Sciencemadness Discussion Board - Calcium Sulphide

Calcium Sulphide

FGP - 18-12-2003 at 04:38

Archives show that calcium sulphide was produced by heating sulphur and oyster shells (presumably in powder form). The latter were regarded as a pure source of calcium carbonate. Can someone on this forum suggest the ideal reaction conditions in order to obtain calcium sulphide from these materials? Please accept old fashioned UK spelling of sulphur and sulphide.
FGP
Herefordshire UK.

chemoleo - 18-12-2003 at 04:49

Lol, I also prefer Sulphide & sulphate - it's respect for the ancient chemists!

Anyway, altough I haven't checked, I would think you would get the reaction going by mixing stoichiometric amounts, and heating/melting until the evolution of SO2 (sulphur dioxide) stops.
SO2 should evolve if the reaction works according to (which is very likely):

1. CaCO3 + S --> CaS + CO2 + 1/2 O2
2. S + O2 --> SO2

Altogether:

2 CaCO3 + 3S --> 2 CaS + 2 CO2 + SO2

SO2 is one of the products, which is detectable by smell (toxic). The oxidation of sulphur should partially drive the reaction.

Homework question?

a_bab - 18-12-2003 at 05:23

Calcium sulphide is phosphorescent (glow-in-the-dark), so it could be a really nice thing to be done.

Tacho - 18-12-2003 at 09:34

Really? Simple as that? No dopants or anything? Sounds too good...

Any first hand experience?

I am a fish - 18-12-2003 at 10:17

Quote:

Originally posted by a_bab
Calcium sulphide is phosphorescent (glow-in-the-dark), so it could be a really nice thing to be done.

Only when doped with zinc sulphide.

unionised - 18-12-2003 at 12:21

Classic synthesis is gypsum and coke.
Just hope that the gypsum you use has the right imputities to dope the sulphide.
A similar trick is still used for getting barium salts from the ore. The sulphate is insoluble and almost inert; reduction to the sulphide gives a product that disolves in acid.

chemoleo - 18-12-2003 at 16:42

But what if you want to recycle BaSO4, back into soluble salts? Always wanted to find an easy way to do this, without massive heat etc...

a_bab - 19-12-2003 at 01:55

Actually, you can use as a doppant Bi or other metals. The tricky part is to create the crystalin structure properly and this is achieved at high temps, and long times.

FGP - 19-12-2003 at 05:17

Quote:

Originally posted by chemoleo
Lol, I also prefer Sulphide & sulphate - it's respect for the ancient chemists!

Anyway, altough I haven't checked, I would think you would get the reaction going by mixing stoichiometric amounts, and heating/melting until the evolution of SO2 (sulphur dioxide) stops.
SO2 should evolve if the reaction works according to (which is very likely):

1. CaCO3 + S --> CaS + CO2 + 1/2 O2
2. S + O2 --> SO2

Altogether:

2 CaCO3 + 3S --> 2 CaS + 2 CO2 + SO2

SO2 is one of the products, which is detectable by smell (toxic). The oxidation of sulphur should partially drive the reaction.

Homework question?

Dear Chemoleo,
You've pointed to what I think I was asking - surly heating the mixture in air will favour your reaction '2'?

"2. S + O2 --> SO2" and so ending up with little or no calcium sulphide.?
Not a homework question - I am one of the ancients transcribing an early chemistry essay.

chemoleo - 19-12-2003 at 09:22

If you heat up CaCO3 and sulphur, the products should be CaS, SO2 and CO2 (equation 3, after 'Altogether'

. True, you lose 1/3 of the sulphur into the formation of SO2, but the remaining 2/3 goes into the formation of 2CaS.
You can heat the reaction in a vacuum if you wish, and it would still work. The oxygen that is needed for equation 2 to form SO2 is derived from the product of reaction 1. Outside air might interfere, if the reaction gets hot enough for the sulphur to selfignite. I doubt you will need temperatures like that though. Even then, if the reaction mix exposure to air is minimal, with no further access to it (i.e. in a closed container, with a pressure valve), then you should have no problem with the air interfering... sulphur losses will be minimal. Just use a very slight excess then, and all will be good

