MSE 06 Transparent Ceramics Experiment

This experiment uses cornstarch or gelatin with binders to create translucent samples that model transparent ceramics, demonstrating how composition and microstructure influence light transmission, strength, and optical clarity compared to advanced materials like ALON or spinel.

Transparent ceramics - Alchetron, The Free Social Encyclopedia (Alchetron)

Introduction

Transparent ceramics are a fascinating topic that combines materials science and engineering. They are crystalline ceramic materials that have been processed in such a way that they transmit light with minimal scattering, which allows them to appear transparent or translucent while retaining the mechanical strength and chemical resistance of other traditional ceramics. They combine the best features of glass and polycrystalline ceramics. While true transparent ceramics require advanced processing techniques – such as precise control of grain boundaries, elimination of porosity, and the use of high-purity raw materials – this experiment offers a simplified model. It uses everyday, safe-to-handle materials such as cornstarch or gelatin, combined with binders and optional additives, to simulate the appearance and some optical qualities of these advanced materials.

Features of transparent ceramics (Konoshima)

Aim

The primary aim of this experiment is to create a translucent or semi-transparent sample that is similar in appearance and certain properties to advanced transparent ceramics, exhibiting the same behavior. Through this experiment, we can demonstrate how the choice of base material can influence the translucency and mechanical strength of the final product. We can also investigate the impact of binders, such as PVA glue, on the structural integrity and clarity of the finished sample. By comparing the resulting sample with commercial transparent materials like glass or acrylic sheets, this experiment aims to highlight the unique balance of properties found in transparent ceramics, while reinforcing fundamental principles in materials science.

Context

Transparent ceramics have found increasing use in applications ranging from military armor and aerospace windows to medical imaging equipment and high-power lasers. Materials such as aluminum oxynitride (ALON), magnesium aluminate spinel, and yttria-stabilised zirconia (YSZ) offer a combination of hardness, thermal stability, and optical clarity that far exceeds glass or plastics. Their origins can be traced back to mid-20th-century research into infrared windows for missile guidance systems. In recent decades, manufacturing advancements – including hot isostatic pressing (HIP), spark plasma sintering (SPS), and advanced sintering aids – have enabled the production of transparent ceramics. Unlike glass, which is amorphous, transparent ceramics have a crystalline structure, giving them higher fracture toughness and thermal resistance. This makes them suitable for environments where glass would not be suitable due to large changes in temperature or mechanical stress.

However, the manufacturing process is costly, energy-intensive, and requires high levels of quality control to avoid scattering sites such as pores or grain boundaries. By contrast, this experiment uses a simplified methodology that trades performance for accessibility.

Theory

The transparency of a material is determined by its ability to transmit light without significant scattering or absorption. In crystalline materials, light scattering primarily occurs at grain boundaries, pores, and inclusions. When these features are smaller than the wavelength of visible light (~400–700 nm), scattering is minimized, and the material can appear transparent. Refractive index plays a key role in light transmission. A difference between the refractive indices of the grains and the surrounding medium can lead to scattering. In transparent ceramics, this mismatch is minimized by removing pores or filling them with materials of similar refractive index. For example, ALON has a refractive index of approximately 1.79, which, when combined with its uniform microstructure, gives it both high transparency and high mechanical strength. In our model system using cornstarch or gelatin, the same effects apply on a much larger scale. The base material and binder form a continuous matrix, whilst additives and air bubbles act to scatter light.  The clarity of the final product depends on how well light is scattered.

Materials

Materials Needed

1. Cornstarch or gelatin (acts as the base material to mimic ceramic translucency).

2. Water (to create the mixture).

3. White glue or polyvinyl alcohol (PVA) (for binding).

4. Plastic mold or flat tray (for shaping the material).

5. Mixing tools:

   • A small bowl and spoon or spatula.

6. Heat source:

   • Microwave, stove, or hot water bath.

7. Optional additives:

   • Food coloring or small particles for experimenting with light scattering.

8. Sandpaper (for smoothing edges after the material dries).

Experimental approach:

The experimental procedure is split into four main steps

Step 1 – Preparing the MixtureOne tablespoon of the chosen base material (cornstarch or gelatin) is mixed with two tablespoons of water in a small bowl until all lumps are dispersed. A tablespoon of PVA glue is then added, and the mixture stirred until uniform. If you want, you can add a drop of food colouring or a small quantity of fine particulate additive at this stage to observe its effect on light transmission.

Step 2 – Heating the MixtureThe mixture is gently heated, either on a stovetop or in a microwave, until it thickens into a gel. Continuous stirring ensures even heat distribution and prevents clumping. Heating promotes partial gelatinisation (in cornstarch) or dissolution (in gelatin), improving the uniformity of the final product.

Step 3 – MoldingThe warm mixture is poured into a plastic mold lined with baking paper. A spatula can be used to spread the mixture evenly to a uniform thickness, as variations in thickness strongly affect translucency.

Step 4 – DryingThe molded sample is allowed to air dry for 24–48 hours. For accelerated drying, a low-temperature oven or warm, ventilated environment may be used. Care is taken to avoid rapid drying, which can cause warping or cracking.

