1. Dilatometer Associate Professor Dr. Banjuraizah Johar School of Materials Engineering Universiti Malaysia Perlis

2. A dilatometer is a scientific instrument (high precision systems) designed to measure dimensional changes caused by a physical or chemical process due to thermal environment. The coefficient of thermal expansion is used: in linear thermal expansion in area thermal expansion in volumetric thermal expansion  Solids mostly expand in response to heating and contract on cooling. This response to temperature change is expressed as its coefficient of thermal expansion. What is Dilatometer?

3. When a body is heated, it is accepting and storing energy in its atoms in the form of kinetic energy. The increase in temperature causes an atom’s natural vibrations to grow stronger. This increase in vibration pushes against the inter-molecular forces, allowing the atoms or molecules to become farther apart and the body to grow larger. The amount by which a substance expands in reaction to a change in temperature is mathematically represented by a coefficient of thermal expansion. The higher a coefficient of thermal expansion a material has, the more it will expand in reaction to being heated

4. Purpose of dilatometer testing determination of thermal expansion coefficient (CTE): Linear / Volumetric thermal expansion coef Dilatometric softening point Annealing characteristic Sintering temperature and sintering steps (sintering mechanism) linear thermal expansion (ΔL) sinter-temperatures and sinter steps determination of glass transition (Tg) phase changes/ phase transformation at high temperature is accompanied by volume changes- So it can be a tools to determine the specific temperature at which phase transformation occurs optimization of burning processes volume changes Rate Controlled Sintering (RCS) decomposition density change

5. DIL 811 Vertical Dilatometer - Vertical pushrod dilatometer - Room Temperature to 2000°C - Vertical design for high temperatures - Ideal for shrinkage and softening

6. Horizontal Push Rod Dilatometer Instrument Optical Dilatometer

7.  A constant programmable force is applied to the sample throughout the experiment, ensuring that contact is maintained with the sample regardless of dimension change.  The contact force can also be applied in a dynamic fashion, permitting the determination of viscoelastic properties. Measuring Principle

8. Principles of measurements

9. Instruments consisting of a specimen holder and a probe that transmits changes in length to a transducer that translates movements of the probe into an electrical signal. The apparatus also consists of a furnace for uniform heating, a temperature-sensing element, calipers, and a means of recording results

11. Measuring systems are available in several materials including fused silica, Al 2 O 3, sapphire, graphite and tungsten. The measuring systems are also available in various forms, bend bearings and gripping devices. Absolute accuracy is ensured and verified with the use of certified reference materials for the calibration of the equipment.

12. Measurement system Sample tube Bearings Pushrod

13. TEMPERATURETYPE HEATING ELEMENT ATMOSPHERE TEMPERATURE SENSOR -180 – 500°CL75/264Thermo coax inert, oxid., red., vac. Type K -180 – 700°CL75/264/700Thermo coax inert, oxid., red., vac. Type K -180 up to 1000L75/264/1000Thermo coax inert, oxid., red., vac. Type K RT – 1000°CL75/220Kanthalinert, oxid., red., vac. Type K RT – 1400°CL75/230Kanthalinert, oxid., red., vac. Type S RT – 1600°CL75/240SiCinert, oxid., red., vac. Type S RT – 1650°CL75/240 PTPlatinuminert, oxid., red., vac. Type S RT – 2000°CL75/260GraphiteN2/Vac.Type C and/or pyrometer RT – 2800°CL75/280GraphiteN2/Vac.Pyromete

15. Coefficient of Thermal Expansion Another common application of a dilatometer is the measurement of thermal expansion. The CTE is also closely related to crystal structure, grain size and bond strength. Materials with a less dense, open structure, a small grain size and high bond strength have the lower CTE. The thermal expansion of materials arises due to the anharmonicity in inter-atomic interactions.

16. 16 Thermal Expansion Materials change size when temperature is changed linear coefficient of thermal expansion (1/K or 1/°C) T initial T final initial final T final > T initial

17. Conversions of Units

18. Explanation on cte results Thermal expansion in material is directly related to strength of the forces between the molecules or atoms. Material with stronger forces for instant harder materials will have lower thermal expansion. Diamond is a very hard material due to its strong covalent bonding and has much lower CTE than softer material such as steel.

