Microstructure and growth kinetics of silicide coatings for TiAl alloy

In order to improve the oxidation resistance of Ti Al alloy, silicide coatings were prepared by pack cementation method at 1273, 1323, and 1373 K for 1-3 hours. Scanning electron microscopy(SEM), energy dispersive spectrometry(EDS) and X-ray diffraction(XRD) were employed to investigate the microstructures and phase constitutions of the coatings. The experimental results show that all silicon deposition coatings have multi-layer structure. The microstructure and composition of silicide coatings strongly depend on siliconizing temperatures. In order to investigate the rate controlling step of pack siliconizing on Ti Al alloy, coating growth kinetics was analyzed by measuring the mass gains per unit area of silicided samples as a function of time and temperature. The results showed that the rate controlling step was gas-phase diffusion step and the growth rate constant(k) ranged from 1.53 mg~2/(cm~4·h~2) to 2.3 mg~2/(cm~4·h~2). Activation energy(Q) for the process was calculated as 109 k J/mol, determined by Arrhenius' equation: k = k0 exp[–Q/(RT)].     

Effect of attapulgite added in plating bath on the properties of Ni/TiC nano-composite coatings

Pure copper plates were coated by Ni-TiC dipulse current plating method. The effects of adding different concentration(ranging from 0.5 g/L to 3.0 g/L) of attapulgite nano particles to the plating bath on the surface morphology, wear resistance, and oxidation resistance of Ni/TiC/Attapulgite nano-composite coatings were investigated. The experimental results show that the composite coating is flat and compact with adding 3.0 g/L in the bath, and the coating preferred orientation is changed from the planes (111) to (200). The coefficient of the composite coatings decreases from 0.68 to 0.18 with increasing content of attapulgite in the bath, a mixed mode of adhesive-abrasive wear occurs for all coatings, and the wear mechanism shows a transition from adhesive-abrasive to predominantly abrasive wear mechanism when the concentration of attapulgite is beyond 1.5 g/L in electrolyte. The oxidation resistance of composite coatings is the best prepared when adding attapulgite particles at 0.5 g/L in the bath, the oxide mainly consists of a NiO phase by X-ray analysis.     

Effect of fiber volume fraction on longitudinal tensile properties of SiC<Subscript>f</Subscript>/Ti-6Al-4V composites

The longitudinal tensile properties of SiC_f/Ti-6Al-4V composites with different fiber volume fractions were simulated by the Monte Carlo 2-D finite element model. The random distribution of fiber strength was expressed by the two-parameter Weibull function. Meanwhile, contact elements and birth-death elements were used to describe the interfacial sliding process after debonding and fiber breakage (or matrix cracking) respectively, which was realized by subroutine complied in ANSYS-APDL (ANSYS Parametric Design Language). The experimental results show that the yield stress and ultimate tensile strength of SiC_f/Ti-6Al-4V composites increase with increasing fiber volume fraction, while the corresponding strain of them is just on the contrary. In addition, almost the same failure mode is obtained in SiC_f/Ti-6Al-4V composites with various fiber volume fractions when the interfacial shear strength is fixed. Finally, the tensile strength predicted by finite element analysis is compared with that predicted by Global load-sharing model, Local load-sharing model and conventional rule of mixtures, thus drawing the conclusion that Local load-sharing model is very perfect for the prediction of the ultimate tensile strength.     

Effect of deposition time on microstructures and growth behavior of ZrC coatings prepared by low pressure chemical vapor deposition with the Br<Subscript>2</Subscript>-Zr-C<Subscript>3</Subscript>H<Subscript>6</Subscript>-H<Subscript>2</Subscript>-Ar System

ZrC coatings were deposited on graphite substrates by low pressure chemical vapor deposition (LPCVD) with the Br₂-Zr-C₃H₆-H₂-Ar system. The effects of deposition time on the microstructures and growth behavior of ZrC coatings were investigated. ZrC coating grew in an island-layer mode. The formation of coating was dominated by the nucleation of ZrC in the initial 20 minutes, and the rapid nucleation generated a fine-grained structure of ZrC coating. When the deposition time was over 30 min, the growth of coating was dominated by that of crystals, giving a column-arranged structure. Energy dispersive X-ray spectroscopy showed that the molar ratio of carbon to zirconium was near 1:1 in ZrC coating, and X-ray photoelectron spectroscopy showed that ZrC was the main phase in coatings, accompanied by about 2.5mol% ZrO₂ minor phase.     

Preparation and performance research of cement-based grouting materials with high early strength and expansion

Main performance of the cement grouting materials made up by Portland cement(PC) and sulphoaluminate cement(SAC) was investigated in this program, a kind of expanding agent(EA) which was mainly constituted by metakaolin and alunite was utilized for the compensation of the shrinkage, the hydration products and micro structure of the grouting materials were researched by X-ray diffraction(XRD) and scanning electron microscopy (SEM). The results showed that a high expansion rate of the grouting materials could be reached as the expanding agent mixed in 6% of PC mass; the addition of SAC in the S2(PC:SAC:EA=34:6:2.25) brought a further improvement of the expansion rate of the grouting materials, the analysis of XRD and SEM showed that due to the reaction of expanding agent and SAC in the grouting materials, more ettringite crystal was generated, which resulted in a higher early strength, the addition of SAC played an expansion and strength reinforcement role in the grouting materials.     

