Effect of Decomposition Kinetics and Failure Criteria on Binder-Removal Cycles From Three-Dimensional Porous Green Bodies

A previously developed algorithm can be used to predict the minimum time for the thermal removal of binder from porous green ceramic bodies. The algorithm combines a variational statement on internal pressure, which is generated by binder decomposition, with a transport model that treats the convective flow of binder decomposition products in a porous medium. The minimum time heating cycles depend on a number of coupled transport, kinetic, and dimensional parameters. The predicted minimum time heating cycles depend on the decomposition kinetics (activation energy, preexponential factor, and decomposition mechanism) and on the temperature and pressure at which failure occurs in the green body.     

Determination of the Minimum Time for Binder Removal and Optimum Geometry for Three-Dimensional Porous Green Bodies

A model is developed to optimize two aspects of the thermal removal of binder from green ceramic components. The model, which accounts for flow in porous media arising from the thermal decomposition of binder in three-dimensional bodies with anisotropic permeability, describes the pressure within the body as a function of position, time, and temperature during the heating cycle. The model is used with variational calculus to predict the heating profile that minimizes the cycle time for the thermal removal of binder. The model is also used to determine which body geometry maximizes the buildup of pressure in parallelepipeds, a common shape of multilayer ceramic capacitors.     

Heat Evolution Tests with Calcium Aluminate Binders and Castables

A simple device is described for the determination of the rate of temperature increase during the hydration of calcium aluminate binders and castables under semiadiabatic conditions. Automatically recorded time-temperature curves are shown for commercial binders of various compositions. The complex relations between the rate of heat evolution and other properties of commercial and synthetic binders were studied by varying such factors as composition, crystal development, and fineness of the binder. The effect of additions of polyelectrolytes was also explored. It was found that, for a given binder composition, the thermal history of the binder and the amount of admixtures influenced the rate of hydration most markedly. Some correlation between heat evolution and strength development was indicated.     

Minimum Time Heating Cycles for Diffusion‐Controlled Binder Removal from Ceramic Green Bodies

An algorithm based on variational calculus has been developed to predict the minimum time heating cycle (MTHC) for thermal binder removal from a ceramic green body when diffusion, as described by the free volume theory, is the governing mass transport mechanism. The algorithm uses a previously derived analytic solution for the diffusant concentration, which was obtained from the governing reaction–diffusion differential equation. Either a constraint on diffusant concentration or on the equilibrium pressure of diffusant is used to predict the MTHC for both a stationary binder model and a shrinking core binder model. For these four cases, the dependence of the MTHC has been determined on a number of model parameters, including the threshold concentration or pressure, the body size, and the reaction order of the binder degradation kinetics. The algorithm determines two important aspects of the MTHC, namely, the starting temperature of the heating cycle and how temperature varies with time during the cycle. The duration and shape of the temperature‐versus‐time heating schedule, whether increasing, decreasing, or almost constant, depends sensitively on parameters in the model.     

一种水性负极黏结剂的合成及性能

黏结剂对电极的性能有着重要的影响。本文设计并制备了一种新型水性聚(乙烯-乙烯醇)-磺酸锂（EVOH-SO₃Li,简称ES-Li）电极黏结剂,并对其键接结构及组成进行分析;对其溶解性、电解液稳定性、热稳定性进行测试;对所制电极柔性、微观形貌及电化学性能进行研究。经与聚(乙烯-乙烯醇)（EVOH）及商业的聚偏氟乙烯（PVDF）黏结剂进行对比。结果表明：ES-Li水性黏结剂具有不溶解于电解液,热稳定性良好等优点;ES-Li黏结剂制备负极柔性及微观形貌优良,采用ES-Li作为负极黏结剂的电池在电化学稳定窗口、界面阻抗、首次循环效率、循环及倍率等方面均表现优异,ES-Li负极的首次库仑效率为89.93%,在1C下循环100次的容量保持率为96.93%,且在2C、5C倍率下的循环性能均优于EVOH及PVDF制备的负极,具有应用潜力及商业化前景。     

Time‐Evolution of TATB‐Based Irreversible Thermal Expansion (Ratchet Growth)

