Ti Particle Size Research Articles

Effect of Reactant Particle Size on the Self-Propagating High-Temperature Synthesis Reaction Behaviors in the Ni-Ti-B4C System

The effect of the reactant particle size on the self-propagating high-temperature synthesis (SHS) reaction behaviors in the Ni-Ti-B4C system was investigated in the present study. The B4C particle size has a significant effect on the ignition behavior and combustion wave velocity, while Ti and Ni particle sizes have only a limited influence. Increasing the B4C particle size retards the reaction initiation and remarkably lowers the combustion velocity and combustion temperature. The reaction products are mainly dependent on the B4C particle size. Nevertheless, decreasing Ni and Ti particle sizes is in favor of perfect products consisting of only TiC, TiB2, and Ni phases.

Modeling and Analysis of Compressive Properties of Porous NiTi Shape Memory Alloy Using Artificial Neural Network

Artificial neural network (ANN) is an intriguing data processing technique. Over the last decade, it was applied widely in the chemistry field, but there were few applications in the porous NiTi shape memory alloy (SMA). In this paper, 32 sets of samples from thermal explosion experiments were used to build a three-layer BP (back propagation) neural network model. According to the registered BP model, the effect of process parameters including heating rate ( ), green density ( ) and particle size of Ti ( d ) on compressive properties of reacted products including ultimate compressive strength ( v D σ ) and ultimate compressive strain (ε ) was analyzed. The predicted results agree with the actual data within reasonable experimental error, which shows that the BP model is a practically very useful tool in the properties analysis and process parameters design of the porous NiTi SMA prepared by thermal explosion method.

Effects of Ti and Zr Substituted on the Electrochemical Characteristics of MgNi‐Based Alloy Electrodes

AbstractMg‐based hydrogen storage alloys MgNi, Mg0.9Ti0.1Ni, and Mg0.9Ti0.06Zr0.04Ni were successfully prepared by means of mechanical alloying (MA). The structure and the electrochemical characteristics of these Mg‐based materials were studied. The X‐ray diffraction (XRD) result shows that the main phases of the alloys exhibit amorphous structure. The scanning electron microscopy (SEM) photograph shows that the particle size of Ti and Zr substituted alloys was about 2–4 µm in diameter. The cycle lives of the alloys were prolonged by adding Ti and Zr. After 50 charge‐discharge cycles, the discharge capacity of Mg0.9Ti0.06Zr0.04Ni was 91.74% higher than that of MgNi alloy and 37.96% higher than that of Mg0.9Ti0.1Ni alloy. The main reason for the electrode capacity decay is the formation of Mg(OH)2 (product of Mg corrosion) at the surface of alloy. The potentiodynamic polarization result indicates that Ti and Zr doping improves the anticorrosion in an alkaline solution. The electrochemical impedance spectroscopy (EIS) results suggest that proper amount of Ti and Zr doping improves the electrochemical catalytic activity significantly.

Radiative transfer modeling of compositions of lunar pyroclastic deposits

While over 100 lunar pyroclastic deposits have been identified remotely, their compositions remain poorly constrained. In this work, we determine the compositions of three lunar regional pyroclastic deposits which are likely to contain large amounts of glass and for which we have high‐quality ground‐based spectra: the Aristarchus Plateau, Mare Humorum, and Sulpicius Gallus. We use radiative transfer theory and employ measured optical constants of glasses to predict the bidirectional reflectance of a particulate glass surface as a function of Fe and Ti concentration, particle size, and maturity in order to find the best spectral match to the remotely observed deposits. Tools are not available to model the optical effects of the unusual geometries of the ilmenite laths in the black beads, so we address their effects on spectra of the regional pyroclastic deposits using computational mixing. We find that model spectra of pure glass (as opposed to devitrified black beads) provide good matches to all three regions. Radiative transfer modeling predicts iron contents of 21, 20, and 17 wt% FeO for Aristarchus, Humorum, and Sulpicius Gallus, respectively, and suggests that all three regions are low in titanium, a result supported by Lunar Prospector neutron spectrometer data. However, we find that a moderate Ti glass mixed with a small fraction of black beads cannot be ruled out for the Sulpicius Gallus region.

