The thermal insulating effects of Quartzene® on painting systems

The thermal insulating effects of

Quartzene® on painting systems

Arwin Zendehrokh, Luis Mariscal, Martin Hunhammar, Ismail Yussuf Hassan,

Albert Pettersson

Abstract

The European Green Deal 2020 goals for reducing emissions are enforcing rules on the energy performance of buildings. Therefore thermally insulating materials used as coatings are

researched to reduce the energy emissions of buildings. An essential field of interest are nanomaterials. Traditional aerogel is a nanomaterial used for insulating applications due to its high porosity and large surface area, resulting in a longer path for heat to travel. However the cost and manufacturing process are highly energy demanding. Svenska Aerogel AB produces Quartzene_​® (Qz)_​, a silica-based nanomaterial with similar properties as traditional aerogel. Qz can be incorporated into different paint systems to improve their thermal insulating properties. The aim of this project was to investigate the thermal insulating effects of Qz on three different painting systems (A, B, and C). Samples were moulded and their thermal properties were measured with TPS (Transient Plane Source). The thermal conductivity decreased as the wt% of Qz increased, up until around 10 wt% for system C. It became apparent that at higher wt%, it became harder to properly mix the samples into a good dispersion. The thermal conductivity started to increase above 10 wt%. Experiments showed that bigger particles were easier to mix into the paint than smaller.

Table of contents

Objective 17 Method 17 Results 20 4.1 Paint system A 20 4.2 Paint system B 24 4.3 Paint system C 25 4.4 SEM results 30 5. Discussion 31 6. Conclusion 36 7. References 37 8. Appendix 39

Acknowledgements

First of all, we would like to thank _{​Roland Ek​ from Svenska Aerogel AB who made it} possible to write this thesis. Your enthusiasm for the subject made us eager to do a good job. It has been a great pleasure.

A huge thanks also to our supervisor _{​Dr. Hanna Bramfeldt​ at Svenska Aerogel AB for} all the guidance and support throughout this study. Thanks for always believing in us in the times of setback and letting us extend our ideas.

Dr. German Salazar Alvarez_{​, our rock, deserves our deepest gratitude for making it}

possible for us to perform this thesis at Ångströmslaboratoriet in Uppsala. Without you our brains would wither away writing a literature study at home during these strange Corona times.

Thank_{​ ​you ​professor Peter Svedlindh ​for your guidance and helping us expand our} ideas.

We would also like to thank _{​Josef Seibt​ and​ Seda Ulusoy​ at Uppsala University. ​Diana} at Svenska Aerogel AB for assistance during our practical experiments and _{​Dr. Daniel}

Nomenclature

CO_​2 Carbon dioxide, a greenhouse gas that contributes to global warming Qz Quartzene®, a silica based nanoporous material

Z1 Hydrophilic Quartzene dried with the standard method

Z2TP Hydrophilic Quartzene (test product) dried with the Hosokawa method Z1H1 Hydrophobic Quartzene dried with the standard method

Z2H1TP Hydrophobic Quartzene (test product) dried with the Hosokawa method λ Thermal conductivity, a material property relating to its ability to conduct heat α Thermal diffusivity, measures the rate of heat passing through a material

ρ Density

ρC_​p Volumetric specific heat C_​p Specific heat

PVC Pigment volume concentration, volume of pigment(s) in a volume of solid paint

CPVC Critical pigment volume concentration, describes the maximum volume of pigment(s) that can be charged into a volume of solid paint in order to get sufficient wetting of the pigment(s) surface and an acceptable film formation SEM Scanning electron microscope

1. Introduction

The primary greenhouse gas, carbon dioxide (CO_​2​) continues to play a big role in the rising average global temperature. As of 2020, buildings are responsible for

approximately 36% of the CO_​2​ emissions in Europe. The European Green Deal is enforcing rules on energy performance of buildings _{​(1)​. Therefore new methods of} insulation are being developed to reduce this number. Materials are being researched and discovered to improve the insulation of roofs, walls, floors and windows. Aerogels, a relatively newly discovered promising material has been developed and is being researched extensively for thermal insulation applications. The material is used for its properties in sectors other than construction, such as electronics and clothing _​(2)​. Manufacturing aerogel is a costly process. To achieve the goals of energy efficiency, manufacturers are emphasising on the cost reduction of the manufacturing process to properly commercialize the product _{​(3)​. Svenska Aerogel AB develops and produces} Quartzene® (Qz), a silica based aerogel, for various industrial applications. The main vision is to achieve high material efficiency, less material consumption and energy reduction. Qz is a powder that can be embedded in various material matrices to improve their thermal insulation. Applications are found in many different areas such as paint and plasters, building panels and coatings for process industry _​(4)​.

1.1 Nanoporous materials

Nanoporous materials are uniquely important in the field of thermal insulation and heat flow management and are most notable for their high porosity _{​(5)​. Nanoporous}

materials have a porous structure that is aided by a solid framework and contains pores with sizes ranging in the nanoscale (less than 100nm). Since the nanopores are very small in size, porosity increases and the material gains higher surface area which is an essential characteristic of nanoporous materials _​(6)​.

