Heat Curing Process Research Articles

Design of 3D vapor chamber for thermal management of permanent magnet synchronous motors

The vapor chamber is a high thermal conductivity device with significant potential for enhancing the power density of permanent magnet synchronous motors. Practical installation requirements and the heat curing process of thermal conductive adhesive impose strict demands on vapor chambers, such as precise 3D profiles and resistance to expansion. This paper presents a novel 3D wave vapor chamber with high thermal conductivity, a design not previously reported. Special internal support structures are engineered to ensure the vapor chamber with performances of thermal conductivity, anti-expansion, and bendability. Simulation results show an anti-expansion deformation of 6.28 % at 125 °C. Heat transfer experiments demonstrate that the 3D vapor chamber achieves an effective thermal conductivity of 4426.73 W/m·K and a thermal resistance of 0.136 °C/W under a 100 W heating load. Furthermore, the 3D vapor chamber-based cooling strategy manages a heat load of 143.93 W at a cutoff temperature of 90 °C, marking an 82.1 % improvement over traditional cooling methods.

Partially Bio-Based Benzoxazine Monomers Derived from Thymol: Photoluminescent Properties, Polymerization Characteristics, Hydrophobic Coating Investigations, and Anticorrosion Studies.

In this work, four thymol-based benzoxazines were synthesized using four primary amines with different chain lengths, namely methylamine, ethylamine, 1-propylamine, and 1-butylamine, which are then named T-m, T-e, T-p, and T-b, respectively. The optical properties of the synthesized thymol-based benzoxazines were examined via the photoluminescent study of their solutions in acetone. The results show that all the prepared benzoxazines emitted blue light with the maximum wavelengths from 425 to 450 nm when irradiated by the excitation wavelengths from 275 to 315 nm. The maximum excitation wavelengths are found to be 275 nm. The polymerization of the thymol-based benzoxazines is triggered by heat treatments with different conditions (160, 180, and 200 °C for 1 h). According to the FTIR results, the heat-curing process introduces a presence of the OH peak, of which intensity increases as the curing temperature increases. Thermal decompositions of thymol-based benzoxazines regarding TGA analyses reveal the enhancement of thermal stability of the benzoxazines with respect to the N-substituent chain length, as significantly observed the change in the first thermal decomposition at temperature ranged from 253 to 260 °C. Synthesized benzoxazine derivatives are further employed to coat the substrate, e.g., the glass slides. The investigation of the water contact angle shows that the coating of the benzoxazines onto the surface improves the hydrophobicity of the substrate, resulting in the enlargement of the contact angle from 25.5° to 93.3°. Moreover, the anticorrosion performance of the polybenzoxazine coatings is examined using potentiodynamic polarization techniques. The results illustrate the anticorrosion efficiency of the thymol-based polybenzoxazine up to 99.99%. Both hydrophobic and electrochemical studies suggest the feasibility for employing benzoxazines in anticorrosion coating applications.

How to understand the effect of relative humidity on the morphology and performance of polypiperazine-amide NF membrane during heat curing process

Recent studies have shown that the temperature and time of the heat curing process have important effects on the nanofiltration (NF) membrane structure and properties. However, the mechanism of the relative humidity (RH), as one of the important factors in the heat curing of NF membranes, is still unclear. To analyze the specific effect of RH, we compared the heat curing results of the NF polyamide (PA) membranes fabricated with different monomer concentrations at various RH. The nanofiltration performance of the membranes appeared to be non-uniform when the RH was in the range of 40 %–60 %. Within the appropriate RH range, the rejection of Na2SO4 was preserved at about 98.5 % for the manufactured NF membranes. At high concentrations, the increasing RH created a discontinuous condensate layer on the PA layer surface, which affected the morphology and physicochemical properties of the NF membrane causing a doubling of pure water permeability (PWP) to 8.33 L m−2 h−1·bar−1. At low concentrations, the PA layer was not significantly changed with the increase of RH, but the evaporation of water from the smaller capillary pores in its PES substrate was slowed down, which reduced the capillary stress on the substrate and prevented the collapse of the substrate pore size, resulting in a nearly 20 times increase in its PWP to 39.7 L m−2 h−1·bar−1. This work reveals the effect of RH during heat curing and gives significant guidance to the design and synthesis of high-performance NF membranes.

