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Overview
In thermogravimetric analysis (TGA), one of the primary objectives is to separate and characterize individual components within a sample based on their thermal decomposition behavior. However, when multiple thermal events occur in close temperature proximity, overlapping mass-loss signals can reduce resolution and limit interpretability.
Factors such as sample mass, purge gas, and heating rate affect this resolution, with heating rate being the most impactful. To address these limitations, AMI has integrated a Step Isothermal function into the InfinityPro software platform for its TGA systems.

What Is Step Isothermal?
Step Isothermal TGA introduces dynamic control over heating conditions by allowing the system to:
•Heat the sample at a defined linear rate
•Monitor real-time derivative weight loss (%/min)
•Automatically switch to an isothermal hold once a predefined Iso Start Threshold isexceeded
•Resume the temperature ramp once the Ramp Resume Threshold is reached
This smart switching improves separation of closely spaced decomposition steps that may otherwise appear merged during traditional linear ramping.

Figure1: TGA software setup window with Step Isothermal option enabled

How It Works
• The Iso Start Threshold defines the rate of weight loss at which the system will enter an isothermal hold. This is typically set at ~1/10th to 1/15th of the expected peak weight loss rate.
• The Ramp Resume Threshold determines when the system will exit the isothermal condition and resume ramping. It is typically ~1/15th or less of the Iso Start Threshold.
This cycle continues throughout the experiment, enabling adaptive thermal profiling based on the material's real-time behavior.

Figure 2: Step Isothermal method setup dialog showing threshold parameters.

Case Study Example
A conventional TGA run on Barium Chloride at 20 °C/min reveals two overlapping mass-loss events—one at approximately 80 °C and another around 110 °C. These transitions appear as a single broadened event in standard TGA.

Figure 3: Conventional TGA curve for Barium Chloride showing overlapping events.

Using Step Isothermal, the same material yields two distinct weight-loss steps, allowing accurate resolution of each component’s thermal behavior. The system automatically pauses heating during high-rate decomposition, improving event separation.

Figure 4: Improved separation using Step Isothermal mode on the same material.

Key Benefits
• Enhanced separation of overlapping decomposition or reaction events.
• Automated transition control based on actual weight loss.
• No need for complex scripting or multiple trial runs.
• Especially useful for polymers, composites, hydrates, and materials with closely spaced transitions.

Conclusion
Step Isothermal TGA, standard on all AMI TGA instruments, enables high-resolution thermal analysis for complex materials by combining real-time mass-loss monitoring with intelligent temperature control. This feature adds analytical power and flexibility while remaining fully accessible through AMI’s intuitive InfinityPro interface.

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Introduction

Differential Scanning Calorimetry (DSC) is a fundamental technique used to study phase transitions, heat

capacity, and thermal stability in materials. However, most conventional DSC systems are limited to

temperatures below 700 °C. For advanced materials research—such as ceramics, metals, high-performance

polymers, and oxides—thermal transitions often occur well above 1000 °C.

To meet this need, Advanced Measurement Instruments (AMI) has developed the DSC 1200 and DSC

1500—two high-temperature DSC systems built on a proven STA platform. This application note outlines

the advantages of using a hang-down STA-derived architecture for DSC-only measurements and highlights

the capabilities of both models for demanding thermal analysis.

Why Use an STA Platform for High-Temperature DSC?

The STA platform is typically used for simultaneous TGA/DSC measurements, but when adapted for DSC

only functionality, it offers significant advantages:

• Elimination of the microbalance simplifies the system, reduces thermal interference, and focuses

entirely on calorimetric precision.

• Hang-down geometry ensures superior thermal isolation from the furnace environment, enhancing

signal stability and minimizing baseline drift.

• A vertical lift furnace ensures consistent sample positioning and safe high-temperature operation.
• The use of high-purity platinum components and precision-machined sensor assemblies

ensures consistent sensitivity and durability at elevated temperatures.

This architecture allows AMI’s high-temperature DSC systems to achieve the same thermal range and

mechanical robustness of an STA, while offering the clarity and simplicity of a pure DSC system.

System Overview: AMI DSC 1200 / DSC 1500

AMI DSC 1200

• Temperature Range: Ambient to 1200 °C
• Heating Rate: 0.1 to 60 °C/min

AMI DSC 1500

• Temperature Range: Ambient to 1500 °C
• Heating Rate: 0.1 to 60 °C/min

Shared Features:

• Calorimetric Accuracy: ±1% (with certified standards)
• Thermocouples: Type R (sample and reference), cold-junction compensated
• DSC Sensor: Platinum-rhodium with integrated sample/reference cups
• Atmosphere Control: Static or Dynamic
• Furnace Cooling: Water-cooled with integrated safety interlocks
• Sensor Access: Tool-free access for pan replacement and calibration
• Software: InfinityPro for instrument control, method development, calibration, and real-time data

visualization

• Communications: RS-232 or USB interface
• Safety: Factory-limited lift range, over-temperature protection, and water flow alarm

Applications

AMI’s high-temperature DSC systems are ideal for advanced thermal characterization in materials that

require extended temperature range and stability. Application areas include:

• Ceramics and oxides: Phase transitions, sintering behavior, and glass crystallization
• Refractory materials: Fusion and degradation temperatures
• Metallic alloys: Solid-state transformations and oxidation
• High-performance polymers: Thermal degradation and glass transition above 600 °C
• Battery materials: Decomposition and thermal runaway characterization

The high sensitivity and stable baseline make these instruments suitable for both large enthalpic events

and subtle thermal transitions.

Figure 1. DSC curve of high-purity silver (Ag) showing a sharp endothermic peak at 961.8 °C corresponding to its

melting point.

