GLASS TESTING

GLASS TESTING

DEFECT IN GLASS BY VISUAL OBSERVATION

SEEDS

These are the small gaseous inclusions or glass bubbles present in the final glass product.

CAUSE
Bad refining.

REMIDIES
Using fining agents which facilate flotation of bubbles of bubble growth facilate dissolution of small bubbles present in small concentration.

BUBBLE ANALYSIS
The occurrence of bubble/blister in glass can lead to significant losses in production. The potential causes of an outbreak are wide ranging. Therefore the identification of gas components and relative pressures can be crucial in determining the possible sources of the bubble/blister and eliminating the problem. A portable quadropole mass spectrometer is used to analyse the gaseous components of bubbles. Gases routinely analysed for are: water (H2O), nitrogen (N2), oxygen (O2), argon (Ar2), carbon dioxide (CO2), sulphur dioxide (SO2), carbon oxy-sulphide (COS), hydrogen sulphide (H2S). Analysis for other gases can be done on request. This is a same / next day service, with experienced opinions provided in addition to analytical results. Our focus is to provide rapid analysis either in house or on site. The service is backed by an extensive range of on-site analytical techniques including scanning electron microscopy (SEM).

THE BENEFITS:

 Same/next day analysis
 On-site analysis available
 Detailed counts and furnace surveys.
 Trouble-shooting / advisory service
 Extensive glass industry experience

EXAMPLES OF THE RANGE OF GLASS PRODUCTS COVERED:

 Bottles and Jars
 Domestic Glass
 Lead Crystal
 Tubing
 Special/ technical Glass
 Flat Glass

RELATED SERVICES:

 Stone and cord analysis
 Redox determination and colour measurement
 Compositional analysis
 Retained sulphur by XRF or wet chemistry


BLISTERS

These are the gaseous inclusion of large volume.

CAUSE
Bad refining.

REMIDIES
Increasing the melting temperature there by reducing viscosity and facilating bubbles floatation.

STONE

These are small crystalline imperfaction found in glass. These are appearing in the form of fine cracks due to the difference in co-efficient in thermal expansion between the material in the stone in glass.

CAUSE
These can be result due to few causes
 The melting period which are too short to permit complete dissolution in the molten glass.
 The melting temperature of the batch which is low enough to melt down such undesirable addition.

SOURCE
These are various source of such undesirable addition resulting stone.
 Sands of large grains size present in the batch.
 The refractory lining of melting furnace, ex: refractory oxides like ZrO2 are often found in stones.
 Due to devitrification.

REMIDIES
 Increasing in melting period.
 Melting temperature should be maintained as high as possible.
 Batch should be well mixed.
 All batch materials particularly of high melting point should be reduced to a size of to pass 20mesh sieve.
 A glass pot should be made less porous with denser body and well vitrified. The pot should be glazed before the glass before charged. The bottom of the pot should never be scraped.
 Floating rings and potters should be properly manufactured and some treatment given to as the pot.
 By adding small quantities of oxides such as alumina, boron, barium able to low temperature.

STONE ANALYSIS

Glass Technology Services Ltd. is an independent laboratory providing a comprehensive range of services related to glass manufacture and use. Our services are provided by experienced, multi-disciplinary staff specialising in all aspects of glass technology. Many of our services are UKAS accredited. Stone and cord in glass can lead to significant losses in production. Rapid analysis identifies the likely cause minimising production losses. Working closely with the customer GTS can identify the cause of the problem and
recommend remedial action. This service is designed for tight production schedules and an express service is available to provide results within a few hours of sample receipt. This service is carried out using an extensive range of analytical facilities including optical microscopy and scanning electron microscopy (SEM) with microanalysis
(EDS) and can be backed up by wet chemical analysis and other analytical techniques.

THE BENEFITS:

 Rapid turnaround
 Glass specialists
 Flexibility

RELATED SERVICES:

 Bubble analysis
 Compositional analysis
 Colour measurement and spectroscopy


CORD

Cords are attenuated throat like amorphous inclusion in the glass which differ in their properties like refractive index from sorrounding glass. It is of two types.
 Composition cords.
 Gathering cords.