Observations:

After the mixture had thoroughly dried out, the prepared samples exhibited notable differences in visual and mechanical properties depending on the choice of base material and binder. Cornstarch-based samples were generally more opaque, with a soft white appearance mimicking a milky color that allowed diffuse transmission of light but little clarity. When held up to a bright light source, they demonstrated strong scattering, giving the illuminated areas a halo-like glow. Gelatin-based samples, in contrast, tended to be more translucent and were a lot clearer than their cornstarch counterparts. Samples containing particulate additives such as silica powder displayed visibly increased scattering, reducing clarity whilst enhancing the evenness of light distribution across the sample. Their mechanical characteristic showed that all samples were more flexible in thin sections and brittle in thicker ones. Gelatin-based samples demonstrated superior flexibility and toughness compared to the stiffer, more friable cornstarch-based variants.

Qualities of transparent ceramics:

The simulated transparent ceramic materials created in this experiment exhibited a range of qualities relevant and similar to the behavior of their real-world counterparts:- Translucency: Achieved to varying degrees, depending on material choice, processing, and mixture quality.- Light scattering: Dependent on the type of substance used in the mixture, whether that be cornstarch or gelatin.- Surface finish: Smoothness improved aesthetics but did not significantly alter transparency.- Mechanical strength: Dependent on binder type, thickness, and curing method, but overall pretty strong and resistant to bending.- Process simplicity: All steps were achievable with common household tools, making this a highly accessible educational activity. These qualities show the trade-offs found in material design, where optical performance, mechanical strength, and manufacturing complexity must be weighed against each other to suit the intended application.

Economic and Environmental factors:

Producing true transparent ceramics on an industrial scale involves significant costs due to the high-purity raw materials, specialized sintering equipment, and precise manufacturing controls required. ALON and spinel, for example, can cost several hundred dollars per kilogram, and the production processes are energy-intensive. This high cost restricts their use to applications where their unique combination of optical and mechanical properties offers clear advantages over cheaper alternatives, such as glass. In contrast, the analogue materials in this experiment have negligible raw material costs—typically less than a few dollars for enough to produce multiple samples—and require no specialized energy inputs beyond household heating. Environmentally, the model materials are low-impact; both cornstarch and gelatin are biodegradable, and PVA glue is water-based and non-toxic in small quantities. Waste generation is minimal, and disposal is straightforward. The stark contrast in cost and environmental footprint between the analogue and the real material highlights why transparent ceramics remain a specialized material, used only where necessary, despite their superior performance in demanding environments.

Applications:

While the materials prepared in this experiment are not suitable for real-world load-bearing or high-performance optical applications, they serve as valuable teaching tools for demonstrating the concepts behind transparent ceramics.

Some viable applications of transparent ceramics in the classroom include:

- Classroom demonstrations of light transmission, scattering, and refraction.

- Visualising the effect of inclusions and defects on optical clarity.

- Comparing samples to glass, acrylic, and other transparent materials.

- Engaging students in hands-on material science experiments without the risks of high-temperature processing.

Real-world transparent ceramics, by contrast, are used in:

- Ballistic windows and transparent armour: Intended use for military vehicles and secure facilities.

- Aerospace canopies and sensor windows: These materials are capable of withstanding high thermal and mechanical stress.

- Laser systems: Which include high-energy and infrared lasers where optical clarity and thermal resistance are critical.

- :Medical devices: Devices such as endoscopes and protective covers for imaging equipment may incorporate transparent ceramics.

Transparent Ceramics for Ballistic Armor Applications | SpringerLink (Handbook of Advanced Ceramics and Composites)

Chemical properties and structure:

True transparent ceramics are polycrystalline materials with a highly controlled microstructure. The crystal grains are typically on the order of a few micrometers in size, with boundaries engineered to minimize refractive index mismatches and thus reduce scattering.

In our experiment, the structural scale is orders of magnitude larger. Cornstarch consists of granules composed of amylose, while gelatin is protein-based. These structures scatter visible light far more strongly than other industrial-grade transparent ceramics. The binder fills gaps between granules, acting in the same sense as a grain boundary phase, though with far less optical uniformity. This stark difference in scale and order explains why the experimental materials created in this experiment cannot achieve the same level of transparency as real ceramics, but they remain valuable for demonstrating the influence of microstructure on optical behavior.

Conclusion:

This experiment produced translucent to semi-transparent materials using cornstarch or gelatin, demonstrating in an accessible way some of the principles and characteristics exhibited by transparent ceramics. By varying base materials, binders, and additives, it was possible to observe how composition and processing influence light scattering and mechanical behavior. Comparisons with real transparent ceramics highlight the importance of microstructural control, grain size, and refractive index matching in achieving high transparency. Whilst the materials created using cornstarch or gelatin in this experiment cannot replicate the clarity or strength of Aluminum Oxynitride or Yttria-stabilized zirconia, they provide a safe, inexpensive, and educationally valuable way to explore these concepts.