with calcium oxide and magnesium oxide, and apparently better thermal-shock resistance. The advantage in regard to resistance during prolonged heating at 1200°C is possessed by the solution ZrO₂-Y₂O₃. The region of the most effective use of goods made from solid solutions of ZrO₂ with CeO₂, Y₂O₃ and La₂O₃ as highly refractory materials should be determined by extra studies.The possibility of reducing CeO₂ (fusing temperature about 2700°C) to Ce₂O₃ (fusing temperature about 1700°C) limits the use of cerium-containing materials as refractories in chiefly oxidizing conditions.     

Densification of Yttria Transparent Ceramics: The Utilization of Activated Sintering

Highly transparent 0.5 at.% Tm:Y₂O₃ ceramics were prepared by using solid‐state reaction combined with vacuum sintering method, with ZrO₂ and Al₂O₃ as sintering aids. Doping amount of ZrO₂ was fixed at 1 at.%, while the effect of Al₂O₃ on densification, microstructure evolution, and transmittance of the Y₂O₃ ceramics was carefully studied. It was found that the addition of Al₂O₃ was very effective in improving densification of Y₂O₃, due to the formation of an Al‐rich eutectic phase Y₄Al₂O₉ (YAM) during the sintering process. As the content of Al₂O₃ was increased from 0 to 81.8 wt ppm, porosity of the ceramics was decreased and transmittance was increased. However, when the content of Al₂O₃ was increased to 137 wt ppm, a secondary phase began to segregate at grain junctions. Further increase in the amount of Al₂O₃ led to an increase in both amount and size of the secondary phase. At the optimized content of Al₂O₃ with 81.8 wt ppm, the Tm:Y₂O₃ ceramics sintered at 1860°C for 13 h exhibited an in‐line transmittance of 83.0% at 2000 nm and 76.5% at 600 nm. It is expected that this finding can be readily applied to other transparent ceramics.     

Effect of parameters of state on phase transitions of carbonized periclase refractories

Thermodynamic physicochemical modelling and calculation methods are used to study the effect of temperature on phase and chemical transitions in the system MgO-C-Al-Al₂OC-Al₈B₄C₇-Al₄O₄C-Al₂O₃-Al₄C₃-H₂O-air at 298–2400 K applied to the behavior of carbonized periclase refractories under production and operating conditions. Partial and total pressure, developed by gaseous reaction products of material with an average pore space (CO₂, CO, CH₄, H₂O, H₂, etc.) are determined in relation to pressure. The effect of gasification for the carbon component, porosity, original and atmospheric moisture, that is not currently subject to experimental observation, are considered. __________ Translated from Novye Ogneupory, No. 10, pp. 44–50, October 2007.     

Atomic Scale Mechanisms of the Reduction of Nickel–Magnesium Aluminate Spinels

The dynamics of the reduction reaction of Ni_xMg_1?xAl₂O₄ to form nickel metal and a remnant oxide was quantified to understand spinel behavior in catalysis applications. X‐ray diffraction, thermogravimetry, and pycnometry were employed to track the evolution of high‐Ni spinels to metastable nonstiochiometric spinels during reduction, but before the phase transformation to theta alumina. Rietveld refinements of X‐ray diffraction data were used to quantify structural changes in the spinel and the phase fraction, crystallite size, and microstrain of all phases during H₂ reduction. During reduction, one O^2? is lost for each Ni²⁺ reduced to Ni metal. Ni_0.25Mg_0.75Al₂O₄ and Ni_0.5Mg_0.5Al₂O₄ were shown to form Ni metal and a non‐stoichiometric spinel of the same Mg‐Al ratio as the starting composition. NiAl₂O₄ and Ni_0.75Mg_0.25Al₂O₄ were found to become unstable as full reduction was approached, and metastable spinel, Θ‐Al₂O₃, and α‐Al₂O₃ formed sequentially given sufficient time at temperature.     