Silver offers an excellent benchmark for high-temperature DSC calibration due to its well-defined melting

point and heat of fusion. The sharp endothermic peak at 961.8 °C illustrates the system’s sensitivity and

temperature accuracy. The flat baseline and low noise level emphasize the DSC’s thermal stability and

precision over extended high-temperature ramps.

Figure 2. DSC curve of high-purity nickel (Ni) demonstrating a strong endothermic melting peak at approximately

1455 °C

This curve demonstrates the DSC system’s capability to operate at elevated temperatures with excellent

resolution. The melting of nickel, a refractory metal, is clearly resolved even near the upper range of the

instrument’s performance. The signal clarity underscores the robustness of the sensor design and heating

system for demanding thermal analysis applications.

Advantages of a High-Temperature Hang-Down DSC

System Configuration and Installation

Each AMI DSC system is shipped with:

• Main module with vertically lifting furnace
• Dedicated DSC sensor and standard sample/reference pans
• Gas inlets
• InfinityPro software license
• Start-up accessory kit: sample holders, tools, thermocouples, communications cable
• Remote installation support, unlimited virtual training, and application support

Conclusion

The AMI DSC 1200 and DSC 1500 systems provide powerful, stable, and high-precision platforms for

thermal analysis beyond the limits of conventional DSC. By leveraging the mechanical strength and thermal

performance of STA architecture—without the complexity of a balance—AMI delivers research-grade

solutions for laboratories working at the forefront of materials science.

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Background

Cement is one of the most widely used construction materials across industries including infrastructure, transportation, agriculture, and marine engineering. Among cement types, silicate cement holds a dominant role due to its versatility, durability, and long-standing industrial adoption.

The primary phase of silicate cement clinker comprises silicate minerals, with alite (C₃S) and belite (C₂S) accounting for over 75% of its composition. Upon exposure to atmospheric conditions, these components react with moisture and carbon dioxide to form secondary products such as:

• Ettringite
• C-S-H gel
• Calcium hydroxide (Ca(OH)₂)
• Calcium carbonate (CaCO₃)

Each of these phases decomposes at distinct temperatures, making thermogravimetric analysis (TGA) a powerful technique to identify and quantify cement hydration and carbonation products based on characteristic mass loss behavior.

Experimental Method

Thermogravimetric analysis was performed using the AMI TGA 1000 under the following conditions:

• Sample Mass: ~20 mg
• Crucible: Platinum
• Atmosphere: Nitrogen (50 mL/min)
• Heating Program: 30°C to 1000°C at 10°C/min

The analysis focused on the thermal decomposition behaviors of Ca(OH)₂ and CaCO₃, allowing their relative quantities to be determined based on water and CO₂ release, respectively.

Results and Discussion

Figures 1 and 2 present the TGA profiles for two silicate cement samples (Sample A and Sample B). The thermograms can be interpreted in four distinct mass loss stages:

Stage 1: < 200°C

• Mass Loss: ~5.25%
• Cause: Evaporation of free moisture and decomposition of low-temperature hydration products such as C-S-H gel and ettringite.

Stage 2: 400–480°C

• Cause: Dehydration of calcium hydroxide (Ca(OH)₂).

Stage 3: 500–800°C

• Cause: Decomposition of poorly crystalline CaCO₃, which typically forms via environmental carbonation during curing.

Stage 4: > 800°C

• Cause: Breakdown of highly crystalline CaCO₃, typically from the original clinker phase or long-term carbonation.

Comparative Analysis: Sample A vs. Sample B

• Both samples exhibit comparable amounts of highly crystalline CaCO₃.
• Sample B shows a higher content of Ca(OH)₂, indicating a more advanced hydration stage or higher water-to-cement ratio.
• Sample A shows a greater amount of poorly crystalline CaCO₃, suggesting more surface carbonation or environmental exposure during curing.

These results demonstrate that the AMI TGA 1000 provides excellent resolution for differentiating hydration and carbonation products in cement and allows for reliable quantitative analysis based on thermal decomposition behavior.

Conclusion

Thermogravimetric analysis using the AMI TGA 1000 enables clear and reliable identification of key hydration and carbonation phases in silicate cement. The system’s high sensitivity and stability allow differentiation between loosely and strongly bound components across a broad temperature range — from ettringite and Ca(OH)₂ to amorphous and crystalline CaCO₃.

The relative amounts of Ca(OH)₂ and CaCO₃ reflect hydration progress and carbonation extent, both of which impact durability and performance in real-world environments.

Figure 1: TGA of Silicate Cement Sample A

Figure 2: TGA of Silicate Cement Sample B

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1. Introduction

Thermal analysis techniques are widely applied in pharmaceutical research for evaluating polymorphism, phase transitions, hydration states, decomposition behavior, purity, compatibility, and stability. Among these techniques, Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) are most frequently used and are officially recognized in many pharmacopeias for drug quality control.

Differential Scanning Calorimetry (DSC) measures heat flow associated with thermal events during a controlled temperature program. This includes endothermic and exothermic transitions such as melting, glass transitions, recrystallization, and polymorphic transformations. In the pharmaceutical field, DSC is often used to determine melting points, glass transitions, drug purity, polymorphs, and compatibility between active pharmaceutical ingredients (APIs) and excipients.

Thermogravimetric Analysis (TGA) records changes in a sample’s mass as a function of temperature under a defined atmosphere. TGA is valuable for characterizing the presence of adsorbed water, crystallization solvents, thermal stability, and decomposition behavior. For hydrates and solvates, TGA can differentiate between loosely bound and tightly bound solvent molecules by observing weight loss patterns across different temperature ranges.