Inter-comparative study of quantitative methods of industrial clinker

Impurities from the raw materials, the grinding and the homogenization of the raw materials, the kiln instability and the complexity of the cooling step, all these factors make it difficult to obtain a perfect evaluation of the mineralogical composition of Portland clinker. We studied the limitations of the most commonly used quantitative methods and recommend some procedures to obtain reliable and reproducible results of quantitative analyses. Different clinker samples (provided by the Bizerte Cement Company (Tunisia)) were subjected to an elemental analysis by X-ray fluorescence and the mineralogical composition was determined by the Bogue calculation and by X-ray powder diffraction combined with the Rietveld method (Different softwares were used: XPert High Score Plus version 2.0 and TOPAS version 4.2). We then compared the results obtained by the Rietveld method and the Bogue calculation to the specific peak areas of each phase. The content of each phase, determined by the Rietveld method, varied proportionally to the change in peak area; a significant difference in these results was found by using the elementary Bogue calculation.     

Synthesis of HTPB based PU-PS IPN membrane for pervaporation recovery of butanol

Hydroxyl terminated polybutadiene(HTPB) based polyurethane(PU)-polystyrene(PS) interpenetrating polymer network(IPN) was prepared and characterized by FTIR, TGA, WCA, swelling experiments, and SEM. The IPN was used for pervaporation(PV) recovery of butanol. Both the permeation flux and separation factor increased with feed temperature, and both water and butanol fluxes increased with feed concentration while no obvious effect of concentration on separation factor was found. Through the formation of IPN structure, the total flux of HTPB based PU increased greatly with the decrease of separation factor. At the feed temperature of 60 °C, the IPN membrane obtained a total flux of 613.3 g/m~2 h with a separation factor of 6.15.     

A new way of strengthening and toughening for carbon fiber reinforced polyphenylene sulfide (CF/PPS) composites via matrix modification

The effect of pressure-induced flow(PIF) processing on the mechanical properties of noncontinuous carbon fiber(CF) reinforced polyphenylene sulfide(PPS) composites was investigated. A series of CF/PPS composites under different processing conditions were prepared through PIF-processing. SEM observations showed that the interfaces adhesion between CFs and PPS became stronger and ductile fracture mainly occurred in PPS matrix. This brought to a great increase of both strength and toughness by about 2 folds, when the composites were processed at 240 ℃ and under 263 MPa. The results in differential scanning calorimetry(DSC) and X-ray diffraction(XRD) measurements indicated more regular crystalline structures and orientation of lamellae formed during PIF-processing.     

Effect of fly ash on drying shrinkage of thermal insulation mortar with glazed hollow beads

Drying shrinkage of thermal insulation mortar with glazed hollow beads was measured by a vertical length comparator, and the influences of fly ash with different contents (0, 18%, 36%, and 54% were used) on the long-term drying shrinkage were discussed. The mass loss was measured by the weighting method and the pore structure was characterized using three different methods, including the light microscopy, the mercury intrusion porosimetry (MIP), and the nitrogen adsorption/desorption (NAD) experiments, and the correlations among them were researched. The results show that drying shrinkage process of thermal insulation mortar includes three steps with increasing curing time: the acceleration period (before 7 d), the deceleration period (7-365 d), and the metastable period (after 365 d). Drying shrinkage in the first stage (7 d before) increases quickly owing to the fast water loss, and its development in the last two stages is attributed to the increment of the pore volume of mortar with the radius below 50 nm, especially the increment of the pore volume fraction of the pore radius within the size range between 7.3 nm and 12.3 nm. There is no change in the drying shrinkage development trend of mortar with fly ash addition, and three steps in the service life, but fly ash addition in the mortar restrains its value. There is a linear relationship between the drying shrinkage and fly ash content, which means that drying shrinkage reduces with fly ash addition.     

Growth and characterization of indium doped zinc oxide films sputtered from powder targets

Indium doped Zn O films were grown on quartz glass substrates by radio frequency magnetron sputtering from powder targets. Indium content in the targets varied from 1at% to 9at%. In doping on the structure, optical and electrical properties of Zn O thin films were studied. X-ray diffraction shows that all the films are hexagonal wurtzite with c-axis perpendicular to the substrates. There is a positive strain in the films and it increases with indium content. All the films show a high transmittance of 86% in the visible light region. Undoped Zn O thin film exhibits a high transmittance in the near infrared region. The transmittance of indium doped Zn O thin films decreases sharply in the near infrared region, and a cut-off wavelength can be found. The lowest resistivity of 4.3×10~(-4) Ω·cm and the highest carrier concentration of 1.86×10~(21) cm~(-3) can be obtained from Zn O thin films with an indium content of 5at% in the target.