Carbon Dioxide Sensor Mechanism of Porous Hydroxyapatite Ceramics

Hydroxyapatite and Cl⁻ -containing hydroxyapatite powders are prepared and characterized. Reversible substitution of CO^2-₃ for OH⁻ at the surface is presumed to be responsible for the sensor function. The role of Cl⁻, which is necessary to realize the sensor function and is incorporated during soaking treatment, is considered as follows. It may reduce the strain caused by the incorporation of CO^2-₃ (which is larger than OH⁻), and, hence, promote the reversible substitution reaction. This behavior is presumed because Cl⁻ -containing hydroxyapatite samples exhibit sensor characteristics typical of CO₂ without any treatment.     

Influence of Speed on the Tribochemical Reaction Products and the Associated Transitions for the Dry Sliding of Silicon Nitride against Steel

Dry sliding of Si₃N₄ against steel has been studied using a pin-on-disk machine as a function of speed at a pressure of 15.5 MPa. Four types of friction and wear behaviors can be observed with associated transition in their values, called regions R1, R2, R3, and R4. R1 (0.1 to 1.25 ms^-1) is associated with high friction as well as the wear rate of the pin and the negligible wear rate of the disk. In R2 (1.25 to 3.5 ms^-1) friction is low and the wear rate of the pin is negligible but the wear rate of the disk is high. The friction and the wear rate of the pin as well as that of the disk are high in R3 (3.5 to 6.5 ms^-1). In R4 (6.5 to 12.0 ms^-1) the friction is low. The wear rate of the pin is similar to that in R3, while that of the disk is very low. SEM, EDXA, XRD, and IR reveal that each of these changes is associated with certain tribochemical interaction. R1 is associated with reaction between Si₃N₄ and water vapor to form hydrated silica (SiO₂·ⁿH₂O), R2 is controlled by softening of SiO₂·ⁿH₂O, R3 is characterized by microfracture and limited formation of Y₂SiO₅, and R4 is associated with increased formation of Y₂SiO₅ and SiO₂.     

Role of Cuspidine (3CaO.2SiO2.CaF2) in the System CaO–SiO2–CaF2

Cuspidine is a well-defined ternary compound with a stability field in the subsystem CaF₂–CaSiO₃–Ca₂SiO₄. Cuspidine is easily formed by solid-state reactions in the subsystem mentioned and is stable above its apparently congruent fusion point if heated in welded platinum containers. Above 1450° decomposition and the formation of a mixture of CaF₂ and Ca₂SiO₄ is observed. Cuspidine also is easily formed by secondary reactions in solid mixtures of the subsystem CaF₂–CaSiO₃ and in ternary mixtures of these with free SiO₂ if heated in open crucibles. The existence of double compounds of CaF₂ and CaSiO₃ is not confirmed.     

电缆用高阻燃耐热软质PVC的制备及性能研究

以软质PVC为基体,选用氢氧化铝-氢氧化镁(ATH/MDH)为复配阻燃剂、硼酸锌(ZB)为阻燃协效剂及钙锌材料为复合热稳定剂(Ca-Zn),通过共混法对PVC进行改性,制备PVC/ATH/MDH、PVC/ATH/MDH/ZB及PVC/ATH/MDH/ZB/Ca-Zn等软质PVC复合电缆料。分析3种电缆料的阻燃性能、拉伸性能及热稳定性。结果表明:相较纯软质PVC,PVC/ATH/MDH与PVC/ATH/MDH/ZB的阻燃性能提高,拉伸性能显著下降,且热稳定性改善不明显。而PVC/ATH/MDH/ZB/Ca-Zn的阻燃性能显著提升,与纯软质PVC相比,其极限氧指数(LOI)增加34.90%,烟密度等级下降29.50%,复合材料的炭层更连续且致密;PVC/ATH/MDH/ZB/Ca-Zn的拉伸强度和断裂伸长率分别提高1.78%和2.48%。Ca-Zn的添加提高软质PVC的残炭率,热稳定性增强。PVC/ATH/MDH/ZB/Ca-Zn的综合性能最佳。     

Influence of Nd2O3 Doping on the Reaction Process and Sintering Behavior of BaCeO3 Ceramics