UV-heat dually curable epoxy resin composites with low filler contents and high curing speed

Epoxy resin composites are a type of polymer-based materials with wide application scopes. A mass of fillers was added to improve thermal properties which may degrades mechanical properties at the same time. In addition, the common heat-curing process takes several hours to completely cure. To improve the performance of epoxy resin composites of low-content fillers, we prepare UV-heat dually curable epoxy resin with silicate ester. The overall curing time of UV-heat curing process is about half of the traditional thermal-curing process. The breakdown voltage of epoxy resin modified by silicate ester is up to 181 MV/m, which is increased by 50 % compared to pure epoxy resin. The silicate ester curing agent can react with both epoxy resin and silica fillers and can thus improve the dispersion of the fillers in the matrix and enhance the interaction between fillers and the resin. As a result, the coefficient of thermal expansion (CTE) of the composites was greatly reduced. The CTE of silicate ester-modified epoxy resin composites is 93 ppm/K and 137 ppm/K over the temperature range below and above its Tg, respectively, which is 25 % lower than those of normal epoxy resin composites.

A novel poly(2-hydroxyethyl acrylamide) copolymer for the fabrication of transparent antifogging coatings on polycarbonate substrates

Although polycarbonate (PC) is widely used in various applications, its inherent hydrophobicity limits its potential in applications that require high light transmittance due to surface fog caused by changes in temperature or humidity in the environment. This work presents a facile method to fabricate transparent antifogging coatings on PC substrates based on poly(2-hydroxyethyl acrylamide-co-2-aminoethyl methacrylate) (P(HEAA-co-AEMA)), in which the AEMA segments have an amino functional group that can react with the ester group on the surface of the PC substrate to form covalent urethane bonds during the heat curing process, avoiding the problems of coating susceptibility to mechanical damage, ease of peeling, etc. Moreover, HEAA units are employed as hydrophilic groups, providing antifogging performance. These antifogging coatings can be easily obtained by coating P(HEAA-co-AEMA) copolymers on PC substrates at room temperature and then curing them by thermal treatment. These transparent coatings exhibited excellent antifogging and self-cleaning performance. Furthermore, the coatings exhibited good adhesion in the cross-cut test and thermal stability in the hot water resistance test. Therefore, the present P(HEAA-co-AEMA) copolymer coatings are promising for practical antifogging applications.

Modified Bacteria Incorporated Geopolymer - A Qualitative Approach for an Eco-friendly, Energy-efficient and Self-healing Construction Material

Cement production consumes huge energy and creates environmental pollution. Cracks present in the cement-based concretes, deteriorate the structural longevity and requires costly repair. An eco-friendly and energy-efficient geopolymeric material is developed by incorporating modified bacterium cells, assuming that the developed material will be a cement-alternatives in construction industries in near future. Transformed Bacillus subtilis cells is incorporated to the alkali-activated fly ash only (100%) for making the geo-polymeric material. The mortar samples prepared by geopolymeric material are cured under various conditions to achieve the best possible energy-efficient curing process. Simulated cracks on mortars are developed by applying 50% (half) of predetermined breaking load for studying the self-healing phenomenon. Artificial cracks on mortars are created by introducing steel bar for studying crack-repairing activity. Mechanical strengths (compressive, tensile and flexural), water permeability, sulfate and chloride resistant activities along with the crack-repairing and the self-healing efficacy of the samples are characterized. Higher mechanical strengths and better longevity in terms of decreased water and chloride ions permeability and increased sulfate resistant activity are noted in the bacterium amended mortars. Ambient temperature modified heat curing process reveals the best possible energy-efficient curing condition. Images and micro-structures analyses show that several new phases (e.g., silicate, mullite, albite and alite etc.) are developed within the bacteria-amended mortars. Eco-friendliness of the bacterium is confirmed by toxicity study against rats models and human cell lines. We hypothesize that the developed geo-polymeric material is a suitable cement alternative in construction industries as well as an eco-friendly and energy efficient material.