Aerogels are low density (∼0.003 g/cm3) nanoporous material with high surface area (500–1200 m_​2​_{/g), high porosity (80–99.8%) and low λ ​(7)​. Silica-based aerogels can be}

synthesized by several methods including sol-gel and co-precursor methods _{​(8)​. The} former is suitable for laboratory conditions and involves the polymerization of sol suspension to form a gel. The gel is then dried supercritically to remove the solvent component and replace it with air without ruining the solid network _{​(9)​. This distinctive} porous structure of aerogels is key for thermal insulation.

However the shortcomings of using aerogels lies in their synthetic processes. The supercritical drying phase in the sol-gel method is expensive and requires a lot of energy in the process. Hence to overcome this challenge, a cost efficient alternative method should be pursued.

Svenska Aerogel AB manufactures Qz that has similar properties to traditional aerogels but manufactured at lower cost and less impact on the environment. In addition, it is considered a mesoporous material that has a disordered structure and contains mesopores with sizes ranging between 20 to 40 nm in diameter. The lower synthetic cost of Qz reduces porosity, as conventional aerogel can have a porosity of 99.5% whilst Qz ranges from 95-98%. The nanopores of Qz contribute less energy transfer across the material due to the Knudsen effect. Collisions between air molecules with pore walls are more likely to occur than collisions between air molecules _​(10)​. Qz can be categorized as hydrophilic (Z1) and hydrophobic (Z1H1). Since

hydrophobization is typically a secondary treatment of the hydrophilic material, the structure of both materials are nearly the same. However, density and porosity could vary slightly between the two materials due to the chemical conversion. The hydrophilic Qz is covered by hydroxyl groups on the surface and during conversion these hydroxyl groups can be converted to methyl groups to form hydrophobic Qz.

Qz is manufactured in a waterborne process ending with a paste containing precipitated silica which is later dried into grained powder to remove moisture. In this project, both hydrophilic and hydrophobic Qz were dried by two drying techniques; air grinder technique, which is also called the standard method and the Hosokawa technique. The standard method involves the formation of a strong airstream using a fan. A

material to be treated is fed into the air stream through a paste inlet where it is subjected to strong vibrations. Drying is done through bombardment between a strong air stream of preheated dry air and individual particles of the material. Moisture is released and processed material is discharged at the top of the instrument _{​(11)​. In contrast, the} Hosokawa drying technique is simplified and uses a device called the drymeister

(DMR-H). Wet material is fed into a spinning disk inside the device and allowed to spin at high speed between 4000-5000 rpm. Drying is done by hot air that is drawn through at the bottom by a fan. In addition, the surface area of the material is magnified so that moisture is evaporated right away. The dry particles will move to the top and be classified according to their sizes by a separator. Particles that fulfill the size

requirement and moisture content will then be discharged at the top, otherwise they are ejected back to the dryer until the requirements are met _​(12)​.

1.2 Thermal properties

The properties mentioned below are necessary for the calculations executed by the chosen analysis method and the setting measurement values investigated in section 1.4.

Thermal conductivity is a measurement of the ability to conduct heat in a material. The SI-unit is W (mK)_​-1​ _{and often denoted as λ. The thermal conductivity depends on}

several different factors such as the temperature gradient, the properties of the material and the length of the path heat travels. λ depends on the temperature of the material and increases with increasing temperature due to increasing movement of the molecules. When molecules move faster, the heat will also travel faster through the material _​(13)​. λ varies in gas, solid or non metal solid compounds because the molecular movement and structure differ between these states. Due to the large spaces between the molecules, gases rely on the free movement of the molecules and the rate which contributes to the low relative heat conductivity. This is why air is low conductive. Compared to solid metal with tightly packed networks, the heat is transferred by vibrations and generates a high heat conductivity. But in both of these groups many variations exist _{​(14)​. The} variation in these groups is caused by the amount of air in the material. The more air in the material, the lower λ will be.

Thermal diffusivity (α) measures the rate of heat passing through a material. It is the λ divided by the volumetric specific heat (ρC_​p​), and with the SI-unit mm_​2​_{/s. λ can be seen}

as a factor of α. To conduct heat efficiently the diffusion proportions have to be effective. The density is one factor of diffusivity. A high density leads to more closely packed molecules and atoms that can reduce the path of the heat thus leading to a higher α_​(14)​.

However the relation between α and λ does not always show the same trend, especially for gases. Air for instance has a low λ but an α almost as high as certain metals. This means that gases diffuse heat at high speed but in very small portions _​(15)​.

Specific heat (C_​p​) describes the amount of heat required to increase one unit of mass by one unit of temperature. It is λ divided by the mass of the sample. The SI-unit is J/(kg K). C_​p​ increases with an increasing amount of atoms that can conduct heat. The TPS measures the ρC_​p​, which refers to the amount of heat energy required to increase one

unit of temperature of a substance per unit of volume. Thus it is the specific heat divided by the volume or times the density J/(m_​3 ​_{K) ​(14)​.}

Qz consists mostly of air due to its porosity resulting in a low λ (∼0.025-0.030 W/m K) as can be seen in table 1 and 2. In comparison, water at 20℃ has a λ of 0.6 W/mK) _​(16)​. The atoms in Qz are widely spaced, leading to an extended path for the heat, therefore a low α is expected. With the lack of atoms that can conduct heat the ρC_​p​ value is

expected to be low. It should also be mentioned that in this experiment λ is _​sought-after

moisture from the environment, which leads to structural collapse due to capillary forces. Therefore the material is reinforced through different methods such as cross linking with epoxies _{​(18)​ or cross-linking the silicon backbone through surface silanol} groups by reacting them with monomers/polymers. The choice of material for the aerogel to be incorporated with depends on the desired properties and functionalities for the coating. These properties range from high transparency, low processing

temperatures and thermal stability _​(19)​.

