This work has been supported by the National S&#38;T Major Project of China (ZX069).

1. Production of MTGS structure with good hermeticity
NOTE: The procedures for MTGS structure include the preparations for components of the combined structure, the heat treatment process, and examinations for the performance of MTGS samples. The complete MTGS structure consists of a steel shell, Kovar conductor, and sealing glass. See the diagram and dimensions shown in Figure 1 and Table 1, respectively.
<ol>
	<li>Pour the granulated glass powder (~1.1 g) into the mold, then place the mold onto the press machine to process the granulated glass as shown in Figure 2a,b.</li>
	<li>Switch on the press machine (push the red button) to compact the granulated glass into the glass cylinder as shown in Figure 2c,d. 
	NOTE: The density control of glass cylinder is important for the performance of the MTGS structure, because too many pores in the glass cylinder will lead to failure of the hermeticity of MTGS structure.</li>
	<li>Place the glass cylinder into the heating furnace to be sintered (see Figure 3).</li>
	<li>The sintered glass cylinder, steel shell, and Kovar conductor are manufactured with a special graphite gasket, as shown in Figure 4. Place this model onto the quartz septum in the heating furnace using a claw for heat treatment (see Figure 4). Keep the cooling rate as 0.5 &#176;C/min to avoid breaking of the optical fiber.</li>
	<li>Use visual inspection to identify the surface topography of sealing glass after retrieving the model from the heating furnace.</li>
	<li>Use the high pressure pipeline to examine the hermeticity of MTGS model. Install the model onto the pipeline by the card sleeve type joint. Slowly change the pressure from 1 MPa to 8 MPa, holding each pressure for 24 h.</li>
	<li>Use the scanning electron microscope (SEM) to identify the microscopic interface between sealing glass and metal parts as shown in Figure 5. Use 15 kV and 500x magnification to observe the interface clearly. 
	NOTE: From the macrography examination and SEM results, the standard maximum heating temperature is set as 450 &#176;C to obtain the MTGS model with good hermeticity. The standard heating treatment is defined as follows: increase the temperature from (room temperature) RT to 450 &#176;C in increments of 5 &#176;C/min, then drop the temperature to RT as 0.5 &#176;C/min.</li>
</ol>
2. Residual stress measurement in sealing glass
NOTE: The FBG sensor is designed as an appropriate method to measure the stress in the MTGS. The grating length of the FBG sensor is 5 mm to match the height of the glass (5 mm) well.
<ol>
	<li>Compact the granulated glass powder into the glass cylinder as described in steps 1.1&#8211;1.2. 
	NOTE: The height of glass cylinder is important, because if the cylinder is too high (&#62;6 mm), it will be difficult to make a through path for the FBG sensor without destroying the glass material.</li>
	<li>Drill the glass cylinder using drill speed of 5,000 rpm to produce three equally spaced through-holes to prepare paths for optical fiber sensors (diameter 0.45 mm). Sinter the glass cylinder with holes using the same heat treatment as shown in Figure 4.</li>
	<li>Manufacture the MTGS model as described in step 1.4. Then, put the fiber through the path in sealing glass and position the grating region of the FBG exactly within the glass. 
	NOTE: Because the flow in the vertical furnace can blow up the grating region, which leads to the mismatching of FBG and glass, the tail of optical fiber must be hung with a small nail to keep the position of FBG accurate.</li>
	<li>Fuse the head of optical fiber with a FC connector by the fusion splicers. Then, match the FC connector with the OPM-T400, which is an interrogator to demodulate the wavelength data and spectrum of FBG. The OPM-T400 is connected to a computer, and the supporting software on the computer can obtain experimental data.</li>
	<li>Process the whole model in a furnace by the standard heat treatment obtained previously. Raise the temperature from RT to 450 &#176;C as 5 &#176;C/min, then drop the temperature to RT in increments of 0.5 &#176;C/min. The grating region will become fused with the sealing glass as it is heated to melt. When the temperature cools down to RT, the glass will solidify and the FBG sensor will become well-fused with the sealing material.</li>
	<li>Record the real-time Bragg wavelength data using the software (shown in Figure 6). The only factor inducing changes of wavelength and spectrum is the residual stress generated in sealing glass, because the temperature before and after this step is both RT.</li>
</ol>
NOTE: The residual stress can be calculated through the strain-wavelength relationship of FBG14 and Hook&#8217;s law, as shown below.
<img alt="Equation 1" src="/files/ftp_upload/60064/60064equ01v2.jpg" />
<img alt="Equation 2" src="/files/ftp_upload/60064/60064equ02v2.jpg" />
Where: the &#916;&#955;B is the Bragg wavelength shift induced by the residual stress, &#955;B is the initial wavelength of FBG, Pe is the strain-optic coefficient, &#949; is the residual strain in the glass, E is the Young&#8217;s modulus of sealing glass, and &#963; is the residual stress in the glass.