Preparation of liquid polysiloxane-based anti-misting agents for application in release coatings

Liquid polysiloxanes are prone to misting in coating processes performed at high roller speeds, and the addition of anti-misting agents is a cost-effective method to address this issue. In this work, a series of mildly cross-linked fluorinated polysiloxane-based viscoelastic fluids were synthetized via the successive hydrosilylation of (perfluorohexyl) ethylene (PFHE) and vinyl-terminated polydimethylsiloxane (PDMS-Vi) with hydride-terminated polydimethylsiloxane (PMHS). As anti-misting agents for high-speed coating process of silicone release agents, their inhibition efficiency can reach 92.1 % with a dosage of 4 wt%. It was also found that the physical properties, rheology, and molecular structure of the agents have various influences on inhibition efficiency depending on the anti-misting mechanisms. Additionally, the agents could significantly reduce the negative impact of coatings, and have no obvious adverse effect on the heat curing process or the transparency. The transparency of the films on the surface of the underlying polyethylene terephthalate (PET) substrate is still in excess of 95 %. Finally, the agents are conducive to improving the thermal stability of the films, and the results show that this type of viscoelastic fluids has the potential to be used in the industrial production of silicone release coatings.

High-Sensitivity and Wide-Range Flexible Ionic Piezocapacitive Pressure Sensors with Porous Hemisphere Array Electrodes.

The development of high-performance flexible pressure sensors with porous hierarchical microstructures is limited by the complex and time-consuming preparation processes of porous hierarchical microstructures. In this study, a simple modified heat curing process was first proposed to achieve one-step preparation of porous hemispherical microstructures on a polydimethylsiloxane (PDMS) substrate. In this process, a laser-prepared template was used to form surface microstructures on PDMS film. Meanwhile, the thermal decomposition of glucose monohydrate additive during heat curing of PDMS led to the formation of porous structures within PDMS film. Further, based on the obtained PDMS/CNTs electrodes with porous hemisphere array and ionic polymer dielectric layers, high-performance ionic piezocapacitive sensors were realized. Under the synergistic effect of the low-stiffness porous hemisphere microstructure and the electric double layer of the ionic polymer film, the sensor based on an ionic polymer film with a 1:0.75 ratio of P(VDF-HFP):[EMIM][TFSI] not only achieves a sensitivity of up to 106.27 kPa-1 below 3 kPa, but also has a wide measurement range of over 400 kPa, which has obvious advantages in existing flexible piezocapacitive sensors. The rapid response time of 110 s and the good stability of 2300 cycles of the sensor further elucidate its practicality. The application of the sensor in pulse monitoring, speech recognition, and detection of multiple dynamic loads verifies its excellent sensing performance. In short, the proposed heat curing process can simultaneously form porous structures and surface microstructures on PDMS films, greatly simplifying the preparation process of porous hierarchical microstructures and providing a simple and feasible way to obtain high-performance flexible pressure sensors.

From whey robocasting to custom 3D porous carbons

We describe how robocasting and carbonisation of partially dehydrated whey, a surplus of the dairy industry, produced 3D porous carbons with custom morphologies. A relatively simple printing device was first used to manufacture 3D structures of whey pastes. The whey pastes behaved as a thermoset polymer when heated hence keeping the original shape of the printed pieces upon carbonisation, albeit an isotropic size reduction (23%) due to thermal shrinkage. The rheological properties of the whey pastes were similar to those of other inks commonly used in direct ink writing, with a shear thinning behaviour and static and dynamic yield stresses that predicted their printability in most robocasting devices. Once the 3D whey structures were printed, a heat-curing process was required to avoid the uncontrolled emission of volatiles that would otherwise distort them. When doing so, 3D lattices of carbon filaments with ca. 500 µm in diameter and ca. 425 µm mesh size were manufactured. The ash content of the carbonised structures, which is related to the salt content of the original whey, was reduced by conventional washing procedures, bringing about 3D hierarchical porous carbons (70% porosity) with modest specific surface areas (500 m 2 /g) and relatively high compressive strengths (5 MPa). • Whey/water pastes can be printed using 3D extrusion printers. • Carbonisation of printed pieces preserves their shape (albeit thermal shrinkage). • 3D carbon pieces combine good mechanical properties and high porosities.