The mixing of Qz and the resin of each paint matrix results in a dispersion where the Qz is embedded in the resin mechanically with some hydrogen bonding contributions _​(20)​. The Qz powder is an agglomerate, which when mixed, re-agglomerates with the binder. An agglomerate refers to a reversible collection of particles held together by physical entanglement and weak chemical bonds such as van der Waals forces _​(21)​.

Incorporating Qz in paint matrices should be done in a way that retains the structure and properties of the paint. In this study a silicone and two acrylate resin systems will be used for incorporating Qz. The performance of the finished coating depends on the pigment volume concentration (PVC), a measurement of the concentration of the pigment in a coating _{​(22)​. The critical pigment volume concentration (CPVC) refers} here to the maximum volume of Qz that can be charged into the binder system to ensure that all particles are fully covered with no voids in between_​​(23)_{​. With a PVC exceeding} the CPVC, voids will emerge, thus the coating will lose some of its properties. This will be apparent when drying as the dried sample will develop cracks on the surface. The appearance of voids can be observed with SEM (see section 1.6) _{​(24)​. The amount of} Qz that can be mixed into the paint depends on its ability to absorb the resin. This in turn depends on the available surface for the binder to apply to. In table 1 and 2, different particle distributions of Qz are shown with the different drying methods. Bigger particles require more powder in the binder to reach the CPVC because of less surface area.

Although challenging, the production of thin and efficient layers of paint is of interest, partially because of microcracking when drying. A good resin in a paint should have certain properties to make it a good quality. Firstly, the resin should be able to properly wet the Qz. Wetting of pigment refers to how the air and moisture from the surface of the pigment is replaced by the resin. Secondly, the mechanical properties are of

importance, where flexibility of the paint system is needed to avoid cracks after drying. Thirdly, the binder should have a viscosity that allows for dispersion without high tension. The wetting efficiency depends on the surface tension properties of the pigment and binder, as well as the viscosity of the resulting dispersion _{​(25)​. A viscosity that is} too high will increase the tension on the particles which can break down the

agglomerates, leading to a larger surface area.

For this investigation, the Qz will be incorporated as a free powder with three paints; A (a silicone based paint), B (acrylic co-polymer) and C (acrylate). Silicone material is resistant to high temperatures (300℃) and is therefore suitable for thermal insulation

(26)_{​. Acrylic resins are commonly used in the paint/coating industry and provide} excellent adhesion, resistance to water and cracks and also low λ.

Moulds of different materials and shapes were investigated during this project to develop a reliable drying method that considers sample quality and dimensions, shrinkage, minimize drying time and waste.

1.3.1 Paint system A & hydrophilic Quartzene

Paint system A is a water based silicone paint and is used because of its chemical and physical properties. The applications provide fast film forming with high flexibility and heat stability for protection of metal and glass. Hydrophilic Qz powder (type Z1 and Z2TP) will be incorporated in the A matrix. Type Z1 is dried using the standard drying method while Z2TP is dried using the Hosakawa drying method. The properties of the Qz powder is shown in table 1.

Table 1. Properties of Qz type Z1 and Z2TP

1.3.2 Paint system B & hydrophobic Quartzene

Paint system B is a water based acrylic copolymer dispersion. Its applications include heat insulation, water and cracking resistance and good durability. An already mixed dispersion of 10 wt% Qz given from the distributor will be investigated. Another

investigation will be made of mixing Qz into the paint. It is known that the paint shrinks by approximately 40% when completely dried.

Hydrophobic Qz (type Z1H1 and Z2H1TP) will be incorporated into the paint matrix. Type Z1H1 is dried using the standard drying method while Z2H1TP is dried using the Hosakawa drying method. The properties of the Qz powder is shown in table 2.

Table 2. Properties of Qz type Z1H1 and Z2H1TP

1.3.3 Paint system C & hydrophobic Quartzene

The paint system C is a water based acrylic paint developed for the production of thermal insulating coatings based on silica aerogels. The properties include good foam building (the insulation effect is achieved by the combined effect of the foam and the aerogel content), good water resistance and high flexibility. Hydrophobic Qz will be incorporated and its properties are shown in table 2.

1.4 Analysis method

The Transient Plane Source (TPS) method is used to determine thermal transport

properties of materials. It measures both λ (see 1.2) and α (see 1.2), which are then used to calculate _{​ρC​p​} capacity with equation 1:

(1)

Cp

ρ = λ

α

The TPS method (see figure 2) can be used to measure a vast amount of materials, whether they are solid, powder or liquid. Different experimental methods are available for different types of samples. If the objective is to measure stacks of samples, then the slab technique is used. If the sample is anisotropic, the anisotropic technique is required to perform measurements. The third method available is the thin film technique, which is used to perform measurements on thin samples. This technique is the one utilized to perform measurements in this project. The sample measurement is explained further below. In order to perform the TPS method a Hot Disk Thermal Constants Analyser is required. The Hot Disk analyser is equipped with a plane sensor that releases heat. The sensor itself is a patterned double spiral made out of Nickel metal _​(27)​.