3. Preventing the failure of MTGS structure under high temperature
NOTE: When working at a high temperature, the hermeticity of the MTGS structure will be affected, because the thermal expansion of steel shell leads to the decrease of residual stress in sealing glass. Thus, it is possible this protocol can prevent the failure of hermeticity due to the online monitoring of residual stress change in sealing glass.
<ol>
	<li>Manufacture the MTGS model as done in step 1.4. The type of FBG to monitor temperature and stress simultaneously is the fiber Bragg grating array sensor, including two grating regions on one fiber, with a 10 mm distance between these two sensors. 
	NOTE: These two grating are defined as FBG-1 and FBG-2. The initial Bragg wavelengths of FBG-1 and FBG-2 are 1545 nm and 1550 nm, respectively.</li>
	<li>Place FBG-1 into the sintered glass cylinder to monitor the stress and temperature. Place FBG-2 outside the glass to monitor the temperature only, as shown in Figure 7a,b. In this way, FBG-1 is affected by both temperature and residual stress change, and FBG-2 is only affected by temperature of sealing glass.</li>
	<li>Place the MTGS model with optical fiber in the furnace as described in steps 2.2&#8211;2.3. Use the standard heat treatment to process the MTGS model with an embedded FBG sensor.</li>
	<li>Impose temperatures of 100 &#176;C, 200 &#176;C, 300 &#176;C, and 400 &#176;C onto the model and hold each temperature for 100 min.</li>
</ol>
NOTE: FBG-1 monitors the stress and temperature simultaneously expressed as the Bragg wavelength shift &#916;&#955;B-1, and FBG-2 monitors the temperature change by &#916;&#955;B-2 as shown in Figure 8a,b. The relationships between Bragg wavelength shift and measured parameters are shown as follows:
<img alt="Equation 3" src="/files/ftp_upload/60064/60064equ03.jpg" />
<img alt="Equation 4" src="/files/ftp_upload/60064/60064equ04.jpg" />
Where: &#958; is thermo-optic coefficient, &#945; is thermal expansion coefficient of optical fiber, and &#916;T is temperature change before and after the experiment. The &#916;&#955;B-3 induced by residual stress can be separated through subtracting &#916;&#955;B-1 from &#916;&#955;B-2 (see Figure 8c). This is the demodulation method for simultaneous temperature and stress monitoring of sealing glass at high temperatures.
4. Monitoring high pressure
NOTE: The pressure loads on the MTGS structure will have effects on the residual stress in sealing glass, so the MTGS model with the embedded FBG sensor is a potential method to monitor the high pressure change.
<ol>
	<li>Prepare the same MTGS model with the FBG sensor as described in step 2.2&#8211;2.3. After the FBG is well-fused with MTGS model, use the claw to take the model out of the furnace.</li>
	<li>Manufacture the MTGS model with the FBG sensor onto a high pressure helium pipeline by the bite type tube fittings as shown in Figure 9. Adjust the pressure from 1 MPa to 7 MPa by pressure reducing the valve to impose changing pressure loads on the sealing structure.</li>
	<li>The Bragg wavelength shift &#916;&#955;B is recorded as shown in Figure 10. At the same time, the related residual stress change can be calculated using Equation 1 and Equation 2.</li>
</ol>
5. Theoretical analysis of MTGS structure
<ol>
	<li>Use the modeling software to build the 3D model for MTGS structure, and the dimensions are taken from Table 1 to keep the experimental model and theoretical model consistent.</li>
	<li>Import the 3D model into the finite element analysis software. Assign mechanical properties to the steel shell, sealing glass and Kovar conductor, as shown in Table 2.</li>
	<li>The grid type of the whole model is Hex shape (see Figure 11). The mesh method of the sealing glass and steel shell are sweep, and the Kovar conductor is meshed by structured method. Refine the mesh of sealing glass to guarantee the accuracy of theoretical results. The elements number of Kovar conductor, sealing glass and steel shell are 143700, 20350, and 13400, respectively.</li>
	<li>Set the initial increment, minimum increment, and maximum increment of the static analysis step as 0.01, 1.00 x 10-8 and 1.00 x 10-2, respectively.</li>
	<li>Ensure that the interfaces between the sealing glass and metal parts are bounded. First, impose the changing temperature load (from 370 &#176;C to 20 &#176;C) to simulate the solidification progress of the MTGS model. The stress distribution after this process is shown in Figure 12.</li>
	<li>Impose different temperatures (from 100 &#176;C to 400 &#176;C) onto the whole model to simulate the online monitoring experiments under thermal loads. Under the other circumstance, changing pressure loads (from 1 MPa to 7 MPa) are imposed on the sealing glass to simulate the online monitoring under high pressure. The boundary conditions are shown in Figure 13.</li>
	<li>The numerical results of stress and strain distribution of the whole model are obtained from the destination file shown in Figure 14. Extract the analysis path in the sealing glass shown in Figure 13, of which the position is the monitoring path for FBG sensors in Figure 6a to provide comparison with the measuring results by FBG.</li>
</ol>

