Thermogravimetric Analyzer TGA - QualiTGA-1000C

Thermogravimetric Measurement Theory & Balance Mechanics

Thermogravimetric Analysis on the QualiTGA-1000C functions by tracking sample mass fluctuations in real time while applying programmed thermal energy from room temperature up to 1000 °C inside a sealed heating body. As thermal energy breaks molecular bonds, extracts absorbed moisture, or pyrolyzes polymer backbones, the specimen vents volatile gases:

Δm (%) = [ ( m(t) − m₀ ) / m₀ ] × 100

Where m₀ represents starting sample weight prior to initiating the thermal run, and m(t) represents the instantaneous weight reading captured at any temperature coordinate.

+-------------------------------------------------------------------------+
|             Fixed-Position Sealed Furnace Body (1000W)                  |
|                                                                         |
|      +-----------------------------------------------------------+      |
|      |   Alumina Ceramic or Platinum Crucible (10mm x 6mm)       |      |
|      +-----------------------------------------------------------+      |
|                                    |                                    |
|              Detachable & Replaceable Sample Support Rod                |
|                                    |                                    |
+------------------------------------|------------------------------------+
                                     | (Core Sensor Stem)
+------------------------------------|------------------------------------+
|              Electromagnetic Force Balance Assembly                     |
|       (Standard 0.01mg to 2g | Optional 1ug/0.1ug & 10g/50g)            |
+-------------------------------------------------------------------------+
                                     |
     [ Liquid-Chilled Thermal Jacket & Gigabit Ethernet Interface ]

The Electromagnetic Balance Principle

Instead of relying on mechanical springs that suffer from thermal hysteresis, the QualiTGA-1000C uses an electromagnetic null-point compensation balance. A continuous optical sensor tracks the balance beam's horizontal position; any mass loss causes beam displacement, which the control board counteracts by adjusting electromagnetic coil current. 

This current change correlates linearly with sample mass loss down to a standard 0.01 mg (10 μg) resolution across a 0.01 mg to 2 g capacity (with optional ultra-trace 1 μg or 0.1 μg sensor setups, and expanded 10 g or 50 g macro options).

Thermal Regulation and Boundary Isolation

The system avoids motorized elevator lifts by utilizing a stationary, fixed furnace structure (eliminating mechanical gear wear and balance alignment shifts). A liquid-cooled water jacket surrounds the heating zone, isolating the weighing cell from thermal drift and maintaining closed-loop PID temperature stability within ±0.1 °C with a 0.01 °C display resolution.

Thermogram (TG) and First-Derivative (DTG) Method Calculations

The QualiTGA-1000C generates two primary analytical profiles: the primary TG Curve (mass loss percentage versus temperature/time) and the DTG Curve (dw/dT), which computes the mathematical first derivative to separate overlapping thermal degradation steps into distinct peaks.

  Mass (%)                                                  dwt/dT (Rate of Mass Loss)
  100% |-----------..                                            |
       |             \                                           |
       |              \  <- (T_onset: Extrapolated Onset)        |
       |               \                                         |    Maximum Loss Rate (T_max)
       |                \            TG Curve                    |             /\
       |                 \                                       |            /  \  DTG Curve
       |      T_50% ->    \                                      |           /    \
       |                   \                                     |          /      \
       |                    ..---------..                        |_________/        \_______
    0% +----------------------------------\----------------------+-------------------------->
       Start Temp                          T_offset                                   Furnace Temp

• Extrapolated Onset Temperature (T_onset): The intersection point where the initial flat baseline meets the tangent line drawn through the inflection point of steepest mass decline.
• Peak Decomposition Rate (T_max): The precise point where mass loss speed reaches its local maximum (d²w/dT² = 0), identifying specific polymer component transitions.
• Midpoint Decomposition Point (T_50%): The temperature mark where exactly half of the degradable organic fraction has evolved as vapor.
• Extrapolated Offset Temperature (T_offset): The thermal point where mass loss ceases and the trace stabilizes back into a horizontal plateau.
• Residual Non-Combustible Mass: The leftover weight percentage corresponding to inorganic fillers, fiberglass reinforcement, or mineral ash.

Standard Operating Methods & Gas-Switching Protocols

1. Dynamic Heating Method

The furnace applies a linear thermal ramp from room temperature up to a programmed target using user-defined speeds between 0.1 and 80 °C/min (with controlled cooling at 0.1 to 30 °C/min above 100 °C). This dynamic approach maps broad decomposition profiles and thermal stability limits.