TATB is an insensitive high explosive, attractive for use because of its safety aspects. TATB compactions, with or without binder, undergo irreversible volume expansion (or ratchet growth) upon thermal cycling. In the past, experimental elucidation of this phenomenon has focused on irreversible expansion as a function of the number of thermal excursions over a given temperature range, where growth is asymptotic with increasing cycle number. In this paper, we demonstrate that ratchet growth also occurs as a function of time at constant temperature, and that growth is substantial at elevated temperatures. We have measured strain response in PBX 9502, a TATB‐based composite, by performing thermal‐cycling tests with different durations at high temperature. Irreversible growth arises from the thermal ramps themselves (increasing and decreasing), as well as from the subsequent isotherms. PBX 9502 specimens with previously‐identified TATB texture/orientation were used in order to eliminate and/or evaluate texture as a variable. Measurements were also performed on dry‐pressed TATB (no binder) to confirm that expansion as a function of time (constant temperature) is not caused by the binder. A simple analysis of the time‐response data demonstrates consistency in the results. We propose that the primary driving force for irreversible expansion is the proximity of the current strain value (due to thermal history) to the strain saturation point of the current cycle (i.e. strain at infinite high‐temperature hold times or an infinite number of cycles). Such tests should aid in the understanding and modeling of ratchet growth response in these materials.     

Liquid-Phase Transport During Removal of Organic Binders in Injection-Molded Ceramics

A method has been developed for calculating hydraulic pressures induced by thermal expansion of liquid binders early in the removal cycle, when evaporative losses are negligible and fully saturated conditions prevail. Specific results were obtained for flat compacts containing a common wax binder, mixed with varying amounts of low-density polyethylne. In general, these results show how the risk of hydraulic fracture increases with heating rate and compact thickness. Although pressures are minimal when the binder consists entirely of wax, the continual addition of polyethylene eventually gives rise to unacceptable risk levels, even for relatively thin compacts. Binder removal at elevated temperatures is considered subsequently. In this case, vapor pressures eventually approach a critical level, thereby allowing mass removal by evaporation to overcome the effect of thermal expansion in maintaining full saturation. With the onset of void formation, the developing capillary pressure supersedes hydraulic pressure as the driving force in liquid transport. Besides representing capillary flow, the present formulation also accounts for thermal degradation of the binder during removal. The resulting system of equations was solved numerically for a variety of representative debinding conditions. Predictions for flat compact containing a balanced wax/polyethylene binder indicate that thermal degradation of the polyethylene can give rise to a marked improvement in debinding rates. It turns out, however, that this enhancement is far more effective in thinner compacts.     

Strengthening of Al2O3 porous composites with a glass-ceramic binder doped with nanocopper

Glass ceramics are the result of controlled crystallisation of one or more crystalline phases embedded in the glass matrix, which usually results in better mechanical properties than conventional glasses. Crystalline phases precipitated in the vitrified bond improve mechanical strength and provide new functions that are not present in the original glass. The most widely encountered issue in standard composites is the presence of inclusions, generated during the process of thermal treatment, of finely dispersed crystalline phases, which are spread in the amorphous phase.Another way of increasing the mechanical properties of composites is via surface crystallisation of the binder. The mechanical strength can be significantly and permanently increased by inducing compressive stress at the glass surface. In the case of the binder designed here, the generated crystalline phase is willemite (Zn₂SiO₄), which is characterised by a low coefficient of thermal expansion (CTE). Zn₂SiO₄ usually crystallises at the glass surface, which results in the development of favourable compressive stresses in the glass-crystalline binder.Transition metal oxides significantly affect the crystallisation characteristics, thus influencing the thermal behaviour of glass ceramics. The majority of current publications focus on studies of the influence of copper on certain properties, and mainly the optical and photonic properties, and the influence of copper on the mechanical properties of silicate systems is still poorly recognised. This article investigates the mechanical and physical properties of porous Al₂O₃ composites with a glass-ceramic bond doped with nanocopper.     

刚玉-莫来石推板的研制与应用

研究了颗粒组成、结合剂种类及含量对刚玉 -莫来石质推板热震稳定性的影响。结果表明 :当颗粒料中莫来石与刚玉的质量比为 3∶1时 ,试样的抗折强度保持率最高 ,与颗粒料全部采用莫来石颗粒或刚玉颗粒相比 ,110 0℃ 水冷 3次后的抗折强度保持率分别提高了 2 5 %和 35 %。另外 ,用硅铝凝胶替代粘土作结合剂 ,也可提高刚玉 -莫来石质推板的热震后抗折强度保持率。研制出的刚玉 -莫来石推板的高温强度高 ,110 0℃ 水冷循环的热震次数超过 4 5次。经国内某厂家试用 ,其寿命可达 12 0次。     

Modeling of the Pressure Distribution in Three-Dimensional Porous Green Bodies during Binder Removal

A model is developed to describe flow in porous media from the thermal decomposition of binder in three-dimensional bodies with anisotropic permeability. The model is able to describe the pressure within the body as a function of position, time, and temperature during the heating cycle. The results from numerical solution of the un-steady-state partial differential equation are compared to those obtained from an analytical solution to the steady-state equation. Under many conditions that are representative of binder removal, the analytical solution provides a reasonable representation of the numerical solution. A criterion is also developed to determine when the analytical solution is valid. Scaling relationships for the buildup of pressure in terms of the dimensions of the body, the rate of reaction, and the permeability are also derived.     