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The authors have nothing to disclose.

The critical steps for the stress measuring of sealing material of MTGS structure at high temperature and high pressure include 1) manufacturing of the MTGS models with the FBG sensor, of which the grating region is located at the middle of sealing glass; 2) heating of the whole model using a standard heat treatment process, and after the model cools to RT, the FBG sensor will becomes well-fused with MTGS model, and the residual stress can be measured by Bragg wavelength shift; 3) placing of the complete model into the f...

Metal-to-glass sealing is a sophisticated technology that combines interdisciplinary knowledge (i.e., mechanics, materials, and electrical engineering) and is widely applied in aerospace1, nuclear energy2, and biomedical applications3. It has unique advantages such as higher temperature and pressure endurance compared with organic material sealing structures. According to the difference of coefficient of thermal expansion (CTE), MTGS can be divided into two types: matched seal and mismatched seal4. As for the matched seal, the CTE of metal (&#945;metal) and sealing glass (&#945;glass) are nearly the same to reduce the thermal stress in sealing materials. However, to keep good hermeticity and mechanical robustness of the seal structure in harsh environments (i.e., high temperature and high pressure), the mismatched seal displays better performance than the matched seal. Due to the difference between &#945;metal and &#945;glass, the residual stress generates in sealing glass after the annealing process of MTGS structure. If the residual stress is too large (even exceeding the threshold value), the sealing glass displays small defects, such as cracks. If the residual stress is too small, the sealing glass loses its hermeticity. As a result, the value of residual stress is an important measurement.
Analysis of residual stress in MTGS structures has aroused research interests of many groups around the world. The numerical model of axial and radial stress was built based on thin shell theory5. The finite element method was applied to obtain the global stress distribution of an MTGS structure after the annealing process, which was consistent with experimental results6,7. However, because of limitations involving small size and electromagnetic interference, many advanced sensors are not suitable for these circumstances. The indentation crack length method was reported to measure the residual stress in the sealing material of MTG; however, this method was destructive and could not achieve real-time online monitoring of stress changes in glass.
Fiber Bragg grating (FBG) sensors are small in size (~100 &#181;m) and resistant to electromagnetic interference and harsh environments8. In addition, the components of the fiber are similar to those of sealing glass (SiO2), so FBG sensors have no effects on the hermeticity and insulation of the sealing material. FBG sensors have been applied to the residual stress measurement in composite structures9,10,11, and results showed that it displayed good measuring precision and signal response. Simultaneous temperature and stress measurements may be achieved by fiber Bragg grating arrays on one optical fiber12,13.
A novel protocol based on an FBG sensor is demonstrated in this study. The appropriate preparation for the special MTGS structure has been explored by adjusting the maximum heat temperature to ensure the good hermeticity of the MTGS structure. The FBG sensor is embedded in the prepared path of sealing glass to fuse the FBG and glass together after the heat treatment. Then, the residual stress can be obtained by the Bragg wavelength shift of the FBG. The MTGS structure with the FBG sensor is placed under high temperature and high pressure environments to achieve online monitoring of residual stress under changing loads. In this study, the detailed steps to produce an MTS structure with a FBG sensor are outlined. The results show the feasibility of this novel protocol and establish the foundation for the failure diagnosis of an MTGS structure.