[Edited on 19-12-2003 by chemoleo]

notagod - 19-12-2003 at 15:55

chemoleo: To get soluble Ba2+ from BaSO4, you just have to boil it with concentrated sodiumcarbonate solution approx. 15 min and then boil off the water until nearly dry. Then put in some more water, stir and let it settle. Decant it and repeat two more times. The Bariumsulfate will have turned into Bariumcarbonate now, so just rinse it and dissolve it with your acid of choice. This works with calciumsulfate and strontiumsulfate as well.

hodges - 19-12-2003 at 16:08

I bet this calcium sulfide production takes very high temperatures. I'm pretty sure I remember trying it years ago with a torch and not having any luck. There is a similar reaction to make calcium carbide using CaO and C. I definitely remember trying this one several times heating the mixture with a torch for long periods of time and never having a bit of success.

If someone does manage to make either calcium sulfide or calcium carbide using nothing hotter than a torch I'd be interested in hearing how they did it.

Hodges

Tacho - 20-12-2003 at 08:49

I found this recipe for a phosphorecent compound in an old italian book, I translated the best I could (my native language is neither italian nor english), and I added the original text in case someone better qualified wants to help:

mix 20g “calce caustica” (I think that’s calcium oxide) with 5g powdered sulfur and 2g starch. Wet this mix with 8ml of a solution made of 0,5g of bismuth’s “sottonitrato”(help needed here) in 100ml alcohol (previous addition of HCl)(?). When alcohol is dry, heat the mix in a closed crucible to bright red for 20 minutes. After it cools, cut the thin superficial layer of “gesso” (plaster?!), pulverize the fused mass and heat it again for 15 min at the same temp.

I made some crude attempts to produce phosphorecence using calcium carbonate, sulfur and a tiny bit of zinc powder. They all failed miserably. Not a hint of light. Awful lot of stench.

Original text:
“Gr. 20 di calce caustica si mescolano com gr. 5 di solfo in polvere e gr. 2 d’amido. Si umeta a goccie questa miscela com 8 cc di d’uma soluz. Di gr 0,5 de sottonitrato de bismuto in 100 cc d’alcool (previa addizione d’ac clorídrico) in modo a ottenere un’intima suddivisionde del bismuto. Quando l’alcool è svaporato all’aria, si scalda il miscuglio, in crogiuolo coperto per circa 20 minuti al rosso chiaro, e dopo reaffreddamento, si toglie il sottile superficiale strato di gesso, si polveriza la massa fusa e si scalda ancora per un quarto d’ora alla temp. di prima.” – Ricettario Industriale – I. Ghersi – Ulrico Hoepli Ed. 1915

Mumbles - 20-12-2003 at 09:19

Calce caustica is probably calcium Hydroxide. You know, caustic soda=NaOH so maybe Calce Caustica=Calcium Hydroxide. Bismuth's Sottonitrato would be bismuth nitrate or nitride maybe?

I don't speak a whole lot of italian so don't take what I suggested as neccesarily true. Perhaps you should try to U2U or wait for Nevermore. His/her prifile says he/she is from Italy. I don't know if that means they speak italian, but I'd say the chances are higher than someone from elsewhere in the world.

CaC2 and CaS

chemoleo - 20-12-2003 at 11:00

Hodges, for the production of CaC2 you need VERY high temperatures. I think it is made under an electric arc. In fact, some time back i managed to get hold of a very good transformer (5 kW), at 42 Volts. With this one, I fused out the power in our house a number of times, possibly because I used more than 5 kW

. Anyway, this way I actually MADE about 4 grams of CaC2, with CaO and carbon. When I put some of those chunks into water, they evolved bubbles, that violently burned with a smoky yellow flame once ignited

.
I believe the high temperature is required (>>2500 K) for the formation of the triple bond, in part. Thought this is a guess.
Anyway, that clearly explains why you can forget making CaC2 with a blowtorch.