Characterization of the stress distribution and evolution inside a thermal barrier coating after initial thermal cycles

The residual stress introduced inside a thermal barrier coating (TBC) during manufacturing and service processes is one of the main causes of thermal barrier failure. The formation and evolution of internal stress in the TBC begin at the early stage of service, but studies on the mechanism of the distribution and evolution of the stress in the TBC during the initial thermal cycle are still lacking. To explore the evolution mechanism of the stress in the TBC interior, an experimental study on the regulation mechanism of the initial thermal cycle on the TBC internal stress was carried out in this paper. First, the internal stress of TBC specimens after thermal cycles was characterized based on photoluminescence spectroscopy (PL) and terahertz time-domain spectroscopy (THz-TDS) technologies, in which the homogenization of the near-interface stress field was observed during the initial thermal cycle. Then, the evolution of the microstructure and phase structure of the TBC specimens was characterized. Finally, the phenomenological model of the evolution of the TBC internal structure was established, revealing that the initial thermal cycle regulated the microstructure of the top coating (TC) through phase transformation to realize the homogenization of the near-interface stress field.     

型煤黏结剂的研究进展

根据黏结剂的结合机理和化学性质分别介绍了型煤黏结剂的两种分类方法。阐述了几种主要黏结剂的研究现状,重点分析了有机黏结剂、无机黏结剂、有机-无机复合型黏结剂的研究和应用情况。有机黏结剂的黏结性能和耐水性均较好,但热稳定性差,且价格昂贵,在一定程度上限制了其进一步的发展和应用。无机黏结剂来源广泛,价格便宜,具有一定的热强度,有的还有固硫作用,在中国的化肥用型煤和民用型煤生产中占很大比例;无机黏结剂生产的型煤热稳定性好,但可燃性差,增加了型煤灰分,降低了型煤发热量,无法满足用户对热值的需求。有机-无机复合黏结剂结合了有机黏结剂和无机黏结剂的优点,使黏结剂的多效性得到充分发挥,制备的型煤具有较高的机械强度和热稳定性,成为近年来研究开发的     

Thermal structural damage and thermal decomposition characterization of GAP propellants with nitrate ester plasticizers

GAP and nitrate ester compounds are introduced into the solid propellant formulation as energetic binders and energetic plasticizing agents, respectively, to further enhance the energy level of solid propellants. However, under abnormal thermal conditions, various components within GAP propellants, especially nitrate ester plasticizers, can collectively result in the generation of a large number of voids within the propellant due to factors such as thermal stress and slow component decomposition. This phenomenon can impact the safety of solid rocket engines, necessitating research into their thermal decomposition processes and thermal damage structures. In this study, the thermal decomposition characteristics and gas products of GAP propellants with different nitrate ester plasticizer formulations were investigated using DSC-TG and FT-IR. The damage structure of GAP propellants heated under unignited conditions was studied through Micro-CT, examining the influence of heating conditions and nitrate ester plasticizers on the thermal damage structure of GAP propellants. During heating, the thermal damage structure of GAP propellants was found to include voids generated within the GAP binder and cracks at the interface between the GAP binder and particles, with nitroglycerin as a plasticizer exacerbating the thermal damage of GAP propellants (about 2.2–2.9 times).     

Effect of binder on performance of intumescent coatings

This study investigates the role of the polymeric binder on the properties and performance of an intumescent coating. Waterborne resins of different types (vinylic, acrylic, and styrene-acrylic) were incorporated in an intumescent paint formulation, and characterized extensively in terms of thermal degradation behavior, intumescence thickness, and thermal insulation. Thermal microscopy images of charred foam development provided further information on the particular performance of each type of coating upon heating. The best foam expansion and heat protection results were obtained with the vinyl binders. Rheological measurements showed a complex evolution of the viscoelastic characteristics of the materials with temperature. As an example, the vinyl binders unexpectedly hardened significantly after thermal degradation. The values of storage moduli obtained at the onset of foam blowing (melamine decomposition) were used to explain different intumescence expansion behaviors.     

