Study on Cure Behavior of a Model Epoxy System by Means of TTT Diagram

Curing behavior of a model epoxies system (E-54/AG-80) with DDS as hardener was studied in this paper. Round disk compression mode DMA was executed to study the gel behaviors at different temperatures to determine the relationship between gel-time (t_ gel) and temperature. The cure kinetics was studied by dynamic DSC analysis. Parameters were obtained for establishing a phenomenological cure reaction model. The relationship between glass transition temperature (T_g) and cure degree (α) was also analyzed by both isothermal and dynamic DSC method based on DiBenedetto equation, which gave a mathematical description of T_g as a function of both time and temperature. Consequently, characteristic temperatures such as T_ g0, gelT_ g and T_ g∞ were determined. Finally, the Time-Temperature-Transition (TTT) diagram was designed based on the data and equations.

C-Curves of Tool Steels for Annealing and Their Application

TTT diagrams,CCT diagrams and critical points of steels H13,S7,S5 for annealing were measured and investigated by means of Formastor-Digital full-automatic phase transformation dilatometer in order to make their annealing technology reasonable and scientific.The basis is provided for making a new annealing technology scientifically.The new technology improves the quality of annealed materials,saves energy and increases productivity.

TTT Diagram Used to Control Phase Structure of 2/4 Functional Epoxy Blends for Advanced Composites

This article uses a 2/4 functional epoxy blend system （E-54/AG-80） cured with diaminodiphenyl sulphone（DDS） as a raw material and develops a methodological procedure to establish a cure kinetic model with isothermal and dynamic differential scanning calorimeter（DSC） method and a gelation model with round-disk compression mode dynamic mechanical analyzer（DMA）, thus acquiring a series of experimental data. Characteristic temperatures such as initial glass transition temperature Tg0, gelation glass transition temperature gelTg, and infinite glass transition temperature Tg∞ are determined. The cure degree at gelation is turned out to be 0.45, while ge1Tg is found to be 70.2 ℃. The data are then used to form time-temperature-transition（TTT） diagram of the system, which serves to be a tool for process optimization of epoxy-matrix composites. A new cure processing is therefore derived from the TTT diagram. The final phase structure obtained from a controllable method is identified through scanning electron microscope（SEM） photographs to be of＂ex-situ＂ phase morphology.

Crystallization Behavior in Fluoride-Free Mold Fluxes Containing TiO_2/ZrO_2

The time-temperature-transformation （TTT） diagrams of fluoride-free mold fluxes containing TiO2/ZrO2 were constructed through the confocal scanning laser microscope （CSLM） technique. It was found that the crystallization temperature of F-free mold fluxes containing TiO2 or ZrO2 increases,while incubation time decreases with increasing basicity. The crystallization tendency increases with the zirconia addition in slag melt,as it may be thought that the addition solubility is limited in molten slag and the solid particles act as heterogeneous nucleation sites. Three types of crystal morphologies were observed,corresponding to different crystallization mechanisms. CaSiO3 and Ca3Si2O7 precipitate in the slag with low basicity,and Ca2SiO4 was formed with increasing basicity. The addition of TiO2 promotes the precipitation of CaTiO3. The logarithm of crystal growth rate increased with increasing isothermal temperature,suggesting that the crystal/melt interface reaction is the controlling step in the present experiment.

Phase separation time/temperature dependence of thermoplastics-modified thermosetting systems

The cure-induced phase separation processes of various thermoplastics(TP)-modified thermosetting systems which show upper critical solution temperature(UCST)or lower critical solution temperature(LCST)were studied with emphasis on the temperature dependency of the phase separation time and its potential application in the cure time-temperature processing window.We found that the phase separation time/temperature relationship follows the simple Arrhenius equation.The cure-induced phase separation activation energy E_(a)(ps)generated from the linear fitting of the Arrhenius equation is irrelevant to the detection means of phase separation time.We also found that E_(a)(ps)is insensitive to TP content,TP molecular weight and curing rate,but it changes with the cure reaction kinetics and the chemical environment of the systems.With the established phase separation time-temperature dependence relation,we can easily establish the whole cure time-temperature transformation(TTT)diagram with morphology information which is a useful map for the TP/TS composites processing industry.