Anyway, that's why I dont think the CaCO3/S thing would require AS MUCH temperature as with the CaC2 production. Sure, it is possible you need higher temperatures than those you can achieve with a blow torch. But I dont know the temperature that is required. Sorry

secret ingredients

Mr. Wizard - 20-12-2003 at 11:24

Trying to decipher old recipes? Could the sottonitrato de bismuto be Bismuth Subnitrate? I've always has a facination for glow in the dark phosphorescent materials too. But no success. If Bismuth is needed as a trace element to dope the Calcium Sulfide, perhaps a little Pepto Bismol , or a generic replacement, would work, as it contains bismuth subsalicylate as its active ingredient. Each 15 ml contains 262 mg of the stuff. Most of the other inert ingredients are organics that would burn off and a little magnesium aluminum silicate.

guaguanco - 20-12-2003 at 13:17

Quote:

Originally posted by chemoleo

Anyway, that's why I dont think the CaCO3/S thing would require AS MUCH temperature as with the CaC2 production. Sure, it is possible you need higher temperatures than those you can achieve with a blow torch. But I dont know the temperature that is required. Sorry

If I were to try this, I'd grind up a powder consisting of CaCO3 and a large excess of Sulfur. I'd pack it into a crucible with a loose fitting lid (to exclude O2 as much as possible) and cook the bejeebers out of it in a small electric kiln or with a high temperature torch.

I don't know if it would work, but the old pioneer chemists were big on crucibles and cooking the bejeebers out of things, so I bet I'm on the right track...

unionised - 20-12-2003 at 14:51

I have this vague memory that the boiling point of sulphur (444.6C) was used as a calibration point for fairly high temperature thermometry. Can anyone imagine why I might mention this fact in this thread?

chemoleo - 20-12-2003 at 15:05

Lol, see, that's why I thought this reaction wouldnt require THAT much heat

However, from the very first post it is not clear whether the reaction was done in a pressurised system (to contain boiling sulphur). Yet, as gases are evolved in due course of the reaction, the pressure would increase, possibly driving the reaction backward to a greater and greater extent (equilibrium).
Anyway, this pressurisation sounds unlikely from this. so yes, it's very likely that the temperatures required for the reaction are below the boiling point of sulphur. good point.

[Edited on 20-12-2003 by chemoleo]

KABOOOM(pyrojustforfun) - 22-12-2003 at 19:50

wouldn't excess S lead to formation of polysulfides?
hmm... if "I" were to try CaS, I would make some Al-plaster comp which will be lots of fun AND as a result it'll give me some CaS in its ash (mixed with aluminum oxide). isolation of CaS seems the hardest step. I would say add the ash in icecold water (do it outside!) let the filtrate evaporate while not letting the sol warm up (cold days)
the problem is that CaS is slightly soluble in water so huge amounts of water is needed which will take a long time to evap specially @ cold temps. I read CaS partly decomposes in water (to slaked lime and hydrogen sulfide) I think it means decomposition continues till it reaches a PH in which the equilibrium stablizes
anyway if it is used as a source of hydrogen sulfide the seperation maybe unnecessary (dependes on what you want it for)

Nevermore - 30-12-2003 at 02:16

Gr. 20 di calce caustica si mescolano com gr. 5 di solfo in polvere e gr. 2 d’amido. Si umeta a goccie questa miscela com 8 cc di d’uma soluz. Di gr 0,5 de sottonitrato de bismuto in 100 cc d’alcool (previa addizione d’ac clorídrico) in modo a ottenere un’intima suddivisionde del bismuto. Quando l’alcool è svaporato all’aria, si scalda il miscuglio, in crogiuolo coperto per circa 20 minuti al rosso chiaro, e dopo reaffreddamento, si toglie il sottile superficiale strato di gesso, si polveriza la massa fusa e si scalda ancora per un quarto d’ora alla temp. di prima.” – Ricettario Industriale – I. Ghersi – Ulrico Hoepli Ed. 1915

translation (where did you get this thing, looks like an hystory book is the oldest italian i've ever seen, rather hard to translate)

mix 30 grams of CaO with 5 grams of powdered S and 2 grams of starch.,This is wetted with 8cc of a solution of Bismuth-NO2 in 100cc of ethanol (adding some HCL in order to obtain a fine mixing of the bismuth). When the ethanol has evaporated warm the mixture in a closed vessel till red for 20 mins, after that cool it, toss the thin layer of gypsum on top, powderize the mass and repeat the process (heating) for 15 mins.

Note, i suppose "calce caustica" is CaO being it caustic, it can be reasonable to be Ca(OH)2 (as with NaOH "soda caustica"

but i suppose the name caustic is given only to the ones that burn the skin, i don't think it should be CaCO3 or should have been called just "calce or calcina"

[Edited on 30/12/2003 by Nevermore]

Tacho - 31-12-2003 at 06:10

Thank you Nevermore.
It's a book that belonged to my grandfather, published in 1915.