The influence of Nd₂O₃ doping on the reaction process and sintering behavior of BaCeO₃ is investigated. Formation of BaCeO₃ is initiated at 800°C and completed at 1000°C. When Nd₂O₃ is added to the starting materials, the formation of BaCe_1–xNd_xO_3–δ is delayed and the temperature for complete reaction is increased to 1100°C. Only a BaCe_1-xNd_xO_3–δ solid solution with an orthorhombic crystal structure is present in the specimens for x ≤ 0.1. A secondary phase rich in Ce and Nd is formed within grains and at grain boundaries, when the Nd₂O₃ content is greater than the solubility limit (x ≥ 0.2). Pure BaCeO₃ is difficult to sinter, even at 1500°C, and only a porous microstructure could be obtained. However, doping BaCeO₃ with Nd₂O₃ markedly enhances its sinterability. The enhancement of the sinterability of Nd₂O₃-doped specimens at x ≤ 0.1 is attributed to the increase in the concentration of oxygen ion vacancies, which increases the diffusion rate. At x ≥ 0.2, the grain size is abnormally coarsened, which is caused by the formation of a liquid phase. While this liquid phase accelerates sintering, its beneficial effect on densification is counteracted by the segregation of the secondary grain-boundary phase which inhibits sintering.     

Preparation of Nanometer-Sized α-Alumina Powders by Calcining an Emulsion of Boehmite and Oleic Acid

This study proposes a method to form ultrafine α-Al₂O₃ powders. Oleic acid is mixed with Al(OH)₃ gel. The gel is the precursor of the Al₂O₃. After it is mixed and aged, the mixture is calcined in a depleted oxygen atmosphere between 25° and 1100°C. Oleic acid evaporates and decomposes into carbon during the thermal process. Residual carbon prevents the growth of agglomerates during the formation of α-Al₂O₃. The phase transformation in this process is as follows: emulsion →γ-Al₂O₃→δ-Al₂O₃→θ-Al₂O₃→α-Al₂O₃. This process has no clear θ phase. Aging the mixed sample lowers the formation temperature of α-Al₂O₃ from 1100° to 1000°C. The average crystallite diameter is 60 nm, measured using Scherrer's equation, which is consistent with TEM observations.     

Engineering practice and economic analysis of ozone oxidation wet denitrification technology

SO₂ and NO emitted from coal-fired power plants have caused serious air pollution in China. In this study, a test system for NO oxidation using O₃ is established. The basic characteristics of NO oxidation and products forms are studied. A separate test system for the combined removal of SO₂ and NO_x is also established, and the absorption characteristics of NO_x are studied. The characteristics of NO oxidation and NO_x absorption were verified in a 35 t·h^-1 industrial boiler wet combined desulfurization and denitrification project. The operating economy of ozone oxidation wet denitrification technology is analyzed. The results show that O₃ has a high rate and strong selectivity for NO oxidation. When O₃ is insufficient, the primary oxidation product is NO₂. When O₃ is present in excess, NO₂ continues to get oxidized to N₂O₅ or NO₃. The removal efficiency of NO₂ in alkaline absorption system is low (only about 15%). NO_x removal efficiency can be improved by oxidizing NO_x to N₂O₅ or NO₃ by increasing ozone ratio. When the molar ratio of O₃/NO is 1.77, the NO_x removal efficiency reaches 90.3%, while the operating cost of removing NO_x per kilogram is 6.06 USD (NO₂).     

Aluminum Infiltration into Molybdenum Silicide Preforms

The presence of Mo₅Si₃ in MoSi₂ preforms hinders the reactive infiltration of aluminum. To understand the role of Mo₅Si₃, the kinetics of aluminum infiltration into pure Mo₅Si₃ is studied. Irrespective of the initial composition (MoSi₂ or Mo₅Si₃) of the preform, the final product always contains Mo(Al,Si)₂. However, the aluminum content in the two cases is different: when the preform is MoSi₂, the aluminum content is 14–18 at.%, and, when the preform is Mo₅Si₃, the aluminum content is 25–27 at.%. The activation energy for the reactive infiltration of aluminum into the Mo₅Si₃ preform is ∼26 kJ/mol.     

Use of Crack Branching Data for Measuring Near-Surface Residual Stresses in Tempered Glass

An analytical procedure based on fracture mechanics is used to obtain the amount of residual stress in glass from measurements on the fracture surface. The technique utilizes the measurement of microcrack branching distances, known as the mirror — mist boundary, which occur at a critical crack branching stress intensity (K _m ) value. This procedurre shows that σ _A r _m ^1/2 Y _F (θ) =σ _R r ^1/2 _m +Ψ₀, where σ _A is the applied stress, r _m is the microcrack branching radius, σ _R is the residual stress, Y _F ( θ ) is the crack-border correction factor, and Ψ₀ is a material constant based on K _m . Thus, the equation is that of a straight line with the slope equal to the magnitude of the residual stress. Data for tempered glass from the literature are used to demonstrate the applicability of the technique.     