Figure 2. TPS setup for measurements of solid samples. a) Shows the kapton sensor. b) Shows the background material. The background material is usually a weight that improves the contact between sample and sensor. The samples are placed between a) and b) on both sides of the sensor (see figure 3). c) Shows the sensor holder that keeps the sensor secured in its position. d) Shows the sensor cable extension. The cable extension is connected to the Hot Disk instrument _​(27)​.

The sensor is positioned between two samples when a measurement is performed. An electrical current is run through the sensor by the Hot Disk instrument. The sensor’s temperature increases by the metal’s resistance. Heat waves from both sides of the sensor are then dispersed through the sample (see figure 3). λ and α are determined by measuring the temperature versus the time response of the sample in the sensor. As explained in section 1.2, these thermal transport properties decide the rate of which the heat will flow through the sample _​(28)​.

Figure 3_{​. ​Schematic of a solid sample measurement. Heat is dispersed from the sensor} upon starting the measurement.

It is assumed that the sensor is surrounded by an infinite amount of sample _{​(29)​. This} way the transient heat waves dispersed through the sample can be followed well by the instrument. To fulfill this assumption the surface and thickness of the sample should preferably be larger than the diameter of the sensor. Ideally the sample is also homogeneous and isotropic, otherwise λ and α can not be obtained. If the sample is anisotropic the heat capacity needs to be known in order to measure the other two thermal properties. The heat capacity can be calculated by the TPS technique, however this means that two measurements are required for anisotropic samples _​(27)​.

As mentioned before the sensor is plane. To obtain precise results the surface of the sample needs to be even. An uneven surface decreases the contact between sample and sensor, leading to incorrect results as the heat is not evenly dispersed throughout the sample _​(29)​.

1.4.1 Measurement evaluation

Besides measuring the thermal transport properties, the Hot Disk instrument also calculates and presents several graphs that are used to evaluate the results.

To obtain optimal results, temperature drift is generally avoided. The Hot Disk software plots a drift graph that shows the temperature variation (K) versus the time (see figure 5). If the temperature points in the graph are scattered horizontally across the time axis, there is no temperature drift in the sample. In cases where drift does occur, the amount of temperature variation decides whether the measurement is to be discarded or kept.

Figure 4. Schematic of a typical drift graph.

A transient curve (see figure 6) will also appear to determine the quality of the

measurement. The transient curve shows the temperature increase of the sample during the measurement. A continuous temperature increase is expected if a measurement is to be accepted.

Figure 5. An example of a transient graph. The yellow vertical line marks the start point for the calculations. The start point is not at the beginning due to the initially slow heat increase.

Calculations of the thermal transport properties are made when a measurement is completed. Along with the calculations follows a residual graph(see figure 7). The residual graph displays the difference between fitted data and measurement data. The results are solid in cases where the residual plot shows a random scatter across a horizontal line.

Figure 6. An example of an acceptable residual graph. The yellow vertical line marks the start point of the calculations, just like in figure 6.

To finalize the evaluation, the probing depth and mean deviation is controlled. The probing depth states the distance travelled by the heat and should not be higher than the thickness of the sample. Finally, the mean deviation should not be higher than values in 10_​-4​_.

1.5 Instrument and parameter selection

The instrument used for the measurements is the Hot Disk 2200. The sensor model used is the Kapton 7577 F with a diameter of 2 mm. Kapton refers to the thin, insulating polyimide sheets that are sandwiched onto the Nickel spiral. Due to the highly

insulating samples a low heating power is required to avoid overheating of the sensor, in this case 10 mW. The measurement time is set to 20 seconds. To avoid heat drifting the samples need to be cooled down to the surrounding temperature in order to achieve best results. Therefore the time in between each measurement is set to 17 minutes. The sample thickness is determined by the sensor size. The sensor used in this report is 2 mm in diameter thus the thickness of the sample can be no less than 2 mm in order to achieve the correct assumption that the sensor is surrounded by infinite material.

1.6 Scanning electron microscopy

The scanning electron microscope (SEM) is used to magnify objects up to 10_​6​ _times

their size. The SEM uses an electron beam with very short wavelength (down to 0,004 nm) accelerated by high voltage to achieve images of the nanostructure of the measured surface. The SEM mainly consists of an electron column and a specimen chamber. Inside the column an electron beam is generated in vacuum and focused onto the surface of the specimen by electromagnetic lenses and scan coils. The electrons interact with the atoms at the surface and give rise to signals which are then received by various

detectors in the chamber. The information emanating from the detectors will then result in an image of the topography of the surface, with resolution in nanometers _​(30)​.

Nonconductive materials must be coated before measured with SEM. The coating needs to be conductive to dissipate current and prevent excess of electrons at the specimen

surface. The reduction of charging effects will remove any contrast variation and image distortion and result in better image quality. To achieve a fracture bulk surface of the sample it can be submerged into liquid nitrogen and smashed prior to the measurement (31)_​.

Wet samples may impair the SEM image. If the specimen is not completely dried it may degrade the vacuum in the microscope. This may cause interference with the electron beam and result in scattered electrons. Thus wet samples are preferably measured in low vacuum _{​(31)​. In this study the SEM is used to investigate how the nanostructure is} affected by the force in which the samples are mixed.

