DPL D-020 [Zoller Gnomix PVT]
Summary Description
The DatapointLabs internal DPL D-020 test standard is commonly referenced for PVT characterization measurements employing a Zoller Gnomix PVT apparatus to generate pressure-volume-temperature measurements using high-pressure dilatometry. PVT data are equation-of-state thermodynamic properties that describe the compressibility and volumetric expansion of a material. Dilatometry measures the change in volume of a specimen subjected to different temperatures and pressures.
Learn more about Pressure-Volume-Temperature (PVT) Testing, about Bulk/Volumetric Mechanical Testing, as well as about Mechanical Testing more generally.
Applications and Use Cases
PVT characterization data generated with the Zoller Gnomix PVT apparatus supports injection molding simulation, providing critical data for modeling shrinkage and warpage behavior. More generally, it supports constitutive model calibration for polymers, elastomers, and thermoplastics in CAE simulation. Additionally, it enables understanding of compressibility, bulk modulus and volumetric expansion over a material’s operational conditions as well as the understanding of a material’s equation-of-state.
Advantages of the Zoller Gnomix PVT Apparatus
The Zoller Gnomix PVT apparatus, based on the confining fluid method, offers several key advantages: Its measurements are highly accurate and repeatable, as the confining fluid method ensures uniform pressure across the sample as well as an absence of voids, bubbles or wall interaction effects. Its methodology is applicable across material phases, capturing both solid and melt phase behavior as well as accurately characterizing behavior under melting or solidification. Its characterization data is directly relevant to simulation inputs for FEA and CAE material models. Its thermal and pressure range support a wide operating envelope (20–400°C and 10–200 MPa), enabling the study of materials under realistic processing conditions.
Confining Fluid Technique Compared to Piston-Die Technique
The confining fluid technique is preferred over the piston-die (piston cylinder) technique for PVT measurements as it guarantees true hydrostatic pressure, avoids device-related friction and leakage, prevents sample wall-sticking and void formation, and yields accurate results for samples in both solid and melt phases throughout the entire measurement range, including melting and solidification phase transitions. The piston-die technique, by contrast, generates non-hydrostatic stress states through axial loading rather than true hydrostatic pressure, is fundamentally limited to liquids or polymer melts with very low shear moduli, and is vulnerable to device-related friction and leakage from piston seals as well as sample wall-sticking and void formation due to die wall interactions.
For further details see Paul Zoller, Youssef A. Fakhreddine, “Pressure-volume-temperature studies of semi-crystalline polymers”, Thermochimica Acta, 238 (1994), 397-415.
Additional Test Standards of Relevance
- No existing ASTM or ISO standards of relevance.
Complete Listing of DatapointLabs Tests Referencing DPL D-020
The entire list of tests in the DatapointLabs test catalog that reference internal DatapointLabs standard DPL D-020 are as follows:
| Test ID | Test Description |
|---|---|
| D-020 | PVT (Isothermal Heating) |
| D-021 | PVT (Isobaric) |
| D-022 | Volumetric Expansion Coefficient by PVT |
| M-014 | Bulk Modulus (Up To 8 Temperatures) |
Characterization Measurements and Relevant Tests
DatapointLabs offers a number of tests that address different properties covered under the DatapointLabs D-020 internal standard for the Zoller Gnomix PVT apparatus. These include the following characterization measurements [bracketed links refer to relevant tests in the DatapointLabs Test Catalog]:
PVT under Isothermal Conditions
PVT under Isobaric Conditions
Volumetric Expansion Coefficient by PVT
- Solid density [D-010]
- Specific volume vs. temperature [D-021]
- Coefficient of volumetric thermal expansion (CVTE) [D-022]
Bulk Modulus
Characterization Measurement Descriptions
Characterization measurements under DPL D-020 are as follows:
- Solid Density: Mass per unit volume of the solid material, measured as baseline density at ambient temperature and pressure.
- Specific Volume vs. Pressure: Inverse of density as a function of pressure.
- Specific Volume vs. Temperature: Inverse of density as a function of temperature, showing thermal expansion behavior.
- Coefficient of Volumetric Thermal Expansion (CVTE): Linear relationship between volume and temperature, in the both the solid and melt phases.
- Bulk Modulus vs. Temperature: Compressibility variation with temperature, measured as change in compressibility across up to 8 temperature levels.