CAUSE
 In homogeneity of molten glass.
 Extreme difference in the density of melts produced on fusion.
 Unequal cooling of the glass to the working temperature.
 Subsequent melting of hotter and cooler glass in the gather.

SOURCE
 In new tanks in which refractory blocks corrode rapidly.
 From a bad mixing of batch.
 Due to sufficient melting temperature weather by the glass is too viscous to become homogenous.
 In glasses containing high amount of alumina which makes the glass too viscous.
 Difference in temperature of the glass surface and inside of the melt.

REMIDIES
 Promoting homogenization of high degree.
 Avoid the cause of the cord as far as possible.

DILATOMETRY

Dilatometry is a thermo-analytical method for measuring the shrinkage or expansion of materials over a controlled temperature regime. Our dilatometer has the capability to accurately measure the thermal expansion of materials at temperatures between ambient and 1000ºC in air or under an atmosphere.
The amount of expansion or shrinkage is dependent on the characteristics of the material itself. It is often very important to match the thermal expansion behaviour of different materials that are in contact with one another in order to avoid unwanted stresses and possible cracking. It is equally important to combine measurements of properties with an understanding of the process itself, expertise that is offered by GTS.

WHAT CAN DILATOMETRY DO?

Most materials can be measured by dilatometry including glasses, ceramics, resins, polymers and metals.
Dilatometry allows measurement of the following
properties:
 Thermal expansion and coefficient of thermalexpansion,
 Sintering temperature and shrinkage steps
 Volumetric expansion
 Density change
 lass transition temperature, Tg
 Dilatometric softening point, Td
 Phase transitions
 Measurement available to BS7030 for glass, and to BS1902 for refractory materials
A customer producing articles manufactured from 2 different glasses fused together discovered during production that many articles were cracking, causing loss of production. Visual analysis of the articles by GTS suggested a mismatch in thermal expansion of the two glasses. Thermal analysis of the glasses by dilatometry allowed GTS to confirm this mismatch was outside acceptable levels. We were then able to offer our customer a solution to their problem by introducing a modified glass composition which allowed better matching of expansion coefficients.

RELATED SERVICES:

 Differential Thermal Analysis (DTA) - For batch reactions, phase changes, glass transition values
 Littleton Softening Point - For ASTM standard method C338 and equivalents
 Liquidus Temperature - For crystallisation behaviour of glasses and ceramics
 High Temperature Viscosity - For measurement of the viscosity-temperature curve
 High Temperature Electrical Measurements – For high temperature resistivity

DIFFERENTIAL THERMAL ANALYSIS (DTA)

DTA detects the release or absorption of heat, which is associated with chemical and physical changes in materials as they are heated or cooled. Such information is essential for understanding thermal properties of materials. Analysis of decomposition of glass batch materials, crystalline phase changes, chemical reactions and glass transition temperature are some of the properties measured with DTA. The temperature range of the instrument is from ambient to 1000º C.

WHAT CAN DTA DO?

A typical DTA trace like this one means we can identify the glass transition temperature shown as Tg, the bulk crystallisation shown as Tb, the liquidus temperature shown as Tl, and minor crystalline phases and other features occurring as other peaks or troughs in the graph. This method can give more detailed information on some of these properties than other techniques such as dilatometry. This service is offered with the expertise and know how of GTS staff, including:
 Fast turnaround
 Interpretation of data,
 Analysis of glasses, ceramics, polymers, batch materials
A customer investigating glass batch conditions wished to measure the temperatures at which certain decompositions took place. A full DTA analysis allowed GTS to provide the required information and advise the customer on the implications for their batch processing.