Thermal Analysis of Ammonium Perchlorate and of its Mixtures with Inorganic Substances

Solid mixtures containing ammonium perchlorate diluted with reputedly inert substances SiC, SiO₂, TiO₂, Al₂O₃ and the salts: KCl, NaCl, BaCO₃, CaCO₃ respectively were studied by TGA and DTA. Undiluted NH₄ClO₄ and the perchlorates of K, Na, Ba, Ca were also examined. The two known temperature regions of NH₄ ClO₄ thermolysis were confirmed. The first DTA exotherm of NH₄ClO₄ seems to be related to its limited decomposition; it can be suppressed by an ammonia atmosphere, by thermal cycles, or by heat-dissipating conditions. The second exotherm is related to the change of the decomposition mechanism of HClO₄ above 330°. TGA rate curves of stoichiometric mixtures of NHClO₄ with salts show two peaks due to decomposition of NH₄ClO₄ and one peak due to the MeClO₄ formed on heating. The formation of MeClO₄ is confirmed by visual observations and by DTA. Thermal cycles followed by DTA of stoichiometric mixtures of (NH₄ClO₄ + KCl), (NH₄ClO₄ + BaCO₃) reveal the systematic formation of MeClO₄ at the expense of NH₄ClO₄. For (NH₄ClO₄ + NaCl), (NH₄ClO₄ + CaCO₃) there appear in the vicinity of the transition endotherm of NH₄ClO₄ new reversible endotherms difcontaining NH₄ClO₄. Only after their thermal decomposition do the transition endotherms of MeClO₄ appear.     

Effect of alkali metal catalysts on gasification of coal char

A detailed study has been conducted of the effects of LiCl, NaCl, KCl, RbCl, CsCl, KOH, and K₂CO₃ on the steam gasification of char produced from a western sub-bituminous coal. Initial screening of results revealed that K₂CO₃ had the greatest catalytic activity for a fixed cation content in the char. Subsequent experiments were performed to determine the effects of K₂CO₃ loading and gasification temperature on the rate of gasification and the product-gas composition. The results show that gasification rate is enhanced with increasing K₂CO₃ loading and reaction temperature. Increasing K₂CO₃ loading causes CO to be formed in preference to CO₂ and H₂ and suppresses the production of CH₄. Increasing temperature also causes CO to be formed in preference to CO₂ and H₂ but enhances the production of CH₄. These results are discussed in the light of a mechanism to explain the unique catalytic behaviour of K₂CO₃.     

Kinetic study of the pyrolysis of tetrachloroethylene in a hydrogen rich environment

Experiments on pyrolysis of C₂Cl₄ with hydrogen in argon bath gas (C₂Cl₄: H₂: AR=0.5:7:92.5) were performed in a laboratory scale flow reactor, to determine reaction paths and kinetic parameters, plus to observe hydrogen as a source to convert chlorocarbons into hydrocarbons and HCl. The reaction was carried out at 1 atmosphere total pressure in the tubular flow reactor, over temperature ranges from 575 to 850 °C, with average residence times in the range of 0.3 to 1.2 s. The major reaction products were C₂HCl₃, CH₂CCl₂, C₂H₆, C₂H₄ and HCl. Trace intermediates including CH₄, C₂H₂, C₃H₆, C₃H₄, C₄H₈, C₄H₆, C₄H₄, C₂H₃Cl, C₂HCl, trans-CHClCHCl, cis-CHClCHCl C₂Cl₂ and aromatic compounds were found. The equation for overall loss of C₂Cl₄ (k (s⁻¹)) was 1.35×10⁶exp(−27055/RT). This study shows that C₂H₄ became the major product for reaction temperatures higher than 700 °C, and became one of the final products together with HCl.A detailed kinetic mechanism consisting of 202 elementary reactions with 59 species was developed to model the results obtained from the experiments. Sensitivity analyses were performed to rank the significance of each reaction in the mechanism. Modeling and sensitivity analysis revealed that C₂Cl₄+H→C₂HCl₃+Cl, C₂Cl₄+H→C₂Cl₃+Cl, and C₂Cl₄→C₂Cl₃+Cl are the primary reactions for the decomposition of C₂Cl₄.     