19. 19 Atomic Perspective: Thermal Expansion Asymmetric curve: -- increase temperature, -- increase in interatomic separation -- thermal expansion Symmetric curve: -- increase temperature, -- no increase in interatomic separation -- no thermal expansion

20. If the thermal expansion is not linear over all the temperature ranges, a different CTE value shall be applied for that particular temperature at which a material is used. Materials that have high CTE exhibit poor thermal shock resistance, i.e. rapid cooling or heating would result in temperature gradient that cause cracks. Most materials exhibit anisotropic behavior, for instant CTE is different along the three axes of the unit cell. This could also lead to microcracks. For engineering purposes, low CTE are desirable.

22. The thermal expansivity is defined as: and is an important engineering parameter.

23. Types There are a number of dilatometer types: - Capacitance dilatometers - Connecting rod (push rod) dilatometer - High Resolution - Laser Dilatometer - Optical dilatometer

24. Capacitance dilatometers -possess a parallel plate capacitor with a one stationary plate, and one moveable plate. When the sample length changes, it moves the moveable plate, which changes the gap between the plates. -The capacitance is inversely proportional to the gap. Changes in length of 10 picometres can be detected.

25. Connecting rod (push rod) dilatometer The sample which can be examined is in the furnace. A connecting rod transfers the thermal expansion to a strain gauge, which measures the shift. Matched low-expansion materials and differential constructions can be used to minimize the influence of connecting rod expansion.

26. High Resolution - Laser Dilatometer Highest resolution and absolute accuracy is possible with a Michelson Interferometer type Laser Dilatometer. Resolution goes up to picnometres. On top the principle of interference measurement give the possibility for much higher accuracy's and it is an absolute measurement technique with no need of calibration.

27. Optical dilatometer is an instrument that measures dimension variations of a specimen heated at temperatures that generally range from 25 to 1400 °C. The optical dilatometer allows the monitoring of materials’ expansions and contractions by using a non-contact method: optical group connected to a digital camera captures the images of the expanding/contracting specimen as function of the temperature with a resolution of about ±70 micrometre per pixel.

28. As the system allows to heat up the material and measures its longitudinal/vertical movements without any contact between instrument and specimen, it is possible to analyze the most ductile materials, such as the polymers, as well as the most fragile, such as the incoherent ceramic powders for sintering process.

29. Result Analysis - Dilatometer Examples

30. A unique glass composition based on GeO 2, MoO 3 and V 2 O 5 (GMV) was designed to act as a sintering aid to enhance the densification and to adjust the dielectric constant of TiO 2. The effect of GMV glass concentration on the densification behaviour and dielectrics properties of TiO 2 was investigated by dilatometer, X-ray diffractometer, scanning electron microscopy and transmission electron microscopy. Microstructure and properties evaluation of TiO 2 ceramics with multi-oxides glass additions Ceramics International Volume 40, Issue 2, March 2014, Pages 3731–3736 Boen Houng, Shih-Jeh Jimmy Wu, Sue Han Lu, Wei Chueh Chien Abstract

31. Fig. 1: The shrinkage behaviour of the TiO 2 with and without GMV glass additives as a function of firing temperature. The shrinkage behaviour of TiO 2 containing various concentrations of GMV glass as sintering aid was examined by dilatometer as shown in Fig. 1. As quantity of glass additives increased shrinkage curves were shifted towards much lower temperatures than the typical sintering temperature of pure TiO 2.

32. The shrinkage of pure TiO 2 appears to occur slowly at approximately 1200 °C. Nevertheless, TiO 2 ceramics with 1 and 5 wt % glass additives showed the apparent shrinkage above 900 °C. As the amount of glass additives increased greater than 10 wt %, TiO 2 exhibited a large shrinkage of approximately 12 % at 900 °C. The results suggest that GMV glass is an effective sintering aid for TiO 2.