<table>
	<tbody>
		<tr>
			<td>ABAQUS</td>
			<td>Dassault SIMULA</td>
			<td>ABAQUS6.14-5</td>
			<td>The software to carry out numerical simulation.</td>
		</tr>
		<tr>
			<td>Fiber Bragg grating sensors</td>
			<td>Femto Fiber Tec</td>
			<td>FFT.FBG.S.00.02 Single</td>
			<td>apodized FBG</td>
		</tr>
		<tr>
			<td>Fusion splicer</td>
			<td>Furukawa Information Technologies and Telecommunications</td>
			<td>S123M12</td>
			<td>FITEL&#39;s line of fusion splicers provides an excellent solution for both field and factory splicing applications&#12290;</td>
		</tr>
		<tr>
			<td>Glass powder</td>
			<td>Shenzhen Sialom Advanced Materials Co.,Ltd</td>
			<td>LC-1</td>
			<td>A kind of low melting-point glass powder (380&#8451;).</td>
		</tr>
		<tr>
			<td>Graphite mold</td>
			<td>Machining workshop of Tsinghua University</td>
			<td>Graphite</td>
			<td>The mold to locate each part of the metal-to-glass structure.</td>
		</tr>
		<tr>
			<td>Heating furnace</td>
			<td>Tianjin Zhonghuan Electric Furnace Technology Co., Ltd</td>
			<td>SK-G08123-L</td>
			<td>vertical tubular furnace</td>
		</tr>
		<tr>
			<td>Kovar conductor</td>
			<td>Shenzhen Thaistone Technology Co., Ltd</td>
			<td>4J29</td>
			<td>A common material used for the electrical penetration in the metal-to-glass seal structure</td>
		</tr>
		<tr>
			<td>Optical interrogator</td>
			<td>Wuhan Gaussian Optics CO.,LTD</td>
			<td>OPM-T400</td>
			<td>FBG spectrum analysis modules</td>
		</tr>
		<tr>
			<td>Pro/Engineer</td>
			<td>Parametric Technology Corporation</td>
			<td>PROE5.0</td>
			<td>The software to establish the 3D geometry.</td>
		</tr>
		<tr>
			<td>Steel shell</td>
			<td>Beijing Xiongchuan Technology Co., Ltd</td>
			<td>316 stainless steel</td>
			<td>A kind of austenitic stainless steel</td>
		</tr>
	</tbody>
</table>

optimized sealing process and real-time monitoring of glass-to-metal seal structures

Residual stress is an essential factor to keeping the hermeticity and robustness of a glass-to-metal seal structure. The purpose of this report is to demonstrate a novel protocol to characterize and measure residual stress in a glass-to-metal seal structure without destroying the insulation and hermeticity of sealing materials. In this research, a femto-laser inscribed fiber Bragg grating sensor is used. The glass-to-metal seal structure that is measured consists of a metal shell, sealing glass, and Kovar conductor. To make the measurements worthwhile, the specific heat treatment of metal-to-glass seal (MTGS) structure is explored to obtain the model with best hermeticity. Then, the FBG sensor is embedded into the path of sealing glass and becomes well-fused with the glass as the temperature cools to RT. The Bragg wavelength of FBG shifts with the residual stress generated in sealing the glass. To calculate the residual stress, the relationship between Bragg wavelength shift and strain is applied, and the finite element method is also used to make the results reliable. The online monitoring experiments of residual stress in sealing glass are carried out at different loads, such as high temperature and high pressure, to broaden functions of this protocol in harsh environments.

From the results of Figure 5, the standard heat treatment to produce the MTGS models with high pressure endurance is explored, and the models can satisfy the examinations (i.e., light transmissions, pressure endurance, SEM, etc.). Thus, the produced MTGS structure can be applied to keep hermeticity in harsh environments.
The FBG can be well-fused with MTGS structure, and the residual strain in sealing glass will be reflected by Bragg wavelength shift after the hea...

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Optimized Sealing Process and Real-Time Monitoring of Glass-to-Metal Seal Structures

Key procedures to optimize the sealing process and achieve real-time monitoring of the metal-to-glass seal (MTGS) structure are described in detail. The embedded fiber Bragg grating (FBG) sensor is designed to achieve online monitoring of temperature and high-level residual stress in the MTGS with simultaneous environmental pressure monitoring.