As unionised pointed out, the boiling point of sulfur is 444.6C. I can't see how you can bring the reactants "till red" without some pressure vessel.

Nevermore - 4-1-2004 at 10:31

i don't know but i suppose the sulphur will react before reaching boiling temperature so overheating it will just burn out the excess sulphur to get a more clean product..

Substitution of Calce caustica

Acid Test - 6-1-2004 at 13:03

Quote:

Originally posted by Tacho
I found this recipe for a phosphorecent compound in an old italian book, I translated the best I could (my native language is neither italian nor english), and I added the original text in case someone better qualified wants to help:

mix 20g “calce caustica” (I think that’s calcium oxide) with 5g powdered sulfur and 2g starch. Wet this mix with 8ml of a solution made of 0,5g of bismuth’s “sottonitrato”(help needed here) in 100ml alcohol (previous addition of HCl)(?). When alcohol is dry, heat the mix in a closed crucible to bright red for 20 minutes. After it cools, cut the thin superficial layer of “gesso” (plaster?!), pulverize the fused mass and heat it again for 15 min at the same temp.

I made some crude attempts to produce phosphorecence using calcium carbonate, sulfur and a tiny bit of zinc powder. They all failed miserably. Not a hint of light. Awful lot of stench.

You could try to use calcium carbide in place of the
calcium oxide.The reasoning behind this theory
is that Calcium Carbide reacts with water to
create Carbon Hydride.

Theoretic - 7-1-2004 at 02:00

It shouldn't be sulfur + CaCO3, sulfur wouldn't reduce carbon easily. Carbon WILL reduce CaSO4,with CaS forming at 1000 C and SO2 forming at 1500 C.

Tacho - 10-1-2004 at 09:23

How about metallic calcium and sulfur?

Mr. Wizard - 10-1-2004 at 11:53

Metalic calcium filings and sulfur react with explosive force. Even in an open one gram pile with a long wooden match I scorched my fingers. The filings were very course. The only thing glowing afterwards were the spots in front of my eyes.
For production of phosphors try looking at:
http://www.belljar.net/content.htm
Vol 5, 1996
This is an index of some of the fantastic DIY projects this newsletter touched on. I'll try to give the highlights later if anyone is interested, as I believe it might be copyrighted material. I'm not sure what I can put on the net without his permission. I did subscribe to the newsletters for a while.

unionised - 10-1-2004 at 11:55

I did that once. Bloody great red flame and burned a hole through the steel crucible. The product didn't glow in the dark.
How about H2S and Ca(OH)2, I know it's a reversible reaction but you should be able to get it to work.

Mr. Wizard - 10-1-2004 at 13:06

unionised,
Maybe you could try some "Dormant Disease Lime Sulfur" spray, used on fruit trees this time of the year. I think its a calcium polysufide solution, and reeks of sulfur. It is a red liquid when it's in the container, but the solution is a clear yellow color. It would be safer than making H2S. Maybe you could just add lime Ca(OH)2.?H2O and heat at 900C-1000C in a covered quartz or suitable crucible for 1 hour. Allow to cool and check. The phosphor article mentions many times how the sulfides have to be heated for this length of time and temp. Perhaps trying forming the CaS in solution and drying it before activating it by heating it.

I'd forgotten about the red flame of the Ca + S! I was more surprised at how hot it was, and the scorched fingers..

Another Way

hodges - 10-1-2004 at 14:25

How about :
3CaSO4 + 8Al --> 3CaS + 4Al2O3

This is similar to thermite. Requires a high temperature to ignite but a vigorous reaction producing the desired product.

Hodges

Nevermore - 14-1-2004 at 03:13

i suppose the CaS should contain some particular impurities to glow in dark..

T_FLeX - 14-1-2004 at 04:34

Do you guys just want to make calcium sulfide because its phosphorescent? or for sulfide precipitate reactions?