33. Thermochimica Acta Volume 359, Issue 1, August 2000, Pages 77–85 Measurement of thermal expansion coefficient of LaCrO 3 Hideko Hayashi,, Mieko Watanabe, Hideaki Inaba Thermal expansion coefficients of LaCrO 3 and Al 2 O 3 were measured using a push-rod type dilatometer in the temperature range from 100 to 873 K. The thermal expansion coefficient of Al 2 O 3 in the temperature range from 100 to 873 K generally agreed with the literature value. Anomalies in the thermal expansion coefficient were observed clearly at 283 and 528.5 K in LaCrO 3. The first anomaly is a volume expansion due to the transition from an anti- ferromagnetic to a paramagnetic state, the second one is a volume shrinkage due to the transition from an orthorhombic to a rhombohedral structure. Abstract

34. Thermal expansion coefficient of LaCrO 3 Fig. 3 shows the thermal expansion of LaCrO 3 at the heating rate of 5 K min −1. An obvious anomaly of the thermal expansion is observed around 530 K and a slight change in the thermal expansion curve is seen around 300 K in Fig. 3. The slight change in the thermal expansion curve around 300 K is probably due to the magnetic transition from an anti-ferromagnetic to a paramagnetic state. The anomaly around 530 K is due to the structural transition from an orthorhombic to a rhombohedral phase as reported to be from 513 to 554 K by thermal expansion measurement. Fig. 3: Thermal expansion of LaCrO 3 at a heating rate of 5 K min −1

35. Journal of the European Ceramic Society Volume 30, Issue 6, April 2010, Pages 1277–1286 A consecutive decomposition–sintering dilatometer method to study the effect of limestone impurities on lime microstructure and its water reactivity D.T. Beruto, R. Botter, R. Cabella, A. Lagazzo In this paper we develop a consecutive decomposition–sintering dilatometer method (CDSD) to study the effect of limestone impurities on lime microstructure features that are formed during the limestone decomposition. Abstract

36. Fig. 4: Comparison of thermogravimetric (a) and dilatometric traces (b) of two identical samples of limestone β obtained from TG and dilatometer analysis carried-out under the same conditions. λ

37. In the region α, which starts when the TG curve shows that the decomposition reaction is beginning, a number of complex thermal steps occur. λ As can be noted the dilatometric trace can be divided into three different regions. In the region λ, where the TG curves do not give weight variation, the sample length increases due to the limestone thermal expansion.

38. The limestone decomposes, the CO 2 diffuses through the formed CaO grains promoting their sintering, the limestone impurities can interact with both the CaCO 3 and CaO or with only one of the solid phases. The actual sample length in this region will be a balance between different contributions. Thermal dilatation (expansion) of CaCO 3 and CaO will tend to increase the sample length, while the reduction in the molar volume due to the limestone–lime reaction and the sintering of the oxide formed will decrease it. Fig. 4 shows that at a certain degree in the advancement of the decomposition reaction, the reduction in length prevails.

39. Exercise 1. What is dilatometer ? 2. Propose THREE (3) applications of dilatometer. 3. Suggest FOUR (4) different types of dilatometer.

40. The alumina addition effects on the sintering behaviors of CaO–MgO– Al 2 O 3 –SiO 2 glass (CMAS) and CaO–MgO–Al 2 O 3 –SiO 2 –ZrO 2 (CMASZ) were investigated using dilatometer. 4. Discuss the shrinkage behaviours of the (a) CMAS and (b) CMASZ glasses added with different amounts of alumina based on Fig. 3(a) and 3(b).

41. The Effect of LBS and LaB on the sintering behavior of Ba-Zn-Ti system was studied using dilatometry test and below plot were obtained. Discuss the shrinkage behavior

42. Case study 1 The initial shrinkage temperature of Ba-Zn-Ti dramatically decreased when LBS was added. LBS and LaB accelerate the sintering process. The liquid phase from LBS and LaB leads to liquid phase sintering mechanism. The liquidus phase promotes the arrangement of particles at the early stage of sintering and speeds up mass transportation in the middle of the sintering process. As the liquid penetrates between the grains, it fills the pores and draws the grains together by capillary attraction

43. If the shrinkage (dL/L 0 ) of the samples was measured against the temperature, and the temperature taken at 3%, 6%, 9%, 12% shrinkage for each run at heating rate k. Then, for each given value of dL/L 0, ln k was plotted against the inverse of temperature in Kelvin, 1/T. The Ea can be calculated using the follow Arrhenius expression

44. Case study 2 Determine the Glass Transition Temperature and Softening Point in glass