Phase change materials sheets for energy-efficient heat curing process: A potential idea and performance evaluation

Many countries experience long cold winter, which delays many in-situ concreting activities. Shifting to precast concrete systems is a common solution to continue and maintain construction progress. However, the heat curing process for precast elements represents a challenge for the precast industry due to its high energy consumption (i.e. high fossil fuels dependency and associated high carbon emissions). Therefore, this study examines the feasibility of utilizing micro-encapsulated phase change materials (MPCMs) to achieve a sustainable curing process. Both direct incorporation of MPCMs in the cementitious mixtures and covering specimens with MPCMs sheets were examined under a simulated heat-curing cycle. Results showed that covering specimens with MPCMs sheet eliminated drawbacks induced by MPCMs direct incorporation (i.e. leakage of paraffin, voids, and loss of function). Moreover, utilizing the MPCMs sheet allowed shortening the heat curing holding period by 50% (i.e. from 10 hrs to 5 hrs) while achieving 96% of the desired strength. Findings confirmed the high potential of using MPCMs sheets to cure, save energy, and boost the precast concrete industry's sustainability level.

Numerical implementation and validation of a viscoelastic-plastic material model for predicting curing induced residual stresses in adhesive bonded joints

One of the main challenges in the joining of multi-material components is the assessment of the nature and magnitude of the residual stresses developing in the adhesive bond during the heat curing manufacturing process. Numerical modeling of these residual stresses can provide insights for making informed decisions related to (i) material substrate properties; (ii) adhesive properties i.e., low, medium, or high stiffness; (iii) bondline geometry i.e., bondline width and bead thickness; (iv) curing cycle characteristics; and (v) fixation design i.e., type, spacing, the number of joints. This work presents a cure history-dependent viscoelastic-plastic material description for the modeling of adhesive bonded joints. The main highlight of the work is the multi-physics modeling package consisting of a curing kinetics model, a cure-dependent viscoelastic model, and a temperature, strain-rate dependent plastic model formulation which can be coded in any finite element solver. The modeling approach can predict the residual stresses in the adhesive bond due to the accumulated viscoelastic as well as plastic strains occurring during the heat curing process. For the purpose of validation, the model is coded into a user-defined material subroutine (UMAT) in LS-DYNA. The modeling approach is verified at a small specimen level by simulating a uniaxial tension specimen at various temperatures and strain rates. The performance of the modeling approach is further evaluated at the component level using specially designed experiments involving heat curing of a sub-sized multi-material automotive roof model. The thermal displacements and distortions in the roof structure captured using 3D digital image correlation are compared to the finite element model predictions. Several design guidelines related to adhesive selection and mechanical fixations are proposed as a result of the study.

Mechanism of C4AF Content and Heat-curing Process on the Abrasion Resistance of High Ferrite Cement

Mechanism of C4AF Content and Heat-curing Process on the Abrasion Resistance of High Ferrite Cement

Improve the long-term property of heat-cured mortars blended with fly ash by internal curing

Due to the satisfactory property and high productivity, heat-cured concretes have been widely used in engineering practice. However, heat curing process also brings some drawbacks that are detrimental to the long-term property of this material. To address this issue, lightweight fine aggregate (LWFA) was employed to provide internal curing (IC) for a heat-cured mortar (HCM) blended with fly ash (FA). The influences of LWFA on the interior relative humidity of HCM and the reaction environment and behavior of FA were measured. It was found that IC of LWFA could mitigate the drop of interior humidity and enhance the reaction degrees of cement and FA. This contributed significantly to the microstructure densification of HCM, higher compressive strength and better resistance to chloride ion. The results indicate that LWFA benefits to enhancing the efficiency of FA in a heat curing system and the combination of LWFA and FA contribute to improving the long-term property of HCM.

Characteristics of Waste Iron Powder as a Fine Filler in a High-Calcium Fly Ash Geopolymer.