If the latter, I would point out this website.

http://www.crscientific.com/nh4sulfide.html

I have been wanting to prepare this reagent myself but have not got around to it. Hope this helps!

markgollum - 9-3-2009 at 20:01

I have reduced calcium sulphate to the sulphide twice. I did it by grinding together the CaSO4 + charcoal in a blender several minutes until it was thoroughly mixed, both ingredients were fine powders before they were ground together. The vessel I used was a piece of 2’’ steel galvanized plumbing pipe and end caps, one end cap had a small hole drilled in it and a small piece of alumina fiber blanket was fitted inside the cap and held in place by a bit of bent copper wire inside the end cap (to act also as a gauge at the max internal temperature buy later checking to se if the wire had melted), all the galvanized parts were stripped of zinc either by letting the parts sit in hydrochloric acid for several hours until some time after the hydrogen evolution ceased or in the case of the pipe by heating them in the open air until the zinc can be visibly seen to be boiling off and burning, the fumes are toxic so I set it up on my concrete deck and watched it from in the house through a window until I was satisfied that the bluish green flames and white smoke had stopped and there was no zinc remaining. I had initially wrapped it with one layer of alumina fiber blanket then with nichrome wire; unfortunately the ZnO dissolved the alumina blanket and severely corroded the wire. The pipe was filled with the calcium sulphate /Carbon mixture and a glass rod was pushed in through the center to produce a cored structure and facilitate the discharge of gasses, the glass rod was removed and the pipe was carefully handled to prevent the core from collapsing. I strategically put the vessel on a large split log in my wood burning stove and built a roaring fire and kept it going for about 4 hours during which the pipe glowed a bright yellow (guestimated temperature ~950C) As it was getting late, I buried the pipe in the glowing coals and went to bed. When the contents of the vessel were examined the next day, they were white and largely free of carbon with the exception of a few larger particles in the center near the core and in the section near the end where the end cap increased the diameter, the copper wire did mot melt so the peak temperature was certainly less then 184C. The white powder rapidly bubbles up H2S when a drop of hydrochloric acid is added. I originally produced the CaS in order to try to make Na2S by leaching it with sodium carbonate but I found that the yields were poor and the product was yellow from reaction with atmospheric oxygen. Also, the product I had isolated outside later liquefied when brought indoors I think this was because the hydrate I had isolated in the cold wintery outdoors was no longer stable a the relatively balmy 25 degrees or so. I used vacuum filtration and evaporated the filtrate until the bumping began to get excessive, I protected the filtrate from oxygen as much as I could by working quickly and covering the Erlenmeyer with saran wrap and cutting a small hole in the top to emit steam in the evaporation step. I tried to perform the metathesis in methanol in the hopes of getting the anhydrous Na2S as it is very soluble and methanol, I hoped that the insolubility of the calcium carbonate would drive the reaction albeit slowly. However, after several hours at close to the boiling point with magnetic stirring, followed by letting it sit for several months I obtained essentially zero yield.

I decided to post in this thread as opposed to this http://www.sciencemadness.org/talk/viewthread.php?tid=11917
one

Edit

I also was very impressed with a group 2 alkali metal + sulfur.
I burned my fingers an was seeing spots after lighting a sulfur+ Mg filings, I was very unprepared for how hot, fast, and violent it was. It seemed more so than many other mixes I have tried.

[Edited on by markgollum]

Magpie - 10-3-2009 at 10:23

Nice work in making CaS Markgollum.

I felt I should say something about the use of galvanized pipe for reaction vessels, however. Instead, try "black iron" or "malleable iron" pipe fittings such as used for natural gas lines. Then you won't have to deal with those nasty zinc fumes. Probably have to burn off a little oil however.

Teen Chemist - 9-8-2012 at 07:02

I know I'm bringing back an old thread but I recently tried to make phosphorecent powder with Tums and sulfur powder. And it worked! I did it in open air and heated it with a small torch for a few min. It didnt work very well. It is just barely visable in a pitch black room. I have a feeling if you did it in a container and heated it more evenly it would work better.

[Edited on 9-8-2012 by Teen Chemist]

Poppy - 10-8-2012 at 05:37

The reaction 2 Ca(OH)2 + 4 S + O2 --> 2CaS + 2SO2 + 2H2O procedes well, although at low temps Ca(SH)2 will form. The reaction is self susteining.

blogfast25 - 10-8-2012 at 05:57

Quote: Originally posted by Poppy

The reaction 2 Ca(OH)2 + 4 S + O2 --> 2CaS + 2SO2 + 2H2O procedes well, although at low temps Ca(SH)2 will form. The reaction is self susteining.