2. Isothermal Dwell Method

The furnace brings the sample to a set temperature and holds it for a programmed incubation period between 0 and 300 minutes. This method measures long-term thermal endurance, volatile organic compound (VOC) outgassing rates, and steady-state moisture desorption behavior.

3. Stepwise Compositional Method (Automated N₂ / O₂ Switching)

The QualiTGA-1000C utilizes integrated dual-channel gas controllers to switch gas feeds automatically during a single test run without manual intervention:

1. Moisture & Solvent Removal (100–150 °C in N₂): Bakes off free surface moisture, plasticizer fractions, and light solvents.
2. Polymer Pyrolytic Cracking (150–600 °C in N₂): Thermally breaks the organic polymer chains into volatile hydrocarbon fragments under an inert blanket.
3. Oxidative Carbon Burn-off (600–900 °C, Automated Switch to O₂): Combusts carbon black, graphite, and pyrolytic carbon into CO₂.
4. Ash / Filler Plateau (900–1000 °C in O₂): Measures non-combustible inorganic fillers (calcium carbonate, silica, titanium dioxide, glass fiber).

Thermal Decomposition Kinetics & Mathematical Modeling

The QualiTGA-1000C data acquisition system records thermal decomposition rates to compute material lifetimes and reaction mechanisms via the fundamental rate equation:

dα / dt = k(T) · f(α) = A exp( −E_a / RT ) f(α)

Where α = (m₀ − m_t) / (m₀ − m_∞) is the fractional extent of conversion (0 ≤ α ≤ 1), k(T) is the temperature-dependent rate constant from the Arrhenius equation, A is the pre-exponential frequency factor (s⁻¹), E_a is the activation energy barrier (kJ/mol), R is the universal gas constant (8.314 J/(mol·K)), and f(α) is the reaction model function representing the physical decomposition mechanism. Solving for [E_a, A, f(α)] determines the complete Kinetic Triplet.

• Model-Free Isoconversional Methods: Calculates activation energy (E_a) at fixed conversion values (α) across multiple heating ramps (β = 2, 5, 10, 20 °C/min) without requiring an assumed reaction model:
  • Friedman Method: ln[ β (dα/dT) ] = ln[ A_α f(α) ] − ( E_a / R T_α )
  • Flynn–Wall–Ozawa (FWO): log β = log[ ( A_α E_a ) / ( R g(α) ) ] − 2.315 − 0.4567 ( E_a / R T_α )
  • Kissinger–Akahira–Sunose (KAS): ln( β / T_α² ) = ln[ ( A_α R ) / ( E_a g(α) ) ] − ( E_a / R T_α )
• Model-Fitting Routines: Applies reaction functions (such as nth-order decay or 3D Jander diffusion) via the instrument's programmable software to isolate individual reaction kinetics in blended polymers.

Experimental Control, Drift Mitigation, and Compliance Standards

• Buoyancy & Aerodynamic Blank Correction: As furnace gas heats up, its density decreases, reducing buoyant force and registering an artificial weight gain on microgram balances. Running an empty 10 mm × 6 mm crucible under matching ramp and flow conditions generates a blank baseline that the software subtracts from raw data to ensure zero baseline drift.
• Thermal Lag Minimization: Operating at moderate heating rates (5 to 10 °C/min) prevents the specimen's core temperature from lagging behind the control thermocouple, avoiding artificial upward shifts in T_onset and maintaining crisp DTG peak separation.
• Sample Mass & Crucible Selection: Standard sample loads between 5 and 20 mg spread across non-reactive alumina or platinum crucibles prevent heat-transfer gradients and allow volatile gases to vent freely. For non-uniform or composite materials, optional 10 g or 50 g macro setups eliminate the need for micro-sampling subdivision.

Supported Standard Testing Methodologies

The QualiTGA-1000C executes standard test procedures in direct alignment with international thermal testing specifications:

• ASTM E1131: Standard Test Method for Compositional Analysis by Thermogravimetry.
• ISO 11358 (Parts 1–3): Plastics — Thermogravimetry (TGA) of Polymers (General Principles, Activation Energy, and Lifetime Determination).
• ASTM D3850: Rapid Thermal Degradation of Solid Electrical Insulating Materials by TGA.
• ASTM D6370: Standard Test Method for Rubber — Compositional Analysis by Thermogravimetry.
• ASTM E1641 & ASTM E1868: Thermal Decomposition Kinetics and Loss-on-Drying Volatile Fraction Assessment.