Since the acquisitions of Baehr and Expert System Solutions, two manufacturers of dilatometry equipment, TA Instruments has continued to invest in dilatometry. Most recently, the company introduced three new lines of mechanical and optical dilatometers well-suited for the ceramic industry: DIL 830, ODP 860 and DIL 820.

All three new dilatometer lines include TA’s True Differential™ technology, which yields a 10x improvement in measurement accuracies, as well as patented optical sensors that can analyze samples with a resolution of up to 1 nm. In addition, new high-speed, no temperature-gradient furnaces provide optimum temperature control and reduce downtime between tests up to 15 times.

DIL 830 Series

The DIL 830 series is a high-resolution platform for horizontal dilatometry offering high accuracy in the measurement of dimensional changes, with a 1-nm resolution optical encoder, a selection of dynamic furnaces, and a linear sample load motor. The combination of these technologies results in a horizontal push rod dilatometer for ceramic industry laboratories to measure linear thermal expansion and to calculate the coefficient of thermal expansion (CTE).

In push rod dilatometry, as the temperature rises above the glass transition temperature (Tg) and approaches the softening temperature (Ts), reliable load force control is key to testing samples without introducing errors caused by the probe penetrating softening materials or losing contact with fast-shrinking samples. The DIL 830 series linear motor sample load range of 0.01 N to 1.00 N, with a force resolution and linearity better than 0.01 N across the total measuring range of 5,000 µm, provides the ideal balance between force and control precision to produce correct values for the most challenging materials.

The heart of the measuring train is the optical encoder with a linear resolution of 1 nm over the entire measuring range, providing sensitivity to allow reducing the sample size to 2.5 mm. A smaller sample size brings lower thermal inertia, hence thermal events and transitions occur over a narrower temperature range. As a result, signal and precision of the temperature readings improve, while the instrument still delivers a ∆L resolution of up to 0.0004%.

Two dilatometer models and a selection of high-performance and fast-cooling furnaces are available: DIL 831, single sample; and DIL 832, featuring True Differential technology. The True Differential design directly compensates for the expansion of the sample holder and sample measuring system during the test, so that the transducer measures only the sample’s dimensional variations. Compared to standard “quasi-differential” designs in which a second sample position is used for a reference standard and dimensional variations are measured by a second transducer, True Differential yields a CTE measured accuracy of 0.01 x 10-6 K-1.

CTE accuracy also depends on the thermal stability of each component in the system. The enhanced design of the measuring head housing includes an active electric thermal stabilization and, most importantly, built-in fluid circulation to cut off the thermal bridge between the contact of the furnace and the measuring head housing. During a test from room temperature up to the maximum temperature, the temperature change inside the housing is less than 1°C.

The proprietary design of the furnace guarantees a 0 temperature gradient along the specimen length, which also helps to increase the precise determination of the temperature at which events take place. DIL 830 series furnaces currently cover the three most popular temperature ranges in the ceramic industry: room temperature up to 1,000°C, 1,500°C, and 1,700°C.

One of the most important issues the new system addresses is the temperature gradient across the sample and the idle time between consecutive tests. While traditional furnaces have no temperature gradient along the specimen, different analytical models may require different times to cool from the maximum temperature down to room temperature. TA furnace options offer a decrease in downtime ranging from five to 15 times faster. An example is demonstrated with the cooling-assisted furnace that allows cooldown in 13 min from 1,000°C to room temperature. Additional features of the series include automatic initial sample length, built-in color touchscreen, motorized furnace, and integrated and compact footprint.

ODP 860 Series

The new ODP 860 series optical dilatometer enables process engineers to optimize the thermal cycles of industrial processes by analyzing samples beyond the limits of classical dilatometry techniques. This includes heating microscopy, dilatometry and bending analysis. The ODP 860 series comprises two models: HM 867, a heating microscope; and ODP 868, a complete, flexible and scalable optical dilatometry platform able to perform all optical dilatometry techniques.

The new large and responsive furnace, motorized and PC controlled, provides ease of operation and the option to test specimens in both horizontal and vertical dilatometry mode. This makes it possible to use both the most suitable dilatometry techniques to measure dimensional changes and the ability to study sintering processes. In addition, heating and cooling temperature rates (100°C/min in controlled scan, 200°C/sec in Flash Mode) enable the DIL 860 series to reproduce industrial manufacturing process conditions and optimize body composition and body-glaze coupling in the laboratory, replacing the expensive and time-consuming tests currently done in industrial kilns. The built-in purge gas system enables the user to control the tests environment and analyze specimens in air, oxidative, and protective atmospheres.