Really? You have tried that?

Poppy - 10-8-2012 at 11:39

Quote: Originally posted by blogfast25

Really? You have tried that?

Yes. Oddly enough I was haunted into a trip of making sulfur dioxide and realized Ca(OH)2 could work as an oxidising agent, in fact in turned to be that it is a reduction agent. Anyway the reaction was extimated: Ca(OH)2 + S --> CaS + H2O + O
So extra sulphur should give:
2Ca(OH)2 + 3S --> 2 CaS + 2H2O + SO2
As it seemed, closing the container caused the reaction somewhat to halt al ambient temperature. It even glows bright when working!
The reaction slowly vanishes thus I think its necessary to push the temperature a little higher to ensure Gibbs free energy will be supportive, considering the releasing of humidity, I would put that around almost exactly the boiling point of water, 100°C.
Oxygen is a strong enough participant I am not sure aboout its need or not, though it would be surprising efficient if the reaction proceds in the absence of oxygen pondering the versatile burn of inner layers of reactant!!
At best temperatures for a continuous flow of the reaction should not exceed that of a match which was used to lit the compost.

Thx, regards
Poppy

Poppy - 10-8-2012 at 11:39

Quote: Originally posted by blogfast25

Really? You have tried that?

AJKOER - 10-8-2012 at 14:51

Quote: Originally posted by Poppy

The reaction 2 Ca(OH)2 + 4 S + O2 --> 2CaS + 2SO2 + 2H2O procedes well, although at low temps Ca(SH)2 will form. The reaction is self susteining.

Per Wikipedia (I believe this comment as I have heard similar remarks on the creation of Aluminum Sulfide), to quote:

"Milk of lime, Ca(OH)2, reacts with elemental sulfur to give a "lime-sulfur", which has been used as an insecticide. The active ingredient is probably a calcium polysulfide, not CaS.[1]"

Alternately, may I suggest the following odorous path:

H2S (g) + CaCl2 (s) ---> CaS (s) + 2 HCl (g)

In words, generate Hydrogen sulfide (caution: a very toxic gas) and pass over heated CaCl2 and lead the exhaust gas into NH3/H2O2, or a large quantity of liquid bleach. Basis, to quote Wiki: "Hydrogen sulfide reacts with metal ions to form metal sulfides, which may be considered the salts of hydrogen sulfide."

[EDIT] Those working with H2S should certainly use appropriate safety equipement and ventilation. To quote Wiki: "Hydrogen sulfide is considered a broad-spectrum poison, meaning that it can poison several different systems in the body, although the nervous system is most affected. The toxicity of H2S is comparable with that of hydrogen cyanide. It forms a complex bond with iron in the mitochondrial cytochrome enzymes, thus preventing cellular respiration." ...."Treatment involves immediate inhalation of amyl nitrite, injections of sodium nitrite, inhalation of pure oxygen, administration of bronchodilators to overcome eventual bronchospasm, and in some cases hyperbaric oxygen therapy". In my opinion, important aspects of this gas are its high toxicity, ability to deaden nasal detection after initial exposure, delayed mortality effect and toxic exposure via skin absorption also.

[Edited on 11-8-2012 by AJKOER]

Poppy - 10-8-2012 at 17:14

Indeed some polysulfide may form, but the specif description for lime-sulfur involves reaction in a vessel of water! Plus sulphur is added largely in excess (3,9 to 1, whereas the described reation with lime makes use of a 3 to 2 fraction)
Certainly, we may put to press, additional purification is necessary. CaS being such a hard material, in meaning so by having a high boiling point and low solubility (its said it decomposed by water, but it is not mentioned how fast), you couldn't think of it as being perfectly rounded equimolar interstices of calcium and sulphur. But we may be impressed wrongly, by the rearrangement is so strong, the reactive area glows bright! Although possibily not many energy escapes.

Think now of calcining calcium hydroxide and putting to react with sulphur, would this proceed aswell?
2CaO + 3S --> 2CaO + SO2
Maybe heating the product of the later reaction with the lime would sublime out unreacted sulfur, as well as release trapped sulfur dioxide.
Useing a ballmill to throughly improve the contact area between reagents I guess would surpass all the difficulties in having a relatively neat desired compost.