Revefenacin, a long-acting muscarinic antagonist (LAMA), is used as a maintenance therapy for chronic obstructive pulmonary disease (COPD). It improves lung function, alleviates symptoms, and slows disease progression. Revefenacin exhibits polymorphism, with multiple crystalline forms (I–IV) reported. Only Form III is currently used in commercial formulations due to better processability. However, challenges such as solvate formation and solvent residue during crystallization necessitate continued development of more stable forms. For example, Revefenacin trihydrate Form A has demonstrated improved chemical stability, higher polymorphic purity, and enhanced solubility.

2. Experimental Method

Thermal analysis was conducted using the AMI DSC 600 and AMI TGA 1000 systems.

DSC Characterization

Powdered Revefenacin samples were placed in aluminum crucibles and analyzed under a nitrogen purge (50 mL/min). Two heating rates—5 K/min and 10 K/min—were evaluated over a temperature range from 5 °C to 200 °C. The impact of crucible type (sealed vs. unsealed) and heating rate on the detection of polymorphic forms was investigated.

TGA Characterization

Powdered samples were placed in platinum crucibles and analyzed under a nitrogen atmosphere (50 mL/min). The temperature was ramped from room temperature to 300 °C at a rate of 5 °C/min.

3. Results and Discussion

Figure 1: DSC curves of Revefenacin at different heating rates

At higher heating rates (10 K/min), the melting peaks are larger and sharper due to faster energy input. At 5 K/min, a secondary melting peak becomes visible, indicating the presence of another polymorph. This suggests that slower heating rates may improve the resolution of closely spaced transitions and help distinguish between multiple crystalline forms. Appropriate heating rate selection is therefore essential for accurate polymorph identification.

Figure 2: DSC curves of Revefenacin using sealed vs. solid crucibles

The melting behavior is influenced by the crucible type. In sealed crucibles, a clean melting peak is observed. In open (solid) crucibles, adsorbed and crystallization water evaporates during initial heating, leading to a broader melting profile beginning near 30 °C. This early peak is attributed to moisture loss rather than actual melting.

The TGA curve supports the DSC findings by showing a stepwise mass loss, corresponding to the removal of adsorbed and crystallization water. A total weight loss of 8.243% was recorded. From the weight loss between plateaus, the molar ratio of crystallization water can be calculated, confirming the hydrate content and its thermal release characteristics.

Conclusion

The AMI DSC 600 and AMI TGA 1000 provided complementary thermal and gravimetric data critical for evaluating Revefenacin’s polymorphic forms and hydration behavior.

• DSC enabled clear differentiation between polymorphs and revealed the influence of heating rate and crucible type.
• TGA verified the presence and amount of crystallization water, supporting accurate formulation development and process control.

These methods play a vital role in the development and quality assurance of pharmaceutical compounds where polymorphic stability, solvate formation, and residual solvent content are major concerns.

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Background

Organic compounds frequently exist in multiple polymorphic forms, each exhibiting distinct physical properties such as solubility, melting point, or heat of fusion. Polymorphism plays a significant role in pharmaceutical development, particularly for poorly soluble drugs.

The following well-known thermodynamic equation relates solubility (X) to heat of fusion (ΔHf), melting point (Tm), and heat capacity change (ΔCp) [1]:

By applying this equation to two anhydrous polymorphs of carbamazepine (Forms I and III), and solving the equations simultaneously, one can derive the ratio of their solubilities. This theoretical approach, when combined with experimental calorimetric data, yields a calculated transition temperature that agrees closely—within 2°C—with the value estimated from experimental solubility data [2].

Experimental Thermodynamic Parameters

Forms I and III of carbamazepine show a melting point difference of 15°C:

• Form I: Melts at 189°C with ΔHf = 26 kJ/mol
• Form III: Melts at 174°C with ΔHf = 29 kJ/mol

These values were used to calculate the solubility ratio profile, as shown in Figure 1 (closed circles). Theoretical curves in the same figure demonstrate the impact of varying the ΔHf difference (4.5, 6.0, 7.5, and 9.0 kJ/mol) between the two forms.

Figure 1

These simulations show that even if the ΔHf difference had been as high as 9.0 kJ/mol, Form I would have been only about three times more soluble than Form III at room temperature—demonstrating the modest influence of heat of fusion differences on solubility ratio.

Effect of Melting Point Differences on Solubility

To further evaluate the influence of melting point, the actual ΔHf values of the two polymorphs were held constant, while the melting point difference was varied across a broad range—up to 37.5°C.

As shown in Figure 2, these simulations again indicate a modest effect: even with large melting point differences, Form I would have been less than twice as soluble as Form III.

Figure 2

Discussion and Implications

The theoretical treatment supports a key observation from previous experimental studies: polymorphs rarely show dramatically different solubilities [2]. This finding has practical consequences for pharmaceutical formulation:

• For highly soluble polymorphs, minor solubility differences may not impact product performance.
• However, for poorly soluble drugs, even small solubility variations can affect bioavailability, absorption, or dosage form performance.
• Additionally, non-solubility properties such as density, compressibility, or crystal shape may affect manufacturability and necessitate strict polymorphic control during formulation development.

Accurate detection of melting points and heats of fusion is critical to these analyses. The DSC 600 by AMI offers high-resolution thermal detection, exceptional baseline stability, and precise integration tools for quantifying enthalpic transitions—making it ideal for evaluating polymorphic behavior and supporting solubility modeling in early formulation work.