Test Procedure
PVT testing examines the relationship between pressure, volume, and temperature to characterize material compressibility and thermal expansion. The test uses an indirect dilatometry method (confining fluid method), where the sample is sealed with mercury in a vacuum-filled cell. The linear displacement of a bellows spring, measured with an LVDT (Linear Variable Differential Transformer), enables the volume change.
PVT under Isothermal Conditions
A solid density measurement is first performed as a reference measurement for specific volume. A dried sample of approximately 1 gram is loaded into a sample cell and placed in the PVT apparatus. The machine is started at ambient temperature (30°C), and isothermal data acquisition begins. Readings of volume are taken by an LVDT for the specified temperature at pressures ranging from 10 MPa up to 200 MPa. The procedure is repeated for increasing temperatures, up to processing temperature. The procedure may also be performed for decreasing temperatures.
PVT under Isobaric Conditions
A solid density measurement is first performed as a reference measurement for specific volume. A dried sample of approximately 1 gram is loaded into a sample cell and placed in the PVT apparatus. The machine is brought to the processing temperature, and isobaric data acquisition begins during the cooling process. Readings of volume are taken by an LVDT for the specified pressure at temperatures ranging from the processing temperature to 50°C. Successive runs at up to 4 different pressures are performed. Isobaric runs can also be performed during heating.
Volumetric Expansion Coefficient by PVT
A solid density measurement is first performed as a reference measurement for specific volume. A dried sample of approximately 1 gram is loaded into a sample cell and placed in the PVT apparatus. The machine is started at ambient temperature (30°C), and isothermal data acquisition begins. Readings of volume are taken by an LVDT for the specified temperature at pressures ranging from 10 MPa up to 200 MPa. The procedure is repeated for increasing temperatures, up to processing temperature. The procedure may also be performed for decreasing temperatures. The slope of the specific volume vs. temperature at atmospheric pressure, corresponding to the coefficient of volumetric thermal expansion, is extracted from the volumetric measurements across the set of temperatures and pressures.
Bulk Modulus
A solid density measurement is first performed as a reference measurement for specific volume. A dried sample of approximately 1 gram is loaded into a sample cell and placed in the PVT apparatus. An isothermal heating scan is performed on the sample. Readings of volume change are recorded by an LVDT for during the pressure sweep for the temperatures selected. Volumetric stress strain curves are generated and used to calculate the bulk modulus of the material. Data may also be gathered while cooling the specimen.
Equipment Used
The Zoller Gnomix PVT apparatus is based on the confining fluid (indirect) dilatometry method. Its core principles of operation involve:
Sample Encapsulation
A small specimen (typically 1–2 grams) is sealed inside a rigid sample cell under vacuum. The cell is completely filled with the test material and a confining fluid (mercury) to ensure uniform pressure distribution even during phase changes like melting or solidifying.
Bellows-Displacement Mechanism
One end of the sample cell is sealed with a flexible metal bellows, which deflects as the internal volume changes due to pressure and temperature shifts. The deflection of the bellows is measured by a Linear Variable Differential Transformer (LVDT), a highly sensitive displacement sensor.
Pressure and Temperature Control
The sample cell is placed within a pressure vessel filled with silicone oil, which allows the application of hydrostatic pressures from 10 MPa to 200 MPa. The temperature is controlled via an electrically heated chamber, typically ranging from 20°C to over 400°C. The equipment allows for both constant-pressure (isobaric) and constant-temperature (isothermal) measurement protocols.
Volume Change Measurement
As temperature or pressure changes, the sample expands or contracts, causing the bellows to move. This movement is precisely recorded by the LVDT. Corrections are applied using a calibration curve obtained by measuring the bellows deflection when the cell is filled with confining fluid only (no sample), ensuring thermal expansion of the mercury does not affect the measurement.
Calculation of Specific Volume and Density
The volume change of the sample is determined from the bellows deflection, its known cross-sectional area, and the calibration data. Specific volume is computed directly, and density is calculated as the inverse of specific volume at each pressure-temperature point.
Sample Conditioning and Non-Ambient Testing
No relevant sample conditioning, apart from pre-test drying, if required (included as part of the test procedure). Similarly, no relevant non-ambient testing conditions, as the testing is inherently non-ambient.
Test Specimen Specification and Description
Specimen specifications under DPL D-020 are as follows:
- Solid test samples of suitable size and of any shape; recommended quantity is about 30g (1oz).
