mjhjmtu

I am attempting to make the following picture

But I would like some elements modified which I have done in the following pstricks image. I do not know how to center text, do multiline text for "material havingthermal conductivity $k$", color the boxes, and add a large curvey arrow. I would like the box labelled $T_2$ to be gray or dark gray and the box labelled $T_1$ to be white. I would like the middle box to be a gradient from gray to white. Also I would like to align the text to the xz plane but it does not seem to work for me.

Here is my code so far:

documentclass[english]article
usepackage[T1]fontenc

makeatletter
usepackagepstricks
usepackagepst-3dplot

makeatother

usepackagebabel
begindocument
beginpspicture
pssetAlpha=160,Beta=20
pstThreeDBox(0,0,0)(1,0,0)(0,4,0)(0,0,2) 
pstThreeDBox(1,0.5,0.5)(6,0,0)(0,0,1)(0,3,0)
pstThreeDBox(7,0,0)(1,0,0)(0,4,0)(0,0,2) 
pstPlanePut[plane=xz](0.5,0,1)$T_2$ 
pstPlanePut[plane=xz,planecorr=xzrot](7.5,0,1)$T_1$ 
pstPlanePut[plane=xz,planecorr=xzrot](1,0,-0.5)$x_1$
pstPlanePut[plane=xz,planecorr=xzrot](7,0,-0.5)$x_1$ 
pstThreeDSquare(4,0.5,0.5)(0,0,1)(0,3,0)
pstThreeDLine(4,2,1)(6,2,3)
pstPlanePut[plane=xz](6,2,3.2)Area $A$ 
pstPlanePut[plane=xz](4,-0.5,0)fbox$T_2>T_1$ 
endpspicture
enddocument

The code produces the following image:

(I wouldn't mind a tikz/tikz-3d solution either)

It is not too difficult to write commands that work in TikZ but are somewhat reminiscent of the PSTricks commands you are using. Note, however, at present these only work for view angles close to what you seem to want.

documentclass[tikz,border=3.14mm]standalone
usetikzlibrary3d,arrows.meta,positioning
pgfkeystikz/.cd,
box color/.code=xdeftkzThreedBoxColor#1,
box color=white

defparsexy(#1,#2,#3)(#1,#2)
defparsexz(#1,#2,#3)(#1,#3)
defparseyz(#1,#2,#3)(#2,#3)
defparsex(#1,#2,#3)#1
defparsey(#1,#2,#3)#2
defparsez(#1,#2,#3)#3

newcommandtkzThreeDBox[5][white]tikzset#1
edeftemp%
noexpandfilldraw[#1,fill=tkzThreedBoxColor!40,canvas is yz plane at x=parsex#3+parsex#2] 
parseyz#2 rectangle (parsey#4+parsey#2,parsez#5+parsez#2);
noexpandfilldraw[#1,fill=tkzThreedBoxColor!30,canvas is xz plane at y=parsey#4+parsey#2] 
parsexz#2 rectangle (parsex#3+parsex#2,parsez#5+parsez#2);
noexpandfilldraw[#1,fill=tkzThreedBoxColor!50,canvas is xy plane at z=parsez#5+parsez#2] 
parsexy#2 rectangle (parsex#3+parsex#2,parsey#4+parsey#2);

temp

begindocument
begintikzpicture[x=(1,0),z=(-1/3,-1/4),y=(0,1),font=sffamily]
tkzThreeDBox[box color=orange,draw=none](0,0,0)(1,0,0)(0,2,0)(0,0,4)
fill[orange!80,canvas is yz plane at x=1] (0.5,0.5) coordinate(X) rectangle ++(1,3);
shade[opacity=0.7,left color=orange!80,right color=blue!50!cyan!60!white,canvas is xy plane at z=0.5]
 (1,0.5) rectangle ++(6,1);
shade[opacity=0.7,left color=orange!80,right color=blue!50!cyan!60!white,canvas is xz plane at y=0.5]
 (1,0.5) rectangle ++(6,3);
shadedraw[draw=red!50,left color=orange!15,right color=orange!40] 
(1.5,0.5,1) -- (1.5,1,1) -- plot[variable=x,domain=0:1.5,samples=60] 
(x+1.5,1+0.1*sin(720*x/1.5),1) --++(0,0.25,0) -- ++(0.5,-0.5,0)
-- ++(-0.5,-0.5,0) --++(0,0.25,0)
 -- plot[variable=x,domain=1.5:0,samples=60] 
(x+1.5,0.5+0.1*sin(720*x/1.5),1) -- cycle;
draw[dashed,draw=orange!20,thick] (X) -- ++(6,0,0);
fill[blue!50!cyan!60!white,opacity=0.6,canvas is yz plane at x=4] (0.5,0.5) rectangle ++(1,3);
tkzThreeDBox[box color=white,fill opacity=0,draw=orange!20,thick](1,0.5,0.5)(6,0,0)(0,1,0)(0,0,3)
tkzThreeDBox[box color=cyan,draw=none](7,0,0)(1,0,0)(0,2,0)(0,0,4)
node at (0.5,1,4) $T_2$;
node at (1,0.9,2) $Q$;
node at (7.5,1,4) $T_1$;
draw[BarLatex-LatexBar] (1,0,4) -- (7,0,4)
node[midway,fill=white](d)$d$;
node[below=1pt of d,draw] $T_2>T_1$;
node[anchor=south,align=center] (mat) at (2,2.2,0) Material having\ thermal
conductivity $k$;
node[anchor=south,align=center] (area) at (5,2.2,0) Area 51;
path (mat) -- (2.5,1,1) coordinate (x3) coordinate[pos=1/3] (x1) coordinate[pos=2/3] (x2);
draw[-Latex] (mat) to[out=-90,in=70] (x1) to[out=-110,in=90] (x2)
to[out=-90,in=100] (x3);
draw[-Latex] (area) to[out=-90,in=30] (4,1,0.5);
endtikzpicture
enddocument

