NETZSCH Instruments to Solve Thermoelectric and Building Materials Applications

Introduction

“Hi! My name is Elizabeth Graham (left picture), and I am the laboratory coordinator for the physical and mechanical properties lab in the Central Analytical Research Facility (CARF) at Queensland University of Technology (QUT). CARF is a group of approximately 50 professional and academic staff managing a portfolio of instruments that service many of the science-based research needs at QUT. My colleague Jun Zhang (right picture) and I provide training and support on thermal analysis to the QUT research community as well as testing and consulting services to Australian research and commercial organisations.

We are located in the heart of the city of Brisbane, Queensland, adjacent to the botanic gardens in a modern purpose-built Science and Engineering facility with over 600 internal clients. Our mission is to provide operational training to QUT HDR students and other QUT researchers so that they graduate from their degree with hands-on training on equipment along with the requisite understanding to get the best results from their data analysis. We currently have 188 trained QUT users across the suite of NETZSCH instruments.

Case 1: The Macromolecular Design of Poly(styrene-isoprene-styrene) (SIS) Copolymers Defines their Performance in Flexible Electrothermal Composite Heaters

_{Hiruni T. Dedduwakumara, Christopher Barner-Kowollik, Deepak Dubal, and Nathan R.B. Boase; ACS Applied Materials & InterfacesArticle ASAP; DOI: 10.1021/acsami.3c19541;
See publication at acsami.org: ACS Publications}

This study focuses on improving the stability and performance of flexible composite electrothermal heaters for electric vehicles. These heaters are used in applications such as automobiles, smart windows, de-icers, displays, thermotherapy pads, and sensors. They are essential for maintaining vehicle efficiency in cold weather, where cabin heating in cold weather significantly affects vehicle range. Metal alloys and transparent conductive oxides (TCOs) are common materials for this application; however, they have limitations such as unsuitable mechanical properties for the application, and material scarcity.

Polymers have been explored here as alternatives to metal heating devices due to their light weight, flexible nature and economic viability. However, pure polymers usually have low Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity and stability. Thus, this research focuses on polymer-based composites comprised of poly(styrene-isoprene-styrene) (SIS) and hydrogenated poly(styrene-ethylene-propylene-styrene) (SEPS) copolymers mixed with varying amounts of Carbon BlackTemperature and atmosphere (purge gas) affect the mass change results. By changing the atmosphere from, e.g., nitrogen to air during the TGA measurement, separation and quantification of additives, e.g., carbon black, and the bulk polymer can become possible.carbon black (CB). The roles in determining thermal properties played by the presence of olefinic bonds, and the loading of CB were investigated in detail.

During the study, the researcher synthesized and characterized three types of SIS/SEPS copolymers and their composites with Carbon BlackTemperature and atmosphere (purge gas) affect the mass change results. By changing the atmosphere from, e.g., nitrogen to air during the TGA measurement, separation and quantification of additives, e.g., carbon black, and the bulk polymer can become possible.carbon black (CB). The Thermal StabilityA material is thermally stable if it does not decompose under the influence of temperature. One way to determine the thermal stability of a substance is to use a TGA (thermogravimetric analyzer). thermal stability properties were assessed using thermogravimetric analysis (NETZSCH Jupiter^® 449 F3 STA) in both inert and oxidative environments. The electrothermal performance was evaluated by measuring the thermal and Electrical Conductivity (SBA)Electrical conductivity is a physical property indicating a material's ability to allow the transport of an electric charge.electrical conductivity and uniformity of heat distribution. Resistance, sheet resistivity, and conductivity of composite thin films were measured using a KSR-4 Four-Point Probe System. Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature. Thermal conductivity was measured using the NETZSCH laser flash analyzer. Specific heat and Glass Transition TemperatureThe glass transition is one of the most important properties of amorphous and semi-crystalline materials, e.g., inorganic glasses, amorphous metals, polymers, pharmaceuticals and food ingredients, etc., and describes the temperature region where the mechanical properties of the materials change from hard and brittle to more soft, deformable or rubbery.glass transition temperatures were measured using the NETZSCH DSC Phoenix^®. A schematic diagram showing the approach to the characterisation is shown below.