Geopolymer (GP) has been applied as an environmentally-friendly construction material in recent years. Many pozzolanic wastes, such as fly ash (FA) and bottom ash, are commonly used as source materials for synthesizing geopolymer. Nonetheless, many non-pozzolanic wastes are often applied in the field of civil engineering, including waste iron powder (WIP). WIPs are massively produced as by-products from iron and steel industries, and the production rate increases every year. As an iron-based material, WIP has properties of heat induction and restoration, which can enhance the heat curing process of GP. Therefore, this study aimed to utilize WIP in high-calcium FA geopolymer to develop a new type of geopolymer and examine its properties compared to the conventional geopolymer. Scanning electron microscopy and X-ray diffraction were performed on the geopolymers. Mechanical properties, including compressive strength and flexural strength, were also determined. In addition, setting time and temperature monitoring during the heat curing process were carried out. The results indicated that the addition of WIP in FA geopolymer decreased the compressive strength, owing to the formation of tetrahydroxoferrate (II) sodium or Na2[Fe(OH)4]. However, a significant increase in the flexural strength of GP with WIP addition was detected. A flexural strength of 8.5 MPa was achieved by a 28-day sample with 20% of WIP addition, nearly three times higher than that of control.

Viscoelastic model to capture residual stresses in heat cured dissimilar adhesive bonded joints

The thermal loading during the curing process of an adhesive-bonded joint induces residual stresses in the joint, thereby affecting its performance. The problem becomes worse in the case of a multi-material joint involving varying coefficients of thermal expansion (CTE) for different parts. A novel approach was developed to model the properties of automotive grade structural adhesives during the heat curing process. The material model was divided into two components: curing kinetics model and viscoelastic mechanical model. The models were calibrated using experimental data from Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) tests performed on an epoxy-based single-component adhesive. The calibrated material model parameters were fed into a finite element simulation and the prediction results were compared to a unique set of experiments utilizing two substrate combinations of adhesive-bonded single lap shear joints. An excellent agreement between the simulated and experimental results (displacement across the bond, force applied by the adhesive) was achieved. The modeling results give a better understanding of the residual stresses and agree with the experimental trend on the effect of bondline thickness on the joint.

Effect of microwave-assisted curing process on strength development and curing duration of cellular lightweight geopolymer mortar

ABSTRACT The heat curing process using an electric oven has been generally applied for curing geopolymer material as it accelerates strength development. However, a microwave curing process is an alternative approach to obtain a shorter heat curing process. This paper focuses on the strength development and required curing duration of a cellular lightweight geopolymer mortar using a microwave-assisted curing process. Other curing approaches, namely (i) room curing process, (ii) typical oven curing process, and (iii) microwave curing process, were also comparatively examined. Bottom ash was used as light-fine aggregate to replace sand by 0%, 25%, 50%, 75%, and 100%. The results revealed that replacing 25% of the sand with bottom ash provided the optimal strength and low density for all mixtures. A 28-day age strength of 12.27 MPa was achieved by the microwave-assisted curing process, while a strength of 5.77 MPa was achieved by the typical oven curing process. The microwave-assisted curing process could significantly improve the early strength development and reduce both the overall curing period and energy consumption by around 75% compared to a typical oven curing process. This approach could be applied as an alternative geopolymer synthesis for the development of environmental-friendly construction material for lightweight applications.

The influences of different size SiO2 nanoparticles on dielectric properties and corona resistance of epoxy composites

In order to optimize the dispersion structure of the filler in polymer composites, 15 nm SiO2 (HL‐150) and 6 nm SiO2 (HL‐380) are added to epoxy (EP). The total content of silica filler is fixed at 15 wt%, and the mass ratio of HL‐380 to HL‐150 in silica filler is adjusted. SiO2/EP nanocomposites are prepared by the sand milling and heat curing process. Transmission electron microscopy results show that the mixed SiO2 fillers are well dispersed in EP. With the increase of HL‐380 filler, the relative permittivity of the SiO2/EP nanocomposites with mixed SiO2 nano‐fillers increases, compared with the nanocomposites added HL‐150 filler alone. The electrical aging threshold and dielectric strength increases, and the inhibiting effect on space charge accumulation is enhanced. When the mass ratio of HL‐380 to HL‐150 is 1/6.89, the corona resistance life are the longest, with the value of 13.23 hours, which is 1.47 times than that of the composites with HL‐150 filler alone.