RELATED SERVICES:

 Dilatometry - For thermal expansion, glass transition values
 Littleton Softening Point - For ASTM standard method C338 and equivalents
 Liquidus Temperature - For crystallisation behaviour of glasses and ceramics
 High Temperature Viscosity - For measurement of the viscosity-temperature curve
 High Temperature Electrical Measurements – For high temperature resistivity

DURABILITY AND CHEMICAL RESISTANCE TESTING

When it comes to compliance to national, European and international glass durability standards GTS is your first point of contact for testing. We offer a comprehensive range of durability testing and related services. Most of our durability testing work is backed by UKAS accreditation.

BENEFITS:

 Independence
 Glass specialists
 Confidentiality
 Flexibility

SERVICES AVAILABLE:

 British, European and US Pharmacopoeia testing
 ISO 7086 release of metals
 BS 6748 release of metals
 AOAC - ASTM 973.2
 USEPA 3050 (CONEG) leachate
 Alkali resistance (various)
 Acid resistance (various)
 Hot-end coating durability
 Other tests available on request

EXAMPLES OF THE RANGE OF GLASS PRODUCTS COVERED:

 Bottles and Jars
 Domestic Glass
 Lead Crystal
 Technical Glass
 Pharmaceutical Glass

RELATED SERVICES:

 Surface Analysis
 Compositional Analysis

DETERMINATION OF THE VISCOSITY OF GLASS

METHOD DESCRIPTION

From a glass fibre the elongation velocity caused by a constant force at constant temperature is measured. The elongation velocity is measured at six different temperatures. The various T [log η] values are determined from graphical interpolation. In the dynamic mode, according to the ASTM
method, the elongation velocity is measured at continuously increasing temperature.

MEASURED QUANTITY

Viscosity η in dPa.s

DERIVED QUANTITY

Strain Point: T [log η = 14.5]
Annealing point: T [log η = 13.0]
Philips softening Point: T [log η = 12.4]
Softening Point: T [log η = 7.6]

MEASURING RANGE

T = 200-1000oC,
η = 108 - 1012 dPa.s

PRECISION

Strain Point: σ = 2oC
Annealing Point: σ = 2oC
Philips softening Point: σ = 2oC
Softening Point: σ = 2oC

ACCURACY

Depends on the accuracy of the reference materials NBS standards. Measurements on NBS standards deviate less than 2oC from the stated values.

POSSIBLE ERRORS

In the range log η > 12, viscosity increases with time. In the static method the determined values represent equilibrium conditions. Measurements in the dynamic mode generally result in somewhat lower values. Practical values also are non-equilibrium values and therefore generally will be somewhat lower.

SAMPLING

2 cm3 material should be available. Special attention should be given to the fact that the sample is representative for the batch.

CALIBRATION

Against reference materials, NBS standards.

DETERMINATION OF THE DENSITY OF GLASS

PURPOSE

The purpose of this experiment is to distinguish between different sources of glass by determining the density.

INTRODUCTION

The density of glass is often used in forensic science to determine if two pieces of glass (one from the crime scene, the other found on the suspects clothing or shoes) have a common origin. If only one piece glass is obtained from either the crime scene or suspect, then the density of the glass helps provide some direction as to what type of glass to look for in order to make a
comparison. Glass from various sources, such as bottles, windowpanes, automobile headlights, and plate glass doors, all have slightly different densities. This can, in some cases, make if possible to place a suspect at the scene of a crime. Of course, they would have to have broken a glass object and small fragments have to become lodged in their clothing. Normally, the glass fragments found at a crime scene would be very small and a very difficult technique would have to be used to determine the density. In this laboratory experiment, we will use larger fragments of glass which will require less technique, but will serve our purpose just the same. It should
also be noted that this technique is not limited to glass and can be used for other materials. The density of an object is determined by measuring its mass and then its volume. Since we think of volume with liquids and not solids, the method for determining the volume of glass is based on a physical relationship known as Archimede’s principle. This principle states that an
object immersed in a fluid displaces a volume of fluid equal to its own volume. If an object displaces 1 milliliter (mL) of water then its volume is also 1mL. In our case today, you will suspend a piece of glass in a beaker of water that has been placed on a balance and you will
convert the mass of the glass fragment suspended in the water to mL by using the density of water (1g/mL). You will perform this method on known samples of glass and then try to match an unknown sample to one of your previously studied samples.