DSC was used to study the impact of the introduction of CB on the Glass Transition TemperatureThe glass transition is one of the most important properties of amorphous and semi-crystalline materials, e.g., inorganic glasses, amorphous metals, polymers, pharmaceuticals and food ingredients, etc., and describes the temperature region where the mechanical properties of the materials change from hard and brittle to more soft, deformable or rubbery.glass transitions in the copolymer systems. The marginal alterations observed suggest that the structure of CB within the composites does not impede the mobility of polymer chains, even at elevated CB concentrations, within the tested compositions, which is highly beneficial for the applications involving composite film heaters. A key limitation of flexible electrothermal heaters is their stability at high temperatures or voltage or under prolonged usage. In an attempt to understand aging and degradation of polymer composites that occurs with electrical failure of devices, 1,4-SIS-28CB, 3,4-SIS-28CB, and SEPS-28CB composite heaters were intentionally subjected to overvoltage (30 V) until current flow ceased. The Glass Transition TemperatureThe glass transition is one of the most important properties of amorphous and semi-crystalline materials, e.g., inorganic glasses, amorphous metals, polymers, pharmaceuticals and food ingredients, etc., and describes the temperature region where the mechanical properties of the materials change from hard and brittle to more soft, deformable or rubbery.glass transition temperature(_Tg) of each electrically failed composite film was determined using DSC analysis. Importantly, it was observed that_Tg of olefinic blocks remained unchanged, confirming that the bulk of the copolymer matrix did not degrade during failure.

Measuring Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.Thermal Conductivity using the NETZSCH LFA 467

Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature. Thermal conductivity plays a vital role in composite film heaters, as it governs the material’s ability to distribute heat. Experiments were conducted on composite films to measure their Thermal DiffusivityThermal diffusivity (a with the unit mm2/s) is a material-specific property for characterizing unsteady heat conduction. This value describes how quickly a material reacts to a change in temperature.thermal diffusivity using the NETZSCH LFA 467 laser flash and Specific Heat Capacity (cp)Heat capacity is a material-specific physical quantity, determined by the amount of heat supplied to specimen, divided by the resulting temperature increase. The specific heat capacity is related to a unit mass of the specimen.specific heat capacity was measured on the NETZSCH Phoenix^® DSC with the aim of calculating Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity values at different CB loadings.

The study found that increasing CB loading from 16 wt.% to 28 wt.% resulted in significant enhancements in Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity for all the copolymers studied. The improved Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity was attributed to CB's ability to create thermal conduction pathways through orientation and alignment within the matrix. The relationship between Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity and filler loading was non-linear, showing a rapid increase as a more perfect filler network formed. Maximum thermal conductivity was observed around 50-75 °C, with a slight decrease up to 150 °C due to the transition of polystyrene to a rubbery state after the Glass Transition TemperatureThe glass transition is one of the most important properties of amorphous and semi-crystalline materials, e.g., inorganic glasses, amorphous metals, polymers, pharmaceuticals and food ingredients, etc., and describes the temperature region where the mechanical properties of the materials change from hard and brittle to more soft, deformable or rubbery.glass transition. The inherent olefinic structure of SIS copolymer composites contributed to their higher thermal conductivity compared to SEPS composites.

Prototype heater devices were fabricated to assess the electrical and heating performance of the materials. The incorporation of CB enhanced the Electrical Conductivity (SBA)Electrical conductivity is a physical property indicating a material's ability to allow the transport of an electric charge.electrical conductivity of all the copolymer materials. Even when subjected to an equivalent carbon loading, it is noteworthy that 1,4-SIS and 3,4-SIS exhibit greater electrical and thermal conductivity compared to SEPS. Therefore, it becomes evident that both the electrical and thermal conductivity of the composite is directly related to the presence of olefinic structures within SIS copolymers and the concentration of CB.