Widely used in the ceramic industry to observe and record the behavior of green bodies, glazes, glasses and frits during firing, heating microscopy (HM) plays a key role in process optimization and becomes a fundamental tool when the characterization of a material has to extend up to its melting behavior. HM 867 and ODP 868’s HM mode use an HD camera to frame the entire specimen and to study its behavior under precisely reproduced industrial firing conditions. Capable of analyzing samples in a wide range of shapes and sizes, the ODP 868 can simultaneously test up to eight samples. The recognition of shapes and the related temperatures can be done according to international standard methods or by user-defined parameters and concepts.

The patented True Differential dual-beam design, with two HD cameras that frame both ends of the specimen, enables the two dilatometry modes in which the absolute measurement of the dimensional changes is done without any mechanical contact with the specimen. This eliminates the need for calibration and correction curves. In addition, the optics are fully motorized and PC controlled; by simply clicking on the corresponding icon, the user can switch between the two optical dilatometry modes.

The horizontal mode is ideal for determining parameters such as linear thermal expansion, CTE, Tg and dilatometric softening, where contact-less measurement is crucial for accurate and reproducible values. In the vertical mode, the specimen is free to shrink/expand along its length, making it suitable for studying sintering processes. The ODP 868 can be used to investigate dimensional changes of incoherent materials (e.g., granular frits applied on raw tiles), softening materials (e.g., glasses above the Tg), sintering kinetics governing the relationship between time and temperature during a sintering process, or extremely thin samples like a single glaze layer of a ceramic tile.

The ODP 868 can also perform bending analysis in the traditional standard fleximeter (FLEX) mode and the True Differential absolute fleximeter (ABS FLEX). Both enable non-contact bending measurements, reproducing in the laboratory industrial thermal cycles that lead to a better understanding of the materials and prevent costly problems such as crazing, chipping, cracking, and planarity defects.

The DIL 860 series also includes a Flash mode. Once the temperature reaches a preset value, the kiln automatically moves toward the sample while the material is heated/cooled at a rate up to 200°C/sec. To guarantee maximum performance and stability throughout the temperature range, the optical bench is equipped with four HD CMOS-based video cameras, as well as a dynamic temperature thermostat control system and a base machined in a thermally ultra-stable material.

The DIL 860 series is completed by Misura™ 4 software, a client/server architecture software suite structured in “Apps” that comprises all instrument control functionalities, a method-editor tool, the shape analysis engine MorphometriX™ and Graphics (a data presentation tool). This image analysis engine translates the intuitive concept of shape into rigorous mathematical parameters with consistent physical foundations. Taking advantage of an acquisition rate of up to 14 fps, its pattern-matching algorithms can recognize materials transformations with a precision superseding the eye of the human operator. In real time, MorphometriX precisely identifies and automatically visualizes a specimen’s characteristic shapes and temperatures, accurately measures its dimensional changes, and records the bending attitude. To ease the sample preparation process and minimize its impact on results reproducibility, MorphometriX algorithms digitally correct for possible asymmetries in sample geometry and enable the user to choose the sample’s area to be analyzed.

DIL 820 Series

The DIL 820 series is designed to operate in a vertical configuration for the analysis of sintering, studies in Rate Controlled Sintering (RCS) mode, and the determination of dilatometry parameters of powder or samples that during a test develop a vitreous glassy phase. The DIL 820 is optimized for samples otherwise difficult to analyze with classic horizontal dilatometers, including samples that if tested in horizontal mode would yield incorrect results.

In the vertical push rod design, the specimen stands upright, with its lower tip resting on the bottom plate and the push rod applying a user-selectable load on its upper tip, leaving the sample free to move frictionless along the direction it expands/shrinks. Placing a specimen vertically prevents the liquid phases (formed during sintering) from interacting with the sample holder. This is a factor known to be a major source of errors in the measurement of dilatometry parameters with horizontal design-based instruments. The vertical orientation prevents the measuring systems and furnace tubes from sagging when used over long test periods at high temperatures, resulting in extended operational life.

The DIL 820 series avoids the “chimney effect” by eliminating the thermal bridge caused by the coupling between furnace and measuring system housing. Additionally, an electric active thermostat control system is located in the housing itself.

Available in four different models, the product family comprises two single-mode systems (DIL 821 and DIL821HT), and two equipped with True Differential technology (DIL 822 and DIL 822HT). All four units feature the 1-nm resolution linear optical encoder. The DIL 822 series, equipped with the True Differential transducer, delivers a CTE accuracy of 0.01 10-6 K-1. In addition, the actuator produces a precise and linear sample load ranging from 0.01-1 N across the operating range of 5,000 µm.

The DIL 830 series offers new furnaces designs with no temperature gradient across the specimen and fast cooling for little downtime between consecutive tests. With the DIL 820HT series, the temperature range is extended up to 2,300°C. In addition, the DIL 830 product family can operate under inert gas, vacuum and air.

For additional information, contact the author at pscotto@tainstruments.com or visit www.tainstruments.com.