Here is a slightly different way to draw the thing. (I also don't know why there are so many ifnums in, if you rotate the thing too much it does not look good at all, so please don't ;-) And as usual one has to do an animation.

documentclass[tikz,border=3.14mm]standalone
usetikzlibrary3d,arrows.meta,positioning,calc
pgfkeystikz/.cd,
box color/.code=xdeftkzThreedBoxColor#1,
box color=white

makeatletter
%from https://tex.stackexchange.com/a/375604/121799
% spherical coordinates along y axis
define@keyy sphericalkeysradiusdefmyradius#1
define@keyy sphericalkeysthetadefmytheta#1
define@keyy sphericalkeysphidefmyphi#1
tikzdeclarecoordinatesystemy spherical% 
 setkeysy sphericalkeys#1%
 pgfpointxyzmyradius*sin(mytheta)*cos(myphi)myradius*cos(mytheta)myradius*sin(mytheta)*sin(myphi)
makeatother
% https://tex.stackexchange.com/a/438695/121799
tikzsetrotate axes about y axis/.code=
path (y spherical cs:radius=1,theta=90,phi=0+#1) coordinate(xpp)
(y spherical cs:radius=1,theta=00,phi=90+#1) coordinate(ypp) 
(y spherical cs:radius=1,theta=90,phi=90+#1) coordinate(zpp);
,
pitch/.style=rotate axes about y axis=#1,x=(xpp),y=(ypp),z=(zpp)
defparsexy(#1,#2,#3)(#1,#2)
defparsexz(#1,#2,#3)(#1,#3)
defparseyz(#1,#2,#3)(#2,#3)
defparsex(#1,#2,#3)#1
defparsey(#1,#2,#3)#2
defparsez(#1,#2,#3)#3

newcommandtkzThreeDBox[5][white]tikzset#1
path let p1=(0,0,1) in pgfextrapgfmathtruncatemacrozxprojsign(x1)
pgfmathtruncatemacrozyprojsign(y1)
xdefzxprojzxprojxdefzyprojzyproj
;
path let p1=(1,0,0) in pgfextrapgfmathtruncatemacroxxprojsign(x1)
pgfmathtruncatemacroxyprojsign(y1)
xdefxxprojxxprojxdefxyprojxyproj
;
ifnumzyproj=1
% front
filldraw[#1,fill=tkzThreedBoxColor!20] 
#2 -- ++ #3 -- ++ #4 -- ++ ($-1*#3$) -- cycle;
else
% back
filldraw[#1,fill=tkzThreedBoxColor!20] 
($#2+#5$) -- ++ #3 -- ++ #4 -- ++ ($-1*#3$) -- cycle;
fi
ifnumzxproj=1
% bottom
filldraw[#1,fill=tkzThreedBoxColor!30] 
#2 -- ++ #3 -- ++ #5 -- ++ ($-1*#3$) -- cycle;
ifnumxxproj=1
% right
filldraw[#1,fill=tkzThreedBoxColor!40] 
($#2+#3$) -- ++ #4 -- ++ #5 -- ++ ($-1*#4$) -- cycle;
% left
filldraw[#1,fill=tkzThreedBoxColor!40] 
#2 -- ++ #4 -- ++ #5 -- ++ ($-1*#4$) -- cycle;
else
% left
filldraw[#1,fill=tkzThreedBoxColor!40] 
#2 -- ++ #4 -- ++ #5 -- ++ ($-1*#4$) -- cycle;
% right
filldraw[#1,fill=tkzThreedBoxColor!40] 
($#2+#3$) -- ++ #4 -- ++ #5 -- ++ ($-1*#4$) -- cycle;
fi
% top
filldraw[#1,fill=tkzThreedBoxColor!30] 
($#2+#4$) -- ++ #3 -- ++ #5 -- ++ ($-1*#3$) -- cycle;
else
% bottom
filldraw[#1,fill=tkzThreedBoxColor!30] 
#2 -- ++ #3 -- ++ #5 -- ++ ($-1*#3$) -- cycle;
% left
filldraw[#1,fill=tkzThreedBoxColor!40] 
#2 -- ++ #4 -- ++ #5 -- ++ ($-1*#4$) -- cycle;
% right
filldraw[#1,fill=tkzThreedBoxColor!40] 
($#2+#3$) -- ++ #4 -- ++ #5 -- ++ ($-1*#4$) -- cycle;
% top
filldraw[#1,fill=tkzThreedBoxColor!30] 
($#2+#4$) -- ++ #3 -- ++ #5 -- ++ ($-1*#3$) -- cycle;
fi
ifnumzyproj=1
% back
filldraw[#1,fill=tkzThreedBoxColor!20] 
#2 -- ++ #3 -- ++ #4 -- ++ ($-1*#3$) -- cycle;
else
% front
filldraw[#1,fill=tkzThreedBoxColor!20] 
($#2+#5$) -- ++ #3 -- ++ #4 -- ++ ($-1*#3$) -- cycle;
fi