This study clearly demonstrated that to maximize the efficiency of electrothermal heaters, polymer structure and properties need to be optimized, alongside the loading and properties of the electroactive filler component. When all the relevant factors related to device performance are considered, it becomes clear that the 3,4-SIS-28CB composite displays exceptional Thermal DiffusivityThermal diffusivity (a with the unit mm2/s) is a material-specific property for characterizing unsteady heat conduction. This value describes how quickly a material reacts to a change in temperature.thermal diffusivity, Electrical Conductivity (SBA)Electrical conductivity is a physical property indicating a material's ability to allow the transport of an electric charge.electrical conductivity, and electrothermal heating performance when compared to the 1,4-SIS-28CB and SEPS-28CB composites.

The study has demonstrated that the incorporation of CB into the polymer matrix improves electrothermal properties without exerting a substantial influence on the inherent structure of the pristine copolymer; however, it does have an adverse impact on the thermo-oxidative stability of the composites at high operational temperatures (<200 °C). The study confirms that the olefinic structure in SIS copolymers plays a crucial role in enhancing the electrothermal performance of composite heaters. The 3,4-SIS-28CB composite stands out as an efficient material for flexible and lightweight electrothermal heaters, suitable for applications in electric vehicles and beyond.

Case 2: Unraveling the Effects of Vermiculite on Fired Clay Bricks Using Advanced Instrumentation

_{Wang, Sen; Gainey, Lloyd; Marinelli, Julius; Deer, Brianna; Wang, Tony; Mackinnon, Ian; & Xi, Yunfei (2022); Effects of vermiculite on in-situ thermal behaviour, microstructure, physical and mechanical properties of fired clay bricks. Construction and Building Materials, 316, Article number: 125828.}

Clay bricks are a staple of the building industry. The performance of these bricks is heavily influenced by their composition, and in this study, the researchers turned their attention to a less-studied component – natural vermiculite.

Vermiculite, a swelling clay, can expand up to 30 times its original size when heated. While the expanded form of vermiculite has been well-studied, natural vermiculite is often overlooked as an additive to bricks due to the perception that its expansion when heated reduces brick strength. But is this perception accurate?

To answer this question, our researchers embarked on a detailed study of vermiculite/clay mixtures, with vermiculite constituting up to 30 wt% of the mixture. They employed a suite of advanced thermal analysis and complimentary techniques, including Thermogravimetric Analysis (TGA), Dilatometry, non-ambient X-ray Diffraction (XRD), and Laser Flash Analysis (LFA) to interpret real-time thermal behaviours and explore the microstructure, physical, and compressive characteristics of fired clay bricks.

The TGA and Dilatometry (DIL) studies were instrumental in understanding the in-situ thermal behaviour of the bricks, while non-ambient XRD shed light on the changes in mineralogy with temperature. LFA, on the other hand, was used to determine whether the addition of vermiculite affected the Thermal DiffusivityThermal diffusivity (a with the unit mm2/s) is a material-specific property for characterizing unsteady heat conduction. This value describes how quickly a material reacts to a change in temperature.thermal diffusivity of the bricks.

The conclusions drawn from the study highlight several important findings regarding the effects of incorporating vermiculite into fired clay bricks.

Mineralogy: Non ambient-XRD was used to understand the mineralogy of these products. The mineralogy of clays is complex. In the sample without vermiculite, initially, the dehydroxylation of kaolinite and illite/mica is observed. Quartz undergoes a Phase TransitionsThe term phase transition (or phase change) is most commonly used to describe transitions between the solid, liquid and gaseous states.phase transition from α- to β-phase, accompanied by potential microcrack development, necessitating controlled heating rates in industrial brick production. The Decomposition reactionA decomposition reaction is a thermally induced reaction of a chemical compound forming solid and/or gaseous products. decomposition of calcite into lime is observed.