The Effect of Cadmium on GFR Is Clarified by Normalization of Excretion Rates to Creatinine Clearance

Erroneous conclusions may result from normalization of urine cadmium and N-acetyl-β-D-glucosaminidase concentrations ([Cd]_u and [NAG]_u) to the urine creatinine concentration ([cr]_u). In theory, the sources of these errors are nullified by normalization of excretion rates (E_Cd and E_NAG) to creatinine clearance (C_cr). We hypothesized that this alternate approach would clarify the contribution of Cd-induced tubular injury to nephron loss. We studied 931 Thai subjects with a wide range of environmental Cd exposure. For x = Cd or NAG, E_x/E_cr and E_x/C_cr were calculated as [x]_u/[cr]_u and [x]_u[cr]_p/[cr]_u, respectively. Glomerular filtration rate (GFR) was estimated according to the Chronic Kidney Disease (CKD) Epidemiology Collaboration (eGFR), and CKD was defined as eGFR < 60 mL/min/1.73m². In multivariable logistic regression analyses, prevalence odds ratios (PORs) for CKD were higher for log(E_Cd/C_cr) and log(E_NAG/C_cr) than for log(E_Cd/E_cr) and log(E_NAG/E_cr). Doubling of E_Cd/C_cr and E_NAG/C_cr increased POR by 132% and 168%; doubling of E_Cd/E_cr and E_NAG/E_cr increased POR by 64% and 54%. As log(E_Cd/C_cr) rose, associations of eGFR with log(E_Cd/C_cr) and log(E_NAG/C_cr) became stronger, while associations of eGFR with log(E_Cd/E_cr) and log(E_NAG/E_cr) became insignificant. In univariate regressions of eGFR on each of these logarithmic variables, R² was consistently higher with normalization to C_cr. Our tabular and graphic analyses uniformly indicate that normalization to C_cr clarified relationships of E_Cd and E_NAG to eGFR.     

Inhibition of abnormal grain growth in BaTiO3 by addition of Al2O3

The effect of additions of up to 1 mol% Al₂O₃ on abnormal grain growth in BaTiO₃ samples sintered at 1200 and 1250 °C has been studied. Samples with and without additions of 0.4 mol% TiO₂ were prepared. For the samples without added TiO₂, addition of 0.1 mol% Al₂O₃ increases the number density of abnormal grains, with further additions reducing the number density. The initial increase in number density is caused by Al₂O₃ forming a solid solution with BaTiO₃ and releasing TiO₂ to the grain boundaries. This excess TiO₂ then reacts with BaTiO₃ to form Ba₆Ti₁₇O₄₀, which promotes {1 1 1} twin formation and abnormal grain growth. Further additions of Al₂O₃ react with BaTiO₃, Ba₆Ti₁₇O₄₀ and excess TiO₂ to form Ba₄Al₂Ti₁₀O₂₇ and BaAl₂O₄ second phases, neither of which are growth sites for abnormal grains. For the samples with added TiO₂, addition of Al₂O₃ decreases the number of abnormal grains due to the Al₂O₃ reacting with the excess TiO₂ and BaTiO₃ to form Ba₄Al₂Ti₁₀O₂₇ and BaAl₂O₄ instead of Ba₆Ti₁₇O₄₀.     