begindocument
foreach X in 0,10,...,350
begintikzpicture
path[use as bounding box] (-2,-4) rectangle (8.5,4);
pgfmathsetmacrotmpangle10*sin(X)
beginscope[pitch=tmpangle,transform shape] % X is *not* the rotation angle
path let p1=(0,0,1) in pgfextrapgfmathtruncatemacrozxprojsign(x1)
pgfmathtruncatemacrozyprojsign(y1)
xdefzxprojzxprojxdefzyprojzyproj
;
tkzThreeDBox[box color=orange,draw=none](0,0,0)(1,0,0)(0,2,0)(0,0,4)
fill[orange!80,canvas is yz plane at x=1] (0.5,0.5) coordinate(X) rectangle ++(1,3);
shade[opacity=0.7,left color=orange!80,right color=blue!50!cyan!60!white,canvas is xy plane at z=0.5]
 (1,0.5) -- ++(6,0) -- ++ (0,1) -- ++(-6,0) -- cycle;
shade[opacity=0.7,left color=orange!80,right color=blue!50!cyan!60!white,canvas is xz plane at y=0.5]
 (1,0.5) -- ++(6,0) -- ++ (0,3) -- ++(-6,0) -- cycle;
shadedraw[draw=red!50,left color=orange!15,right color=orange!40] 
(1.5,0.5,1) -- (1.5,1,1) -- plot[variable=x,domain=0:1.5,samples=60] 
(x+1.5,1+0.1*sin(720*x/1.5),1) --++(0,0.25,0) -- ++(0.5,-0.5,0)
-- ++(-0.5,-0.5,0) --++(0,0.25,0)
 -- plot[variable=x,domain=1.5:0,samples=60] 
(x+1.5,0.5+0.1*sin(720*x/1.5),1) -- cycle;
draw[dashed,draw=orange!20,thick] (X) -- ++(6,0,0);
fill[blue!50!cyan!60!white,opacity=0.6,canvas is yz plane at x=4] (0.5,0.5) rectangle ++(1,3);
tkzThreeDBox[box color=white,fill opacity=0,draw=orange!20,thick](1,0.5,0.5)(6,0,0)(0,1,0)(0,0,3)
tkzThreeDBox[box color=cyan,draw=none](7,0,0)(1,0,0)(0,2,0)(0,0,4)
node at (0.5,1,4) $T_2$;
node at (1,0.9,2) $Q$;
node at (7.5,1,4) $T_1$;
draw[BarLatex-LatexBar] (1,0,4) -- (7,0,4)
node[midway,fill=white](d)$d$;
node[below=1pt of d,draw] $T_2>T_1$;
node[anchor=south,align=center] (mat) at (2,2.2,0) Material having\ thermal
conductivity $k$;
node[anchor=south,align=center] (area) at (5,2.2,0) Area 51;
path (mat) -- (2.5,1,1) coordinate (x3) coordinate[pos=1/3] (x1) coordinate[pos=2/3] (x2);
draw[-Latex] (mat) to[out=-90,in=70] (x1) to[out=-110,in=90] (x2)
to[out=-90,in=100] (x3);
draw[-Latex] (area) to[out=-90,in=30] (4,1,0.5);
endscope
endtikzpicture
enddocument