References

[1] David J. W. Grant and Takeru Higuchi in Techniques of Chemistry, Volume XXI, Solubility Behavior of Organic Compounds; J. Wiley & Sons: New York, 1990.
[2] Behme, R. J.; Brooke, D. J. Pharm. Sci. 1991, 80, 986–990.

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Research Background

Shape Memory Alloy (SMA) is a metallic material composed of more than two metal elements that exhibits a shape memory effect—the ability to return to a pre-set shape after deformation when heated. This unique property results from a thermoelastic martensitic phase transformation and its reversibility.

Martensitic transformation is a non-diffusion solid-state phase change, characterized by atomic movement in a cooperative but localized way. It forms a metastable phase via twinning without altering the alloy’s chemical composition. SMAs are commonly categorized into NiTi-based, Cu-based, and Fe-based alloys [1]. Among these, NiTi-based alloys are the most commercially successful due to their superior shape recovery, superelasticity, corrosion resistance, and biocompatibility [2].

In NiTi alloys, the high-temperature phase is austenite (B2 structure), and the low-temperature phase is martensite (B19’ structure). The transformation is reversible and temperature-dependent:

• Cooling initiates the transformation from austenite to martensite, beginning at the martensite start temperature (Ms) and finishing at Mf.
• Heating triggers the reverse transformation from martensite to austenite, beginning at the austenite start temperature (As) and completing at Af.

NiTi alloys are usually fixed into a preset shape at high temperature (austenitic phase), then cooled below Ms to become soft and deformable. Upon reheating above Af, the alloy returns to its original shape. Therefore, accurately measuring the phase transformation temperatures (Ms, Mf, As, Af) is essential.

Why Use DSC for NiTi Phase Measurement

Due to the limitations of chemical composition analysis for NiTi (e.g., insufficient accuracy to predict transition temperatures), differential scanning calorimetry (DSC) is the preferred method for determining phase transformation behavior in samples with known thermal processing history.

DSC measures the difference in heat flow between a sample and an inert reference during controlled heating and cooling. The technique detects endothermic and exothermic events, corresponding to the energy changes during phase transitions.

Experimental Method

In this paper, the DSC 600 differential scanning calorimeter from AMI was used for testing NiTi-based SMA samples provided by our partner. The sample shapes are shown as follows:

Figure 1 Ni-Ti-based Shape Memory Alloy

Sample Preparation
The sample was cut to match the crucible’s inner diameter and placed inside a solid crucible. It was then pressed flat to ensure optimal contact between the sample and the crucible wall.

Test Conditions:

• Atmosphere: Nitrogen, 50 ml/min
• Sample Mass: 6.58 mg
• Temperature Range: –20 °C to 50 °C
• Heating/Cooling Rate: 10 K/min

Testing Procedure:

1. Heat from room temperature (25°C) to 50°C
2. Cool to –20°C
3. Reheat to 50°C
   The cycle from –20°C to 50°C was analyzed.

Figure 2 DSC Curve of Ni-Ti-based Shape

Results and Discussion

As shown in Figure 2, the cooling curve (black) shows an exothermic peak corresponding to the austenite-to-martensite transformation in the NiTi alloy.

Phase transformation temperatures were determined using the tangent method, as illustrated in Figure 3, via the DSC Peak Area and DSC Onset functions provided by the software.

Martensitic Transformation (Cooling)

• Ms (start temperature): 14.00 °C
• Mf (finish temperature): 8.18 °C
• Mp (peak temperature): 11.18 °C

An endothermic peak is observed on the heating curve (red), indicating the reverse transformation from martensite to austenite:

Austenitic Transformation (Heating)

• As (start temperature): 10.18 °C
• Af (finish temperature): 18.51 °C

• Ap (peak temperature): 13.64 °C

Figure 3: Analysis Functions of DSC 600 Software

These results demonstrate the precise sensitivity of DSC in detecting reversible phase changes in NiTi-based shape memory alloys.

Conclusion

This study confirms that DSC (DSC 600 by AMI) is the most direct and accurate method for identifying phase transition behavior in NiTi SMAs. The results provide reliable determination of Ms, Mf, As, and Af—critical values for SMA performance in devices ranging from medical stents to aerospace actuators.

References

[1] Wang Shuo, Wang Yuanhao. Overview of research progress on shape memory alloys [J]. Scientific and Technological Innovation. 2020(21): 39-40

[2] Mei Hai. Study on martensitic transformation and shape memory effect of NiTi shape memory alloy [D]. Harbin Engineering University, 2023

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Overview

Conventional differential scanning calorimetry (DSC) can be used to quantify the amount of one crystalline form in a mixture of two forms—even when thermal transitions are not fully resolved. The compound studied has two crystalline anhydrous forms that melt at 173 °C and 189 °C, with heats of fusion of 29.3 kJ/mol and 26.4 kJ/mol, respectively.

The AMI DSC 600, with its high sensitivity, baseline stability, and flexible heating control, enables precise quantification of overlapping thermal events critical for polymorph analysis.

DSC Behavior of the Pure Forms

A sample composed entirely of the lower-melting form behaves differently depending on the heating rate:

• At slow heating rates (e.g., 5 °C/min) – Figure 1, the sample undergoes a spontaneous endothermic solid-state phase transformation into the higher-melting form before melting.

At fast heating rates (e.g., 10 °C/min) – Figure 2, the conversion does not complete in time. Instead, the lower-melting form:

• • Melts
  • Crystallizes into the higher-melting form
  • Then melts again

This results in a thermal curve with an initial melting endotherm, an overlapping crystallization exotherm, and a second melting endotherm.

A sample comprised entirely of the higher-melting form shows a single melting peak, without intermediate transitions.