BP neural network prediction of the mechanical properties of porous NiTi shape memory alloy prepared by thermal explosion reaction

BP neural network model was developed for prediction of the mechanical properties of porous NiTi shape memory alloy (SMA) prepared by thermal explosion. In this paper, the model can well reflect the relationship between the process parameters including heating rate ( v ) , green density ( D) and particle size of Ti ( d) and product mechanical properties including the compressive yield strength ( σ 0.2) and Young's modulus ( E). The model can satisfactorily predict σ 0.2 and E in the ranges used to build the model. The predicted results agree with the actual data within reasonable experimental error. So the model is critical for the quality control of the porous NiTi SMA and will be widely used in thermal explosion process. At the same time, it also provides a novel method for the study of thermal explosion products.

GI-XRD studies on surface structure of ultrafine Ti(C 0.5N 0.5)-WC-Ni cermets at high temperature

Influence of coarse and ultrafine particle size of Ti(C 0.5N 0.5) on the high-temperature stability of various Ti(C 0.5N 0.5)-WC-Ni cermets under oxidizing atmosphere were compared. The evolved surface microstructure was correlated to the wear performance of the cermet exposed to similar thermophysical conditions. Investigation by glancing incidence X-ray diffraction revealed a considerable fraction of TiO 2, TiC and TiN in the near surface layer of the cermet heat treated at ∼873 K. Ultrafine cermets showed good high-temperature wear resistance, which was ascribed to the homogenous distribution of the ultrafine hard phase grains along with high total hard phase content of ∼82–85 vol.%. Comparable wear performance in coarse cermets with 5 and 15 wt.% WC was also observed in spite of a low total hard phase content (66–72 vol.%), which was attributed to the high TiN in the surface. The presence of high amount of NiO (∼22 vol.%) and low Ni in the surface layer of WC-rich (25 wt.%) coarse grade cermet contributed to its poor high-temperature wear resistance

STRUCTURE AND PROPERTIES OF TITANIUM–POLYMER THIN FILM NANOCOMPOSITES

Thin film titanium/poly-para-xylylene nanocomposites with controlled Ti content are prepared by vacuum coevaporation and cocondensation of Ti and paracyclophane. The structure and chemical composition of as-deposited samples and the changes of electrical resistivity, which they undergo upon heating, are studied by atomic force microscopy, optical absorption spectroscopy, and the temperature coefficient of the electrical resistivity. It is shown that vacuum coevaporation results in the production of nanocomposite thin films with average Ti particle size of 10–50 nm. The inorganic phase is shown to be amorphous Ti for the samples with high metal content, whereas for the low-filled nanocomposites it consists of amorphous titanium oxide. Two types of kinetics of the nanocomposite oxidation process have been found and modeled by (i) inverse logarithmic and (ii) logarithmic functions depending on the metal content within the thin film. After a long preconditioning period in air the electrical conductivity of the thin film nanocomposites was carefully investigated by two-probe DC measurements. A strong correlation between the concentration of Ti in the thin films and the electrical conductivity dependency on temperature is found and modeled by a heterogeneous model of conductivity.

Microstructural correlations between reaction medium and combustion wave propagation in heterogeneous systems

The combustion synthesis (CS) of materials is an advanced approach in powder metallurgy. Our previous studies of various CS systems have shown that at small time scales ( 10 - 3 – 10 - 4 s ), the behavior of self-propagating high-temperature reaction waves in heterogeneous mixtures follows two modes, classified according to their microstructures: quasihomogeneous and scintillating reaction waves. The latter is a novel phenomenon where the reaction propagates in a form of short and high-temperature flashes, so-called scintillations, which randomly arise in vicinity of the combustion front and promote its local movement. Using Ti–Si mixture as an example, this work is aimed to find quantitative relationship between reactant particle size and microstructural characteristics of the reaction front, including scintillation size and its distribution, as well as lifetime. It was shown that, for coarse powders ( > 40 μ m ) , specific number of Ti particles approximately equals the number of hot spots observed during the combustion process. This means that essentially every Ti particle forms a hot spot. However, for finer Ti particles, average hot spot is formed by several (3–5) such particles. Since size of scintillation decreases to a lesser extent than Ti particle size, the scintillation regime does not vanish when using finer Ti powders. These results confirm the general assumption of the relay-race model that the limiting factor of combustion wave propagation is heat transfer between reaction cells rather than reaction within the cell itself.