Residual stress is an essential factor to keeping the hermeticity and robustness of a glass-to-metal seal structure. The purpose of this report is to ...

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7.2K Views.  Tsinghua University. Key procedures to optimize the sealing process and achieve real-time monitoring of the metal-to-glass seal (MTGS) structure are described in detail. The embedded fiber Bragg grating (FBG) sensor is designed to achieve online monitoring of temperature and high-level residual stress in the MTGS with simultaneous environmental pressure monitoring.

Video: Optimized Sealing Process and Real-Time Monitoring of Glass-to-Metal Seal Structures

Real-Time DC-dynamic Biasing Method for Switching Time Improvement in Severely Underdamped Fringing-field Electrostatic MEMS Actuators

Mechanically underdamped electrostatic fringing-field MEMS actuators are well known for their fast switching operation in response to a unit step input bias voltage. However, the tradeoff for the improved switching performance is a relatively long settling time to reach each gap height in response to various applied voltages. Transient applied bias waveforms are employed to facilitate reduced switching times for electrostatic fringing-field MEMS actuators with high mechanical quality factors. Removing the underlying substrate of the fringing-field actuator creates the low mechanical damping environment necessary to effectively test the concept. The removal of the underlying substrate also a has substantial improvement on the reliability performance of the device in regards to failure due to stiction. Although DC-dynamic biasing is useful in improving settling time, the required slew rates for typical MEMS devices may place aggressive requirements on the charge pumps for fully-integrated on-chip designs. Additionally, there may be challenges integrating the substrate removal step into the back-end-of-line commercial CMOS processing steps. Experimental validation of fabricated actuators demonstrates an improvement of 50x in switching time when compared to conventional step biasing results. Compared to theoretical calculations, the experimental results are in good agreement.

The robust device design of fringing-field electrostatic MEMS actuators results in inherently low squeeze-film damping conditions and long settling times when performing switching operations using conventional step biasing. Real-time switching time improvement with DC-dynamic waveforms reduces the settling time of fringing-field MEMS actuators when transitioning between up-to-down and down-to-up states.

Mechanically underdamped electrostatic fringing-field MEMS actuators are well known for their fast switching operation in response to a unit step input ...

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a stable and continuous operation of the plasma is possible and the plasma torch can be used for many different applications. On one hand, the hot (3,600 K gas temperature) plasma can be used for chemical processes and on the other hand the cold afterglow (temperatures down to almost RT) can be applied for surface processes. For example chemical syntheses are interesting volume processes. Here the microwave plasma torch can be used for the decomposition of waste gases which are harmful and contribute to the global warming but are needed as etching gases in growing industry sectors like the semiconductor branch. Another application is the dissociation of CO2. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 to CO and O2. The CO can be further processed to gaseous or liquid higher hydrocarbons thereby providing chemical storage of the energy, synthetic fuels or platform chemicals for the chemical industry. Applications of the afterglow of the plasma torch are the treatment of surfaces to increase the adhesion of lacquer, glue or paint, and the sterilization or decontamination of different kind of surfaces. The movie will explain how to ignite the plasma solely by microwave power without any additional igniters, e.g., electric sparks. The microwave plasma torch is based on a combination of two resonators &#8212; a coaxial one which provides the ignition of the plasma and a cylindrical one which guarantees a continuous and stable operation of the plasma after ignition. The plasma can be operated in a long microwave transparent tube for volume processes or shaped by orifices for surface treatment purposes.

This movie shows how an atmospheric plasma torch can be ignited by microwaves with no additional igniters and provides a stable and continuous plasma operation suitable for plenty of applications.

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a ...

Development of an Experimental Setup for the Measurement of the Coefficient of Restitution under Vacuum Conditions

The Discrete Element Method is used for the simulation of particulate systems to describe and analyze them, to predict and afterwards optimize their behavior for single stages of a process or even an entire process. For the simulation with occurring particle-particle and particle-wall contacts, the value of the coefficient of restitution is required. It can be determined experimentally. The coefficient of restitution depends on several parameters like the impact velocity. Especially for fine particles the impact velocity depends on the air pressure and under atmospheric pressure high impact velocities cannot be reached. For this, a new experimental setup for free-fall tests under vacuum conditions is developed. The coefficient of restitution is determined with the impact and rebound velocity which are detected by a high-speed camera. To not hinder the view, the vacuum chamber is made of glass. Also a new release mechanism to drop one single particle under vacuum conditions is constructed. Due to that, all properties of the particle can be characterized beforehand.