PROCEDURE

It should be noted that you will be working with sharp fragments of glass. Please BE CAREFUL and throw your samples in the glass waster when you are finished! Record all of your data on the results page at the end of this handout.
1. Obtain a glass sample, a piece of string or copper wire, a graduated cylinder and a 100 mL beaker.
2. Take your glass sample to an analytical balance and determine its mass to the nearest 0.0001g.
3. After step 2, take your glass sample and tie it securely with your string or copper wire. Leave some string or wire so that you can suspend the glass fragment in your beaker.
4. Measure approximately 75 mL of tap water and place it in your 100 mL beaker.
5. Using the SAME analytical balance as in step 3, place your beaker with the water on the balance. (If you spill any water, please clean it immediately as it could damage the balance.)
6. With your beaker still on the balance, press the zero or tare bar so that your balance now reads 0.0000 with your beaker on the balance.
7. Very carefully, suspend your glass fragment in the beaker of water taking special care not to touch the sides or bottom of the beaker. Record this mass to the nearest 0.0001 g when everything has stabilized. The density of the glass fragment is determined by the following relationship:
Density of Object = mass of the object/mass of the object suspend in water
8. Repeat steps 2 through 7 for all of the known samples available.
9. When you are finished, obtain an unknown sample from your instructor. It should be labeled

HIGH-TEMPERATURE ELECTRICAL MEASUREMENTS

The electrical properties of glasses and related materials are often of great importance, particularly at elevated temperatures, in all-electric melting and electric booster melting glass tanks. This service is offered on both a predictive and measured basis. Predicted resistivity measurements offer a quick, inexpensive solution based on literature values for appropriate glasses in our database. Accurate measurement of high-temperature resistivity of glass is sometimes preferred, and this service is also offered.

WHY DO I NEED HIGH TEMPERATURE ELECTRICAL
MEASUREMENTS?

Electrical melting of glass utilises the bulk resistivity of the glass, hence it
is essential to know what this is and how it varies at elevated
temperatures. Different types of glass can have very different resistivities
so it is also necessary to take this into account. Changes in composition,
particularly in alkali type and content, can strongly influence electrical
properties.

In the graph, glass compositions 2 and 10 are very dissimilar glasses, and
each would require very different melting technology.As with all our services, the expertise and experience of GTS staff is offered to present a full interpretation of the data gathered for our customers.

RELATED SERVICES:

 Dilatometry - For thermal expansion, glass transition values
 Differential Thermal Analysis (DTA) - For batch reactions, phase changes, glass transition values
 Liquidus Temperature - For crystallisation behaviour of glasses and ceramics
 Littleton Softening Point - For ASTM standard method C338 and equivalents
 High Temperature Viscosity - For measurement of the viscosity-temperature curve

HIGH-TEMPERATURE VISCOSITY

The temperature - viscosity relationship of glass is directly linked to its chemical composition. Knowledge of this relationship is necessary for determining melting and heat treatment regimes in glass manufacture and processing. A standard measurement may include viscosities at temperatures between approximately 800ºC and 1400ºC, although this range can be extended if necessary. This measurement range is sufficient for most commercial glasses, allowing extrapolation to higher and lower temperatures if required. For container glasses, float glasses and a range of other compositions, GTS also offer predictive computer modelling of the viscosity – temperature relationship. This is an inexpensive, rapid turnaround service, although in certain circumstances we recommend measurement in conjunction with predictive modelling.

 High Temperature Viscosity Measurement is offered as a Rapid turnaround Predictive Modelling Service

Measurement of High Temperature Viscosity allows a fuller understanding of glass properties. By determining the fixed points for glasses, shown in the diagram, it is possible to accurately estimate the working range and
the relative machine speed of different glass compositions. Glass articles or fibres must often be melted and formed within tight viscosity ranges, so it is vital to know exact temperature – viscosity relations for different glasses, as
these will be affected by composition, melting behaviour, time, temperature and other factors, all of which may impact upon production. One customer wished to investigate the effects of introducing a new material in their glass composition. GTS were able to demonstrate the effects of different levels of addition on viscosity, and hence the probable consequences on production. GTS expertise and assistance in data interpretation allowed the customer to make the correct additions for the required effect on production.