[Edited on 8-11-2012 by Poppy]

camurgo - 7-9-2019 at 09:54

@markgollum said something in his post I didn't understand: "...the copper wire did mot melt so the peak temperature was certainly less then 184C."
Sadly it seems he's not around anymore to respond.

I really want to make Calcium Sulfide. It seems the easiest route is:

CaSO4 + 2C → CaS + 2CO2

Or am I wrong about this being the easiest path?
Prepchem website (http://www.prepchem.com/synthesis-of-calcium-sulfide/) describes this same reaction and tells me to use Plaster of Paris (CaSO4 • 1/2H2O).

My question is, would anhydrous Calcium Sulfate work better or worse, or not at all? Would Gypsum (CaSO₄·2H₂O) work too?

Boffis - 8-9-2019 at 00:17

Hi camurgo, plaster of paris looses its remaining water and becomes anhydrous well before the carbon starts to reduce the sulphate to sulphide so the answer to your question is Yes. If you are going to start with gypsum then I would dehydrate it first in the oven at about 200 C. The resulting crumbly mass is easily powdered. Good luck with the carbon reduction.

unionised - 8-9-2019 at 00:24

Quote: Originally posted by camurgo

@markgollum said something in his post I didn't understand: "...the copper wire did mot melt so the peak temperature was certainly less then 184C."
Sadly it seems he's not around anymore to respond.

Should be 1084C- the melting point of copper.

camurgo - 8-9-2019 at 06:46

Thank you @Boffis and @unionised !

AJKOER - 8-9-2019 at 12:29

Per a source (see http://web.iiar.org/membersonly/PDF/CO/databook_ch2.pdf ), a simple low temperature path to a sulfide (and not a polysulfide), to quote:

"Sulfur vapor and ammonia react to give ammonium sulfide and nitrogen. Sulfur also reacts with liquid ammonia to produce nitrogen sulfide."

with the cited reaction in the case of liquid ammonia:

10 S + 4NH3 → 6H2S + N4S4

However, with sulfur vapors, a possible reaction with dry ammonia gas:

4 NH3 (g) + S (vapor) --> (NH4)2S (s) + N2 (g) + 2 H2S (g)

And, with excess NH3:

8 NH3 (g) + 3 S (vapor) --> 3 (NH4)2S (s) + N2 (g)

which is precisely as was claimed per the source above.

Now, dry ammonium sulfide is apparently unstable even at room temperature, liberating NH3 and H2S.

(NH4)2S (s) + Heat --> 2 NH3 (g) + H2S (g)

So, in the presence of a heated mix of dry CaCl2 and (NH4)2S, I would expect:

H2S (g) + CaCl2 (s) --> CaS + 2 HCl (g)

Note, the reaction is reversible (see https://en.wikipedia.org/wiki/Calcium_sulfide#targetText=Cal... ), so it is important to vent the HCl gas from the system. Note also:

NH3 (g) + HCl (g) --> NH4Cl (s)

NH3 (g) + CaCl2 (s) = CaCl2.NH3 (s)

[Edited on 8-9-2019 by AJKOER]

camurgo - 9-9-2019 at 19:30

Thanks @AJKOER!

teodor - 10-9-2019 at 01:57

It seams there are several threads started with something but now all resulted in trying to make a calcium sulfide by a dry process. So, look at http://www.sciencemadness.org/talk/viewthread.php?tid=153772 and especially the comment by MrHomeScientist :

"

CaSO4 and aluminum is used as a heat booster in some thermite reactions (I did this for silicon thermite). That reaction produces calcium sulfide, which reacts with water to release copious amounts of H2S. So zinc would probably also work, if you can find powdered Zn.

"

This is definitely more affordable route than one with charcoal.

Also there are several active threads with discussion of other metal sulfides preparations. There are a lot of repeats indeed.

[Edited on 10-9-2019 by teodor]

camurgo - 11-9-2019 at 07:50

Thanks @teodor.
Couldn't find a local supplier that would sell aluminium powder to individuals. I can import it, but that would make it less affordable than charcoal.
Also, it seems it would be pretty hard to separate the products (which I believe are CaS and Al2O3).

Zn is easily available, but I can't find sources supporting that it could, as @MrHomeScientist seems to imply, react with CaSO4 somehow.