2. Objective

The primary objective is to investigate how different weight percentages of Qz affects the thermal properties of painting systems. The expectations are that will decreaseλ with an increasing amount of Qz, since heat has to travel further because of the porous structure of Qz. Adding too much Qz to the paint material could lead to cracks in the material because of the binder to pigment ratio. Thus, there should be an upper limit to how much Qz can be incorporated. Secondly, the behaviour of α is expected to behave differently than . α is expected to decrease with the addition of Qz.λ

The drying methods produce Qz powder with different particle sizes. The Hosakawa method generates larger particle sizes and therefore more Qz can be mixed and

incorporated to the paint than with the standard method. With a PVC above CPVC, the material will get voids and cracks, this can be seen with the eye and also measured with SEM.

Mixing the Qz into the matrix by rough handling will affect the structure of the Qz. If the structure is damaged, the is expected to increase, because of less density andλ damaged structure. Therefore, another goal will be to compare samples mixed by normal mixing and by rough handling using mortar and pestle by measuring their λ using TPS and investigate their structure with SEM.

3. Method

The paint samples in table 3 were mixed by slowly and gradually adding Qz powder into paint using an overhead stirrer _​(_​IKA® RW 20 digital). The stirring time and rate differed depending on the type and amount of Qz and the paint system. The Qz and paint were both weighed before mixing to achieve desired ratio.

The samples were then dried in different moulds depending on their viscosity and type of paint. Moulds of different materials and shapes were tested. A silicone form and

up to several weeks. The samples were then named as

TypeOfPaint_wt%Qz__Batch_Date. When the samples had dried they were cut in half and measured in the TPS. Two measurements on each sample were performed.

Measurements that failed to fulfill the evaluation mentioned in section 1.4.1 were discarded and redone.

Table 3 shows all the combinations of paint systems, type of Qz, drying techniques and wt% Qz investigated. Two to four samples of each concentration were made (see appendix).

Table 3. Information about the combinations of paint systems and Qz types produced.

A vast majority of the samples were mixed at the same rate, around 500 rpm. However, three samples of A with 10 wt.% Z1 were initially mixed at 500 rpm to then be mixed at 1400 rpm for the last 10 minutes. Two additional samples were also initially mixed at 500 rpm following 10 minutes of mixing with mortar and pestle. All samples of A with 10 wt% Z1 were dried in a low vacuum oven for 4 hours at 55 _​°_​C the day before they were measured with the TPS. Some of the B samples were already mixed by either Svenska Aerogel AB or the supplier of the paint and ready for moulding.

Attempts were made of mixing as much Qz as possible in paint system C, both for Z1H1 and Z2H1TP.

Lastly, three samples of A with 10 wt% Z1 prepared at different mixing rates and C with 5 wt% and 13 wt% Z2H1 were analysed in SEM. The specimens were prepared by dipping them in liquid nitrogen and smashing them with a hammer. Small bulk fractions of each sample were then sputtered and coated with a 3 nm layer of platina before measured in a SEM. The SEM images were processed by the supervisor.

Results

4.1 Paint system A

During the analysis of different moulding techniques it was obvious that samples with A were best casted and dried on plexiglas of all the materials investigated. It did not stick to the surface of the glas and resulted in samples with even and homogeneous surfaces as seen in figure 8. The drying time of 1 cm samples of A containing 10 wt% Z2TP were very long, around 3-4 weeks, while the samples of 5 wt% were much shorter. However, the sample with 10 w% felt slightly moist to the touch at the time of measuring.

Figure 8. Samples with smooth and homogeneous surfaces. Easily removed from the plexiglas surface.

Figure 9. A samples cut in half and ready for measuring by TPS. Surfaces were very smooth to the touch.

The two samples that had been mixed in a mortar following the regular mixing showed a different colour compared to the other samples. Instead of white they displayed a blue tint, see figure 10.

Figure 10. Samples of A 8005 with 10 w% Z1, mixed regularly and then with mortar and pestle.

​

Measurement values for paint system A and Z1.

Samples with * is either mixed at a higher rate or mixed with mortar and pestle and are not used in the calculations of the mean values in table 5.

Table 5. Mean values for every wt% in table 4

Table 7. Mean values for every wt.% in table 6.

4.2 Paint system B

The B samples with 10 wt% added Z1H1 that had been mixed by the supplier and then moulded in silicone form resulted in great surface quality considering the demands. Paint system B prepared by the manufacturer was moulded around 0.8 cm thick and felt dry in 3 days.

Figure 13. Delivered B samples finished after using a silicone mould.

However, the samples of paint system B and Z1H1 prepared in the lab during this project failed completely. They were entirely inhomogeneous and brittle with an uneven surface (see figure 14). They showed a tendency of cracks already after one hour of drying. Even the mixtures prepared by Svenska Aerogel AB showed equally poor results when moulded and dried. The reference sample of paint system B was also brittle and uneven at the surface. This made it impossible to measure them in the TPS.

Figure 14. Paint system B samples mixed in the lab. (From left to right) Picture 1 shows developed cracks on the surface. Picture 2 shows a cross-section, further showing how the paint has formed a cracked skin with paint on the bottom section. Picture 3 shows free powder on the bottom.

Table 8. Measurement values for paint system B and Z1H1

Table 9. Mean values measurements in table 8.

4.3 Paint system C

Paint system C was best suited for the silicone form. It stuck to the Plexiglas (figure 15) but showed great results in surface quality in silicone mould. Z2H1TP was perceived to be easier to add to the paint than Z1H1. The drying time for 1 cm thick samples was 6-7 days.