DSC Behavior of Mixtures and Quantification

Samples containing mixtures of both polymorphs typically produce thermal curves that resemble those of the lower-melting form. Depending on the heating rate, they may show combinations of solid-state transition, melting, and recrystallization. The key analytical parameter is the net enthalpy of the full transformation process.

According to the first law of thermodynamics, the total energy to convert the lower-melting form to the higher-melting form is constant, regardless of the mechanism. For mixtures, this net energy is directly proportional to the amount of the lower-melting material – Figure 3

The AMI DSC 600 allows for accurate integration of these overlapping transitions, enabling reliable quantification even when peaks are not fully resolved.

Conclusion

The AMI DSC 600 enables quantitative analysis of polymorphic mixtures using conventional DSC methods, even when transitions are complex or overlapping. By measuring net enthalpy across the transformation sequence, users can determine the relative proportions of polymorphs with confidence.

This capability is especially useful in pharmaceutical development, materials science, and quality control applications—where understanding polymorph content can be critical to product performance and stability.

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Introduction

Nylon is a widely used engineering thermoplastic in industries ranging from automotive to consumer goods. However, nylon components can sometimes fail in service—becoming brittle, discolored, or dimensionally unstable. One of the most efficient tools for uncovering the root cause of such failures is Differential Scanning Calorimetry (DSC).

Whether you're comparing raw material pellets to molded parts or screening materials for consistency, the AMI DSC 600 offers the sensitivity, reproducibility, and thermal range necessary to evaluate critical transitions like melting, crystallization, and glass transition temperature.

Can DSC Detect Degradation Between Pellets and Molded Parts?

Yes. While degradation may not always be obvious visually or mechanically, DSC can identify subtle thermal changes that result from:

• Over-processing during molding
• Thermal oxidation due to poor purge conditions
• Pigment-induced crystallization shifts

In these cases, comparing the heat of melting (ΔH) and the onset temperatures between raw pellets and molded parts can reveal whether the polymer structure has changed—suggesting degradation, increased crystallinity, or contamination.

What Should You Look For in Nylon DSC Data?

• Heat of Melting (ΔH):
  Indicates the degree of crystallinity. Excess crystallinity often correlates with brittleness and cracking in molded parts. If a pigment or filler acts as a nucleating agent, ΔH will increase.
• Onset of Melting:
  A shift to lower melting onset temperatures may suggest thermal degradation or molecular weight reduction.
• Small Peaks After Melting:
  Occasionally, a minor endothermic peak appears just above the main melt. With nylon, this is often an experimental artifact—caused by sample movement inside the pan. The AMI DSC 600’s stable temperature control and pan sealing options help minimize these artifacts.
• Cooling Curve:
  Differences in crystallization behavior during cooling can be just as important as melting behavior during heating. The DSC 600’s fast, accurate cooling rate control enables clear observation of crystallization onset and kinetics—critical for understanding processing impact.

Why Use the AMI DSC 600 for Nylon?

The AMI DSC 600 is ideal for polymer QC and failure analysis:

• High Sensitivity:
  Detects subtle differences in melting and crystallization events even in partially degraded or pigmented samples.
• Excellent Reproducibility:
  Reduces uncertainty in comparing similar materials—essential for determining batch consistency or subtle degradation.
• User-Friendly Software:
  Streamlined interface for rapid data comparison, overlay plotting, and automated heat/cool cycles.
• Programmable Cooling:
  Enables precise control of crystallization conditions for process simulation.
• Purge Flexibility:
  Allows use of inert gases (e.g., nitrogen or argon) to avoid oxidation—especially important for nylons.

Practical Tips for Nylon Analysis

• Run Under Nitrogen:
  Oxidation in air or oxygen can cause exothermic reactions unrelated to normal melting—use inert purge to get accurate data.
• Compare Crystallinity:
  Increased crystallinity may indicate improper cooling or pigment-induced changes. ΔH is your key metric.
• Check for Yellowing:
  When possible, run unpigmented nylon. Yellowing in DSC samples often indicates oxidative degradation.

Conclusion

Whether you're investigating a failure or verifying material consistency, DSC analysis with the AMI DSC 600 provides clear, actionable data on nylon degradation and crystallinity. From production monitoring to troubleshooting molded parts, our DSC platform is your lab’s essential tool for polymer performance assurance.

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Background

Barium chloride dihydrate (BaCl₂·2H₂O) is a stable hydrate that retains its water of crystallization under ambient conditions. Upon heating, it undergoes a two-step dehydration process:

1. Loss of one mole of more loosely bound water
2. Followed by release of a second, more tightly bound mole

This predictable thermal behavior makes it an excellent system for evaluating both mass loss and enthalpy changes associated with dehydration, and an ideal reference material for evaluating STA instrument performance.

 

Experimental Conditions

• Instrument: AMI STA1000
• Crucible: Open alumina
• Heating Rate: 10 °C/min
• Temperature Range: 10 °C to 210 °C
• Atmosphere: Nitrogen, 25 mL/min

Simultaneous thermogravimetric (TGA) and differential scanning calorimetric (DSC) signals were recorded using the AMI STA1000.

 

Results and Discussion

 

Figure 1 presents the DSC and TGA curves for barium chloride dihydrate. The TGA profile shows a clear two-step mass loss:

• Molecular weight of BaCl₂·2H₂O: 244.27 g/mol
• Theoretical water content: 14.74%
• Observed loss: ~7% per step
• Final residue: 85.85%, closely matching the theoretical 85.26% for anhydrous BaCl₂

 

This close agreement confirms the high precision of the AMI STA1000 in quantitative mass analysis.