Experimental methods to capture curing induced effects in adhesive bonded joints

The rapidly increasing use of structural adhesives, especially in the joining of automotive body structures has motivated various investigations of the effects of adhesive curing process on joints. The automotive-grade structural adhesives require heat curing, which, in the meantime, performs thermal loading on the substrates and causes undesirable effects in the joint. For example, the curing process results in complex residual stresses in the adhesive bond which are detrimental to the performance of the adhesive bond and thereby the automobile body structure, particularly the crashworthiness. To thoroughly evaluate such effects, this paper consists of two parts. The first part presents an innovative experimental method to characterize the thermal effects of the heat curing process on a multi-material single lap shear joint using digital image correlation. The second part of the study compares the performance of residual stress-induced joints against stress-free joints under tension loading at different strain rates. The proposed experimental method and the corresponding results from this study are expected to help comprehensively understand the adhesive joining process and its potential side effects on the automobile body structure.

Influence of nano SiO2 and nano CaCO3 particles on strength, workability, and microstructural properties of fly ash‐based geopolymer

AbstractThe influence of nano SiO2(NS) and CaCO3(NC) particles on the properties of class F fly ash based geopolymer mortar activated with different sodium ion concentrations have been investigated. Mortar mixture proportions were 1:3:0.3 for binder, sand, and water, respectively. Nano SiO2 and CaCO3 particles were replaced with a binder by weight basis at the ratios of 1, 2, and 3% in the mixtures. Sodium concentrations amount used were 8, 10, and 12% Na+ of binder content. Geopolymer mortar samples were cured at 60, 75, and 90°C in a furnace for 24, 48, and 72 hr. After the heat curing process, flexural, and compressive strength tests were performed. The changes in the microstructure of geopolymer due to influence of nanoparticles were examined by utilizing isothermal calorimetric studies on geopolymer paste, and field‐emission scanning electron microscopy (FESEM). Based on laboratory work results, it was concluded that for all sodium ion concentrations, the addition of nano SiO2 and CaCO3 particles improved the flexural and compressive strengths after 24 hr heat curing. However, the favorable effects of nanoparticles on strength properties tend to disappear after 48 and 72 hr heat curing. The results of isothermal calorimetric studies showed that nano SiO2 and CaCO3 particles accelerated the geopolymeric reactions at an early age. FESEM results showed that additions of nanoparticles made the microstructure of geopolymer products more intense and compact.

Effect of GGBS Addition on Reactivity and Microstructure Properties of Ambient Cured Fly Ash Based Geopolymer Concrete

Geopolymer concrete is an eco-friendly alternate to conventional concrete that considerably lower green house gases emitting into the atmosphere. Fly ash based geopolymer concrete is reported to become hardened during heat curing process which comes as a major constraint for cast in in-situ applications. In this study, the aluminosilicate materials such as Ground Granulated Blast Furnace Slag (GGBS) with varying percentages such as 0%, 10%, 20%, and 30% replaces the fly ash (FA) in geopolymer concrete was used. Manufactured sand (M-sand) is used as full replacement material for natural sand as fine aggregate owing to its increasing demand. This work aims at investigating the effect of alumino silicate materials on strength properties, characterization and micro structural analysis using Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray spectroscopy (EDX), Fourier Transform Infrared spectroscopy (FTIR) and X-ray diffraction (XRD) in geopolymer concrete under ambient curing condition. The SEM and EDX results reveals that, the micro structural properties of fly ash, GGBS materials, CaO, Si/Al ratio, and gel formation have a significant effect on compressive strength and setting time of geopolymer concrete. The FTIR analysis reveals that the stretching vibration of fly ash shifts to low wave number values due to changes in geopolymerization. The X-ray diffraction (XRD) reports show that the C-S-H gel formed around 27–30° 2theta value due to increase of GGBS in geopolymer concrete.