Furthermore, the evolution of other phases, including feldspar family members, high-temperature related phases like mullite and cristobalite, and the appearance of trace minerals like anatase, is elucidated. The addition of vermiculite in the clay mixture introduces new phases and alters the mineralogical composition, affecting the dehydration behaviour of vermiculite and the onset temperature of kaolinite dehydroxylation. Additionally, the formation of Mg-related silicates/aluminosilicates and other phases is observed, influenced by the presence of vermiculite, and associated mineral interactions. Overall, the mineralogical transformations provide insights into the complex thermal behaviour of clay bricks and the effects of vermiculite addition on their properties.

The figure below shows the evolution of the mineralogy as the sample is heated in the clay with and without vermiculite addition.

Thermal behaviour: Between 25 and 1150 °C, five different weight loss steps and six dilatometric/contraction steps are defined.

Non ambient in-situ XRD on the clay mixture without vermiculite and the 30% vermiculite sample shows the effect of the vermiculite addition on the mineralogy. The main Phase TransitionsThe term phase transition (or phase change) is most commonly used to describe transitions between the solid, liquid and gaseous states.phase transitions and their relationship to the mass loss data are summarised below.

The addition of V not only brings a substantial expansion between 450 and 750 °C but shrinkage after 950 °C is also exacerbated due to the modified content and species of clay minerals.

The dilatometry data suggests that larger dimensional changes are observed as the vermiculite content increases. The rapid expansion seen for higher vermiculite content in area “4″ is caused by severe exfoliation of interstratified vermiculite-biotite (vrm-bt) combined with a slight volumetric increase of vermiculite.

The main Phase TransitionsThe term phase transition (or phase change) is most commonly used to describe transitions between the solid, liquid and gaseous states.phase transitions, as elucidated by non-ambient XRD and their relationship to the dimensional change data are summarised below.

Mechanical and Insulation properties: the drying shrinkage, firing shrinkage and DensityThe mass density is defined as the ratio between mass and volume. density rise considerably with vermiculite addition. The compressive strength increases up to 5% with vermiculite addition, and then drops.

In the 30% vermiculite sample, cracks appeared between 450 and 750°C due to the exfoliation of vrm-bt and vermiculite. Despite vitrification and shrinkage above this temperature, the cracks do not entirely disappear even after firing at 1150°C.

The Thermal DiffusivityThermal diffusivity (a with the unit mm2/s) is a material-specific property for characterizing unsteady heat conduction. This value describes how quickly a material reacts to a change in temperature.thermal diffusivity of the sample remains unchanged at 5% vermiculite addition and increases above that, suggesting that the insulation properties are preserved up to 5% vermiculite. The mechanical and insulation properties are summarised below.

Based on the thermal performance and mechanical properties, 5 wt% of raw, untreated vermiculite is considered an optimum ratio to add into a clay mixture for brick production.

In summary, the study highlights the significant benefits of incorporating vermiculite into fired clay bricks, including improved thermal behavior, enhanced mechanical properties, and potential sustainability advantages. These findings underscore the importance of exploring novel materials and techniques to address the challenges faced by the construction industry in creating energy-efficient and durable buildings.

“We always appreciated the good service”

We had NETZSCH equipment already in place (STA 449 F3 and Dilatometer) when I started at QUT in 2015. Since then, we have installed a second STA (2015), a Laser Flash (2015), a Heat Flow meter (2016) and a low-temperature DSC (Phoenix^®, 2018). The STAs were upgraded in 2018 to include autosamplers on both instruments and again in 2020 to include FTIR and GCMS evolved gas analysis.

We have always had excellent customer service response from NETZSCH and their applications support has been outstanding. We have minimal downtime due to instrument issues. Once we report an issue, the team at NETZSCH Australia take immediate action to begin rectifying the problem. The team are extremely responsive and knowledgeable.

The local team in Sydney can answer most applications questions, and they have access to the team in Selb (Germany) for any applications requests they have been unable to solve. We have been able to work with NETZSCH to solve every applications problem we have ever encountered. To clarify, we currently have 188 trained users. Over the lifespan of the instruments the number of users we have trained to competency would be more like 500. HDR students come and then complete their studies and leave for other jobs, hopefully with good skills!”

Liz, thank you very much for your deep insights into these interesting case studies! We look forward to continuing to support your research in the future!