Compositional Model for Calcium Silicate Hydrate (C-S-H) Gels, Their Solubilities, and Free Energies of Formation

A compositional model based on available structural evidence is proposed for amorphous calcium silicate hydrogel. It is applicable to gels in the (Ca/Si),_solid range 1.0 to 1.4 and is formulated to take account of dimeric silicate species in the solid. Its composition is represented by Ca _x H_{6−2 x} Si₂O₇· z Ca(OH)₂· n H₂O where x and z are not independently obtainable; x + z , however, is evaluated from the Ca/Si ratio. The model is applied to representative solubility data; K_sp and free energies of formation for C-S-H's in this composition range are evaluated.     

Synthesis of High-Purity Zirconium Fluoride for Fluoride Glass Fibers by Chemical Vapor Deposition

A technique for synthesizing ultra-high-purity ZrF₄ using chemical vapor deposition in a ZrBr₄–HF system is developed and a purification mechanism is clarified. The Fe concentration in ZrF₄ is evaluated at less than 10 ppb based on analysis of the transmission loss spectrum of a fiber prepared using synthesized ZrF₄. Purification is achieved mainly in a sublimation process of ZrBr₄, and purification efficiency is determined by sublimation temperature and activity of impurities in ZrBr₄. The concentration of transition-metal impurities in ZrF₄, synthesized by chemical vapor deposition in the ZrBr₄–HF system, is expected to be less than 1 ppb.     

Polymorphic Phase Transformation of Lead Monoxide and Its Influence on Lead Zirconate Titanate Formation

The polymorphic phase transformation of PbO from massicot to litharge phase is easily produced by mechanical force. The transformation is relatively quick by wet ball-milling. The additions of TiO₂ and ZrO₂ tend to retard it. A second-order exponential relation is observed between the fractional conversion and the milling time for pure PbO, PbO-TiO₂, and PbO-ZrO₂-TiO₂ systems with a rutile constituent. This exponential relation is changed into a first-order logarithmic relation when anatase instead of rutile is used. Although the PbO _ss phase is observed irrespective of the phase of the PbO in the raw materials, this PbO _ss peak is more obvious when massicot PbO or anatase TiO₂ is used. The formation of PbO _ss phase is also dependent on the reactivity of the ZrO₂, and its presence can affect the formation and piezoelectric properties of PZT ceramics.     

The glass temperature of polymer blends

The entropy theory of glasses is used to derive the glass temperature, T_g, of a binary polymer blend in terms of the glass temperatures of the two substituents. The formula is T_g = B₁T_g1 + B₂T_g2, where B_i is the fraction of flexible bonds of substituent i. A bond is flexible if rotation about it changes the shape of the molecule. Bonds in side groups as well as in the backbone are to be counted. This formula assumes that the free volume, taken here to be the volume fraction of empty lattice sites, is the same for each of the three materials. It has no parameters. The above equation expressed in weight fractions, W_i, is (T_g − T_g1)W₁(γ₁/ω₁) + (T_g − T_g2)W₂(γ₂/ω₂) = 0, where ω_i is the weight of a monomer unit and gg_i is the number of flexible bonds per monomer unit. A more general treatment is given. One variation of the more general treatment which expresses the properties of the blend in purely additive terms gives T_g = B₁T_g1 + B₂T_g2 + KB₁B₂(T_g1 − T_g2)(V₀₁ − V₀₂), where V_0i are the free volume fractions of the homopolymers at their glass temperatures and K is a constant. The added term is usually small. The most general form of the equation requires the energy of interaction between the two unlike molecules, which can be estimated by volume measurements on the blend.     

Supported MoO3 catalysts: preparation by the new “slurry impregnation” method and activity in hydrodesulphurization

A new preparation of supported MoO₃ is described. Slurry MoO₃/water is used instead of the solution (NH₄)₆Mo₇O₂₄. Preparation and HDS activity are illustrated for MoO₃ supported over Al₂O₃, active carbon and ZrO₂. Another application of the new principle is the preparation of high surface area MoO₃/MgO by the reaction of MgO with slurry (NH₄)₆Mo₇O₂₄/methanol. Texture of MgO that is deteriorated in aqueous solution of (NH₄)₆Mo₇O₂₄ is stable in that slurry. “Slurry impregnation” is a special case of equilibrium adsorption impregnation. It is simple and it provides monolayer dispersion of molybdena.     

