Which crucible material should I use for ashing at 550 degrees Celsius?

Porcelain is the standard choice for muffle furnace ashing at 550 to 900 degrees Celsius. It is dense, easy to clean, stable in air and inexpensive. Use high-purity alumina when the ash must be low in silica or when the sample contains fluxes, and use quartz when you need very low contamination or rapid heating and cooling. Nickel crucibles are for alkaline fusions, not for routine ashing.

Why do porcelain crucibles crack in the furnace?

Almost always thermal shock. Porcelain tolerates gradual heating but not a cold crucible placed into a hot furnace or a hot crucible set on a cold bench. Heat and cool at no more than about 5 degrees Celsius per minute, place hot crucibles on a ceramic board or wire gauze, and never quench them in water. Mechanical damage from a chipped rim or a lid that has been forced also starts cracks that open on the next cycle.

Can crucibles be cleaned and reused?

Yes, if the glaze and shape are intact. Remove residue by soaking in dilute nitric or hydrochloric acid, rinse with deionised water, and dry before the next use. Do not use hydrofluoric acid on porcelain or alumina, and do not use abrasive powders that remove the glaze. For trace-metal work, dedicate crucibles to one type of analysis and keep a record of their use.

Does JWRESEARCH supply crucibles and evaporating dishes in Singapore?

Yes. JWRESEARCH supplies porcelain crucibles and lids from 10 to 300 mL, high-purity alumina crucibles, quartz crucibles, nickel and zirconium crucibles for fusion work, and flat-bottom and round-bottom evaporating dishes in porcelain and borosilicate glass, delivered across Singapore with certificate options on request.

Laboratory Crucibles and Evaporating Dishes Singapore

Published: {{NEW_ARTICLE_DATE}} | By JWRESEARCH | Category: Laboratory Glassware and Porcelain

A crucible is a simple object until it fails. A porcelain crucible that cracks during ashing takes the sample with it, and in a trace-metal or ash-content method the loss is not recoverable. Most failures come from three causes: the wrong material for the chemistry, thermal shock, and contamination from a crucible that was not properly cleaned.

At JW RESEARCH SUPPLY, we supply porcelain, alumina, quartz and metal crucibles, together with lids, evaporating dishes and supporting labware, to testing laboratories, universities, cement and food analysis labs across Singapore. This guide covers the materials, the limits, and the handling rules that keep crucibles serviceable.

Crucible Materials Compared

Material	Max Working Temperature	Chemical Resistance	Typical Use
Porcelain (glazed)	1,050 – 1,200 °C	Good against acids; attacked by HF and hot alkalis	Ash content, ignition residue, general gravimetry
High-purity alumina	1,600 – 1,750 °C	Excellent; resistant to fluxes and molten salts	High-temperature ashing, sintering, low-silica work
Fused quartz	1,100 – 1,200 °C continuous	Excellent against acids; poor against hot alkali	Trace analysis, low contamination, rapid cycling
Nickel	600 – 800 °C	Good against alkaline fusion; attacked by acids	Sodium peroxide and alkali fusions
Zirconium	800 – 900 °C	Good against alkali fusion	Fusion of ores and refractories
Platinum	1,400 – 1,500 °C	Excellent, but attacked by aqua regia and metals	Critical gravimetric work, fluoride ashing

Specification Reference

Parameter	Typical Range	What It Affects
Capacity	10, 15, 25, 30, 50, 100, 150, 300 mL	Sample mass and headspace for expansion
Top diameter	25 – 90 mm	Access for sample addition and coverage by the lid
Height	20 – 60 mm	Flame or furnace exposure and spatter control
Wall thickness	1.5 – 3.0 mm	Thermal mass; thin walls heat faster but crack more easily
Max heating rate	5 °C per minute	Prevents thermal shock in porcelain and quartz
Glaze	Glazed interior and exterior, or unglazed	Glaze reduces sticking; unglazed is used where glaze would contaminate
Ash / leachable content	Specified per batch for high-purity grades	Blank value in trace and ash determinations

Choosing the Material

Porcelain is the default for ashing and ignition because it is dense, dimensionally stable and cheap enough to keep a stock of. It handles 550 °C ashing indefinitely and will survive 900 °C with careful ramping. It does not like hydrofluoric acid, hot concentrated alkali, or being taken from a 900 °C furnace straight to a bench.

Alumina is the choice when the sample contains fluxes, when the crucible will be used above 1,200 °C, or when silica contamination matters. High-purity alumina has a low blank and resists molten salts that would eat porcelain. It costs more and is more brittle, so handle it with the same care as porcelain and avoid sharp temperature gradients.

Quartz suits trace analysis and work where rapid heating or cooling is needed. It tolerates high temperatures and has very low metallic impurity levels, but it is attacked by hot alkali and by HF, and it is expensive. Nickel and zirconium crucibles belong to alkali fusion methods, where the flux would destroy ceramic ware; they are not general-purpose ashing vessels.

Heating and Cooling Practice

Ramp the furnace at 5 °C per minute or slower; do not drop a cold crucible into a hot chamber.
Place crucibles on a ceramic board, silica tray or wire gauze, never directly on a cold metal bench.
Use tongs with serrated tips and support the crucible from below, not by the rim.
Allow crucibles to cool in a desiccator; porcelain absorbs moisture while warm and will gain weight.
Never quench a hot crucible in water or oil, even if the method says "cool rapidly".

Weighing is part of the same discipline. Cool to room temperature in a desiccator, weigh immediately, and use the same balance and the same cooling time for every replicate. A crucible that is still warm will convect air across the balance pan and read light.

Evaporating Dishes

Evaporating dishes are shallower than crucibles and are made for driving off solvent, not for ignition. Porcelain dishes are the general choice for water-bath and hotplate evaporation; borosilicate glass dishes are useful when the residue must be seen through the wall or when the sample attacks porcelain glaze. Round-bottom dishes reduce spitting, flat-bottom dishes give a larger surface area and faster evaporation.

Choose a dish with at least twice the volume of the liquid you intend to evaporate, and cover it with a watch glass to keep dust out while allowing vapour to escape. Do not evaporate to dryness on an open hotplate if the residue can spatter; use a water bath or a heating mantle at a controlled temperature.

Cleaning and Care

Soak used crucibles in dilute nitric or hydrochloric acid, then scrub gently with a soft brush and rinse with deionised water. Do not use hydrofluoric acid on porcelain, alumina or quartz, and do not use abrasive powders that strip the glaze. For ash and trace work, run a blank crucible through the same heating cycle to confirm that the cleaning has removed the previous residue.

Retire any crucible with a chipped rim, a star crack, a detached glaze patch or a lid that no longer seats. These defects concentrate stress and will fail at temperature, usually with the sample inside.

Ordering Checklist

Maximum temperature and heating rate of the method
Sample chemistry: acids, alkalis, fluxes, oxidants
Capacity and whether a lid is required
Glazed or unglazed, and blank/ash specification
Compatibility with the furnace tray and tongs
Evaporating dishes and watch glasses for the same workflow

Tell us the method temperature and the sample matrix, and we will recommend the crucible material, capacity and lid configuration, delivered across Singapore.

Contact JWRESEARCH

JW RESEARCH SUPPLY — laboratory equipment and consumables, Singapore.
Telephone / WhatsApp: +65 8039 3660
Email: SINGAPORE@JWSHY.COM
Website: www.jwresearch.cn