Micropyretic synthesis of NiTi in propagation mode

The microstructure of NiTi formed by micropyretic synthesis, carried out in the propagation mode, was investigated with preheat and Ti particle size as the two process variables. These variables were found to exert a significant influence on the microstructure. as well as the process. Unstable combustion was observed in specimens combusted without preheat. The microstructure of specimens undergoing unstable combustion showed some features which were similar to those developing during rapid solidification of NiTi in terms of the nature of the phases and their morphology. The microstructure essentially comprised the martensitic phase, the B2 parent phase and the Ti 2Ni intermetallic phase. In some specimens the Ti 11Ni 14 phase was found to form in an unusual lamellar morphology. The microstructural features of the micropyretically synthesized alloy were compared with those of the conventionally processed alloy. The structures of the B2, Ti 2Ni and Ti 11Ni 14 phases and of their interfaces with the matrix phase were examined by high resolution electron microscopy (HREM). The mechanism of synthesis of the alloy from elemental powders was studied by stopping the combustion front and carrying out detailed microstructural characterization around the arrested front.

Microstructure and tribo-mechanical properties of ultrafine Ti(CN) cermets

Role of Ti(CN) particle size on the microstructure of the Ti(CN)–WC–Ni cermets has been evaluated. The systems containing ultrafine grade Ti(CN) shows better structural homogeneity and a large volume fraction of rim phase in the core-rim structure when compared to the coarse Ti(CN) cermets. Measurable shift in the lattice parameter of the Ti(CN) core occurs in the ultrafine grade cermet possibly due to the diffusion of W and/or Ni. The improved structural features in the ultrafine grade led to considerably enhanced tribo-mechanical properties of the cermets.

Rapid exfoliation of a layered titanate by ultrasonic processing

The application of ultrasound dramatically increases the rate of exfoliation of H x Ti 2− x/4 O 4· yH 2O (H–Ti) in the presence of aqueous tetrabutylammonium (TBA) hydroxide. The effect of ultrasonication power and processing time on particle size distributions are evaluated. Applied powers of 60–300 W and reaction times of 2–30 min effectively reduce the H–Ti particle size to <100 nm. Both particle size distribution analysis and UV–Vis spectroscopy were used to study the effect of ratio of TBA ion to exchangeable protons in H–Ti; a minimum ratio of TBA/H≥0.5 is required for rapid exfoliation.

Fabrication of Thick Intermetallic Compound Al&lt;SUB&gt;3&lt;/SUB&gt;Ti Layer on Metal Substrate by Combustion Synthesis of Ball-milled Powder

A thick intermetallic compound Al 3 Ti layer was formed on a Cu or Ti substrate by a novel coating process, using combustion synthesis of a ball-milled Al-Ti powder mixture. The relation between the initial Ti particle sizes and heat treatment conditions required to react with Al completely was estimated by a spherical model incorporating diffusion kinetics to obtain homogeneous compound layer free from unreacted elements. Based on the calculated relation, a homogeneous Al 3 Ti layer was formed by using finely ball-milled powder particles with a microstructure such that Ti particles less than 1.0μm are dispersed in the Al matrix. This layer had almost the same wear property and hardness as that of a cast Al 3 Ti.

Microstructural evolution in the phase mixtures of Ti(C,N)–Mo at 1600°C

Abstract The microstructural evolution occurring during sintering at 1600°C in two different phase mixtures of Ti(C,N) and Mo was studied. The mixture of Ti(C,N)–Mo (I) was prepared using as-received commercial powders of Ti(C,N) (particle size, 1.5–10 μm) and Mo 2 C (1.5–2.5 μm), and Ti(C,N)–Mo (II) using wet ball-milled powders of Ti(C,N) (0.2–1.5 μm) and Mo 2 C (0.2–1.5 μm), followed by a decomposition treatment of Mo 2 C to Mo. It was shown that, in both mixtures studied, most Mo atoms remained as an independent phase component even after 40 h at 1600°C. During the sintering treatment, particles of Mo were transformed into a coating of Mo around the Ti(C,N) particles via surface/boundary diffusion. No (Ti,Mo)(C,N) rim structure could be detected. The present results showed that there is hardly any inter-diffusion and reaction between Mo and Ti(C,N) at high temperatures. The diffusion mechanism therefore cannot be responsible for the formation of mixed carbide or carbonitride rims during the sintering of Ti(C,N)-based cermets.