The coefficient of restitution is a parameter that describes the loss of kinetic energy during collision. Here, a free-fall setup under vacuum conditions is developed to be able to determine the coefficient of restitution parameter for particles in micrometer range with high impact velocities.

The Discrete Element Method is used for the simulation of particulate systems to describe and analyze them, to predict and afterwards optimize their ...

Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent

The aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with sufficient heavy metal adsorption capacity. To this end, blast furnace slag, a residue from iron-making, is utilized as the starting material. Calcium is selectively extracted from the slag by leaching with acetic acid (2 M CH3COOH) as the extraction agent. The filtered leachate is subsequently physico-chemically purified and then carbonated to form precipitated calcium carbonate (PCC) of high purity (&lt;2 wt% non-calcium impurities, according to ICP-MS analysis). Sodium hydroxide is added to neutralize the regenerated acetate. The morphological properties of the resulting calcitic PCC are tuned for its potential application as a filler in papermaking. In parallel, the residual solids from the extraction stage are subjected to hydrothermal conversion in a caustic solution (2 M NaOH) that leads to the predominant formation of a particular zeolitic mineral phase (detected by XRD), namely analcime (NaAlSi2O6&#8729;H2O). Based on its ability to adsorb Ni2+, as reported from batch adsorption experiments and ICP-OES analysis, this product can potentially be used in wastewater treatment or for environmental remediation applications.

A protocol for the parallel production of precipitated calcium carbonate and zeolitic material from blast furnace slag via mineral carbonation and alkaline hydrothermal conversion, respectively, is presented. The performance of the zeolitic material towards nickel adsorption is tested.

The aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with ...

Challenges in Rheological Characterization of Highly Concentrated Suspensions &#8212; A Case Study for Screen-printing Silver Pastes

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the manifold requirements during processing and application of such complex fluids. In this investigation, measuring protocols for a conclusive assessment of different process relevant rheological parameters have been evaluated. This includes the determination of yield stress, viscosity, wall slip velocity, structural recovery after large deformation and elongation at break as well as tensile force during filament stretching.
The importance of concomitant video recordings during parallel-plate rotational rheometry for a significant determination of rheological quantities is demonstrated. The deformation profile and flow field at the sample edge can be determined using appropriate markers. Thus, measurement parameter settings and plate roughness values can be identified for which yield stress and viscosity measurements are possible. Slip velocity can be measured directly and measuring conditions at which plug flow, shear banding or sample spillover occur can be identified clearly. 
Video recordings further confirm that the change in shear moduli observed during three stage oscillatory shear tests with small deformation amplitude in stage I and III but large oscillation amplitude in stage II can be directly attributed to structural break down and recovery. For the pastes investigated here, the degree of irreversible, shear-induced structural change increases with increasing deformation amplitude in stage II until a saturation is reached at deformations corresponding to the crossover of G' and G'', but the irreversible damage is independent of the duration of large amplitude shear. 
A capillary breakup elongational rheometer and a tensile tester have been used to characterize deformation and breakup behavior of highly filled pastes in uniaxial elongation. Significant differences were observed in all experiments described above for two commercial screen-printing silver pastes used for front side metallization of Si-solar cells.

Challenges in Rheological Characterization of Highly Concentrated Suspensions &amp;#8212; A Case Study for Screen-printing Silver Pastes

A protocol for a robust and application relevant rheological characterization of highly concentrated suspensions is presented. Silver pastes used for screen-printing application in solar cell production are employed as model systems.

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the ...

Fabrication Procedures and Birefringence Measurements for Designing Magnetically Responsive Lanthanide Ion Chelating Phospholipid Assemblies