Mechanism of hexamethylcyclotrisiloxane polymerization in the presence of siloxanediols

Polymerization of hexamethylcyclotrisiloxane (D₃ ) in CH₂Cl₂ at 30°C, initiated by triflic acid (TfOH) was studied in the presence of siloxanediols (HD₂OH or HD_xOH) which polycondense giving water, or in the presence of water alone for comparison. D represents a siloxane unit OSiMe₂. In the second case, the relative amounts of cyclic oligomers (D₆, D₉) and of linear high polymer (HP) vary strongly with the molar ratio r =[H₂O]/[TfOH]. When r increases from 1 to 100 (in homogeneous phase), D₉ /D₆ increases from 0.2 to 2 and D₆ /HP decreases from 1 to 0.3. The large decrease of D₆ amount and the increase in D₉/D₆ are attributed to the suppression of their formation through oxonium ions and to their exclusive formation, for r>100, by cyclization of silanol-esters, which is more rapid for HD₉OTf than for HD₆OTf. For polymerization of D₃ in the presence of HD₂ OH, there is a fast and limited ring-opening of D₃ (about 10% conversion over 6 min) at the beginning, without formation of cyclics (D₆, D₉ , etc). Then reaction with D₃ stops. Polymerization of HD₂OH takes place simultaneously, at the same rate as in the absence of D₃, with slow formation of high polymer. At the end of the polycondensation (after, eg, 4 h) D₃ polymerization starts again, giving D₆ , D₉, etc, and HP. The inhibition period for D ₃ is attributed to the complexation of triflic acid hydrates by silanol groups. These activated silanol groups do not react with D₃. A comparison of D₃ polymerization with the addition of water, HD₂OH or HD₁₅OH leads to the conclusion that when r is not too large, propagation involves silylester end-groups, but that for large r ratios (100 or higher), it probably occurs mainly on silanol groups reacting with an activated monomer. © 1999 Society of Chemical Industry     

Some principles of the recrystallization of oxides of the M2O3 composition

Conclusions In the series of oxides under discussion, A1₂O₃, Sc₂O₃, and Y₂O₃, the greatest tendency for recrystallization is found in Al₂O₃. Marked structural changes occur at 1400°C. The Y₂O₃ and Sc₂O₃ oxides are stable up to a temperature of 1600°C.The method of preparing the ceramic has a significant effect on the absolute recrystallization rates of the material. The structure of the sintered materials after a 20–50 h dwell at 1400–1800°C is stabilized while there is a monotonic increase in the size of the grains for hot-pressed specimens after heat treatment for 50 h.The addition of small quantities of MgO to A1₂O₃ and ThO₂ and ZrO₂ plus W to Y₂O₃ is very effective in preventing active recrystallization. A prolonged thermal dwell in vacuo leads in the case of an Al₂O₃-based ceramic to the intense redistribution of impurities and additives.Translated from Ogneupory, No. 6, pp. 46–51, June, 1980.     

Influence of Cu on the mechanical and tribological properties of Ti3SiC2

Ti₃SiC₂/Cu composites with different contents of Cu were fabricated by mechanical alloying and spark plasma sintering method. The phase composition and structure of the composites were analyzed by X-ray diffractometry and scanning electron microscopy equipped with energy dispersive spectroscopy. The mechanical and tribological properties of Ti₃SiC₂/Cu composites were tested and analyzed compared with monolithic Ti₃SiC₂ in details. The results show that the Cu leads to the decomposition of Ti₃SiC₂ to produce TiC_x, Ti₅Si₃C_y, Cu₃Si, and TiSi₂C_z. The friction coefficient and wear rate of the composites are lower than that of monolithic Ti₃SiC₂, which is ascribed to the fixing effect of hard TiC_x, Ti₅Si₃C_y, and Cu₃Si to inhibit the abrasive friction and wear. However, at elevated temperatures (ranging from room temperature to 600 °C) the friction and wear of the composites are higher than those at room temperature. Plastic flowing and tribo-oxidation wear accompanied by material transference contribute to the increased friction and wear at elevated temperatures.     