Figure 15. Paint system C samples containing 5 and 10 w% molded on a plexiglas. Picture 1 shows the residue of the sample after trying to take it off. Picture 2 shows a rough surface, so the top side had to be used.

Figure 16. (from left to right) Picture 1 shows a C sample drying in a silicone mould. Picture 2 and 3 show different weight percentages of Qz in paint system C.

The maximum amount Z2H1TP possible to add in paint system C before the Qz lumped together and resulted in an inhomogeneous mixture was 16 wt%. While the maximum Z1H1 was 14.3 wt%. Figure 17 shows the two types at the wt% Qz maximum limit.

Figure 17. Left picture shows the C sample at 14.3 w% Z1H1. Right picture shows C at 16 w% Z2H1TP.

Table 11. Mean values for every wt% in table 10.

Table 12. Measurement values for paint system C and Z2H1TP

Figure 18. Shows wt.% vs λ for the results shown in table 11 and table 13.

4.4 SEM results

The SEM results are shown in figure 20, 21, 22 and 23.

Figure 20. SEM results for paint system A with 10 w% Z1.

Figure 21. SEM results for paint system A with 10 w% Z1, mixed with mortar and pestle.

Figure 22. SEM results for paint system C with 13 w% Z1H1.

Figure 23. SEM results for paint system C with 5 w% Z1H1.

5. Discussion

Concerning the used moulds a couple things could be said. A reference sample of the A paint was poured in a silicone mould. A is a silicone based paint, therefore because of similar molecular structures the paint was strongly bonded to the mould. PMMA was a much more suitable mould for A, and the paint was easily dried and removed. The same principle applied to the acrylic based paints, as they have a similar structure to PMMA and got stuck to the surface of the mould. Thus a silicone mould was suitable for acrylic based paints.

paint system did not become very viscous at higher wt%, and the foam texture might help against the tension that occurs when a liquid becomes too viscous. The already mixed paint system B was not very viscous, and not much could be said about it due to no reference existing without Qz. Also the B paint system had problems solving in the Qz powder, even after following the instructions given by the manufacturer thus no samples nor reference were done. Paint A acted like a paste with higher wt% of Qz. The mixing of A with Z1 and Z2TP was done without problems as the powder is hydrophilic and the paint is water-based. Both Z1 and Z2TP contain hydroxyl groups that allow them to form hydrogen bonds with water and other polar substances in the paint. However, the very high viscosity at higher wt% may have contributed to tension between the pigments and the binder, which leads to higher surface area, and therefore requiring more binder. This might explain the high σ of paint A. The properties of being a silicone based paint contributed to no visible cracks in the surface.

On the other hand, mixing C with Z1H1 and Z2H1TP occurred with difficulties due to hydrophobicity. Since paint system C is water-based paint while both Z1H1 and Z2H1TP are hydrophobic and nonpolar in nature, their interactions with water solvent in the paint will not be energetically favored. The C samples were able to dry quicker since both Z1H1 and Z2H1TP did not absorb water from the binder or moisture from the air during drying. However, mixing Z1H1 in paint C was more difficult than Z2H1TP because of their different surface areas. A higher ratio of fine powder leads to more surface area for the resin to wet. This takes a longer time, and the closer to CPVC, the slower the process.

The drying times for both Z1 and Z2TP with A 10 wt% samples were surprisingly long. After around three weeks of drying they still did not seem dry, especially the samples mixed with mortar and pestle. To speed up the process they were put in a low vacuum furnace for 4 hours at 55 °C, but that was apparently not enough. Another indication of moisture was observed after submerging a A 10 wt% Z1 sample in liquid nitrogen for 1 hour, but it was still elastic. With this result one can suspect that none of the samples of that specific concentration had dried completely. An important note is that the Z1H1 samples were much harder at the end of the project than they were at the time of measuring. The increased hardness could be an indication of a much drier sample,

which would then mean that water was present in the sample when measuring with TPS. A future solution to the problem concerning moisture would be to reduce the sample thickness. For our A samples, before knowing the drying times, the samples were moulded 1 cm thick. This proved to be too thick, especially for a hydrophilic and hygroscopic sample. These samples could easily be moulded thinner. Another solution is to allow longer drying time while also utilizing a furnace for drying. However, the practical significance is not of importance. As the thermal paint is supposed to be used as a coating, it will in practice absorb moisture from the environment. Therefore the resulting measurements may be of more practical usage than a completely dried sample. Paint system B did not behave as expected, as seen in figure 14. Several parameters were examined. However, no good sample was able to be made. As the paint system

was expected by the manufacturer to shrink by approximately 40%, both silicone mould and plexiglas mould were experimented with, but no good results were obtained.

Another experiment was made with longer mixing and higher rotational speed, but the samples did not seem to mix well. The experiment produced a layer of skin on top of the paint, while the paint had settled on the bottom of the sample. Finally, a mixed sample produced by Svenska Aerogel AB was given. This sample was allowed to sit overnight in order to get rid of the air inside the sample. Before moulding, it was mixed very carefully. However, this produced the same result as the others (figure 14). No further testing was made on the Paint system B, other than the samples given by the manufacturer, which gave satisfying results.