Bicelles are tunable disk-like polymolecular assemblies formed from a large variety of lipid mixtures. Applications range from membrane protein structural studies by nuclear magnetic resonance (NMR) to nanotechnological developments including the formation of optically active and magnetically switchable gels. Such technologies require high control of the assembly size, magnetic response and thermal resistance. Mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and its lanthanide ion (Ln3+) chelating phospholipid conjugate, 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA), assemble into highly magnetically responsive assemblies such as DMPC/DMPE-DTPA/Ln3+ (molar ratio 4:1:1) bicelles. Introduction of cholesterol (Chol-OH) and steroid derivatives in the bilayer results in another set of assemblies offering unique physico-chemical properties. For a given lipid composition, the magnetic alignability is proportional to the bicelle size. The complexation of Ln3+ results in unprecedented magnetic responses in terms of both magnitude and alignment direction. The thermo-reversible collapse of the disk-like structures into vesicles upon heating allows tailoring of the assemblies&#39; dimensions by extrusion through membrane filters with defined pore sizes. The magnetically alignable bicelles are regenerated by cooling to 5 &#176;C, resulting in assembly dimensions defined by the vesicle precursors. Herein, this fabrication procedure is explained and the magnetic alignability of the assemblies is quantified by birefringence measurements under a 5.5 T magnetic field. The birefringence signal, originating from the phospholipid bilayer, further enables monitoring of polymolecular changes occurring in the bilayer. This simple technique is complementary to NMR experiments that are commonly employed to characterize bicelles.

Fabrication procedures for highly magnetically responsive lanthanide ion chelating polymolecular assemblies are presented. The magnetic response is dictated by the assembly size, which is tailored by extrusion through nanopore membranes. The assemblies&#39; magnetic alignability and temperature-induced structural changes are monitored by birefringence measurements, a complimentary technique to nuclear magnetic resonance and small angle neutron scattering.

Bicelles are tunable disk-like polymolecular assemblies formed from a large variety of lipid mixtures. Applications range from membrane protein structural ...

Predicting Catalyst Extrudate Breakage Based on the Modulus of Rupture

The mechanical strength of extruded catalysts and their natural or forced breakage by either collision against a surface or by a compressive load in a fixed bed are important phenomena in catalyst technology. The mechanical strength of the catalyst is measured here by its bending strength or flexural strength. This technique is relatively new from the perspective of applying it to commercial catalysts of typical sizes used in the industry. Catalyst breakage by collision against a surface is measured after a fall of the extrudates through the ambient air in a vertical pipe. Quantifying the impact force is done theoretically by applying Newton's second law. Measurement of catalyst breakage due to stress in a fixed bed is done following the standard procedure of the bulk crush strength test. Novel here is the focus on measuring the reduction in the length to diameter ratio of the extrudates as a function of the stress.

Here we present a protocol to measure the modulus of rupture of an extruded catalyst and the breakage of said catalyst extrudates by collision against a surface or by compression in a fixed bed.

The mechanical strength of extruded catalysts and their natural or forced breakage by either collision against a surface or by a compressive load in a ...

Combining Microfluidics and Microrheology to Determine Rheological Properties of Soft Matter during Repeated Phase Transitions

The microstructure of soft matter directly impacts macroscopic rheological properties and can be changed by factors including colloidal rearrangement during previous phase changes and applied shear. To determine the extent of these changes, we have developed a microfluidic device that enables repeated phase transitions induced by exchange of the surrounding fluid and microrheological characterization while limiting shear on the sample. This technique is &#181;2rheology, the combination of microfluidics and microrheology. The microfluidic device is a two-layer design with symmetric inlet streams entering a sample chamber that traps the gel sample in place during fluid exchange. Suction can be applied far away from the sample chamber to pull fluids into the sample chamber. Material rheological properties are characterized using multiple particle tracking microrheology (MPT). In MPT, fluorescent probe particles are embedded into the material and the Brownian motion of the probes is recorded using video microscopy. The movement of the particles is tracked and the mean-squared displacement (MSD) is calculated. The MSD is related to macroscopic rheological properties, using the Generalized Stokes-Einstein Relation. The phase of the material is identified by comparison to the critical relaxation exponent, determined using time-cure superposition. Measurements of a fibrous colloidal gel illustrate the utility of the technique. This gel has a delicate structure that can be irreversibly changed when shear is applied. &#181;2rheology data shows that the material repeatedly equilibrates to the same rheological properties after each phase transition, indicating that phase transitions do not play a role in microstructural changes. To determine the role of shear, samples can be sheared prior to injection into our microfluidic device. &#181;2rheology is a widely applicable technique for the characterization of soft matter enabling the determination of rheological properties of delicate microstructures in a single sample during phase transitions in response to repeated changes in the surrounding environmental conditions.

We demonstrate the fabrication and use of a microfluidic device that enables multiple particle tracking microrheology measurements to study the rheological effects of repeated phase transitions on soft matter.