The DSC curve shows two distinct endothermic peaks, corresponding to the two dehydration steps. These peaks reflect the enthalpy required to break the lattice interactions that hold the water molecules in place. The difference in peak shape and temperature indicates different binding energies between the first and second hydration waters.

Figure 1: STA Curve

 

Why Hangdown Design Matters

The AMI STA1000 is the only true hangdown-style STA currently available on the market. In this configuration, the sample is suspended from the balance above the furnace, rather than resting on a platform or arm beneath it.

This design offers key advantages:

• Minimized buoyancy effects: The suspended geometry reduces artifacts from convective gas flow and buoyancy, ensuring more accurate weight measurements.
• Enhanced baseline stability: Physical isolation of the balance from furnace heat improves thermal and signal stability.
• Greater visibility and accessibility: Hanging geometry makes sample and thermocouple positioning more straightforward and reliable.

 

For laboratories requiring high precision in mass loss and thermal event detection, this configuration offers clear performance advantages over conventional STA geometries.

 

Conclusion

This study confirms the AMI STA1000’s exceptional precision in simultaneous DSC and TGA analysis. The dehydration of barium chloride dihydrate — a classic two-step thermal event — was measured with close agreement to theoretical values in both mass and enthalpy. The clarity of the thermal transitions and mass loss profile demonstrates the system’s reliability and resolution.

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1. Introduction

Polymeric materials have been essential to human life since ancient times, serving basic needs such as clothing, food storage, shelter, and transportation. The evolution of polymer science and industry has closely paralleled the development of human civilization. From natural polymers like cotton, silk, and wood to synthetic fibers, plastics, and rubbers, scientists have continually designed, synthesized, and modified materials to meet practical needs and evolving demands.

Since the turn of the 21st century, polymer research has shifted toward high-performance materials with advanced functionalities. Emerging areas of focus include self-healing polymers, conductive materials, and thermally stable compounds.

1.1 Structure of Nylon Materials

Polyamides (PAs), commonly referred to as nylons, are polymers containing repeating amide groups (—CONH—) along their molecular chains. As one of the five major engineering thermoplastics, nylons exhibit excellent mechanical strength, wear resistance, chemical stability, and electrical insulation. These properties make them widely applicable in electronics, automotive components, aerospace systems, and industrial machinery.

Figure 1: Nylon Nomenclature

Polyamides are typically classified based on their monomer sources:

• AB-type polyamides, synthesized via ring-opening polymerization of amino acids or lactams (e.g., PA6, PA11, PA12)
• AABB-type polyamides, produced via condensation polymerization of diamines and dicarboxylic acids (e.g., PA66, PA46, PA610)

They can also be categorized by chain structure into aliphatic, aromatic, or copolymerized polyamides.

Aliphatic polyamides, formed from aliphatic diacids and diamines (or amino fatty acids), crystallize rapidly, exhibit high crystallinity, and possess balanced mechanical properties. Among these, nylon 11 (PA11) is a key representative.

PA11 is synthesized from 11-aminoundecanoic acid (molecular structure shown in Figure 2), forming a semicrystalline polymer due to its strong intermolecular hydrogen bonding. Polyamides with more than 10 carbon atoms in the backbone are termed long-chain nylons.

Figure 2: Structure of PA11

PA11 is a translucent, milky white solid with a density of 1.04 g/cm³ and a melting range of 186–190°C. Its key properties include:

• Crystallinity: Strong hydrogen bonding leads to a crystalline structure, though uneven bond distribution results in lower overall crystallinity. Melt crystallization forms irregular lamellae. X-ray diffraction shows at least three polymorphs (α, δ, γ), with hydrogen bonding strength ranked α < δ < γ.
• Moisture Resistance: Due to the low concentration of polar amide groups, PA11 absorbs minimal water.
• Thermal Behavior: Dual melting peaks (185°C and 190°C) appear after annealing at 180°C. Glass transition temperature (Tg) is ~43°C.
• Electrical Properties: Low water uptake ensures stability in humid environments.

PA11 is known for its wear resistance, surface smoothness, and corrosion resistance—ideal for:

• Piping: Used in pneumatic brake lines, fuel lines, and pipeline systems.
• Coatings: Powder coatings improve adhesion, appearance, and durability for equipment
• such as hospital beds, office furniture, and sporting goods.

Aromatic polyamides contain benzene rings and amide groups in their backbone and fall into two categories: fully aromatic and semi-aromatic.

Fully aromatic polyamides, formed by condensing aromatic diamines and diacids, feature rigid, densely packed benzene rings and strong intermolecular hydrogen bonds. This results in high strength, thermal resistance, and low moisture absorption.

Figure 3: Structure of PPTA

A classic example is poly(p-phenylene terephthalamide) (PPTA), shown in Figure 3, which has a linear, rigid-rod structure. Its extended conformation enables high crystallinity, rigidity, and a melting point above 500°C. However, PPTA decomposes before it can melt, making it unsuitable for conventional melt processing like extrusion or injection molding. Applications include aerospace, defense, flame-retardant clothing, and ballistic protection.

Semi-aromatic polyamides, such as poly(hexamethylene terephthalamide) (PA6T), are synthesized by reacting aromatic and aliphatic monomers. The chemical structure of PA6T, derived from terephthalic acid (PTA) and hexamethylenediamine (HMDA), is shown in Figure 4.

Figure 4: Structure of PA6T

PA6T retains some flexibility and crystallinity while gaining thermal stability and rigidity through aromatic ring incorporation. It exhibits:

• Higher mechanical strength and thermal resistance than aliphatic nylons
• Lower water absorption and superior dimensional stability
• Excellent chemical resistance, tolerating oils, fuels, antifreeze, and high temperatures.