The drying methods produce different particle sizes, as seen in table 1 and 2. Z2H1TP has a bigger particle size than Z1H1. The hypothesis was that the bigger particles would require less binder for the particle to be completely coated, which in turn means that more Hosakawa powder could be mixed into the paint system. Experiments showed that Hosakawa powder was much easier to mix into the paint. The C samples for Z1H1 and Z2H1TP allowed approximately 14.3 w% and 16 w% of Qz respectively before lumps started forming. The values from table 2 for Z2H1TP are not within an interval because it is a relatively new test product. However a conclusion can still be made. Hosokawa powder has a surface area of ~217 m_​2​_{/g and a particle size distribution of 1-70 μm.}

Compared to Z1H1 which has a surface area of 250-300 m_​2​_{/g and a particle size}

distribution of 1-20 μm. This means that the binder has to come in contact with a bigger area when mixing Z1H1. 14.3 wt% of Z1H1 took 57 minutes to mix while 16 wt% of Z2H1TP took 46 minutes. According to the manufacturer of the paint system, the binder is able to solve a maximum of 13.5 wt% aerogel powder. The number indicates the point where the PVC is above the CPVC. While this number depends on the type of pigment used, it showed to be approximately correct for the Z1H1 powder, while Z2H1TP allowed for more before forming lumps. The dried sample of the 14.3 wt% Z1H1 was brittle, with cracks and voids on the surface, which is another indication of a PVC being above the CPVC. The sample containing 16 wt% Z2H1TP was not moulded due to time constraints.

As can be seen in table 10, the C with Z1H1 samples showed a decrease in λ as the wt% increased, up until 10 wt% where λ then started to increase. There is a significant decrease in λ when comparing the reference to 3 wt% Qz. The addition of 3 wt% Qz results in a 45% decrease in λ. When instead comparing the reference to 10 wt% Qz, which had the lowest mean λ in the system C, a 57 % decrease of λ is calculated. By comparing these decreases it tells us that increasing the wt% from 3 to 10 wt%, an additional decrease of 12 percent points of λ is obtained. Figure 18 further confirms this by showing the slow decrease in λ between 3-10 wt%. Mixing a nanoporous material into the paint matrix is expected to decrease the λ, as its properties are embedded into the matrix, thus giving the brittle Qz a reinforced structure. As discussed earlier, 13.5

nanopores of the Qz. This will give the heat a shorter path, compared to nanopores, where heat has to travel a longer and more complicated way.

As for the C samples with Z2H1TP only two different wt% were made (see figure 18). Still, Z2H1TP seems to have a similar effect on λ as Z1H1 has. A significant decrease in λ occurs in the initial addition of Qz. The decrease of λ between 0 wt% to 5 wt% is at around 44%. The value of λ further decreases for the sample with 10 wt%. The total decrease is at 53% relative to the reference. The λ values for this paint system seem to follow the same trend regardless of the Qz type. Though it is unknown if λ would increase or decrease until the CPVC was to be reached.

Not much can be said about the paint system B results since only 10 wt% was moulded and measured successfully. Since these samples were already mixed, discussing the sample preparation is of no relevance. The λ for all three samples were relatively low (see table 8) and at an expected value considering the values for the C samples. Neither did λ deviate much between the samples, implying that the samples were homogenous. Concerning the attempts to mix our own samples, they were not successful.

The A sample was mixed with 5 and 10 wt% Z2TP and Z1. The effects of both Z1 and Z2TP on λ are similar. At 5 wt% λ shows the lowest decrease of 44.2% for Z1 and 40.1% for Z1TP compared to the A reference, as can be seen in table 5 and 7. At 10 wt% λ had decreased again with 4.9% for Z1 and 21.7% for Z2TP compared to the A reference. At 5 wt% the decrease of λ is similar but at 10 wt% much less effect is shown for Z1 compared to Z2TP. The drying time was very long and it was hard to acquire good measurements for the A paint as mentioned before. As can be seen in table 5 and 7 the σ(λ)-value was much higher around 10_​-2 ​_W/mK​​_{compared to other measurements}

where σ(λ) is around 10_​-3​_{W/mk. This indicated that for both Z1 and Z2TP the quality of}

the measurements is not as expected. A reason for this can be that the samples were not completely dry and made λ higher as mentioned in section 1.2.

If the samples still contained water it could result in incorrect values when measuring the thermal properties with TPS. All water in the samples may not have evaporated when performing the measurements. Due to time constraints measurements on the allegedly drier samples could not be performed. This was especially the case for the A samples, and even more so for the A samples containing 10 wt% Qz. As mentioned previously, Z1 is a hydrophilic and hygroscopic powder that draws moisture from the environment. This led to very long drying times for the A samples. The A samples felt slightly sticky to the touch when performing the measurements about 1 month after moulding. If the samples did contain moisture, the resulting λ would be greater than it should. This is due to water having a λ of 0.6 W/mK, compared to Z1 that has a λ of 0.025-0.030 W/mK.

The effect the drying methods have on λ for both C and A paints can be seen in figure 11 and 18. For C, the minimum value of λ for both Qz types was obtained at 10 wt%. However, the decrease in λ is slightly higher for Qz dried by the standard method than

the one dried by the Hosokawa method. For the A paint, the minimum value of λ for both Qz types was obtained at 5 wt%. However, the effect is seen above 5 wt%. λ decreases at a higher rate for Qz dried by the Hosokawa method than the standard method.