The coloring of geopolymers by the addition of copper compounds

The development of a new coloring technique is desirable to increase the commercial value of geopolymers. Selected copper compounds, i.e. Cu(OH)₂, CuO, Cu₂O, CuCO₃?Cu(OH)₂?H₂O, CuCl₂?2H₂O and CuSO₄?5H₂O, were added to the initial reactants in order to color the geopolymers in the same manner as naturally occurring minerals. When Cu(OH)₂, CuO and Cu₂O were used, these compounds remained in the geopolymer matrix following hardening of the material. On the contrary, CuCO₃?Cu(OH)₂?H₂O, CuCl₂?2H₂O and CuSO₄?5H₂O were not detected in the final products. XAFS analyses were performed to investigate the local structure of copper in the geopolymers produced. The results showed that the copper spectra of geopolymers incorporating Cu(OH)₂, CuO and Cu₂O correspond to those of pure Cu(OH)₂, CuO and Cu₂O, respectively. However, when CuCO₃?Cu(OH)₂?H₂O, CuCl₂?2H₂O and CuSO₄?5H₂O were added, the copper generated spectra similar to that of the mineral chrysocolla ((Cu, Al)₂H₂Si₂O₅(OH)₄?nH₂O) than the respective copper compounds.     

Simulation of partial oxidation of natural gas with detailed chemistry: Influence of addition of H2, C2H6 and C3H8

The partial oxidation (POX) of natural gas to produce acetylene was studied using detailed chemistry simulation to determine the influences of adding H₂, C₂H₆ and C₃H₈ to the CH₄ feed. Four detailed chemistry mechanisms, codenamed GRI 3.0, GRI 486, Petersen, and Curran, for describing the POX of natural gas under fuel-rich conditions were evaluated by comparing calculated results with ignition delay time and homogeneous oxidation data. The Curran mechanism gave the best performance, and was further used to examine the influences brought about by changes in the natural gas composition due to the addition of H₂, C₂H₆ and C₃H₈. The addition of H₂, C₂H₆ and C₃H₈ reduced the consumption of natural gas per ton of acetylene produced, and would enhance the economy of the POX process and help use up excess H₂, C₂H₆ and C₃H₈ from other processes in chemical plants. For natural gases that contain small amounts of higher hydrocarbons, the adding of H₂, C₂H₆ and C₃H₈ significantly decreased the ignition delay time, and the residence time of the feed in the mixing zone has to be reduced when adding these species to avoid uncontrolled combustion.     

Infrared studies of reaction of ethylene with syngas on Ni/SiO2

Ni/SiO₂, a methanation catalyst, has been shown to exhibit CO insertion activity. In situ infrared studies of CO/H₂ and C₂H₄/CO/H₂ reactions on Ni/SiO₂ show that carbonylation of Ni/SiO₂ to Ni(CO)₄ leads to an inhibition of methanation in CO hydrogenation but an enhancement of formation of propionaldehyde in the C₂H₄/CO/H₂ reaction.     

Effect of chemical composition of intergranular glass on superplastic compressive deformation of β-silicon nitride

The effect of chemical composition of Y₂O₃–Al₂O₃–SiO₂-based intergranular glass on superplastic deformation of β-Si₃N₄ was studied by compression tests at 1873 K. All hot isostatically pressed Si₃N₄ materials had essentially the same microstructure and the same amount of glass phase, which was different in composition only. The relation between flow stress and glass composition qualitatively corresponded to the effect of chemical composition on viscosity of Y₂O₃–Al₂O₃–SiO₂ glass. However, the flow stress was not proportional to the viscosity of Y₂O₃–Al₂O₃–SiO₂ glass, probably because the composition of intergranular glass phase had changed by dissolving Si₃N₄. The strain hardening (increase of flow stress with deformation) was dependent on the chemical composition of intergranular glass. Actually, the apparent strain hardening was not proportional to the strain but was proportional to time. The crystallization of Si₂N₂O was also proportional to time, and was dependent on the chemical composition of the intergranular glass in a similar way to the strain hardening. Thus, it was suggested that the crystallization of Si₂N₂O reduced the amount of the intergranular glass, thereby increasing flow stress.