However, like PPTA, PA6T’s high melting point (~370°C) exceeds its decomposition temperature (~350°C), requiring copolymer modification to reduce processing temperatures. For example, PA66/PA6T copolymers allow better processability due to structural similarity between monomers, enabling cocrystallization with minor lattice defects while preserving hydrogen bonding. (Structure shown in Figure 5.)

Figure 5: Structure of PA6T/66 Copolymer

Key properties of PA6T-based nylons include:

1. High melting points, glass transition temperatures, and crystallinity
2. Low water absorption and minimal dimensional change
3. Excellent solvent and oil resistance
4. Low thermal expansion
5. Outstanding wear, fatigue, and creep resistance
6. Excellent shape retention with minimal warping
7. Strong weldability for dip or reflow soldering

These materials are widely used in automotive and electronics, especially in high-temperature or high-performance applications. Common commercial grades include:

• Series A: Standard mechanical and thermal grades
• Series C: High-flow materials for film and molding
• Series AE: Low-friction variants for rotating or sliding parts

1.2 Melting and Crystallization Behavior of Nylons

Crystallization in polymers involves two stages: nucleation and crystal growth. Nucleation may be homogeneous, occurring spontaneously within the melt, or heterogeneous, typically initiated at impurities or filler surfaces. In practice, heterogeneous nucleation dominates due to unavoidable impurities.

Crystallizability depends on molecular structure: polymers with simple, symmetric, flexible chains and small side groups tend to crystallize more easily.

In nylons, amide groups form strong hydrogen bonds (-NH⋯O=C-) that promote two-dimensional sheets, which then stack into three-dimensional crystalline structures. Differences in hydrogen bond arrangements and stacking yield various polymorphs.

Polyamides crystallize both during melt cooling and from the amorphous state. Imperfect crystals formed during initial cooling may undergo secondary crystallization. Upon reheating, these structures reorganize into more thermodynamically stable forms.

This study uses TGA (thermogravimetric analysis) and DSC (differential scanning calorimetry) to investigate the thermal stability and melting/crystallization behavior of two representative nylons: aliphatic PA11 and semi-aromatic PA6T.

2. Test

2.1 Instrumentation

Thermal properties were measured using the TGA-1000 thermogravimetric analyzer and DSC-600 differential scanning calorimeter, both developed by AMI. The DSC system was equipped with a mechanical refrigeration unit. (Figure 6)

Figure 6 (a) TGA-1000 Thermogravimetric Analyzer, (b) DSC-600 Differential Scanning Calorimeter

2.1.1 TGA Analysis

• Atmosphere: High-purity nitrogen (99.999%) at 50 mL/min
• Sample: ~15 mg in ceramic crucibles
• Program: Heated from 25°C to 1000°C at 10°C/min

2.1.2 DSC Analysis

• Atmosphere: High-purity nitrogen (99.999%) at 30 mL/min

PA11 Test Conditions:

• Sample: ~20 mg in sealed aluminum crucibles
• Temperature range: -90°C to 300°C at 20°C/min

PA6T Test Conditions:

• Sample: ~5 mg in sealed aluminum crucibles
• Two heating-cooling cycles: 50°C ↔ 350°C at 20°C/min

3. Results and Discussion

3.1 Thermal Stability Analysis

The TGA curves for PA11 and PA6T are shown in Figure 7.

Figure 7 (a) TGA Curve of PA11, (b) TGA Curve of PA6T

Both materials showed two-stage decomposition:

• Stage 1 (30–105°C):
  • Minor weight losses from moisture evaporation
  • PA11: 0.036%
  • PA6T: 0.415%
  • Consistent with low hygroscopicity of polyamides
• Stage 2:
  • Major decomposition due to random scission of C–C and C–N bonds
  • PA11: 99.364% weight loss
  • PA6T: 95.885% weight loss

Decomposition temperatures reflect material stability:

• PA11 (aliphatic): 293.7°C
• PA6T (semi-aromatic): 343.7°C
• Increased thermal resistance in PA6T is attributed to aromatic ring content and stronger hydrogen bonding.

3.2 DSC Analysis

PA11 DSC Curve – see Figure 8:

Figure 8 DSC Thermogram of PA11

• Glass transition onset: ~37°C
• Tg: 43.31°C
• Melting onset: 173°C
• Melting peak: 188.13°C
• Enthalpy of fusion (ΔHm): 159.55 J/g
• Thermal stability confirmed: Decomposition occurs well above melting

PA6T DSC Curve – see Figure 9:

Figure 9 DSC Thermogram of PA6T

• First heating shows dual melting peaks, indicating recrystallization.
• Second heating shows a single sharp peak at 304.6°C.
• ΔHm: 61.21 J/g
• Higher glass transition (89°C) and crystallization temperature (275.43°C) than PA11
• Superior thermal properties make PA6T ideal for high temperature environments

4. Conclusion

This study examined the thermal stability and melting/crystallization behavior of aliphatic PA11 and semi-aromatic PA6T using TGA and DSC.

Key findings include:

• Thermal decomposition:
  • PA11: 293.7°C
  • PA6T: 343.7°C
• Melting temperature:
  • PA11: 188.13°C
  • PA6T: 304.6°C

The aromatic structure in PA6T significantly improves thermal resistance and structural stability, making it well-suited for demanding engineering applications. These results highlight the critical role of molecular architecture in determining nylon performance across temperature-sensitive environments.

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Introduction

In thermogravimetric analysis (TGA), maintaining a truly inert environment is essential when studying materials prone to oxidation at elevated temperatures. While most commercial TGAs provide sufficient oxygen exclusion for polymer or hydrocarbon testing, more sensitive applications—such as metal oxidation or catalyst studies—require a higher level of oxygen control.