High-Temperature Elastic Properties of Polycrystalline MgO and Al2O3

Adiabatic bulk modulus, B_s , of polycrystalline MgO and Al₂O₃ was measured from 298° to 1473°K using the resonance technique. The Grüneisen constant, calculated from the measured bulk modulus, was constant over the whole temperature range (1.53 for MgO and 1.34 for Al₂O₃). Another important parameter,     , is constant at high temperature and is 3.1 for MgO and 3.6 for Al₂O₃. The Poisson's ratio increases linearly with temperature for MgO and Al₂O₃. To describe the change of bulk modulus with temperature a theoretical equation was verified by using the foregoing constants. A practical form of this theoretical equation is where B_s⁰ is the adiabatic bulk modulus at 0°K, δ is the quantity     , γ is the Grüneisen constant, H is the enthalpy. The experimental data are described very well by this equation, which is equivalent to the empirical equation suggested by Wachtman et al., B_s^T= B_s⁰ - CT exp (-T_c/T) , where C and T_c are empirical constants.     

Growth of Yttrium-Aluminum Garnet Single Crystals

Single crystals of yttrium-aluminum garnet have been grown from molten PbO-xB₂O₃ by program cooling, where x is between 0 and 0.36 mole. The field of stability of yttrium-aluminum garnet is found to widen with increasing B₂O₃ content in the solvent. A portion of a pseudo phase diagram for the quaternary system PbO-B₂O₃-Y₂O₃-Al₂O₃ is presented. The effect of substituting certain transition metal oxides in the crystals is discussed.     

Investigation of the Phase Diagram for the Pseudobinary System Li2SO4–La2(SO4)3 and Its Ionic Conductivity

The phase diagram of the pseudobinary system Li₂SO₄–La₂(SO₄)₃ has been investigated by means of X-ray diffraction and differential thermal analysis. LiLa(SO₄)₂ is formed by a peritectic reaction in this system; the peritectic temperature is 653±3°C. The eutectic reaction of Li₂SO₄ and LiLa(SO₄)₂ occurs at 553±3°C; the composition at the eutectic point is 17 mol% La₂(SO₄)₃. LiLa(SO₄)₂ is monoclinic with a=1.375 nm, b=0.6744 nm, c=0.7068 nm, and β=105.4°. The ionic conductivity of LiLa(SO₄)₂ has been studied from room temperature to 350°C and is found to be relatively low at room temperature or at lower temperatures. Its activation energy is 0.66 eV. Thus it is not suitable as a fast ion conductor.     

The Systems PbF2-AlF3 and CaF2-AlF3

The compound Pb₃Al₂FI₁₂ is reported in the system PbF₂-AIF₃. It is tetragonal, I 4/m, d₀ = 14.23 å, c_o = 7.20 Å. A phase diagram for the system is presented on the basis of DTA and X-ray Powder Patterns. The compound melts incongruently at 649°C. Solid solubility of AlF₃ in PbF₂ occurs with up to 15 mol% AlF₃. Data for the system CaF₂-A1F₃ is compared with previous reports.     

Use of Boron Phosphate in the Solid-State Preparation of Crystalline Iron(III) Phosphate and Manganese(II) Diphosphate

The possibility of using BPO₄ for the solid-state preparation of crystalline phosphates of trivalent iron, manganese, and chromium has been investigated. If BPO₄ and Fe₂O₃ are heated at 900°C, a complete conversion of BPO₄ to the quartz form of FePO₄ results after 9 h. If FeCl₃.6H₂O is used instead of Fe₂O₃, a multiphase crystalline product is obtained in which the dominant phase is the quartz form of FePO₄. The reaction of BPO₄ with Mn₂O₃ or MnO₂ at 830°C yields Mn₂P₂O₇; the amount of conversion of BPO₄, to Mn₂P₂O₇ after 4 h is 80% (if Mn₂O₃ is used) and 75% (if MnO₂ is used). However, the method is not successful in the preparation of phosphates of chromium: the reaction of BPO₄ and some chromium compounds yields α-Cr₂O₃ as the only chromium-containing product.     

中试平台SCR低温催化剂测试与氨逃逸分布特征

目前燃煤机组低负荷运行的情况越来越多,研究机组低负荷运行时NO_x控制技术可有效降低燃煤机组的NO_x排放浓度。本文利用已建成的20000m³/h的实际燃煤烟气的污染物脱除试验平台,安装低温段脱硝催化剂整体模块,测试该催化剂的性能指标,现场取样并重点分析氨逃逸和转化率指标,得出实际烟气条件下氨逃逸分布特征。结果表明：该低温脱硝催化剂的低温段在290~250℃范围内,脱硝效率可达到80%,脱硝出口NO_x可控制在50mg/m³（标准）以内,甚至20mg/m³以内,氨逃逸最高为1.68mg/m³,小于标准要求值2.28mg/m³,SO₂/SO₃转化率最高为0.73%,小于标准要求值1%,满足运行要求。文中进一步研究了氨逃逸浓度沿程分布情况,经测试表明,290℃时沿程氨逃逸浓度不断降低,除尘器前降低32.2%,除尘器后降低65.5%。