Thermal Decomposition of AMMO/AP Composite Propellants

Thermal decomposition of AMMO/AP composite propellants was studied by DTA, TGA and DSC in helium atmosphere. The effects of accelerated aging at 347 K for 370 days on decomposition kinetics were also measured. AMMO/AP propellant showed two different decomposition steps, which were mainly the AMMO binder decomposed region and the reaction of AP dominated region. These regions were separated at around 20 % weight loss point at the condition used in this study. AMMO binder decomposition and AP decomposition were strongly related each other. The heat generated by the AMMO binder decomposition initiated and accelerated the thermal decomposition of AP. Although both Fe₂O₃ and CFe activated the thermal decomposition of AMMO/AP propellants, CFe mainly accelerated the decomposition of AMMO binder and Fe₂O₃ catalyzed the AP reactions which consisted of the AP decomposition and the reaction between decomposed AP and decomposed AMMO binder. AMMO/AP composite propellants were thermally stable even after aging at 347 K for 370 days.     

Partial wick-debinding of low-pressure powder injection-moulded ceramic parts

Al₂O₃-based green bodies were shaped using low-pressure injection moulding. The binder content and the binder distribution during the thermal debinding inside a wicking embedment were analyzed. A distinct trailing front, which separates the binder-lean and binder-rich regions, was observed. This kind of binder distribution forms suddenly, after the moulded piece is heated above the melting point of the binder and is then cooled down. Mechanisms that can explain the observations are presented. The non-uniform binder distribution is explained by a capillary extraction of the binder with two different mobilities, which depend on the size of the pores inside the moulded piece. A sudden loss of binder at the beginning of the debinding process is the result of exudation, caused by a large thermal expansion of the binder as it melts. During cooling, the binder solidifies, which significantly affects the binder distribution due to a contraction of the binder.     

Unmolded refractories with a silica sol binder

Results are provided for a study of unmolded refractories based on silica sol binder, and comparison of them with unmolded refractories with a binder based on high-alumina cement. It is shown that with respect to strength and thermal shock resistance unmolded refractories with a silica sol binder surpass those with a cement binder. Refractories with a silica sol binder make it possible to use them for drying up to 110°C, and this reduces considerably the preparation time to use for a molded refractory.     

Modeling of mass transfers in a porous green compact with two-component binder during thermal debinding

Mass transfers and phase changes of two-component binder in a porous green compact during thermal debinding process are modeled. The evaporation of low molecular weight (LMW) component and volatile fragments, the thermal degradation of high molecular weight (HMW) component, the capillary driven and pressure driven liquid phase transports, the binary diffusion in solutions, the convection and diffusion of gas phases, and the heat transfer in a porous medium are captured in the model. The model is validated with experimental data. The simulated results show that mass transfers during the early stage of thermal debinding are mainly due to capillary driven and pressure driven liquid transports. During the final stage of thermal debinding, both convective liquid and gas transports are important in binder removal. The developed model provides physical understanding of binder removal mechanisms that are essential for process optimization.     

DSC evaluation of binder content in latex paints

The estimate by differential scanning calorimetry of the enthalpy of thermal decomposition of the organic fraction in a complex material can be used, in proper conditions, for evaluating the concentration of the organic components. The application of this technique of thermal analysis to latex paints aimed at identification of binder content is discussed in this paper. On the one hand it gives good results on binder content estimate; on the other hand it highlights some aspects of the thermal decomposition of polymers enclosed in an inorganic matrix. The phenomena of thermal decomposition are studied for the main components of latex paints, i.e. for polymers, and for complete paint formulations. The materials considered include widely used binders for the manufacture of latex paints such as vinyl acetate/Versatate copolymers and styrene/acrylic copolymers, rheology modifiers such as cellulose ethers and other standard components of latex paints. Formulations representing typical latex paints with different binder content and simplified polymer/filler systems are considered. Although decomposition paths are very different for different polymers and for the same polymer in different concentrations, the overall heat output is consistent and proportional to the amount of polymer in the sample. Therefore identification by DSC measurements of the binder content in a latex paint appears as a feasible technique.     

陶瓷注射成型中粘结剂的热脱脂特性评价

脱脂是陶瓷注射成型工艺的制约性步骤.通过热分析的方法研究了PW+EVA+SA的热特性.通过计算的方法和实测的方法得到粘结剂整体的热失重曲线,发现两者较为接近,继而提出了一个定量评价粘结剂脱脂特性的物理参量--脱脂惯量.通过对脱脂惯量的计算发现PW78%+EVA21%+SA1%粘结剂体系具有最好的脱脂特性.