A time-resolved x-ray diffraction study of Ti5Si3 product formation during combustion synthesis

Time-resolved x-ray diffraction (TRXRD) was performed during Ti5Si3 synthesis by the self-propagating high-temperature synthesis mode for different Ti size fractions. It was determined that the time for product formation (ca. 15 s) was independent of Ti particle size. However, the formation of Ti5Si4 phase occurred when relatively large titanium particles were used. A simultaneous measurement of the temperature and TRXRD allowed us to attribute the shifting of XRD peaks at high temperature to thermal expansion of the Ti5Si3 product. The thermal expansion coefficients differ for different crystal planes, and their numerical values compare well with those reported previously in the literature.

放電プラズマ 燃焼合成法により作製したＴｉ‐Ａｌ金属間化合物系複合材料の形成過程とその組織

The aims of this study were to observe the microstructure and the tormed phases of Ti-Al intermetallic compound system composites made by spark plasma-combustion synthesis and to investigate the phase formation mechanism.During the spark plasma sintering of the Ti:Al=1:1 powders, combustion synthesis was indicated by the abruptly shringkage in sample volume at Al melting point. The microstructure and the formed phase of spark plasma-combustion synthesized composites varied according to Ti particle size. For example, TiAl3 phases were formed when 100μm Ti powders were used, and TiAl, Ti2Al and Ti3Al phases were formed when 10μm Ti powders were used (the sintering temperature was 973K). The formation mechanism of compounds using spark plasma sintering has two processes; combustion synthesis at Al melting point and diffusion in the high temperature region.

TiAl金属間化合物の燃焼合成における反応機構

The reaction mechanism of combustion synthesis of a TiAl intermetallic compound was analyzed by the observation of the reaction process in Ti and Al mixed powder compacts and by a model calculation of the reaction kinetics. A premix of Ti and Al powders was vacuum-heated in an electric furnace to cause self-sustaining reaction. The measurement of the rise in the temperature, the observation of microstructural evolution involved in the reaction process and X-ray phase analysis of the product were performed. It was observed that at the melting point of Al, Al melt surrounded Ti particles and the reaction started and proceeded towards the center of the Ti particle. The synthesis reaction has been analyzed using a spherical shell model which takes into account the microstructural change. The analysis has shown that the reaction is accelerated with reaction time, which is in accordance with the observed self-sustaining reaction. The relative contribution of the diffusion of Al in TiAl and the interface reaction between TiAl and Ti has also been quantified in dependence on the Ti particle size.

Effect of Particle Dispersion on the Mechanism of Combustion Synthesis of Titanium Silicide

The combustion synthesis (SHS) of titanium silicide (Ti5Si3) was investigated. The main combustion reaction (thermal explosion) occurs in the presence of a liquid phase and is usually preceded by a relatively small reaction in the solid state. The influence of Ti particle size on the dominance of each of these types of reactions was investigated. SEM observations and X‐ray diffraction analyses indicate that the combustion synthesis of Ti5Si3 proceeds according to the following sequence: TiSi2→ TiSi → Ti5Si4→ Ti5Si3.

Ti(CN) precipitation in microalloyed austenite during stress relaxation

Stress relaxation tests were carried out on a 0.05 pct C-0.007 pct N-0.25 pct Ti steel preheated to 1260 °C and then held in the temperature range 900 to 1050 °C. The precipitation of Ti(CN) that took place was followed by extraction replication. Dense precipitates were observed when stress plateaus appeared on the relaxation curves. The cube-shaped Ti(CN) precipitates were heterogeneously distributed in either a chain-like or a cell-like manner, indicating that the precipitates were nucleated on dislocations or on dislocation substructures. The changes in the size distribution of the precipitates during relaxation were also followed and analyzed in terms of the Zener diffusion controlled particle growth theory. The results suggest that Ti(CN) precipitation under the present experimental conditions proceeds in three sequential stages: (i) nucleation and growth according to a parabolic law; (ii) nucleation site saturation accompanied by growth alone; and (iii) Ostwald ripening. The time dependence of the mean Ti(CN) particle size is nonlinear during the first, and becomes linear during the second stage.

Factors Affecting the Porosity and Bending Strength of Ti(CN)‐TiB2 Materials

This paper describes the effects that the particle size of Ti(CN) and TiB2 powder, oxygen content of the TiB2 powder, and Co impurity content in the starting raw materials have on the porosity and bending strength ofTi(CN)‐30% TiB2 materials obtained by ordinary sintering.