This application note demonstrates how simple, practical tests can verify purge gas effectiveness. It also highlights how AMI’s micro-furnace and dual-purge architecture achieve exceptional oxygen removal without relying on high flow rates or mass flow controllers (MFCs)—reducing both cost and system complexity.

How Much Oxygen Removal Is Enough?

The necessary level of oxygen exclusion depends on the sample. While trace O₂ is tolerable for routine polymer analysis, materials like finely divided metals or sensitive catalysts may oxidize even in low-oxygen environments. For these applications, it is essential that the TGA system:

• Rapidly displaces oxygen during purge
• Maintains a stable inert atmosphere throughout the experiment
• Prevents reintroduction of oxygen during sample loading or cooling

Micro-Furnace + Dual-Purge: A Smarter TGA Design

AMI TGA systems utilize a compact micro-furnace that reduces dead volume and shortens gas paths, paired with a dual-zone purge system:

• Sample zone purge: Directly surrounds the crucible to displace oxygen at the reaction site
• Balance zone purge: Isolates and protects the balance from reactive gases or vapor intrusion

This architecture ensures efficient oxygen exclusion without requiring high flow rates or expensive gas control hardware.

Experimental Validation: Carbon Black Oxidation Test

To validate purge effectiveness, carbon black was used as a sensitive test material:

• Method: A 10 mg sample was held isothermally at 700 °C under flowing inert gas
• Observation: Oxidation of carbon black causes mass loss; minimal loss indicates effective O₂ removal
• AMI Result: <1% mass loss over 30 minutes, confirming stable, oxygen-free conditions using only ~50 mL/min N₂

This test demonstrates the system's ability to maintain an inert environment under thermal stress.

Do You Really Need High Flow Rates or MFCs?

Many systems rely on purge rates of 300+ mL/min, controlled by MFCs, to sweep oxygen from the furnace. AMI’s results show that:

• High flow rates are unnecessary when furnace volume is minimized and purge paths are optimized
• Dual-zone purging is more effective than single-zone high-volume flushing
• Eliminating MFCs lowers cost and simplifies maintenance—without compromising oxygen exclusion

Conclusion

The AMI TGA-1000 proves that superior oxygen control can be achieved through smart system architecture rather than brute-force gas handling. With its micro-furnace and dual-purge design, it offers:

• Excellent purge performance
• Reliable data even for oxygen-sensitive materials
• Lower operational cost and complexity

For labs demanding precision and affordability, AMI provides a powerful and practical solution for high-quality thermal analysis.

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Introduction
Thermogravimetric analysis (TGA) is a powerful tool for studying crystalline hydrates. In addition to quantifying water of hydration, TGA provides detailed insight into dehydration kinetics and mechanisms. This application note explores the thermal behavior of a hemi-hydrate compound using both isothermal and scanning TGA experiments. The results highlight sequential dehydration behavior, model-based kinetic evaluation, and the role of diffusion-controlled mechanisms.

Experimental Overview
A crystalline organic hemi-hydrate was analyzed via isothermal TGA at multiple temperatures: 50°C, 55°C, 60°C, and 77°C. Each sample was held under constant temperature while weight loss was recorded over time. The total dehydration corresponds to the release of 0.5 mol of water per mole of compound, or approximately 2.7% of the sample’s initial mass.

Results and Observations

1. Sequential Dehydration Behavior

Across all isothermal conditions, water release occurred in distinct stages. At lower temperatures, the dehydration began abruptly, then slowed, accelerated again, and gradually tapered off as full dehydration approached. This behavior indicates a complex sequence of water loss rather than a single kinetic step.

2. Kinetic Modeling and Activation Energy

Weight loss data were processed to generate fractional decomposition profiles (α). Despite the sequential nature of the dehydration, a global linear regression approach was used to estimate apparent rate constants for each temperature. These values were then used in an Arrhenius plot to estimate the activation energy (Ea), yielding a value of approximately 29 kcal/mol.

Figure 1: Fractional weight loss profiles (α vs. time)

3. Diffusion-Controlled Mechanisms

To better understand the stepwise kinetics, a detailed kinetic model analysis was applied to the 55°C isotherm. Two common diffusion-controlled models were considered, as described in Byrn’s work on solid-state chemistry [1]:

• One-dimensional diffusion: α² ∝ kt
• Three-dimensional diffusion (Jander equation): 1 - (2/3)α - (1 - α)⁰·⁶⁶⁶ = kt

Figure 2: Comparison of model fits to experimental data at 55°C.

These observations suggest that water at the crystal surface escapes rapidly once liberated, while deeper hydration layers require diffusion through dehydrated material, a classic feature of diffusion-limited kinetics.

Conclusion
Thermogravimetric analysis offers more than just quantitative mass loss data. It provides real-time visibility into dehydration mechanisms and supports kinetic modeling. In this study:

• Sequential water loss was observed in a hemi-hydrate compound.
• Activation energy for overall dehydration was determined to be ~29 kcal/mol.
• A shift from one- to three-dimensional diffusion mechanisms was detected across time.

These findings demonstrate how TGA can be used not only to monitor weight loss, but to understand complex solid-state transformations relevant to pharmaceuticals, materials science, and process engineering.

AMI TGA systems provide the sensitivity, stability, and flexibility needed to conduct high-resolution kinetic studies without the complexity or cost of mass flow controllers. For more information, contact us at info@ami-instruments.com.

Reference
[1] Stephen R. Byrn, Solid State Chemistry of Drugs, Academic Press: New York, 1982.