Besides λ, the measured values for α have also been presented in the results. Figure 12 shows an increase in α for the A system. Although λ first decreases at 5 wt% and then increases at 10 wt%, α does not behave similarly. α appears to increase during the whole plot. The reason for this odd behaviour could lie in the earlier discussed faults of the sample preparation for the A samples. An explanation for this suspicion is the behaviour of α in the C system. Figure 19 shows a general decreasement of α when Qz is added. However it is difficult to draw any precise conclusions as there are differentials within the paint system. The lowest α value for the C system is found at different wt%

depending on the Qz type. As mentioned in section 1.2, α was expected to behave differently than λ. Other than α being highest in the reference, any direct conclusions are not drawn as the α values fluctuate between ~0.12-0.8 mm_​2​_/s.

As can be seen in the tables presenting the thermal property results, the σ is generally low (10_​-3​_{W/m/K) for the λ value, with the exception of 10 wt% in the B system. It is}

important to note that this σ is not the same as the one mentioned in section 1.4.1. As specified in the method, every sample measurement consisted of two measurements. The values presented in the result tables are the mean values of these two

measurements. This leads to one wt% having at least 4 performed measurements. A low σ suggests that the measurements are accurate and trustworthy. The reliability and reproducibility of these types of measurements are high provided that the samples are well mixed. Further validation can be done in future projects where the density is measured and compared with the ρC_​p​-values for more reliable values._{​ The density could} be calculated using a simple Archimedes principle method_{​. Time constraints prevented} us from making validation using the calculated ρC_​p.

The images from the SEM were difficult to interpret. It is hard to distinguish the binder from the Qz. Due to this, the following discussion is only speculative. In the future, it would be of importance to analyse a reference sample to learn more about the structure of the paint content._{​ For the preparation of the SEM pictures it was important that the} samples did not contain water. Therefore, the samples would need more time to dry before using SEM. Further investigations could be made with SEM, such as analyzing other wt% to see how the dispersion is affected.

Figure 20 shows paint system A with 10 wt% Z1. The small white dots in image a) may show agglomerates of Qz with good dispersion compared to a) in figure 21. Picture a) in figure 21 shows more lumped white dots and less smaller dots, which indicates a worse dispersion. This is more apparent in image b) in figure 20 compared to figure 21. In

technique. The voids in image b) are likely explained by the wt% of the mixture being close to CPVC.

When incorporating Qz into the paint, it is of interest to see how much of the agglomerates retain their structure. We could partially see this with the use of SEM, where the soft mixing (figure 20) has much more continuous dispersion, while the hard mixing (figure 21) shows layers and cracks in the dispersion. Another way of

determining how well the structure is retained could be to analyse the density. A weakened structure of the silica network will lead to less air percentage and

consequently a higher density. Another aspect that affects the structure could be found in the drying time of the material. As it is with some metal systems and their cooling rates, the structure and hardening of Qz incorporated paint systems could depend on the drying times of the material.

The images of paint system C with 5 and 10 wt% Z1H1 was even more difficult to interpret because of the poor quality and lack of knowledge concerning the structure of a reference sample. The lower wt% shows a distinct structure for the Qz, while the higher wt% seems to show a big collection of Qz. The white spheres is probably an indication of the mixing difficulties of the hydrophobic Qz into the paint.

Future testing should take several things in consideration in order to optimise the incorporation of Qz. For this investigation, different RPM was not tested, and a RPM of around 500 was used for all paint systems. Different paint systems require different RPM and mixing times in order to become properly mixed. Therefore it is important to examine what RPM and mixing time each paint system requires. Another important aspect is to continue testing several wt% to see where λ starts to increase. This was only done for paint system C.

6. Conclusion

The results show that Quartzene has a significant impact on λ. The addition of Qz led to a decrease in λ for all samples. However, the samples containing the largest amount Qz did not result in the lowest λ. This is due to the ratio of Qz being close to the CPVC, which leads to imperfections in the sample. For paint system A 5 wt% proved to have better thermal insulation properties than 10 wt%, although it is believed that the samples were defective. For paint system C 10 wt% Qz showed the lowest thermal conductivity of the weight percentages examined. Between 3 and 10 wt% the system C did not vary much in λ.

There was no significant difference in λ between the standard dried Qz and the Hosokawa Qz for paint systems A and C.

A conclusion made from the study is that the quality of the binder is of great

importance. It has a large effect on the resulting mixture. A suitable binder should have a high resin to pigment ratio, so the ability to mix Qz increases. It should have a high

flexibility, to prevent cracks when drying. Not as in the results for paint system B. Furthermore it is of big advantage that its viscosity does not contribute to shredding the mixture.

The measurement results show good accuracy with their low standard deviation. This shows that the TPS is an effective analysis method with good reproducibility when measuring thermal transport properties. However the requirements for the samples must be fulfilled for this to be correct.

The SEM pictures were difficult to interpret. It has been speculated that rough handling of the sample has a great impact on the structure. This contributes to bad dispersion compared to regular handling. The conclusion from the SEM pictures is that a good dispersion is difficult to achieve at high wt% because of a PVC being close to the CPVC. The hypothesis of voids being present was also seen in the pictures.

Quartzene in paint systems used for isolation and energy savings is only one of its many applications. The future possibilities of this material are endless. Hopefully Quartzene is one of the solutions in achieving the goals of the European _{​Green Deal, in others words} to be the first climate neutral continent in the world.

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8. Appendix

Paint system A

Table A1. Sample information concerning paint system A and Z1

Paint system B

Paint system C