The microstructure of soft matter directly impacts macroscopic rheological properties and can be changed by factors including colloidal rearrangement ...

Parallel Active Cantilever Arrays in AFMS to Enable High-Throughput Inspections

Active Probe Atomic Force Microscopy with Quattro-Parallel Cantilever Arrays for High-Throughput Large-Scale Sample Inspection

An Atomic Force Microscope&#160;(AFM) is&#160;a powerful and versatile tool for nanoscale surface studies to capture 3D topography images of samples. However, due to their limited imaging throughput, AFMs have not been widely adopted for large-scale inspection purposes. Researchers have developed high-speed AFM systems to record dynamic process videos in chemical and biological reactions at tens of frames per second, at the cost of a small imaging area of up to several square micrometers. In contrast, inspecting large-scale nanofabricated structures, such as semiconductor wafers, requires nanoscale spatial resolution imaging of a static sample over hundreds of square centimeters with high productivity. Conventional AFMs use a single passive cantilever probe with an optical beam deflection system, which can only collect one pixel at a time during AFM imaging, resulting in low imaging throughput. This work utilizes an array of active cantilevers with embedded piezoresistive sensors and thermomechanical actuators, which allows simultaneous multi-cantilever operation in parallel operation for increased imaging throughput. When combined with large-range nano-positioners and proper control algorithms, each cantilever can be individually controlled to capture multiple AFM images. With data-driven post-processing algorithms, the images can be stitched together, and defect detection can be performed by comparing them to the desired geometry. This paper introduces principles of the custom AFM using the active cantilever arrays, followed by a discussion on practical experiment considerations for inspection applications. Selected example images of silicon calibration grating, highly-oriented pyrolytic graphite, and extreme ultraviolet lithography masks are captured using an array of four active cantilevers (&#34;Quattro&#34;) with a 125 &#181;m tip separation distance. With more engineering integration, this high-throughput, large-scale imaging tool can provide 3D metrological data for extreme ultraviolet (EUV) masks, chemical mechanical planarization (CMP) inspection, failure analysis, displays, thin-film step measurements, roughness measurement dies, and laser-engraved dry gas seal grooves.

Author Spotlight: Introduction to Active Probe Atomic Force Microscopy with Quattro-Parallel Cantilever Arrays

Large-scale sample inspection with nanoscale resolution has a wide range of applications, especially for nanofabricated semiconductor wafers. Atomic force microscopes can be a great tool for this purpose, but are limited by their imaging speed. This work utilizes parallel active cantilever arrays in AFMs to enable high-throughput and large-scale inspections.

An Atomic Force Microscope&#160;(AFM) is&#160;a powerful and versatile tool for nanoscale surface studies to capture 3D topography images of samples. ...

Visualizing Polymer Dynamics for Optimizing 3D Printing Quality

Real-Time Imaging of Bonding in 3D-Printed Layers

In recent times, 3D printing technology has revolutionized our ability to design and produce products, but optimizing the print quality can be challenging. The process of extrusion 3D printing involves pressuring molten material through a thin nozzle and depositing it onto previously extruded material. This method relies on bonding between the consecutive layers to create a strong and visually appealing final product. This is no easy task, as many parameters, such as the nozzle temperature, layer thickness, and printing speed, must be fine-tuned to achieve optimal results. In this study, a method for visualizing the polymer dynamics during extrusion is presented, giving insight into the layer bonding process. Using laser speckle imaging, the plastic flow and fusion can be resolved non-invasively, internally, and with high spatiotemporal resolution. This measurement, which is easy to perform, provides an in-depth understanding of the underlying mechanics influencing the final print quality. This methodology was tested with a range of cooling fan speeds, and the results showed increased polymer motion with lower fan speeds and, thus, explained the poor printing quality when the cooling fan was turned off. These findings show that this methodology allows for optimizing the printing settings and understanding the material behavior. This information can be used for the development and testing of novel printing materials or advanced slicing procedures. With this approach, a deeper understanding of extrusion can be built to take 3D printing to the next level.

Author Spotlight: Real-Time Imaging of Bonding in 3D-Printed Layers  

With a non-invasive and real-time technique, nanoscopic polymer motion inside a polymer filament is imaged during 3D printing. Fine-tuning this motion is crucial for producing constructs with optimal performance and appearance. This method reaches the core of plastic layer fusion, thus offering insights into optimal printing conditions and material design criteria.