LIQUIDUS T HIGH-TEMPERATURE VISCOSITY EMPERATURE

The liquidus temperature of glass is the temperature above which no crystals can exist. Prolonged heat treatment of most glasses can lead to crystallisation if the temperature is not controlled properly. In glass manufacture this can be disastrous, so knowledge of the liquidus temperature is vital. This test is carried out using a temperature gradient furnace. The glass is placed in a platinum or ceramic boat within the gradient furnace and held for the required time. Test times are tailored to suit the sample, and can vary between several hours and several days depending upon customer requirements. The temperature profile through the furnace is
monitored, so that once the boat is removed and the glass is allowed to cool, the temperature profile across the sample is known. Observation of the sample by polarised-light optical microscopy, as shown in the picture, allows determination of the liquidus temperature of the glass and identification of the primary crystalline phase if required.

LIQUIDUS TEMPERATURE MEASUREMENT CAN GIVE ME:
 Liquidus Temperature
 Primary Phase Identification
 Rapid turnaround service available
 GTS also run a training course specifically for
 Liquidus temperature determination
Measurements of liquidus temperature have regularly been made for many of our customers. These may be problems related to crystals forming during changes in production, or in the fibreglass industry, where the drawing process is interrupted by fibre breakage caused by devitrification in the glass. In one specific case, a customer needed to investigate the effects of changes to their glass batch composition on melting and processing behaviour before implementing these changes in full-scale production. Liquidus Temperature measurements were very useful as they identified significant changes in the liquidus temperature of the new glass when compared with the old glass, which directly impacted upon manufacturing conditions. GTS assisted the customer in reformulating their glass as a result of obtaining this invaluable information on the liquidus temperature.

GLASS COATINGS AND SURFACES

Glass Technology Services Ltd. is an independent laboratory providing a comprehensive range of services related to glass manufacture and use. Our services are provided by experienced, multi-disciplinary staff specialising in all aspects of glass technology. Many of our services are UKAS accredited.
The surface of glass can be a source of unique and wide-ranging problems. The properties of glass surfaces can be very different to the bulk properties. This is critical to issues such as adhesion, coatings and durability. GTS has
extensive capability and knowledge in the analysis and understanding of glass surfaces to tackle a range of surface related issues. An extensive range of analytical facilities, including advanced surface analytical techniques backs the services provided.

THE BENEFITS:

 Specialists in glass
 Confidentiality
 Flexibility

RELATED SERVICES:

 Durability testing
 Compositional analysis

CHEMICAL ANALYSIS

BENEFITS:

 Independent analysis
 Confidentiality
 Specialists in glass

SERVICES AVAILABLE:

 Raw Materials Analysis
 Glass Analysis
 Durability Testing
 Environmental Monitoring/ Analysis
 General Analysis
 Development / R&D work

SPECIFIC ANALYSES AVAILABLE:

 Release of Metals » ISO 7086 / ASTM-AOAC / BS 6748 + others
 Pharmacopoeia Testing » USP / EP / BP
 Raw Materials » XRF and Wet Chemical Techniques
 Glass Analysis » XRF and Wet Chemical Techniques
 Packaging (Essential Requirements) » LACOTS Pb, Cd, Hg, Cr(VI)
 Coatings Analysis » FTIR, UV-VIS, HECM, SEM
 Physical Properties » Predicted & Measured
 Colour Analysis » CIE, Lab and Unknown Contaminants
 Flue Dusts and Disposal Wastes » XRF & Wet Chemical

EXAMPLES OF THE RANGE OF GLASS PRODUCTS COVERED:

 Bottles and Jars
 Domestic Glass
 Lead Crystal
 Technical Glass
 Pharmaceutical Glass